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International Heat Transfer Conference 6

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

THE LEIDENFROST PHENOMENON AT PRESSURES UP TO THE CRITICAL

T. R. Rhodes
Nelson Electric Co., Tulsa, Oklahoma USA

Kenneth J. Bell
School of Chemical Engineering, Oklahoma State University Stillwater, Oklahoma 74078, U.S.A.

DOI: 10.1615/IHTC6.3900
pages 251-255

Abstract

The Leidenfrost Phenomenon (film boiling of discrete liquid masses) was studied experimentally and analytically for FreonR 114 (dichlorotetra-fluoroethane) up to its critical pressure (32.2 atma = 3.27 × 106 N/m2).
The experimental portion of this study consisted of photographic determination of drop lifetimes and diameter histories at reduced pressures of 1/8, 1/4, 1/3, 1/2, 3/4, and 1. A high pressure cell with a quartz window and a nitrogen atmosphere was employed. Surface temperatures up to 274°C were studied and the Leidenfrost temperature (minimum surface temperature for stable film boiling) determined as a function of pressure. Nucleate and film boiling were observed at the critical pressure.
An analytical model was developed, based upon the Gottfried-Lee-Bell model earlier proposed for the Phenomenon in the open atmosphere. The model purports to predict the fluid mechanics of the vapor underneath the drop, the heat transfer rates by radiation and conduction from the bottom surface and the walls of the enclosure, and the mass transfer by diffusion from the upper surface of the drop. The problem is formulated in non-linear, highly coupled algebraic and differential equations, and a fairly large and fast computer is required to carry out the computations for a drop lifetime. This has been done for the present case, and satisfactory agreement was found between model and experiment up to a reduced pressure of 3/4. The discrepancy at the critical condition is likely due to the very great variations in properties and even physical state with very small changes in pressure and temperature.

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