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放射温度計を用いた瞬時伝熱面温度分布測定によるプール沸騰熱伝達機構解明に関する研究

Study on heat transfer mechanism elucidation during pool nucleate boiling by measuring instantaneous surface temperature distribution with infrared radiation camera

小泉 安郎; 高橋 和希*; 上澤 伸一郎; 吉田 啓之 ; 高瀬 和之

Koizumi, Yasuo; Takahashi, Kazuki*; Uesawa, Shinichiro; Yoshida, Hiroyuki; Takase, Kazuyuki

核沸騰熱伝達素過程解明を目的として、大気圧条件でプール沸騰熱伝達実験を行った。伝熱面には銅プリント基盤を用い、伝熱面の大きさは一辺10mmの正方形とした。伝熱面背部のベークライト板部分を7$$times$$10mmにわたり取り除き、剥き出しになった銅薄膜背面の瞬時温度分布を赤外線放射温度計により計測した。その結果、限界熱流束直前まで伝熱面は比較的低い温度に維持されているが、限界熱流束近傍で表れた小さな高温部が拡大縮小を繰り返しつつ拡大し、伝熱面全体が高温になることで限界熱流束に至るという、沸騰熱伝達における課程を明らかにした。また、瞬時温度分布より評価した熱流束分布より、水で濡れて低温・高熱流束である領域と、高温・低熱流束である二つの領域に区分されることを確認した。

Pool nucleate boiling heat transfer experiments were performed for water at 0.101 MPa to examine the elementary process of the nucleate boiling. The copper printed circuit board of a 1.57 mm thick bakelite plate coated with a 0.035 mm thick copper membrane was used for a heat transfer surface. The size of the heat transfer surface was 10 mm $$times$$ 10 mm. direct current was supplied to it to heat it up. The bakelite plate of the backside of the copper layer was taken by 7 mm $$times$$ 10 mm. The instantaneous variation of the backside temperature of the heat transfer surface was measured with an infrared radiation camera. The time and the space resolution of the infrared cameras used in experiments were 120 Hz and 0.315 mm $$times$$ 0.315 mm, respectively. Surface temperatures just before the burn-out measured with 120 Hz suggest that the surface temperature was steadily low at a large part of the heat transfer surface. A small hot-dry area came out at the critical heat flux condition. Then, this small hot-dry area iterated to expand and shrink and gradually grew. Other area was still wetted and kept at low temperature. Eventually the small hot-dry area started to grow continuously and a whole part of the heat transfer surface became hot-dry to reach the physical burn-out. The heat transfer surface was divided into two large areas; the hot-dry area and the low-temperature wetted area until the physical burn-out. The local surface heat flux variation derived from measured surface temperature variation clearly illustrated that the boundary between the dried area and the wetted area moved back and forth and the dried arear gradually grew to reach physical bourn-out at the critical heat flux condition.

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