TED-AJ03-320 Numerical Analysis of Nucleate Boiling Heat Transfer by a Single Bubble

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Although there have been a huge number of experimental investigations on the boiling heat transfer, exact numerical simulations of the nucleate boiling have become available only recently due to the progress of numerical techniques and the performance of computer. However, there is very few investigation which compares numerical and experimental results on the heat transfer rate. In addition, the effect of fluid properties on the boiling heat transfer is not well clarified by exact numerical simulations. From these view points a numerical analysis of a single bubble behavior in a pool nucleate boiling has been carried out, and the results were compared with corresponding experimental results. In the experiment, only a narrow circular region (4mm in diameter as small as a bubble departure size) at a center of stainless sheet was heated by a copper rod blazed on its backside, as shown in Fig. A-1,in order to obtain the heat transfer rate by a single bubble. By using such a special heating surface the heat transfer field was restricted to the vicinity of the small heating area. Therefore the whole heat transfer field can be included in the computational domain as shown in Fig. A-2. The bubble behavior was recorded by a high-speed video camera. In order to examine the effect of fluid properties on the bubble dynamics and heat transfer characteristics, experiments and numerical analysis were made both for water and ethanol. In the numerical analysis a level set approach was used to capture the vapor-liquid interface. Flow and temperature fields of the fluids and the wall heat conduction were solved simultaneously. At the three-phase contact line on the wall, the micro layer evaporation model was incorporated. Generally, the level set approach has a fault that the bubble volume is not well conserved. To overcome this fault, the bubble volume was corrected to an accurate value at each step of the time marching. The contact angle and the waiting period of the bubble nucleation are assumed to be constant, and they were given by the experimental observation. The calculations were made for various wall superheat, departure frequency and working fluids, and the results of bubble shape and whole heat transfer rate roughly agreed with the corresponding experimental results, as shown in Fig. A-3[figure]
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TED-AJ03-320 Numerical Analysis of Nucleate Boiling Heat Transfer by a Single Bubble

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