table of contents - jazan ucolleges.jazanu.edu.sa/sites/en/eng/labs/engm523 refrigeration and... ·...

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KINGDOM OF SAUDI ARABIA المملكة العربية السعىدية

Ministry of Higher Education وزارة التعليم العالي

JAZAN UNIVERSITY جامعة جازان

College of Engineering الهندســـــة كليـــــة

Mechanical Engineering Department الميكانيكيةقسم الهندسة

Table of Contents

No. Experiment/Test Title Page no.

1. Central Air Conditioning System with Climate Chamber 2

2. Computer controlled Refrigeration system 8

3. Vapour Compression Refrigeration Cycle 12

4. Refrigeration - heat pump system 13

5. Steam Jet Refrigeration system 18

6. Reverse Cycle Refrigeration Training System 24

7. Computer controlled ِ Air Conditioning Duct 29

8. Computer controlled ِ Air Conditioning Duct with

recirculating air

32

9. Air conditioning training split unit and Refrigeration

Cycle training unit

37

Course code and Name: EngM 523 – Refrigeration and Air Conditioning

Level: 10

Lab. Name: Refrigeration and Air Conditioning

Supervisor Name: Dr. Salem M. Abdelsamad

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Experiment no. (1)

Title: Central Air Conditioning System with Climate Chamber

EXPERIMENT / TEST DESCRIPTION

Test Description: Full air conditioning system with full-size chamber for comfort testing, suitable for one

person. HVAC system controller with PLC. System components widely used in air

conditioning and ventilation engineering. Data acquisition software.

Test Objectives: The objectives of this test:

The system demonstrate all operating states that characterize a complete air conditioning

system:

- Heating of the chamber

- Cooling of the chamber

- Humidification of the air

- Application of the mixing line

- Investigations on human comfort

Theoretical Background: Air-conditioning involves control of temperature, humidity, cleanliness of air and its

distribution to meet the comfort requirements of human beings. The experiment setup is

used as simulation unite of the real central air conditioning system. It has the same

components for measuring, control and fault diagnostics of the air conditioning

parameters.

3






TEST ACTIVITIES

Equipment and Tools: Air Conditioning System with Climate Chamber Fig. 1.1 contains those components that

appear in systems used in actual building services and also provides a great deal of

information of practical relevance. The built-in programmable logic controller (PLC)

provides the automatic mode. The measured values recorded electronically are shown on

displays. The air is conveyed into the climate chamber by a radial fan, which is positioned

in the ventilation duct after the mixing point for fresh and circulated air.

Figure 1.1 The components of the air conditioning system with climate chamber

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Test Procedure: The climatic controller is set to manual mode. The following settings are made in the

“Switches” menu: – Fan:= Auto, – Chiller:= Auto, – Flaps:= On (fresh air mode)

– Heater:= Off, – Chiller valve:= A-open (maximum cooling), – Humidifier:= Off

A temperature setpoint of 15°C has been set on the water chiller. To obtain a larger

temperature difference, the cooling water flow has been reduced to 600 l/h.

After a few minutes, once the system is in a steady operating state, the measured values of

The dry bulb temperatures , relative humidity, air flow velocity, water flow rate and the

power consumption are recorded, Fig. 1.2.

The following sensors are used at the located points::

T1 - T9 Temperature sensors

H1 - H7 Relative humidity sensors

F1 - F2 Air flow speed sensors

F3 flowmeter

E1 - E4 Power consumption

Figure 1.2 Measured parameters of the air conditioning system with climate chamber.

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Test Results: For cooling the climate chamber, the dry bulb temperature and the relative humidity are

measured at point 2 and point 3. These two points has to be located on the Psychometric

chart, Fig. 1.3. Table 1.1 has to be filled with the test results.

Figure 1.3 Point out the cooling process on the psychometric chart.

Table 1.1 the measured and calculated parameters during cooling the chamber.

6






Conclusions:

Comments:

7






8






Experiment no. (2)

Title: Computer controlled Refrigeration system


Test Description: A simple refrigeration circuit is demonstrated with this clearly laid out experimental unit. The

evaporation and condensation processes are easily observed through the glass components. The

function of the expansion valve (in the form of a float valve) can be seen. The changes in the

refrigerant state can also be followed by measuring pressures and temperatures. A special

environmentally friendly refrigerant is used at low pressure.

Test Objectives: The objectives of this test is to do the following testes:

- Evaporation and condensation

- Cyclic process on the log p-h diagram

- Calculation of the heat transfer rate at evaporator and condenser

- Determination of efficiency and coefficient of Performance

Theoretical Background: The basis for the function of a refrigeration system is a thermodynamic cyclic process.

In a thermodynamic cyclic process a refrigerant (e.g. SES36) passes through various changes of

state in a defined sequence. The changes in state repeat cyclically, the working medium thus

returns to its initial state time and again. For this reason the term cyclic process is used.

The term change of state refers to compression, expansion, heating or cooling:

_ Compression signifies the absorption of mechanical energy

_ Expansion signifies the emission of mechanical energy

_ Heating signifies the absorption of thermal energy (heat)

_ Cooling signifies theemission of thermal energy

TEST ACTIVITIES

Equipment and Tools: Air Conditioning System with Climate Chamber Fig. 2.1 contains those components that

appear in systems used in actual building services and also provides a great deal of

information of practical relevance. The built-in programmable logic controller (PLC)

provides the automatic mode. The measured values recorded electronically are shown on

displays. The air is conveyed into the climate chamber by a radial fan, which is positioned

in the ventilation duct after the mixing point for fresh and circulated air.

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Figure 2.1 The components of the

vapor compression refrigeration

system

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Test Procedure: Placing the System in Operation

_ Hand valves 1 and 3 must be open, _ Hand valves 3 and 4 must be closed

_ Switch on water supply, adjust required flow rates for hot and cold water at the regulator

valves on the related flowmeter (e.g. 200cm3/ min on each)

_ Set master switch to „ON“ position, _ Fully open regulator valve on the refrigerant

flowmeter _ Start compressor by operating the ON/OFF switch,

_ Adjust required refrigerant flow rate (e.g. 150 l/h) at the regulator valve on the refrigerant

flowmeter

_ Leave system to run for a while, the experiments an then be commenced Transfer of Heat at Condenser and Evaporator The amount of energy can be calculated using equation

Test Results:

Figure 2.2 Point out the cooling process on the p-h diagram.

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The following are read from the diagram:

_ The specific refrigerating capacity h1 - h4

_ The specific cooling capacity h2 - h3

_ The specific compressor work h2 - h1

Multiplied by the refrigerant mass flow rate the specific values read produce

_ Refrigerating capacity

_ Cooling capacity

_ Actual internal compressor power output

As a further system parameter the performance

number for the system can be determined from the enthalpies read.

Evaluation of the diagram:

h1 = 343 kJ/kg

h2 = 375 kJ/kg

h3 = 247 kJ/kg

h4 = 247 kJ/kg

Calculation of the refrigerant mass flow rate:

Calculation of the system parameters:

1) Refrigerating capacity Q0: 96 kJ/kg * 4,29 *10 -4 kg/s = 41,2 W

2) Cooling capacity QK : 128 kJ/kg * 4,29 *10 -4 kg/s = 54,9 W

3) Actual, internal compressor power output Pi :

32 kJ/kg * 4,29 *10 -4 kg/s = 13,7W

4) Performance number _ : (h1 - h4) / (h2 - h1) = 3.0

Conclusions:

Comments:

12






Experiment no. (3)

Title: Vapor Compression Refrigeration system

It is the same experiment like experiment (2) but without computer control

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Experiment no. (4)

Title: Refrigeration - heat pump system


Test Description: The basis for the operation of a heat pump is a cyclic thermodynamic process. In a cyclic

thermodynamic process a working medium flows through a set sequence of changes of

state. The changes of state are repeated cyclically, the working medium thus repeatedly

returns to its initial state. It is for this reason that the term cyclic process is used.

Test Objectives: The objectives of this test:

- Layout, function and main components of a heat pump

- Measurement of relevant pressures, temperatures, flow rates, current and voltage

- Illustration of the thermodynamic cyclic process in a log p-h diagram

- Comparison of different operating modes

- Determination of: efficiency, coefficient of performance, specific compressor work,

compressor pressure ratio, specific cooling capacity and specific refrigerating capacity

- Heat balance

Theoretical Background: "heat pump" can be explained as follows:

heat is pumped from a low temperature region

to a higher temperature region using mechanical

energy. The mechanical energy is not lost, but is

also discharged in the higher temperature

region in the form of thermal energy. A compressor compresses the vaporous working

medium, during this process mechanical energy Win

is absorbed.

• Heat Qout is extracted (at constant temperature)

from the working medium in the condenser, the

working medium condenses.

• The liquid working medium expands in an

expansion valve, during this process the

working medium cools.

• The working medium is evaporated in an evaporator, heat being absorbed during this process

Qin. The working medium is now fed back to the compressor and the cyclic process begins again.

Fig. 4.1 Heat pump cyclic processes

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TEST ACTIVITIES

Equipment and Tools:

Figure 4.2 The Heat pump system Components.

15






Test Procedure: Experimental Determination of the Ideal / Real Output Coefficient

Here the output coefficient is determined from the differences in the enthalpies on the log p-h

diagram. To do this the cyclic process must be plotted on the log p-h diagram. Performing the Experiment

• Switch on the compressor., • Switch on the fans., • Switch on the circulation pump., • If cooling

via tap water, connect to the cold water supply with hoses., • Leave the test stand to run until the

pressures on the suction and delivery side have stabilized., • At the control valve set the flow in

the water circuit such that the flow rate is around 20l/h.

• Read off and note the working medium pressures on the suction and delivery side.

Figure 4.3 Measured parameters of the heat pump system.

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Test Results: Derivation from the p-h diagram

The quantities of energy converted in the cyclic process can be taken directly from the p-h

diagram as differences in the enthalpies. Thus the output coefficient for the ideal process can be

derived in a very straight forward manner

For the real process with suction gas superheating and liquid supercooling the following applies

Figure 4.4 Point out the heat pump process on the p-h diagram.

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Conclusions:

Comments:

18






Experiment no. (5)

Steam Jet Refrigeration system


Test Description: The experimental unit has a steam jet

thermocompressor instead of a mechanical

compressor, with the advantage that any heat source

can be used to produce the steam that drives the

process. The unit has a refrigerant circuit and a

vapour circuit that are connected via a condenser and

steam ejector. Both the evaporator and the steam

generator are heated electrically. The evaporator and

condenser are transparent so that the processes can be

clearly observed. The steam generator can be

operated with an external source of hot water instead

of electrical heating.

Test Objectives: The objectives of this test is to do the following testes:

- Application of Rankine cycle in refrigeration technology

- Cyclic process on the log p-h diagram

- Determination of the energies used and converted

- Calculation of the system-specific data

- Behavior of the system under load

Theoretical Background: The Clausius-Rankine process is used as a comparison process for anticlockwise operating

cyclic processes with vapours. The machine can be used as a heat pump or refrigeration system

depending on the application. The working process is largely in the wet vapour region at low

temperatures, hence the use of the terms cold vapour and cold vapour machines.

TEST ACTIVITIES

Equipment and Tools: The steam jet refrigeration system is shown in Fig. 5.1.

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Figure 5.1 The components of the steam jet refrigeration system

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Test Procedure: Turn master switch (30) to ON • Switch on pump using the switch (22). Switch off the pump

again when the inspection glass (27) is half full of refrigerant. • Close regulator valve (5).

• Place an over flow valve on the fit ting (33) and place the end of the house in a waste pipe

• Allow water to flow into the vapour generator by opening the top up valve (16) until water

escapes from the fit ting (33). To prevent the dry trip on the electric heater (31) from

triggering, it must be ensured that the water level does not fall below the mark on the water

level gauge (28) during operation. • Turn on the supply of water for coo ling the con den ser

and use the water regulator valve (13) to set a medium to maximum mass flow rate. • Switch

on the heater (31) with the switch (24). Observe the water level in the vapour generator. Pay

attention to the pressure gauge (3) for the vapour generator and ensure that the ma xi mum

permissible pressure at the pressostat (1) is not exceeded.

Table 5.1 worksheet for experiment evaluation

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22






Test Results:

23






Conclusions:

Comments:

24






Experiment no. (6)

Reverse Cycle Refrigeration Training System

TEST DESCRIPTION

Test Description: The unite contains a hermetic compressor, 4 heat

exchangers, 3 expansion valves and 4 different

interchangeable capillaries. The unit can be operated in

different modes. 11 manually operated valves allow

corresponding changes to be made to the refrigeration

circuit. The relevant measured values are displayed

directly on indicator instruments. Therefore, sequences

and consequences of switching operations within a cooling

unit can be directly investigated. Sight glasses in the

refrigerant circuit allow direct observation of the

refrigerant status. A coaxial tube bundle heat exchanger

can be operated as a counter flow condenser or as a

parallel flow evaporator. This heat exchanger is used to

heat or cool a glycol/water mixture circuit. Refrigerating

loads are created by different fan speeds on the finned tube

evaporators.

Test Objectives: The objectives of this test are: - Layout, function and main components of a heat pump

- Measurement of relevant pressures, temperatures, flow rates, current and voltage

- Illustration of the thermodynamic cyclic process in a log p-h diagram

- Comparison of different operating modes

- Comparison of different expansion elements (expansion valve, 4 capillaries)

- Determination of: efficiency, coefficient of performance, specific compressor work,

compressor pressure ratio, specific cooling capacity and specific refrigerating capacity

- Heat balance

Theoretical Background: The basis for the operation of a heat pump is a thermodynamic cyclic process. In a

thermodynamic cyclic process, an operating fluid (such as R134a) is subject to a fixed sequence

of different state changes. The state changes are cyclically repeated so that the operating fluid

always returns to its initial state. For this reason, it is termed a cyclic process. To be understood

as a „state change“ are compression, expansion, heating or cooling:

- Compression means the absorption of mechanical energy

- Expansion means the release of mechanical energy

- Heating means the absorption of thermal energy (heat)

- Cooling means the release of thermal energy In a state change

25






TEST ACTIVITIES

Equipment and Tools:

1Valve to drain the glycol/water mixture 2 In-/ outlet cooling water connection

3 Refrigerant collector 4 On/Off switch for the compressor

5 Ampere meter 6 Voltmeter

7 Hermetically sealed compressor 8 Pressostat pressure switch

9 Main switch 11 Evaporator 2

12 On/Off switch for the axial-flow fan 13 Thermostatic expansion valve

14 Suction gas controller 16 Evaporator 1

17 On/Off switch for the axial-flow fan 18 Thermostatic expansion valve

19 Capillary tube 20 Condenser

21 Thermostatic expansion valve 22 Refrigerant flow meter

23 Water-cooled condenser and evaporator 24 Inspection glass for the water level

25 Water tank(35% glycol, 65% water) 26 Flow meter for water/glycol

27 On/Off switch for axial-flow fan 29 Filter

30 Pressostat pressure switch 31 On/Off switch of the circulation pump

32 Circulation pump V1-V11 Manual valves

T1-T11 Bimetal thermometer RV Check valves

S Inspection windows with moisture indicator

26






Figure 6.1 The components of the Reverse Cycle Refrigeration System

Test Procedure:

Test Results:

27






Worksheet for recording measured data:

28






Conclusions:

Comments:

29






30






Experiment N0. (7)

Computer controlled ِ Air Conditioning Duct

TEST DESCRIPTION

Test Description: The unit has as objective to introduce the student in the air conditioning installations, as well as

to study and determine the good parameters for the unit operation in function of the

environmental demands (humidity, heat, temperature and refrigeration).

Test Objectives: The objectives of this test are:

1- Determination of the airflow, cooling, humidification, de-humidification of an airstream

2- Demonstration of the processes and components used in heating,

3- Efficiency determination of the preheating resistance.

4- Preheating effect in an air conditioning installation.

5- Dehumidification process study.

6- Material balance in the evaporator.

7- Energy balance in the evaporator.

8- Re-heat effect.

9- Experimental determination of the air specific heating capacity.

10- Usage of Psychrometric chart.

11- Enthalpy-Pressure diagram for the refrigerant R134a.

12.-Example of the air properties determination.


distribution to meet the comfort requirements of human beings. The experiment setup is

used as simulation unite of the duct air conditioning system. It has the same components

for measuring, control and fault diagnostics of the air conditioning parameters.

TEST ACTIVITIES

Equipment and Tools: Tunnel of 300 x 300 x 1600 mm. , made of stainless steel with 2 windows of 200 x 300 mm. to

visualize the tunnel inside.

Electrical heating resistances: one of 2000W (pre-heater) to the inlet of the evaporator and other

of 1000 W (re-heater) to the outlet of the evaporator.

Hygrometers placed along the tunnel, formed each one by 2 temperature sensors (wet and dry

bulb).

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3 Fan, with speed variation, 0.25KW, 2500 r.p.m, Qmax 2160 m /h., Evaporator. Compressor,

1/2 CV. Condenser unit. At 5 C =1591W. 980 m /h. High-pressure cut-out, tared at 14 bar.

Filter dryer. Bourdon manometers (3):

1 Bourdon manometer (outlet of the condenser).

1 Bourdon manometer (inlet of the evaporator).

1 Bourdon manometer (outlet of the

evaporator).

Manometer for air flow measurement.

Temperature sensors (11):

4 dry buld “J” type.

4 wet bulb “J” type.

1 “J” type (inlet of the evaporator).

1 “J” type (outlet of the evaporator).

1 “J” type (outlet of the condenser).

o Sensors range: -40 to 750 C.

Flow meter for refrigerant flow measurement.

Psychometric chart and Enthalpy diagram of

R134a.

Electronic Console: Metallic box. Temperature sensors connections. Selector for temperature

sensors. Digital display for temperature sensors. Resistances controllers. Compressor switch.

Fan regulator. High pressure control connection. Cables and accessories, for normal operation.

Test Procedure:

32






Test Results: .

Conclusions:

Comments:

33






Experiment N0. (8)

Computer controlled ِ Air Conditioning Duct with recirculating air

TEST DESCRIPTION

Test Description: The unit has as objective to introduce the student in the air conditioning installations, as well as

to study and determine the good parameters for the unit operation in function of the

environmental demands (humidity, heat, temperature and refrigeration).

Test Objectives: The objectives of this test are:

1- Determination of the airflow, cooling, humidification, de-humidification of an airstream

2- Demonstration of the processes and components used in heating,

3- Efficiency determination of the preheating resistance.

4- Preheating effect in an air conditioning installation.

5- Dehumidification process study.

6- Material balance in the evaporator.

7- Energy balance in the evaporator.

8- Re-heat effect.

9- Experimental determination of the air specific heating capacity.

10- Usage of Psychrometric chart.

11- Enthalpy-Pressure diagram for the refrigerant R134a.

12.-Example of the air properties determination.


distribution to meet the comfort requirements of human beings. The experiment setup is used as

simulation unite of the duct air conditioning system. It has the same components for measuring,

control and fault diagnostics of the air conditioning parameters.

TEST ACTIVITIES

Equipment and Tools: Tunnel made in stainless steel of 300 x 300 x 4000 mm, in which there has been installed 4

windows of 200 x 300 mm. to visualize the tunnel inside.

2 Electrical heating resistances (computer controlled): one of 2000W (pre-heater)

at the inlet of the evaporator and other of 1000 W (re-heater) at the outlet of the

evaporator. Axial fan, with speed control from computer, three-phase, 2500 r.p.m, flow

34






3 maximum 2160 m /h. Evaporator. Compressor, 1/2 Cv, 4.48 A. 3 Condenser unit,

1591BTU’s, Air flow 900 m /h. High-pressure cut-out, tared at 14 bar. It switch off the

compressor when the pressure reach the fix

pressure. Filter dryer. Flow meter and

refrigerant flow sensor, range: 0-60 l./h. 5

Hygrometers placed along the tunnel, formed

each one by 2 temperature sensors

(wet and dry bulb). Temperature sensors (13):

10 Temperature sensors to form five

hydrometers: 5 dry bulb “J” type and 5 wet

bulb “J” type. 3 Temperature sensors in the

refrigeration circuit: 1 “J” type (inlet of the

evaporator), 1 “J” type (outlet of the

evaporator) and 1 “J” type(outlet of the

condenser). Sensors range: -40 to 750 C.

Pressure sensors (4): High pressure sensor 0-

25 bar (outlet of the condenser). Low pressure

sensor 0-10 bar (inlet of the

condenser). Very low pressure sensor 0-1 water inch. It is used to take measure of inlet air flow

by help of an orifice plate 0-100 l/s. Very low pressure sensor 0-1 water inch. It is used to take

measure of outlet air flow by help of an orifice plate 0-100 l/s. Bourdon manometers (3), two of

10 bar and one of 25 bar: 1 Bourdon manometer (outlet of the condenser), 1 Bourdon

manometer (inlet of the evaporator), 1 Bourdon manometer (outlet of the evaporator).

With the trapdoor we can adjust the percentage of recirculating air. Psychrometric chart and

Enthalpy diagram of R134a. .

35






Test Procedure:

36






Test Results:

Conclusions:

Comments:

37






38






Experiment N0. (9)

Air conditioning training split unit and

Refrigeration Cycle training unit

CALCULATION OF COEFFICIENT OF PERFORMANCE OF A SIMPLE REFRIGERATION CYCLE


Test Description: The performance of refrigerators and heat pumps is expressed in terms of coefficient of performance, so basic cooling training set is used to calculate this coefficient.

Test Objectives: The objectives of this test: To observe and understand the principle operation of an ideal refrigeration cycle and calculation of coefficient of performance experimentally.

Theoretical Background: Refrigeration: Is a process of removing heat from one space or substance, and maintaining the temperature of that space or substance below the general temperature of its surrounding. The performance of refrigerators and heat pumps is expressed in terms of coefficient of performance (COP), defined as

C.O.P = Cooling effect / Work input = QL / Wnet,in

The Ideal Vapor-Compression Refrigeration Cycle Figure 1 indicates the main components of the ideal vapor - compression refrigeration cycle and Fig.2 shows P-h diagram for this cycle.

39






Fig.(1) Fig.(2)

Fig.(3)

For this cycle Process Description 1-2 Isentropic compression. 2-3 Constant pressure heat rejection in the condenser. 3-4 Throttling in an expansion valve 4-1 Constant pressure heat addition in the evaporator.

40






1- Compression process (1-2)

Compression of the refrigerant vapour by the compressor is represent by the line(1-2). The compressor adds heat energy to the refrigerant. The line (1-2) represents the gain in enthalpy is called heat of compression. It is work done by the compressor force each 1 Kg of refrigerant circulated through the system. Heat compression equal to change in enthalpy occurring during Compression process.

2- Condensation process (2-3) Condensation takes place at constant pressure in the condenser. As heat is rejected from refrigerant by cooling medium ,refrigerant vapor condensed completely into liquid at point A. The condensation process is represented by line (2-3). Heat rejected in the condenser equal to heat absorbed by the evaporator (hC-hB) plus the heat energy supplied by the compressor (hD –hC ).Heat rejected in the condenser equal to change in enthalpy occurring during condensation process.

3- Expansion process (3-4) Expansion of liquid refrigerant takes place as refrigerant moves through the expansion device from point A to point B. Expansion process is represented by the constant enthalpy line (3-4) .At point B the refrigerant mixed vapour and liquid zone also point B is a lower pressure than A. The refrigerant expand through expansion device without heat gain.

4- Evaporation process (4-1) Evaporation of liquid refrigerant takes place in the evaporator .Evaporation process is represented by constant line (4-1) .It also represented by change in enthalpy resulting heat gain by absorbing heat from refrigerated space, at point C all refrigerant is vaporized. Refrigerating effect is equal to heat absorbed in the evaporator. 2.5 Analysis of The Ideal Vapor-Compression Refrigeration Cycle Using Fig.(3) 1-The shaft work/kg input is given by:

W D= h2 - h1 Where: W D: Work-Done of the compressor. h2 : the enthalpy at discharge of the compressor. h1 : the enthalpy at suction of the compressor. 2-The heat removed is given by :

H.R = h2 - h3 Where:

41






H.R: the heat rejected from the condenser. h2 : the enthalpy at discharge of the compressor h3 : the enthalpy of liquid leaving the condenser. 3-Through expansion process, there is no heat transfer or work..The vertical line showing that h 3 = h 4 4-The heat absorbed (refrigerating effect ) is given by:

R.E = h 1 - h 4 Where: R.E: the heat absorbed by refrigerant in the evaporator. h1 : the enthalpy of vapour leaving the evaporator. h4 : the enthalpy of vapour leaving the expansion device. Also from P-h diagram coefficent of performance can be clculated as follows:

C.O.P = (h1 – h4) /(h2 – h1)

TEST ACTIVITIES

Equipment and Tools: Using the basic cooling training set located in the thermodynamics lab. to calculate the coefficient of performance of an ideal refrigeration cycle. Fig. 4 shows the basic cooling training set.

42






The Basic Cooling Training Set should have been designed to operate and observe the cooling system and also to study the performance of this set. TECHNICAL SPECIFICATIONS

Supply Voltage : 220V - 240V AC, 50/60Hz.

The structure should show the basic cooling system.

Low and High pressure indicators.

The transparent Plexiglass structure should exam and observe the system.

The sight glass to observe the gas flow.

Start - Stop - Emergency stop buttons.

Leakage current and fuse protection.

Block scheme of operation of the system.

Digital heating indicator.

The following items have been avaible on the set.

Digital thermostat, Manometers, Hermetic Compressor.

43






Evaporator and Condenser. As indicated in Fig. 4, two pressures gauges are connected to the high and low sides of the unit.

Test Procedure:

1- Start the unit.

2- Record the evaporator and condenser pressures every ten min.

3- Calculte the absolute pressure.

4- Using the steam tables to find the values of enthalpies or p-h chart.

5- Calculate the coefficient of performance for each case.

6- Compare between the different values.

Test Results:

Condenser pressure

Evaporator pressure

h1 h2 h3 h4 C.O.P

Conclusions:

Comments:

44






Refrigerant Charging and Evacuation Station

Technical Description

ET 150.01 enables the student to study how to empty and

evacuate a refrigerating unit with the aid of a vacuum

pump. Then, the unit can be charged with the correct

amount of refrigerant using a filling balance. The unit is

intended for use with the CFC free refrigerant R134a.

Learning Objectives / Experiments

- Preparing the charging station

- Evacuating a refrigeration system

- Charging a refrigeration system

Advanced Modular Refrigeration System

Technical Description A condensing unit and a refrigeration chamber with integrated evaporator and an electric heater, a

power supply and a frame to mount training panels form the basic module ET 910. The condensing

unit is used to increase the pressure of the working medium and to recool it.

Panels from the available set of training panels ET 910.10 are required to form a complete

refrigeration unit. The selected components are connected with the accessories included in ET

910.12. The ET 150.01 Refrigerant Charging and Evacuation Station is recommended for

charging the system.

Learning Objectives / Experiments Together with ET 910.10, ET 910.12 and ET 910.13

- Layout of compression type refrigeration circuits

- Evacuating and charging of refrigeration systems

- Functioning of components of refrigeration systems

- Cyclic process of refrigeration

- Fault finding

- Different operation modes of the collector

* with and without collector

* pump down

* charging of the refrigeration circuit

- Comparison of different expansion elements

Electrically Heated Absorption Refrigeration unite

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Technical Description

Absorption systems use thermal energy directly. There are three circuits in the system: a

water circuit, an ammonia circuit and a hydrogen circuit. The system comprises a condenser,

an evaporator with heater, an absorber and a cooker with vapour bubble pump for stripping

of ammonia. A cooling load can be simulated at the evaporator using an electrical heater.

Learning Objectives / Experiments

- Operation of an absorption refrigeration system with electrical heater

- Familiarization with the individual components in such a unit

- Demonstration of the refrigeration process.

- Temperature measurement at relevant points in the system

Principles of cooling by absorption

46






Compressor and absorption refrigeration systems differ in terms of the type of drive energy

supplied and in the method they use to increase the pressure.

In an absorption refrigerator, the refrigerant is expelled from an aqueous solution by

supplying heat energy and is then compressed to a high pressure.

The refrigerant vapour is then condensed in a downstream condenser and releases heat.

Reducing the pressure condenses the refrigerant again and absorbs heat from the

environment to be cooled.

The gaseous refrigerant then comes into contact with water again and goes into solution.

This restores the initial condition and completes the process cycle.

The function of an absorption refrigerator without a mechanically powered compressor is

based on two fundamental facts:

• Water has the property that it can absorb large quantities of ammonia when cold and at low

pressure. This ammonia can be expelled again at a higher temperature and pressure.

• Ammonia vapour can be condensed in an enclosed system by pressure and at room

temperature. If it absorbs a large amount of heat, it can be condensed again at a lower

temperature in the presence of an auxiliary gas.

Absorption refrigeration process 1 Boiler: Expels the ammonia NH3 from the rich solution by supplying heat.

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2 Condenser: (warm side) Condenses the ammonia NH3 by releasing heat to the ambient air.

3 Evaporator: (cold side) Depressurises the ammonia using a capillary tube as a restrictor and with

the addition of hydrogen H2 as an auxiliary gas. As a result, the ammonia condenses and absorbs

heat from the material to be cooled.

4 Absorber: Discharges the absorption heat by air cooling, enriches the lean solution with ammonia.

Water circuit

In the supply tank is a mixture of ~65% water(H20) and ~35% ammonia (NH3) This mixture is

known as a “rich solution”. It flows out of the supply tank and into the boiler. Here, ammonia

vapour is expelled from the solution at ~150-180°C and

passes up the riser pipe as bubbles. This results in a pump effect that keeps the entire process

moving. The remaining liquid is known as the “lean solution”.

The vapour pressure presses this solution through the liquid heat exchanger, in which the rich

solution is preheated and into the absorber. The lean solution trickles through the pipe coils in the

absorber back into the supply tank. This completes the liquid circuit.

Ammonia circuit

The ammonia vapour expelled in the boiler reaches the condenser at ~70°C. The condenser is kept at

room temperature by cooling fins. At this temperature and a system pressure of ~25 bar (absolute),

the ammonia vapour condenses. The liquid ammonia flows through a capillary tube, which acts as a

restrictor, through the gas heat exchanger and into the evaporator, where it is depressurized and

moistens the inner surface of the evaporator. At the same time, hydrogen is blown in as an auxiliary

gas. At the lower pressure, the ammonia evaporates by absorbing heat energy from the medium to

be cooled. The ammonia / water gas mixture reaches the supply tank and rises through the pipe coils

in the absorber. Here, it comes into contact with the lean solution from the water circuit and the

ammonia dissolves almost completely back into this solution. The lean solution turns back into a

rich solution.

Hydrogen circuit

The lean solution in the absorber absorbs the ammonia almost completely, while the hydrogen

remains totally unaffected by these processes. The almost pure and lightened hydrogen gas exits the

absorber at the upper end into the evaporator,

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where it is blown over the surface that is moistened with ammonia. The temperature spontaneously

drops to very low values (approx. -15°C), as the liquid ammonia immediately evaporates into the

hydrogen although the overall pressure here is also 25 bar (absolute). However, in terms of the

evaporation of the ammonia only its partial pressure of ~ 1 bar (absolute) is important. Thus, the

pressure in the evaporator is made up as follows:

1 bar (absolute) ammonia vapour + 24 bar (absolute) hydrogen = 25 bar (absolute) total pressure

The continuous evaporation of ammonia means that the partial pressure of the ammonia in the gas

now rises slowly, as does the evaporation temperature.

The gas mixture and liquid pass through the gas heat exchanger and the partial pressure of the

ammonia gradually increases to ~ 3 bar (absolute) and the partial pressure of the hydrogen falls to

22 bar (absolute). The last remaining liquid ammonia

evaporates at a temperature of around -5°C. The weight of a gas mixture made up of hydrogen and

ammonia gas is significantly greater than the weight of pure hydrogen. This heavy gas mixture sinks

downwards into the supply tank from where it flows upwards through the pipe coils in the absorber,

where the gas rich in ammonia meets the lean solution returning from the boiler. The absorber has a

large surface and is also kept close to room temperature by cooling fins. Therefore, the lean solution

is and remains relatively cold and absorbs practically all of the ammonia. What remains is almost

pure hydrogen gas, thus completing this circuit. At the lower end of the absorber, the rich solution

with a high ammonia content drips back into the supply tank.

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