Tetsuro Ogushi

Measurement and analysis of effective thermal conductivities of lotus-type porous copper

Lotus-type porous copper is a porous medium made of copper that contains many straight pores. To effectively employ lotus-type porous copper as a heat sink, it is necessary to clarify the pore effect on the thermal conductivity of lotus copper. This article describes an experimental and analytical investigation on the effective thermal conductivities of lotus copper parallel and perpendicular to the pores. The lotus copper displayed anisotropy of the effective thermal conductivity. The effective thermal conductivity keff⊥ perpendicular to the pores was lower than that of the parallel ones keff∥ and was 40% that of lotus copper material ks with porosity e of 0.4. Experimental data for keff∥ showed good agreement with analytical results derived from the assumption that heat flow through the cross-sectional area parallel to the pore axis is proportional to (1−e). Experimental data for keff⊥ showed good agreement with the analytical results derived from the assumption of orthorhombic symmetry and with the num...

Snow Melting Using Heat Pipes

ABSTRACT Field tests using stored earth energy and water energy in combination with heat pipes for snow melting were conducted at the Nojiri Snow Removal Station, Lake Nojiri, Nagano Prefecture, and Karls Hot Spring, Noboribetsu, Hokkaido, during 1978 and 1981. The results of these test show that the capability of the earth heat systems ranged from 40 to 100 W/m2, while the water system was capable of delivering a maximum of about 400 W/m2. Earth heating systems are the effective means of snow melting and deicing in moderate climate zones. One of several merits of these systems is that maintenance and power costs are eliminated. But the demerits are high construction costs and low power generation. Studies conducted over a three-year period show that the energy dissipated during the winter is naturally restored to the earth by the following October. However, owing to an insufficient thermal capacity, the snow melting capability decreases in late winter. This creates the problem of ensuring the earth heat systems performance capability in climates of unpredictable severity. This paper gives an outline of the designs, construction, and test results of these systems at two test sites in Japan; also included is a discussion on the economic feasibility of utilizing the two systems discussed.

Steady state comparative-longitudinal heat flow method using specimen of different thicknesses for measuring thermal conductivity of lotus-type porous metals

Lotus-type porous metal with many straight pores is attractive as a heat sink, because larger heat transfer capacity is obtained, owing to the small diameter of the pores. In order to use lotus-type porous metal effectively as a heat sink, it is important to clarify the effective conductivity and to consider the pore effect on heat conduction in the lotus-type porous metal. Because lotus-type porous metal is an anisotropic material, a steady state comparative-longitudinal heat flow (SCHF) method for thermal conductivity, referring to the ASTM standard, is thought to be better than a nonsteady method such as a laser flash method. This paper investigated the variable of the steady state comparative-longitudinal heat flow method by using specimens of different thicknesses (SCHF-DT) method for measuring the effective thermal conductivity. As a result, the uncertainty of effective thermal conductivity of a specimen was found to be smaller, as the diameter of a rod became larger and the length of a rod became shorter. In addition, it was found by error analysis that a dominant factor in the uncertainty of this method was the contact thermal difference between the rod and specimen.

Development of Heat Sinks for Air Cooling and Water Cooling Using Lotus-Type Porous Metals

In recent years, since heat dissipation rates and high frequency electronic devices have been increasing, a heat sink with high heat transfer performance is required to cool these devices. Heat sink utilizing micro-channels with several ten microns are expected to provide an excellent cooling performance because of their high heat transfer capacities due to small channel. Therefore, various porous materials such as cellular metals have been investigated for heat sink applications. However, heat sink using conventional porous materials has a high pressure drop because the cooling fluid flow through the pores is complex. Among the described porous materials, a lotus-type porous metal with straight pores is preferable for heat sinks due to the small pressured drop. In present work, cooling performance of the lotus copper heat sink for air cooling and water cooling is introduced. The experimental data for air cooling show 13.2 times higher than that for the conventional groove fins. And, the data for the water cooling show 1.7 times higher than that for the micro-channels. It is concluded that lotus copper heat sink is the most prospective candidate for high power electronics devices.Copyright

Effect of Pore Diameter Distribution on Heat Transfer Capacity of Lotus-Type Porous Copper Heat Sink for Air Cooling

Lotus-type porous metal with many straight pores is attractive as a heat sink because larger heat transfer capacity is obtained due to the small diameter of the pores. The heat transfer capacity of the lotus-type porous copper heat sink was calculated using the model with the pores of uniform diameters. However, actual lotus-type porous metals have a distribution of pore diameter. In the present work, we investigated the lotus-type porous copper fin model by considering size distribution of the lotus-type porous copper fin. Prediction of the heat transfer characteristics for the lotus-type porous copper heat sink shows a good agreement with the experimental data.

Prediction of Capacity of a Heat Exchanger by Thermal Network Method (Influence of Thermal Conduction in Fins on Capacity of a Condenser)

This paper presents an influence of heat flow from high temperature refrigerant to low temperature refrigerant through fins by thermal conduction. For estimating the influence, we applied thermal network method that can consider refrigerant quality distribution in the heat exchanger. At a same time, for verifying the estimation, an experiment was performed with 2 row-2 pass heat exchanger. Prediction shows that heat transfer capacity of a condenser is reduced by 3% for a simple 2 row-2 pass heat exchanger by heat conduction in fins. By comparison between the experimental results and the predicted results, it was proved that predicting error was within 1% for condenser capacity.