scholarly journals Нeat transfer processes in the gas placed into a newtonian gravitation field

2021 ◽  
Vol 57 (1) ◽  
pp. 77-84
Author(s):  
V. I. Saverchenko
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Centrifugal Force ◽  
Convective Heat ◽  
Heat Conductivity ◽  
Thermal Equilibrium ◽  
Normal Gravity ◽  
Gravitation Field ◽  
Newtonian Gravitation ◽  
Transfer Processes

In this paper, using the theoretical and numerical investigation of molecular motion, we study heat transfer processes in the gas placed in a Newtonian gravitational field. The influence of gravity on the heat conductivity of the gas is analyzed. The gravity considered is more than 100 000 times higher than that of the Earth. The main differences of the gas heat conductivity under such high gravity from the one detected under normal gravity are demonstrated and explained. It is shown how the thermal equilibrium for the heat conductivity of the gas depends on gravity and the type of gas. The difference between natural gravity and the centrifugal force is discussed. It is shown how the gas density influences the thermal equilibrium for the heat conductivity under a strong centrifugal force. The convective heat transfer in the gas placed into a gravitational or centrifugal field is analyzed. It is shown that the thermal equilibrium of the convective heat transfer under intensive gravity is not the same as under normal gravity. The horizontal convection mechanism is discussed. A technical way of the realization of gravity thermal effects in the gas is represented. All necessary parameters of the experimental setup are given.

scholarly journals Aerodynamics and convective heat transfer processes in cyclone chambers with external recirculation of gases

2021 ◽  
Vol 2088 (1) ◽  
pp. 012021
Author(s):  
M Konoplev ◽  
D Onokhin ◽  
A Zagoskin ◽  
S Karpov
Keyword(s):  
Heat Transfer ◽  
Theoretical Calculation ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Side Surface ◽  
Aerodynamic Characteristics ◽  
Geometric Parameters ◽  
Transfer Processes ◽  
Gas Recirculation

Abstract The paper presents the results of an experimental and theoretical calculation study of aerodynamics and convective heat transfer on the side surface of cyclone recirculation furnace devices. The possibility of controlling the main aerodynamic characteristics without changing the geometric parameters of the cyclone devices by organizing external gas recirculation is shown.

Numerical Model for Heat Transfer Processes in Dry Ash Conveyors

2021 ◽  
Author(s):  
Thomas Schmidt
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Power Plants ◽  
Bottom Ash ◽  
Transfer Processes ◽  
Temperature Solution ◽  
Coke Combustion ◽  
Cooling Air

Abstract The dry handling of bottom ash from coal-fired power plants has become more and more important in recent years, e.g. due to a lack of water availability at the location of power plants, or for environmental reasons. Thereby it is crucial that a sufficient cooling of the bottom ash can be ensured by the dry cooling air. Within this work, a numerical model for the assessment of heat transfer processes in dry ash conveyors is developed and implemented into Wolfram Mathematica. The model uses a newly introduced representative geometric quantity for the ash particle geometry. Moreover, in addition to the ash, the cooling air is considered as an own phase, for which a temperature solution is obtained. A numerical example, considering geometrical and operational data of an existing facility, shows that the main heat transfer between the ash and the cooling air takes place in the ash hopper, whereby convective heat transfer from ash to cooling air outweighs the effects from coke combustion and radiation from the boiler outlet area. The convective heat transfer in the ash hopper predominantly depends on the geometrical appearance, i.e. size and shape, of the particles, as well as on the grain density, and on the falling time/velocity. Conservatism of the calculation approach is indicated based on comparison of computed temperatures with measured data and literature values. The derived model can be used in future designs and projections of dry ash handling systems.

scholarly journals Experimental Study of the Convective Heat Transfer and Local Thermal Equilibrium in Ceramic Foam

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1490
Author(s):  
Siqi Xu ◽  
Zhiyong Wu ◽  
Hongyan Lu ◽  
Lixin Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Cell Size ◽  
Convective Heat ◽  
Thermal Equilibrium ◽  
Sample Thickness ◽  
Ceramic Foam ◽  
Local Thermal Equilibrium

Foam materials have been widely used in various industrial applications, where higher and higher heat and mass transfer performances are pursued. However, the mechanism of many factors on the heat transfer performances is still unclear. The main purpose of this article is to investigate how the porous properties, porosity, cell size and the sample thickness affect the volumetric convective heat transfer. In this study, the single-blow method is used to determine the volumetric heat transfer coefficient of ceramics foam in the temperature range from 283 K to 323 K. In particular, sensitivity analysis of the foam porosity, cell size, velocity and the sample thickness on the volumetric heat transfer coefficient within the ceramics foam were all conducted. The results indicate that the sample thickness has a significant effect on the volumetric heat transfer coefficient which decreases with the sample thickness. In addition, the local thermal equilibrium phenomenon is verified and its influence on the volumetric heat transfer coefficient discussed. Based on the experimental data, a new correlation is proposed that includes sample thickness, porosity, superficial velocity and fluid properties. This study is crucial to the theory of the convective heat transfer inside the porous media, and can be used to guide the design and optimization of volumetric solar air receivers, compact heat exchangers, heat sinks, heat regenerators, packed bed reactors and so on.

scholarly journals Quantification of the Radiative and Convective Heat Transfer Processes and their Effect on mSOFC by CFD Modelling

2014 ◽  
Vol 16 (2) ◽  
pp. 51-55 ◽  
Author(s):  
Paulina Pianko-Oprych ◽  
Ekaterina Kasilova ◽  
Zdzisław Jaworski
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cell Voltage ◽  
Solid Oxide ◽  
Air Velocity ◽  
Cfd Modelling ◽  
Transfer Processes ◽  
Performance Predictions

Abstract The CFD modelling of heat transfer in a microtubular Solid Oxide Fuel Cell (mSOFC) stack has been presented. Stack performance predictions were based on a 16 anode-supported microtubular SOFCs sub-stack, which is a component of the overall stack containing 64 fuel cells. Both radiative and convective heat transfer were taken into account in the modelling. The heat flux value corresponded to the cell voltage of 0.7 [V]. Two different cases of the inlet air velocity of 2.0 and 8.5 [ms–1] were considered. It was found that radiation accounted for about 20–30 [%] of the total heat flux from the active tube surface, which means that the convective heat transfer predominated over the radiative one.

Analytical and Numerical Modeling of Conductive and Convective Heat Transfer Through Open-Cell Metal Foams

2012 ◽  
Author(s):  
Mehrdad Taheri ◽  
Sanjeev Chandra ◽  
Javad Mostaghimi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Numerical Modeling ◽  
Convective Heat Transfer ◽  
Effective Thermal Conductivity ◽  
Convective Heat ◽  
Thermal Equilibrium ◽  
Metal Foams ◽  
Local Thermal Equilibrium ◽  
High Porosity

In this paper, a comprehensive analytical and numerical study of conductive and convective heat transfer through high porosity metal foams is presented. In the first part a novel theoretical model for determination of effective thermal conductivity of metal foams is introduced. This general analysis can be applied to any complex array of interconnected foam cells. Assuming dodecahedron unit cell for modeling the structure of metal foams, an approximate equation for evaluation of effective thermal conductivity of foam with a known porosity is obtained. In this approximation method, unlike the previous two-dimensional (2D) models, porosity is the only geometric input parameter used for evaluation of effective thermal conductivity, while its predictions of effective thermal conductivity are in excellent agreement with the previous models. In the second part a 3D numerical model for conduction in metal foam is constructed. The foam has a square cross section and is exposed to constant temperature at both ends and constant heat flux from the sides. We assume local thermal equilibrium (LTE), i.e., the solid and fluid temperatures are to be locally equal. Comparison of the 3D numerical results to the experiments shows very good agreement. The last part of the study is concerned with the 3D numerical modeling of convective heat transfer through metal foams. Experimentally determined values of permeability and Forchheimer coefficient for 10 pores per inch (PPI) nickel foam are applied to the Brinkman-Forchheimer equation to calculate fluid flow through the foam. Local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) methods were both employed for heat transfer simulations. While LTE method resulted in faster calculations and also did not need surface area to volume ratio (αsf) and internal convective coefficient (hsf) as its input, it was not accurate for high temperatures. LTNE should be used to obtain distinct local solid and fluid temperatures.

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