Plate heat exchanger; local heat transfer coefficient; flow boiling; visualization, R245fa
This paper presents an experimental study of the local heat transfer coefficient in evaporation and simultaneous flow visualization in plate heat exchangers. The fluid used is R245fa. The temperature profile, local heat flux, and heat transfer coefficient are measured and calculated along the plate using an internally developed heat flux meter. The flux meter is built from two original plates with thermocouples soldered to their surface and sandwiched with a thermal infill material in between. After calibrating the flux meter to determine its local thermal resistance, the flux meter is assembled in a three-channel setup to measure the heat transfer from one side while visualizing the evaporating R245fa from the other. To visualize two-phase flow, we substituted one inner plate and one end plate with transparent replicated plates. The experimental results focus on the complete evaporation of saturated R245fa by heating water placed vertically with ascending flow. The results also discuss the effect of mass fluxes between 10-20 kg/m2s in a 60° chevron angle commercial plate heat exchanger. The measured data showed that the average heat transfer coefficient increases with mass flux except, which is also indicated from the local values. The approach relates local heat transfer with flow regime within a plate channel while preserving the real geometry and operating condition, creating fundamentals for improving geometry.