BEM and FEM based numerical simulations for biomagnetic fluid flow

We investigate numerically the biomagnetic fluid flow between parallel plates imposed to a magnetic source placed below the lower plate. The biomagnetic fluid is assumed to be Newtonian, viscous, incompressible, electrically nonconducting, and has magnetization varying linearly with temperature and magnetic field intensity. Both steady and unsteady, laminar, two-dimensional biomagnetic fluid flow equations taking into care the heat transfer between the plates are solved using both finite element and dual reciprocity boundary element methods. Treatment of nonlinear terms by using only the fundamental solution of the Laplace equation, and discretization of only the boundary of the region are the advantages of dual reciprocity boundary element method giving small algebraic systems to be solved at a small expense. Finite element method is capable of giving very accurate results by discretizing the region affected by the magnetic source very finely, but it results in large sized algebraic systems requiring high computational cost. The results indicate that the flow is appreciably affected with the presence of magnetic source in terms of vortices at the magnetic source area. The lengths of the vortices, and temperature increase with an increase in the intensity of the magnetic field.     

Entropy generation in the flow system generated in between two parallel plates due to bivertical motion of the top plate

Thermodynamic irreversibility in the flow system provides information on the energy and power losses in the system. Minimization of entropy generation in the flow system enables for the parametric optimization of the system operation. In the present study, parallel plates, in between, filled with the fluid are considered. The fluid motion resulted from the bi-vertical compression of the top plate of the parallel plates is examined. The entropy generation rate in the flow system is formulated after considering the constant movement of the top plate, constant applied load, and the combination of the constant velocity and applied load to the top plate. The optimum operating conditions related to the fluid motion in between the parallel plates is determined through the entropy analysis. It is found that the combination of the constant velocity and the constant applied load resulted in the low entropy generation rate.     

The critical conditions of the thermal regime in a generalized couette flow

We examine the nonisothermal steady-state flow of a Newtonian fluid between two parallel plates with consideration of the energy dissipation and in the assumption of a hyperbolic relationship between viscosity and temperature under various temperature boundary conditions. It is assumed that the upper plate is moving at a constant speed and that there is a pressure difference across the space between the plates in the direction of plate motion.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 1, pp. 86–94, July, 1969.     

Three-dimensional aspects of boundary-layer transition

A review is made in this paper of the three-dimensional nature of instability leading to transition in a two-dimensional flow on a flat plate (Blasius boundary layer) or between parallel plates (plane Poiseuille flow), with additional reference to the flow on a concave wall. Instability and transition in a three-dimensional boundary layer are then reviewed, with particular attention to the flow due to a rotating disk and the flow perturbed by a three-dimensional roughness element on a flat plate. The growth of a turbulent spot is discussed as a phenomenon exhibiting a similar feature of instability. Only the flow of an incompressible fluid is considered.     

Laminar flow of a non-Newtonian fluid in channels with wall suction or injection

The one-dimensional approximate equation in the rectangular Cartesian coordinates governing flow of a non-Newtonian fluid confined in two large plates separated by a small distance of h, with the upper plate stationary while the lower plate is uniformly porous and moving in the x-direction with constant velocity, is derived by accounting for the order of magnitude of terms as well as the accompanying approximations to the full-blown three-dimensional equations by using scaling arguments, asymptotic techniques and assuming the cross-flow velocity is much less than the axial velocity. The one-dimensional governing equation for a power-law fluid flow confined between parallel plates, with the upper plate is stationary and the bottom plate subjected to sudden acceleration with a constant velocity in the x-direction and uniformly porous, is solved analytically for a Newtonian fluid case (n = 1) and numerically for various values of power-law index to determine the transient velocity and thus the overall transient velocity distribution. The effects of mass suction/injection at the porous bottom plate on the flow of non-Newtonian fluids are examined for various values of time and power-law index. The results obtained from the present analysis are compared with the data available in the literature.     

Some peculiarities of the asymmetric Graetz problem

A numerical simulation and an analysis of the steady state forced convection heat transfer with plane laminar flow confined by two parallel plates that are kept at constant but different temperatures are presented. We name this heat transfer configuration shortly the asymmetric Graetz problem. The essential features of the asymmetric in comparison to the symmetric Graetz problem are the reversal of the heat flux and the jump of the Nusselt number from positive to negative region at the plate having the temperature closer to the fluid inlet temperature. These phenomena occur at different axial positions, which depend on the thermal asymmetry and the fluid inlet conditions. The numerical results agree excellently with an analytical solution obtained in terms of Kummer confluent hypergeometric function and Hermite polynomials.     

O-Sepa选粉机转子结构对流场特性的影响

针对O-Sepa选粉机转子底部的不同结构进行分析和数值建模,采用FLUENT软件对其进行计算流体动力学的分析,探讨底部结构对选粉机流场特性的影响,分别对4种不同底部结构的O-Sepa选粉机模型进行相关分析和计算流体动力学的模拟仿真。结果表明:不同底部结构其底盘周围的流场也不同,对环形区域的流场也有一定的影响。     

On heat transfer to pulsatile flow of a viscoelastic fluid

Summary A study is made of a problem of heat transfer to pulsatile flow of a viscoelastic fluid between two parallel plates of which the upper one is at a temperature higher than the lower one. The solutions for the steady and the fluctuating temperature distributions are obtained. The rate of heat transfer at the plates is also calculated. Numerical solutions are discussed with graphical representations. It is shown that the elasticity of the fluid significantly increases the temperature in the boundary layers near the plates. The magnitude of heat transfer at the plates is also greatly affected by the elasticity of the fluid and the Eckert number.     

三个关键几何参数对人字形波纹钎焊板式换热器换热性能影响的分析

以水-水热交换器为例,以CFD模拟软件为手段,以κ-ε模型为基础构建人字形波纹板式换热器模型,并系统分析波纹倾角、波纹深度、波纹间距这3个重要几何参数对换热器内部温度场、压力场、流场及平均努塞尔数和流动阻力的影响。研究结果表明,触点是板间换热效果最好的点,触点的扰流作用使流体在触点周围湍流程度最高,传热得到强化,这也是板式换热器内流体在雷诺数较低时发生湍流的主要原因;另一方面,流体经过触点后压力损失较大,是产生阻力损失的主要原因。波纹倾角是最重要的一个影响参数,最优波纹倾角在60°附近,此时换热效果较好而阻力尚未达到最大;波纹深度增加,平均努塞尔数增大,换热效果趋于好转,板间压力降也逐渐降低。但随着波纹深度的增加,结垢的倾向也会增加,因此较为合理的波纹深度应该在4～5mm之间;在给定的边界条件下,通过计算所得的波纹间距与波纹深度之比在3～4范围内时换热器性能较好。     

Impact of plate design on the performance of welded type plate heat exchangers for sorption cycles

Numerical and experimental analysis was carried out to examine the heat transfer and pressure drop characteristics of welded type plate heat exchangers for absorption application using Computational Fluid Dynamics (CFD) technique. The simulation results based on CFD are compared with experimental results. A commercial CFD software package (FLUENT) has been used to predict the characteristics of heat transfer, pressure drop and flow distribution within the plate heat exchangers. In this paper, a welded plate heat exchanger with a plate of chevron embossing type was tested by controlling mass flow rate, solution concentration, and inlet/outlet temperatures. The working fluid is H₂O/LiBr solution with the LiBr concentration of 54–62% in mass. The numerical simulation examines the internal flow patterns, temperature distribution and the pressure distribution within the channel of the plate heat exchanger. Three plates of embossing types; chevron embossing, elliptic and round, are proposed and simulated in this paper. The simulation results show reasonably good agreement with the experimental results. Also, the numerical results show that the plate with the elliptical shape gives better performance than the plate of the chevron shape from the viewpoints of heat transfer and pressure drop.     

Thermal radiation effects on magnetohydrodynamic mixed convection flow of a micropolar fluid past a continuously moving semi-infinite plate for high temperature differences

Summary An analysis is presented to study the effect of radiation on magnetohydrodynamic mixed convective steady laminar boundary layer flow of an optically thick electrically conducting viscous micropolar fluid past a moving semi-infinite vertical plate for high temperature differences. A uniform magnetic field is applied perpendicular to the moving plate. The density of the micropolar fluid is assumed to reduce exponentially with temperature. The usual Boussinesq approximation is neglected because of the high temperature differences between the plate and the ambient fluid. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The resulting governing equations are transformed using a similarity transformation and then solved numerically by applying an efficient technique. The effects of radiation parameter R, magnetic parameter M, couple parameter Δ and density/temperature parameter n on the velocity, angular velocity and temperature profiles as well as the local skin friction coefficient, wall couple stress and the local Nusselt number are presented graphically and in tabular form.     

Low-temperature solar-plate-assisted heat pump: A developed design for domestic applications in cold climate

Solar energy and wasted heat in buildings are capable of supplying enough energy to answer the total demand of energy in dwellings. However, fluctuation in fuel prices and gas emissions are the main driving forces behind efforts. In this experimental study, a direct expansion solar-assisted heat pump system (DX-SAHP) using a bare ternary “retrofitted collectors with black paint” is investigated at the laboratory with a solar simulator and tested for domestic hot water (DHW) and space heating under quasi-static conditions. Unglazed solar collector absorber plates are used as an evaporator, and these are composed of two aluminium plates which are placed externally whilst another plate is mounted internally in the loft space of the house, where operating liquid from the heat pump is directly evaporated. The influence of outside temperature, solar irradiation and/or waste heat on the heating performance of DX-SAHP is investigated. The impact of the parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid is also assessed. Preliminary results elucidate that the refrigeration cycle can be a promising substitute for space heating and hot water when compared to the heat pump systems. This design technique results in higher solar collector/evaporator efficiency and lower system losses due to low evaporating temperature.     

Dispersion analysis of stabilized finite element methods for acoustic fluid interaction with Reissner–Mindlin plates

The application of stabilized finite element methods to model the vibration of elastic plates coupled with an acoustic fluid medium is considered. A complex‐wavenumber dispersion analysis of acoustic fluid interaction with Reissner–Mindlin plates is performed to quantify the accuracy of stabilized finite element methods for fluid‐loaded plates. Results demonstrate the improved accuracy of a recently developed hybrid least‐squares (HLS) plate element based on a modified Hellinger–Reissner functional, consistently combined with residual‐based methods for the acoustic fluid, compared to standard Galerkin and Galerkin gradient least‐squares plate elements. The technique of complex wavenumber dispersion analysis is used to examine the accuracy of the discretized system in the representation of free waves for fluid‐loaded plates. The influence of fluid and coupling matrices resulting from consistent implementation of pressure loading in the residual for the plate equation is examined and clarified for the different finite element approximations. Copyright © 2001 John Wiley & Sons, Ltd.     

Free convection heat transfer to steady radiating non-Newtonian MHD flow past a vertical porous plate

Non-Newtonian fluid motion generated by a vertical porous hot plate in the presence of a transverse magnetic field is studied when viscous and ohmic dissipations are significant. When the temperature of the plate is very large, a general differential approximation for the radiative flux enables the asymptotic flow, valid far away from the tips of the plate, to reduce to a set of nonlinear and coupled ordinary differential equations. The solutions of these differential equations are studied for both small and large values of the absorption coefficient. The temperature, velocity and magnetic field distributions are discussed quantitatively. A primary conclusion of the analysis is that the distributions of temperature, velocity and magnetic field are much larger for a fluid with a large absorption coefficient than for a fluid with a small absorption coefficient.     

Hydromagnetic couette flow of an Oldroyd-B fluid in a rotating system

The motion of electrically conducting, Oldroyd-B and incompressible fluid between two infinitely extended non-conducting parallel plates under a uniform transverse magnetic field, fixed relative to the fluid has been considered. The lower plate is at rest and the upper plate is oscillating in its own plane. The governing partial differential equation of this problem, subject to boundary conditions are solved analytically. The expressions for the steady and unsteady velocity fields for the conducting Oldroyd-B fluid are obtained. The graphs are plotted for different values of dimensionless parameters of the problem and the analysis of the results showed that the flow field is appreciably influenced by the applied magnetic field, the rotation and the material parameters of the fluid.     

Unsteady hydromagnetic couette flow in a rotating system

Unsteady hydromagnetic flow of an electrically conducting viscous incompressible fluid in a rotating system under the influence of a uniform transverse magnetic field is investigated when one of the plates is set into motion with the time dependent velocity $\text{U(t)}$ in its own plane. Two cases of interest, namely, impulsive start as well as accelerated start of the moving plate are discussed. The asymptotic behaviour of the solution is also analysed for both small and large time to highlight the transient approach to the final steady state and effects of rotation parameter as well as Hartmann number. The shear stresses at the moving plate due to the primary and secondary flows are derived in both cases. It is found that the shear stress components due to the primary flow decrease, whereas that due to the secondary flow increase with the increase in rotation parameter.     

Performance of extended surface from a cryocooler for subcooling liquid nitrogen by natural convection

Natural convection of subcooled liquid nitrogen under a horizontal flat plate is measured by experiment. This study is motivated mainly by our recent development of cryocooling systems for HTS power devices without any forced circulation of liquid nitrogen. Since the cold surface of a GM cryocooler is very limited, the cooling plate immersed in subcooled liquid nitrogen is thermally anchored to the cryocooler located at the top in order to serve as an extended surface. A vertical plate generating uniform heat flux is placed at a given distance under the cooling plate so that subcooled liquid may generate cellular flow by natural convection. The temperature distributions on the plates and liquid are measured during the cool-down and in steady state, from which the heat transfer coefficients are calculated and compared with the existing correlations for a horizontal surface with uniform temperature. A fair agreement is observed between two data sets, when the heat flux is small or the plate temperatures are relatively uniform in horizontal direction. Some discrepancy at higher heat flux is explained by the cellular flow pattern and the fin efficiency of the extended surface, resulting in the non-uniformity of the horizontal plate.     

Experimental study of dynamic buckling of plates under fluid–solid slamming

This paper describes the experimental investigation of the elastic–plastic dynamic buckling properties of rectangular plates under in-plane fluid–solid slamming. Based on the observation of elastic–plastic dynamic response characteristics of the plates, a dynamic buckling criterion and a dynamic yielding criterion are defined. The corresponding critical impulse are determined from the experimental results for each tested plate. The effect of different boundary conditions on the elastic–plastic dynamic buckling properties of plates is also examined. The results indicate that dynamic buckling always takes place elastically for the types of rectangular plates tested under fluid–solid slamming. The dynamic buckling modes of the plates are governed by the plate fundamental transverse free vibration mode. It is also found that boundary conditions strongly affect the dynamic buckling properties of plates subjected to fluid–solid slamming loads. Strengthening plate boundary constraint is a very effective way to enhance the plates’ ability to resist dynamic buckling.     

An alternative approach to study periodically fully-developed flow and heat transfer problems subject to isothermal heating conditions

Periodically fully-developed flow (PFD) and heat transfer in a channel subject to isothermal conditions must either be formulated as an eigenvalue problem and solved iteratively or the PFD solution must be extracted as a part of developing flow (DF) solution by considering the entire flow domain. The first approach is mathematically complex and the second approach is computationally inefficient. In this work, an alternative approach is proposed wherein a PFD flow solution is used as an input to all modules of a DF domain and the PFD temperature field is extracted by monitoring variation in module-averaged Nusselt number. The proposed method was validated by comparing results obtained by the proposed method with results in the literature for three sample problems: flow between parallel plates, flow over round tubes in parallel plate channel, and flow in a parallel plate channel with staggered plate fins. Flow and energy equations were solved by using a control volume based finite element method in conjunction with SIMPLER algorithm. Results obtained by the proposed approach compared very favorably with the results published in the literature.     

Numerical solution of free convection micropolar fluid flow between two parallel porous vertical plates

The fully developed free convection micropolar fluid flow between two vertical porous parallel plates is studied in the presence of temperature dependent heat sources including the effect of frictional heating. The basic equations are solved using quasi-linearization finite difference technique with an error of order 0.5 × 10₋₆. The velocity, microrotation and temperature are displayed in graphs whereas the skin friction, couple stress and Nusselt numbers at the plates are shown in tables. It is noted that the couple stress on either plates increases numerically with increase in micropolar parameter. Also the Nusselt number follows the same pattern for a negative suction velocity.