Wataru Nakayama

Effects of Pore Diameters and System Pressure on Saturated Pool Nucleate Boiling Heat Transfer From Porous Surfaces

The porous surface structure was manufactured with precision for the experimental study of nucleate boiling heat transfer in R-11. Boiling curves and the data of bubble formation were obtained with a variety of geometrical and operational parameters; the pore diameters were of 50, 100, 150 ..mu..m, there was a combination of pores of different sizes; and the system pressures were of 0.04, 0.1, 0.23 MPa. The boiling curves exhibit certain trends effected by the diameter and population density of pores. A combination of high system pressure and pore sizes of 100 or 150 ..mu..m dia enables boiling to persist even when the wall superheat is reduced to an extremely low level of 0.1 K. A noteworthy feature of porous surface boiling is that intense bubble formation does not necessarily yield a high heat-transfer performance. Examination of the data indicates that liquid suction and evaporation inside the cavities are a proable mechanism of boiling with small temperature differences.

Optimized Performance of Condensers with Outside Condensing Surfaces

The purpose of this paper is to find an optimum surface geometry of vertical condenser tubes where condensation takes place on the outer surfaces. The guiding principle on optimum condensation performance is to make the thickness of condensate liquid on the surfaces as thin as possible. A vertical tube with longitudinally parallel tiny fins is preferable because condensate is made thinner over the widest possible region. According to an analysis, there are four controlling factors for the optimum fin; sharp leading edge, gradually changing curvature of fin surface from tip to the root, wide groove between fins to collect condensate and horizontal discs attached to the tube to remove condensate. The analytical result is checked by experiments using R-113. The optimum fin shape, fin pitch and spacing of discs are found by numerical calculations for R-113 and water.

Flow in Rotating Cylinder of a Gas Centrifuge

Thermal convection and weak forced flows in a rotating cylinder were studied theoretically to find the mass velocity distributions in a gas centrifuge. Compressibility of the gas is taken into account in the form of a density stratification in the radial direction. First of all, a scaling analysis was made to verify the dominance of Coriolis force in the field of flow. The result of this analysis indicated that the body of the fluid in the centrifuge is composed of inviscid cores separated by a viscous layer concentric to the axis of rotation, and enveloped by other viscous layers lining the side and end faces of the cylinder. The transport of the gas from the feed ports to the discharge ports is made through these viscous layers. The thermal convection has its largest component near the side wall in the form of a recirculating flow, and its pattern is controlled by the temperature distribution of the wall. These theoretical results were verified in part by an experiment devised to permit visual observati...

Forced Convective Heat Transfer from LSI Packages in an Air-Cooled Wiring card Array

The resistance to heat flow from finned LSI packages to the cooling air flow has been studied by combining the physical models with the results of heat transfer experiments, flow visualization experiments, and pressure drop measurements. Although crude assumptions are employed in analytical modeling, the proposed method of prediction of heat transfer and pressure drop has proved useful to cooling system designers. A notable finding is the advantage obtained by placing the packages in a staggered arrangement on the card. This reduces the local air temperature rise by as much as 70% over the conventional in-line arrangement, where the fan power is given as a constraint.

Numerical Analysis of Separative Power of Isotope Centrifuges, (I)

It is found from numerical analysis that a strong influence is exerted on the separative efficiency of centrifuges by the thermal convection arising from the temperature difference prevailing between the end plates of a centrifuge drum—known as “Ekman suction”. The numerical method previously developed by Nakayama & Torii is used to compute the distributions of concentration resulting from considerations of both thermal convection and forced flow. The effect of Ekman suction is represented by the parameter λE(≡(a2√E ρpsV∇T)/(16 lρDT0)), different values of which were adopted in the calculations, as were other parameters such as λ(≡GF/(∇ηlρpD), GF: feed rate) for the forced flow and θ representing the cut. The separative efficiency of an exemplified counter-flow type centrifuge is found to reach 58% when λe≒0.7, λ≒1.0 and θ≒O.3, with a product port radius r p= 0.5. It is also shown that the thermal convection in the Stewartson layer near the side wall of a centrifuge drum affects the separative, efficiency...

On the accommodation of coolant flow paths in high-density packaging

An analytical study was carried out to highlight the need to work out a tradeoff between the switching speed of logic gates and the average wiring distance, taking into account coolant flow distribution within the information processing system, in order to achieve the maximum processing speed at the system level. One of the models is composed of a row of gate-carrying cards flanked by side boards with networks to complete the three-dimensional wiring. The gates are cooled by forced convection of FC-77 or water. It is shown that the advantage of the 3D configuration in the reduction of wiring distance is seriously compromised by the need to make room for coolant channels within the system to such an extent that in certain cases the single-card system is favored over multiple-card systems. As a model of the single-card system, a square array of logic gates cooled by impinging liquid jets is considered. Again, it is concluded that the space requirement of coolant flows could set the upper bound for the density of logic gate packing. The case studies indicate that a gate-level heat flux of 100 W/cm/sup 2/ is a difficult target to achieve on a processor composed of a large number of gates. >

Temperature distribution in IC plastic packages in the reflow soldering process

Temperature distribution in the packages is evaluated by both experimental method and an analytical finite-element method (FEM). It is found that the FEM analysis is useful for the temperature estimation of the packages. Temperature sensors imbedded in silicon chips were used to measure the temperature distribution in the package in both the reflow soldering process and the dip-coating process. These sensor chips were encapsulated in the actual DIP (dual in-line package) type package and SOJ (small outline j-bend package) type package. Temperature distributions of these packages were measured under various soldering conditions.<<ETX>>

A new approach to the design of complex heat transfer systems: notebook-size computer design

A new approach for solving heat-transfer problems in geometrically complex systems has been developed. The purpose of this new approach is to develop a methodology whereby the packaging designers is freed from the task of performing detailed numerical analysis. The approach utilizes templates of components and electric devices rather than working on actual components, without simulation of the detailed complex geometry. By varying the template dimensions, the effects of geometrical configurations on cooling airflow and heat-transfer can be studied systematically. The approach is applicable to heat-transfer analysis of portable computers. Available numerical analysis tools, such as computational fluid dynamics (CFD) codes, are used to create heat-transfer databases from which fast design codes can be developed.