A Transient Model for Minimum Film Boiling Point in Subcooled Film Boiling PDF Download

Author: Laung-Kuang Toby Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 398

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Author: Илья Григорьевич Йофф
Publisher:
ISBN:
Category :
Languages : en
Pages : 60

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Author: Saeed Rezakhany
Publisher:
ISBN:
Category : Film boiling
Languages : en
Pages : 666

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Author: LeRoy Alton Bromley
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 40

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Author: Chunkuan Shih
Publisher:
ISBN:
Category : Film boiling
Languages : en
Pages : 466

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Author: Howard Hong-Yuang Yen
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 186

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Author: Frederick F. Simon
Publisher:
ISBN:
Category : Film boiling
Languages : en
Pages : 44

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Author: Juliana Pacheco Duarte
Publisher:
ISBN:
Category :
Languages : en
Pages : 206

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The post-critical heat flux (post-CHF) heat transfer is a complex two-phase flow phenomenon divided in two regions: a so-called 'transition boiling' regime characterized by the rapid degradation of heat transfer from a heated surface to a liquid/vapor mixture, and a so-called 'stable film boiling' regime characterized by heat transfer from the heated surface to the vapor. The limit between these two regimes is usually referred as the minimum film boiling temperature (TMFB), and has been interpreted as a temperature from which the liquid no longer can contact the heated surface. To better understand these phenomena, experiments were performed at LWR conditions in the High Pressure Heat Transfer Facility at the University of Wisconsin-Madison. These experiments and subsequent prototypic experiments from the KATHY facility, in Germany, contribute to the limited experimental database on this topic. KATHY data were collected under BWR conditions during Anticipate Transient Without Scram that leads to cycles of dryout and rewet events and ultimately to a failure to rewet of at least one thermocouple. The data were analyzed using a 2D inverse heat transfer computational tool to obtain the surface heat fluxes and temperatures during post-CHF. It was observed that the transition to the film boiling heat transfer regime is a hydrodynamic mechanism dependent on both the pressure and the mass flux, while the local quality affects the mechanism of film formation between a film dryout at high qualities and bubbles coalescence at low qualities. The homogeneous nucleation temperature, which is a thermodynamic mechanism, acts as a lower bound for this transition temperature. The analysis also quantifies different transient boiling curves for flow regimes that differ qualitatively and quantitatively from the typical boiling curve considered in steady-state two-phase heat transfer analysis. The results provide insights into boiling heat transfer and they can change the way we currently model the two-phase post-CHF.

Author: Frank Kreith
Publisher: Springer Science & Business Media
ISBN: 3662301822
Category : Science
Languages : en
Pages : 400

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Book Description
to increase the use of direct contact processes, the National Science Foundation sup ported a workshop on direct contact heat transfer at the Solar Energy Research Insti tute in the summer of 1985. We served as organizers for this workshop, which em phasized an area of thermal engineering that, in our opinion, has great promise for the future, but has not yet reached the point of wide-spread commercial application. Hence, a summary of the state of knowledge at this point is timely. The workshop had a dual objective: 1. To summarize the current state of knowledge in such a form that industrial practi tioners can make use of the available information. 2. To indicate the research and development needed to advance the state-of-the-art, indicating not only what kind of research is needed, but also the industrial poten tial that could be realized if the information to be obtained through the proposed research activities were available.

Author: H. R. Nagendra
Publisher:
ISBN:
Category : Aerodynamic measurements
Languages : en
Pages : 52

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An approach for the solution of transient-forced convection film boiling on an isothermal flat plate using the boundary layer model is developed. The similarity variables are used to convert the governing partial differential equations to ordinary ones. The results of numerical solutions of these ordinary equations indicate that the transient process can be classified as one-dimensional conduction, intermediate, and the steady state regions. The time required for the one-dimensional conduction and the time necessary to attain a steady state condition are obtained. The influence of interfacial shear is seen to be negligible while the Prandtl Number and the ratio (C sub p delta T divided by h sub fg times Pr) have major influence. The use of local similarity approximations for the intermediate regime facilitates prediction of complete boundary layer growth. Using the ratio of time at any instant to the steady state time as abscissa, the curves representing the boundary layer growth can be merged into a single mean curve within 5 percent. Further, the analysis shows that the average rate of heat transfer during transient is 50 to 100 percent higher than those at steady state. The average rate of vapor convected away is 10 to 15 percent lower than at steady state while the average rate of accumulation to form the vapor layer is 1 to 14 times larger. Further, the total heat transferred during transient increases and the evaporation decreases for increasing values of C sub p delta T divided by h sub fg times Pr.