Takeyuki Fukuda

Experiment and analysis of practical-scale solar pond stabilized with salt gradient☆

Abstract A large-scale solar pond with salty water was constructed in the suburbs of Kitami in 1985. Its performance has been measured and analyzed by the authors after that. The solar pond body is circular of 44 m diameter, and the pond water is of 3 min total depth. After, 15 months, the depth of the salt gradient zone (S.G.Z.) was thinned by 10 cm in the top and by 20 cm in the bottom due to convection of the top and bottom zones. The temperature in the convective storage zone (C.S.Z.) reached 70°C, its maximum, at the beginning of September in 1985, however, it was not as high in 1986 due to contamination of the pond water. The temperature of the storage zone was reduced from November to April due to ice covering on the pond surface. The collected heat yielded largely and the collection efficiency reached more than 30% in summer, but decreased to negative values in winter. The thermal performance of the solar pond was predicted by a simulation calculation, and the calculated result compared well with the measurements.

Mixed, forced and natural convective heat transfer in cavities heated from bottom surface.

This experimental study concerns the mixed, forced and natural convection heat transfer in rectangular cross-section cavities heated from bottom surface. Flow visualization, temperature profiles and measurements of heat transfer from bottom heating surface are performed for various free-stream velocities, temperature differences between the free-stream and the heating surface and dimensions of the cavity. It is found that flow pattern and amount of convective heat transfer are influenced by an interaction between forced and natural convection, and there is an existence of Reynolds numbers region which the amount of convective heat transfer is decreased with increasing Reynolds number. This paper correlates the experimental data in terms of Nusselt number, dimension ratio of cavity (depth/width of cavity), Grashof and Reynolds numbers according to the region of Reynolds numbers.

Numerical simulation of thermal performance of a salt-gradient solar pond in a cold climate.

A one-dimensional numerical model which simulates the dynamic thermal performance of stratified salt-gradient solar pond is described. The model simulates the thermal performance in the upper convective layer, the nonconvective layer and the lower convective layer in a cold climate. In addition to the energy flux in the solar pond, the model simulates the varying ice thickness appearing in the upper convective layer during the winter season. From the results, it is noticed that it is important to maintain the optimum thickness of the nonconvective layer and the clearness of the upper convective layer for the high thermal efficiency of the salt-gradient solar pond.

Natural Connective Heat Transfer in an Inclined Rectangular Cavity under a Constant Heat Flux Heating Condition

等熱流束加熱条件下の傾斜く形空気層内の自然対流熱伝達に関する実験が広範囲な傾斜角θ、アスペクト比 H/W (縦横比)および等熱流束条件にて行なわれた。傾斜角に応じて、ペナードセル形の三次元流れ、スクリュ状の流れおよび二次元境界流れに分類できることが判明した。0=θ≦60°にてヌセルト数 Nu-修正レーレー数 Ra cos θ および60<θ≦120°にて Nu-Ra sin θ の関係にて層流・乱流熱伝達量を無次元式にて整理することができた。

Natural convection heat transfer in an inclined air layer packed with spherical particles.

Experiments of natural convection heat transfer in an inclined air layer with spherical particles under isothermal heating and cooling conditions were carried out for the ranges of inclination angles (θ=0180°), aspect-ratios (H/W=2.57.9), modified Prandtl numbers (P*r=1.145), ratios of diameter of spherical particles to width of the porous layer (d/W=0.040.516) and modified Rayleigh numbers (R*a=2.2×101.03×103). According to the inclination angle, the convection heat transfer in the porous layer varied because of the change of the convection flow type. In addition, useful correlations of non-dimensional convection heat transfer were derived in the relations Nusselt number Nu=f[P*r, d/W, R*a cos(θ-60°)] for θ=015°, and Nu=f[P*r, H/W, R*a (θ-60°)] for θ=0120°.