Locally Measured Heat Transfer Coefficient with Simultaneous Visualization of Evaporating Fluid Flow in the Plate Heat Exchanger

This paper presents an experimental investigation of the local heat transfer coefficient and simultaneous flow visualization of evaporating refrigerant in plate heat exchangers. The fluid used is the low-pressure refrigerant R245fa. The local temperature, heat flux, and heat transfer coefficient profiles are measured along the real stainless steel plate using a new internal developed heat flux meter. The heat flux meter is assembled in a two or three-channel setup to measure the heat transfer on one side while visualizing the evaporating R245fa from the other. The outer plates on the other side of the heat flux meter are substituted with transparent plates to capture evaporating flow regimes. The tested plate heat exchanger is in a counterflow arrangement with the refrigerant flow is flowing vertically upward. The paper presents the effect of different inlet/outlet conditions in a 60° chevron angle commercially available plate heat exchanger. Different flow regimes are identified and related to the measured heat transfer coefficient. The middle part of the channel shows a uniform behavior of flow and consistent heat transfer coefficient. However, the regions near the inlet and outlet region show a maldistribution behavior. Heat transfer coefficients and related flow regime images are presented to help describe and analyze phenomena. These additional insights create a path for further improvement of the plate geometry.