scholarly journals Effect of the flow velocity on bubble boiling characteristics

2019 ◽  
Vol 128 ◽  
pp. 06002
Author(s):  
Levin Anatoliy ◽  
Khan Polina
Keyword(s):  
Experimental Data ◽  
Heat Release ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Cylindrical Wall ◽  
Initial Stage ◽  
Temperature State ◽  
Three Phase ◽  
Formation Dynamics

The present research considers the initial stage of nucleate boiling with high heat fluxes releasing from the technical surface. We show new experimental data on the dynamics of the vapor phasein subcooled water flow in the channel under nonstationary heat release conditions. The heat release dissipation on the heater was performed by passing a controlled three–phase rectified electric current through a tube with a pulse duration of τimp = 60—300 ms with a heating rate of 1000—6000 K/s. We studied the formation dynamics and the structure of the vapor–liquid layer near the heat releasing wall and monitored the temperature state of the wall depending on the parameters of the heater’s flow and the intensity of heating of the cylindrical wall.

scholarly journals On modeling of the initial stage of nonstationary nucleate boiling for the high heat fluxes

2018 ◽  
Vol 240 ◽  
pp. 01018
Author(s):  
Anatoliy Levin ◽  
Polina Khan
Keyword(s):  
Heat Release ◽  
Growth Dynamics ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Nucleation Density ◽  
Fluid Temperature ◽  
Explosive Boiling ◽  
Initial Stage ◽  
General Outcome

During recent years, there have been made significant achievements in the numerical description of the bubble boiling, particularly, in the calculation of the bubble growth dynamics, the nucleation density, and the bubble boiling threshold [1, 2]. However, the numerical prediction is mostly based on the empirical correlations, the accuracy of which does not exceed 20%. Boiling is a complicated process, where each parameter affects not only the general outcome but other parameters, too. The non-stationary heat release is most difficult for modeling, because many of the existing researches are based on analytical expressions for the fluid temperature distribution. The basic stages of the explosive boiling are: (i) heating of the wall to the nucleation temperature; (ii) nucleation of the isolated bubbles; (iii) merging of bubbles and coverage of the entire surface by the steam phase; (iv) heating of the surface to the Leidenfrost temperature and transition to the boiling crisis. This paper presents results of the experimental study for the initial stages of the explosive boiling (i) and (ii), as well as an attempt to simulate them in order to clarify whether the existing approaches can be extended to the case of the nonstationary heat release.

Analytical Model Quantifying the Net Coolant Flow Rate to a Microstructured Copper Surface validated with Two-Phase PIV Measurements

2021 ◽  
Author(s):  
Matt Harrison ◽  
Joshua Gess
Keyword(s):  
Heat Transfer ◽  
Analytical Model ◽  
Flow Rate ◽  
Circular Disk ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Two Phase

Abstract Using Particle Image Velocimetry (PIV), the amount of fluid required to sustain nucleate boiling was quantified to a microstructured copper circular disk. Having prepared the disk with preferential nucleation sites, an analytical model of the net coolant flow rate requirements to a single site has been produced and validated against experimental data. The model assumes that there are three primary phenomena contributing to the coolant flow rate requirements at the boiling surface; radial growth of vapor throughout incipience to departure, bubble rise, and natural convection around the periphery. The total mass flowrate is the sum of these contributing portions. The model accurately predicts the quenching fluid flow rate at low and high heat fluxes with 4% and 30% error of the measured value respectively. For the microstructured surface examined in this study, coolant flow rate requirements ranged from 0.1 to 0.16 kg/sec for a range of heat fluxes from 5.5 to 11.0 W/cm2. Under subcooled conditions, the coolant flow rate requirements plummeted to a nearly negligible value due to domination of transient conduction as the primary heat transfer mechanism at the liquid/vapor/surface interface. PIV and the validated analytical model could be used as a test standard where the amount of coolant the surface needs in relation to its heat transfer coefficient or thermal resistance is a benchmark for the efficacy of a standard surface or boiling enhancement coating/surface structure.

Statistical Modelling of Bubble Nucleation and Heat Transfer Using Interface Tracking in TransAT CMFD Code

2010 ◽  
Author(s):  
Chidambaram Narayanan ◽  
Siju Thomas ◽  
Djamel Lakehal
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Statistical Modelling ◽  
Nucleate Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Conductive Heat Transfer ◽  
Transfer Model ◽  
Conductive Heat

This paper presents results of numerical simulations of various processes that demonstrate phase change heat transfer at high heat fluxes using the level-set method. The model used for the purpose has been first validated for the growth of an evaporating bubble in infinite medium, and fim boiling in 2D and 3D. It has then been applied to simulate the nucleation and departure of a single bubble from a solid body subject to conductive heat transfer. Unlike our previous investigations where phase change induced evaporation rate was incorporated like a sub-grid scale heat transfer model applied to the triple contact line, the present work reports simulations with direct phase change modelling by integrating energy fluxes at the interface. The effect of the conductive heat transfer in the solid from which the bubble departs is also taken into account. Comparison with visual images suggests that accounting for conjugate heat transfer is important to capturing micro-hydrodynamics in nucleate boiling, at least qualitatively.

scholarly journals Non-Isothermal Kinetic Model of the Methane Hydrate Dissociation Process at Temperatures Below Ice Melting Point

2020 ◽  
Author(s):  
I. Donskoy ◽  
S. Misyura
Keyword(s):  
Experimental Data ◽  
Methane Hydrate ◽  
High Heat ◽  
Transport Processes ◽  
Heat Fluxes ◽  
Collective Effects ◽  
Powder Layer ◽  
Gas Filtration ◽  
Hydrate Dissociation ◽  
Kinetic Coefficients

The paper proposes a new model of gas hydrate particles dissociation at high heat fluxes. In this model, the process of hydrate decomposition occurs under the conditions of competition between heterogeneous kinetics and gas filtration. An analysis of the experimental data gives new values ​​of the kinetic coefficients for the hydrate dissociation at low temperatures. The calculation results make it possible to reproduce experimental data on the dynamics of methane hydrate powder dissociation (including dissociation under the conditions of gas burning above the surface) and to describe the phenomenon of self-conservation in terms of changes in the pore structure of the ice crust. The submodel of dissociation of a single particle is embedded in the mathematical model of transport processes in the powder layer, which allows analyzing the heterogeneity of heating and the collective effects of dissociation.

Saturated pool nucleate boiling mechanisms at high heat fluxes

1993 ◽  
Vol 36 (15) ◽  
pp. 3859-3868 ◽  
Author(s):  
Kemal O. Pasamehmetoglu ◽  
Padmanabha R. Chappidi ◽  
Cetin Unal ◽  
Ralph A. Nelson
Keyword(s):  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes

Effect of Velocity on Heat Transfer to Boiling Freon-113

1980 ◽  
Vol 102 (1) ◽  
pp. 26-31 ◽  
Author(s):  
Salim Yilmaz ◽  
J. W. Westwater
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Atmospheric Pressure ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Film Boiling ◽  
Square Root ◽  
Peak Heat Flux

Measurements were made of the heat transfer to Freon-113 at near atmospheric pressure, boiling outside a 6.5 mm dia horizontal steam-heated copper tube. Tests included pool boiling and also forced flow vertically upward at uelocities of 2.4, 4.0 and 6.8 m/s. The metal-to-liquid ΔT ranged from 13 to 125° C, resulting in nucleate, transition, and film boiling. The boiling curves for different velocities did not intersect or overlap, contrary to some prior investigators. The peak heat flux was proportional to the square root of velocity, agreeing with the Vliet-Leppert correlation, but disagreeing with the Lienhard-Eichhorn prediction of an exponent of 0.33. The forced-flow nucleate boiling data were well correlated by Rohsenow’s equation, except at high heat fluxes. Heat fluxes in film boiling were proportional to velocity to the exponent 0.56, close to the 0.50 value given by Bromley, LeRoy, and Robbers. Transition boiling was very sensitive to velocity; at a ΔT of 55° C the heat flux was 900 percent higher for a velocity of 2.4 m/s than for zero velocity.

Nucleate Pool Boiling of a TURBO-B Bundle in R-113

1994 ◽  
Vol 116 (3) ◽  
pp. 670-678 ◽  
Author(s):  
S. B. Memory ◽  
S. V. Chilman ◽  
P. J. Marto
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Tube Bundle ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Smooth Tube ◽  
Vertical Array ◽  
Wall Superheat

Heat transfer measurements were made during nucleate boiling of R-113 from a bundle of 15 electrically heated, copper TURBO-B tubes arranged in an equilateral triangular pitch, designed to simulate a portion of a flooded evaporator. Five of the tubes that were oriented in a vertical array on the centerline of the bundle were each instrumented with six wall thermocouples. For increasing heat flux, the incipient boiling wall superheat of upper tubes decreased as lower tubes were activated. In the boiling region at low heat fluxes (≈ 1 kW/m2), the average bundle heat transfer coefficient was 4.6 times that obtained for a smooth tube bundle (under identical conditions) and 1.6 times greater than that obtained for a single TURBO-B tube; a similar bundle factor has been reported for a smooth tube bundle. At high heat fluxes (100 kW/m2), the average bundle heat transfer coefficient was 3.6 times that of a smooth tube bundle. Furthermore, there was still a significant bundle factor (1.22), contrary to a smooth tube bundle, where all effect of lower tubes was eliminated at high heat fluxes.

Optimization of Enhanced Surfaces for High Flux Chip Cooling by Pool Boiling

1993 ◽  
Vol 115 (1) ◽  
pp. 89-100 ◽  
Author(s):  
I. Mudawar ◽  
T. M. Anderson
Keyword(s):  
Experimental Data ◽  
Boundary Conditions ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Metallic Surface ◽  
High Flux ◽  
Base Area ◽  
Chip Cooling ◽  
Low Profile

A high flux electronic chip was numerically and experimentally simulated to investigate pool boiling capabilities of enhanced metallic surface attachments built upon a 12.7 × 12.7 mm2 base area. It is shown how experimental nucleate boiling data for a flat chip and for chips with low-profile microstructures can be used as input boundary conditions in the numerical prediction of boiling performances of high flux, smooth and microstructured extended cylindrical surfaces. A technique for extending the applicability of the numerical results to cylindrical fin arrays is demonstrated with the aid of experimental data obtained for these surfaces. Surface enhancement resulted in chip planform heat fluxes of 105.4 and 159.3 W/cm2, for saturated and 35°C subcooled FC-72, respectively.

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