Studies on enclosed pool flash evaporation

Sridhar Gopalakrishna, University of Pennsylvania

Abstract

The objective of this study is to gain an overall understanding of the phenomenon of flash evaporation using a theoretical simulation model and results from scaled-down experiments. Four aspects of the problem are considered: (a) Numerical solution of bubble growth in a varying pressure field, (b) Analysis of bubble motion and drag during flashing, (c) Experimental correlation for flashing from a pool of liquid, and (d) Conjugate heat transfer analysis for transient natural convection in a thermal storage tank. The numerical scheme for bubble growth considers a single bubble growing and translating in a time-varying pressure field in the liquid. The energy equation for the liquid with the appropriate energy interface equation at the bubble interface are solved for a flow situation described by the Hadamard-Rybczynski solution. A finite difference solution method using the Alternating Direction Implicit (ADI) scheme is employed. Results are obtained for a range of initially imposed pressure reductions. The growth rate of a bubble is seen to increase with the degree of superheat imposed by this pressure reduction, and the effect of simultaneous translation of the bubble is seen to be quite significant, especially at lower superheats. The effect of pressure reduction on the translation of a single bubble is also examined using a force balance on the bubble. Results of Runge-Kutta integration of the equation of motion indicate that the form of the drag expression plays a very important role. Based on previous experiments on a scaled-down flash chamber, the mass of flashed steam is correlated in nondimensional form with a variety of parameters such as the imposed superheat, depth of the pool and initial temperature. The effect of wall heat transfer on the stratification history of an initially stably stratified fluid inside a rectangular enclosure is examined using a numerical finite difference scheme. The results of the integration of the governing equations, in the vorticity-stream function formulation, indicate that the decay of initially stable depends strongly on the wall-to-fluid thermal property ratios, and proceeds at a faster rate for highly conducting walls.

Subject Area

Mechanical engineering

Recommended Citation

Gopalakrishna, Sridhar, "Studies on enclosed pool flash evaporation" (1989). Dissertations available from ProQuest. AAI8922505.
https://repository.upenn.edu/dissertations/AAI8922505

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