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of these works, the transient heat transfer coefficients have been obtained
for step changes in wall temperature or wall heat flux.
Concerning the transient non-boiling heat transfer under exponential
power increase, there are a few analytical works and experimental works
conducted by Siegel et al. [3], Soliman et al. [17,18] and Kataoka et al.
[27]. However,reliable correlations based on a physical model have not
been available due to the complexity of the phenomena.
One of the characteristic features of the transient non-boiling heat
transfer coefficient for exponentially increasing heat flux is that the
heat transfer coefficient attains asymptotic value after a certain time from
the initiation of heating and remains constant until the inception of boiling
(Fig. 1). The experimental data of Soliman et al. [17,18] and Kataoka
et al. [27] show this tendency. Their results show that the ratio
between the asymptotic value of transient heat transfer coefficient and the
steady state one is approximately correlated in terms of one dimensionless
parameter composed of velocity,-heater length and exponentially increas-
ing rate of heat flux, (u/24.1)). Here, u is the velocity, 9, is the representative
heater length and w is a parameter which represents the rate of exponen-
tially increasing heat flux (or heat generation rate), q = q 0 exp(wt).
In recent years, the advances in numerical analysis for heat transfer
process have made it possible to accurately predict the heat transfer co- _.
efficient for considerably complicated geometry. For the analysis of
transient heat transfer, such techniques have been applied and numerical
analyses have been carried out for step wall temperature rise or step
heat flux rise [10-12, 21-26].Basically, these techniques will be a pp-
lied to the case for exponentially increasing heat flux . However, it
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