Conjugate heat transfer on a non-isothermal rotating disc

A derivation of the conjugation criterion for a rotating disc is reported. Characteristics of conjugate heat transfer on a single disc and in a cavity formed by two discs, one rotating and the other stationary, are analysed.     

Effect of slip boundary condition on flow and heat transfer of a double fractional Maxwell fluid

The purpose of the present paper is to investigate the flow and heat transfer of a double fractional Maxwell fluid with a second order slip model. The fractional governing equations are solved numerically by using the finite difference method. By comparing the analytical solutions of special boundary conditions, the validity of the present numerical method is examined. The effects of the two slip parameters and the fractional parameters on the velocity and temperature distribution are presented graphically and discussed. The results reveal that the fractional Maxwell fluid exhibits a stronger viscosity or elasticity for different fractional parameters, and the oscillation phenomenon will gradually decrease as expected with an increase in slip parameters.     

Casson fluid flow and heat transfer over a nonlinearly stretching surface

A boundary layer analysis is presented for non-Newtonian fluid flow and heat transfer over a nonlinearly stretching surface. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. By using suitable transformations, the governing partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations. Numerical solutions of these equations are obtained with the shooting method. The effect of increasing Casson parameter is to suppress the velocity field. However the temperature is enhanced with the increasing Casson parameter.     

Turbulence in a Maxwell fluid

Three-dimensional homogeneous isotropic turbulence is formulated in terms of a discrete stochastic process in Fourier space. The time-dependent joint probability distribution of the stochastic Fourier modes is governed by a multivariate master equation. It is demonstrated that the characteristic functional of the stochastic process obeys the Hopf functional equation. As a first application of the method stochastic simulations of the Burgers's turbulence model are performed and shown to yield the expected energy spectrum.     

竖直细圆管中超临界氮的对流换热研究

在内径为2mm的竖直细圆管内进行了向上流动的超临界对流换热实验。通过实验发现,质量流量、进口温度对壁面温度分布以及压降有很大影响;并讨论了换热发生增强和恶化的原因;用浮升力和热加速准则解释了其中的一些热流体现象。并基于FLUENT软件进行了数值计算,与实验结果进行比较,分析表明,数值计算预测壁面温度分布和压降有一定的适用性。     

Variable fluid properties and variable heat flux effects on the flow and heat transfer in a non-Newtonian Maxwell fluid over an unsteady stretching sheet with slip velocity

The effects of variable fluid properties and variable heat flux on the flow and heat transfer of a non-Newtonian Maxwell fluid over an unsteady stretching sheet in the presence of slip velocity have been studied. The governing differential equations are transformed into a set of coupled non-linear ordinary differential equations and then solved with a numerical technique using appropriate boundary conditions for various physical parameters. The numerical solution for the governing non-linear boundary value problem is based on applying the fourth-order Runge-Kutta method coupled with the shooting technique over the entire range of physical parameters. The effects of various parameters like the viscosity parameter, thermal conductivity parameter, unsteadiness parameter, slip velocity parameter, the Deborah number, and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. Comparison of numerical results is made with the earlier published results under limiting cases.     

Boundary layer flow and heat transfer of a Casson fluid past a symmetric porous wedge with surface heat flux

The aim of this paper is to investigate numerically the boundary layer forced convection flow of a Casson fluid past a symmetric porous wedge. Similarity transformations are used to convert the governing partial differential equations into ordinary ones. With the help of the shooting method, the reduced equations are then solved numerically. Comparisons are made with the previously published results in some special cases and they are found to be in excellent agreement with each other. The results obtained in this study are illustrated graphically and discussed in detail. 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. Fluid velocity is suppressed with the increase of suction. The skin friction decreases with the increasing value of Casson fluid parameter. It is found that the temperature decreases as the Prandtl number increases and thermal boundary layer thickness decreases with the increasing value of Prandtl number. A significant finding of this investigation is that flow separation can be controlled by increasing the value of the Casson fluid parameter as well as by increasing the amount of suction.     

MHD swirling flow and heat transfer in Maxwell fluid driven by two coaxially rotating disks with variable thermal conductivity

We develop a mathematical modeling for an electrically conducting non-Newtonian Maxwell fluid flow occurring between two coaxially parallel stretchable rotating disks at constant distant apart. The pressure and heat transfer analysis is carried out subject to the effects of axial magnetic field and temperature dependent thermal conductivity. The stretching and rotating rates of both disks are assumed different from each other. The two diverse phenomena, such as, when both disks are rotating with different angular velocities in the same as well as in the opposite directions are discussed. The similarity procedure adopted by von Kármán is utilized to reduce the governing momentum and energy equations into nonlinear ordinary differential equations. The solution of the governing problem is obtained numerically using bvp4c scheme in Matlab. The effects of active parameters including stretching rates, Deborah number, magnetic number, Prandtl number, thermal conductivity parameter and Reynolds number are examined for same as well as opposite rotation direction for radial, azimuthal, and axial flows, pressure and temperature fields. The classical flow pattern happening between the disks is significantly altered by the stretching action which is a main physical significances of this study. The azimuthal flow is observed higher for the same direction of disks rotation as compared to opposite disks rotation. The pressure field drops near the lower disk with increasing values of Reynolds number. The role of thermal conductivity parameter is quite useful to enhance the fluid temperature.     

Maxwell stress in fluid mixtures

We examine the structure of Maxwell stress in binary fluid mixtures under an external electric field and discuss its consequence. In particular, we show that, in immiscible blends, it is intimately related to the statistics of domain structure. This leads to a compact formula, which may be useful in the investigation of electrorheological effects in such systems. The stress tensor calculated in a phase separated fluid under a steady electric field is in a good agreement with recent experiments.     

Microscale heat transfer in a free jet against a plane surface

A new two-layer model has been proposed to study microscale heat transfer associated with a developing flow boundary layer. As an example, a cold, microscale film of liquid impinging on an isothermal hot, horizontal surface has been investigated. The boundary layer is divided into two regions: a micro layer at microscale away from the surface and a macro layer at macroscale away from the surface. An approximate solution for the velocity and temperature distributions in the flow along the horizontal surface is developed, which exploits the hydrodynamic similarity solution for microscale film flow. The approximate solution may provide a valuable basis for assessing microscale flow and heat transfer in more complex settings.     

Enhancement of transient heat transfer at boiling on a plate surface with low thermoconductive coatings

An experimental study of transient cooling in liquid nitrogen of strongly overheated copper plate coated with a low thermoconductive coating with thickness δ from 0.09 to 0.67 mm was performed. It is shown that the low thermoconductive coating has a significant effect on the character of temperature curves and total time of plate cooling. It was revealed that the most significant decrease in the time of plate cooling by the factor of 2.6 is achieved for the thickness of the low thermoconducting layer of 0.09 mm as compared to the case without coating.     

Dynamics of explosive boiling and third heat transfer crisis at subcooling on a vertical surface

Results of experimental studies on dynamics of explosive boiling and third heat transfer crisis under the conditions of liquid subcooling are presented for the vertical arrangement of the heat-transfer surface. Acetone was used in experiments at the pressure in the working volume from 20 to 46 kPa and subcooling from 0 to 20 K. The studied processes were recorded. Data on the velocity of evaporation front propagation at liquid subcooling were obtained. These data are compared with the results of calculations according to the models available in the literature. The effect of liquid subcooling on the regions of regime parameters corresponding to explosive boiling and third heat transfer crisis is studied.     

Exact solutions for the flow of Casson fluid over a stretching surface with transpiration and heat transfer effects

The effects of transpiration on forced convection boundary layer non-Newtonian fluid flow and heat transfer toward a linearly stretching surface are reported.The flow is caused solely by the stretching of the sheet in its own plane with a velocity varying linearly with the distance from a fixed point.The constitutive relationship for the Casson fluid is used.The governing partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations by using similarity transformations.Exact solutions of the resulting ordinary differential equations are obtained.The effect of increasing Casson parameter,i.e.,with decreasing yield stress(the fluid behaves as a Newtonian fluid as the Casson parameter becomes large),is to suppress the velocity field.However,the temperature is enhanced as the Casson parameter increases.It is observed that the effect of transpiration is to decrease the fluid velocity as well as the temperature.The skin-friction coefficient is found to increase as the transpiration parameter increases.     

Some duct flows of a fractional Maxwell fluid

The aim of this paper is to establish the analytical solutions corresponding to two types of unsteady flows of fractional Maxwell fluid in a duct of rectangular cross-section. The fractional calculus approach is used in solving the problems. With the help of the methods of separation of variables and Laplace transforms, the expressions for the velocity field and the volume flux are presented under series forms in terms of the generalized G functions. Similar solutions for Newtonian and ordinary Maxwell fluids, performing the same motions, are also obtained as the limiting cases of our solutions. Furthermore, the influence of pertinent parameters on the flows is delineated and appropriate conclusions are drawn.     

Accelerated simulation of heat transfer in magnetic fluid hyperthermia

We have created a fast algorithm for calculating the temperature profile in a living tissue treated by magnetic fluid hyperthermia. Our algorithm solves an equation by the finite difference method. This equation includes the “heat sink” and “K-effective” effects. The algorithm need not an initial solution and it has the peculiarity that it makes a recursive division of the network, reducing thus the calculation period 5–9 times.     

Convection in thick and in thin fluid layers with a free surface – The influence of evaporation

Convective systems are examined by stability analysis as well as numerical solutions of the hydrodynamic basic equations in three spatial dimensions. Instabilities caused by surface tension gradients (Marangoni effect) are analyzed. The effect of evaporation of a volatile oil is studied by a two-layer system as well as by means of an effective Biot number. In thin fluid layers (a few 100 nm), an instability caused by the interaction between free surface and solid substrate manifests itself in form of surface deformation. We discuss this situation using the lubrication approximation. Special emphasis is layed on the influence of evaporation which may stabilize the system and which may lead to interesting new periodic structures.     

Model for density variation at a fluid surface

A fluid model with freely propagating longitudinal density waves is modified by the imposition of an external field. A relation between the resulting density inhomogeneity and the applied potential is obtained, depending only upon the uniform fluid pair distribution function. This is solved for a container-bounded fluid. The resulting surface density profiles for classical and zero-temperature Bose hard-sphere fluids compare very well with numerical experiments.Supported in part by U.S. ERDA, Contract No. E(11-1)-3077.Based on a talk given at Johns Hopkins Physics Colloquium, November 1974.