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1

Thermodynamic Analysis of a Cascade Refrigeration System

100%

Karaali R.

Acta Physica Polonica A

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2016

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vol. 130

|

issue 1

101-106

EN

There is a need for cooling by using the waste heat energy in food industry. Absorption cycles can be driven by waste thermal, geothermal, solar or industrial processes energies. In this study, cascade refrigeration system is thermodynamically modeled, and analyzed by using first law of thermodynamics, and exergy method. Thermodynamic properties such as pressure, temperature, entropy, enthalpy, exergy, mass flow rate in each stream are calculated for 50, 75, 100°C and for 0.8, 1.0, and 1.5 MPa pump pressure. A computer program is used that was prepared in FORTRAN by the author for the analyses. It is found that the compression-absorption cascade cooling cycle is appropriate for most of the kind of waste heat applications. Increase of the generator inlet heat temperature increases the generator inlet heat, the absorber outlet heat and the condenser 2 outlet heat energies and decreases the coefficient of performance of the absorption and the overall cycles. The generator heat decreases with increase of the pump pressure. Also increase of the pump pressure decreases the coefficient of performance of the absorption and the overall cycles. Increase of the pump pressure and the generator temperature decreases the exergetic coefficient of performance. Increase of the generator temperature and pump pressure increases the generator inlet exergy. It is concluded that increase of the generator temperature and the pump pressure increases the total destructed exergy of the cycle.

2

Effect of Phase Change Materials on Time Lag, Decrement Factor and Heat-Saving

80%

Bilgin F., Arıcı M.

Acta Physica Polonica A

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2017

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vol. 132

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issue 3

1102-1105

EN

In this study, the effect of phase change materials on the time lag, decrement factor and heat-saving is examined numerically. The calculations are conducted for four different cities located at different climatic zones in Turkey, considering both summer and winter conditions, in order to explore the potential heating and cooling energy savings by employing phase change materials. A solar-air temperature, which is a function of time and solar radiation, was taken into consideration as external boundary condition for each city. The results of the present study show that employment of phase change materials in walls of the buildings has a pronounced effect on the time lag and decrement factor. It is concluded that a significant amount of heating energy can be saved and thermal comfort can be enhanced considerably by incorporating phase change materials into external walls. However, a proper phase change material must be selected, considering different climatic conditions.

3

Exergy Analysis of a Combined Power and Cooling Cycle

80%

Karaalı R.

Acta Physica Polonica A

|

2016

|

vol. 130

|

issue 1

209-213

EN

Ammonia-water power cycles are important for efficient utilization of low temperature heat sources such as geothermal, solar, waste heat sources, etc. For some special conditions ammonia-water power cycle is an important and economical option. This paper presents an exergetic analysis of a combined power and cooling cycle that uses ammonia-water mixture as working fluid. Such cycles, use solar or geothermal energy or waste heat energy from a conventional power cycle. Ammonia-water power cycle can be used as independent cycles to provide power output and cooling. For a range (25-55 Bar) of boiler pressure the performance of the combined power and cooling cycle is investigated. The exergy of the boiler is very low compared to its energy. There is a boiling process and a heat transfer process at low temperature, both of which destruct the energy given to the boiler, so that the energy efficiency is low; however the exergy efficiency is higher than the energy efficiency. Increasing the turbine inlet pressure decreases the energy and exergy efficiencies.

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3 Acta Physica Polonica A

1 2017

2 2016

1 Arıcı M.

1 Bilgin F.

1 Karaali R.

1 Karaalı R.

Thermodynamic Analysis of a Cascade Refrigeration System

Effect of Phase Change Materials on Time Lag, Decrement Factor and Heat-Saving

Exergy Analysis of a Combined Power and Cooling Cycle