Numerical and experimental investigation on the condensing heat transfer of R134a outside plain and integral-fin tubes

Condensing heat transfer of R134a on horizontal single plain and integral-fin tubes was investigated by both computational and experimental methods. The VOF model and Lee condensation model were utilized in the simulation. Validation of the model was performed with two different refrigerants. Condensing heat transfer coefficient for plain and integral-fin tubes were calculated in comparison with the experimental data and Nusselt analytical solution. Instantaneous film flow characteristics of condensation on horizontal single plain and integral-fin tubes were discussed respectively. Contours of liquid volume fraction for the plain tube and condensing heat transfer coefficient for the plain tube at different time with Tw = 303 K are presented. For integral-fin tubes, contours show that the thickness of liquid film at lateral fin surface is much smaller than that at root fin surface. Comparison between R134a and R11 were made and it was found that different surface tension could lead to different liquid film distribution which could result in different heat transfer performance. Experiments involving the same fin structure were also conducted to verify the theoretical model and a satisfactory agreement between simulation and experimental results was found.