報告書番号

N10030

タイトル（和文）

調理器近傍における熱流動現象の解明（その4）―模擬加熱調理器実験における水平局所加熱平面上部での対流伝熱機構の同定―

タイトル（英文）

Investigation on heat and fluid flow above a cooking oven (part 4)-Disclosing convective heat-transfer structures above a locally heated horizontal flat plate with a model cooker experiment-

概要 （図表や脚注は「報告書全文」に掲載しております）

調理器を模擬した加熱源として，空気中に設置された加熱円板を取り上げ，その上部に形成される熱境界層の乱流特性を実験的に調べた．加熱円板の表面温度および半径は，473K，0.15mであり，その半径に基づくレイレー数は9×10^7となる．この値は，境界層が乱流状態に発達していることを意味する．2種類の測定を実施した．一つは冷線計測による温度測定でもう一つは可視化流速計測による2次元2成分速度測定である．これらにより，高次モーメントを含む乱流統計量を測定した．そして，加熱源極近傍には，乱流特性の異なる二層構造が存在することを明らかにした．加熱源に近い下層では，低温度流体塊の侵入に起因する周方向風速変動が活発化するが上層では，高温流体の間欠的な湧き出しによる軸方向風速変動が支配的となることを把握した．また，無次元化した乱流統計量がレイレーベナール対流との相似性を有することを示した．

概要 （英文）

Turbulence characteristics of a thermally boundary layer in air above an isothermally heated round plate, which corresponds to a cooker, is experimentally investigated. The surface temperature and radius of the heated source are 473 K and 0.15 m, respectively, and thus, the Rayleigh number based on the radius of plate is 9x107, implying that the boundary layer develops into fully turbulence. Turbulence statistics of the boundary layer, including the near-surface region, is measured with a particle image velocimetry technique, the accuracy of which has been verified through the comparison with a hot-wire measurement. The measurements clearly shows that below z/R = 0.2 (z: vertical distance from the surface, R: radius of the plate, = 0.15 m), buoyant plume is very weak. And, simultaneously the Reynolds shear stress becomes almost zero, whereas intensities of velocity fluctuations are quite large, implying the existence of peculiar turbulence generation mechanism. For the weak plume region, with the help of temperature measurements by using a cold wire technique, the measurements including higher order moments reveals that the two layer structure exists near the heated plate; in the lower layer, the velocity fluctuation of radial component is active compared with that of axial component with the incursion of low temperature fluids, whereas, in the upper layer, the contribution of axial velocity fluctuation with high temperature fluid becomes dominant. Also, the normalized vertical profiles of statistics are similar to those for the boundary layer flow of Rayleigh-Benard convection, indicating the universality of scaling for convective boundary layer.

報告者

キーワード