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Heat exchange of refrigerants during condensation in minichannels

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This paper gives ananalysis of the lawsof heat transferduring condensationof differentrefrigerants inminichanneltaken from available literature. Dependences of heat transfer coefficient on vapor quality of working substance and on channel length are presented at different vapor-to-surface temperature differences and different vapor mass fluxes, for two various shapes of channels (square and triangular). Working substances-R134a, R152, R22, R410A, propane, ammonia and CO2 are reviewed. Influence of the sizes and shapesof the channel on heat exchange is shown. The important mechanism of improvement of heat transfer during condensation in non-circular shape channels is the surface tension creating the transverse pressure gradient in a condensate film. . It leads to a condensate flow in the direction of corners and does a film layer more thinner along sides of the channel, leading to growth of intensity of heat transfer. The available numerical methods of an assessment of intensity of heat exchange at condensation in minichannels are applicable mainly for Freons. Their use for calculations of coefficients of heat transfer at condensation of ammonia can lead to an essential error.

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