Flow and heat transfer in a rotating enclosure with axial throughflow

An analysis is made of the fluid flow and heat transfer processes in a circular cylindrical enclosure rotating about its own axis. A coolant is passed through the enclosure, entering and leaving through centrally located apertures in the end walls. This configuration is intended as a model of rotating enclosures in devices such as gas turbines and air compressors. The Navier-Stokes and energy equations were solved by a finite-difference formulation which can accommodate either steady or transient conditions. Buoyancy forces associated with the rotational body forces were included in some cases. All solutions were performed for laminar flow. For the parameter ranges investigated it was found that rotation inhibited the recirculating motion within the enclosure and thereby decreased the heat transfer relative to that for the stationary enclosure. Buoyancy further reduced the heat transfer owing to the break up of residual circulatory motions in the outer portion of the enclosure. Still stronger buoyancy brought about a slight increase in the heat transfer. The coolant flow was confined to a corridor adjacent to the axis of the enclosure, and there was no mixing between the coolant and the fluid in the enclosure proper.     

An experimental analysis of the flow pattern in heat exchangers with an egg carton configuration (parallel,convergent and divergent cases)

An experimental analysis about the flow patterns that appear in the channel formed between two corrugated plates with an egg carton configuration is reported. The types of flow instabilities caused by the corrugated plates are identified and described by means of flow visualization experiments, and photographic sequences illustrate the flow features present for each case. The influence on flow instabilities of Reynolds number, phase angle, convergence/divergence angle and spacing between corrugated plates is investigated. The corrugated plates are set divergent and convergent in order to investigate if recirculations are broken by chaotic advection. The improvement of heat transfer in the laminar regime has become an essential task in many applications and therefore the experiments are conducted in this regime.The corrugated plates geometry provides two main advantages over the conventional plane plates: the recirculation zones observed in the longitudinal direction and the three-dimensionality of the flow, i.e. the recirculations reduce the thermal resistances while the three-dimensionality of flow generates a better mixing and a more uniform temperature distribution.This experimental study contributes to the general knowledge on the subject being the first that addresses the analysis of convergent and divergent egg carton plates. It is expected that the results presented here will shed some light as to advantageously use these geometries in the near-future heat exchangers. (Because of the improve chaotic mixing in divergent corrugated plates, this configuration may be a good option to improve heat exchangers performance, because a better mixing is always related to the presence of core fluid near exchange surfaces, and consequently an increase in temperature gradients and heat transfer.)     

Direct Numerical Simulation of particulate flow with heat transfer

Numerical simulations of heat transfer in non-isothermal particulate flows are important to better understand the flow pattern. The complexity of numerical algorithms coupling the heat and mass transfer and the considerable computational resources required limit the number of such direct simulations that can be reasonably performed. We suggest a Distributed Lagrange Multiplier/Fictitious Domain (DLM/FD) method to compute the temperature distribution and the heat exchange between the fluid and solid phases. The Boussinesq approximation is considered for the flow/temperature fields coupling. We employ a Finite Element Method (FEM) to solve the fluid flow conservation equations for mass, momentum and energy. The motion of particles is computed by a Discrete Element Method (DEM). On each particle, heat transfer is solved using a FEM. For each class of particles, we generate a single FEM grid and translate/rotate it at each time step to match the physical configuration of each particle. Distributed Lagrange multipliers for both the velocity and temperature fields are introduced to treat the fluid/solid interaction. This work is an extension of the method we proposed in Yu et al. (2006). Two two-dimensional (2D) test cases are proposed to validate the implementation by comparing our computational results with those reported in the literature. Finally, the sedimentation of a single sphere in a semi-infinite channel is presented and the results are discussed.     

Pattern analysis of viscous oscillation in a shear flow induced by an exothermic reaction

An investigation is made of oscillatory phenomenon induced by an exothermic reaction. This oscillatory phenomenon occurs in a very thin mixing layer between two miscible and reacting fluids. A qualitative model based on the interaction among reaction, molecular momentum transfer, molecular heat transfer, molecular mass transfer and forced convective transfer was proposed by Kuroda and Ogawa [1994. Nonlinear waves in a shear flow with a diffusive exothermic reaction and its qualitative reasoning. Chem. Eng. Sci. 49(16), 2699-2708]. It is experimentally shown in the present study that the oscillatory patterns change in the flow direction. In the upstream area where oscillatory patterns are nearly straight stripes, effects of viscosity on those stripes are investigated. In the downstream area where stripes are wavy and disordered, fractal analysis is introduced to investigate the relationship between the transition of oscillatory flow patterns and process factors, i.e. the viscosity ratio, the entire viscosity, flow rate and the flow rate ratio. Fractal analysis is also applied to temperature oscillation, and it is confirmed that the characteristic patterns of oscillation become obscure as the entire viscosity increases. The entire viscosity is an important factor for controlling both oscillatory patterns of flow and temperature in this reactive flow system.     

Flow and heat transfer over a generalized stretching/shrinking wall problem—Exact solutions of the Navier-Stokes equations

In this paper, we investigate the steady momentum and heat transfer of a viscous fluid flow over a stretching/shrinking sheet. Exact solutions are presented for the Navier-Stokes equations. The new solutions provide a more general formulation including the linearly stretching and shrinking wall problems as well as the asymptotic suction velocity profiles over a moving plate. Interesting non-linear phenomena are observed in the current results including both exponentially decaying solution and algebraically decaying solution, multiple solutions with infinite number of solutions for the flow field, and velocity overshoot. The energy equation ignoring viscous dissipation is solved exactly and the effects of the mass transfer parameter, the Prandtl number, and the wall stretching/shrinking strength on the temperature profiles and wall heat flux are also presented and discussed. The exact solution of this general flow configuration is a rare case for the Navier-Stokes equation.     

Unsteady heat and mass transfer in MHD flow over an oscillatory stretching surface with Soret and Dufour effects

In this paper, we study the unsteady coupled heat and mass transfer of two-dimensional MHD fluid over a moving oscillatory stretching surface with Soret and Dufour effects. Viscous dissipation effects are adopted in the energy equation. A uniform magnetic field is applied vertically to the flow direction. The governing equations are reduced to non-linear coupled partial differential equations and solved by means of homotopy analysis method （HAM）. The effects of some physical parameters such as magnetic parameter, Dufour number, Soret number, the Prandtl num- ber and the ratio of the oscillation frequency of the sheet to its stretching rate on the flow and heat transfer characteristics are illustrated and analyzed.     

Mathematical simulation of radial heat transfer in packed beds by pseudohomogeneous modeling

Uniform flow regime and constant effective thermal conductivity inside packed beds are commonly accepted in the evaluation of the fluid dynamics and heat transfer in such systems.However,several authors have confirmed the presence of an oscillatory velocity profile caused by the effective contribution of porosity profile in the fluid dynamic behavior of packed beds,which directly influences the heat transfer inside the beds.This paper describes the application of a pseudo-homogeneous mathematical ...     

The influence of rotation on turbulent flow and heat transfer in an annulus between independently rotating tubes

Experimental and numerical investigations of turbulent flow and heat transfer have been performed in a concentric annulus between independently rotating tubes. Numerical predictions, applying a Reynolds stress turbulence model, are compared with experimental fluid flow and heat transfer results for the case of a heated outer tube and an adiabatic inner tube. Compared to the above mentioned boundary conditions for the conservation equation of energy, differences in heat transfer in case of a heated inner tube and an adiabatic outer one, are examined by analysis, applying a mixing length turbulence model. Numerical investigations with both kinds of models about the influence of annulus radius ratio make evident that due to different superimpositions of centrifugal force and additional shear stress there is a wide variation of effects on fluid flow and heat transfer caused by the rotation of the inner and the outer tube.     

A two-phase,two-component model for natural convection in a porous medium

A numerical study of natural convection in a two-phase, two-component flow in a porous medium heated from below is presented. Interphase mass and energy transfer, latent heat and bouyancy effects are major physical features. This study extends earlier studies of natural convection based on single-phase, saturated porous medium models. The appearance of two-phase heat pipe zones in the flow has a marked effect on the fluid and heat flows as well as on the performance of the numerical methods. The numerical techniques for handling phase change, Jacobian construction and time step selection are discussed.     

振荡管流换热的理论解

本文从流体在管内振荡的运动方程和流体及管壁的能量方程出发,经过变量转换对常微分方程组进行求解,得到了计及管壁影响的振荡流体轴向换热的一般理论解。由这解,可以导出各种特殊条件下的表达式,包括已有的各种解析解。本解经数字化而制成各种图线,它们与已有的实验数据基本吻合。