Non-uniform Wall Temperature Research Articles

DSMC Study of Pressure-Driven Slip Flow through Microchannel at Non-Uniform Wall Temperature

ABSTRACTThe present study is to investigate the pressure-driven gas flow in microchannel at no-uniform wall temperature. DSMC is employed to generate the flow field details which are then used in analysis of the slip flow characteristics. The major concern is the influences of thermal creep effect on the pressure-driven slip flow. Thermal creep is resulted from tangential wall temperature gradient. In this work, two kinds of thermal boundary condition are considered. One is the linearly varied temperature (LVT) applied to both walls, the other is that has the bottom wall at a thermal condition combined LVT and adiabatic (AD) wall, i.e. LVT-AD-LVT condition. The present DSMC results reveal that the fluid slip is weakened (enhanced) in the case with a negative (positive) wall temperature gradient. Relatively, thermal creep effect on fluid slip over the adiabatic wall is more pronounced in the presence of negative wall temperature gradient. The mass flowrate is a strong function of the wall temperature gradient. However, there is only little difference between the mass flowrates predicted under the two kinds of thermal conditions studied in the present work.

A Note on Radiative Heat Transfer to Peristaltic Flow of Sisko Fluid.

This paper looks at the effects of radiative heat transfer on the peristaltic transport of a Sisko fluid in an asymmetric channel with nonuniform wall temperatures. Adopting the lubrication theory, highly nonlinear coupled governing equations involving power law index as an exponent have been linearized and perturbation solutions are obtained about the Sisko fluid parameter. Analytical solutions for the stream function, axial pressure gradient, axial velocity, skin friction, and Nusselt number are derived for three different cases (i.e., shear thinning fluid, viscous fluid, and shear thickening fluid). The effects of Grashof number, radiation parameter, and other configuration parameters on pumping, trapping, temperature, Nusselt number, and skin friction have been examined in detail. A good agreement has been found for the case of viscous fluid with existing results.

Hermite- Padé projection to thermal radiative and variable conductivity MHD flows through channel with a sliding wall

The combined effect of variable thermal conductivity and radiative heat transfer on steady flow of a conducting optically thin viscous fluid through a channel with sliding wall and non-uniform wall temperatures under the influence of an externally applied homogeneous magnetic field are analyzed in the present study. The similarity transformation reduces the time dependent governing equations for momentum and thermal energy into a set of coupled ordinary differential equations which are solved using perturbation method together with Hermite- Padé approximation. The velocity and temperature profiles are presented graphically to interpret the effect of various physical parameters of the problem. The critical relationships among the parameters are also performed qualitatively.Keywords: Thermal radiation, variable thermal conductivity, sliding wall, non-uniform wall temperature, Hermite- Padé approximationInternational Journal of Engineering, Science and Technology Vol. 6, No. 1, 2014, pp. 88-97

J0550301 重力と非一様な壁面温度場により誘起される半無限空間の定常希薄気流([J055-03]マイクロ・ナノスケール熱流体現象(3))

J0550301 重力と非一様な壁面温度場により誘起される半無限空間の定常希薄気流([J055-03]マイクロ・ナノスケール熱流体現象(3))

Thermal Diffusion and Diffusion Thermo Effects on Peristaltic Flow of Sisko Fluid in Nonuniform Channel With Dissipative Heating

This investigation deals with thermal diffusion and diffusion thermo effects on the peristaltic flow of a Sisko fluid in an asymmetric channel. The mode of dissipative heat transfer is taken into account with nonuniform wall temperatures. Long wavelength approximation is utilized. Solutions for the highly nonlinear coupled governing equations involving power law index as an exponent are derived by employing the perturbation technique in a Sisko fluid parameter. Closed form solutions for the stream function, the axial pressure gradient, the skin friction, the temperature, the concentration, and the Nusselt number are presented. Effects of various interesting parameters are graphically interpreted. A comparative study between Newtonian, shear thinning, and shear thickening fluids is also presented. Comparison with published results for the case of viscous fluid is observed in good agreement.

Similarity Theory for Forced Convection over Horizontal Plates

A similarity analysis is performed to study the fluid flow and heat transfer characteristics for the steady laminar forced convection boundary-layer flow past a semi-infinite horizontal plate in the presence of mass transfer, i.e., suction or blowing. The plate is subjected either to a nonuniform heat flux or nonuniform wall temperature. The heat flux is assumed to vary in the following form , whereas the wall temperature is assumed to vary as . Numerical results are obtained for various values of Prandtl number, suction or injection parameter , as well as for various levels of heating or . The effects of various values of Prandtl number , suction or injection parameter , and the index or on velocity profiles, temperature profiles, skin-friction coefficients, and local Nusselt number are presented. The results of the present general theory agree well with previously published results for the case of constant wall temperature (the only case with quantitative solutions that were available in the literature). Subtle new flow physics, such as a sharp reduction in the Nusselt number with increasing Prandtl number when mass injection is present and the Prandtl number is large, has been elucidated.

Heat Transfer to Magnetohydrodynamic Non-Newtonian Couple Stress Pulsatile Flow Between two Parallel Porous Plates

This paper investigates the effect of radiative heat transfer to oscillatory hydromagnetic non- Newtonian couple stress fluid flow through a porous channel with non-uniform wall temperature due to periodic heat input at the heated wall. Based on some simplifying assumptions, the dimensionless partial differential equations are transformed into a set of ordinary differential equations and then solved using the Adomian decomposition method. The effects of the flow parameters on temperature and velocity profiles are shown graphically and discussed.

Numerically investigating the influence of tube support plates on thermal-hydraulic characteristics in a steam generator

A three-dimensional “unit pipe” model coupled with broached tube support plates (TSPs) is developed to investigate the influence of TSPs on the thermal-hydraulic characteristics of the primary and secondary side of steam generator (SG). The model reasonably captures the unbalanced boiling phenomena in the SG secondary side, particularly in the regions surrounding the TSPs. At these points, there is an abrupt increase in secondary fluid velocity, generating recirculation distribution and local vortex. Nonuniform outer wall temperatures periodically fluctuate around the circumference of the tubes at the TSPs, with the corresponding temperature difference between the support location and flow hole gradually decaying in the primary flow direction. These thermal-hydraulic distributions are then used to determine the cross-flow energy, which is strongly related to flow-induced vibration (FIV) damage. According to the FIV distributions, FIV damage is predicted to be most severe at angles of θ = 65° on the cold-leg side and θ = 120° on the hot-leg side of the U-bend tube bundles. These simulated FIV damage results are in agreement with the measured plant data from a prototypical SG. Therefore, this developed “unit pipe” model can provide technical support to help alleviate FIV damage and minimize the probability of tube failure.

Forced turbulent heat convection in a square duct with non-uniform wall temperature

In the present work, the numerical simulation to calculate the problem of the turbulent convection with non-uniform wall temperature in a square cross-section duct was adopted. To solve this problem some assumptions for the flow, such as: the condition of fully developed turbulence and incompressible flow have been assumed. The methodology of the dimensionless energy equation was used to calculate the fluid temperature field in the square cross-section in function of the non-uniform wall temperatures prescribed. Numerical simulations were done using two different turbulent models to resolve the momentum equations and two more models to resolve the energy equation. The models of turbulence k–ε Nonlinear Eddy Viscosity Model (NLEVM) and the Reynolds Stress Model (RSM) were used to determine the turbulent intensities as well as the profiles of axial and secondary mean velocities. The turbulence model RSM was simulated using a commercial software. The thermal field was determined from other two models: Simple Eddy Diffusivity (SED), based in the hypothesis of the constant turbulent Prandtl number; and Generalized Gradient Diffusion Hypothesis (GGDH). In this last model, as the turbulent heat transfer depends on the shear tensions, the anisotropy is considered. These two last equation models of the energy equation of the fluid have been implemented in FORTRAN, a code of programming. The performances of the models were evaluated by validating them based in the experimental and numerical results published in the literature. Two important parameters of great interest in engineering are presented: the friction factor and the Nusselt number. The results of this investigation allow the evaluation of the behavior of the turbulent flow and convective heat fluxes for different square cross-sectional sections throughout the direction of the main flow, which is mainly influenced by the temperature distribution in the wall.

Investigation on the influence of nonuniform initial temperature on the transient heat transfer measurement of film cooling

Numerical and experimental investigations on the influence of nonuniform initial temperature on the transient heat transfer measurements are presented in this paper. The case of film cooling is investigated. When the initial wall temperature is nonuniform, the results of heat transfer coefficient and film cooling effectiveness, which are calculated by the equations derived with constant initial temperature, could deviate from the true values badly, especially in the condition of short test duration. Using initial wall temperature which is higher than the real values causes the results of heat transfer coefficient and film cooling effectiveness lower than the true values. And lower initial wall temperature produces higher results of heat transfer coefficient and film cooling effectiveness. However, when the initial temperature distribution in the region where conduction plays more influence on the wall surface temperature than the convection is well fitted by the cubic polynomial, accurate results can be obtained by the new equation which is derived from 1-D unsteady conduction model with nonuniform initial wall temperature. Some suggestions are also introduced to reduce the influence of nonuniform initial temperature when the initial temperature distribution is difficult to obtain and the equation derived from constant initial temperature has to be employed.

Steady flows of a highly rarefied gas induced by nonuniform wall temperature

Steady behavior of a rarefied gas between parallel plates with sinusoidal temperature distribution is investigated on the basis of the Boltzmann equation. The Cercignani–Lampis (CL) model or the Lord model for diffuse scattering with incomplete energy accommodation is adopted as the boundary condition on the plates. Most of the analysis is carried out numerically with special interest in the free-molecular limit. In the case of the CL model, the nonuniform temperature distribution of the plates may induce a steady free-molecular flow, which is in contrast with the earlier results for the Maxwell-type model [Y. Sone, J. Méc. Théor. Appl. 3, 315 (1984); J. Méc. Théor. Appl. 4, 1 (1985)]. This fact is confirmed through an accurate deterministic computation based on an integral equation. In addition, computations for a wide range of parameters by means of the direct simulation Monte Carlo method reveal that the flow field changes according to the accommodation coefficients and is classified into four types. The effect of intermolecular collisions on the flow is also examined. In the case of the Lord model, no steady flow of the free-molecular gas is induced as in the case of the Maxwell-type model. This result is extended to the case of a more general boundary condition that gives the cosine law (Lambert’s law) for the reflected molecular flux.

Film Cooling Performance of Converging-Slot Holes With Different Exit-Entry Area Ratios

Film cooling performances of two kinds of converging-slot-hole (console) with different exit-entry area ratios have been measured using a new transient liquid crystal measurement technique, which can process the nonuniform initial wall temperature. Four momentum ratios are tested. The film cooling effectiveness distribution features are similar for the two consoles under all the momentum ratios. Consoles with smaller exit-entry area ratio produce higher cooling effectiveness. And the laterally averaged cooling effectiveness results show that the best momentum ratio for both consoles’ film cooling effectiveness distribution is around 2. For both consoles, the heat transfer in the midspan region is stronger than that in the hole centerline region in the upstream but gradually becomes weaker as flowing downstream. With the momentum ratio increasing, the normalized heat transfer coefficient h∕h0 of both consoles increases. In the upstream, the heat transfer coefficient of console with small exit-entry area ratio is higher. But in the downstream, the jets’ turbulence and the couple vortices play notable elevating effect on the heat transfer coefficient for large exit-entry area ratio case, especially under small momentum ratios. Consoles with smaller exit-entry area ratio provide better thermal protection because of higher cooling effectiveness. And the distributions of heat flux ratio are similar with those of cooling effectiveness because the influence of η on q∕q0 is larger. For the consoles, smaller exit-entry area ratios produce lower discharge coefficients when the pressure variation caused by the hole shape is regarded as flow resistance.

Macroscopic modeling of thermal dispersion for turbulent flows in channels

In this paper, laminar and turbulent flows in channels are considered. The primary interest for industrial purpose is a macroscale description of mean flow quantities derived from the microscopic details of the flow in each subchannel. A double averaging procedure [16,17] has been used to derive balance equations for mean flow variables within laminar and turbulent regimes. This up-scaling procedure results in additional contributions, amongst which dispersion predominates. Thermal dispersion might be seen as the sum of a first contribution, hereafter denoted “passive”, due to velocity heterogeneities, and a second one, called “active”, due to wall heat transfer. The aim of the present work is to propose practical models for thermal dispersion that account for laminar and turbulent regimes. Embedded in CFD code, they are validated against RANS simulations. Our results illustrate the importance of thermal dispersion for heated flows in the presence of nonuniform wall heat flux or temperature jumps.

LOCAL NONSIMILARITY SOLUTION ON MHD CONVECTIVE HEAT TRANSFER FLOW PAST A POROUS WEDGEIN THE PRESENCE OF SUCTION/INJECTION

The behavior of the steady convective heat transfer of an electrically conducting fluid flow over a porous wedge with uniform suction or injection was investigated. The wall of the wedge is embedded in a uniform porous medium in order to allow for possible fluid wall suction or injection. The governing boundary layer equations are written into a dimensionless form by similarity transformations. Because of the effect of suction/injection on the wall of the wedge with buoyancy force and variable wall temperature, the flow field is locally nonsimilar. The nonsimilar ordinary differential equations were obtained by means of a local nonsimilarity method. The resulting ordinary differential equations are solved by Runge-Kutta-Gill with a shooting method for finding a skin friction and a rate of heat transfer. The effects of suction/injection, nonuniform wall temperature and buoyancy force parameters on the dimensionless velocity and temperature profiles are shown graphically. Comparisons to previously published works are performed, and excellent agreement between the results is obtained. The conclusion is drawn that the flow field and temperature profiles are significantly influenced by these parameters. Copyright © 2010 Begell House, Inc.

UNSTEADY MAGNETOHYDRODYNAMIC OSCILLATORY FLOW AND HEAT TRANSFER ANALYSIS OF A VISCOUS FLUID IN A POROUS CHANNEL FILLED WITH A SATURATED POROUS MEDIUM

In this article, unsteady oscillatory flow of a magnetohydrodynamic fluid and heat transfer analysis with nonuniform wall temperature through a planar channel filled with a saturated porous medium are studied. It is assumed that the walls of the channel are porous so that suction/injection may take place. The exact analytic closed-form solution is obtained for velocity and temperature fields. The mathematical results are then plotted to see the effect of different parameters on the flow phenomenon.

Experimental research on the thermal performance of converging slot holes with different divergence angles

Thermal performances of two kinds of converging slot-hole ( console) with different divergence angles have been measured using transient liquid crystal measurement technique which can process the nonuniform initial wall temperature. Four momentum ratios are tested. Consoles with different divergence angles produce different cooling effectiveness distributions in the upstream region. However, the cooling effectiveness distributions of the two consoles are similar in the downstream. The laterally averaged cooling effectiveness results show that the differences between the two consoles are very small and the best momentum ratio for both consoles’ cooling effectiveness distribution is around two. With the momentum ratio increasing, the normalized heat transfer coefficient h/ h 0 of both consoles increases, but the h/ h 0 value of small divergence case is higher and becomes progressively higher than that of large divergence case. Moreover, the effect of the couple vortices on the heat transfer coefficient distributions is more significant for the large divergence case. Both consoles provide the surface a certain degree of thermal protection, especially in the upstream region. The distributions of heat flux ratio q/ q 0 are similar with those of η because the influence of η on q/ q 0 is much larger than that of h/ h 0 on q/ q 0.

Mathematical simulation of dispersed phase dynamics for the nonisothermal free convection of a heterogeneous medium in a vertical cylindrical reactor

The motion of monodisperse spherical particles in a heterogeneous medium for the nonisothermal free convection of the carrying viscous incompressible liquid in a cylindrical reactor with nonuniform wall temperature profiles is mathematically simulated. The simulation is based on the simultaneous solution of the Navier-Stokes equations written in terms of Eulerian variables for the carrying liquid in the Boussinesq approximation and the equations written in terms of Lagrange variables for the dispersed particle. The system of Navier-Stokes equations is solved in terms of curl-stream function variables using the alternating direction implicit finite difference scheme. The monotone Samarskii’s approximation is used for the convective terms in the curl equation. The calculated results demonstrate the evolution of the curl, stream function, temperature, and particle trajectory.

Entropy-generation analysis for variable-viscosity channel flow with non-uniform wall temperature

This paper is an analytical study of inherent irreversibility in the flow of a variable-viscosity fluid through a channel with a non-uniform wall temperature. It is assumed that the channel is narrow and the fluid viscosity varies linearly with temperature. Analytical expressions for fluid velocity and temperature are derived and employed to obtain expressions for volumetric entropy-generation numbers, irreversibility distribution ratio and the Bejan number in the flow field.

Turbulent Film Condensation on a Nonisothermal Horizontal Tube

AbstractA simple model has been developed for the study of turbulent film condensation from downward flowing vapors onto a horizontal circular tube with variable wall temperature. The interfacial shear at the vapor condensate film is evaluated with the help of Colburn analogy. The condensate film flow and local/or mean heat transfer characteristics from a horizontal tube with non-uniform temperature variation under the effect of Froude number, sub-cooling parameter and system pressure parameter has been conducted. Although the non-uniform wall temperature variation has an appreciable influence on the local film flow and heat transfer; however, the dependence of mean heat transfer on the non-uniform wall temperature variation is almost negligible.

Turbulent film condensation on a non-isothermal horizontal tube—effect of eddy diffusivity

A theoretical study is made into the process of heat transfer with vapor condensation on a non-isothermal horizontal tube submerged in a forced vapor flow. The interfacial eddy diffusivity effect included in the energy relation is first considered here. The interfacial shear at the vapor condensate film is evaluated by employing the Colburn analogy. The condensate film flow and condensing heat transfer characteristics from a non-isothermal horizontal tube under the effects of the non-uniform wall temperature variation, the Froude number, sub-cooling parameter and system pressure parameter have been investigated. As the wall temperature variation amplitude increases, the value of the dimensionless mean heat transfer result, Nu ¯ Re - 1 / 2 , with the inclusion of the eddy diffusivity effect, decreases insignificantly.