Article,
Refrigerant R134a condensation heat transfer and pressure drop inside a small brazed plate heat exchanger
International Journal of Refrigeration, 31 (5): 780 - 789 (2008)
DOI: 10.1016/j.ijrefrig.2007.11.017
Abstract
This paper presents the experimental tests on HFC-134a condensation inside a small brazed plate heat exchanger: the effects of refrigerant mass flux, saturation temperature and vapour super-heating are investigated.
A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20 kg/m2 s. For refrigerant mass flux lower than 20 kg/m2 s, the saturated vapour heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt Nusselt, W., 1916. Die oberflachenkondensation des wasserdampfes. Z. Ver. Dt. Ing. 60, 541–546, 569–575 analysis for vertical surface. For refrigerant mass flux higher than 20 kg/m2 s, the saturated vapour heat transfer coefficients depend on mass flux and are well predicted by the Akers et al. Akers, W.W., Deans, H.A., Crosser, O.K., 1959. Condensing heat transfer within horizontal tubes. Chem. Eng. Prog. Symp. Ser. 55, 171–176 equation. In the forced convection condensation region, the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8–10% higher than those of saturated vapour and are well predicted by the Webb Webb, R.L., 1998. Convective condensation of superheated vapour. ASME J. Heat Transfer 120, 418–421 model. The heat transfer coefficients show weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on the refrigerant mass flux.
