AN EXPERIMENTAL-STUDY OF LAMINAR-FILM CONDENSATION WITH STEFAN NUMBER GREATER THAN UNITY

Experimental laminar condensation heat transfer data are reported for fluids with Stefan number up to 3.5. The fluid used is a member of a family of fluorinated fluids, which have been used extensively in the electronics industry for soldering, cooling, and testing applications. Experiments were performed by suddenly immersing cold copper spheres in the saturated vapor of this fluid, and heat transfer rates were calculated using the quasi-steady temperature response of the spheres. In these experiments, the difference between saturation and wall temperature varied from 0.5-degrees-C to 190-degrees-C. Over this range of temperature difference, the condensate properties vary significantly; viscosity of the condensate varies by a factor of nearly 50. Corrections for the temperature-dependent properties of the condensate therefore were incorporated in calculating the Nusselt number based on the average heat transfer coefficient. The results are discussed in light of past experimental data and theory for Stefan number less than unity. To the knowledge of the authors, this is the first reported study of condensation heat transfer examining the effects of Stefan number greater than unity.