Abstract

The effect of fluid properties on electrohydrodynamically enhanced heat transfer in pool boiling was studied using R-123, R-134a, and R-407c as the working fluids at various pool temperatures. Two experimental boiling apparatuses were used, one electrically heated and suitable for high pressure refrigerants, and the other water heated, suitable only for low pressure refrigerants. In both cases, the pool boiling consisted of a single horizontal copper tube with the same surface finish, heated length, and outer diameter. The electrode design consisted of eight straight wires spaced radially at equal angles around the tube. The electrical properties of working fluids as a function of temperature were measured using a unique test cell.

Results show that of the three refrigerants, R-123 and R-134a both demonstrate significant EHD enhancement at 4 °C and 20 °C pool temperatures. Enhancements at 4 °C are larger than those at 20 °C for both refrigerants. Measured electric charge relaxation time and estimated bubble departure time indicate that negligible enhancement should be realized with R-407c at 4 °C pool temperature, while some enhancement should be achieved at 20 °C and 35 °C pool temperatures. Experimental results confirm this and clarify the relationship between bubble departure time and electric charge relaxation time.

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