scholarly journals The Dependence of the Heat Transfer Coefficient on Film Boiling Modes in He II

2006 ◽  
Vol 41 (6) ◽  
pp. 252-257
Author(s):  
Suguru TAKADA ◽  
Masahide MURAKAMI ◽  
Masakazu NOZAWA ◽  
Nobuhiro KIMURA
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Boiling ◽  
The Heat Transfer Coefficient

Role of Taylor Instability on Sublimation of a Horizontal Slab of Dry Ice

1977 ◽  
Vol 99 (3) ◽  
pp. 411-418 ◽  
Author(s):  
V. K. Dhir ◽  
J. N. Castle ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Boiling ◽  
Dry Ice ◽  
Ice Surface ◽  
Hypothetical Accident ◽  
Square Array ◽  
The Heat Transfer Coefficient

Sublimation of a horizontal slab of dry ice (≃ 190 K) placed beneath a pool of warm water or benzene (278–340 K) has been observed experimentally. Data for the heat transfer coefficient have been obtained in both steady and quasi-static states. The heat transfer coefficient for this pseudo film boiling process is found to be strongly dependent on the pool temperature. In the temperature range of stable film boiling, the heat transfer coefficient depends on the laminar or turbulent nature of the gas film. However, when the pool temperatures are such that a stable film can no longer be maintained, and the overlying liquid starts to freeze at the interface, the heat transfer coefficient data are correlated with the parameter cpΔTf/hsf for the liquid. Post-experiment visual observations of the dry ice surface show the presence of valleys and ridges arranged in a nearly square array spaced about one Taylor wavelength apart. An application of the present study to the fast reactor hypothetical accident situations in which a pool of molten fuel may be formed on horizontal steel surfaces is discussed.

Influence of Pressure on Film Boiling Heat Transfer

1976 ◽  
Vol 98 (2) ◽  
pp. 166-172 ◽  
Author(s):  
G. Hesse ◽  
E. M. Sparrow ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Points ◽  
Bubble Columns ◽  
Film Boiling ◽  
Nusselt Numbers ◽  
Heating Wire ◽  
The Heat Transfer Coefficient

Experiments on film boiling of carbon dioxide were performed covering the range of pressures from the triple point to the critical point. Measurements were also made at supercritical pressures. Three different heating wire sizes were employed with diameters of 0.0508, 0.1, and 0.4 mm. The boiling curves, plotted in terms of heat flux and temperature difference, were found to be pressure dependent, with a more marked dependence for smaller diameter heating wires. The role of pressure level was exhibited in greater detail in a presentation in which the heat transfer coefficient is plotted against pressure at fixed values of heat flux. The most rapid variations of the heat transfer coefficient with pressure occur in the neighborhoods of the triple and critical points, with relatively gradual variations in evidence in the intermediate range of pressures. The curves of heat transfer coefficient versus pressure take on minimum values at the triple and critical points. Nusselt numbers evaluated from the experimental data agree satisfactorily with available predictive equations. Photographs of the vapor separation patterns revealed that with increasing pressure, the bubble columns which break away from the vapor film successively evolve into vapor columns and vapor sheets. As the critical pressure is approached, the height of the sheet diminishes.

Numerical Analysis on Heat Transfer Characteristics of Looped Minichannel Using Phase-Change VOF Method

2013 ◽  
Author(s):  
Hajime Onishi ◽  
Motoya Kawamura ◽  
Yukio Tada ◽  
Akira Takimoto
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Film Condensation ◽  
Film Boiling ◽  
Heat Transfer Characteristics ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

This study develops a numerical simulation of liquid-vapor two phase flows accompanied with the phase change. In the developed simulation, the VOF (Volume of Fluid) method is adopted for tracking the liquid-vapor interface and the temperature recovery method for estimating mass transfer due to the phase change. Firstly, the numerical simulation is performed for film-boiling and film-condensation problems for validating the evaporation (boiling) and condensation calculation. The numerical result for the film-boiling problem is in good agreement with the Berenson’s semi-empirical correlation in terms of the heat transfer coefficient. Moreover, the numerical results for the film-condensation problem are also in good agreement with the theoretical analysis by Nusselt in terms of the film growth rate and the heat transfer coefficient. These have confirmed the reliability of the developed simulation. Then, the developed simulation is applied to investigate the heat transfer characteristics of the heat transport device with a pump-driven looped minichannel. The result reveals a new interesting feature of the minichannel heat device.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Test and Analysis on the Heat Transfer Coefficient of the Mixed Plate Heat Exchanger

2014 ◽  
Vol 552 ◽  
pp. 55-60
Author(s):  
Zheng Ming Tong ◽  
Peng Hou ◽  
Gui Hua Qin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Mixed Mode ◽  
Plate Heat Exchanger ◽  
Plate Heat ◽  
Fitting Method ◽  
Engineering Significance ◽  
The Heat Transfer Coefficient

In this article, we use BR0.3 type plate heat exchanger for experiment,and the heat transfer coefficient of the mixed plate heat exchanger is explored. Through the test platform of plate heat exchanger, a large number of experiments have been done in different mixed mode but the same passageway,and lots experimental data are obtained. By the linear fitting method and the analysis of the data, the main factors which influence the heat transfer coefficient of mixed plate heat exchanger were carried out,and the formula of heat transfer coefficient which fits at any mixed mode plate heat exchanger is obtained, to solve the problem of engineering calculation.The fact , there is no denying that the result which we get has great engineering significance

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