Experimental Investigation and Visualization Study of the Condensation Characteristics in a Propylene Loop Heat Pipe

At present, the structural design of a loop heat pipe (LHP) condenser mostly relies on experience. To analyze the condensation flow pattern in an LHP and to find a more accurate empirical correlation that can better guide condenser design in existing empirical correlations, a test system was designed and fabricated to observe the condensation phenomenon in the condenser and to evaluate the LHP’s heat transfer performance. Since propylene has a wide temperature range to different temperature control requirements, it was chosen as the working fluid. In this paper, the condensation process in the condenser was observed, and the operating parameters of a propylene LHP were measured at 283 K. The condensation flow patterns in the 2.5 mm ×2.5 mm channel mainly included stratified flow, wavy flow and intermittent flow. By comparing the experimental results with four typical condensation flow regime maps, it was found that the Breber and Cavallini flow regime maps can successfully predict most of the condensation flow patterns of the LHP even with ultra-small mass flux. In addition, four condensation heat transfer coefficient correlations were selected to compare the predicted values of heat transfer coefficient with the experimental results. The study showed that the predicted values from the correlation by Cavallini et al. matched 90% of the experimental values well with an error of less than 20%, and this correlation is recommended for highly accurate LHP design.