A Thermo-Mechanical Model for a Counterflow Biomass Gasifier

2014 ◽  
Vol 354 ◽  
pp. 227-235
Author(s):  
Marcelo J.S. de Lemos
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Control Volume ◽  
Simple Algorithm ◽  
Thermal Capacity ◽  
Macroscopic Model ◽  
Algebraic Equations ◽  
Medium Permeability ◽  
Mechanical Approach ◽  
Volume Method

This article presents a thermo-mechanical approach to investigate heat transfer between solid and fluid phases in a model gasifier. A two-temperature equation approach is applied in addition to a macroscopic model for laminar flow through a porous moving bed. Transport equations are discretized using the control-volume method and the system of algebraic equations is relaxed via the SIMPLE algorithm. The effects on inter-phase heat transfer due to variation of medium permeability, thermal conductivity and thermal capacity are analyzed. Results indicate that for smaller medium permeabilities, as well as for higher solid-to-fluid thermal capacity and thermal conductivity ratios, enhancement of heat transfer between phases is observed.

Nusselt Number and Temperature Distribution in an Horizontal Cavity Containing a Layer of Porous Material at the Bottom

2003 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Viviani T. Magro
Keyword(s):  
Heat Transfer ◽  
Porous Material ◽  
Numerical Solutions ◽  
Control Volume ◽  
Simple Algorithm ◽  
Flow Region ◽  
Porous Matrix ◽  
Layered Porous Media ◽  
Energy Equations ◽  
Volume Method

Horizontally-layered porous media in enclosures represents an important configuration with many technological applications in mechanical and aerospace engineering. This work presents numerical solutions for flow and heat transfer in square cavities partially obstructed with porous material. The microscopic flow and energy equations are integrated in a representative elementary volume in order to obtain a set of equations valid in both the clear flow region and in the porous matrix. A unique set of equations is discretized with the control volume method and solved with SIMPLE algorithm. Heat transfer enhancement across the porous cavity is calculated as the permeability or the porosity of the porous substrate increase.

Simulation of Heat Transfer in a Counterflow Porous Bed Reactor With a Thermal Non-Equilibrium Model

2011 ◽  
Author(s):  
Marcelo J. S. deLemos ◽  
Ana C. Pivem
Keyword(s):  
Heat Transfer ◽  
Control Volume ◽  
Fluid Velocity ◽  
Velocity Ratio ◽  
Thermal Capacity ◽  
Equation Model ◽  
Porous Bed ◽  
Geometrical Properties ◽  
Porosity Ratio ◽  
Volume Method

The objective of this work is to study the influence of physical and geometrical properties on heat transfer between solid and fluid phases in a counter-flow porous bed, for cases where the fluid moves in opposite direction with respect to the permeable matrix. For simulating the flow and heat transfer, a two-energy equation model is applied in addition to a mechanical model. Transport equations are discretized using the control-volume method. The effects of solid-to-fluid velocity ratio, permeability, porosity, ratio of solid-to-fluid thermal capacity and ratio of solid-to-fluid thermal conductivity on flow and heat transport are analyzed. Results for a counterflow, that is similar to the heat exchangers in a countercurrent, indicate that there is more heat exchange for the smaller values of the parameters analyzed resulting in more uniform heat transfer between phases along the channel.

Porous media to intensify natural convection in rectangular enclosures used in building techniques

2020 ◽  
Vol 31 (04) ◽  
pp. 2050061
Author(s):  
A. Baïri ◽  
A. Martín-Garín ◽  
J. A. Millán-García
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Control Volume ◽  
Vertical Wall ◽  
Simple Algorithm ◽  
Constant Heat Flux ◽  
Physical Parameters ◽  
Volume Method

This numerical study quantifies the natural convective heat transfer occurring in an elongated rectangular cavity whose hot vertical wall generates a constant heat flux while the opposite one is kept isothermal at cold temperature. The study shows that when a layer of porous material is affixed to the hot wall, the aerodynamic phenomena are modified and increase the natural convective transfer. Several configurations were processed, obtained by varying the matrix’s thermal conductivity of the layer, the aspect ratio of the cavity and the Rayleigh number in wide ranges. The numerical solution is obtained by means of the control volume method based on the SIMPLE algorithm. A correlation of the Nusselt–Rayleigh type is proposed, allowing determination of the convective heat transfer for any combination of these physical parameters. It can be applied in various engineering fields including passive heating in building which can be improved by the simple and easy-to-implement assembly version discussed here.

Effect of Thermal Conductivity Ratio on Laminar Double-Diffusive Free Convection in a Porous Cavity

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Paulo H. S. Carvalho ◽  
Marcelo J. S. de Lemos
Keyword(s):  
Free Convection ◽  
Thermal Equilibrium ◽  
Control Volume ◽  
Simple Algorithm ◽  
Thermal Conductivity Ratio ◽  
Control Volume Method ◽  
Algebraic Equations ◽  
Square Cavity ◽  
Volume Method ◽  
Double Diffusive

This work presents a study on double-diffusive free convection in a porous square cavity using the thermal equilibrium model. Transport equations are discretized using the control-volume method, and the system of algebraic equations is relaxed via the SIMPLE algorithm. The effect of ks/kf on average Nusselt and Sherwood values was investigated. Results show that increasing ks/kf affects Nuw and Shw boosting mass transfer at the expense of reducing overall heat transport across the enclosure.

Use of Foam-Like Materials to Enhance Heat Transfer From Surfaces Subjected to Impinging Jets

2009 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Cleges Fischer
Keyword(s):  
Thermal Conductivity ◽  
Porous Layer ◽  
Control Volume ◽  
Simple Algorithm ◽  
Impinging Jets ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
System Pressure ◽  
Volume Method ◽  
Range Of Values

In this paper, numerical simulation of a jet impinging against a flat plane covered with a layer of a porous material is presented. The plate is kept at a temperature higher than that of the incoming fluid. Macroscopic transport equations are obtained based on a volume average concept. Discretization of such governing equations is accomplished by means of the control volume method applied with a boundary-fitted nonorthogonal coordinate system. Pressure-velocity coupling is treated with the use of the SIMPLE algorithm. Parameters such as permeability, thickness of the porous layer and thermal conductivity ratio are varied in order to analyze their effects on the local distribution of Nu. Results indicate that inclusion of a porous layer decreases the peak in Nu avoiding excessive heating or cooling at the stagnation point. Also found was that the integral heat flux from the wall is enhanced for certain range of values of layer thickness, porosity, and thermal conductivity ratio.

Turbulent Double-Diffusive Free Convection in a Porous Square Cavity Simulated With the Two Temperature Approach

2016 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Paulo H. S. Carvalho
Keyword(s):  
Solid Phase ◽  
Control Volume ◽  
Chemical Species ◽  
Simple Algorithm ◽  
Fluid Phase ◽  
Solid Matrix ◽  
Thermal Conductivity Ratio ◽  
Algebraic Equations ◽  
Square Cavity ◽  
Volume Method

This work investigates the influence of thermal conductivity ratio on energy and mass transport across a porous square cavity. Modeling of heat transfer from side to side of the enclosure assumed the hypothesis of thermal non-equilibrium between the solid matrix and the fluid phase. Transport equations were discretized using the control-volume method and the system of algebraic equations obtained was relaxed via the SIMPLE algorithm. Results showed that Shw, mass flux of chemical species and heat flux in the solid phase are strongly dependent of ks/kf, significantly increasing their values as such ratio increases.

Effect of Periodic Imposed Heat Flux on Three-Dimensional Natural Convection in a Partially Heated Cubical Enclosure

2016 ◽  
Vol 831 ◽  
pp. 83-91
Author(s):  
Lahoucine Belarche ◽  
Btissam Abourida
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Control Volume ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Maximum Temperature ◽  
Cubical Enclosure ◽  
Simplec Algorithm ◽  
Volume Method

The three-dimensional numerical study of natural convection in a cubical enclosure, discretely heated, was carried out in this study. Two heating square sections, similar to the integrated electronic components, are placed on the vertical wall of the enclosure. The imposed heating fluxes vary sinusoidally with time, in phase and in opposition of phase. The temperature of the opposite vertical wall is maintained at a cold uniform temperature and the other walls are adiabatic. The governing equations are solved using Control volume method by SIMPLEC algorithm. The sections dimension ε = D / H and the Rayleigh number Ra were fixed respectively at 0,35 and 106. The average heat transfer and the maximum temperature on the active portions will be examined for a given set of the governing parameters, namely the amplitude of the variable temperatures a and their period τp. The obtained results show significant changes in terms of heat transfer, by proper choice of the heating mode and the governing parameters.

Influence of Shape of Nanoparticles on Nanofluid Hydrothermal Behavior

2018 ◽  
pp. 331-388
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Finite Element Method ◽  
Finite Element ◽  
Stream Function ◽  
Shape Factor ◽  
Control Volume ◽  
Flow And Heat Transfer ◽  
Shape Of Nanoparticles ◽  
Stream Function Formulation

The shape of nanoparticles can change the thermal conductivity of nanofluid. So, the effect of shape factor on nanofluid flow and heat transfer has been reported in this chapter. Governing equations are presented in vorticity stream function formulation. Control volume-based finite element method (CVFEM) is utilized to obtain the results. Results indicate that platelet shape has the highest rate of heat transfer.

Numerical Survey of the Melting Driven Natural Convection Using Generation Heat Source: Application to the Passive Cooling of Electronics Using Nano-Enhanced Phase Change Material

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Hamza Faraji ◽  
Mustapha Faraji ◽  
Mustapha El Alami
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Phase Change ◽  
Phase Change Material ◽  
Metallic Nanoparticles ◽  
Simple Algorithm ◽  
Bottom Side ◽  
Volume Method ◽  
Change Material

Abstract The present paper reports numerical results of the melting driven natural convection in an inclined rectangular enclosure filled with nano-enhanced phase change material (NePCM). The enclosure is heated from the bottom side by a flush-mounted heat source (microprocessor) that generates heat at a constant and uniform volumetric rate and mounted on a substrate (motherboard). All the walls are considered adiabatic. The purpose of the investigation is analyzing the effect of nanoparticles insertion by quantifying their contribution to the overall heat transfer. Combined effects of the PCM type, the inclination angle and the nanoparticles fraction on the structure of the fluid flow and heat transfer are investigated. A 2D mathematical model based on the conservation equations of mass, momentum, and energy was developed. The governing equations were integrated and discretized using the finite volume method. The SIMPLE algorithm was adopted for velocity–pressure coupling. The obtained results show that the nanoparticles insertion has an important quantitative effect on the overall heat transfer. The insertion of metallic nanoparticles with different concentrations affects the thermal behavior of the heat sink. They contribute to an efficient cooling of the heat source. The effect of nanoparticles insertion is also shown at the temperature distribution along the substrate.

Numerical Simulation of Fluid Flow and Heat Transfer in the Micro-Nozzle

2005 ◽  
Author(s):  
Longjian Li ◽  
Yihua Zhang ◽  
Wenzhi Cui ◽  
Tien-Chien Jen ◽  
Qinghua Chen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Control Volume ◽  
Slip Model ◽  
Control Volume Method ◽  
Propulsion Performance ◽  
Micro Nozzle ◽  
Flow And Heat Transfer ◽  
Finite Control ◽  
Mems Technology ◽  
Volume Method

Micro-nozzle, based on the MEMS technology, has played an important role in orbit positioning, attitude adjusting and other applications of micro-satellites. The continuous no-slip model of two-dimensional compressible laminar flow in the micro-nozzle was proposed and solved numerically by finite control volume method. The flow and heat transfer in the micro-nozzle were computed under different conditions, including different inlet pressures, different inlet temperatures and different divergent angles. Flow field and effects of these conditions on the propulsion performance were analyzed. Finally, simulated solutions were compared and validated with the experimental results.

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