Thermophoresis particle deposition on unsteady two-dimensional forced convective heat and mass transfer flow along a wedge with variable viscosity and variable Prandtl number

In this paper, the effects of thermophoresis particle deposition on an unsteady two dimensional forced convective heat and mass transfer flow past a wedge taking into account the variation of fluid viscosity and fluid Prandtl number with temperature are studied. The local similarity equations are derived and solved numerically using Nachtsheim–Swigert shooting iteration technique along with the sixth order Runge–Kutta integration scheme. Comparisons with previously published work are performed, and the results are found to be in excellent agreement. Results for the non-dimensional velocity, temperature, concentration, Prandtl number and thermophoretic velocity are displayed graphically whereas thermophoretic deposition velocity is shown in the tabulated form for various values of the pertinent parameters. The obtained numerical results show that in modeling the thermal boundary-layer flow with a temperature-dependent viscosity, consideration of the Prandtl number as a constant within the boundary layer produces unrealistic results, and therefore, it must be treated as a variable rather than a constant within the boundary layer. The results also show that the thermophoretic particle deposition velocity decreases as the thermophoretic coefficient increases.     

Experimental study on the unsteady laminar heat transfer downstream of a backwards facing step

The objective of this work is to study experimentally the unsteady heat transfer downstream of a backward-facing step in the 2-D laminar regime when the inlet flow is pulsated. To this aim, an experimental set-up has been prepared with water as the working fluid. The Reynolds number based on the hydraulic diameter of the inlet channel and average inlet velocity is 300. Inlet flow temperature is 30 °C and a region downstream of the step is heated up to 74 °C. Pulsation is achieved using a piston pump and heat transfer is studied up to a maximum pulsation Strouhal number of 1.2. The results obtained confirm previous numerical simulation work in the sense that pulsation could be used to partially recover the heat transfer efficiency that is lost in steady flow conditions downstream of a backward-facing step. It has also been confirmed that the behaviour of the averaged Nusselt number versus pulsation Strouhal number is of the resonant type. That is: the Nusselt number increases from the steady situation up to a certain value of the Strouhal number (0.41 in our case) and, then, it degrades as the frequency of the pulsation is further increased.     

Combined effect of grid turbulence and unsteady wake on convective heat transfer around a heated cylinder

Experiments are conducted to investigate the effects of free stream turbulence and unsteady wake on convective heat transfer of a heated cylinder. To serve as a heater, a stainless steel needs to be pasted on exterior surface of the bakelite test cylinder. In order to determine the heat transfer coefficient, 17 T-type thermocouples are placed in unequal distance around the circumference at the mid-span of the test cylinder. The range of Reynolds number is 30,000 to 120,000. The results and contributions of this study display that the higher wake passing frequency produces more frequent velocity fluctuations, more broad velocity profiles, and stronger degree of turbulence intensity which are caused by the upstream wake generator and turbulence grid to enhance the heat transfer.     

Casson fluid flow and heat transfer past a symmetric wedge

Boundary‐layer forced convection flow of a Casson fluid past a symmetric wedge is investigated. Similarity transformations are used to convert the governing partial differential equations to ordinary ones and the reduced equations are then solved numerically with the help of the shooting method. Comparisons with various previously published works on special cases are performed and the results are found to be in excellent agreement. A representative set of graphical results is obtained and illustrated graphically. The velocity is found to increase with an increasing Falkner–Skan exponent whereas the temperature decreases. With the rise of the Casson fluid parameter, the fluid velocity increases but the temperature is found to decrease in this case. The skin friction decreases with increasing values of the Casson fluid parameter. It is found that the temperature decreases as the Prandtl number increases and thermal boundary layer thickness decreases with increasing values of the Prandtl number. A significant finding of this investigation is that flow separation can be controlled by increasing the value of the Casson fluid parameter. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(8): 665–675, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21065     

Radiation effect on the flow and heat transfer over an unsteady stretching sheet

The effect of radiation on the heat and fluid flow over an unsteady stretching surface is analyzed. Using a similarity transformation the governing time dependent boundary layer equations for momentum and thermal energy are reduced to a set of ordinary differential equations. The resulting three-parameter problem is solved numerically for some representative values of the unsteadiness parameter A, the radiation parameter R and Prandtl number Pr. It is shown that the heat transfer rate is increased with increasing R, A and Pr. Also the effect of radiation parameter on the heat transfer rate is found to be more noticeable at larger values of A and Pr.     

Short-time solution for unsteady forced convection heat transfer from an impulsively started circular cylinder

Short-time solution for unsteady heat transfer from an impulsively started circular cylinder is presented. Consideration is given to the case where unsteady temperature field is produced by the sudden imposition of a constant temperature difference between the body and the fluid as the impulsive motion is started. The present theory should be valid for any Prandtl number and for any Reynolds number larger than about 100. The Nusselt number results obtained are compared with the available numerical and theoretical ones.     

Unsteady stagnation flow and heat transfer towards a shrinking sheet

The unsteady stagnation flow towards a shrinking sheet is investigated. With assumptions that the sheet is shrunk impulsively from rest, and simultaneously the surface temperature is suddenly increased from that of surrounding fluid, the boundary layer equations are transformed to a set of nonlinear partial differential equations by means of a similarity transformation. The highly accurate analytical approximations are given, which match the numerical results given by the Keller–Box scheme.     

On the non-periodic unsteady heat transfer through walls

Existing calculation methods of the transient heat flow through walls for air-conditioning applications, assume periodic outdoor conditions. Therefore, the effect of a temporary temperature rise on the indoor heat flow is usually neglected. In the present work an attempt is being made to model the related non-periodic transient problem. The method of approach is based on a finite-difference solution of the transient heat conduction equation within the wall. Outdoor air temperature deviation parameters are introduced, which characterize any temporary deviation of the outdoor air-temperature from periodicity. Indoor heat flow deviation characteristics are defined, which describe the deviation of the indoor heat flow from periodicity, provoked by the corresponding outdoor air temperature deviation. A parametric study is conducted, where the effects of the temperature deviation parameters on the indoor heat flow deviation characteristics are examined. It has been found that (a) the maximum heat flow deviation varies linearly with the mean temperature difference, (b) the restoration ratio is practically independent of the temperature amplitude difference, and (c) an increase in the wall thermal diffusivity results in a decrease of the maximum heat flow deviation. The practical importance of the present analysis is that it helps towards the estimation of peak loads under non-periodic outdoor conditions.     

Flow and heat transfer over an unsteady stretching surface with non-uniform heat source

The non-uniform heat source/sink effect on the flow and heat transfer from an unsteady stretching sheet through a quiescent fluid medium extending to infinity is studied. The boundary layer equations are transformed by using similarity analysis to be a set of ordinary differential equations containing three parameters: unsteadiness parameter (S), space-dependent parameter (A?) and temperature-dependent parameter (B?) for heat source/sink. The velocity and temperature fields are solved using the Chebyshev finite difference method (ChFD). Results showed that the heat transfer rate, − θ′(0) and the skin friction, − f″(0) increase as the unsteadiness parameter increases whereas decrease as the space-dependent and temperature-dependent parameters for heat source/sink increase.     

Radiation and mass transfer effects on two-dimensional flow past an impulsively started infinite vertical plate

The interaction of free convection with thermal radiation of a viscous incompressible unsteady flow past an impulsively started vertical plate with heat and mass transfer is analyzed. The fluid is gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative flux in the energy equation. The dimensionless governing equations are solved using an implicit finite-difference method of Crank–Nicolson type. Numerical results for the velocity, the temperature, the concentration, the local and average skin-friction, the Nusselt number and Sherwood number are shown graphically. It is observed that, when the radiation parameter increases, the velocity and temperature decrease in the boundary layer. The local and average skin-friction increases with the increase in radiation parameter. For increasing values of radiation parameter the local as well as average Nusselt number increases.     

Effects of chemical reaction, heat and mass transfer along a wedge with heat source and concentration in the presence of suction or injection

An approximate numerical solution for the steady laminar boundary-layer flow over a wall of the wedge with suction or injection in the presence of species concentration and mass diffusion has been obtained by solving the governing equations using numerical technique. The fluid is assumed to be viscous and incompressible. Numerical calculations up to third level of truncation are carried out for different values of dimensionless parameters and an analysis of the results obtained shows that the flow field is influenced appreciably by the chemical reaction, heat source and suction or injection at the wall of the wedge.     

Numerical analysis of laminar heat transfer in a channel with diamond-shaped baffles

Laminar periodic flow and heat transfer in a two dimensional horizontal channel with isothermal walls and with staggered diamond-shaped baffles is investigated numerically. The computations are based on the finite volume method, and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 100 to 600. Effects of different baffle tip angles on heat transfer and pressure loss in the channel are studied and the results of the diamond baffle are also compared with those of the flat baffle. It is observed that apart from the rise of Reynolds number, the reduction of the baffle angle leads to an increase in the Nusselt number and friction factor. The computational results reveal that optimum thermal performance is at the baffle angle of 5° for baffle height and spacing of 0.5 and 1 times of the channel height, respectively. The thermal performance of the 5°–10°diamond baffle is found to be higher than that of the flat baffle for all Reynolds numbers used.     

Correlations for natural convection heat transfer in two-layer fluids with internal heat generation

Two simple semiempirical correlations for an estimate of heat transfer in horizontal layers of superposed immiscible fluids with internal heat sources are suggested. Different boundary conditions are considered. The predicted results are compared with the known experimental correlations. The results are of interest to post-accident heat removal in fast and light water reactors.     

Theoretical analysis of fluid flow and heat transfer in stoichiometric combustion in a naturally-ventilated control-volume

Using the conservation equations for mass, momentum and energy, a theoretical analysis of buoyancy driven flow and heat transfer for a ventilated control-volume, with an internal heat-source, has been made. The special case of stoichiometric combustion in a naturally-ventilated brick walled room, with a single rectangular opening, has been used to demonstrate the numerical calculation procedure for the prediction of the histories of the fire temperature, gas flow rate, fuel burn rate, fire power and boundary-wall temperature. The analysis may be extended for more complex space geometries and wall structures; a typical case being a railway carriage with a composite wall.     

Homotopy analysis method for heat radiation equations

Here, the homotopy analysis method (HAM), one of the newest analytical methods which is powerful and easy-to-use, is applied to solve heat transfer problems with high nonlinearity order. Also, the results are compared with the perturbation and numerical Runge–Kutta methods and homotopy perturbation method (HPM). Here, homotopy analysis method is used to solve an unsteady nonlinear convective–radiative equation containing two small parameters of ?₁ and ?₂. The homotopy analysis method contains the auxiliary parameter h¯, which provides us with a simple way to adjust and control the convergence region of solution series.     

Experimental study of the interactions between long and short-term unsteady heat transfer responses on the in-cylinder and exhaust manifold diesel engine surfaces

The paper presents the results from the analysis of an experimental investigation with the aim to provide insight to the cyclic, instantaneous heat transfer phenomena occurring in both the cylinder head and exhaust manifold wall surfaces of a direct injection (DI), air-cooled diesel engine. The mechanism of cyclic heat transfer is investigated during engine transient events, viz. after a sudden change in engine speed and/or load, both for the combustion chamber and exhaust manifold surfaces. These results are then compared with relevant experimental data from steady state operation which in the present case are used as reference helping to reveal any potential influences of each transient event on cyclic heat transfer. The experimental installation allowed both long- and short-term signal types to be recorded on a common time reference base during the transient event. Processing of experimental data was accomplished using a modified version of one-dimensional heat conduction theory with Fourier analysis, capable to cater for the special characteristics of transient engine operation. Based on this model, the evolution of local surface heat flux during a transient event was calculated. Two engine transient events are examined, which present a key difference in the way the load and speed changes are imposed on each one of them. From the analysis of experimental results it is confirmed that each thermal transient event consists of two distinguished phases the “thermodynamic” and the “structural” one which are appropriately configured and analyzed. In the case of a severe variation, in the first 20 cycles after the beginning of the transient event, the wall surface temperature amplitude on cylinder head was almost three times higher than the one observed at the “normal” temperature oscillations occurring during the steady state operation. At the same time, peak pressure values in the same cycles are increased by almost 15% above their corresponding values at the final steady state. The same phenomena are valid for the exhaust manifold surfaces but on a moderated scale.     

Mass transfer effects on MHD flow and heat transfer past a vertical porous plate through a porous medium under oscillatory suction and heat source

This paper considers the effect of mass transfer on free convective flow and heat transfer of a viscous incompressible electrically conducting fluid past a vertical porous plate through a porous medium with time dependant permeability and oscillatory suction in presence of a transverse magnetic field and heat source. The solutions for velocity field, temperature field and concentration distribution are obtained using perturbation technique. The effects of the flow parameters such as magnetic parameter M, Grashof number for heat and mass transfer G_r,G_c, porosity parameter K_p, Prandtl number P_r, Schmidt number S_c, frequency parameter ω and heat source parameter S on the velocity, temperature and concentration distribution of the flow field and the skin friction, heat flux and the rate of mass transfer are studied analytically and presented with the aid of figures and tables. It is observed that the magnetic parameter and the Schmidt number retard the velocity of the flow field while the Grashof number for heat and mass transfer, the porosity parameter and the heat source parameter have accelerating effect on the velocity of the flow field at all points. Further, the Prandtl number reduces the temperature and the Schmidt number diminishes the concentration distribution of the flow field at all points. The skin friction coefficients τ₀ and τ increase due to increase in G_r,G_c and K_p while decrease due to increase in S_c, M, ω and P_r. Further, the rate of mass transfer S_h increases due to increase in S_c while an increase in ω results a decrease in S_h.     

Thermal and heat transfer characteristics in a latent heat storage system using lauric acid

The thermal and heat transfer characteristics of lauric acid during the melting and solidification processes were determined experimentally in a vertical double pipe energy storage system. In this study, three important subjects were addressed. The first one is temperature distributions and temporal temperature variations in the radial and axial distances in the phase change material (PCM) during phase change processes. The second one is the thermal characteristics of the lauric acid, which include total melting and total solidification times, the nature of heat transfer in melted and solidified PCM and the effect of Reynolds and Stefan numbers as inlet heat transfer fluid (HTF) conditions on the phase transition parameters. The final one is to calculate the heat transfer coefficient and the heat flow rate and also discuss the role of Reynolds and Stefan numbers on the heat transfer parameters. The experimental results proved that the PCM melts and solidifies congruently, and the melting and solidification front moved from the outer wall of the HTF pipe (HTFP) to the inner wall of the PCM container in radial distances as the melting front moved from the top to the bottom of the PCM container in axial distances. However, it was difficult to establish the solidification proceeding at the axial distances in the PCM. Though natural convection in the liquid phase played a dominant role during the melting process due to buoyancy effects, the solidification process was controlled by conduction heat transfer, and it was slowed by the conduction thermal resistance through the solidified layer. The results also indicated that the average heat transfer coefficient and the heat flow rate were affected by varying the Reynolds and Stefan numbers more during the melting process than during the solidification process due to the natural convection effect during the melting process.     

On the influence of heat transfer in peristalsis with variable viscosity

This study concentrates on the heat transfer characteristics and endoscope effects for peristaltic flow of a third order fluid. Two models of variable viscosity are chosen. Both perturbation and numerical solutions are obtained in each case. A comparative study is also made between the two solutions. The importance of pertinent flow parameters entering into the flow modeling is discussed.     

Application of Optimal Homotopy Asymptotic Method for solving nonlinear equations arising in heat transfer

We consider one of the newest analytical methods, the Optimal Homotopy Asymptotic Method (OHAM), to solve nonlinear equations arising in heat transfer. Two specific applications are considered: cooling of a lumped system with variable specific heat and the temperature distribution equation in a thick rectangular fin radiation to free space. Results obtained by OHAM, which does not need small parameters are compared with numerical results and a very good agreement was found. This method provides us with a convenient way to control the convergence of approximation series and adjust convergence regions when necessary. The results reveal that the proposed method is explicit, effective and easy to use.