Abo Bibliothek: Guest

ISSN Online: 2377-424X

ISBN Print: 0-89116-130-9

International Heat Transfer Conference 6
August, 7-11, 1978, Toronto, Canada

A STUDY OF TRANSIENT EFFECTS LEADING UP TO INCEPTION OF NUCLEATE BOILING

Get access (open in a dialog) DOI: 10.1615/IHTC6.3710
pages 139-144

Abstrakt

When the temperature of a solid surface in contact with a liquid is rapidly increased above the saturation temperature, nucleation boiling begins only after some time delay. The various elements which combine to make up this delay period are examined.
A semi-transparent thin gold film on Pyrex glass is used simultaneously as a heater and resistance thermometer. Recordings of instantaneous surface heat flux and surface temperature are synchronized with high speed motion pictures taken through the heating surface from beneath. Average surface temperature measurements are made with an uncertainty of ± 0.9K, using R113 and liquid nitrogen at atmospheric pressure. Step input power to the thin film is varied from 0.1 to 10 w/cm2 for test surface orientations of horizontal-up and vertical.
Distinct conduction and convection regimes in the fluid are observed during the interval from the step power input to the onset of boiling. The solution to the conduction problem for a plane heat source at the interface of two semi-infinite solids compares well with the measured transient temperature of the gold film. Equations are derived to predict the onset of natural convection. The experimental results for the horizontal-up orientation fall between the relations obtained using critical Raylcigh numbers of 800 and 1100. For the vertical orientation the agreement between the experimental results and the theoretical predictions are reasonably good at lower levels of heat flux.