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1 Zeszyty Energetyczne

1 2017

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Pressure drop and temperature uniformity during flow boiling of refrigerant R245fa in microchannels

Sandler Stanisław, Zajączkowski Bartosz, Białko Bogusław

Zeszyty Energetyczne

2017

T. 4

1--12

Cooling computer processors (CPUs) requires dissipating heat from small heat transfer areas. This results in high heat flux densities to be rejected from the microprocessor. Flow boiling in microchannels receives much attention as a potential solution for CPU cooling. It is characterized by high heat transfer coefficients and requires less working fluid inventory than air-based solutions. However, large pressure drop occurs during phase transition. Moreover, CPU cooling system should provide wall temperature uniformity of the cooled component. Heat transfer coefficient, pressure drop and microprocessor wall temperature depend on microchannel geometry, thermophysical properties of refrigerant, and saturation temperature at which the process is held. This paper focuses on studying pressure drop and temperature uniformity of 40 X 40 mm microchannel evaporator with R245fa as a working fluid. The analysed heat flux density is 80 kW/m2 and the vapor quality change along the heat exchanger is 0.2. The study covers saturation temperatures ranging from 30 to 70°С and microchannel diameters varying between 0.35 and 2 mm. Results of the analysis show that the heat transfer coefficient and wall temperature uniformity increase with increasing saturation temperature and decreasing hydraulic diameter. The maximum and minimum observed non-uniformities were 2.58 and 0.69 K, respectively. Decreasing hydraulic diameter increases pressure losses in the micro-evaporator. The observed pressure drop ranged from 38 to 3753 Pa. Saturation temperature has negligible impact on pressure drop.