WenHua Wang

Boiling heat transfer on machined porous surfaces with structural optimization

Boiling heat transfer on porous surfaces needs further research for augmentation. Analysis of the microfilm evaporation and two-phase flow inside the microstructure was used to develop new microscale heat transfer model for boiling heat transfer on porous surfaces. Simulation results were used to study in detail the effects of fluid parameter and microstructure dimensions on the heat transfer performance during the bubble formation period. For boiling on porous surfaces with such working fluids as R11, R22, R134a and water, optimum microstructure dimensions were determined for the given conditions. The calculated results fit previous experimental data well. An experimental rig was developed to measure the pool boiling heat transfer to test the predictions of the optimization. The experimental data verified the optimization results.

Two-phase flow patterns and transition characteristics for in-tube condensation with different surface inclinations

Abstract In-tube condensation of R-11 was experimentally investigated with various surface inclination angle between the direction of the vapor flow and the gravitational force, φ. The two-phase flow patterns were observed visually and the transition locations between different flow patterns were measured in a transparent test section. The vapor quality distribution along the test tube and the measured transition locations were used to prepare a flow pattern map. The experimental results indicated that the surface inclination, φ, strongly influenced the vapor and condensate distribution. Annular flow spanned the whole tube for φ = 0° at various vapor flow rates. Annular flow and stratified flow patterns were observed for φ = 45° and 60°. Annular flow, stratified flow, half-slug flow, and slug flow exist in sequence for φ = 90–120°. Annular flow, churn flow and slug flow occurred for φ = 180°. The possible prediction of flow patterns for in-tube condensation in a microgravity environment was discussed briefly.

Condensation heat transfer of a non-azeotropic binary mixture on a horizontal tube

Abstract Natural convection condensation heat transfer of a binary HFC152a-HCFC22 mixture on the outside of a horizontal tube was investigated experimentally and analytically. A new model is advanced in which the interface temperature between the liquid and vapor phases is not constant in the flow direction. A non-similarity solution for the flow, temperature and concentration fields on the outside of a smooth horizontal tube is obtained. The calculated results agree well with the experimental results.