OS1-4 マイクロ熱交換器用極細管群の伝熱挙動の実験と数値計算の比較(OS1 マイクロエネルギー変換,循環型社会における動力エネルギー技術)

概要

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Heat transfer and flow behavior in the mini tube bank was examined. The tube bank was composed of 1mm diameter wires and a 30W×15H mm flow channel. The wires were arranged 5×5 or 1×5 in an inline lattice. Water was used as the test fluid. A flow rate was varied in a range of the Reynolds number Re=uD/v of 1〜400, where u was the approaching velocity. In usual size tube banks, a heat transfer coefficient increases as the tube row goes downwards. The increase saturates around 10th row. Contrary to it, the heat transfer coefficient decreased as the flow proceeded downwards. A flow state was visually observed by mixing a fluorescent dye and illuminating fluorescent dye particles by a YAG laser beam sheet. The flow state was recorded with a high speed video camera. The visualization revealed that the down stream wire was surrounded by the wake of the upstream wire, which made the flow state around the stagnant point region of the down stream wire less turbulent. The heat transfer deterioration with flow going downstream was observed until the Reynolds number 120〜150. Around Re=150, the jumping up of the heat transfer coefficient in the rear bank occurred. Flow and heat transfer analyses were performed with a STAR-CD code. The same trend was confirmed in the analyses.
2007-06-13