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The Isolated Bubble Regime in Pool Nucleate BoilingWe consider an isolated bubble boiling regime in which vapour bubbles are intermittently produced at a prearranged set of nucleation site on an upward facing overheated wall plane. In this boiling regime, the bubbles depart from the wall and move as separate entities. Except in the matter of rise velocity, the bubbles do not interfere and are independent of one another. However, the rise velocity is dependent on bubble volume concentration in the bulk. Heat transfer properties specific to this regime cannot be described without bubble detachment size, and we apply our previously developed dynamic theory of vapour bubble growth and detachment to determine this size. Bubble growth is presumed to be thermally controlled. Two limiting cases of bubble evolution are considered: the one in which buoyancy prevails in promoting bubble detachment and the one in which surface tension prevails. We prove termination of the isolated regime of pool nucleate boiling to result from one of the four possible causes, depending on relevant parameters values. The first cause consists in the fact that the upward flow of rising bubbles hampers the downward liquid flow, and under certain conditions, prevents the liquid from coming to the wall in an amount that would be sufficient to compensate for vapour removal from the wall. The second cause is due to the lateral coalescence of growing bubbles that are attached to their corresponding nucleation sites, with ensuing generation of larger bubbles and extended vapour patches near the wall. The other two causes involve longitudinal coalescence either 1) immediately in the wall vicinity, accompanied by the establishment of the multiple bubble boiling regime, or 2) in the bulk, with the formation of vapour columns. The longitudinal coalescence in the bulk is shown to be the most important cause. The critical wall temperature and the heat flux density associated with isolated bubble regime termination are found to be functions of the physical and operating parameters and are discussed in detail.
Document ID
20020027525
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Buyevich, Y. A.
(NASA Ames Research Center Moffett Field, CA United States)
Webbon, Bruce W.
(NASA Ames Research Center Moffett Field, CA United States)
Callaway, Robert
Date Acquired
August 20, 2013
Publication Date
January 1, 1995
Subject Category
Fluid Mechanics And Thermodynamics
Funding Number(s)
PROJECT: RTOP 199-61-62
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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