Solar Thermal Storage Using PCM

 

 

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Acknowledgements

 

We would like to thank the following people who gave their time, assistance and consideration during this training period.

Firstly, we are extremely grateful to our supervisor Dr. Kenneth Ip who has provided support, advice and constructive comments throughout.

We would also like to thank Mr. Jonathan Gates for his help and the continuous supply of information during all this period.

Finally, thanks are also due to Dr. Andrew Miller for his kindness and the good times spent in Rouen, and to Ms Michele Terrier who made possible this exchange with the University of Brighton.

 

 

Page

Acknowledgements 1

 

Content 2

Abstract 4

  1. Introduction 5
  2. Solar Heating 7
    1. Solar energy 7
    2. Solar collectors 8
    3. Energy transfer 15
  3. Phase Change Materials 16
    1. Energy storage: an introduction 16
    2. Organic compounds 20
    3. Inorganic compounds 21
    4. Eutectics 22
  4. System design 23
    1. Description of the system 23
    2. System dimension and layout 25
      1. Schematic of the Laboratory 25
      2. Layout of the model 26
      3. Isolation box 28
    3. Identification of components 30
      1. Components for the system 30
      2. Components for the measurement 34
    4. PCM and solar panel selection 37
      1. PCM selection 37
      2. Solar panel selection 39

    Page

  5. Heat transfer process 40
    1. Heat transfer for a pipe 40
      1. Heat loss along a pipe 40
      2. Cylinder in a cross flow 42
    2. Radial heat transfer 43
    3. Heat transfer during the phase change 46
    4. Equation for the solar panel 47
  6. Experimental set-up 48
    1. Parameters to be measured 48
    2. Measurement procedure 50
    3. Break down of costs for the system 51
    4. Be careful about… 52
  7. Conclusion 54

Appendix 55

Glossary 67

References 68

Bibliography 69

 

 

 

Abstract

The aim of this project was to determine the experimental set-up for the measurement

of thermal storage system using phase change materials.

The report covers solar panels and phase change materials and the operating principles

behind them.

A solar thermal storage system using phase change material is proposed and background

heat transfer equations and total cost established.

A method of experimental measurement is proposed in order to measure the performance

of the proposed system.

 

 

I. Introduction

 

During our second year in thermal engineering at the IUT (University Institute of Technology) situated in Rouen, Normandy, are required to enter into a period of training. The duration of this period is ten weeks, and is usually done in a company or industry. However we chose to do this period in a university in England, in order to improve our English and apply the theory learnt at the IUT. The institute that we chose was the University of Brighton, which is situated in the south of England, in East-Sussex.

This university, was last year declared "University of the year" by the Sunday Times.

The University of Brighton offers courses in the following areas:

engineering
science and mathematics
built environment
computing and information
business and management
teacher education
health
social science
art and design

 

The University has four different sites:

Moulsecoomb
Grand Parade
Falmer
Eastbourne

 

The department that we carried out our period of training in was the School of the Environment situated in the Cockcroft building, at the Moulsecoomb site under Dr. Kenneth Ip’s supervision and in collaboration with Jonathan Gates, a MPhil/PhD student.

The aim of our studies was to propose an experimental set-up for the measurement of thermal performance of a solar thermal storage system.

An effective solar thermal storage system must form an integral part of a solar heating system for without this maximum utilisation of solar energy is not possible. Thermal storage can also address the problem in trying to match supply to demand were maximum solar availability occurs during the day, but maximum demand occurs at times when there is a little if any solar availability.

This project forms part of a current research to develop and analyse the performance of such a system for use in domestic buildings.

 

The report is organised into chapters which correspond with the objectives of the project.

The first part of the report covers solar energy, the different ways to store energy, and Phase Change Materials (PCMs).

The second part covers system design including description of the system, identification of components, PCM selection, all of which should allow a model of the system to be built.

The third part details the heat transfer equations, for each part of the system.

The final part of the report details the experimental set-up, which describes the parameters to be measured, the measurement procedure and the cost of the system.

 

Keywords: PCM, solar panel, latent heat storage, heat transfer energy, latent energy.

 

 

 

II. Solar Heating

2.1. Solar Energy

At the 1992 conference on climate change, the United Nations Inter-governmental panel concluded that a 60% reduction in the use of fossil fuel would have to be made in order to freeze the level of CO2 emissions by the year 2005 [1]. This has a tremendous implication on the way in which fuel is currently being used, placing greater emphasis on the use of alternative, renewable energy sources. This will have a large impact on the way buildings are operated as currently they account for over 50% of fuel consumption, with heating and lighting residential buildings responsible for 60% of emissions [1].

 

Solar power has enormous potential for use in residential buildings for approximately 30000 times as much solar energy reaches the earth than is actually needed to meet human demand [2]. It is also a clean source of energy in that it does not produce any CO2 and it is totally renewable.

However there are several major problems with harvesting solar energy; it’s availability is unpredictable, intermittent and is often subject to interruptions due to changes in weather. Due to this and the fact that for approximately for half of the 8760 hours per year any location is in darkness [3], a form of thermal storage is required to match supply with demand.

 

 

2.2. Solar collectors

 

A solar collector is made up of the following elements:

An opaque body which absorbs the solar radiation by getting overheated,

A thermal heat transfer fluid,

Thermal insulation (back and sides)

A transparent cover (fore face exhibited to the radiation)

A heat exchanger called absorber plate

 

In each collection device, the principle that is usually used is to expose a dark surface to solar radiation so that the radiation is absorbed then, a part of the radiation absorbed in this way is transmitted to a fluid: air or water by means of a heat exchanger.

Concerning this heat exchanger, all solar energy systems using indirect water heating require one or more exchangers; heat exchangers influence the effectiveness with which collected energy is made available in domestic water.

They also separate and protect the potable water supply from contamination when non-potable heat transfer fluids are used.

Like transport fluid selection, absorber plate selection considers thermal performance, cost effectiveness, reliability and safety, and the following characteristics:

Heat exchange effectiveness

Pressure drop, operating power, and flow rate

Physical design, design pressure, configuration, size, materials, and location in the system

Cost and availability

Thermal compatibility with system design parameters such as operating temperatures, flow rate, and fluid thermal properties.

 

Actually, there are two main different sorts of collectors:

Flat-plate and evacuated-tube collectors.

 

 

Flat-plate collectors

 

A flat-plate collector is the most important type of solar collector since it does not

require a lot of maintenance and is really simple to design. Moreover, the flat-plate collector can be used for applications where temperatures are set between 40° C and 100° C. Which make it suitable for space heating applications.

A schematic diagram of a liquid flat-plate collector is shown in Fig.1.

 

 

A flat-plate collector consists of an absorber plate on which the radiation of the sun falls after having come through one transparent cover made of plastic or glass either single or double-glazed.

The absorbed radiation is transferred to a liquid via the absorber plate and it is this energy gain which is the most useful.

The remaining part of the radiation absorbed in the plate is lost by convection to the surroundings, and by conduction through the back and edges.

The transparent cover helps in reducing the losses by convection and a selective coating can reduce the amount of lost to the surroundings.

The liquid most commonly used is water, although oil can be used.

 

 

Evacuated-tube collectors

The evacuated-tube collector is the other form of solar collector

These are typically more efficient at higher temperatures than flat-plate collectors. In an evacuated-tube collector, sunlight enters through the outer glass tube and strikes the absorber, where the energy is converted to heat. The heat is transferred to the liquid flowing through the absorber. The collector consists of rows of parallel transparent glass tubes, each of which contains an absorber covered with a selective coating. The absorber typically is of tin-tube design, although cylindrical absorbers also are used.

 

Evacuated-tube collectors are generally more efficient on an all year round basis as they can still operate under cloudy conditions, however they are considerably more expensive than flat-plate collectors -around 80%- and if the vacuum seal fails then they become inefficient.

A solar selective coating absorbs the solar radiation and converts it into thermal energy that is transported from inside the inner tube to an application.

 

 

Flat-plate collectors for heating air

 

However, there is also another sort of collector, whose construction is rather similar to the one of a liquid flat-plate; this is the conventional flat-plate collector for heating air. The only difference in its construction concerns the passages through which the air flows.

A schematic diagram of such one collector is shown below in Fig.3.

 

However, it needs ductwork which can take up considerable amount of space and if we need to store, it needs to use either a rock-bed or water for storage which again takes up space.

 

 

A thermal application: water heating

 

Of all the solar thermal applications, solar hot water heating is the most popular and may be the most economically viable.

A diagram of a simple natural circulation system is shown in Fig.4.

 

 

The two main elements of this system are the liquid flat-plate collector and the storage tank that is located above the level of the collector.

When the water in the collector is heated by solar energy, it flows automatically to the top of the water tank and it is replaced there by cold water from the bottom of the tank. Hot water for use is withdrawn from the top of the tank, and cold water enters automatically at the bottom.

The main disadvantage with a thermosiphon system is that the storage vessel needs to be located higher than the collector which means the collector may have to be sighted on the ground or on a porchroof.

 

Finally, in Fig.5 is shown a pumped system because this is one as this, that we will use.

 

 

When designing a solar heating system, it is important to consider the local climatic conditions. The most important climate variable(s) is (are) the solar irradiation (and the local ambient temperature).

The plane where we will install our panel is inclined around 30° (what is the typical inclination for solar collector in the United Kingdom).

The solar irradiation on such an inclined plane varies about 950 kWh/m2 per year in the North of the UK (Scotland) to about 1250 kWh/m2 per year in the South West (see Fig.6).

 

 

 

 

Fig.6 Variations in annual mean values of solar irradiation on a 30° inclined plane in the UK (kWh/m2)

 

 

(Source European Solar Radiation Atlas-1984)

 

 

Concerning the design of active solar system for the UK, there is also an important point, it is the fact that the monthly solar irradiation varies between the summer and the winter months. 

For an installation in Brighton, the seasonal variations for a surface in the South of England are shown below in Fig.7

 

Fig.7 Monthly distribution of annual solar irradiation received at 30° South in the South of England

 

 

(Source European Solar Radiation Atlas-1984)

 

 

 

2.3. Energy transfer

 

The energy collected by the solar collector is transferred to the heat transfer medium via the absorber plate. This heat is transferred to a storage tank or vessel.

 

This transfer occurs either by free circulation or by forced circulation

 

Transfer by water free circulation.

 

In these installations, the transfer of energy is based on the difference in density between hot and cold water.

Water entering at bottom of the collector is heated by the sun which reduces its density and causes it to expand it to rise to the storage tank which must be situated at least 60 cm above the collector.

Due to thermal stratification, hot water remains at the bottom of the tank, from which the solar collector is fed.

 

Transfer by forced circulation.

 

In addiction to the elements used in the previous system, this system uses a circulation pump driven by a temperature regulation.

The role of the circulation pump is to enable a faster transfer of the heat absorbed by the heat transfer fluid from the solar collector.

The utilisation of this pump also enables the system to be shut down if the water in collector is not hotter than that inside the tank.

 

 

The role of the regulating thermostat is to compare the two temperatures (at the solar panel exit and in the storage tank) and to drive the pump solely when the first temperature is higher than the second one (usually 5-10° C). In practice, the regulators available on the market enable the user to independently set the temperature difference.

 

 

III. Phase Change Materials

 

3.1. Energy storage: an introduction

 

Energy storage is a fundamental requirement of all solar energy systems.

Storage can either be thermal or chemical.

 

Thermal storage can either take the form of sensible heat storage where energy is stored by raising the temperature of a storage medium, for instance water or rock, or latent heat storage where energy is stored by altering the physical state of the storage medium, which can be solid-solid, liquid-gas or solid-liquid. The most common form of sensible heat storage in dwellings is the incorporation of thermal mass in a building’s structure to act as a heat store.

 

However there are several disadvantages with sensible heat storage; it is often difficult to judge the correct thermal mass required for space heating requirements and energy cannot be stored or released at a constant temperature. This method of storage is also inefficient as it takes less energy to raise the temperature of a material than it requires to change a solid or crystalline structure into a liquid.

 

Consequently to store the same amount of energy, significantly larger quantities of storage medium are required for sensible heat stores in comparison to latent heat stores. This is illustrated by the fact that the sensible heat capacity of concrete is approximately 1.0 kJ/kg [4], compared with calcium chlorine, which during phase transition, can store or release 190 kJ/kg [5]. Due to the large volume of material required, sensible heat storage is not suitable for retrofit applications and does not conform to the current trend for lightweight structures.

 

Furthermore, these systems take up a lot of space and have weight penalties which can have major cost implications in commercial property.

The use of latent heat storage is ideally suited where space is at a premium, such as refurbishments as larger amounts of energy can be stored per unit volume in comparison with sensible heat storage, which results in large space savings.

Another major advantage with latent heat storage is that heat is stored under isothermal conditions, which means they can deliver or store energy at a constant temperature. The use of latent heat storage is especially suited to the storage of solar energy where it can result in high solar collection efficiency, which can mean that solar collector area can be reduced by 30% [5].

 

So as to explain what a Phase Change Material is, we must show the example of water, the most simple and used of them.

Alternatively, water in a liquid state cooled to the point of crystallisation (0° C) will discharge heat.

This process is similar at the other phase (100° C) with boiling resulting in heat storage and condensing resulting in heat discharge.

 

Latent heat storage and discharge for water at 100° C is termed latent heat of vaporisation and heat storage and discharge at 0° C is termed latent heat of fusion, this is that latent heat which will only be considered during our study.

The principle of latent heat storage using phase change materials (PCMs) can be incorporated into a thermal storage system suitable for use in dwellings, where roof-mounted solar panels are used to collect the available solar energy during the day, which is then stored in the PCM for later use.

The water phase changes are shown in the schematic diagram in Fig.6

 

Fig.6 Water Phase changes

By comparing the values of steel, copper, water and a typical PCM compound called sodium sulphate; we can see that steel and copper exhibit the lowest heat of fusion for such high melting points.

 

 

 

Material Melting point (° C) Latent heat (kJ/kg) Density (kg/m3)

Steel 1400 247 7800

Copper 1086 206 8900

Ice 0 335 917

Sodium sulphate 32 252 1495

 

 

Characteristics of steel, copper, ice and sodium sulphate

 

(Source IHVE Guide. Unit and miscellaneous data)

 

 

 

 

By measuring density values we can also see that larger volumes of space are required.

Although ice has the optimum set of readings, the melting temperature is far too low to be useful as a means of heat storage.

 

It is clear that the PCM exhibits the optimum qualities, it provides a minimal amount of volume for its heat of fusion as well as having a low melting point.

That’s why PCM can be used as heat storage.

Now, we have to identify the required PCM to integrate in our proposed heating system.

 

This chapter reviews the characteristics of suitable PCMs for use in buildings and the methods of storage and control.

There are several types of PCMs but the three most common groups of PCMs are organic compounds, inorganic compounds and eutectics.

 

3.2. Organic compounds

 

These are compounds based on paraffin where the melting temperature of the material varies in relation to the amount of carbon atoms it possesses. Pure paraffins contain 14-40 C-atoms, whereas paraffin waxes contain 8-15 C-atoms [6]. Organic PCMs offer several advantages in that they possess a wide range of melting points, are non toxic, non corrosive, non hygroscopic, chemically stable, compatible with most building materials, have a high latent heat per unit weight, melt congruently and most importantly exhibit negligible supercooling which has plagued some inorganic compounds [5].

Some disadvantages of organic PCMs are; high cost which has led some researchers to investigate technical grade organic [7], low density, and low thermal conductivity in comparison to inorganic compounds, although this can be addressed by the addition of a filler with a high thermal conductivity or the use of aluminium honeycombs or matrixes [8].

 

They are also subject to substantial changes in volume upon melting, which can result in the material detaching from the sides of it’s container when it freezes, which can affect the heat transfer process. Flammability is often sighted as a potential disadvantage with organic PCMs, however some authors argue that their low vapour pressure presents little risk of fire, and they exhibit unstable characteristics notably large volume changes during liquefaction and solidification and low thermal conductivity.

 

 

Name Melting point (° C) Heat of fusion (kJ/kg)

Octadecane 28 244

Eicosane 36.7 247

Paraffin 116 45-48 210

Paraffin 6403 62-64 189

 

 

Organic Phase Change Materials

 

(Source- CIBS Guide C3 Heat transfer (1976))

3.3. Inorganic Compounds

 

These mainly consist of chemicals such as hydroxides or oxides, which have been diluted in an acid solution and are termed as salt hydrates or molten salt. The advantages that salt hydrates offer are; low cost in comparison to organic PCMs, they have a high latent heat per unit mass and volume, they possess a high thermal conductivity compared to organic compounds and offer a wide range of melting points from 7-117° C [9]. However, they can also suffer from loss of water when subjected to long-term thermal cycling due to vapour pressure, although the use of airtight containerisation can prevent this.

Problems with corrosion have also been experienced with salt hydrates. The major drawback with salt hydrates is that they can degrade over time due to a process known as decomposition. This is where the PCM melts incongruently and produces two separate parts, an aqueous phase and a solid phase, which possesses different densities, consequently the denser solid phase settles at the bottom of the container and this process is irreversible.

 

Many salt hydrates exhibit this weakness. Attempts at addressing this problem have centred on using thickening agents with varying degrees of success. However Merks observed that whilst Glauber’s salt thickened with attapulgite clay withstood thermal cycling better than an un-thickened, solution its thermal storage capacity still declined over time [5].

However, the problem with this sort of compounds occurs from repeated phase change cycles during solidification, the salt hydrates melt incongruently. This result is in a compound of a lower hydrate of the same salt [3]. That is to say that the original compound is no longer the same and a lower heat of fusion results.

 

Name Melting point (° C) Heat of fusion (kJ/kg)

Sodium sulphate decahydrate 32.4 252

Calcium chloride hexahydrate 27-29.7 170

Zinc nitrate hexahydrate 36 147

 

Inorganic Phase Change Materials

3.4. Eutectics

 

A eutectic PCM is a combination of two or more compounds of either organic, inorganic or both which may have a more interesting melting point to their individual and separate compounds. They behave themselves as salt hydrates.

The main problem with these compounds is the cost, actually some two or three times greater than organic or inorganic.

 

 

Name Melting point (° C) Heat of fusion (kJ/kg)

Palmatic acid (organic) 63 187

Mystiric acid (inorganic) 54 187

Stearic acid (organic/inorganic) 70 203

 

 

Eutectics Phase Change Materials

 

(Source- CIBS Guide C3 Heat transfer (1976))

 

 

 

Phase transition temperature

 

It is essential that the output of heating system is not less than the overall temperature required to melt the PCM permitting the desired heat transfer to take place. Those compounds with the lowest congruent melting points are therefore more desirable.

 

IV. System design

 

 

4.1. Description of the system

 

This project proposes to realise a model of a heating system. The heat in this system is obtained by a solar panel and the storage of this heat will be done in phase change material, sandwiched inside two pipes, surrounding a water pipe.

In the end, the model will be install in a laboratory, inside the university. The laboratory is for the moment used for another field of studies. Before all we had to make the measurement of the size of the laboratory, in order to propose a schematic drawing of a possible model.

The pictures below show the laboratory, in its current condition.

 

 

 

 

 

Above, picture of the laboratory, one of the entrances.

 

Above, picture of the laboratory, other view.

 

The photo below, is a photo of the roof, where the solar panel will be installed.

 

4.2.System dimension and layout

4.2.1. Laboratory’s schema

For this part we have taken the measures of the room size and made a schema of he laboratory; in order to after make the drawings of the implantation of the model inside the laboratory’s room.

 

 

 

 

4.2.2. Layout of the model

 

 

 

 

 

4.2.3. Isolation box

 

Monitoring the temperature of the internal space is vital in the case of space heating. In our case, the model we propose will be install in a room inside a laboratory of the university. This room has big dimension, and those dimensions could have an influence on the parameters we would like to measure. Indeed, if the size of the room is too big it can happen that the temperature is not uniform and then it exists a temperature gradient inside the room. Furthermore, we can not measure easily the airflow, which flows cross the PCM pipes. So to measure the real impact of the PCM, and the heat exchanged, we need to have a less big room around the PCM pipes.

In order to do that, we propose to build a sort of box around the system. This box will be insulated, so as to have a room isolate from the rest of the laboratory’s room.

We propose to install this insulated box like in the schema below.

 

 

 

We propose also, a simply way to build this box, but this is just a guide to do it.

First built a frame in wood, to have the skeleton of the room. After that, put plasterboards at the outside surface of the wood frame, screwed on the post of the frame.

Then, put insulation behind the plaster boards, inside and between the frame

Posts. Finally put the rest of the plasterboards inside the room, screwed on the posts of the frame. You have a room, insulate, to protect your system from the outside, and the laboratory’s room.

 

 

 

4.3. Identification of components

 

 

4.3.1.Components for the system

 

Choice of the pipes

 

For the most important part of the system, we can use a copper pipe for the water flow. But for the size of the pipes we must take care about the implantation of the system, indeed it could be installed under the floor, so the pipes could pass through some joists. The size of the pipes in this case is regulated, the maximal diameter for the holes made inside the joists is 0.25 times the width of the joist.

[appendix A.1]

For the Phase Change Material we need nine meters of plastic pipes. We take a nominal diameter of 36mm (UPVC Class E), to have a mean internal diameter of 32mm. As the pipes of PCM will be the bigger ones, a diameter of 36 mm leads to have a joist with a minimum width of 150 mm. Which is not too big and could be correct for a lots of situations. [appendix B.1]

We take fifty meters of copper pipes, with a nominal diameter of 15mm, That is to say a mean internal diameter of 14mm.

For the pipes around the Phase Change Material we need to take plastic pipes, because of the corrosion of the copper by the Phase Change Material chosen. Actually, the PCM in our case is Salt Hydrate, which are efficient but corrosive to the plastic. The length of plastic pipes we need is nine meters, with a nominal diameter of 15mm, to have a mean internal diameter of 11mm for this part. [appendix B.1]

 

Choice of the valves

 

To isolate the system, if it need, we can use valves.

The valves we chose are Gate valves and have

a diameter of 15mm. [appendix B.1]

 

Choice of the insulation

 

Pipes or ducts need not to be insulated if they contribute to the useful heat requirement of a room or space. In this project, the aim is to give to the PCM the largest possible quantities of heat, so we need to insulate the pipes to avoid the heat loss by the water, while it circulates inside the pipes.

We insulate the water pipes, with an insulation of 15mm for the diameter and 25mm for the thickness.

[appendix B.1]

 

Choice of the pump

 

We need a pump to make the water circulate, with a flow of one meter per second up to five meters per second. However we are limited for the choice, indeed we do not need a heavy pump if we consider the size of the water pipe, but the problem there is that the water needs to go up to 12 m easily. So we need to take a pump with a big head capacity.

The choice of pump was made after consulting manufacturer catalogues.

[appendix B.2]

 

 

Applications

Water circulation in commercial heating and air conditioning systems.

Options

Single or twin head.

Temperature range:

Pressure rating:

Pump connections: -10 to +130°C

6 Bar

1.25"BSP to 80mm

Choice of the fan

 

We need to known the size of the isolation room in the laboratory to make the choice of the fans. By calculation, we found eighty cubic meters. We take a fan, which can deliver a volume of air, equal to two hundred cubic meters per hour with a velocity, which can change. We place the fan as the schema below shows it.

 

 

 

 

 

The choice of fan was made after consulting manufacturer catalogues.

[appendix B.3]

 

 

Fan CC-CCI

 

 

The CCI fans are acoustically insulated by a double internal wall made up of a double sheet perforated metal structure full of 50 mm of mineral wool; by the way, they are one of the quietest fans in the market.

 

The four main characteristics of those fans are:

Their optimal curve, in spite of a minimal electric consumption;
Their really low noise level, particularly for the CCI;
Their compact size;
They’re easy installation and utilisation, then maintenance, thanks to the assembly of the tank, the doors and the power driven turbine group.
The CC-CCI are compliant.

 

 

4.3.2 Components for the measurement

 

Choice of the thermocouples

 

We need thermocouples to make the measurement of the temperature, at different places. The range of temperature we have is –20ºC (just in case) up to 100ºC. So we can take a thermocouple type T which have a range of –250ºC to 395ºC.

The choice of thermocouples was made after consulting manufacturer catalogues.

[appendix B.4]

 

 

 

Choice of the data logger

 

We need a device to store and make the acquisition of the data obtained by the measures, a data logger is the more useful device to make this acquisition.

We have chosen the following data logger, because it is expendable, and it offers a lot of different input.

See appendix B.5

Expandable Data Logger

HHP34970A

Up to 120 analogue input
Scan rates up to 250 channels/s
Measures 11 different signal types
6 1/2 digit readings (22 bits) with up to 0.005% accuracy (for 1 volt range)
Can hold up to three expansion

modules internally

Scaling and alarms available on

each channel

Stand-alone configuration
Non-volatile memory for 50,000

readings and five instrument

configurations

 

Digital I/O, analogue output, and relay

outputs available

Intuitive front panel

Task-oriented self guiding menus
Battery-backed real-time clock for

pacing scans and timestamping

readings

Software included for analysis and display of readings
GPIB and RS-232 interface
Three year warranty

 

Universal input channels

In all, the HP 34970A can measure and convert 11 different types of input signals which eliminates the need for expensive external signal conditioning.

These signal types are:

• temperature with thermocouples, RTDs, and thermistors B, E, J, K, N, R, S, T

 

• DC and AC voltage 100mV, 1V, 10V, 100V, 300V

• 2 and 4 wire resistance 10W to 100MW in 7 decades

• frequency and period 5Hz, 10Hz, 40Hz, 300kHz

• DC and AC current 10mA, 100mA, 1A

 

 

 

COMMON SPECIFICATIONS

DC CHARACTERISTICS

Offset voltage ` <3uV, 6 uV for 34902A

Initial closed channel R <1W , <0.2W for 34903A

Channel/channel isolation >10 W

AC CHARACTERISTICS

Bandwidth 10 MHz

Capacitance (HI-LO) <50 pF

<10 pF for 34903A

Capacitance (LO-Earth) <80 pF

Volt-hertz limit 108

 

OTHER

T/C CJC accuracy 0.8°C

Switch life (no load typ.) 100M

Rated resistive load (typ.) 100W

Operating temp. range 0 to 55°C

Storage temp. range -20 to 70°C

Humidity (non-condensing) 40°C / 80% RH

 

ACCURACY SPECIFICATION

±(percent of reading + percent of range) over one

year, for example by each input type

VDC 10v 0.0035 + 0.0005

VAC (10hz – 20kHz) 10v 0.0600 + 0.04

Resistance 1W , 0.0100 + 0.001

Frequency 40Hz-300kHz 0.01

DC current 100mA 0.050 + 0.005

(34901A only)

True RMS AC current 1A 0.10 + 0.04

(34901A only)

Thermocouple Type k ±1°C

 

Amplicon Liveline Ltd.

Centenary Industrial Estate

Hollingdean Road

Brighton BN2 4AW

United Kingdom.

Tel: - 01273 570220 & Fax: - 01273 570215

 

Choice of the water flowmeter

 

We need a water flowmeter, in order to have the value of the water flow inside the water pipes. The value of the water flow is used in the equations to have the amount of the heat exchanged inside the water pipes. So we take a flowmeter which can be fixed on a pipe of 13mm for the diameter.

The choice of water flowmeter was made after consulting manufacturer catalogues.

[appendix B.6]

 

 

Choice of the air flowmeter

 

We need an air flowmeter, to measure the airflow passing cross the PCM pipes. Indeed to calculate the heat took from the PCM, we need the temperature at inlet and outlet of the insulated room, and the airflow.

The choice of air flowmeter was made after consulting manufacturers catalogues.

[appendix B.7]

 

 

4.4. PCM and solar panel selection

 

4.4.1 PCM selection

Latent heat of fusion per unit of volume

of selected phase change materials

Organic compounds:

  1. Paraffin 6403
  2. Octadecane
  3. Eutectics:

  4. Myristic acid
  5. Palmitic acid
  6. Stearic acid
  7. Inorganic compounds:

  8. Calcium chloride hexahydrate
  9. Sodium sulphate decahydrate
  10. Zinc nitrate decahydrate

Density

 

High density is important because more heat can be stored in a given volume.

However, density increase is often accompanied by a decrease in heat of fusion since the substance becomes self-insulated.

 

Safety

 

The material must not be dangerous, flammable or toxic, and must be disposable.

 

 

PCM

Phase Transition Temperature

Heat of fusion

Density

Toxicity

Flammability

Cost

Scores

Calcium chloride

3

3

7

3

3

3

53 /17

Sodium sulphate

3

3

7

7

3

3

43 /27

Zinc nitrate

3

7

7

3

3

3

43 /27

Octadecane

3

3

3

7

7

3

43 /27

Eisocane

7

3

3

7

7

3

33 /37

Paraffin

116

7

3

3

7

7

3

33 /37

Paraffin 6403

7

7

3

3

3

7

33 /37

Myristic acid

7

7

3

3

7

7

23 /47

Palmatic acid

7

7

3

7

7

7

13 /57

Stearic acid

7

7

3

7

7

7

13 /57

 

By reading this table and seeing the chart, it appears that the best Phase Change Material to choose is the Calcium chloride hexahydrate.

Actually, it is a good compromise between a low Phase transition temperature and such an important latent heat of fusion, moreover, there is absolutely no danger in using this PCM and it is one of the cheapest.

 

 

4.4.2 Solar panel selection

 

A Flat-plate collector was selected for the following reasons:

 

They are considerably cheaper than evacuated tube collectors.
If a flat-plate collector with a selective coating is used then these can have efficiencies approaching that of evacuated tube collectors (manufacturer Filsol Ltd (Oxide of Chromium, Iron and Nickel)).
They are most suited to temperatures up to 100° C so which is well within the parameters needed for space heating.

 

 

V. Heat transfer process

 

We have to take into consideration for the heat transfer, that the transfers are not the same for each situation. That is why this chapter is divided into different parts describing the different situations we have in this project.

 

5.1. Heat transfer for a pipe

 

The first part describes the heat transfer for a pipe in two situations, firstly the heat loss along the pipe when the water circulates inside the tube.

And then the situation, when a fan is blowing air on the pipe, for recovering the heat transmitted by the pipe. In our case, the heat is recovered from the PCM.

 

 

5.1.1. Heat loss along the length of a pipe

 

Assumptions:

 

Steady-state conditions exist.
Radiation exchange between the pipe and the room is between a small surface in a much larger room.

The heat loss from the pipe is by convection to the room air and by radiation exchange with the walls.

Hence,

 

The heat loss per unit of pipe length is then,

 

 

The convection coefficient may be obtained thanks to:

 

 

where,

with,

 

 

See appendix C, table C.1 for the values of n, a, b to obtain Pr and Gr.

 

5.1.2. Cylinder in a cross flow

 

When the pipes are under the airflow blown by the fan, the air after the pipe is warmer than the air just outside of the fan.

So during the passage under the pipe, there is a transfer of heat between the pipe and the air.

 

The equation describing the heat loss is the same form as before:

 

So per unit of length,

 

The only difference is for the convection coefficient, because the Nusselt number is expressed in another form which dependant on the blown air.

         

 

 

Where U¥ is the air velocity.

 

We have a different expression for the Nusselt number as the case may be.

 

See appendix B, table B.2 for the values of C and m.

 

Where all properties are evaluated at T¥ , except Prs, which is evaluated at Ts.

If Pr£ 10, n= 0.37; if Pr> 10, n= 0.36.

See appendix C, table C.3 for the values of C and m.

 

 

5.2. Radial heat transfer

 

The pipe, considered in the following equations, is formed by two concentric pipes. Water flows through the smaller inner pipe and the outer pipe contains a Phase Change Material. (See figure below)

 

 

For the equations we consider a little part of the pipe, so we have:

 

 

Where

i, o, s subscripts for inlet, outlet, surface

Tm is the mean temperature of the fluid

 

Assumptions:

The flow is fully developed

Incompressible flow

 

We have,

 

Hence,

Now for the radial heat transfer we take a "slice" of a pipe and then a little part of this slice,: Temperature of the inside surface

 

The governing radial heat transfer equations for a unit section along the length of a concentric pipe containing phase change material are then:

 

 

 

with

 

     : mass flow rate of fluid [kg.s-1]

m : mass [kg]

 

 

5.3. Heat transfer during the phase change

 

The storage mechanism for all solid-liquid PCM is the same. Once the melting temperature of a PCM is reached it changes phase from crystallisation to fusion. This is called the charge period, as during this stage considerable quantities of latent heat are stored. The PCM will continue to store heat all the time it is at or above it’s melting point, or until it’s saturation point is reached. When the temperature falls below the melting point of the material it will begin to discharge the stored latent heat, which it needs to do in order to crystallise and change phase from liquid to solid.

 

When phase change occurs the latent heat effect is significantly greater than the sensible heat, hence the radial temperature distribution within each thin layer of the phase change material is assumed to be uniform.

This temperature uniformity is further maintained by subdividing the phase change material into thinner layers.

 

At phase change temperature Tphc, the heat energy is used for the phase change process.

 

 

If Qlhtmax > Qlht >0

 

 

Tpcm = Tphc

 

 

 

Where,

Qlht : latent heat content of the phase change material [J. kg-1]

Qlhtmax : maximum latent heat capacity of the phase change material [J. kg-1]

Tpcm: temperature of the phase change material [K]

Wpcm : rate of heat flow to the phase change material [W.kg-1]

 

 

 

 

5.4. Equation for the solar panel

 

For the solar panel it is assumed that there are no heat losses through the back and the sides of the panel, and the air temperature at the front of the solar panel is inclusive of the sky temperature and the sky velocity.

The basic equation for the quantity of energy released from the solar panel (to the water passing through) is calculated using the following formula:

 

Q=F. [I.(t.a)-U.(Ti-Ta)]

 

Where Q is the quantity of energy released from the collector per meter squared of area.

 

 

The constants of the equations are:

 

F represents the collector heat removal factor and is a ratio of the heat actually delivered by the collector to the heat that would be delivered if the absorber were at the same temperature of the water exiting the panel.
I is the total solar irradiance [W.m-2], which are identified for the country, by the CIBSE guide.
t.a is the product of transmittance and absorptance. It is a ratio representing the net irradiance absorbed through the plate whilst receiving solar energy.
U represents the upward heat loss coefficient and is the steady state heat loss of the collector [W.m-2.K-1].
Ta is the atmospheric air temperature

 

 

The variable of the equation is:

Ti the temperature of the water entering the collector. This value varies because of the initial temperature of the water when the heating system is first activated and its heat loss to the PCM pipe once the collector is working.

 

 

 

 

 

VI. Experimental set-up

 

6.1. Parameters to be measured

Normally, so as to calculate the heat loss along the length of the pipe (equation (1)), we need three temperatures:

Ts
Tsurf

But, due to the fact that the pipes will be enough isolated (thickness=25mm) in order to reduce at the maximum the heat loss by the pipes, it is only necessary to measure the temperature at the exit of the solar panel and at the entrance of the PCM so as to determine the loss of energy in the pipe by using the equation (14).

What we also need so as to calculate the quantity of energy is the water flow rate, that’s why we have to use a flowmeter which we will install just after the pump.

Concerning the cylinder in a cross flow, to use the equation describing the heat loss (8) we need two thermocouples in order to measure the temperature of the pipe surface (Ts) and the temperature of the ambient air (T¥ ).

But there is also a parameter which is necessary to know, it is about the air velocity called U¥ . Actually, we must know this velocity so as to calculate the Reynolds number (10) in order to find the convection coefficient (3).

Given that a box will be installed around the PCM pipes, it is now possible to measure the global energy got back by air, so as to do that, we need two temperature acquisitions: one at the exit of the fan, and another one at the exit of the box.

We can consider thanks to the size of the box and to the blown air velocity that there will not be any temperature gradient.

For the radial heat transfer equations, several points must be taken into consideration more particularly the mean temperatures of the fluid at the inlet and outlet of the pipe (14) for the quantity of heat.

 

In view of the fact that it is relatively hard to determine mean temperatures, we will use two thermocouples (one for the inlet and the other one for the outlet) situated at the middle of the pipe, corresponding to the ray of the pipe, what gives such a good rough estimate while temperature at the middle of the tube and temperature of the inside pipe must be really close.

Concerning the radial heat transfer in the strict sense of the word, four temperatures are useful, it is about the temperature of the inner (16) and outer plastic pipe (18), the temperature inside the PCM (17), and the temperature of the outside surface (19).

About the solar panel equation (21), the only variable is the temperature of the water entering the collector, therefore the only thing we will have to carry out is to note down the measurement done by a thermocouple situated inside the pipe just before the solar panel.

For an additional calculation, we can use the equation concerning the quantity of heat (14), in order to determine the quantity of heat absorbed by the water passing through the solar collector, for that we can input another thermocouple at the exit of the solar panel so as to have a the two necessary temperatures for the calculation; the water flow rate remaining the same as the one measured before.

We propose in order to see the temperature evolution inside the PCM, to take several measurements on the same pipe.

These measurements consist in the acquisitions of water temperature and the temperature of the PCM at different depths.

This representation is proposed in the figure below.

 

 

 

6.2 Measurement procedure

All the equations written below are simpler than the ones given in the fifth chapter which are too theoretical for such an application. We do not need these complicated equations so as to obtain a quiet good approximation of the real heat exchanges.

  1. Heat loss per unit of copper pipe
  2. The aim of this measurement is to characterize for a given duct the heat loss per unit length of copper pipes (Q/L) with a determined water flow rate.

    It is necessary for this calculation to know three different temperatures: the temperature at the outlet of the solar panel and the temperature at the first PCM pipe inlet

    For the calculation we need the following equation:

  3. Heat recovered by the water circulating inside the solar panel

The aim of the measurement is to estimate quantitatively and for a given water flow rate, the heat recovered by the water circulating inside the solar collector.

It is necessary for this calculation to know the two following temperatures: the temperature at the

inlet and the outlet of the solar panel.

The existing relation between these two temperatures in order to determine the heat recovered is:

 

 

  1. Heat gained by the air

The aim of this experimental study is to determine the heat gained by the air passing cross the PCM pipes through the insulation "box".

For this we need the temperature at the outlet of the fan and at the outlet of the box and the value of the air flow.

For the calculation we need the following equation:

f, pcm, a, fo, bo: subscript for fluid, phase change material, air, fan outlet, box outlet

spi, spo, : subscripts for solar panel inlet and outlet.

 

6.3 Break down of costs for the system

 

 

Product

Size

Unit

Quantity

Price per unit

Total

£

£

Copper pipes, 50m

Diam. 15mm

3m

17

3.27

55.59

Plastic pipes, 9m

Diam. 15mm

2m

5

2.69

13.45

Plastic pipes, 9m

Diam. 32mm

2m

5

2.99

14.95

Insulation, 50m

Diam. 15mm

1m

50

1.98

99

Valves

Diam.15mm

1 valve

6

2.85

17.1

Plaster board

2400*1200*95mm

1 board

40

4.99

199.6

Insulation

7000*370*200mm

1 roll

22

11.99

263.78

Thermocouples

Length 150mm

1 item

10

12

120

Data logger

 

1 item

1

899

899

Water flowmeter

Diam.15mm

1 item

1

271.6

271.6

Anemometer

 

1item

1

 

 

Fan CCI

1 item

1

Pump

1 item

1

263

263

Solar panel

2.6m2

1 item

1

298

298

TOTAL

2515.07

 

In this table are the materials we need to build the system and the prices we obtained after contacting the specialised companies.

You can see below the final total which gives a quite good approximation of the final cost of this system.

 

6.4 Be careful about

Concerning the solar panel.

So as to have a maximum efficiency of the solar panel, this one must be situated in a place without any trees, in order that the solar radiation should be absorbed by the flat-plate collector and not by the leafs.

Another important point concerning the solar panel is the freeze protection, solar heating systems that use liquids as the heat transfer fluid need protection from freezing in any area where temperatures fall below 42°F (6°C), because of the wind that can cause water in pipes to freeze before the air temperature reaches 32°F (0°C).

There are two basic methods for protecting the collector and piping from damage due to freezing temperatures: using an antifreeze solution as the heat transfer liquid; or draining the collector and piping, either manually or automatically, when the collector temperature falls below a certain level. Since the main purpose for insulating the collector and piping is to reduce heat loss and increase performance, heavy insulation may not keep the collector loop from freezing in very cold weather.

There are several cases of antifreeze protection, as much as there are solar heating systems, that’s why we will only explain our case.

The only heat transfer fluid used in our system is water, what make our system be the most vulnerable to freeze damage. "Draindown" or "drainback" systems typically use a controller to drain the collector loop automatically. Sensors on the collector and storage tank tell the controller when to shut off the circulation pump, to drain the collector loop, and when to start the pump again. Improper placement or the use of low-quality sensors can lead to their failure to detect freezing conditions. The controller may not drain the system, and expensive freeze damage may occur. We also have to be sure that the sensors are installed according to the manufacturer's recommendations, and check the controller at least once a year to be sure that it is operating correctly. To ensure that the collector loop drains completely, there should also be a means to prevent a vacuum from forming inside the collector loop as the liquid drains out. Normally an air vent is installed at the highest point in the collector loop. It is good practice to insulate air vents so that they do not freeze up and to make sure they remain unobstructed by anything that could block the air flow into the system when the drain cycle is active.

Collectors and piping must slope properly to allow the water to drain completely. All collectors and piping should have a minimum slope of 0.25 inches per foot (2.1 cm per meter).

 

Concerning the PCMs.

 

There are two major problems with the phase change materials, phase segregation and supercooling.

The phase change behaviour of salt hydrate PCM’s is more complex than that of organic compounds because hydration/dehydration occurs, rather than simple melting/freezing. Salt hydrates exhibit three general types of phase-change behaviour : congruent, incongruent and semi-congruent melting. The desirable behaviour is congruent melting which occurs when the solid phase composition is the same as the liquid phase composition. Semi-congruwent melting occurs when a material has two or more hydrate forms with differing solid compositions and melting points. Incongruent melting materials yield two distinct phase upon melting: a saturated solution and a precipitate of insoluble unhydrous salt.[10]

The problem of segregation occurs after a certain amount of cycle done by the phase change material, in that case the hydration/dehydration process does not appear identical to the melting/freezing process. The material can be transformed into other hydrate form(s) before either complete melting or freezing occurs, resulting in a temporary loss in thermal storage capacity.

 

Several PCM’s exhibit supercooling that is on attempting to freeze the material, the temperature drops well below the melting point before freezing initiates. Once the freezing process begins, the temperature rises to the melting point and remains until the material is entirely frozen. If supercooling is excessive it can prevent the withdrawal of heat from the PCM.[11]

To minimize supercooling, two approaches to nucleation have been tried: the addition of a chemical nucleating agent to the PCM and the use of a cold finger. Nucleating agents are substances upon which the PCM crystal will deposit with little or no supercooling. The use of cold finger is a surface within the storage container is maintained at a cooler temperature than the maximum supercooling temperature needed to promote nucleation.[10]

 

Finally, in order to avoid a "water hammer" in the system, we can install a protection valve for the water flowmeter and a by-pass for the pump.

Thus, before starting the pump, it is necessary to check that the valve is turned off and that the by-pass is open.

 

 

VII. Conclusion

 

This training period seemed to be for us a chance to apply our knowledge and skills; but in fact, it was more than a single application, we have learnt lots of things and improved our skills.

We discovered another way to organise our work, to take some decisions and to solve problems with the facilities available to us.

Furthermore, we were fortunate to discover another field of study, which has aroused our interest, this being solar energy, and the storage of this energy inside of phase change materials.

Communication was one of the most important skills that we developed during this period, both written and verbal.

This stay in England has brought to us a lot, especially the ability to work as a team with people we have never previously met.

Finally, our work was important to us but also to the team.

With all the objectives set being met, our study will allow Dr. Kenneth Ip’s team to follow their project, and build the model we designed. In order to carry out tests on the storage capacity of phase change materials.

In addition we discovered the English way of life and way of working, which was really important to us due to our wish to continue our studies and to work in England.

 

 

 

Appendix B

B.1 Choice of the components for the construction of the system

All the devices on this appendix have been found in the building furniture shop, named B&Q, in Brighton. The following prices wee find in this shop.

 

Copper pipes

Size: 15mm´ 3m

Price: £3.27

Plastic pipes

Speedfit class S, for water

Size: 15mm´ 2m

Price: £2.69

Size: 32mm´ 2m

Price: £2.99

Insulation for pipes

Size: 15mm´ 25mm´ 1m

Price: £1.98

Insulation for wall

Miraflex fiber, R=4.6

Size: 7000mm´ 370mm´ 200mm

Price: £11.99

Plasterboards

Size: 2400mm´ 1200mm´ 95mm

Price: £4.99

Gate valves

Size: 15mm

Price: £2.85

Lewes Road
Pavillion Retail Park
Brighton
East Sussex
BN2 3QA

Tel: 01273 679926

Fax: 01273 689098

 

 

B.2 Choice of the pump

 

 

 

 

Applications

 

Water circulation in commercial heating

and air conditioning systems.

 

Options

 

Single or twin head.

Temperature range:

Pressure rating:

Pump connections: -10 to +130°C

6 Bar

1.25"BSP to 80mm

 

Contact Information

 

For all enquiries originating from the UK the following contacts should be used.

 

Telephone: 01283 523000

FAX: 01283 523099

 

Wilo Salmson Pumps Limited

Centrum 100

Burton-on-Trent

Staffordshire

England

DE14 2WJ

 

 

 

 

 

 

B.3 Choice of the fan

Dimensions in mm


CC125

CCI125

CC160

CCI160

CC200

CCI200

Diameter Ø (mm)

125

125

160

160

200

200

A

260

360

300

400

325

425

B

130

180

150

200

162

212


Technical characteristics

Engine 220/230V

Power

Intensity

Velocity

Temperature maxi of air

Weight

Velocity

noise level

- 50 Hz

(watt)

(Amp)

(tr/min)

(°C)

(kg)

Regulator

at 1m (dB(A))

CC125

75

0,39

2500

50

5,5

R 200

39

CCI125

75

0,39

2500

50

13,0

R 200

35

CC160

98

0,48

2130

60

7,0

R 200

41

CCI160

98

0,48

2130

60

16,0

R 300

38

CC200

191

0,91

2330

60

9,0

R 300

49

CCI200

191

0,91

2330

60

19,0

R 300

45

 

 

CODUME

General Information: info@codume.com
Commercial : a.ogiers@codume.com
Technique : j.hallaert@codume.com
s.wittouck@codume.com
Internet site : http://www.condume.com

 

B.4 Choice of the thermocouples

 

 

 

 

The OMEGA low noise thermocouple probes and connectors maintain an electrical connection from the sheath of the probe, through the connectors, all the way to your instrumentation. This system assures high accuracy measurements, providing protection against electrical noise. The external strap maintains the electrical connection of the ground wire, and also strengthens the mechanical connection between the two connectors. The female connector features a handy write-on area, for easy identification.

 

Junction Types

 

Grounded Exposed Ungrounded

Thermocouple T, Alloy COPPER-CONSTANTAN, 304 SS Sheath

Sheath Diam.

Model number

Price

Model number

Price

 

150mm Length

G/E

U

300mm Length

G/E

U

1.0mm

HGTMQSS-M100(*)-150

£19

20

HGTMQSS-M100(*)-300

£19

21

2.0mm

HGTMQSS-M150(*)-150

17

18

HGTMQSS-M150(*)-300

17

18

3.0mm

HGTMQSS-M300(*)-150

17

18

HGTMQSS-M300(*)-300

17

18

*Specify junction type: E (Exposed), G (Grounded), or U (Ungrounded).

 

Omega Engineering Ltd.

 

One Omega Drive

River Bend Technology Centre

North Bank

Irlam, Manchester M44 5EX

Telephone: 161-777-6611

FAX: 161-777-6622

Free Phone: 0800-488-488

e-mail: info@omega.co.uk

Internet site: http://www.omega.co.uk/uk/index.html

 

 

B.4 Choice of the thermocouples

 

 

 

 

The OMEGA low noise thermocouple probes and connectors maintain an electrical connection from the sheath of the probe, through the connectors, all the way to your instrumentation. This system assures high accuracy measurements, providing protection against electrical noise. The external strap maintains the electrical connection of the ground wire, and also strengthens the mechanical connection between the two connectors. The female connector features a handy write-on area, for easy identification.

 

Junction Types

 

Grounded Exposed Ungrounded

Thermocouple T, Alloy COPPER-CONSTANTAN, 304 SS Sheath

Sheath Diam.

Model number

Price

Model number

Price

 

150mm Length

G/E

U

300mm Length

G/E

U

1.0mm

HGTMQSS-M100(*)-150

£19

20

HGTMQSS-M100(*)-300

£19

21

2.0mm

HGTMQSS-M150(*)-150

17

18

HGTMQSS-M150(*)-300

17

18

3.0mm

HGTMQSS-M300(*)-150

17

18

HGTMQSS-M300(*)-300

17

18

*Specify junction type: E (Exposed), G (Grounded), or U (Ungrounded).

 

Omega Engineering Ltd.

 

One Omega Drive

River Bend Technology Centre

North Bank

Irlam, Manchester M44 5EX

Telephone: 161-777-6611

FAX: 161-777-6622

Free Phone: 0800-488-488

e-mail: info@omega.co.uk

 

Internet site: http://www.omega.co.uk/uk/index.html

 

B.5 Choice of the data logger

 

In order to have an easier reading of the measurement done by the thermocouples, it is better to use a laptop, which also enables to have a really good data acquisition.

 

 

B.6 Choice of the water flowmeter.

Steel Turbines - Liquid applications

Type TB

Threaded male BSPP

Pmax: 300 bar

 

Pressure Loss Liquid (0.8 s.g.): 300mbar at Qmax

Temperature: -20 to + 120 degrees C

Internals: Stainless Steel

Body: Stainless Steel

Rotor: Stainless Steel

 

 

 

Liquid Turbines

Size

 

Flowrate

Linearity

Length

(inches)

(metric)

(Litres/min)

 

LTB

1/2"

13mm

2 to 20

+/- 0.5%

70mm

5/8"

16mm

5 to 50

+/- 0.5%

70mm

3/4"

19mm

14 - 140

+/- 0.5%

82mm

1"

25mm

27 - 270

+/- 0.5%

88mm

1 1/2"

38mm

55 - 550

+/- 0.5%

114mm

2"

51mm

114 - 1140

+/- 0.5%

133mm

3"

76mm

227 - 2270

+/- 0.5%

---

4"

102mm

454 - 4540

+/- 0.5%

---

6"

152mm

908 - 9080

+/- 0.5%

---

8"

203mm

1820 - 18200

+/- 0.5%

---

 

Westcroft Estate,

Rhodes,

Middleton,

Manchester,

M24 4GJ

Tel: + 44 (0) 161 643 3681

Fax: + 44 (0) 161 655 3785

Internet site: http://www.emoltd.co.uk

 

 

B.7 Choice of the air flowmeter

 

 

WAA151 Anemometer

- Optoelectronic sensor

- Low intertia and starting threshold

- Excellent linearity up to 75 m/s

- Shaft heating

The WAA151 is a low-threshold precision cup wheel anemometer with excellent linearity over the entire operating range, up to 75 m/s. The output frequency is directly proportional to wind speed.

A heating element in the shaft tunnel keeps bearings above the freezing level in cold climates.

The instrument is typically mounted at the southern end of Vaisala's standard WAC151 Cross Arm.

Measuring range 0.4 ... 75 m/s
Accuracy ±0.17 m/s (standard deviation)
Starting threshold < 0.5 m/s
Distance constant 2.0 m
Operating power supply 9.5 ... 15.5 VDC, 20 mA typical
Operating temperature -50 ... +55°C (with shaft heating)
Weight 560 g

 

VAISALA Ltd, Birmingham Operations.

Vaisala House

349 Bristol Road

Birmingham B5 7SW

UNITED KINGDOM

Phone (nat.): (0121) 683 1200

Telefax: (0121) 683 1299

Managing Director: Jonathan Lister e-mail: jonathan.lister@vaisala.com

 

Sales&Marketing: Andy McDonald e-mail: andy.mcdonald@vaisala.com

Brooke Pearson e-mail: brooke.pearson@vaisala.com

 

Internet site: http://www.vaisala.com

 

 

 

 

Appendix C

 

Table C. 1

Thermophysical properties of air at Atmospheric Pressure.

 

T r Cp m.106 n.106 k.103 a.106 Pr

(K) (kg/m3) (kJ/kg.K) (N.s/m2) (m2/s) (W/m.K) (m2/s)

Air

100 3.5562 1.032 71.1 2.00 9.34 2.54 0.786

150 2.3364 1.012 103.4 4.426 13.8 5.84 0.758

200 1.758 1.007 132.5 7.590 18.1 10.3 0.737

250 1.3947 1.006 159.6 11.44 22.3 15.9 0.720

300 1.1614 1.007 184.6 15.89 26.3 22.5 0.707

350 0.9950 1.009 209.2 20.92 30.0 29.9 0.700

400 0.8711 1.014 230.1 26.41 33.8 38.3 0.690

450 0.7740 1.021 250.7 32.39 37.3 47.2 0.686

500 0.6964 1.030 270.1 38.79 40.7 56.7 0.684

550 0.6329 1.040 288.4 45.57 43.9 66.7 0.683

600 0.5804 1.051 305.8 52.69 46.9 76.9 0.685

650 0.5356 1.063 322.5 60.21 49.7 87.3 0.690

700 0.4975 1.075 338.8 68.10 52.4 98.0 0.695

750 0.4643 1.087 354.6 76.37 54.9 109 0.702

800 0.4354 1.099 369.8 84.93 57.3 120 0.709

 

850 0.4097 1.110 84.3 93.80 59.6 131 0.716

900 0.3868 1.121 398.1 102.9 62.0 143 0.720

950 0.3666 1.131 411.3 112.2 64.3 155 0.723

1000 0.3182 1.141 424.4 121.9 66.7 168 0.726

1100 0.3166 1.159 449.0 141.8 71.5 195 0.728

1200 0.2902 1.175 473 162.9 76.3 224 0.728

1300 0.2679 1.189 496 185.1 82 238 0.719

1400 0.2488 1.207 530 213 91 303 0.703

1500 0.2322 1.230 557 240 100 350 0.685

1600 0.2177 1.248 584 268 106 390 0.688

 

1700 0.2049 1.267 611 298 113 435 0.685

1800 0.1935 1.286 637 329 120 482 0.683

1900 0.1833 1.307 663 362 128 534 0.677

2000 0.1741 1.337 689 396 137 589 0.672

2100 0.1685 1.372 715 431 147 646 0.667

Table C.2

Constants of equation (11) for the circular cylinder in cross flow.

 

Red C m

 

0.4 – 4 0.989 0.330

4 – 40 0.911 0.385

40 – 4000 0.683 0.466

4000 – 40,000 0.193 0.618

40,000 – 400,000 0.027 0.805

 

 

Table C.3

Constants of equation (12) for the circular cylinder in cross flow.

Red C m

 

1 – 40 0.75 0.4

40 – 1000 0.51 0.5

103 – 2.105 0.26 0.6

2.105 – 106 0.076 0.7

 

 

Glossary

 

absorption The light energy that is captured by a surface.

insolation A measure of the amount of solar radiation striking a surface. Maximum insolation on the Earth's surface occurs when the sun is directly overhead, and is about 1000 watts per square meter.

insulation Material used to slow the transfer of heat. Used to make buildings more energy efficient. Do not confuse with "insolation" above!

joule (J) One joule is the amount of work required to exert a force of one Newton through a distance of one meter.

kilowatt hour (kWh) Unit used to describe the power produced by an energy source; one kWh equals 1000 watts sustained for one hour.

phase change material Material used for the storage of energy

power The rate of doing work or the amount of work done in a given time. The unit of power is the watt (W).

reflection The light energy that bounces off of a surface.

renewable energy Energy that can be efficiently replenished or obtained from waste products. Examples include solar energy, geothermal energy, wind power, and tidal power.

solar panel Instrument used to absorb the solar radiation

solar radiation Energy as visible light and other forms of electromagnetic radiation originating from our Sun.

watt (W) Unit of power. Equal to one joule of work per second (J/s).

References

http://www.eren.doe.gov/solarbuildings/techdescr.html

1.Association of Conservation of Energy. Association of Conservation of Energy Briefing Notes. Association of Conservation of Energy, 1994(13): p. 1.

2.Weider, S., An Introduction To Solar Energy For Scientists and Engineers. 1982, New York: John Wiley & Sons.

3. Unknown, Applications Handbook. 1991.

4.CIBSE. Guide A3 Thermal Properties of Building Structures. 1986, London: The Chartered Institution of Building Services Engineers.

5.Lane, G.A., Solar Heat Storage: Latent Heat Materials Volume I: Background and Scientific Principles. Vol. I. 1983, Florida: CRC Press, Inc.

6.Abhat, A., Low temperature latent heat thermal energy storage: Heat storage materials. Solar Energy, 1983. 30(4): p. 313-332.

7.Ghoneim, A.A. and S.A. Klein, The effect of phase change material properties on the performance of solar air based heating systems. Solar Energy, 1989. 42: p. 441-447.

8.Hoogendoorn, C.J. and G.C.J. Bart, Performance and modelling of latent heat stores. Solar energy, 1992. 48: p. 53-58.

9.Lane, G.A., Solar Heat Storage: Latent Heat Materials Volume II: technology. 1983, Florida: CRC Press Inc.

10.Eissenberg and al., what’s in store for phase change thermal storage materials for active and passive solar applications. 1980. P. 12-16.

11. Lane, G.A., Low temperature heat storage with phase change materials. The international journal of ambiant energy. . Vol. I. 1980. P. 155-168.

 

Bibliography

 

Davis, L. (1991)

Guide to the Building Regulations. Butter Worth Architecture

Ferraro, R. and al. (1983).

Performance monitoring of solar heating systems in dwellings.

Groday, R. and al., (1983).

Solar space heating: an analysis of design and performance from 33 systems.

Incropera, F

Fundamentals of Heat & Mass transfer. Forth edition

Sukhatme S P

Solar energy, principles of thermal collection and storage.

 

http://www.jademountain.com/waterProducts/thermomax.html.

 

http://www.eren.doe.gov/millionroofs/spaceheat.html

CIBS Guide C3 Heat transfer (1976)

IHVE Guide C7 Units and miscellaneous data (1974)

IHVE Guide C4 Flow of fluids in pipes and ducts (1977)

 

 

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