Film boiling over a moving horizontal surface
Abstract
To study forced, subcooled film boiling over a horizontal surface both theoretical and experimental methods have been utilized. Using a two phase boundary layer model, with the application of similarity (local similarity) and integral methods, heat transfer results for both laminar and turbulent flows over a moving plate were obtained. In order to gain confidence in the theoretical models and to provide justification for their use in engineering practice (for example, in building comprehensive models to simulate thermal behavior of a steel strip cooled by water jets), comparisons were made between the experimental data and theoretical results. Transient boiling experiments, were performed with a preheated test specimen exposed to a wall jet on its top surface. Temperatures measured at strategic locations on the test specimen, together with known heat fluxes at some of the surfaces (adiabatic surfaces), were used as boundary conditions to solve the transient heat conduction equation for the entire temperature field. The heat flux at the boiling surface was then calculated and boiling curves were generated. Comparisons between predictions and measured film boiling convective heat transfer coefficient are found to be in generally good agreement. The largest discrepancy (underprediction of up to approximately 40%) occurs at locations close to the quench front and may be due to the increased possibility of liquid/solid contact. Much better agreement was achieved in the zones for which film boiling is expected, and the model assumptions are more appropriate. A convenient and accurate method was developed to measure apparent rewetting and rewetting temperatures. The measured apparent rewetting and rewetting temperatures show that, contrary to some previous studies, these temperatures depend not only on the flow and surface conditions but also on the specimen temperature prior to quenching.
Degree
Ph.D.
Advisors
Incropera, Purdue University.
Subject Area
Mechanical engineering
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