Abstract:

In refrigeration systems, the use of natural refrigerants become widespread instead of artificial refrigerants that cause global warming. 〖CO〗_2 is a natural refrigerant used in refrigeration systems due to its environmentally friendly, low cost, ozone layer depletion potential and low global warming potential. However, since the energy efficiency of systems working with 〖CO〗_2 is lower than that of artificial refrigerants, the performance of the refrigeration system is increased by adding an internal heat exchanger. In the refrigeration industry, it is desirable in many applications to obtain environments with different evaporator temperatures. In this study, 〖CO〗_2 refrigeration cycle with two evaporators with two different evaporator temperatures is investigated separately for the cases with and without an internal heat exchanger. It is assumed that 〖CO〗_2 changes state above the critical point in the gas cooler. The dimensions of the gas cooler and evaporators are compared at different gas cooler pressures and evaporator temperatures. By obtaining the optimum gas cooler pressures, it was investigated how the situation with the internal heat exchanger improves the performance of the system and how it affects the dimensions of the system. As the pressure of the gas cooler increases, the length of the gas cooler decreases and the length of the evaporators increases. For all studied cases, the optimum gas cooler pressure is reduced by around 3% with the use of the internal heat exchanger, and the COP values are increased by around 6%. 〖COP〗_max and optimum gas cooler pressure were obtained as 1.887 and 9685 kPa at T_(b,1)=5 °C and T_(b,2)=0 °C. At this optimum gas cooler pressure, the use of the internal heat exchanger reduced the length of the gas cooler by approximately 17%, while the length of evaporator 1 increased by 6.02% and the length of evaporator 2 by 9.35%.

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