KURENAI : Kyoto University Research Information Repository

parallel to the water flow. The effects of subcooling, velocity, press-
ure and heater size on transient boiling heat transfer coefficients and
maximum heat fluxes have been studied for exponential heat increase with
periods up to 5 millisecond. The experimental correlation for transient
maximum heat flux was presented in collaboration with dimensional analy-
sis of forced convective transient boiling.
In Chapter It, the transient non-boiling heat transfer coefficient
under forced convection condition has been analysed for exponentially
increasing Jieat flux. When the power transient accident occurs in
a pressurized water reactor or in a liquid metal cooled reactor, the
heat transfer process in an initial stage is considered to be a transient
non-boiling forced convective heat transfer. Therefore, in analysing the
problem associated with the reactivity accident, the knowledge of the
transient non-boiling heat transfer is also indispensable. The boundary
layer approximation was applied to this problem. Approximate but simple
analytic solutions for transient non-boiling heat transfer coefficient
have been obtained for laminar and turbulent flow over a wide range of
Prandtl number. For an exponentially increasing heat flux, transient
heat transfer coefficients attain asymptotic values and these values
were correlated by one dimensionless parameter including heat flux
increasing rate.
Another important phase of a reactor accident is loss of c oolant
accident (LOCA) and subsequent rewetting and quenching phenome na of the re-
actor core. In this case, a large amount of vapor is generated
and high
quality two-phase flows are often encountered. One of the most import-
ant flow regimes under these circumstances is annular dispers
iv
ed flow.