Takuji Torii

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...

Temperature distribution in semiconductor wafers heated in a vertical diffusion furnace

The transient temperature distribution in a row of wafers heating in a vertical diffusion furnace was calculated as the heating power of the furnace was PID (proportional plus integral plus derivative) controlled. Radiative heat transfer was combined with axisymmetric unsteady conduction in wafers and the furnace. With feedforward control of the heating power (which means that when wafers are inserted into the furnace, the heater temperature is set higher than the desired heating temperature), the temperature of the wafers reached the heating temperature rapidly. The radiative properties of silicon wafers changed from semitransparent to opaque at 500 degrees C, and the effect of this change on the temperature distribution in the wafers was calculated. Thermoplastic deformation of the wafers is more likely to occur during withdrawal than during insertion.<<ETX>>

RADIATION THERMOMETRY OF SILICON WAFERS IN A DIFFUSION FURNACE WITH ROD-TYPE AND PRISM-TYPE OPTICAL GUIDES

This article examines the accuracy of radiation thermometry in measuring the temperature of silicon wafers in a diffusion furnace. This technique uses optical guides to bring thermal radiation from the wafers to the outside of the furnace. The error due to veiling glare of a rod-type optical guide is 40°C and that of a prism-type is 0.5°C at steady state.