In Tube Condensation: Changing the Pressure Drop into a Temperature Difference for a Wire-on-Tube Heat Exchanger

A theoretical study based on the Penalty factor (PF) method by Cavallini et al. is conducted to show that the pressure drop occurring in a wire-on-tube heat exchanger can be converted into a temperature difference for two types of refrigerants R-134a and R-600a typically used for charging refrigerators and freezers. The following conditions are considered: stratified or stratified-wavy flow condensation occurring inside the smooth tube of a wire-on-tube condenser with diameter 3.25, 4.83, and 6.299 mm, condensation temperatures 35 & DEG;C, 45 & DEG;C, and 54.4 & DEG;C and cover refrigerant mass flow rate spanning the interval from 1 to 7 kg/hr. The results show that the PF variation is not linear with vapor quality and attains a maximum when the vapor quality is 0.2 and 0.18 for the R-134a and R-600a refrigerants, respectively. The PF increases with the refrigerant mass flow rate if the inner diameter and saturation temperature constant, and it decreases on increasing the inner diameter to 6.299 mm for constant refrigerant mass flow rate and saturation temperature. The PF for R-600a is higher than that for R-134a due to the lower saturation pressure in the first case. Furthermore, a stratified flow produces higher PF in comparison to the annular flow due to the effect of the surface tension.