Transient flow of a conducting fluid with heat transfer due to an infinite rotating disk

The unsteady MHD flow of an incompressible viscous electrically conducting fluid above an infinite rotating disk is studied with heat transfer. The effect of an external uniform magnetic field on the velocity and temperature distributions as well as the heat transfer is considered. Numerical solutions of the nonlinear equations which govern the magnetohydrodynamics and energy transfer are obtained.     

Unsteady flow and heat transfer of a ferrofluid between two rotating,vertical moving and stretching disks

Unsteady flow and heat transfer of a magnetic fluid between two rotating disks is investigated. Both the disks are stretchable and the lower disk moves in the vertical direction. A new approach of similarity transformation is adopted to transform the equation of continuity, momentum, and the energy equation into ordinary nonlinear coupled differential equations. The numerical solution of the converted nonlinear differential equations is obtained using the finite element method. The effects of magnetization force, rotational viscosity, Prandtl number, and Eckert number on the velocity and temperature distributions are studied. The impact of stretching, movement, and rotation of the disk is also considered in this computational study. The skin friction coefficients and heat transfer rate on the lower disk for different physical parameters are calculated. Different types of motion of the disks and the magnetization force are crucial aspects in the stress distribution and heat transfer rate near the lower disk.     

Flow structure and heat transfer between two disks rotating independently

In the present paper, fluid flow and convective heat transfer between two co-axial disks rotating independently are dealt with mainly based on the author's recent research on that topic. Three rotational modes, i.e. co-rotation, rotor-stator, and counter-rotation, are considered. Theory of rotating non-isothermal fluids with the presence of disk rotation and thermal effects is addressed. Rotational buoyancy effects on the flow structure development are highlighted. Results of flow visualization and heat transfer measurements are discussed to explore the thermal flow mechanisms involved in the two-disk flows at various rotational and geometric conditions. Potential issues open to the future investigation are also proposed.     

Magnetohydrodynamics stability of a rotating flow with heat transfer

We study the magnetohydrodynamic stability of an axisymmetric rotating flow in a cylindrical enclosure filled with a liquid metal (Pr = 0.015), having an aspect ratio equal to 2, and subjected to a vertical temperature gradient and an axial magnetic field. The finite volume method is used in order to solve the equations of continuity, momentum, energy, and electric potential. Without magnetic field, the critical Reynolds number is a decreasing function of the Richardson number owing to the destabilizing contribution of natural convection. In the presence of a vertical magnetic field, the flow stability is preserved for higher values of the Reynolds number. The stability diagram which is established shows the dependence of the critical Reynolds number with the increase of the Hartmann number, Ha, for various values of the Richardson number. This study confirms the possibility of stabilization of a liquid metal flow in mixed convection by application of an axial magnetic field.     

Effects of hall current and wall temperature oscillation on free convective and mass transfer flow in a rotating porous medium with constant heat source

The combined effects of Hall current and a constant heat source on the hydromagnetic free convective and mass transfer flow past an infinite vertical porous plate in a rotating porous medium are considered, when the temperature of the plate varies with time about a nonzero constant mean and the temperature of the free stream is constant. The problem is solved analytically and the velocity profiles are shown on graphs. Effects of m (Hall parameter) and α (heat source parameter) on velocity are discussed extensively.     

Fluid flow and heat transfer model for high-speed rotating heat pipes

A new complete model has been developed to predict the performance of high-speed rotating heat pipes with centrifugal accelerations up to 10 000 g. The flow and heat transfer in the condenser is modeled using a conventional modified Nusselt film condensation approach. The heat transfer in the evaporator has previously been modeled using a modified Nusselt film evaporation approach. It was found, however, that natural convection in the liquid film becomes more significant at higher accelerations and larger fluid loadings. A simplified evaporation model including the mixed convection is developed and coupled with the film condensation model. The predictions of the model are in reasonable agreement with existing experimental data. The effects of working fluid loading, rotational speed, and pipe geometry on the heat pipe performance are reported here.     

Laminar flow and heat transfer near rotating axisymmetric surface

Results of calculations are obtained for similar boundary layers on axisymmetric surfaces rotating in an infinite motionless medium. An electronic computer was employed. The power dependence of the distance from the rotation axis on the length of the generating line is the condition of the existence of similar layers.Characteristics of velocity and thermal boundary layers, velocity and temperature distributions are calculated.Using the class of exact solutions obtained, an approximate method for calculating velocity and thermal boundary layers on arbitrary-shaped rotating surfaces is developed. The method employed is to choose on each section a closely approximate surface with power dependence of radius on the component length; taking into account the continuous consolidation of the boundary layer.Using, as an example the case of a rotating sphere, it is shown that the calculation results obtained with this method agree with both the data of other calculations and experiment.     

Entropy generation due to flow and heat transfer in nanofluids

Present study provides a theoretical investigation of the entropy generation analysis due to flow and heat transfer in nanofluids. For this purpose, the most common alumina–water nanofluids are considered as the model fluid. Since entropy is sensitive to diameter, three different diameters of tube in their different regimes have been taken. Those are microchannel (0.1 mm), minichannel (1 mm) and conventional channel (10 mm). To consider the effect of conductivity and viscosity, two different models have been used to represent theoretical and experimental values. It has been found that the reduced equation with the help of order of magnitude analysis predicts microchannel and conventional channel entropy generation behaviour of nanofluids very well. The alumina–water with high viscosity nanofluids are better coolant for use in minichannels and conventional channels with laminar flow and microchannels and minichannel with turbulent flow. It is not advisable to use alumina–water nanofluids with high viscosity in microchannels with laminar flow or minichannels and conventional channels with turbulent flow. Also there is need to develop low viscosity alumina–water nanofluids for use in microchannel with laminar flow. It is observed that at lower tube diameter, flow friction irreversibility is more significant and at higher tube diameter thermal irreversibility is more. Finally, for both laminar and turbulent flow, there is an optimum diameter at which the entropy generation rate is the minimum for a given nanofluid.     

The rate of heat flow through a flat vertical wall due to conjugate heat transfer

Free convection along both sides of a vertical flat plate is studied within the framework of the laminar boundary-layer theory and for the case where only the temperature of the fluid far away from the wall is prescribed. Corrections to the Pohlhausen solution for the temperature at the plate surface are calculated. It is found that for good thermal conductors, the corrections are small (within a few percent), while for poor thermal conductors the corrections may be substantial (～30% for a wall with conductivity similar to brick). In addition, expressions for the heat transfer coefficient h as well as for the Nusselt number are derived and the corresponding convective heat transfer rate is determined.     

Analytical solution for slip flow and heat transfer due to a stretching sheet

An analysis has been carried out to investigate the analytical solution to the flow and heat transfer characteristics of a viscous flow over a stretching sheet in the presence of second‐order slip in flow. The governing partial differential equations of flow and heat transfer are converted into non‐linear ordinary differential equations by using suitable similarity transformations. The exact solution of momentum equation is assumed in exponential form and analytical solutions of heat transfer for both PST and PHF cases are obtained by the power series method in terms of Kummer's hypergeometric function. The temperature profiles are drawn for different governing parameters. The numerical values of wall temperature gradient and wall temperature are compared with earlier numerical results which have a good agreement. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21044     

Unsteady mhd flow and heat transfer on a rotating disk in an ambient fluid

An unsteady flow and heat transfer of a viscous incompressible electrically conducting fluid over a rotating infinite disk in an otherwise ambient fluid are studied. The unsteadiness in the flow field is caused by the angular velocity of the disk which varies with time. The magnetic field is applied normal to the disk surface. The new self-similar solution of the Navier–Stokes and energy equations is obtained numerically. The solution obtained here is not only the solution of the Navier–Stokes equations, but also of the boundary layer equations. Also, for a simple scaling factor, it represents the solution of the flow and heat transfer in the forward stagnation-point region of a rotating sphere or over a rotating cone. The asymptotic behaviour of the solution for a large magnetic field or for a large independent variable is also examined. The surface shear stresses in the radial and tangential directions and the surface heat transfer increase as the acceleration parameter increases. Also the surface shear stress in the radial direction and the surface heat transfer decrease with increasing magnetic field, but the surface shear stress in the tangential direction increases.     

Large eddy simulation of flow and heat transfer in a rotating ribbed channel

The internal cooling passage of a gas turbine blade equipped with ribs is modeled as a rotating ribbed channel. The flow and heat transfer in the ribbed channel have been investigated by conducting large eddy simulations with a dynamic subgrid-scale model. The Reynolds number considered is 30,000 and rotation numbers are 0, 0.1 and 0.3. The time-averaged results show good agreement with the experimental data. By comparing the present data with those of the smooth channel, it is observed that the vortices shed from the rib induce strong wall-normal motions, and they are augmented on the trailing-wall side by the rotation, resulting in a significant increase in the heat transfer due to rotation. It is also shown that the similarity between the streamwise velocity and temperature is significantly destroyed by both the rotation and the rib itself.     

Steady flow and heat transfer of the power-law fluid over a rotating disk

This paper deals with the steady flow and heat transfer of a viscous incompressible power-law fluid over a rotating infinite disk. Assumed the thermal conductivity follows the same function as the viscosity, the governing equations in the boundary layer are transformed into a set of ordinary differential equations by generalized Karman similarity transformation. The corresponding nonlinear two-point boundary value problem was solved by multi-shooting method. Numerical results indicated that the parameters of power-law index and Prandtl number have significant effects on velocity and temperature fields. The thickness of the boundary layer decays with power-law index. The peak of the radial velocity changes slightly with power- law index. The values near the boundary are affected dramatically by the thickness of the boundary layer. With the increasing of the Prandtl number the heat conducts more strongly.     

Unsteady flow of a non-Newtonian fluid above a rotating disk with heat transfer

The unsteady flow of an incompressible viscous non-Newtonian fluid above an infinite rotating disk is studied with heat transfer. The effect of the non-Newtonian fluid characteristics on the velocity and temperature distributions as well as the heat transfer is considered. Numerical solutions for the non-linear partial differential equations which govern the hydrodynamics and energy transfer are obtained.     

Unsteady flow of viscous incompressible fluid with temperature-dependent viscosity due to a rotating disc in presence of transverse magnetic field and heat transfer

This paper studies the effect of a magnetic field and temperature-dependent viscosity on the unsteady flow and heat transfer for a viscous laminar incompressible and electrically conducting fluid due to an impulsively started rotating infinite disc. The unsteady axisymmetric boundary layer equations are solved using three methods, namely, (i) perturbation solution for small time, (ii) asymptotic analysis for large time and (iii) finite difference method together with Keller box elimination technique for intermediate times. The solutions are obtained in terms of local radial skin friction, local tangential skin friction, and local rate of heat transfer at the surface of the disc, for different values of the pertinent parameters: the Prandtl number Pr, the viscosity variation parameter ε and magnetic field parameter m. The computed dimensionless velocity and temperature profiles for Pr=0.72 are shown graphically for different values of ε and m.     

Convective heat transfer inside a rotating cylinder with an axial air flow

This article presents an experimental identification technique for the convective heat transfer coefficient inside a rotating cylinder with an axial airflow. The method consists in heating the outer face of the cylinder using infrared lamps, and acquiring the evolution of the external surface temperature versus time using an infrared camera. Heat transfer coefficients are identified via three methods. The first one is based on an inverse model, the second one assumes the wall of the cylinder as a thermally thin wall and the third one is based on an analytical method permitting to obtain the temperature field within the whole cylinder. The experiments were carried out for a rotational speed ranging from 4 to 880 rpm corresponding to rotational Reynolds numbers varying from 1.6×10³ to 4.7×10⁵ and an air flow rate varying from 0 to which corresponds to an axial Reynolds numbers ranging from 0 to 3×10⁴. Correlations connecting the Nusselt number to the axial and rotational Reynolds numbers are also proposed.     

A numerical study of fluid flow and heat transfer in eccentric curved annuli

In this article fluid flow and heat transfer in curved eccentric annuli are studied numerically. A second order finite difference method based on the Projection algorithm is implemented to solve the governing equations including the full Navier–Stokes, the continuity, and the energy equations in a toroidal coordinate system. For convenience a bipolar based toroidal coordinate system is employed to discretize the governing equations in the annulus domain using a uniform staggered grid which is required in finite difference methods. Considering hydrodynamically and thermally fully developed conditions, the effects of different physical parameters such as eccentricity, Dean number, curvature, Prandtl number on the flow field and thermal characteristics at different thermal boundary conditions are investigated in detail. It is also shown that in contrast to straight eccentric annuli, heat transfer rates can be augmented in the eccentric curved annuli comparing with the straight concentric annuli at the large dean numbers.     

Thermal-diffusion and diffusion-thermo effects on combined heat and mass transfer of a steady MHD convective and slip flow due to a rotating disk with viscous dissipation and Ohmic heating

Thermo-diffusion (Soret effect) and diffusion-thermo (Dufour effect) effects on combined heat and mass transfer of a steady hydromagnetic convective and slip flow due to a rotating disk in the presence of viscous dissipation and Ohmic heating is investigated. The partial differential equations governing the problem under consideration have been transformed by a similarity transformation into a system of ordinary differential equations which are solved numerically by applying the shooting method. For fluids of medium molecular weight (H₂, air), profiles of the dimensionless velocity, temperature and concentration distributions are shown graphically for various values of slip parameter γ, magnetic field parameter M, Eckert Ec, Schmidt Sc, Dufour Du and Soret Sr numbers. Finally, numerical values of physical quantities, such as the local skin friction coefficient, the local Nusselt number and the local Sherwood number are presented in tabular form.     

Effects of a flow disturbing plate on pool boiling heat transfer

Effects of width and location of a flow disturbing circular plate on nucleate pool boiling heat transfer of water at atmospheric pressure have been investigated experimentally. Through the tests, changes in the degree of intensity of liquid agitation and its effect on heat transfer on a heated tube have been analyzed. According to the results, the plate changes fluid flow around the tube as well as heat transfer coefficients on the tube. It is identified that plate width changes the rate of circulating flow whereas its location changes the growth of active agitating flow. Moreover, flow chugging was observed at the downside of the plate.     

哥氏力对旋转方通道内流动与换热的影响

在雷诺数亿为6000,旋转数助为0～0．26内,数值模拟了旋转光滑径向出流通道的内流动与换热分布,分析了哥氏力对旋转管流的作用机理。计算结果表明,切向哥氏力推动了通道截面内的双涡二次流,径向哥氏力则使得近侧壁流体加速和中心流体减速。换热计算结果从定性趋势上吻合公开文献中的实验现象。反映了旋转附加力的基本影响规律。