Experimental study of coupling heat transfer characteristics of boiling and condensation in an asymmetric phase change chamber

The output power of an automobile exhaust thermoelectric generator can be greatly improved by adding a phase change chamber with the condensation area smaller than the boiling area between the hot side of the thermoelectric modules and the exhaust channel. By decreasing the condensation area, the heat flux through the modules increases, which increases the temperature difference between the hot side and the cold side of the modules. Hence, the output power increases. However, the heat transfer characteristics of such kind of chamber with the confined space, the unequal boiling and condensation areas and the coupling interaction between the boiling and the condensation have not been fully studied. In this paper, the boiling and condensation heat transfer characteristics of deionized water in a chamber with the boiling to condensation area ratio of 5:2 were experimentally studied at boiling heat fluxes from 4.50 kW/m(2) to 22.70 kW/m(2) and filling ratios from 20% to 70%. The results show that the chamber total thermal resistance decreases and the temperature uniformity increases with increasing heat flux. The filling ratio has little effect on the total thermal resistance. The heat transfer coefficients obtained from the experiments were compared with those predicted by the correlations. The results show that the Cooper correlation (the deviation range of -41.3% similar to -9.7% from the experimental results), has a higher accuracy than the Rohsenow correlation (the deviation range of -73.6% to +43.9% from the experimental results) for predicting the boiling heat transfer coefficient. Neither the Nusselt correlation nor the Gerstmann-Griffith correlation can accurately predict the condensation heat transfer coefficients. Besides, the behavior of bubbles and condensate was observed during the experiment, explaining the variations of the boiling and condensation heat transfer coefficients versus heat flux.