Visualization of Two-Phase Refrigerant Flow Through an Ice-Maker Evaporator

A transparent evaporator plate has been affixed to a commercial ice-maker refrigeration system and high-speed visualization of the two-phase boiling of the R134a has been made as water is frozen on the top of the plate. The startup transient period of the freeze cycle, characterized by superheated vapor throughout the evaporator, can last up to 10 minutes as the water is pre-cooled, and the freeze cycle follows. The two-phase flow patterns have been observed as distance along the evaporator plate during the freeze cycle, and observations about the liquid phase distribution are made. The refrigerant path is a series of spiral turns, which sets up a flow pattern of the liquid phase gathering along the inner wall of the channel and being dragged by the high speed vapor. This is not an optimal flow pattern for heat transfer because the liquid is not distributed to the top of the channel.