Modeling and experimental analysis of direct contact heat exchangers for R718 refrigeration system

Abstract

Natural refrigerants are taking an increasing place in the refrigeration market today. Water is one of the most abundant and safest working fluids. However, the literature on water based refrigeration systems is very scarce, in particular regarding experimental works. Besides, the design of heat exchangers for water-based systems is very specific. The design quality has a huge consequence on the performance and capacity of such systems. Thus, the development and validation of mathematical models used for the sizing and the design of such heat exchangers are very important. This paper presents mathematical models of direct contact lowpressure heat exchangers for steam evaporation and condensation. These models are part of a complete refrigeration system model developed on Dymola. The modeling results are compared to experiments done on a 10kW chiller. The Dymola model combined to a one-dimensional model of the heat exchanger predicts well the operating pressures and the heat transfer performances. The experimental results were also used to build empirical models of the global heat transfer coefficient. The heat transfer appears to be mainly affected by the steam to liquid flow rates fraction, the liquid flow rate and the condensing power