Heat transport of hybrid nanomaterial in an annulus with quadratic Boussinesq approximation

The convective heat transfer of hybrid nanoliquids within a concentric annulus has wide engineering applications such as chemical industries, solar collectors, gas turbines, heat exchangers, nuclear reactors, and electronic component cooling due to their high heat transport rate. Hence, in this study, the characteristics of the heat transport mechanism in an annulus filled with the Ag-MgO/H_2O hybrid nanoliquid under the influence of quadratic thermal radiation and quadratic convection are analyzed. The nonuniform heat source/sink and induced magnetic field mechanisms are used to govern the basic equations concerning the transport of the composite nanoliquid. The dependency of the Nusselt number on the effective parameters(thermal radiation, nonlinear convection,and temperature-dependent heat source/sink parameter) is examined through sensitivity analyses based on the response surface methodology(RSM) and the face-centered central composite design(CCD). The heat transport of the composite nanoliquid for the spacerelated heat source/sink is observed to be higher than that for the temperature-related heat source/sink. The mechanisms of quadratic convection and quadratic thermal radiation are favorable for the momentum of the nanoliquid. The heat transport rate is more sensitive towards quadratic thermal radiation.     

Mixed convection from an upward facing horizontal flat plate: effect of conduction and radiation

Experiments have been conducted in a low speed horizontal wind tunnel to study the interaction of radiation and conduction on mixed convective heat transfer from an upward facing horizontal flat plate in air. Differential interferometer has been used to measure local convective heat fluxes. It has been observed that interaction between surface radiation and convection is significant for a low thermal conductivity plate material. On the basis of the previous and current studies, it can be stated that the multi-mode interaction problem is an outcome of the nature of convective boundary layer. The interaction between different modes of heat transfer would remain similar irrespective of the nature of convection (free/mixed or forced).     

Effects of bubble size on heat transfer enhancement by sub-millimeter bubbles for laminar natural convection along a vertical plate

Injection of sub-millimeter bubbles is considered a promising technique for enhancing natural convection heat transfer for liquids. So far, we have experimentally investigated heat transfer characteristics of laminar natural convection flows with sub-millimeter bubbles. However, the effects of the bubble size on the heat transfer have not yet been understood. The purpose of this study is to clarify the effects of the bubble size on the heat transfer enhancement for the laminar natural convection of water along a vertical heated plate with uniform heat flux. Temperature and velocity measurements, in which thermocouples and a particle tracking velocimetry technique are, respectively used, are conducted to investigate heat transfer and flow characteristics for different bubble sizes. Moreover, two-dimensional numerical simulations are performed to comprehensively understand the effects of bubble injection on the flow near the heated plate. The result shows that the ratio of the heat transfer coefficient with sub-millimeter-bubble injection to that without injection ranges from 1.3 to 2.2. The result also shows that for a constant bubble flow rate, the heat transfer coefficient ratio increases with a decrease in the mean bubble diameter. It is expected from our estimation based on both experimental data and simulation results that this increase results from an increase in the advection effect due to bubbles.     

Effect of radiation on natural convection in an L-shaped corner

An experimental investigation of the interaction of surface radiation and natural convection in an L shaped corner is presented. Parametric studies to explore the influence of surface emissivity and aspect ratio on the total heat transfer rate from the isothermal vertical wall of the L corner, have been carried out. For an L corner with highly polished walls, the present experimental results are compared with results available in literature, and are found to be in good agreement. A new semi-experimental method for solving this class of problems is discussed, and a correlation for estimating the total Nusselt number is proposed. It is found that surface radiation has a significant effect on the total heat transferred from the vertical wall of the L-shaped corner. Received: 18 February 1999/Accepted: 21 July 1999     

Natural convection and radiation heat transfer of an externally-finned tube vertically placed in a chamber

A three-dimensional numerical study was made to investigate effects of fin angle, fin surface emissivity, and tube wall temperature on heat transfer enhancement for a longitudinal externally-finned tube placed vertically in a small chamber. The numerical model was first validated through comparison with experimental measurements and the appropriateness of general boundary conditions was examined. The numerical results show that the mean Nusselt number increases with Rayleigh number for all the fin angles investigated. The maximum heat transfer rate per mass occurs when the fin angle is about 60° for fin surface emissivity between 0.7 and 0.8 and 55° when the surface emissivity increases to 0.9. With increasing tube wall temperature, both the natural convection and radiation heat transfer are enhanced, but the fraction of radiation heat transfer decreases in the temperature range studied. Radiation fraction increases with increasing fin surface emissivity. Both convection and radiation heat transfer modes are important.     

Surface condition effects on flame impingement heat transfer

Flame impingement heating is used in many industrial applications, including the heating and melting of both glass and metal. This heating process usually comprises multiple heat transfer mechanisms, such as forced convection, thermal radiation, and thermochemical heat release. However, little experimental data are available that can be used to determine the importance of each mechanism. This information would be useful for optimizing the heating process and for developing computer models. The objective of this study was to determine the relative importance of thermal radiation and to determine how the thermochemical heat release is affected by the surface properties of the target.This study investigated the heat transfer from oxygen-enhanced, natural gas flames (15 kW) impinging normal to a water-cooled metal disk (d_b = 135 mm) segmented into concentric calorimetric rings. Polished, untreated, and blackened surfaces were used to study emissivity effects. The heat flux to the blackened and polished surfaces was the highest and lowest, respectively. The flux to untreated surfaces was between the highest and lowest fluxes. The largest difference in the flux, between the polished and blackened surfaces, was only 9.8%. Catalyticity effects were investigated by using alumina-coated (nearly noncatalytic), untreated, and platinum-coated (highly catalytic) surfaces. The heat flux to platinum-coated surfaces was the highest. The fluxes to untreated surfaces were similar to those for alumina-coated surfaces. The largest difference in the flux, between the platinum-coated and the alumina-coated surfaces, was only 12%. Therefore, both nonluminous flame radiation and the thermochemical heat release from surface catalytic reactions were relatively small fractions of the total heat flux.     

Experimental and Numerical Modeling of the Thermal Conductivity of High-Viscosity Hydrocarbon Systems

A mathematical model is developed to numerically predict the heating of heavy hydrocarbon systems. A comparative analysis of numerical and experimental data is performed. It is found that the thermal conductivity of a hydrocarbon system under study heated from an initial temperature of 24°C to 100°C increases by a factor of 40 and, with allowance for free convection, an additional substantial (up to 16 times) increase in heat transfer due to enhanced effective thermal conductivity is observed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 96–102, November–December, 2005.     

Melting heat and thermal radiation effects in stretched flow of an Oldroyd-B fluid

The incompressible flow of a non-Newtonian fluid with mixed convection along a stretching sheet is analyzed. The heat transfer phenomenon is discussed through thermal radiation. The effects of the melting heat transfer and heat generation/absorption are also taken. Suitable transformations are utilized to attain the nonlinear ordinary differential expressions. The convergent series solutions are presented. The fluid flow, temperature,and surface heat transfer rate are examined graphically. It is observed that the velocity decreases when the relaxation time increases while increases when the retardation time is constant. The results also reveal that the temperature distribution reduces when the radiation parameter increases.     

The discrete transfer radiation model in a natural gas‐fired furnace

The performance of the discrete transfer radiation model is assessed in a swirling natural gas diffusion flame confined in an axisymmetric furnace. The predictions are evaluated as part of a complete prediction procedure involving the modeling of the simultaneously occurring flow, combustion, convection and radiation phenomena. Computational results with and without radiation effects are compared with experimental data and the discrete transfer model is evaluated in terms of computational efficiency, ease of application and predictive accuracy. The results have demonstrated that the effect of thermal radiation is important, even in light flames, and that the discrete transfer model can be applied in industrial gas furnaces, yielding accurate predictions. Copyright © 2000 John Wiley & Sons, Ltd.     

Interaction of thermal radiation with laminar natural convection from a horizontal cylinder in air

The heat transfer rates from a horizontal cylindrical surface of an internally heated tube under constant heat flux conditions are evaluated with the aid of integral analysis giving due consideration to both natural convection and thermal radiation to ambient medium of air. It is observed that non-isothermal conditions around the periphery of the tube arise due to the conjugate effects of the three modes of energy transmission viz., conduction, convection and radiation. The theoretical analysis is further validated with the experimental results and the coincidence is found to be very satisfactory.Die Wärmeübertragungsraten einer horizontalen zylindrischen Oberfläche eines innen erwärmten Rohres mit konstantem Wärmestrom sind mit Hilfe von Integralrechnungen berechnet worden, die sich auf die freie Konvektion und thermische Strahlung mit Luft als Umgebungsmedium beziehen. Es ist beobachtet worden, daß nicht-isotherme Bedingungen am Umfang des Rohres aus den drei Energieübertragungsarten Leitung, Konvektion und Strahlung entstehen. Die theoretische Berechnung wurde mit experimentellen Ergebnissen bestätigt und die Koinzidenz stellte sich als sehr zufriedenstellend heraus.     

Radiative mixed convection flow of an Oldroyd-B fluid over an inclined stretching surface

A mixed convection flow of an Oldroyd-B fluid in the presence of thermal radiation is investigated. The flow is induced by an inclined stretching surface. The boundary layer equations of the Oldroyd-B fluid in the presence of heat transfer are used. Appropriate transformations reduce partial differential equations to ordinary differential equations. A computational analysis is performed for convergent series solutions. The values of the local Nusselt number are numerically analyzed. The effects of various parameters on velocity and temperature are discussed.     

An analytical treatment for combined heat transfer by radiation,convection and conduction within a heat insulating wall structure

An analytical procedure has been proposed to attack a highly conjugate thermal problem associated with radiation, convection and conduction within a heat insulating wall structure. Firstly, an analytical solution is derived for fully-developed mixed convective flow through parallel plates. Secondly, the resulting expressions for convection are coupled with radiation and conduction equations to form a set of heat balance equations for each heat transfer surface. Illustrative calculations are conducted to estimate heat transfer rates through a heat insulating roof structure with an aluminum partition with high reflectivity, subject to solar radiation in summer. The effect of an aluminum partition on the heat insulation is elucidated.     

Simulation studies on multi-mode heat transfer from an open cavity with a flush-mounted discrete heat source

Prominent results of a simulation study on conjugate convection with surface radiation from an open cavity with a traversable flush mounted discrete heat source in the left wall are presented in this paper. The open cavity is considered to be of fixed height but with varying spacing between the legs. The position of the heat source is varied along the left leg of the cavity. The governing equations for temperature distribution along the cavity are obtained by making energy balance between heat generated, conducted, convected and radiated. Radiation terms are tackled using radiosity-irradiation formulation, while the view factors, therein, are evaluated using the crossed-string method of Hottel. The resulting non-linear partial differential equations are converted into algebraic form using finite difference formulation and are subsequently solved by Gauss–Seidel iterative technique. An optimum grid system comprising 111 grids along the legs of the cavity, with 30 grids in the heat source and 31 grids across the cavity has been used. The effects of various parameters, such as surface emissivity, convection heat transfer coefficient, aspect ratio and thermal conductivity on the important results, including local temperature distribution along the cavity, peak temperature in the left and right legs of the cavity and relative contributions of convection and radiation to heat dissipation in the cavity, are studied in great detail.     

Use of experiment and an inverse method to study interface heat transfer during solidification in the investment casting process

A technique to determine the thermal boundary conditions existing during the solidification of metallic alloys in the investment casting process is presented. Quantitative information about these conditions is needed so that numerical models of heat transfer in this process produce accurate results. In particular, the variation of the boundary conditions both spatially and temporally must be known. The method used involves the application of a new inverse heat conduction method to thermal data recorded during laboratory experiments of aluminium alloy solidification in investment casting shell moulds. The resultant heat transfer coefficient for the alloy/mould interface is calculated. An experimental programme to determine requisite mould thermal properties was also undertaken. It was observed that there is significant variation of the alloy/mould heat transfer coefficient during solidification. It is found to be highly dependent on the alloy type and on the vertical position below the initial free surface of the liquid metal. The aluminium casting alloys used in this study were 413, A356, 319 (Aluminum Association designations), and commercially pure aluminium. These alloys have significantly different freezing ranges. In particular, it was found that alloys with a high freezing range solidify with rates of heat transfer to the mould which are very sensitive to metallostatic head.     

Elimination of the radiant component of measured liquid thermal conductivities

Experimental determination of the thermal conductivity of liquids requires to eliminate reliably thermal radiation heat transfer. Using an approximate calculation method such eliminations have been done on several liquids in a plane layer with a steady-state heat transfer by simultaneous conduction and radiation. The method, the admissibility of simplifications, and the results are discussed. It is demonstrated that the knowledge of the optical properties of the liquid is very important, especially that of the IR-absorption spectrum. As the quantitative accuracy of available spectra is not sufficient, such spectra have to be determined particularly. The calculation method has been used to eliminate thermal radiation from effective thermal conductivities measured on a liquid within several layers of different thickness, where convection heat transfer was not present. The resulting “pure” thermal conductivities are independent of layer thickness. Thus the validity of the calculation method is verified.     

Nonlinear three-dimensional stretched flow of an Oldroyd-B fluid with convective condition,thermal radiation,and mixed convection

The effect of non-linear convection in a laminar three-dimensional Oldroyd-B fluid flow is addressed. The heat transfer phenomenon is explored by considering the non-linear thermal radiation and heat generation/absorption. The boundary layer assumptions are taken into account to govern the mathematical model of the flow analysis. Some suitable similarity variables are introduced to transform the partial differential equations into ordinary differential systems. The Runge-Kutta-Fehlberg fourth-and fifth-order techniques with the shooting method are used to obtain the solutions of the dimensionless velocities and temperature. The effects of various physical parameters on the fluid velocities and temperature are plotted and examined. A comparison with the exact and homotopy perturbation solutions is made for the viscous fluid case, and an excellent match is noted. The numerical values of the wall shear stresses and the heat transfer rate at the wall are tabulated and investigated. The enhancement in the values of the Deborah number shows a reverse behavior on the liquid velocities. The results show that the temperature and the thermal boundary layer are reduced when the nonlinear convection parameter increases. The values of the Nusselt number are higher in the non-linear radiation situation than those in the linear radiation situation.     

Flow of couple stress fluid with variable thermal conductivity

The steady flow and heat transfer of a couple stress fluid due to an inclined stretching cylinder are analyzed. The thermal conductivity is assumed to be temperature dependent. The governing equations for the flow and heat transfer are transformed into ordinary differential equations. Series solutions of the resulting problem are computed. The effects of various interested parameters, e.g., the couple stress parameter, the angle of inclination, the mixed convection parameter, the Prandtl number, the Reynolds number, the radiation parameter, and the variable thermal conductivity parameter, are illustrated. The skin friction coefficient and the local Nusselt number are computed and analyzed. It is observed that the heat transfer rate at the surface increases while the velocity and the shear stress decrease when the couple stress parameter and the Reynolds number increase. The temperature increases when the Reynolds number increases.     

Mixed convection heat transfer from a horizontal plate with variable surface heat flux in a porous medium

In this article nonsimilarity solution for mixed convection from a horizontal surface in a saturated porous medium was obtained for the case of variable surface heat flux. The entire mixed convection regime, ranging from pure forced convection to pure free convection, is considered by introducing a single nonsimilarity parameter. Heat transfer results are predicted by employing four different flow models, namely, Darcy's law, the Ergun model, and the Brinkman-Forchheimer-extended Darcy model with constant and variable porosity. The variable porosity effect is approximated by an exponential function. Effects of transverse thermal dispersion are taken into consideration in the energy equation, along with variable stagnant thermal conductivities. The formulation of the present problem shows that the flow and heat transfer characteristics depend on five parameters, that is, the power in the variation of surface heat flux, the nonsimilarity mixed-convection parameter, the inertia effect parameter, the boundary effect parameter, and the ratio of thermal conductivity of the fluid phase to that of the solid phase. Numerical results for the local Nusselt number variations, based on the various flow models, are presented for the entire mixed convection regime. The impacts␣of different governing parameters on the heat transfer results are thoroughly investigated. Received on 7 August 1997     

Heat exchange between a selectively emitting liquid and a laminar gas flow in the presence of an external source of radiation

An investigation is conducted in the solution of a number of practical problems of the radiative and combined heat exchange in nonuniform systems having widely different physical properties. The processes of thermal interaction between the ocean and the atmosphere have been treated in the paper [1], the effect of thermal radiation on the melting and solidification of semitransparent crystals has been investigated in [2], the flow of a selectively emitting gas around the lateral surface of an object evaporating under the action of radiative heating has been discussed in [3], and heat transfer from a jet to the molten mass of glass in a glassmaking furnace tank has been investigated in [4]. The radiative and combined heat exchange between a selectively emitting liquid and a transparent heat-conducting laminar gas flow in the case of a specified external thermal radiation field is discussed in this paper. The energy conservation equations are set up taking into account the heat transfer by radiation, convection, and molecular thermal conduction. A differential approximation is used in calculating the values of the radiation fluxes. A system of fundamental computational equations is solved by the method of finite differences and iterations and by the Runge-Kutta method. The results of the calculations are presented in the form of graphs.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 116–122, May–June, 1976.     

Thermo-mechanical response of tension panels under intense rapid heating

The temperature dependence of the fracture strength of 7075-T6 aluminum alloy was determined under rapid heating (0.02–.50 sec) conditions by exposing thin-section specimens to intense surface irradiation while under constant tensile load. When combined with a numerical thermal analysis and an appropriate limit analysis, these data enabled accurate prediction of the heating time required to produce ductile fracture in spot irradiated tension panels. The transient heat transfer model employed in the computations incorporated material removal due to melting, temperature-dependent material properties, and convection/radiation losses.