Hydrodynamic Prediction of Peak Pool-boiling Heat Fluxes from Finite Bodies

1973 ◽  
Vol 95 (2) ◽  
pp. 152-158 ◽  
Author(s):  
J. H. Lienhard ◽  
V. K. Dhir
Keyword(s):  
Heat Flux ◽  
Flat Plate ◽  
Pool Boiling ◽  
General Concept ◽  
Heat Fluxes ◽  
The Body ◽  
Cross Sectional ◽  
Vapor Velocity ◽  
General Ground ◽  
Peak Heat Flux

Since Zuber made a hydrodynamic prediction of the peak pool-boiling heat flux on an infinite flat plate, his general concept has been used to predict the peak heat flux in two finite heater configurations. These latter predictions have differed from Zuber’s in the introduction of a largely empirical variable—the thickness of the vapor escape path around the body. The present study shows how measurements of this thickness can be combined with the hypothesis that the vapor velocity within the vapor blanket must match the vapor velocity in the escaping jet above the heater. The result is a more exact description of the hydrodynamics of vapor removal. This idea is used to suggest the possibility of a universal value for the ratio of the cross-sectional area of escaping jets to the heater area for large finite heaters and for long slender heaters. A set of general ground rules is developed for predicting the peak heat fluxes on both large and small heaters. These rules are used in turn to predict the peak heat flux from horizontal ribbons. They are also used to correct the traditional prediction for infinite-flat-plate heaters. The predictions are supported with new data.

Peak Pool Boiling Heat-Flux Measurements on Finite Horizontal Flat Plates

1973 ◽  
Vol 95 (4) ◽  
pp. 477-482 ◽  
Author(s):  
J. H. Lienhard ◽  
V. K. Dhir ◽  
D. M. Riherd
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Flat Plate ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Hydrodynamic Theory ◽  
Organic Liquids ◽  
Flat Plates ◽  
Peak Heat Flux ◽  
Flux Measurements

Experimental data obtained at both earth-normal and elevated gravity, in a variety of organic liquids and water, are used to verify the hydrodynamic theory for the peak pool boiling heat flux on flat plates. A modification of Zuber’s formula, which gives a 14 percent higher peak heat flux, is verified as long as the flat plate is more than three Taylor wavelengths across. For smaller heaters, the hydrodynamic theory requires a wide variation in heat flux owing to discontinuities in the number of escaping jets. Data for smaller plates bear out this predicted variation with heat fluxes that range between 40 percent and 235 percent of Zuber’s predicted value. Finally, a method is suggested for augmenting the peak heat flux on large heaters, and shown experimentally to be viable.

Rewetting Velocity of High-Temperature Vertical-Narrow-Annular Flow Passages Under Counter-Current Flow Condition

2003 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Masanori Tsukudo ◽  
Naoki Sakamoto
Keyword(s):  
Heat Flux ◽  
Annular Flow ◽  
Pool Boiling ◽  
Outer Wall ◽  
Heat Fluxes ◽  
Annular Gap ◽  
Wall Superheat ◽  
Peak Heat Flux ◽  
Inner Diameter ◽  
Counter Current

Quenching of a thin gap annular flow passage by gravitational liquid penetration was examined experimentally by using R-113. The outer wall was made of copper. The inner wall was made of copper or glass. The inner diameter of the outer wall of the annular flow passages was 40 or 41 mm and the annular gap clearance δ was 0.5, 1.0, 2.0 and 5.0 mm. The outer wall was heated initially up to 250 °C and also the inner wall was heated when the copper inner wall was used. The quenching was observed in δ ≥ 1.0 mm. When δ = 0.5 mm, the wall was just gradually cooled down. The relation between the wall superheat and the heat flux during quenching process was similar to the boiling curve of pool boiling. However, the peak heat flux as well as the heat flux in the film and the transition boiling was lower than those in the pool boiling. These heat fluxes became lower as the gap clearance became narrow. The rewetting velocity became slow as the gap clearance became narrow. The rewetting velocity seemed to have a unique relation for the Peclet number Pe = (ρSCSδSU/λS) and the Biot number Bi = hδs/λs ; Pe ∝ Bi which was the same as that of the Yamanouchi correlation. A decrease in the heat flux (the heat transfer coefficient) in the rewetting front region, which corresponds to the peak heat flux, results in a decrease in the rewetting velocity as the gap clearance becomes narrow.

The Mechanism of and Stability Criterion for Nucleate Pool Boiling of Sodium

1969 ◽  
Vol 91 (3) ◽  
pp. 315-328 ◽  
Author(s):  
I. Shai ◽  
W. M. Rohsenow
Keyword(s):  
Heat Flux ◽  
Liquid Metals ◽  
Bubble Formation ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Nucleate Pool Boiling ◽  
Thermal Layer ◽  
Minimum Heat ◽  
Bubble Growth And Departure ◽  
Recorded Temperature

Experimental data for sodium boiling on horizontal surfaces containing artificial cavities at heat fluxes of 20,000 to 300,000 Btu/ft2 hr and pressures between 40 to 106 mm Hg were obtained. Observations are made for stable boiling, unstable boiling and “bumping.” Some recorded temperature variations in the solid close to the nucleating cavity are presented. It is suggested that for liquid metals the time for bubble growth and departure is a very small fraction of the total bubble cycle, hence the delay time during which a thermal layer grows is the most significant part of the process. On this basis the transient conduction heat transfer is solved for a periodic process, and the period time is found to be a function of the degree of superheat, the heat flux and the liquid thermal properties. A simplified model for stability of nucleate pool boiling of liquid metals is postulated from which the minimum heat flux for stable boiling can be found as a function of liquid-solid properties, liquid pressure, the degree of superheat, and the cavity radius and depth. At relatively low heat fluxes, convection currents have significant effects on the period time of bubble formation. An empirical correlation is proposed, which takes into account the convection effects, to match the experimental results.

Pool Boiling Using Thin Enhanced Structures Under Top-Confined Conditions

2006 ◽  
Vol 128 (12) ◽  
pp. 1302-1311 ◽  
Author(s):  
Camil-Daniel Ghiu ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Single Layer ◽  
Temperature Limit ◽  
Heat Fluxes ◽  
The Other ◽  
Vapor Flow ◽  
Maximum Heat ◽  
Maximum Heat Flux

An experimental study of pool boiling using enhanced structures under top-confined conditions was conducted with a dielectric fluorocarbon liquid (PF 5060). The single layer enhanced structures studied were fabricated in copper and quartz, had an overall size of 10×10mm2, and were 1mm thick. The parameters investigated in this study were the heat flux (0.8-34W∕cm2) and the top space S(0-13mm). High-speed visualizations were performed to elucidate the liquid/vapor flow in the space above the structure. The enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. On the other hand, the maximum heat flux for a prescribed 85°C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime.

Peak Pool Boiling Heat Flux in Viscous Liquids

1974 ◽  
Vol 96 (1) ◽  
pp. 71-78 ◽  
Author(s):  
V. K. Dhir ◽  
J. H. Lienhard
Keyword(s):  
Heat Flux ◽  
Viscous Liquid ◽  
Critical Velocity ◽  
Functional Form ◽  
Pool Boiling ◽  
Gas Jet ◽  
Flat Plates ◽  
Viscous Liquids ◽  
Peak Heat Flux ◽  
The Stability

The stability of a gas jet in a surrounding viscous liquid is studied. An expression is developed for the critical velocity at which the jet becomes unstable in a returning viscous liquid. The stability analysis is made to correspond with the geometrical configuration of gas jets and liquid columns similar to those observed near the peak pool boiling heat flux. The critical velocity of the gas jet is then used to obtain the functional form of the peak heat flux on flat plates and cylindrical heaters. The expressions are compared with original observations of the peak heat flux in very viscous liquids on flat plate, and cylindrical, heaters at both earth-normal, and elevated, gravities.

Effect of Acoustic Excitation on R134a/Al2O3 Nanolubricant Mixture Boiling on a Reentrant Cavity Surface

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
M. A. Kedzierski ◽  
S. E. Fick
Keyword(s):  
Heat Flux ◽  
Volume Fraction ◽  
Power Level ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Cavity Surface ◽  
Test Surface ◽  
Acoustic Excitation ◽  
Al2o3 Nanoparticles ◽  
Maximum Enhancement

This paper quantifies the influence of acoustic excitation of Al2O3 nanoparticles on the pool-boiling performance of R134a/polyolester mixtures on a commercial (Turbo-BII-HP) boiling surface. A nanolubricant with 10 nm diameter Al2O3 nanoparticles at a 5.1% volume fraction in the base polyolester lubricant was mixed with R134a at a 1% mass fraction. The study showed that high-frequency ultrasound at 1 MHz can improve R134a/nanolubricant boiling on a reentrant cavity surface by as much as 44%. This maximum enhancement occurred for an applied power level to the fluid of approximately 6 W and a heat flux of approximately 6.9 kW/m2. Applied power levels larger and smaller than 6 W resulted in smaller boiling heat transfer enhancements. In total, five different applied power levels were studied: 0 W, 4 W, 6 W, 8 W, and 12 W. The largest and smallest enhancement averaged over the tested heat flux range were approximately 12% and 2% for the applied power levels of 6 W and 4 W, respectively. In situ insonation at 1 MHz resulted in an improved dispersion of the nanolubricant on the test surface. An existing pool-boiling model for refrigerant/nanolubricant mixtures was modified to include the effect of acoustic excitation. For heat fluxes greater than 25 kW m−2, the model was within 4.5% of the measured heat flux ratios for mixtures, and the average agreement between measurements and predictions was approximately 1% for all power levels.

Exploration of uniform heat flux on the flow and heat transportation of ferrofluids along a smooth plate: Comparative investigation

2018 ◽  
Vol 11 (04) ◽  
pp. 1850048 ◽  
Author(s):  
Muhammad Usman ◽  
Muhammad Hamid ◽  
Syed Tauseef Mohyud Din ◽  
Asif Waheed ◽  
Wei Wang
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Heat Flux ◽  
Flat Plate ◽  
Convergence Analysis ◽  
Skin Friction ◽  
Heat Fluxes ◽  
Uniform Heat Flux ◽  
Wavelet Method ◽  
Dimensionless Velocity

The paper is devoted to a new extension in Gegenbauer wavelet method (GWM) to investigate the transfer of heat and MHD boundary-layer flow of ferrofluids beside a flat plate with velocity slip. A homogenous model study is conducted in which we assumed the heat transfer and forced convective flow of ferrofluids along a flat plate with a uniform wall heat flux. In the direction of transverse to plate, a magnetic field is imposed. Three various magnetic nanoparticle types including Mn–ZnFe2O4, CoFe2O4, Fe3O4are incorporated inside the base fluid. Two types of base fluids (water and kerosene) with bad thermal conductivity as compared to nanoparticles of solid magnetic have been assumed. The mathematical model is tackled via modified Gegenbauer wavelet method (MGWM). A simulation is accomplished for individual ferrofluid mixture by assuming the prevailing impacts of uniform and slip heat fluxes. The variation of heat transfers and skin friction were also observed at the surface of the plate and we analyzed the better heat transfer for every mixture. Kerosene-based magnetite (Fe3O4) delivers the better rate of heat transfer at wall due to its association with the kerosene-based Mn–Zn and cobalt ferrites. The slip velocity and magnetic field effects on the temperature, dimensionless velocity, rate of heat transfer and skin friction are examined for various magnetic nanoparticles inside the kerosene oil and water. We observed that the primary influence of magnetic field reduces the dimensionless surface temperature and accelerates the dimensionless velocity as compared to the hydrodynamic case, thus enhancing the rate of heat transfer and skin friction ferrofluids. Moreover, a detailed evaluation of outcomes obtained by MGWM, already published work and numerical RK-4 were found to be in excellent agreement. The error and convergence analysis are presented. Comparison of results, graphical plots, error and convergence analysis reveal the appropriateness of proposed method. The proposed algorithm can be extended for other nonlinear problems.

An Experimental Study of Miniature-Scale Pool Boiling

2003 ◽  
Vol 125 (6) ◽  
pp. 1074-1086 ◽  
Author(s):  
Tailian Chen ◽  
Jacob N. Chung
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Boiling Curve ◽  
Feedback Control System ◽  
Electronic Feedback ◽  
Fundamental Understanding ◽  
Peak Heat Flux ◽  
Different Temperatures

By generating single bubbles on a micro-heater at different wall superheats, an experimental study of miniature-scale pool boiling heat transfer has been performed to provide a fundamental understanding of the heater size effect. In this study, the constant-temperature microheater is set at different temperatures by an electronic feedback control system. The heat transfer history during the lifetime of a single bubble which includes nucleation, growth, detachment and departure has been measured. The boiling curve obtained from the microheater is composed of two regimes which are separated by a peak heat flux. It is suggested that in the lower superheat regime, the boiling is dominated by liquid rewetting and micro-layer evaporation, while in the higher superheat regime, conduction through the vapor film and micro-convection plays the key heat transfer role as the heater is covered by vapor all the time. In general, boiling on microheaters is characterized by larger bubble departure sizes, smaller bubble growth rates due to the dryout of microlayer as the bubble grows, and higher bubble incipience superheat. As the heater size decreases, the boiling curve shifts towards higher heat fluxes with corresponding higher superheats.

The Dominant Unstable Wavelength and Minimum Heat Flux During Film Boiling on a Horizontal Cylinder

1964 ◽  
Vol 86 (2) ◽  
pp. 220-225 ◽  
Author(s):  
J. H. Lienhard ◽  
P. T. Y. Wong
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Flat Plate ◽  
Transverse Direction ◽  
Horizontal Cylinder ◽  
Heat Fluxes ◽  
Taylor Instability ◽  
Film Boiling ◽  
Minimum Heat ◽  
Effect Of Surface

Predictions of the dominant unstable wavelength and the minimum heat flux during film boiling above a flat plate are found to be inapplicable in the case of boiling on small wires. New expressions are developed for the case of a horizontal cylinder, by accounting for the effect of surface tension in the transverse direction upon the Taylor instability of the interface. Original measurements of wavelengths and minimum heat fluxes on small wires are also provided. These data support the predictions.

Transient Heat Flux Measurements in a Divided-Chamber Diesel Engine

1985 ◽  
Vol 107 (2) ◽  
pp. 439-444 ◽  
Author(s):  
A. C. Alkidas ◽  
R. M. Cole
Keyword(s):  
Heat Flux ◽  
Diesel Engine ◽  
Fluid Motion ◽  
Local Heat ◽  
Relative Increase ◽  
Heat Fluxes ◽  
Main Chamber ◽  
Peak Heat Flux ◽  
Flux Measurements ◽  
Local Heat Flux

Transient surface heat flux measurements were performed at several locations on the cylinder head of a divided-chamber diesel engine. The local heat flux histories were found to be significantly different. These differences are attributed to the spatial nonuniformity of the fluid motion and combustion. Both local time-averaged and local peak heat fluxes decreased with decreasing speed and load. Retarding the combustion timing beyond TDC decreased the peak heat flux in the antechamber but increased the peak heat flux in the main chamber. This is attributed to the relative increase in the portion of fuel that burns in the main chamber with retarded combustion timing.

Sign in / Sign up

Export Citation Format

Share Document