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Design, optimization and testing of micro-evaporator and micro-condenser components used in a miniature vapor compression refrigeration cycle

Türkakar, Göker
This study aims to optimize the dimensions and operating conditions of two main components of a miniature vapor compression refrigeration cycle (MVCRC), evaporator and condenser by using entropy generation minimization (EGM). In addition, some performance tests are conducted on a MVCRC which is constructed based on the EGM analysis as long as the manufacturing constraints permit. R134a is used as the coolant. Entropy generation rate in the evaporator of the MVCRC is investigated under the effects of exit vapor quality, mass and heat flux, saturation temperature, and channel dimensions. Dimensionless entropy generation number for the condenser of the MVCRC is investigated under the effects of fin pitch, fin height, louver angle and air vi mass flow rate on the air side, hydraulic diameter of the channel for the refrigerant side. The exit vapor quality of the evaporator yielding the minimum entropy generation rate is found as 0.846. The optimum channel and fin widths are 66 and 50 μm, respectively, for 700 μm channel height. Heat transfer is the major source of the total entropy production for 200-400 μm wide channels, while the contribution of pressure drop becomes comparable for narrower channels. The optimum air mass flow rate interval for the condenser is found to be between 0.055-0.1 kg/s for a given fin pitch interval of 1-1.6 mm. The entropy generation number due to pressure drop on the air side becomes dominant for mass flow rates greater than 0.08 kg/s. Experimental results match well with the theoretical calculations. A maximum COP of 7.71 is obtained under 96 W cooling load.