Effects of Vapor Superheat and Condensate Subcooling on Laminar Film Condensation

Abstract

Nusselt’s model is employed to illustrate the effects of vapor superheat and condensate subcooling on laminar film condensation occurring under simultaneous actions of gravity and interfacial shear. The vapor superheat affects the condensation kinetics in cooperation with heat transfer in both phases. Under comparable conditions, the condensate film is thinner and the heat transfer coefficient larger for superheated than for saturated vapor. The heat flux on the cooling surface arising from the sensible heat of condensate increases as the critical point of the condensing substance is approached and, at this point, the Nusselt condensation model gives the single-phase boundary layer solutions. [S0022-1481(00)00701-5]

R32 partial condensation inside a brazed plate heat exchanger

“…Considering the effect of the superheating at 40 kg m -2 s -1 , at low mean vapour quality the ratio of HTCs seems to be independent on superheating, while at high mean vapour quality, the ratio of HTCs increases with the superheating. Similar results have been found by other authors, among them: Minkowycz andSparrow (1966 and1969), Mitrovic (2000) and Longo (2011).…”

“…The authors obtained practically simple correlations for predicting the heat transfer and mass flow rate during condensation of saturated steam. Mitrovic (2000) studied the effects of vapour superheat, condensate subcooling, gravity interfacial shear, and vapour convection on the basis of the Nusselt theory (1919). The results show that the vapour superheat affects the condensation kinetics in cooperation with heat transfer in both phases; under comparable conditions, the condensate film is thinner and the heat transfer coefficient larger for superheated than for saturated vapour.…”

Refrigerant R134a condensation heat transfer and pressure drop inside a small brazed plate heat exchanger

“…Vapour super-heating affects condensation kinetics reducing the condensate film thickness and increasing the heat transfer coefficient with respect to saturated vapour as demonstrated analytically by Fujii (1991) and by Mitrovic (2000) for laminar film condensation on a vertical surface both under gravity and vapour shear control. The i n t e r n a t i o n a l j o u r n a l o f r e f r i g e r a t i o n 3 1 ( 2 0 0 8 ) 7 8 0 -7 8 9 enhancement measured in present tests is higher than that reported by Sparrow (1966, 1969) for gravity controlled condensation and forced convection condensation of steam, or those suggested by referenced heat transfer handbooks (Rohsenow et al, 1985;Hewitt, 1990).…”