Numerical and Experimental Transient Analysis of Water Flash Heating of Mini Channel Heat Exchangers

This study aims to design and simulate the dynamic behavior of three prototypes of mini-channel heat exchangers, with water as the working fluid, using COMSOL Multiphysics software and experimentation. The experimental setup comprised a thermally insulated aluminum - Mini Channel Heat Exchanger, where the channels were 3 mm deep and 2 mm wide, with a total exchange area of 0.02 m2. The inlet was connected to a recirculating water-storage tank at 80°C. Calibrated thermocouples were placed at the fluid inlet and outlet to measure the absolute temperature throughout the experiment. The fluid flow rate was maintained at a constant rate of 500 ml/min using PID controllers and monitored continuously using the LabVIEW software. Six resistive heaters were placed symmetrically at the center of each geometry, where the voltage was regulated to achieve the required power for the experiment. The prototypes differ in the amount of metal (aluminum), excluding the heating elements, where the channel geometry remains the same, to check the influence of the dimensions on the material efficiency and its thermal performance. The three prototypes weigh 288 g, 196 g, and 178 g, respectively. Two different heating powers provided by resistive heaters, 675 W, and 1000 W, were considered for this study. The focus of this study, owing to the requirement of instantaneous heating of the working fluid, is the transient study for a very short time, that is, for 10 s and 20 s. During the experimental testing and simulations, the outlet of the third prototype reached 100°C in 6.2 seconds, compared with 15 s and 7 s for the first and second prototypes, respectively