When steam-water two-phase mixtures flow in inclined or horizontal rubes that are heated by alternation current, the circular angle-dependent temperatures on the outer radius imply that the inner heat transfer coefficients also cary with circular angle. The inner heat transfer coefficients are difficult to measure directly, but may be determined with the aid of inverse heat conduction theory. The direct model calculates the temperature field inside a half-pipe. This is subjected to a given teat transfer coefficient angular profile on its inner radius. The inverse heat conduction model calculates the temperature field under the conditions of the measured discrete temperatures and the heat-insulated boundary on the outer radius. Variation of the cylinder heat conductivity and specific resistance versus temperatures are considered in both models. The prediction accuracy is analyzed with a numerical test. The inverse heat conduction problem solution is verified as a useful tool for obtaining the inner heat transfer coefficient.

The transient two-fluid model has been used to develop a general relation for acoustic waves with steam-water two-phase mixture in one-dimensional flowing system. The analysis is valid in principle over the whole void fraction region. Both the mechanical and thermal nonequilibrium are considered. The vapor-liquid interface heat flux is derived from the one dimensional Fourier heat conduction equation to evaluate the interphase evaporation or condensation rate. Calculations are performed for pressures from 0.07 to 16.0MPa, void fractions from 0.0 to 1.0. Higher frequency limit of sonic velocities are only relied on the pressures and void fractions, and are insensitive to the bubble radius, tube diameter, and the velocity difference between the two phases. The predicted sonic velocities are compared with some experimental data for low pressures. Good agreement has been achieved between the predictions and the experimental data.

The present article is aimed at evaluating six typical flow boiling heat transfer correlations selected from the open literature with experimental results. The selected correlations are correlations of Chen, Shah, Gungor and Winterton, Liu and Winterton, Klimenko, and Kandlikar. Experiments of upward flow boiling heat transfer with kerosene in a vertical smooth tube were conducted. The test tube has a length of 2.5m and its outer and inner diameters are 19mm and 15mm, respectively. The experiments were performed at an absolute atmospheric pressure of 3. The input heat flux ranged from 28.5 to 93.75kW/m2 and the mass fluxes were selected at 410, 610, and 810kg/m2 s, respectively. The experimental flow boiling heat transfer coefficients were compared with flow boiling heat transfer coefficients calculated with the six typical correlations. By comparison, the most suitable correlations are recommended for the calculation of flow boiling heat transfer coefficients with kerosene in a smooth tube.

Experiments of upward flow boiling heat transfer with water in a vertical smooth tube and a tube with axial microgrooves were conducted. Both of the tested tubes have a length of 2.5m, an inner diameter of 15mm, and an outlet diameter of 19mm. The tube with axial microgrooves has many micro rectangle grooves in its inner wall along the axial direction. The grooves have a depth of 0.5mm and a width of 0.3mm. The tests were performed at an absolute pressure of 6bar. The heat flux ranged from 0 to 550kW/m2 and the mass flux was selected at 410, 610, and 810kg/m2s. By comparison, flow boiling heat transfer coefficients in the enhanced tube are 1.6 to 2.7-fold that in the smooth tube, while the frictional pressure drop in the enhanced tube is slightly greater than that in the smooth tube. The augmentation of flow boiling heat transfer in the tube with axial microgrooves is apparent. Based on the experimental data, a correlation of flow boiling heat transfer is proposed for the enhanced tube. Finally, the mechanisms of heat transfer enhancement are analyzed.

Experiments of flow boiling heat transfer and two-phase flow frictional pressure drop in a spirally internally ribbed tube (φ22×5.5mm) and a smooth tube (φ19×2mm) were conducted, respectively, under the condition of 6×105Pa (absolute atmosphere pressure). The available heated length of the test sections was 2500mm. The mass fluxes were selected, respectively, at 410, 610 and 810kg/m2s. The maximum heat flux was controlled according to exit quality, which was no more than 0.3 in each test run. The experimental results in the spirally internally ribbed tube were compared with that in the smooth tube. It shows that flow boiling heat transfer coefficients in the spirally internally ribbed tube are 1.4-2 times that in the smooth tube, and the flow boiling heat transfer under the condition of smaller temperature differences can be achieved in the spirally internally ribbed tube. Also, the two-phase flow frictional pressure drop in the spirally internally ribbed tube increases a factor of 1.6-2 as compared with that in the smooth tube. The effects of mass flux and pressure on the flow boiling heat transfer were presented. The effect of diameters on flow boiling that transfer in smooth tubes was analyzed. Based on the fits of the experimental data, correlations of flow boiling heat transfer coefficient and two-phase flow frictional factor were proposed, respectively. The mechanisms of enhanced flow boiling heat transfer in the spirally internally ribbed tube were analyzed.