[en] Melting of ice in cylindrical capsules by natural and forced convections was studied by flow visualization technique. Surface temperatures were changed by the effect of natural convection in a cylindrical capsule with large diameter. In case of natural convection melting, the process was well simulated by axisymmetric heat conduction analysis when capsule diameters were small. In case of forced convection melting, surface temperatures were considerably scattered and the stagnation point showed the highest value. The shape of the solid liquid boundary became considerably asymmetric. (author)

[en] Experimental study was performed on heat transfer of an open thermosyphon with constant wall heat flux. Water and aqueous glycerin were used as working fluids. Experimental range of modified Rayleigh Number was 1 x 10³ < Ra_m < 3 x 10⁵. Average and local heat transfer coefficients, vertical temperatures distributions of the tube wall and fluid at the center line of the tube, temperature fluctuation of the fluid were measured. Flow patterns were observed by adding tracer powder in the fluid. Fluid velocities were measured by L. D. V (Laser Doppler Velocimeter). Experimental results indicate that there exists three different heat transfer characteristics and corresponding flow patterns. For 1 x 10³ < Ra_m < 4 x 10³, flow was laminar and thermal boundary layer reaches near the center of the tube. Heat was exchanged between wall and descending flow. Wall temperature rose towards downward. For 4 x 10³ < Ra_m < 3 x 10⁴, no turbulence was observed in the flow and thermal boundary layer was localized in the vicinity of the wall. Wall temperature rose towards upward. For 3 x 10⁴ < Ra_m < 3 x 10⁵, flow is considerably disturbed by the mixing of upward and downward flow in the upper part of the tube. However, flow is almost laminar in the lower part of the tube. Reduction of flow rate induced by the flow mixing at high Ra_m would be one of the major causes of the deterioration of heat transfer from the Light hill's theory. (author)

[en] Effects of walls on shedding vortex in developed channel flow were investigated putting a cylinder at the center of channels or on a wall for the value of w/d from 2 to 4. Results were compared with the uniform flow result. When a cylinder was put at the center of the channels, non-dimensional frequency plotted against Reynolds number agreed with the uniform flow result at low Reynolds number. However, it increased rapidly with Reynolds number, then it lay considerably above the uniform flow results at high Reynolds number. When a cylinder was put on a wall, non-dimensional frequency was considerably lower than the uniform flow result in the cases of w/d = 3 and 4. In the case of w/d = 2, however, frequency was higher than the uniform flow result at high Reynolds number. In all cases in the present study, the transition Reynolds number increased with decrease in the value of w/d. These results indicate that the increase in shedding frequency was due to the shift in velocity distribution from Poiseuille parabora in the wake region, which obviously increased with Reynolds number and with decrease in channel width. (author)

[en] Effect of channel walls on inviscid flow around a circular cylinder placed in the midstream is evaluated by a model with a source in a mapping plane. Comparison is made between the present theory and experimental data of several investigators in subcritical and supercritical regions. The present theory requires empirical values of back pressure coefficient and separation angle for a circular cylinder. In subcritical region, the present theory agrees well with the experimental data for h/d = 0 to h/d = 0.667. In supercritical region, a slight difference was observed in the vicinity of the separation point. Generally, agreement between the present theory and experiments is well. (author)

[en] Heat storage technique of high temperature and high density latent heat can be applied to an accumulator of heat generated by nuclear power plant in the night and to a thermal load absorber. For the practical use of the heat storage technique, it is important to improve heat exchange characteristics between heat storage medium, such as molten salts, and heat transfer fluid because of low thermal conductivity of the molten salts, to improve durability among molten salt and structure materials and to develop the molten salt with stable thermal properties for a long period. Considering the possibility for the improvement of heat exchange characteristics of phase change heat storage system by absorbing molten salt in porous ceramics with high thermal conductivity, high temperature proof and high resistance to corrosion, several samples of the ceramics heat storage unit were made. Basic characteristics of the samples (strength, thermal properties, temperature characteristics during phase change) were measured experimentally and analytically to study the utility and applicability of the samples for the heat storage system. The results show that the heat storage unit should be used in inactive gas condition because water in the air absorbed in the molten salts would yield degeneration of properties and deterioration of strength and that operation temperature should be confined near fusion temperature because some molten salts would be vaporized and mass would be decreased in considerable high temperature. The results also show that when atmospheric temperature changes around the melting temperature, change in ceramic temperature becomes small. This result suggests the possibility that ceramic heat storage unit could be used as thermal load absorber. (J.P.N.)

[en] Heat transfer to laminar flow in converging plane walled channels with both walls heated and one wall heated one wall adiabatic is analytically obtained. The analysis is carried out for the two thermal boundary conditions of prescribed wall heat flux q ∼ 1/r and q ∼ r^δ. The Nusselt number for flow in converging plane walled channels depends on Reynolds number and half taper angle α. If differences in velocity distribution are ignored, there is a direct correspondence between wall heat flux q ∼ e^{-α(δ + 1)x} in parallel flow and heat flux q ∼ r^δ in converging plane walled channels. In case of q varying as 1/r, Nusselt number is usually higher than that for laminar flow in parallel channel with constant heat flux. It increases as the value of ⁺Re⁺α increases, and approaches a limit value at r → 0 when ⁺Re⁺α → ∞. In case of q varying as r^δ, however, when δ < -1, Nusselt number is higher than that with q ∼ 1/r. When delta > -1, Nusselt number at r → 0 falls below that for constant heat flux case in parallel channel. It decreases as the value ⁺Re⁺α increases, and reduces to zero as ∣Re∣α exceeds a critical value. (author)

No abstract available

[en] Reactor core reverse flow experiments were made to observe heat transfer and fluid characteristics of forced cooling failure accident of HTGR reactor core. Two channels (heated and cooled) were used in this experiment to simulate HTGR multi-channel core. Wall temperature, flow rate and temperature distribution in fluid were measured for natural and mixed convections. The results show that natural convection flow rate is proportional to Grashof number and that hysteresis between wall temperature and flow rate is observed for mixed convection. (author)

[en] Free convection heat transfer from the inner surface of a sphere was studied by using integrated boundary layer equations. Analysis was made for the condition that the sphere surface was cooled; and the top of the sphere was a stagnation point. Approximate solutions agreed well with numerical solutions for a Prandtl number range of Pr ≥ 1. The analytical results were compared with the experimental results of free convection made in a hemishere. The Nusselt number of both results agreed within about 15 %. (author)

[en] Flow around a circular, square and trapezoid-type turbulence promoter was studied putting it in a center of channels or on a wall for low Reynolds number. Frequencies and power spectrum intensities of shedding vortices behind a promoter were measured. Results show that vortices behind the trapezoid cylinder were the strongest and the widest. Flow characteristics behind the trapezoid cylinder were similar to that behind the circular cylinder. Vortices behind the square cylinder were the weakest and the narrowest. Adequate shape of turbulence promoter for augmentation of heat transfer was discussed. (author)