A NEW MODEL FOR REFRIGERANT CONDENSATION INSIDE A BRAZED PLATE HEAT EXCHANGER (BPHE)

This paper presents a new computational procedure for condensation heat transfer coefficient of pure refrigerants inside a Brazed Plate Heat Exchanger (BPHE). The new model was based on a set of 338 experimental data points from the present authors on saturated vapour condensation inside a commercial BPHE which includes HFC refrigerants (HFC236a, HFC134a, HFC410A), HC refrigerants (HC600a-Isobutane, HC290-Propane, HC1270-Propylene) and the new low Global Warming Potential HFO refrigerants (HFO1234yf, HFO1234ze(E)). A transition point between gravity controlled and forced convection condensation was found for an equivalent Reynolds number around 1600. At low equivalent Reynolds number (< 1600) the heat transfer coefficients are not dependent on mass flux and are well predicted by a simple model based on the Nusselt (1916) equation for vertical surface: the condensation process is gravity-dominated. For higher equivalent Reynolds number (> 1600) the heat transfer coefficients depend on mass flux and condensate drainage is controlled by the combined actions of gravity and vapour shear: forced convection condensation occurs. A new specific non dimensional equation based on the equivalent Reynolds number and the liquid Prandtl number was developed for predicting the heat transfer coefficients in the forced convection condensation region. This new model was also applied to super-heated vapour condensation by using the equation of Webb (1998) to account for super-heating effects. The new computational procedure was compared against data from the literature. A set of 516 experimental data points which includes both saturated and super-heated HCFC, HFC, HC refrigerants and Carbon Dioxide with different plate geometry was considered: the mean absolute percentage deviation between experimental and calculated heat transfer coefficients was lower than 16%.