On the Expediency of Developing a Two-Stage Model of Boiling Crisis of a Liquid Wetting a Heating Surface
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SCUSSION
On the Expediency of Developing a Two-Stage Model of Boiling Crisis of a Liquid Wetting a Heating Surface E. D. Fedorovich* Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia *e-mail: [email protected] Received October 15, 2019; revised October 15, 2019; accepted November 20, 2019
Abstract—This short report substantiates the advisability of developing a two-stage model for the emergence and development of a boiling crisis. One of the stages is the violation of the stability of the two-phase wall layer, and the other is the appearance and fusion of dry spots on the heating surface. The use of a two-stage (“temporary”) model makes it possible to combine both well-known approaches to crisis analysis—hydrodynamic and thermal—in a single logical system. In the first approach, the characteristics of the boiling crisis are characteristic of high pressures in a boiling liquid, while those in the second are for low pressures. Keywords: boiling crisis, two-stage model, thermal model, hydrodynamic model, low pressures, high pressures, loss of stability, dry spots DOI: 10.1134/S0040601520110051
An assumption about the advisability of creating this model arose with the author when reading a report published in the collection [1]. This report states that the results obtained explain the mechanism of the heat transfer crisis during boiling under conditions of natural convection and in forced flow as follows. At the base of the vapor channels in the liquid film under the steam conglomerates or in the troughs of the waves under the dispersed-circular flow regime, the evaporation at the critical heat flow is so great that the reactive forces displace the liquid from the wall layer with the subsequent formation of a dry spot. If we consider the above explanation of the crisis mechanism to be correct, which is such in the opinion of the author of this article since this explanation corresponds to both experimental observations and “ordinary” common sense, then we can imagine a model of crisis that can be called “two-stage.”
reactive forces sufficient in value to violate the stability of the two-phase layer. Under these conditions, the onset of the heat transfer crisis is delayed (apparently, we are talking about fractions of a second). When the number of dry spots on the surface does not become such that they begin to close together on some part of the surface and then merge into a single large dry spot, then a boiling crisis will occur. In favor of the validity of such an explanation of the mechanism of the crisis at low pressures is the fact that the thermal model of the crisis by Yagov [4] is in good agreement with the experimental data obtained for this pressure range, while the hydrodynamic model of the crisis by Kutateladze [2] for this pressure range gives a significant underestimation of the values of critical heat flux densities in comparison with the experimental data. The formula proposed by Kutateladze in [2] has the following form:
At the first time stage of a steam jet, it brea
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