Simulation On The Performance of a Stirling Cooler For Use in Solar Powered Refrigerator
Solar electricity produced bj. photovoltaic (PV) solar cells is one of the promising sources of power for solar refrigerator. Presently, solar PV is used to power conventional vapor compression or Rankine refrigerators. In this work, three photovoltaic freezers with different capacities and volum...
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Format: | Thesis |
Language: | English English |
Published: |
2004
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Online Access: | http://psasir.upm.edu.my/id/eprint/6374/1/FSAS_2004_47.pdf |
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Summary: | Solar electricity produced bj. photovoltaic (PV) solar cells is one of the promising
sources of power for solar refrigerator. Presently, solar PV is used to power
conventional vapor compression or Rankine refrigerators. In this work, three
photovoltaic freezers with different capacities and volumes of 100, 230 and 330
liters have been designed and tested. The freezers used the conventional vapor
compression Rankine cycle. For the 100-liter freezer a minimum cabinet
temperature of -20.1°C was obtained. The maximum and minimum cooling
capacity were semi-empirically computed to be 304W and 85.8W and the
corresponding power consumptions were 139W and 70.1 W respectively.
Coefficient of performance was calculated to be 2.19 and 1.22 respectively at the
maximum and minimum temperatures. For the 230-liter freezer, a temperature of
-1 5.2"C was achieved. The cooling capacity. power consumption, coefficients of
performance \+ere obtained semi-empiricall!~. Similar experimental analysis was
done on the 330-liter freezsr to achieve a temperature of -5°C. All these freezers
were tested for condenser teniperati~reo f 54°C and ambient temperature of 38°C.Limitations of the vapor compression refrigerator were highlighted; these include
insufficient power from the 75W solar panel to run the refrigerator's compressor
and therefore a backup battery is always required. But, battery is expensive and
has a limited charge /discharge cycles.
To allow for the use of photovoltaic module to power bigger size refrigerator, a
new age of refrigeration technology such as a free piston Stirling cooler is used to
replace the vapor compression refrigerator. The free piston Stirling cooler uses
small amount of power effectively besides elimination of battery since free piston
Stirling cooler can use phase change material to store cooling when there is
insufficient power (low solar insolation and night time operation).
The general principle in which a Stirling machine self-limits its operation was
presented. The proposed design of the Stirling cooler was described and 'the
performances of the cooler were simulated using the MATLAB computer
software. Three types of analyses were carried out i.e. ideal adiabatic, Schmidt
and non-ideal adiabatic.
Results from the ideal adiabatic analysis showed that the total power output was
101.2W. Coefficient of performance of 3.6 was obtained, which was found to be
about 21.5% of the Carnot COP. The COP was calculated for cold space
temperature of -1 0°C and warm space temperature of 27°C. The heat absorbed by
the acceptor was found to be 44.28W while the heat released by the rejector was
computed to be 56.51 W.For isothermal conditions of the working space and heat exchangers, Schmidt
analysis was carried out for cold space temperature of -lO°C and warm space
temperature of 23OC. From the MATLAQ results, work done on the expansion and
by the compression spaces were found to be 8.813~10" and -9.283~10-'J
respectively. Total work done was calculated to be 1.1451~0 -'J.
The effects of the non-ideal heat exchangers and the difference in the working gas
and wall temperatures were determined through a non-ideal adiabatic analysis.
The gas temperature was obtained through iteration until convergence was
achieved. Coefficient of performance of 3.8 was obtained for ideal regenerator
and then reduced to 2.4 for a non-ideal regenerator when pumping loss was taken
into account for the same temperatures of the working spaces.
Performance of operation, in terms of power consumption and cooling capacity, of
the vapor compression refrigerator and Stirling type refrigerator was carried out.
The comparison was based on the experimental data obtained for the vapor
compression refrigerator and output data derived from MATLAB analysis for the
Stirling refrigerator. The power consumption of the Stirling refrigerator was
calculated to be 20W while that of the vapor compression was computed to be
139W. |
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