A new method for estimating the refrigerant distribution in plate evaporator based on infrared thermal imaging

Abstract

For plate heat exchangers (PHEs) used in refrigeration, the uniformity of fluid distribution is an important factor affecting heat transfer performance and system stability. This paper presents an experiment for infrared monitoring of plate evaporators with R410a as refrigerant, and proposed a processing method for the obtained thermal images to comprehensively estimate the channel-to-channel refrigerant maldistribution and the in-channel refrigerant maldistribution. In the experiment, the thermal images of the side and end surfaces of evaporators were taken with an infrared camera, and on-site calibration of infrared temperature measurement was carried out. Then a simplified evaporator model representing the division of refrigerant two-phase region and superheating region was established using the modified thermal images. Based on the model, the volume proportions of both regions and the area of the boundary surface between two-phase region and superheating region were calculated. Furthermore, to demonstrate the feasibility and reliability of the new method proposed above, a case study was carried out. Two similar evaporators were tested, one with distributor and the other without. It was shown that the uniformity improvement of refrigerant distribution revealed by larger volume proportion of two-phase region was significantly relevant with better heat transfer performance. The method provides a new tool for PHE manufacturers to improve product design and for refrigeration system manufacturers to evaluate the operational state of plate evaporators.