Refrigeration Unit Lab Report fkk

ABSTRACT.

This experiment demonstrated the general operation of vapor compression heat pump.

In order to determine the power input and coefficient of performance of the heat pump, the

temperature and pressure of water and refrigerant are observed. The process cycle of heat

pump is clearly illustrated in pressure enthalpy diagram. The compressor pressure ratio and

volumetric efficiency are also calculated. The objectives of this experiment successfully

achieved. This experiment is successful achieved although the experiment do not produce a

good result since the execution of the procedure is not fully accurate.

.

INTRODUCTION.

A refrigeration unit is a unit composed of several machineries that can transfer heat

from a low-temperature region to a high-temperature region. Normally heat can only be

transfer from a high temperature region to low, so to reverse this process, a refrigerator is

needed. Refrigerator consists of four main components which are; compressor, evaporator,

expansion valve and condenser. Each component works together to perform a series of

process. The process includes a cycle of refrigerant and a flow of cooling water.

In the experiment, the refrigeration unit used is SOLTEQ Mechanical Heap Pump

(Model: EH165). The device is design to give understanding to the user on how refrigeration

process worked.

The SOLTEQ Mechanical Heat Pump (Model: HE165) is a bench top unit with all

components and instrumentations mounted on the sturdy base. The heat pump consists of a

hermetic compressor, a water-cooled plate heat exchanger, a thermostatic expansion valve

and a water heated plate heat exchanger. The arrangements of the components are in a

manner similar to many domestic air- water heat pumps where they are visible from the front

of the unit.

During the operation, slightly superheated refrigerant (R-134a) vapor enters the

compressor from the evaporator and its pressure is increased. Thus, the temperature rises

and the hot vapor then enters the water cooled condenser. Heat is given up to the cooling

water and the refrigerant condenses to liquid before passing to the expansion valve. Upon

passing through the expansion valve, the pressure of the liquid refrigerant is reduced. This

causes the saturation temperature to fell to below that the atmospheric. Thus, as it flows

through the evaporator, there is a temperature difference between the refrigerant and the

water being drawn across the coils. The resulting heat transfer causes the refrigerant to boil,

and upon leaving the evaporator it has become slightly superheated vapor, ready to return to

the compressor.

The temperature at which heat is delivered in the condenser and the evaporator is

controlled by the water flow rate and its inlet temperature. Instrumentations are all provided

for the measurement of flow rates of both refrigerant and cooling water, power input to the

compressor and all relevant temperatures.

AIMS/OBKECTIVES.

i.Experiment 1

The objectives of this experiment is to determine the power input, heat output and coefficient

of perfomance.

ii.Experiment 2

The objectives of this experiment is to determine the production of heat pump perfomance

curves over a range of source and delivery temperatures.

iii.Experiment 3

The experiment is to determine the production of vapor compression cycle on p-h diagram

nd energy balance study

iv.Experiment 4

The experiment is to study determine the production of heat pump perfomance curves over a

range of evaporating and condensation temperature.

v.Experiment 5

The objectives of this experiment is to estimate the effect of compressor pressure ratio on

volumetric efficiency.

THEORY.

A heat pump is a mechanism that absorbs heat from waste source or surrounding to

produce valuable heat on a higher temperature level than that of the heat source. The

fundamental idea of all heat pumps is that heat is absorbed by a medium, which releases the

heat at a required temperature which is higher after a physical or chemical transformation.

Heat pump technology has attracted increasing attention as one of the most

promising technologies to save energy. Areas of interest include heating of buildings,

recovery of industrial waste heat for steam production and heating of process water for e.g.

cleaning, sanitation.

Generally, there are three types of heat pump systems:

i) Closed cycle vapor compression heat pumps (electric and engine driven)

ii) Heat transformers (a type of absorption heat pump)

iii) Mechanical vapor recompression heat pumps operating at about at 200°C

Closed Cycle Vapor Compression Heat Pump

Most of the heat pumps operate on the principle of the vapor compression cycle. In this

cycle, the circulating substance is physically separated from the heat source and heat

delivery, and is cycling in a close stream, therefore called ‘closed cycle’. In the heat pump

process, the following processes take place:

i) In the evaporator the heat is extracted from the heat source to boil the circulating

substance

ii) The circulating substance is compressed by the compressor, raising its pressure

and temperature

iii) The heat is delivered to the condenser

iv) The pressure of the circulating substance (working fluid) is reduced back to the

evaporator condition in the throttling valve.

Figure 1: The closed loop compression cycle

Vapor Compression Heat Pump System Principles

Figure 2: Vapor compression heat pump cycle

The components are;

1) Condenser

2) Compressor

3) Expansion Valve

4) Evaporator

Four basic processes or changes in the condition of the refrigerant occur in a Vapor

Compression Heat Pump Cycle. These four processes shall be illustrated in the most

simplistic way with the aid of above figure.

i) Compression Process (t 1¿ t 2)

The refrigerant at the pump suction is in gas at low temperature and low

Pressure. In order to be able to use it to achieve the heat pump effect

continuously, it must be brought to the liquid form at a high pressure. The first

step in this process is to increase the pressure of the refrigerant gas by using a

compressor. Compressing the gas also results in increasing its temperature.

ii) Condensing Process (t 2¿ t 3)

The refrigerant leaves the compressor as a gas at high temperature and

pressure. In order to change it to a liquid, heat must be removed from it. This is

accomplished in a heat exchanger called the condenser. The refrigerant flows

through one circuit in the condenser. In the other circuit, a cooling fluid flows

(normally air or water), at a temperature lower than the refrigerant.

Heat is therefore transferred from the Refrigerant to the Cooling fluid and as a

result, the refrigerant condenses to a liquid state (3). This is where the heating

takes place.

iii) Expansion Process (t 3¿ t 4)

At Point (3), the refrigerant is in liquid state at a relatively high pressure and

temperature. It flows to (4) through a restriction called the flow control device or

expansion valve. The refrigerant loses pressure going through the restriction. The

Pressure at (4) is so low that a small portion of the refrigerant flashes (vaporizes)

into a gaseous. In order to vaporize, it must gain heat (which it takes from that

portion of the refrigerant that did not vaporize).

iv) Vaporizing Process (t 4 ¿ t1)

The refrigerant flows through a heat exchanger called the evaporator. The heat

source is at a slightly higher temperature than the refrigerant, therefore heat is

transferred from it to the refrigerant. The refrigerant boils because of the heat it

receives in the evaporator. By the time it leaves the evaporator (4) it is completely

vaporized.

Understanding the Pressure Enthalpy Diagram

Figure 3: A pictorial representation of a P-H diagram

Using the chart of R-134a Refrigerant (Figure 3), we shall attempt to explain the use of it:

The Chart is divided into THREE areas. These three areas are separated from each other by

the following:

a) Saturated liquid

b) Saturated vapor line

The area on the chart to the left of the Saturated Liquid line is called the SUBCOOLED

region. At any point in the sub-cooled region, the refrigerant is in the LIQUID phase and its

Temperature is below Saturation temperature corresponding to its Pressure.

The area to the right of the Saturated Vapor line is the SUPERHEATED region, and the

refrigerant is in the form of a SUPERHEATED VAPOR.

The area between the SATURATED LIQUID and the SATURATED VAPOR lines is the

mixture region and represents the change in phase of the refrigerant between the liquid and

Vapor phases. Thus, at any point between the two saturation lines the refrigerant is in the

form of liquid-vapor mixture.

The distance between the two lines along any constant pressure line is known as the

“latent heat of vaporization” at that pressure.

The Saturated Liquid line and Saturated Vapor line are not exactly parallel to each other

because the "latent heat of vaporization" varies with the pressure at which the change in

phase occurs.

This change of phase from liquid to vapor phase takes place progressively from LEFT to

RIGHT and the change in phase from vapor to liquid phase occurs from RIGHT to LEFT.

At any point on the Saturated Liquid line, the refrigerant is at SATURATED LIQUID and

at any point along the SATURATED VAPOR LINE, the Refrigerant is a SATURATED

VAPOR.

The HORIZONTAL LINES, extending across the chart are CONSTANT PRESSURE Lines.

The VERTICAL Lines are Lines of CONSTANT ENTHALPY.

The Lines of Constant Temperature varies, depending on the phase stage. It is

almost VERTICAL in the SUBCOOLED region and is PAPALLEL to lines of CONSTANT

ENTHALPY.

It however changes at the CENTRE section, since the refrigerant changes state at a

CONSTANT TEMPERATURE AND PRESSURE, the lines of Constant Temperature are

now, parallel to constant Pressure line. At the Saturated Vapor line, the lines of Constant

Temperature changes direction again and upon entering the SUPERHEATED VAPOR

REGION, it falls off sharply towards the bottom of the chart.

The ENHALPY Values are found on the Horizontal scale at the bottom of the chart.

The Magnitude' of the Pressure in bar/MPa is read on the vertical scale at the left side of the

chart.

Temperature values in degrees Celsius are found adjacent to constant temperature

lines in sub-cooled and superheated regions of the chart on both Saturated Liquid and

Saturated Lines.

It is worthwhile to note that the p-h diagram is based on a limb mass of the

refrigerant, the volume given is the specific volume, the Enthalpy is in kJ per kg, and the

entropy is in kJ per kg per degree of absolute temperature.

Obtain the Enthalpy Values from P-H Diagram

To obtain the following values, we first refresh our memory from the previous chapter on:

a) Flow diagram of a Simple Saturated Cycle

b) Enthalpy or p-h diagram of R-134A, Simple Saturated Cycle, as shown below;

Figure 4: Flow diagram of a simple saturated cycle

Figure 5: Comparison of two simple saturated cycles operating at different

vaporizing temperatures (figure distorted) (Refrigerant-134a)

Figure 6a: Skeleton P-H chart illustrating the three regions of the chart and the

direction of phase changing

Figure 6b: Skeleton P-H chart showing oaths of constant pressure, constant

temperature constant volume, constant enthalpy, and constant entropy

(Refrigerant-134a)

Figure 6c: Pressure-enthalpy diagram of a simple saturated cycle operating at a

vaporization temperature of 200F and a condensing temperature of 1000◦F

(Refrigerant – 134a)

In recalling, and referring back to Figure 5 and 6, of a Simple Saturated Cycle, we now thus

obtained the following values:

h1 = The Enthalpy at Point 1, which is the point where “Compression Process" begins

(This is also where we obtained the Temperature Reading, TT1 for the process)

h2 = The Enthalpy at Point 2, which is the point where "Compression Process" ends.

h3 = The Enthalpy at Point 3, which is the point where "Condensation" is complete.

(This is also where we obtained the Temperature Reading, TT3 for the process)

Thus,

h2 – h3 = Refrigerating Effect (See figure 5)

While,

h2 – h1 = Heat of Compression (See figure 5)

Figure 7: Pressure-enthalpy diagram of a simple saturated cycle operating at a

vaporizing temperature of 20oF and a condensing of 100◦F (Refrigerant- 134a)

Coefficient of Performance

The Coefficient of Performance, (COPH) of a heat pump cycle is an expression of the cycle

efficiency and is stated as the ratio of the heat removed in the heated space to the heat

energy equivalent of the energy supplied to the Compressor.

COPH = Heat removed from heated space / Heat energy equivalent of the Energy supplied

to the compressor.

Thus, for the Theoretical Simple Cycle, this may be written as:

COPH = Heating Effect

Heat of Compression

= (h2−h3)(h2−h1)

APPARATUS.

Figure 8: Unit construction for Mechanical Heat Pump (Model: HE165)

1. Pressure switch

2. Receiver tank

3. Compressor

4. Condenser

5. Pressure transmitter

6. Control panel

7. Evaporator

8. Refrigerant flow meter

9. Water flow meter

PROCEDURES.

i. General Operating Procedures

A. General Start-Up Procedures

1. The unit and all instruments are checked to ensure they are in proper conditions.

2. The water source and drain are checked to ensure they are connected. The water supply is

open and the cooling water flowrate is set as 1.0 LPM

3. The drain hose at the condensate collector is checked to ensure it is connected.

4. Power supply is connected. The main switch is on at the main power and main switch on

control panel.

5. Refrigerant compressor is switch on.when the temperature and pressure is constant, the unit

is ready for experiment.

B. General Shut-Down Procedures

1. The compressor is switched off followed by the main switch and power supply.

2. The water supply is closed.

Experiment 1

1. Geeral start up procedure is performed.

2. The cooling wate r flow rate is adjusted to 40%

3. The system is run for 15minutes.

4. The reading is recorded.

Experiment 2

1. The The general start-up was run.

2. The cooling water flow rate was adjusted to 60%..

3. The system was allowed to run for 15 minutes.

4. All the necessary reading was recorded in the table.

5. The procedure 1 to 4 was repeated with different cooling water flow rate. (40% and 20%)

6. All the necessary reading was recorded in the table

.

Experiment 3

1. The general start-up was run.

2. The cooling water flow rate was adjusted to 40%.



Experiment 4





5. The procedure 1 to 4 was repeated with different cooling water flow rate. (40% and

20%)


Experiment 5





RESULTS AND CALCULATIONS

EXPERIMENT 1

Cooling Water Flow Rate, FT1 % 40

Cooling Water Flow Rate, FT1 LPM 2

Cooling Water Inlet Temperature, TT5 °C 30.3

Cooling Water Outlet Temperature , TT6 °C 31.5

Compressor Power Input W 165

Cooling water flow rate (LPM) = Coolingwater flow rate(%)

100% x 5 LPM

Refrigerant flow rate (LPM) = Refrigerant flow rate(%)

100% x 1.26 LPM

Heat output

2000 mLmin

x 1 g1mL

x 1kg1000g

x 1min60 s

= 0.033 kg/s

T (K )=T (℃)+273.15

C p@25℃−50℃=4.18 kJkg . K

Q=mC pdT

¿0.033kg (4180 Jkg . K )(31.5−30.3)K

¿165.53W

Coefficient of performance

COPR=Desired outputRequired input

=QL

W net ,∈¿¿

¿ 165.53165.0

¿1.0032

EXPERIMENT 2

1 2 3

Cooling Water Flow Rate, FT1 % 60 40 20

Cooling Water Flow Rate, FT1 LPM 3 2 1

Cooling Water Inlet Temperature, TT5 °C 30.2 30.3 30.2

Cooling Water Outlet Temperature , TT6 °C 31.3 31.3 33.0

Compressor Power Input W 164 165 167

Heat Output W 151.73 206.91 386.23

COPR 0.92 1.25 2.31

*The calculations are similar to that in Experiment 1.

31.2 31.4 31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.2162.5

163

163.5

164

164.5

165

165.5

166

166.5

167

167.5

164

165

167

Power input vs temperature

Temperature ( )℃

Pow

er In

put (

W)

31.2 31.4 31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.20

50

100

150

200

250

300

350

400

450

151.73

206.91

386.23

Heat output vs temperature

Temperature ( )℃

Heat

out

put (

W)

31.2 31.4 31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.20

0.5

1

1.5

2

2.5

0.92

1.25

2.31

COP vs temperature

Temperature ( )℃

COP

EXPERIMENT 3

Refrigerant Flow Rate, FT2 % 61.3

Refrigerant Flow Rate, FT2 LPM 0.77

Refrigerant Pressure (Low), P1 Bar

(abs)

2.0

Refrigerant Pressure (High), P2 Bar

(abs)

7.1

Refrigerant Temperature, TT1 °C 28.7




Cooling Water Flow Rate, FT1 % 40.1

Cooling Water Flow Rate, FT1 LPM 2.01

Cooling Water Inlet Temperature, TT5 °C 30.3

Cooling Water Outlet Temperature , TT6 °C 31.9

Compressor Power Input W 165

Point 1 2 3 4

Pressure (bar) 2.0 7.1 7.1 2.0

Temperature (℃¿ 28.7 82.0 31.1 24.7

Enthalpy (kJ/kg) 277.76 320.15 269.56 274.27

*All of the enthalpy value was obtained from the property table of R-134a (interpolation)

P2−P1P3−P1 = T 2−T 1T 3−T 1

277.76 320.15 269.56 274.270

1

2

3

4

5

6

7

8

2

7.1 7.1

2

Pressure

Enthalpy (kJ/kg)

Pres

sure

(bar

)

*The cycle is out of the curve (all of the state is in superheated vapor)

Figure 9: Ideal vapor compression cycle

Compressor energy balance

Q¿

−W¿

=m¿

(Δh−Δpe−Δke )

Q¿

=0 , Δke=0 , Δ pe=0

W¿

=m¿

Δh

Condenser energy balance

Q¿

−W¿

=m¿

(Δh−Δpe−Δke )

W¿

=0 , Δke=0 ,Δ pe=0

Q¿

=m¿

Δh

Q¿

=∑in

m¿

h−∑out

m¿

h

EXPERIMENT 4

1 2 3

Refrigerant Flow Rate, FT2 % 61.2 61.2 61.3

Refrigerant Flow Rate, FT2 LPM 0.77 0.77 0.77

Refrigerant Pressure (Low), P1 Bar (abs) 2.0 2.0 2.0

Refrigerant Pressure (High), P2 Bar (abs) 7.1 7.1 7.1

Refrigerant Temperature, TT1 °C 28.8 28.6 28.3




Entalphy 1 (P1, TT1) kJ/kg 277.84 277.67 277.41



Evaporating Temperature (TT4) °C 24.5 24.4 24.5

Condensing Temperature (TT3) °C 30.8 31.1 32.30

Compressor Power Input W 163 165 164

Heat Delivered in Condenser (Refrigerant) W 0.665 0.659 0.634

COPH 1.204 1.193 1.169

*All of the enthalpy value was obtained from the property table of R-134a (interpolation)

0.77 Lmin X

1000mLL X

gmL X

kg1000g X

min60 s = 0.013 kg/s

Trial 1

Q = m∆h

= m(h2-h3)

= 0.013(320.35-269.18)

= 0.665 kW

COPH = HeatingEffect

Heat of Compression

= (h2−h3)(h2−h1)

= 321.55−268.7321.55−276.74

= 1.179

*The same calculations are used for Trial 2 and 3.

EXPERIMENT 5

Refrigerant Flow Rate, FT2 % 61.1

Refrigerant Flow Rate, FT2 LPM 0.77

Refrigerant Pressure (Low), P1 Bar

(abs)

2.0

Refrigerant Pressure (High), P2 Bar

(abs)

7.1


Compressor pressure ratio = Suction pressure of refrigerantDischarge pressure of refrigerant =

P1P2

= 27.1

= 0.282

Volumetric efficiency = Actualmass flow rate

Theoreticalmass flow rate

DISCUSSIONS.

Boyle’s law stated that the pressure of gas inversely proportional to the volume of a

container. From the results recorded, some calculation have been made in order to know the

difference value between before and after of the experiment one. These values are very

small and close with the theoretical value, therefore the Boyles’s Law is verified. According to

the data tabulated, it can been said that the pressure and volume inversely proportional.

When the pressure increase, the volume start to decrease. This is happen because if the gas

of the same pressure with constant temperature injected into small and big container which

means have different volume. The gas molecule in small container have less spacious room

and will collide to the wall and with each other more often which exert more pressure.

Gay-Lussac’s Law stated that pressure is directly proportional to the temperature which

means if the pressure increase, the temperature also increase with constant volume.

Experiment two has been conducted in order to know the relationship between pressure and

temperature. Therefore, from the data tabulated and graph plotted, it can be said that the

Gay-Lussac’s Law is verified. The same concept applied here, if the temperature of a gas in

a container increase, the heat energy of the system transfer its energy into the molecule of

gas which actually increase the frequency of collision in that container which exert more

pressure.

Isentropic expansion process occur when the system are reversible and adiabatic

where no heat will be transferred in or out and no energy transformation occurs. From the

data recorded, a constant k are now known which is equal to 1.443. It was obtained that both

temperature and pressure of the gas before expansion were higher compared to after the

expansion. The process is said to be isentropic since there was no change in the entropy

throughout the process.

Stepwise depressurizationis a strategy to adopt an equal time-stepwise

depressurization approach in this study yield a more reliable result for an example in the

production sector in industries. The molecule in the container affected when the number of

them decreasing slowly as they do not have to collide between them more often. The

depressurization shown that pressure decrease with time and also affecting the temperature.

As the pressure decrease, the temperature also decrease in the system.

Brief depressurization shown in the graph plotted in result section which is decrease

more linear compared to stepwise. The expansion occur when the pressure of gas increase.

Expansion of gas decrease as the gas is free to flow out time by time.

Ratio volume can be determined by manipulating the equation of Boyle’s law.

Boyle’s law proposed an equation P1V1=P2V2 and after manipulate the equation ratio

volume can be determine by V2/V1=P1P2. This experiment test in three different condition

where first condition the gas is flow from tank 1 to tank 2, while gas flow from tank 2 to tank 1

in second condition and both were filled with gas in third condition. The theoretical value is

0.495 in this experiment where the error or percentage difference was between 10 and -10.

There must be environmental factors that affect the stability of pressure and temperature or

random mistake during experiment. The percentage error is high due to some error during

conducting the experiment. Some of air probably left from chamber due to not properly close

the valve or before the experiment, the gas did not left out completely from the chamber.

Determination of ratio of heat capacity using the expression of the heat capacity ratio and

it gives the 1.1584. The theoretical value of this experiment is 1.4. The deviation which now

is equal to 21%. The deviation is due to measurement error. The actual intermediate

pressure supposed to be lowered that the measured one. Unfortunately the error occur due

to heat loss and sensitivity of pressure sensors. Supposed, the intermediate pressure taken

as the lowest pressure at the moment the valve is closed. Since the percentage difference is

more than 10%, the experiment can be declared as failed.

COCLUSIONS.

In conclusion, the experiment was aimed at determining the properties of measurement /PVT

according to the Boyle’s law, Gay-Lussac’s Law, isentropic expansion, and heat capacity

equation. In fact, in this experiment, we have proven the Boyle’s law and Gay-Lussac’s law.

Although our experiment failed, but we have the reason behind the failure. For experiment 7,

the failure was due to the fact that an intermediate pressure was not taken after the valve

closed. However, the experiment was successfully done in final, and the objective of the

experiment was accomplishedly achieved.

RECOMMENDATIONS.

There are several improvements that can be performed so as to obtain a more satisfying

result in future. Before starting this experiment, we are supposed to do a start-up and shut-

down step in order to make sure there is no gas left in the chamber. Most importantly, during

recording data, keep an eye on the sensor while monitoring the board because the

parameter can increase and decrease really fast and read the procedure carefully.

In addition, obtain an average reading by repeating the experiment for three times in

order to reduce the range of deviation. Handle the valve carefully and try not to make

mistake by choosing the valve because it will affect the data. The place where the

experiment is conducted also must be at stable and no vibration. All the equipment must be

handled carefully in order to avoid explosion because over-pressure in the tank would cause

an explosion.

REFERENCES.

Engineering Sciences 182: PVT Measurement And Properties Of a Simple Compressible

Substances. (n.d). Retrieved from

http://sites.fas.harvard.edu/~es181/handouts/lab01_PVT_f05_v9.pdf

Charles's Law. (2010). Retrieved from Sparknotes:

http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter5section8.rhtml

Charles's Law. (n.d.). Retrieved from how stuff works:

http://science.howstuffworks.com/dictionary/physics-terms/charles-law-info.htm

Calculating PVT Properties. (n.d). Retrieved from

http://petrowiki.org/Calculating_PVT_properties

http://petrowiki.org/Calculating_PVT_properties

http://science.howstuffworks.com/dictionary/physics-terms/charles-law-info.htm

http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter5section8.rhtml

http://sites.fas.harvard.edu/~es181/handouts/lab01_PVT_f05_v9.pdf

APPENDIX.

1. Pressure switch

2. Receiver tank

3. Compressor

4. Condenser

5. Pressure transmitter

6. Control panel

7. Evaporator

8. Refrigerant flow meter

9. Water flow meter

Documents

Refrigeration Unit Lab Report fkk