presentation - assignment 2 - energy systems - refrigeration cycle - c. hill - 11-1-2016 5.00am -...

MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 1

University of Central LancashireSchool of Engineering

MP4709 - Energy systems

Refrigeration and heat pump

Presented by:

Tutor: Dr. C. Hill22 January 2016

Hatem AmliGraham WalwynIftikhar BokhariWaqas AkramIllias Lazos


Item

Introduction

Equations

Results

Discussion

Conclusion

References

Contents


Figure 1 vapor compression cycle

Image Source: Refrigeration news [On-Line]: http://refrigerationnew.blogspot.co.uk/2013/02/t-s-refrigeration-cycle.html, accessed in 23rd Dec, 2015

• Consumption of energy and production of electricity drives the modern world and people living in the developed world can’t live without it.

• The illustrated cycle has been developed over many decades –and shows the vapour compression cycle (Figure 1).

• The Vapour Compression Cycle is used in refrigeration systems and uses a refrigerant liquid which is circulated through 4 components i.e. Compressor, Condenser, expansion valve and an evaporator.

• The system works by extracting heat from one source and transmit it to another source.

• This transmission of heat is done through the changing the status of the refrigerant from liquid to gas then liquid again.

• The efficiency of the system is increased by selecting the appropriate refrigerant, with specific properties i.e. volume, heat capacity, mass flow and other thermodynamic properties [1,2], as will be concluded.

Introduction

http://refrigerationnew.blogspot.co.uk/2013/02/t-s-refrigeration-cycle.html


Results KLEA® 134a

Readings Enthalpy (KJ/Kg) Temperature (Co) Pressure (Bar)

H1

H2

H3

H4

326

364

110

110

29.5

81.6

5.7

5.7

2.5

12

12

2.5

Work done on

1kg of

Refrigerant

Heat rejected by

1kg of

refrigerant

Throttling

process

Heat absorbed

by 1kg of

refrigerant

h2 - h1 (kJ/kg) h2 – h3 (kJ/kg) h3 = h4 (kJ/kg) h1 - h4 (kJ/kg)

38 254 110 216

COPRef (134a) 5.6 COPHP (134a) 6.6

Table 1 Results for the refrigerant 134a


ResultsFORANE® 141b

Readings Enthalpy (KJ/Kg) Temperature (Co) Pressure (Bar)

H1

H2

H3

H4

460

504

204

204

37.9

67.6

8.6

8.6

0.3

1.1

1.1

0.3

Work done on

1kg of

Refrigerant

Heat rejected by

1kg of

refrigerant

Throttling

process

Heat absorbed

by 1kg of

refrigerant

h2 - h1 (kJ/kg) h2 – h3 (kJ/kg) h3 = h4 (kJ/kg) h1 - h4 (kJ/kg)

44 300 204 256

COPRef (141b) 5.8 COPHP (141b) 6.8

Table 2 Results for the refrigerant 141b


Results

Figure 4 P-H chart for refrigerant 134a, the closed cycle is illustrated with dots and labels from H1 to H4


Results

Figure 5 P-H chart for refrigerant 141b, the closed cycle is illustrated with dots and labels from H1 to H4


Discussion

• Although accuracy was taken into consideration during the experiment, there still

would be percentage of error in the readings -due to having a system that is affected

by its immediate surrounding environment.

• The pipes in the system are not properly isolated. So the system losses some of its

heat. But, since the system is connected to an external electrical source, The power

received would include work to the system to maintain the performance that the

system was designed to give.

• The difference in the two main properties in thermodynamics, (Temperature and

Pressure), can result in adjusting the system’s input and output according to the need.


Discussion

As for the vapour compression cycles

for the two systems, one case was

taken as an example for full

explanation as follows:

H1 to H2

• isentropic compression

• H2 - H1 forms the work paid to

the system in order to increase the

pressure, and temperature

• From evaporator, to the

compressor

• converts the refrigerant from a

saturated vapour state to a

superheated vapour.Figure 4 P-H chart for refrigerant 134a, the closed cycle is illustrated with dots and labels from H1 to H4

MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016


12

Discussion

H2 to H3

• isothermal heat rejection

• The refrigerant exits the compressor

and passes through the condenser

• The super heated vapour converts to

sub cooled liquid

• It cools down by the effect of cooling

medium like surrounding air or water

• Pumps heat

• The difference indicates the heating

effect the system delivers



13

Discussion

H3 to H4

• isentropic expansion

• The pressure maintained and

faces an other decrease in

temperature.

• Throttling

• the refrigerant converts from

sub cooled liquid to saturated

liquid

• The expansion valve

• Increase in its volume, and the

temperature drops



14

Discussion

H4 to H1 (Final stage)

• Isothermal heat addition

• The refrigeration effect of the

system is acquired

• Goes from the expansion valve to

the evaporator

• It converts from saturated liquid

to liquid and vapour state.

When it reaches stage H1 again, the

refrigerant converts to saturated

vapour, and this completes the cycle.


Figure 4 P-H chart for refrigerant 134a, the closed cycle is illustrated with dots and labels from

H1 to H4

15

Compression

Figure 1 vapor compression cycle


Conclusions

• The refrigeration and heat pump cycles for two lab machines where investigated. The

efficiency of refrigerants was benchmarked. In order to have a more efficient

refrigerating system, the refrigerant has to have the following properties: It should

have a small vapour specific volume, require the minimum amount of work to be

applied for compression, require small mass flow rate.

• These properties would result in a cooling or heating system (depending on the

application) that requires lower power input, and smaller compressor volume. In

addition, low specific heat, low condensing pressure properties would increase the

efficiency of the system and reduce maintenance.

• It was noted that COP for heat pump is always higher than it is for refrigeration. This is

because heating effect is always greater than cooling effect in the same cycle, as

acquired form the charts Figure 4 and Figure 5.


Conclusions

• There is no ideal closed system, since that all processes are not reversible and all heat

flow occur with finite temperature difference. This causes increase in Entropy and

requires more work to be paid for the system.

• The same system can be used as refrigeration system, or as heat pump system,

depending on the application. In case of refrigeration, refrigerants evaporate and

absorb heat at low temperature and pressure. As well as rejecting heat by condensing

at higher temperature and pressure.

• Key features in the refrigerants that significantly affect the performance of the system

are pressure, temperature, and volume. In addition to that, thermodynamic properties,

entropy and enthalpy are prime features which must be taken into consideration in the

system design.

• The Pressure-Enthalpy chart gives clear idea on how the system works, nevertheless,

for a more accurate figures, steam tables from literature is preferred.


• [1] BOLES, M. y CENGEL, Y. Thermodynamics: An Engineering Approach. McGraw-Hill

Education, 2014.

• [2] MORAN, M.J., SHAPIRO, H.N., BOETTNER, D.D. y BAILEY, M.B. Fundamentals of

Engineering Thermodynamics, 8th Edition: Wiley, 2014.

References

presentation - assignment 2 - energy systems - refrigeration cycle - c. hill - 11-1-2016 5.00am -...

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