Single-phase Flow Pressure Drop of R134a Vapor and Liquid in the Vertical Header of Multi-Pass Microchannel Heat Exchanger

摘要

????Refrigerant maldistribution in the microchannel heat exchange (MCHX), though mainly due to phase separation in the headein two-phase flow is also affected by the pressure drop in the header. This paper investigates the single phase flow pressure drop of nitrogen, R134a vapor, and R134a liquid in the vertical header of a-pa?? microchannel heat exchanger. The objective ??elop a model for the single-phase pressure dro??p the header and provide the basis for two phase flow pressure dropode. The fluid entes into thevertical headerthroughfive microchannel tubes in the bottom pass and exthrough fivemicrochannel tubes in the top pass representing the flow in the outdoor MCHX of a reversible system underheat pump mode. The local pressire dropacross each exit microchannetubein the header isneasured at variou?? mass flow rates For nitrogen and R134a vapor, the local pressure drop usua??ducesalong the upward flow?? the headerFor R134a liquid, the local pressure dis??p highest across the second exit tu??ad then it decreases along the upward flow??he measurech overall local pressure dropincludes theacceleration, gravitation friction, and minor pressure dropue to the protruded microchannel tubeThe minor pressur??rop coefficient based on the experimental results??paredwith the empirical correlationlt is found that thempirical correlatiorworks well for nitrogen and R134a vapor but not for R134a liquid A new correlation for R134a liquid is proposed with the same format, but the coefficients are derived based on the experimental results of this ??? the least square cur?? method.