Reduction of thermal resistance of naturally-cooled cooling system has been investigated. Pin-fin type heat sink was utilized as to clarify the effect of pin arrangement on the thermal performance of heat sink. The pitch of fins was set 1, 2, 3, 4, 5mm where the surface area of all heat sink was set as the same. The results show that the thermal resistance of heat sink decreases with increasing pitch of fin arrangement from 1 to 4mm, whereas the thermal resistance gets increase when the pitch was set 5mm. The results also show that even the slight decrease in fin efficiency causes the increase in the thermal resistance.
A newly developed flat heat pipe FGHPTM (Morex Kiire Co.) was experimentally investigated by using neutron radiography. The test sample of the FGHP heat spreader was 65 × 65 × 2 mm3 composed of several etched copper plates and pure water was used as the coolant. Neutron radiography was performed at the E-2 port of the Kyoto University Research Reactor (KUR). The coolant distributions in the wick area of the FGHP and its heat transfer characteristics were measured at heating conditions. Experimental results show that the coolant distributions depend slightly on its installation posture and that the liquid thickness in the wick region remains constant with increasing heat input to the FGHP. In addition, it is found that the wick surface does not dry out even in the vertical posture at present experimental conditions.
In a fluidized bed, particle agglomeration and channeling have been observed when the fluidizing gas is switched from lower to higher density. This defluidization is a transient phenomenon, and fluidization is restored after several minutes. In this paper, we assume this behavior can be explained by non-equimolar diffusion, which causes pressure gradients in the bed and subsequently leads to viscous flow. To verify this assumption, pressure changes were measured for several binary diffusion systems in a packed bed. After the packed bed was filled with a gas, another gas was supplied to the bed's outer surface to replace the first gas. These gases were exchanged by diffusion, and the pressure at the closed end of the column either increased or decreased due to differences in the gases' molecular weights. The pressure changes were compared with pressure changes calculated from a model based on both an unsteady-state diffusion equation and the Kozeny-Carman equation. The measured pressure changes in the packed beds could be correlated with the calculated values without any adjustable parameters. In a fluidized bed, after the gas switched from lower to higher density, differences in diffusion rates due to the gases' various molecular weights caused a net molecular flow from the emulsion phase to the bubble phase. This flow caused a decrease in gas velocity in the emulsion phase and a contraction of the emulsion phase; channeling and defluidization were then observed.
