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Refrigerant Distribution in Minichannel Evaporator Manifolds

The effects of geometry and operating conditions on the distribution of refrigerant R-410A in heat exchangers with horizontal manifolds and vertically oriented minichannels were experimentally investigated to provide the essential design information for the minichannel evaporators. Flow visualization in the horizontal manifold showed that the flow patterns of the two-phase refrigerant before and after the liquid-vapor transition are in stratified flow for the end-inlet location and in bubbly and stratified flows for the side-inlet location. Test results showed that the normalized standard deviation of the liquid mass flow rate, which indicates the degree of maldistribution, changes from 0.088 to 0.263 with manifold inlet location changes, from 0.034 to 0.141 with manifold inlet mass flow rate changes, from 0.037 to 0.082 with tube number changes, and from 0.027 to 0.055 with tube pitch changes. The normalized standard deviation of the liquid mass flow rates showed that the liquid refrigerant flow distribution is strongly affected by the manifold inlet location and the manifold inlet mass flow rate but is primarily independent of tube pitch. The side-inlet location showed a better liquid refrigerant flow distribution than the end-inlet location by more effectively mixing of the liquid and the vapor refrigerant from the inlet. Therefore, the side-inlet location is preferred to the end-inlet location.