|Alternative Title||Study on Pool Boiling Heat Transfer and the Thermal Dynamical Characteristics of Single Bubble in Microgravity|
|Place of Conferral||北京|
|Keyword||微重力 沸腾 临界热流密度 单气泡池沸腾 气泡热动力学 实践十号卫星|
Boiling phenomenon has a very high heat transfer efficiency due to the use of the latent heat of phase change. It has a very wide and important application in daily life and many industry practices, so that the research on boiling heat transfer mechanism has been paid much attention by academia.
Under the terrestrial normal gravity environment on the ground, buoyancy force often dominates the boiling phenomenon, masking the mesoscopic flow and heat transfer process near the heating surface, which are directly related to boiling heat transfer. In microgravity environment, the buoyancy force is suppressed, so the spatial and temporal scale of bubble growth process are increased, which will help to study the local and transient processes in boiling phenomenon and reveal the true mechanism of boiling heat transfer.
In this paper, the pool boiling heat transfer experiment was carried out in microgravity environment by using the returnable scientific experimental satellite SJ-10. The contents and achievements of this paper are as follows:
First of all, I participated in the development of the space experimental device “SOBER-SJ10” and the development of integrated micro-heater. The experimental device used local pulsed overheating to excite the “seed” bubbles, so that bubble generation could be positioned in precise location and time. The bubble will continue to grow under the heating of the main heater on the backside of the integrated micro-heater. The local temperature on top and the average temperature on back side of the heater were measured by the 10 local temperature sensors and the main heater respectively, so that the heat conduction in the heating solid wall could be inverted. The calibration of the temperature, pressure, integrated micro-heater, and the ground environmental test of the "SOBER-SJ10" device were completed to verify the reliability of the device.
Secondly, a comparative experimental study on the pool boiling heat transfer in ground normal gravity was carried out using flight module of the experimental facility. A syn-calibration method was used to calibrate the temperature of local temperature sensors and the main heater. Non-condensable gas concentration in each ground experiment was estimated by using data from the thermal test. The data analysis shows that the single-phase natural convection in normal gravity experiment is consistent with the prediction of the classical model. There is obvious temperature overshoot at the beginning of the nucleate boiling, and the nucleate pool boiling curve is consistent with the prediction of Rohsenow’s correlation.
Thirdly, the on-orbit experiment aboard the SJ-10 satellite was successfully carried out, and data analysis of the microgravity pool boiling experiments was completed. The syn-calibration method of integrated combined heater was improved to solve the calibration problem caused by overheat and fast-cooling of integrated micro-heater in space experiments. In space experiments, the special variation of the surface temperature and bubble behavior at the onset of boiling indicates that the bubble motion and aggregation form on the heating surface influence the boiling heat transfer process. The comparison of the results of nucleate boiling heat transfer process in space and ground experiments reveals the effects of subcooling and gravity on heat transfer efficiency. In the space experiments, the transition to transition boiling or to film boiling occurs at a very low heat flux density, and the critical heat flux is greatly reduced in microgravity.
Finally, using the local pulse superheating method, the single bubble pool boiling experiments were successfully carried out in the on-orbit flight experiment. The analysis of image data reveals the dynamical characteristics of bubble growth under microgravity. The variation and distribution of local temperature on the heating surface reveals characteristics of the spatial-temporal evolution of the surface temperature, as well as the dynamical evolution of three-phase contact line and the dry spot on heating surface, during the single bubble growth. In addition, according to the equilibrium relationship of heat conduction inside the micro-layer, the initial thickness of the micro-layer at the bottom of the growth bubble was evaluated. These results provide good and basic information for further revealing the mechanism between the bubble thermal dynamical behavior and heat transfer performance.
|吴克. 微重力池沸腾传热与单气泡热动力学特征研究[D]. 北京. 中国科学院大学,2019.|
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