scholarly journals A map of regimes of evaporation and boiling in the horizontal liquid layer on the modified surface

2021 ◽  
Vol 2039 (1) ◽  
pp. 012033
Author(s):  
D A Shvetsov ◽  
A N Pavlenko ◽  
A E Brester ◽  
V I Zhukov
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Liquid Layer ◽  
Heat Fluxes ◽  
Convection Regime ◽  
Boiling Crisis ◽  
Wide Range ◽  
Modified Surface ◽  
Horizontal Layers

Abstract The paper presents the results of the study of the evaporation and boiling regimes in thin horizontal layers of liquid on a modified surface in a wide range of changes in the pressure and height of the liquid layer. Depending on the heat flux, pressure, and height of the liquid layer, the formation of various structures was observed. In this paper, maps of the evaporation and boiling regimes are obtained, which show the heat fluxes from the natural convection regime up to the boiling crisis, depending on the height of the liquid layer. The results are compared with the calculation dependencies.

Local Measurements of Disk Heat Transfer in Heated Rotating Cavities for Several Flow Regimes

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
André Günther ◽  
Wieland Uffrecht ◽  
Stefan Odenbach
Keyword(s):  
Heat Flux ◽  
Flow Regimes ◽  
Local Heat ◽  
Heat Fluxes ◽  
Flow Structures ◽  
Back Side ◽  
Wide Range ◽  
Toroidal Vortices ◽  
Axial Heat ◽  
Cooling Air

This paper discusses experimental results from a two-cavity test rig representation of the internal air system of a high-pressure compressor. Thermal steady-state measurements of the time-averaged local heat fluxes on both sides of the middle disk are presented for three different flow regimes: pure axial throughflow of cooling air and axial throughflow of cooling air in two directions with a superposed radial inflow of hot air in one cavity. Mass flow ratios between 1/40 < mrad/max < 2/1 are measured. Tests were carried out for a wide range of non-dimensional parameters: Reφ up to 107, Rez up to 2 × 105, and Cw up to −2.5 × 104. In all cases, the shroud is uniformly heated to approximately 100 °C. The local axial heat fluxes are determined separately for both sides of the middle disk from measurements of the surface temperatures with open spot-welded thermo-couples. The method of heat flux determination and an analysis approach calculating the uncertainties and the sensitivity are described and discussed. The local heat flux results of the different flow paths are compared and interpreted by assumed flow structures. The time-averaged heat flux results can be adequately interpreted by flow structures of two toroidal vortices for axial throughflow and a source-sink flow for the radial inflow. The measurements show that the axial heat flux can change direction, i.e., areas exist where the disk is heated and not cooled by the flow. For axial throughflow, a local minimum of heat flux exists on the impinged side in the range of x = 0.65. On the back side, a heating area exists in all tests in the lower half of the disk (x < 0.6) due to recirculated air of higher temperature. This heating area corresponds to the range of the inner vortex and increases with higher axial and rotational Reynolds numbers.

scholarly journals Thermal regime of the local working zone in the industrial premises under radiant heating conditions

2021 ◽  
Vol 2057 (1) ◽  
pp. 012124
Author(s):  
G V Kuznetsov ◽  
V I Maksimov ◽  
T A Nagornova ◽  
A V Vyatkin
Keyword(s):  
Natural Convection ◽  
Mixed Convection ◽  
Experimental Studies ◽  
Heat Fluxes ◽  
Radiant Heating ◽  
Air Masses ◽  
Convection Regime ◽  
Working Zone ◽  
Exhaust Ventilation ◽  
Panel Surface

Abstract The results of experimental studies on recording temperatures and heat fluxes for the local working zone in industrial premises under radiant heating conditions and supply and exhaust ventilation operation are presented. The characteristics are measured on the surface of the horizontal remote panel directly under the radiator and along the wall with the ventilation inlet. Experimental results show that mixed convection caused by the operation of air exchange systems leads to mixing of air masses and more intensive cooling of the horizontal panel surface, as well as air, compared to the natural convection regime.

A Numerical Analysis of Heat Transfer to Fluids Near the Thermodynamic Critical Point Including the Thermal Entrance Region

1976 ◽  
Vol 98 (4) ◽  
pp. 609-615 ◽  
Author(s):  
N. M. Schnurr ◽  
V. S. Sastry ◽  
A. B. Shapiro
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Fluxes ◽  
Entrance Region ◽  
Graphical Form ◽  
Constant Property ◽  
Thermodynamic Critical Point ◽  
Wide Range ◽  
Flux Parameter ◽  
Flow Through

A two-dimensional numerical method has been developed to predict heat transfer to near critical fluids in turbulent flow through circular tubes. The analysis is applicable to the thermal entry region as well as fully developed flows. Agreement with experimental data for water at 31.0 MN/m2 is quite good. A correlation in the form of the heat flux parameter of Goldmann was found to be satisfactory for water at that pressure. Results are presented in graphical form which apply to a wide range of heat fluxes, mass velocities, and tube diameters. Preliminary results in the entrance region show that film coefficients remain well above the corresponding fully developed values for a larger distance downstream than would be the case with a constant property fluid. This effect becomes more pronounced as the heat flux is increased.

Experimental and Computational Analysis of Natural Convection Over Flat Plate

2008 ◽  
Author(s):  
Farhana Afroz ◽  
Chowdhury Md. Feroz
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flat Plate ◽  
Convection Heat Transfer ◽  
Boussinesq Approximation ◽  
Heat Fluxes ◽  
Navier Stokes ◽  
Heated Plate ◽  
Wide Range ◽  
Energy Equations

Natural convection heat transfer over a flat plate with a heat source at bottom side of plate is studied experimentally and numerically. We consider the two-dimensional problem of both steady and unsteady natural convection over the flat plate at vertical, horizontal and inclined position. Experimental analysis is done for three different constant heat fluxes for each angle position. The Navier-Stokes and Energy equations with the Boussinesq approximation are written in Cartesian coordinate system. The problem is solved in the physical variables on the basis of a completely implicit Finite element Method order to examine the heat transfer characteristics. To see the effects of different angle position phenomena of natural convection over flat plate, the computational results presented in the form of streamlines for a wide range of Grashof number at different heat fluxes. The average Nusselt number of heated plate for different angle position has been observed.

The Measurement of Surface Heat Flux Using the Peltier Effect

1989 ◽  
Vol 111 (3) ◽  
pp. 798-803 ◽  
Author(s):  
E. C. Shewen ◽  
K. G. T. Hollands ◽  
G. D. Raithby
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Physical Models ◽  
Peltier Effect ◽  
Absolute Accuracy ◽  
Measuring Surface ◽  
Wide Range

Calorimetric methods for measuring surface heat flux use Joulean heating to keep the surface isothermal. This limits them to measuring the heat flux of surfaces that are hotter than their surroundings. Presented in this paper is a method whereby reversible Peltier effect heat transfer is used to maintain this isothermality, making it suitable for surfaces that are either hotter or colder than the surroundings. The paper outlines the theory for the method and describes physical models that have been constructed, calibrated, and tested. The tested physical models were found capable of measuring heat fluxes with an absolute accuracy of 1 percent over a wide range of temperature (5–50°C) and heat flux (15–500 W/m2), while maintaining isothermality to within 0.03 K. A drawback of the method is that it appears to be suited only for measuring the heat flux from thick metallic plates.

Nu-Ra correlations for natural convection at high Ra numbers in air-filled tilted hemispherical cavities with dome oriented upwards. Disk submitted to constant heat flux

2015 ◽  
Vol 25 (3) ◽  
pp. 504-512 ◽  
Author(s):  
Abderrahmane Baïri ◽  
Juan Mario García de María ◽  
Nacim Alilat ◽  
Najib Laraqi ◽  
Jean-Gabriel Bauzin
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Solar Energy ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Content Type ◽  
Turbulent Natural Convection ◽  
Wide Range ◽  
Building Safety ◽  
Rayleigh Numbers

Purpose – The purpose of this paper is to propose correlations between Nusselt and Rayleigh numbers for the case of inclined and closed air-filled hemispherical cavities. The disk of such cavities is subjected to a constant heat flux. The study covers a wide range of Rayleigh numbers from 5×107 to 2.55×1012. Design/methodology/approach – Correlations are obtained from numerical approach validated by experimental measurements on some configurations, valid for several angles of inclination of the cavity between 0° (horizontal disk) and 90° (vertical disk) in steps of 15°. Findings – The statistical analysis of a large number of calculations leads to reliable results covering laminar, transitional and turbulent natural convection heat transfer zones. Practical implications – The proposed correlations provide solutions for applications in several fields of engineering such as solar energy, aerospace, building, safety and security. Originality/value – The new relations proposed are the first published for high Rayleigh numbers for this type of geometry. They supplement the knowledge of natural convection in hemispherical inclined cavities and constitute a useful tool for application in various engineering areas as solar energy (thermal collector, still, pyranometer, albedometer, pyrgeometer), aerospace (embarked electronics), building, safety and security (controlling and recording sensors).

scholarly journals Numerical solutions of compressible convection with an infinite Prandtl number: comparison of the anelastic and anelastic liquid models with the exact equations

2019 ◽  
Vol 873 ◽  
pp. 646-687 ◽  
Author(s):  
Jezabel Curbelo ◽  
Lucia Duarte ◽  
Thierry Alboussière ◽  
Fabien Dubuffet ◽  
Stéphane Labrosse ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Viscous Dissipation ◽  
Numerical Solutions ◽  
Ideal Gas ◽  
Heat Fluxes ◽  
Necessary Condition ◽  
Earth Planet ◽  
Viscous Forces ◽  
Wide Range

We developed a numerical method for the set of equations governing fully compressible convection in the limit of infinite Prandtl numbers. Reduced models have also been analysed, such as the anelastic approximation and the anelastic liquid approximation. The tests of our numerical schemes against self-consistent criteria have shown that our numerical simulations are consistent from the point of view of energy dissipation, heat transfer and entropy budget. The equation of state of an ideal gas has been considered in this work. Specific effects arising because of the compressibility of the fluid are studied, like the scaling of viscous dissipation and the scaling of the heat flux contribution due to the mechanical power exerted by viscous forces. We analysed the solutions obtained with each model (fully compressible model, anelastic and anelastic liquid approximations) in a wide range of dimensionless parameters and determined the errors induced by each approximation with respect to the fully compressible solutions. Based on a rationale on the development of the thermal boundary layers, we can explain reasonably well the differences between the fully compressible and anelastic models, in terms of both the heat transfer and viscous dissipation dependence on compressibility. This could be mostly an effect of density variations on thermal diffusivity. Based on the different forms of entropy balance between exact and anelastic models, we find that a necessary condition for convergence of the anelastic results to the exact solutions is that the product $\unicode[STIX]{x1D716}q$ must be small compared to unity, where $\unicode[STIX]{x1D716}$ is the ratio of the superadiabatic temperature difference to the adiabatic difference, and $q$ is the ratio of the superadiabatic heat flux to the heat flux conducted along the adiabat. The same condition seems also to be associated with a convergence of the computed heat fluxes. Concerning the anelastic liquid approximation, we confirm previous estimates by Anufriev et al. (Phys. Earth Planet. Inter., vol. 152, 2005, pp. 163–190) and find that its results become generally close to those of the fully compressible model when $\unicode[STIX]{x1D6FC}T{\mathcal{D}}$ is small compared to unity, where $\unicode[STIX]{x1D6FC}$ is the isobaric thermal expansion coefficient, $T$ is the temperature (here $\unicode[STIX]{x1D6FC}T=1$ for an ideal gas) and ${\mathcal{D}}$ is the dissipation number.

Design and Testing of a Natural Convection Experimental Setup on the External Surface of Heated Inclined Cylinders With a Constant Heat Flux Boundary Condition: Tests for Naked Cylinders

Volume 1 ◽  
2004 ◽  
Author(s):  
Jaime Antonio Sa´nchez Baquerizo ◽  
Jorge W. Duque Rivera
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Experimental Setup ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Heat Flux Boundary Condition

An experimental setup for natural convection heat transfer from inclined heated cylinders with a constant heat flux boundary condition has been designed and tested for various heat fluxes and inclination angles. For the horizontal cylinder experiment the results are in good agreement with [2] within the range of Ra* (1E5 to 1E6). For the variable inclination experiments, comparisons were made with a correlation available for inclined isothermal cylinders [1]. It was observed, that although the boundary conditions that have been compared are different, the decreasing tendency of the Nusselt number holds as the inclination of the cylinder increases. The results have been correlated in an experimental equation shown at the end of this paper.

Natural Convective Heat Transfer From an Array of Square Vertical Plates Mounted on a Large Plane Vertical Adiabatic Surface and With One High Heat Flux Element

2009 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Jane T. Paul
Keyword(s):  
Heat Flux ◽  
High Heat ◽  
Heat Fluxes ◽  
The Other ◽  
Uniform Heat Flux ◽  
High Heat Flux ◽  
Wide Range ◽  
The Mean ◽  
Adiabatic Surface ◽  
Flux Element

An array of nine square heated elements mounted in a square three-by-three pattern with no gap between the elements on a large vertical adiabatic surface with natural convective flow over the elements has been considered. Each of the elements has a uniform heat flux over its surface, the heat fluxes over eight of the elements being the same and the heat flux over the ninth element being higher than that over the other eight elements. The basic aim of the study was to determine the effect the position of the higher heat flux element on the mean temperatures of the other eight elements. The situation considered is an approximate model of situations that can arise in electronic cooling. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables using the commercial cfd code FLUENT. The solution has the heat flux Rayleigh number, the Prandtl number, the ratio of the heat flux over the high heat flux element to the heat flux over the other eight elements, and the position of the high heat flux element as parameters. Because of the application that motivated this work results have only been obtained for Pr = 0.7. Results have been obtained for a wide range of values of the other input parameters and the effect of these parameter values on the mean surface temperatures of each of the elements has been studied.

Interaction Between Film Condensation on One Side of a Vertical Wall and Natural Convection on the Other Side

1986 ◽  
Vol 108 (3) ◽  
pp. 560-566 ◽  
Author(s):  
D. Poulikakos
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Natural Convection ◽  
Vertical Wall ◽  
Flow Characteristics ◽  
The Other ◽  
Film Condensation ◽  
Convection Boundary Layer ◽  
Wide Range

This paper reports a theoretical study of conjugate film condensation on one side of a vertical wall and boundary layer natural convection on the other side. Each phenomenon is treated separately and the solutions for each side are matched on the wall. The main heat transfer and flow characteristics in the two counterflowing layers, namely, the condensation film and the natural convection boundary layer, are documented for a wide range of the problem parameters. In addition, the wall heat flux and the wall temperature distribution resulting from the interaction of the two heat transfer modes (condensation and natural convection) are determined. Important engineering results regarding the overall heat flux from the condensation side to the natural convection side are summarized at the end of the study.

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