presentation - assignment 2 - energy systems - refrigeration cycle - c. hill - 11-1-2016 5.00am -...
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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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 2
Item
Introduction
Equations
Results
Discussion
Conclusion
References
Contents
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 3
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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 4
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 5
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 6
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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 7
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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 8
Results
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 9
Results
Figure 5 P-H chart for refrigerant 141b, 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 10
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.
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 11
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
Figure 4 P-H chart for refrigerant 134a, the closed cycle is illustrated with dots and labels from H1 to H4
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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016
Figure 4 P-H chart for refrigerant 134a, the closed cycle is illustrated with dots and labels from H1 to H4
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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016
Figure 4 P-H chart for refrigerant 134a, the closed cycle is illustrated with dots and labels from H1 to H4
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.
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016
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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 16
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.
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 17
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.
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 18
• [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
MP4709 | Energy Systems | Refrigeration and Heat pump | Student: Hatem Amli | Tutor: Dr. C. Hill | 17 th Jan, 2016 19