Combined free and forced convection flow past a vertial porous plate

Local similarity solutions of the forced and free convection flow past a semi-infinite vertical porous plate have been obtained numerically. Velocity and temperature profiles are shown for air (Pr = 0.72) and for different values of Gr (Gr > 0, cooling of the plate and Gr<0, heating of the plate) (Grashof number), E (Eckert number) and f_w (f_w>0, suction, f_w <0, injection). the effects of these parameters are discussed.     

Laminar forced convection in a heat generating bi-disperse porous medium channel

Thermal management of heat generating electronics using the Bi-Disperse Porous Medium (BDPM) approach is investigated. The BDPM channel comprises heat generating micro-porous square blocks separated by macro-pore gaps. Laminar forced convection cooling fluid of Pr = 0.7 saturates both the micro- and macro-pores. Bi-dispersion effect is induced by varying the porous block permeability Da_I and external permeability Da_E through variation in number of blocks N². For fixed Re, when 10^?5 ? Da_I ? 10^?2, the heat transfer Nu is enhanced four times (from ～200 to ～800) while the pressure drop Δp1 reduces almost eightfold. For Da_I < 10^?5, Nu decreases quickly to reach a minimum at the Mono-Disperse Porous Medium (MDPM) limit (Da_I → 0). Compared to N² = 1 case, Nu for BDPM configuration is high when N² ? 1, i.e., the micro-porous blocks are many and well distributed. The pumping power increase is very small for the entire range of N². Distributing heat generating electronics using the BDPM approach is shown to provide a viable method of thermo-hydraulic performance enhancement χ.     

Laminar forced convection in eccentric annuli

Forced convection to hydrodynamically and thermally fully developed laminar flow in eccentric annuli is studied. Following Reynolds et al. [1], we determine the solutions of the energy equation which satisfy certain fundamental boundary conditions. These fundamental solutions can be superposed to satisfy a wide variety of boundary conditions. Exact solutions of the energy equation could not be found, so an approximate solution was determined. Nusselt numbers, wall temperature and heat fluxes, wall-fluid temperature differences, and mean fluid temperatures are presented for a wide range of eccentricities and radius ratios. It is believed that these results are accurate to within 1 per cent.     

Laminar forced convection from a rotating horizontal cylinder in cross flow

The influence of non-dimensional rotational velocity, flow Reynolds number and Prandtl number of the fluid on laminar forced convection from a rotating horizontal cylinder subject to constant heat flux boundary condition is numerically investigated. The numerical simulations have been conducted using commercial Computational Fluid Dynamics package CFX available in ANSYS Workbench 14. Results are presented for the non-dimensional rotational velocity α ranging from 0 to 4, flow Reynolds number from 25 to 40 and Prandtl number of the fluid from 0.7 to 5.4. The rotational effects results in reduction in heat transfer compared to heat transfer from stationary heated cylinder due to thickening of boundary layer as consequence of the rotation of the cylinder. Heat transfer rate increases with increase in Prandtl number of the fluid.     

Laminar forced convection flow over a backward facing step using nanofluids

Laminar forced convection flow of nanofluids over a 2D horizontal backward facing step placed in a duct is numerically investigated using a finite volume method. A 5% volume fraction of nanoparticles is dispersed in a base fluid besides using various types of nanoparticles such as Au, Ag, Al₂O₃, Cu, CuO, diamond, SiO₂, and TiO₂. The duct has a step height of 4.8 mm, and an expansion ratio of 2. The Reynolds number was in the range of 50 ≤ Re ≤ 175. A primary recirculation region has been developed after the sudden expansion and it starts to change to become fully developed flow downstream of the reattachment point. The reattachment point is found to move downstream far from the step as Reynolds number increases. Nanofluid of SiO₂ nanoparticles is observed to have the highest velocity among other nanofluids types, while nanofluid of Au nanoparticles has the lowest velocity. The static pressure and wall shear stress increase with Reynolds number and vice versa for skin friction coefficient.     

Combined free and forced convection flow through a porous medium

Local similarity solutions of the forced and free convection flow past a porous medium bounded by a semi-infinite vertical porous plate are obtained numerically.     

平板对流换热的(火用)传递特性研究

通过对平板紊流对流换热的炯传递特性进行分析,定义了两个无因次量——局部传（火用）Nu及平均传（火用）Nu,并给出相关表达式;以空气为介质,详细讨论了平板几何尺寸、Re及其他运行参数对传（火用）Nu的影响,并将传（火用）与传热性能作了比较,为工程中确定合理的运行参数及最佳结构参数提供参考。     

Laminar Forced Convection in Curved Channel with Vortex Structures

Theoretical and experimental investigations of heat transfer in flat curvilinear channel have been carried out. Linear and non-linear effects of Dean vortexes on intensity of heat transfer were taken into account. The linear effect, which describe harmonic (sinuous) variation of the heat transfer coefficient near the concave surface of the channel and the non-linear effect causes the general increase of the heat transfer coefficient due to augmentation of heat transfer engendered by the Dean vortexes. For both effects, mathematical relations were obtained in the form of quadratures. These numerical results were modified to the form convenient in engineering calculations. The investigations have shown that both linear and nonlinear components grow up with the Dean number. Nonlinear component Q0T increases more abruptly, while the linear one Q1T is more conservative. This is a confirmation of stability of vortex structures.     

Study on single layer flow insulation utilizing NiCr open-cellular porous plate

The performance of flow insulation by using NiCr open-cellular porous plate has been examined experimentally and numerically. Experiment was performed under the condition that the upstream radiation temperature is lower than gas temperature at the inlet of a porous plate. The gas temperature drop across a porous plate was measured by varying inlet gas temperatures and mass flow rate. On the other hand, the P₁ approximation is applied to solve a combined forced-convection and radiation equation with the aid of Kamiuto's radiative properties. It is cleared that lowering the surface reflectivity of the solid phase of a porous converter is quite effective to raise the gas temperature drop. The measured equivalent blackbody radiation temperature does not depend on the gas flow rate. The porous converter is with high efficiency at low gas flow rate. In addition, the calculation results agree well with not only experimental data but also with the numerical solution by Barkstrom's finite difference method.     

Laminar forced convection with viscous dissipation in a Couette–Poiseuille flow between parallel plates

In this study, analytical solutions are obtained to predict laminar heat-convection in a Couette–Poiseuille flow between two plane parallel plates with a simultaneous pressure gradient and an axial movement of the upper plate. A Newtonian fluid with constant properties is considered with an emphasis on the viscous-dissipation effect. Both hydrodynamically and thermally fully-developed flow cases are investigated. The axial heat-conduction in the fluid is neglected. Two different orientations of the thermal boundary-conditions are considered: the constant heat-flux at the upper plate with an adiabatic lower plate (Case A) and the constant heat-flux at the lower plate with an adiabatic upper plate (Case B). For different values of the relative velocity of the upper plate, the effect of the modified Brinkman number on the temperature distribution and the Nusselt number are discussed. Comparison of the present analytical results for a special case with those available in the literature indicates an excellent agreement.     

Free and forced convection boundary layer flow through a porous medium with large suction

An analytical study is made of the free and forced convection boundary layer flow past a porous medium bounded by a semi-infinite vertical porous plate. Locally similar solutions are then obtained by a perturbation method for large suction. Solutions for the velocity and temperature distributions are shown graphically for various suction velocities and values of the driving parameter G_r/R, where G_r is the Grashof number and R_e is the Reynolds number. The corresponding values of the skin friction coefficient and the Nusselt number are finally shown in tabular form.     

Laminar forced convection in circular and flat ducts with wall axial conduction and external convection

An analytical solution is obtained for laminar forced convection in circular and flat ducts with the presence of axial duct wall conduction and external convection at the outer surface of the duct wall. The eigenvalues for the problem are determined using the solution for the constant temperature boundary condition. The heat transfer results depend on four nondimensional numbers. The wall and fluid temperatures depend strongly on the wall conductance parameter while the heat flux enhancement due to wall conduction is large at short distances from the duct inlet.     

Laminar forced convection heat transfer with phase change material emulsions

Results of an experimental study of laminar forced convection heat transfer in a circular duct with a phase change material emulsion (n-octadecane in water) are presented in this paper. The bulk Stefan numbers considered in this study range up to 3.0 and the concentration of phase change material range up to 30% by volume. The results show that the heat transfer characteristics for phase change material emulsions are similar to those of microencapsulated phase change material suspensions, thus confirming that the microcapsule walls do not affect the heat transfer process significantly.     

Laminar forced convection heat transfer with phase change material suspensions

This paper presents results related to laminar forced convection heat transfer to a phase change material suspension in a circular duct with constant wall heat flux. An effective specific heat approach has been used to model the heat transfer process for a flow with a fully developed velocity profile. The model has been verified by comparing its numerical predictions with previous theoretical results as well as well as experimental data. A simple correlation for wall temperature rise as a function of the tube length that can be used for future design has been developed based on a parametric study.     

An analysis on the thermal instability of forced convection flow over isothermal horizontal flat plate

Thermal instability of forced convection flow over an isothermal horizontal flat plate in the form of longitudinal vortices is examined by introducing three-dimensional spatial dependence of the perturbation quantities. The system of stability equations has been simplified significantly by considering the limiting case of very large Prandtl numbers and by seeking similarity solutions for the amplitude functions of the perturbation quantities. The effect of x-dependent temperature perturbation is shown to stabilize the flow as compared with x-independent temperature perturbation, which explains very well the extant theoretical results and experimental observations.     

Laminar forced convection slip-flow in a micro-annulus between two concentric cylinders

Forced convection heat transfer in hydrodynamically and thermally fully developed flows of viscous dissipating gases in annular microducts between two concentric micro cylinders is analyzed analytically. The viscous dissipation effect, the velocity slip and the temperature jump at the wall are taken into consideration. Two different cases of the thermal boundary conditions are considered: uniform heat flux at the outer wall and adiabatic inner wall (Case A) and uniform heat flux at the inner wall and adiabatic outer wall (Case B). Solutions for the velocity and temperature distributions and the Nusselt number are obtained for different values of the aspect ratio, the Knudsen number and the Brinkman number. The analytical results obtained are compared with those available in the literature and an excellent agreement is observed.     

Laminar forced convection heat transfer around two rotating side-by-side circular cylinder

The present study numerically investigates two-dimensional laminar force convection heat transfer past two rotating circular cylinders in a side-by-side arrangement at a various range of absolute rotational speeds (|α| ? 2) for four different gap spacings (g1) of 3, 1.5, 0.7 and 0.2 at Reynolds number of 100, and a fixed Prandtl numbers of 0.7 (air). As |α| increases, the thermal field became stabilized and eventually steady beyond the critical rotational speed depending on the gap spacing. In general, as |α| increases, because the vertical motion of flow in the region of gap is strongly inhibited, the inner isotherms are early merged and shorter than the outer isotherms in the free-stream sides elongating further downstream. As |α| increases, because the rotating fluid near the cylinders surrounded much space where the steady conduction mode is predominant to the heat transfer, the behavior of the time- and surface-averaged Nusselt number has the decaying pattern with increasing |α| for all gap spacings considered in this study.