Heat Transfer and Pressure Drop Characteristics of a Manifold Microgroove Aerospace Condenser
Boyea, David L.
Ohadi, Michael M
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High performance condensers are an essential component in many energy conversion, electronics and process systems. Increased capacity and functionality with less and less available space has been a main driving force for development of smart condensers in energy systems. A literature survey of microchannel condensation shows that microchannels are useful for enhancing condensation heat transfer. Our previous work in this area has demonstrated that manifold microgroove heat exchangers operating in single-phase or two-phase modes offer substantially higher heat transfer performance with a greatly reduced pumping power when compared to state-of-art microchannel heat exchangers. Out previous microchannel condensation experiments was using have involved use of small scale manifold microgroove condensers (7 cm2 base area) and a manifold microgroove condenser of this size and capacity has not been investigated before. The goal is to enhance heat transfer performance while minimizing the pumping power, volume and weight. A compact lightweight manifold microgroove condenser, with 60 x 600 micron microgrooves and cooling capacity of 4kW, was fabricated, assembled and tested using two different manifold designs. Experiments using R134a and R236fa as working fluids and two different refrigerant side manifolds were performed. Overall heat transfer coefficient and the pressure drop across a manifold microgroove condenser were calculated and refrigerant side heat transfer coefficient was determined based on water side heat transfer coefficient. 4kW capacity was achieved with an LMTD of 8C. The manifold geometry was found to have a large effect on pressure drop and heat transfer performance as well as flow distribution. A majority of the pressure drop was found to be in the manifold creating poor flow distribution. Future work should focus on optimization of the refrigerant manifold design to reduce pressure drop, increase heat transfer and flow distribution as well as explore the effect of microchannel geometry. Unfortunately current stage of development CFD optimization techniques does not allow optimization of two-phase flow system. An optimization of the airside surface and manifold geometry of heat exchanger that potentially will be coupled with high performance condenser has been performed. It has been concluded that for high performances of single phase flow manifold flow area has to be comparable to microgrooves flow area.