Study on heat transfer, pressure drop and flow behaviour visualization during evaporation in small channels of a rectangular shape
The demand for reduction of the amount of refrigerant charge in the heat pump and refrigeration application is nowadays a growing trend. This demand is motivated by several benefits among which are: the reduced impact of the refrigerant on the environment and surroundings; reduced cost of the primary material for manufacturing of a smaller heat exchanger with the same or even higher efficiency; reduced space necessary for the system installation; reduced run and maintenance costs etc. In order to design a system for lower charges smaller internal volume heat exchangers with reduced tube diameters should be considered. Such heat exchangers have been studied in a few research projects but are not yet generally in commercial use. One of the specific objectives of the proposed project is to investigate the two-phase flow characteristics of the refrigerant evaporating in small rectangular channels with different aspect ratios. The hydraulic diameters of the channels are of the order of 200 – 1500 μm. The experiments will be carried out for single-channel heat exchangers made of IR-transparent glass and the scope is to collect precise data for heat transfer in these channels. The comparison to previous studies in the field will help determining the best predicting correlation for this type of channels and place the collected data in the world-wide database to facilitate studying this still not fully covered topic. Visualization with the high-speed IR camera will also provide temperature distribution data around the moving bubbles, important for understanding the evaporation process. We believe this information will be quite unique worldwide. After the completion of the project the collected data can be used for further work on developing heat exchangers manufactured from rectangular small channels for implementation in heat pump and refrigeration systems.