Refrigerant flow distributary disequilibrium caused by configuration of two phase fluid pipe network

Abstract

The refrigerant mass flow distribution in a two phase fluid network of multi-connected air conditioning units (MAU) is generally uniform in the available literature based on the assumption that the fluid resistance of the pipes connecting the evaporators is ignored. However, such a fluid network of multiple evaporators and connecting pipes is actually a complex two phase direct return system, which leads to refrigerant flow distributary disequilibrium, for which few investigations have been conducted. In this paper, with pipe and local fluid resistance considered, fluid network theory was employed to develop a MAU fluid network model as a series of fluid circuits of components including single phase and two phase pipes, two phase electronic expansive valve (EEV), evaporator and pipes in parallel or series. A particular iterating control algorism was designed to distribute the refrigerant mass flow in proportion to the corresponding fluid resistance. For a given refrigerant fluid network with five indoor units, it is concluded by the model that the closer an indoor unit is to the centre of the fluid network, the less its mass flow deviates from its nominal value, and the units at the greatest distance from the centre of the fluid network are the ones with maximum disequilibrium. Furthermore, for a fluid network with multiple indoor units, an IDDR was proposed to evaluate the refrigerant distributary disequilibrium.