EHD boiling heat transfer enhancement of R123 and R11 on a tube bundle

The results of an experimental study of electrohydrodynamic (EHD) enhancement of pool boiling are presented in this paper. A high intensity de electric field was applied to R123 and R11 boiling on the shell side of a smooth five-tube shell and tube heat exchanger. The tubes were electrically heated and were arranged in three rows. The electrode system carrying the high voltage comprised fourteen mild steel rods placed in between and around the tubes. Experiments were performed at heat flux values of 20-5 kW m(-2) and applied voltages of 0-25 kV. The enhancement ratio for R123 increased linearly with an applied voltage of up to 15 kV and was strongly dependent on heat flux. Increasing the voltage beyond 20 had no effect on the enhancement ratio at heat flux values greater than 10 kW m(-2). At lower heat flux, some further increase in the enhancement ratio was obtained when increasing the voltage from 20 to 25 kV, The enhancement with R11 was marginal, indicating the importance of fluid properties to electrohydrodynamic enhancement. The effect of pressure on the enhancement was also examined. (C) 1998 Elsevier Science Ltd. All rights reserved.