Transient Pool Boiling Heat Transfer—Part 1: Incipient Boiling Superheat

Abstract

Incipient boiling superheat for exponentially increasing heat inputs to a platinum wire supported horizontally in a pool of water was measured for exponential periods ranging from 5 ms to 10 s and for subcoolings ranging from 25 to 75K under atomospheric pressure. The heat transfer coefficient before the initiation of boiling was related to those by conduction and by natural convection. The heat flux at the incipient boiling point increased with the decrease in the period. The log-log plot of the heat flux against the superheat at the incipient boiling point had a single asymptotic line of slope 2 which was independent of subcoolings in the high heat flux region. On the other hand, as the heat flux decreased to zero, the superheat tended to approach to a constant value for each subcooling. This asymptotic superheat at zero heat flux was higher for higher subcooling. Transient incipient boiling superheat was reasonably explained by the combination of two kinds of incipient boiling models.

Experimental Study on Transient Boiling Heat Transfer and Critical Heat Flux on Horizontal Vertically-Oriented Ribbon with Different Surfaces under Atmospheric Conditions

“…For desired time [22] was supplied to test heater. The voltage drops across a standard resistance, across the potential taps of the heater and the output voltages of the double bridge circuit were passed to computer via amplifiers and analog-todigital (A/D) converter.…”

“…Consequently, h can be categorized as non-boiling heat transfer coefficient and nucleate heat transfer coefficient. Non-boiling heat transfer coefficients due to exponential increasing heat inputs governed by natural convection heat transfer, transient conduction heat transfer and combined natural convection and transient conduction heat transfer [22] play role the different physical mechanisms of CHF. Generally, the transient conduction at non-boiling condition due to exponential increasing heat inputs is a major potential model to outcome CHF at i q .…”

Experimental investigation of transient critical heat flux of water-based zinc–oxide nanofluids

“…It is well documented that the value of the transient CHF can be significantly different from the steady state CHF value [25][26][27][28][29][30][31][32][33]. Most of the studies reported are for an exponentially increasing volumetric power input given by , where Q o is the initial power level per unit volume in the heater and is the time constant for the transient.…”

“…Most of the studies reported are for an exponentially increasing volumetric power input given by , where Q o is the initial power level per unit volume in the heater and is the time constant for the transient. There have been several attempts to understand the mechanism for transitions from conduction, natural convection and nucleate boiling regimes to film boiling regime, due to exponentially increasing heat inputs with various fluids, such as water, and highly wetting fluids such as liquid nitrogen, liquid helium and ethanol [25][26][27][28][29][30][31][32][33]. Sakurai and Shiotsu, first, suggested that the boiling curve for transient tests is slightly different from that of steady heat flux tests [26,27].…”

“…There have been several attempts to understand the mechanism for transitions from conduction, natural convection and nucleate boiling regimes to film boiling regime, due to exponentially increasing heat inputs with various fluids, such as water, and highly wetting fluids such as liquid nitrogen, liquid helium and ethanol [25][26][27][28][29][30][31][32][33]. Sakurai and Shiotsu, first, suggested that the boiling curve for transient tests is slightly different from that of steady heat flux tests [26,27]. Sakurai et al also observed that for a fixed heat flux value, HTC for transient tests after boiling initiation was lower than that for steady state tests [29].…”