EFFECT OF THE SURFACE ROUGHNESS ON THE NUCLEATE BOILING HEAT TRANSFER OVER THE WIDE RANGE OF PRESSURE
The purpose of the present investigation is to clarify the effect of pressure and the effect of surface roughness on nucleate boiling heat transfer. We performed the experiments by using Freons R11, R21 , R113 and R114 on the horizontal circular copper plates under the condition of saturated pool boiling. We experimented at different pressures, ranging from the reduced pressure p/pc = 0.030 to 0.98. It has become clear that the heat transfer coefficient remarkably increases at high pressure near the critical point. As for the effect of surface roughness, we performed the measurement also over the wide range of pressure for seven grades of surface roughness, ranging from Glattungstiefe Rp = 0.022 to 4.31 µm. The results show that the effect of surface roughness changes with pressure and it gradually vanishes as pressure approaches to the critical point. Finally both the effects of pressure and surface roughness are formulated to establish the simplified correlation for nucleate boiling heat transfer.