A theoretical study of the relationship between contact angles and the shape of a vapor stem
- Univ. of California, Los Angeles, CA (United States). Mechanical, Aerospace and Nuclear Engineering Dept.
The effect of heater surface wettability on the shape of vapor stems, which are formed in fully developed nucleate boiling, has been investigated theoretically. Lay and Dhir`s (1994) vapor stem model, which describes the liquid flow and heat transfer in an evaporating two-dimensional vapor stem formed in saturated nucleate boiling, is used in the present study. The static contact angle is a measure of surface wettability. The contact angle depends on the relative magnitude of solid-liquid adhesive forces and liquid-liquid cohesive forces, which can be represented by the well-known dispersion constant, {bar A}. The Girifalco-Good-Fowkes-Young equation is employed to quantify the relationship between dispersion constant, {bar A}, and contact angle through the calculated interfacial tensions. Water is used as the test fluid. The results show that the value of the dispersion constant, {bar A}, changes from a negative value to a positive value as the surface contact angle changes from partially wetting to completely wetting. The influence of the value of {bar A} on the shape of a vapor stem is reflected in the results. For a liquid film with a finite contact angle at one atmosphere pressure, the interfacial tension of the substrate surface and the contact angle decrease as the saturation temperature increases. For a partially wetting surface, the contact angle vanishes and complete wetting condition occurs near the critical pressure of the liquid. The effect of increase in pressure and contact angle is to reduce the size of the vapor stems.
- Sponsoring Organization:
- National Aeronautics and Space Administration, Washington, DC (United States)
- OSTI ID:
- 442590
- Report Number(s):
- CONF-950828-; ISBN 0-7918-1707-5; TRN: IM9712%%15
- Resource Relation:
- Conference: 1995 National heat transfer conference, Portland, OR (United States), 5-9 Aug 1995; Other Information: PBD: 1995; Related Information: Is Part Of 1995 national heat transfer conference: Proceedings. Volume 6: Basic aspects of two phase flow and heat transfer; HTD-Volume 308; Dhir, V.K. [ed.] [Univ. of California, Los Angeles, CA (United States)]; PB: 152 p.
- Country of Publication:
- United States
- Language:
- English
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