TED-AJ03-168 EXPERIMENTAL EXAMINATION OF TRIGGERING MECHANISM OF CHF OF SUB-COOLED FLOW BOILING
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概要
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Forced-convection flow boiling experiments of sub-cooled water were conducted to examine the triggering mechanism of CHF. The flow channel was 10×20mm rectangular and 830mm long. The test section used was 5×40×0.2mm stainless sheet and embedded in the bottom wall of the flow channel so as to be flush with the wall. The test section was heated by DC Joule heating. The experiments covered the water mass flux of 170∿3,400kg/m^2s with inlet sub-cooling 50K and were conducted at atmospheric pressure. Local heat transfer surface temperature variation was measured with a K-type thermocouple of 50μm in diameter. A flow state was recorded with a high-speed video camera from the top and the side of the flow channel focusing on bubble behavior on the heat transfer surface. Bubbles coalesced to form large bubbles with an order of ∿ 4mm in diameter. The large coalescent bubbles sitting on the heat transfer surface departed from the heat transfer surface periodically. The heat transfer surface temperature under the coalescent bubble varied periodically coinciding with coalescent bubble formation and its departure from the surface (Fig. A-1). A liquid sublayer under the coalescent large bubble was pictured. Many vapor columns were perceived in the liquid sublayer. When the liquid sublayer was vaporized out for the surface to be exposed to vapor, a film boiling-like state was brought about and abrupt excursion of the surface temperature occurred to cause physical burn-out of the heat transfer surface. The thickness of the liquid sublayer under the large-coalescent bubble (Fig. A-2), the time period of the departure of the large coalescent bubble from the heat transfer surface, the nucleation site density and the diameter of the vapor columns in the liquid sublayer were measured. The CHF was calculated from these so that when the liquid sublayer was vaporized out before the breakaway of the large-coalescent bubble from the heat transfer surface, the sudden excursion of the surface temperature occurred to cause the burn-out of the surface. The calculation reproduced the experimental results of the CHF well.[figure]
- 一般社団法人日本機械学会の論文
著者
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Koizumi Yasuo
Department Of Mechanical Engineering Kogakuin University
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Ohtake Hiroyasu
Department Of Mechanical Engineering Kogakuin University
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MATSISHITA Naohiro
Department of Mechanical Engineering, Kogakuin University
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Matsishita Naohiro
Department Of Mechanical Engineering Kogakuin University
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