Experimental And Theoretical Study Of Convective Evaporation And Condensation Heat Transfer In Herringbone And Dimple-Texture Tubes

During past several decades, technologies for enhancing heat transfer have developed very fast. Enhancing heat transfer can increase efficiency of heat exchangers, and decrease weight and size. With industry developing, more and more study for enhancing heat transfer is needed. What is more, with concerning environment problem more and more, newer generation refrigerants with no greenhouse effect are needed to protect environment.In this paper, experimental investigation of single-phase, condensation and evaporation in smooth tube, Herringbone tube and Dimple-Texture tube were performed. Outer and inner diameters are 12.7mm and 11.43mm respectively. Length of the test section was 1.9mm. Refrigerants are R22, R410A and R32.R22 was used for single-phase experiment with saturation temperature of 49℃, mass flow rate of 130-246.8kg/(m2s), heat flux of 6.43-14.9kW/m2. Smooth tube provides lowest single-phase heat transfer coefficient. Herringbone is higher, about 1.16-1.35 times that in smooth tube. Dimple-Texture tube is the highest, about 1.75-1.95 times that in smooth tube. Experimental single-phase heat transfer coefficient in smooth tube is about 1.24-1.31 times of predicted values calculated by Gnielinski correlation. Pressure drop in smooth tube is lowest. Pressure drop in Herringbone tube is higher, but goes closer with increasing of Re. Pressure drop in Dimple-Texture tube is the highest, about 2.14-2.70 times that in smooth tube. PEC of Dimple-Texture tube is 1.34-1.4. PEC of Herringbone tube is 0.91-1.37.R22, R410A and R32 were used for condensation experiment with mass flux 56.2-178.5 kg/(m2s), heat flux 9.9-30.4kW/m2. Saturation temperature, inlet vapor quality and outlet vapor quality of R22 and R410A are 47℃,0.9 and 0.1 respectively. Saturation temperature, inlet vapor quality and outlet vapor quality of R32 are 45℃, 0.9 and 0.2 respectively. Smooth tube has lowest condensation heat transfer coefficient. Herringbone has the highest condensation heat transfer coefficient(HTC), about 2.3-3.2 times that of smooth tube, condensation HTC in Dimple-Texture tube is about 1.3-2.0 times that of smooth tube. Haraguchi correlation, Shah correlation, Dobson and Chato correlation and Cavallini correlation are used to predict condensation HTC in smooth tube. Kedzierski and Goncalves correlation, Cavallini correlation and Olivier correlation are used to predict condensation HTC in Herringbone tube.R22, R410A and R32 were used for evaporation experiment with saturation temperature of 6℃, mass flux 53.1-140.9kg/(m2s), heat flux 13.9-36kW/m2. Inlet and outlet vapor quality are 0.1 and 0.9 for R22 and R410A,0.1 and 0.8 for R32. Smooth tube has lowest evaporation HTC. Evaporation HTC in Herringbone tube is higher. Evaporation HTC in Dimple-Texture tube is highest. The model developed by Wojtan was used to calculate flow patterns. Evaporation flow are located in the Slug+Stratified/Wavy flow and Stratified/Wavy flow regions. The flow is not annulus flow. Modified Leszek Wojtan correlation and Liu correlation are used to predict evaporation HTC in smooth tube.R22 was used to measure two-phase pressure drop in Herringbone tube and Dimple-Texture tube, average vapor quality of inlet and outlet is 0.55. Two-phase pressure drop in Herringbone tube is higher than predicted pressure drop in smooth tube, two-phase pressure drop in Dimple-Texture tube is highest. Two-phase pressure drop in smooth tube fits very well with correlations.