The household refrigerator accounts for a significant proportion of energy consumption in households. Therefore, one of the most important guidelines for the development of these appliances focuses on improving the energy efficiency of both the system and the individual components. Among these, the capillary tube is one of the key elements of the refrigerator, and a good knowledge of the processes taking place in it is a fundamental step towards its optimisation. This work presents a visualization of the flow of the refrigerant R600a through a polymer capillary tube installed in a small vapor compression system. The purpose of the visualization was to observe and determine the flow patterns along the capillary tube and the influence of the operating conditions on them. We found that several different flow patterns occur in the capillary tube, among which plug flow predominates, with the plugs expanding and accelerating as they move along the refrigerant flow. Changing operating conditions had a major impact on the frequency of bubble formation during evaporation and on their growth. We also investigated the influence of geometric irregularities of the capillary tube on the flow patterns. The increased roughness of the inner surface of the capillary tube caused evaporation at several different locations simultaneously, which led to a homogenization of the two-phase flow.
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