TED-AJ03-219 HEAT TRANSFER MECHANISM BASED ON TEMPERATURE PROFILES AND BUBBLE MOTION IN MICROBUBBLE EMISSION BOILING

概要

論文の詳細を見る
In subcooled boiling under certain conditions of subcooling and velocity of the liquid, the heat flux does not decrease with increasing of the surface temperature in transition boiling regime, but increases steeply. In this phenomenon a lot of minute bubbles are emitted from the surface accompanied by extraordinary loud sound. Therefore, we call this phenomenon microbubble emission boiling, abbreviated as MEB. The high heat flux in MEB far exceeding CHF should be considered a result of violent growing and collapsing behavior of coalescent bubbles in that region which strongly introduces subcooled liquid to the heated surface. In a previous study, the authors showed that the fluid temperature just above the heat transfer surface fluctuates corresponding to the bubble motion of growth and collapse. In this study, the liquid temperature profiles were measured at the process of growing and collapsing of bubbles separately, by using a thermocouple set at a suitable position above the center of the surface as a detecting prove of bubble motion. The mean temperature profile averaged over whole sampling period showed a high temperature region of relatively large volume above the surface. The region of large temperature fluctuation located at a distant position upward from the surface by about 2mm. In the temperature profile in the bubble growing period, high temperature zone spread as a very thin layer on the whole surface, showing that the collapse of bubbles had induced subcooled liquid onto the surface. In the period of bubble collapse, on the other hand, the high temperature appeared only on the central part of the surface. This high temperature region indicates the position of high provability for vapor phase to have existed. With a observation of bubbles which once spread over a wide space above the surface, that temperature profile suggests that the bubbles shrink and collapse toward the center on the surface. The bubble motion can be monitored directly by an electrode void probe. The frequency of the fluctuation of the void signal indicates the frequency of the chance of liquid supply onto the surface. Therefore, the peak frequency of the power spectrum of the void signal fluctuation should be an index of heat transfer, and heat flux must be a function of the frequency. The relation between the peak frequency and heat flux was obtained for various condition of liquid subcooling and velocity. Though the data show a wide scattering, a trend of higher peak frequency is distinguished in lower liquid subcooling. It was rearranged for excess heat flux from CHF, to get a correlation function shown in Fig. A-1 as linear lines.[figure]
社団法人日本機械学会の論文

TED-AJ03-219 HEAT TRANSFER MECHANISM BASED ON TEMPERATURE PROFILES AND BUBBLE MOTION IN MICROBUBBLE EMISSION BOILING

スポンサーリンク

概要

著者

関連論文

スポンサーリンク