Numerical Computation Of Heat Transfer Research Articles

Numerical computation of heat transfer, moisture transport and thermal comfort through walls of buildings made of concrete material in the city of Douala, Cameroon: An ab initio investigation

The buildings of the city of Douala in Cameroon have been experiencing degradation for several decades due to the climate characterized by high humidity and oppressive heat. As a result, large grayish or black stains can be observed on these buildings. We sometimes witness the subsidence of the slab of the balconies, the cracking of the walls and the collapse of the buildings worn by the humidity. These damages are generally caused by infiltration and capillary rise. In addition, it has been demonstrated that people living in damp buildings are at risk of illnesses such as asthma and lung infections. Therefore, the novelty of this work is threefold: (i) it proposes for the very first time a numerical study of the transport of humidity and heat through the porous walls of buildings constructed with concrete material, the main construction material in the city of Douala; (ii) It was determined what level of indoor thermal comfort was appropriate for sleeping inside a real three-dimensional G+1 complex residential building constructed with concrete blocks; and (iii) Using the geographical coordinates, and time data, the sun radiation's direction of incidence was assessed throughout the simulation. The computation was performed using Comsol Multiphysics 6.0 software. The distributions of temperature, relative humidity as well as moisture level were presented at various periods. It appears from the results that face to this high humidity, the concrete material retains a large quantity of water for a considerable periods of time, which weakens the steel reinforcement of concrete which is corroded by rust. The computation of thermal comfort in the 3D building showed that the various rooms of the building were not comfortable during the night since temperature inside the building increased progressively due to diffusion of heat. In addition, the numerical solutions indicated that the energy stored within the walls diffused from the external walls to the internal walls during the night. It was also demonstrated that the walls of the building were warmer than the windows, doors and the roof at the computational times, which simply revealed a greater storage capacity of heat in the concrete blocks material. The findings highlighted that the temperature decreased rapidly in a thickness of 0.06 m of the concrete block during the nine days and this decrease was attenuated in the second part of the thickness of the concrete block (0.14 m).

Numerical Computation of Heat Transfer on Reentry Capsules at Mach 5

The heat transfer over various reentry axisymmetric configurations is studied numerically by solving time-dependent compressible laminar Navier-Stokes equations. The governing fluid flow equations are disrectized in spatial coordinates employing a finite volume approach, which reduces the equations to semi-discretized ordinary differential equations. Temporal integration is performed using multi-stage Runge-Kutta time stepping scheme. A local time step is used to achieve steady state solution. The numerical simulation is carried out on a mono-block structured grid. The numerical computation is carried out for freestream Mach number of 5.0. The numerical scheme captures well all the essential flow field features such as bow shock wave, sonic line, expansion fan on the corner, recompression shock wave and recirculating flow in the base region. Comparisons of the flow field, surface pressure, skin friction coefficient and wall heat flux results are made between different configurations of the reentry capsules such as ARD (ESA’ s Atmospheric Reentry Demonstrator), CARINA, Apollo, Muses-C (Mu Science Engineering Satellite), OREX (Orbital Reentry Experiments) and Beagle-2. The effects of geometrical parameters of the different reentry capsules on surface pressure, skin friction coefficients and heat flux and forebody aerodynamic drag are analyzed. Base pressure is independent of the forebody shape of the reentry capsules. The effects of module geometry on the flow field are numerically analyzed which may be useful for optimization of the reentry capsule.

Interaction of mixed convection with non-gray gas radiation in a partially heated horizontal pipe: entropy generation analysis

PurposeThis paper aims to numerically analyze the effect of non-gray gas radiation on mixed convection in a horizontal circular duct with isothermal partial heating from the sidewall. The influence of heater location on heat transfer, fluid flow and entropy generation is given and discussed in this study.Design/methodology/approachThe numerical computation of heat transfer and fluid flow has been developed by the commercial finite element software COMSOL Multiphysics. Radiation code is developed based on the T10 Ray-Tracing method, and the radiative properties of the medium are computed based on the statistical narrow band correlated-k model.FindingsThe obtained results depicted that the radiation considerably contributes to the temperature homogenization of the gas. The findings highlight the impact of the heater location on swirling flow. It is also shown that the laterally heating process provides better energy efficiency than heating from the top of the enclosure.Originality/valueThis study is performed to improve heat transfer and to minimize entropy generation. Therefore, it is conceivable to improve the model design of industrial applications.

Numerical Simulation of Hydrogen–Air Boundary Layer Flows Augmented by Catalytic Surface Reactions

Catalytic combustion of hydrogen–air boundary layers involves the adsorption of hydrogen and oxygen into a platinum coated surface, chemical reactions of the adsorbed species, and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners and catalytic reactors that use low equivalence ratios. In this case, the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in hydrogen–air mixture boundary layers that flow over platinum coated hot plates and inside rectangular channels. Chemical reactions are included in the gas-phase as well as on the solid platinum surface. In the gas-phase, eight species are involved in 26 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 16 additional surface chemical reactions. The platinum surface temperature distribution is prespecified, while the properties of the reacting flow are computed. The flow configurations investigated in the present paper are those of a flat plate boundary layer and a rectangular channel reacting flow. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Hybrid differencing is used to ensure that the finite-difference coefficients are always positive or equal to zero to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations are solved iteratively for the reacting gas flow properties. On the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically. A nonuniform computational grid is used, concentrating most of the nodes in the boundary sub-layer adjoining the catalytic surface. For the flat plate boundary layer flow, the computed OH concentration is compared with experimental and numerical data of similar geometry. The obtained agreement is fairly good, with differences observed for the location of the peak value of OH. Surface temperature of 1170 K caused fast reactions on the catalytic surface in a very small part at the leading edge of the catalytic flat plate. The flat plate computational results for heat and mass transfer and chemical surface reactions at the gas-surface interface are correlated by nondimensional relations. The channel flow computational results are also compared with recent detailed experimental data for similar geometry. In this case, the catalytic surface temperature profile along the x-axis was measured accurately and is used in the present work as the boundary condition for the gas-phase energy equation. The present numerical results for the gas temperature, water vapor mole fraction, and hydrogen mole fraction are compared with the corresponding experimental data. In general, the agreement is very good especially in the first 105 mm. However, some differences are observed in the vicinity of the exit section of the rectangular channel.

Mathematical Modeling of Impinging Hydrogen-Air Flows Augmented by Catalytic Surface Reactions

The catalytic combustion of hydrogen-air mixtures involves the adsorption of the fuel and oxidant into a platinum surface, chemical reactions of the adsorbed species, and the desorption of the resulting products. Readsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners that use low equivalence ratios. In this case, the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in hydrogen-air mixtures that impinge perpendicularly on a platinum-coated hot plate. Chemical reactions are included in the gas phase as well as in the platinum layer. In the gas phase, eight species are involved in 24 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 14 additional surface chemical reactions. The platinum surface temperature is fixed, whereas the properties of the reacting flow are computed. The flow configuration investigated in the present paper is that of impinging jets. Finite volume equations are obtained by formal integration over control volumes surrounding each grid node. Upwind differencing is used to ensure that the influence coefficients are always positive to reflect the real effect of neighboring nodes on a typical central node. The finite volume equations are solved iteratively for the reacting gas flow properties. On the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically. A nonuniform computational grid is used, concentrating most of the nodes near the catalytic surface. The computed heat transfer numerical results are compared with the empirical data of similar geometry. A surface temperature of 1150 K caused fast reactions on the catalytic surface and in the flowing gas for some species, such as OH, HO 2 , and H 2 O 2 . The computational results for heat transfer, mass transfer, and surface reaction rate at the gas-surface interface are correlated by nondimensional relations. These relations can be used as a submodel for the more complicated catalytic reactors.

Real-time thermal characterization of 12nl fluid samples in a microchannel

This work presents a novel method and a device for real-time simultaneous measurement of the thermal conductivity and heat capacity of 12 nl fluid samples. The device uses a micromachined thermal sensor composed of a microchannel and a thin-film probe. The method, based on the 3 omega technique, employs a multiparameter-fitting scheme to determine the thermal properties with numerical computation of heat transfer. The thermal properties of 12 nl samples have been measured successfully by the sensor. Furthermore, real-time thermal characterization of fluid samples flowing in a microchannel has been demonstrated, manifesting strong potential of the proposed technique as an in situ probe in various microfluidic applications.

Numerical study of heat transfer over banks of rods in small Reynolds number cross-flow

This work presents numerical computations of heat transfer over banks of square rods in aligned and staggered arrangements with porosity in the range 0.44–0.98. It is focused on low Reynolds number flows (0.05–40). Two thermal boundary conditions were investigated, namely constant wall temperature and constant volumetric heat source. The effects of bank arrangements and porosity as well as the effects of Prandtl and Reynolds numbers on the Nusselt number are examined. In the case of constant volumetric heat source, the results are approximated with a power equation adapted for the case of low Re number flows. This study shows that the thermal boundary condition on the solid surface influences heat transfer when thermal equilibrium is reached in the bank of rods.

Mathematical Modeling of Catalytic-Surface Combustion of Reacting Flows

Catalytic combustion of methane-air mixtures involves the adsorption of the fuel and oxidant into a platinum surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as NOx. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in flowing methane-air mixtures impinging on a platinum coated hot plate. Chemical reactions are included in the gas phase and in the solid platinum surface. In the gas phase, 16 species are involved in 49 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 24 additional surface chemical reactions. The platinum surface temperature is fixed, while the properties of the reacting flow are computed. The flow configuration investigated here is impinging jet. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Up-wind differencing is used to ensure that the influence coefficients are always positive to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations are solved, iteratively, for the reacting gas flow properties. In the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically. A non-uniform computational grid is used, concentrating most of the nodes near the catalytic surface. The computed species concentrations and temperature are compared with existing data of similar geometry. The obtained agreement is fairly good for all main combustion products, while differences are observed for the unstable species such as OH, HO2 and H2O2. The computational results for heat and mass transfer at the gas-surface interface are correlated by non-dimensional relations. These relations can be used as sub-models for the more complicated catalytic burners.

A Mathematical Model for Heat and Mass Transfer in Methane-Air Boundary Layers With Catalytic Surface Reactions

Abstract Catalytic combustion of hydrocarbon mixtures involves the adsorption of the fuel and oxidant into a platinum surface, chemical reactions of the adsorbed species, and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners that use low equivalence ratios. In this case, the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitric oxide. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in flowing methane-air mixtures over a platinum coated hot plate. Chemical reactions are included in the gas phase and in the solid platinum surface. In the gas phase, 16 species are involved in 49 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 24 additional surface chemical reactions. The platinum surface temperature is fixed, while the properties of the reacting flow are computed. The flow configuration investigated here is the parallel boundary layer reacting flow. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Up-wind differencing is used to ensure that the influence coefficients are always positive to reflect the physical effect of neighboring nodes on a typical central node. The finite-volume equations are solved iteratively for the reacting gas flow properties. On the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically by an under-relaxed linear algorithm. A non-uniform computational grid is used, concentrating most of the nodes near the catalytic surface. Surface temperatures, 1150 K and 1300 K, caused fast reactions on the catalytic surface, with very slow chemical reactions in the flowing gas. These slow reactions produce mainly intermediate hydrocarbons and unstable species. The computational results for the chemical reaction boundary layer thickness and mass transfer at the gas-surface interface are correlated by non-dimensional relations, taking the Reynolds number as the independent variable. Chemical kinetic relations for the reaction rate are obtained which are dependent on reactants’ concentrations and surface temperature.

Estimation of Average and Local Heat Transfer in Parallel Plates and Circular Ducts Filled With Porous Materials

Accurate estimation of heat transfer to a fluid passing through a porous medium located between impermeable walls is of practical interest. Generally, the numerical computation of heat transfer to porous media can become time consuming and correlations are needed to enable practitioners to determine this quantity rapidly. In this paper, correlations for two cases are considered: one when porous materials are between two parallel plates and the other when they are within a circular pipe. This presentation includes correlations for both local and average heat transfer coefficients in these two passages for incompressible laminar flow. These correlations require knowledge of local and average heat transfer for unobstructed fluid flowing through these passages with sufficient accuracy. Because existing correlations lack sufficient accuracy, this presentation includes an appendix that emphasizes correlations for heat transfer to fluids passing through unobstructed parallel plate channels and also for circular pipes.

An engineering method of numerical calculation of heat transfer and friction resistance in boundarylayer laminar and turbulent flow in a tube

A simple gradient-balance method is suggested for numerical computation of heat transfer and resistance, which is realizable on a microcomputer.