Heat transfer in a porous saturated wavy channel with asymmetric convective boundary conditions

The viscous flow in a wavy channel with convective boundary conditions is investigated. The channel is filled with a porous viscous fluid. Two cases of equal and different external convection coefficients on the walls are taken into account. Effect of viscous dissipation is also considered. The governing equations are derived employing long wavelength and low Reynolds number approximations. Exact closed form solutions are obtained for the simplified equations. Important physical features for peristaltic flow caused by the wavy wave are pumping, trapping and heat transfer rate at the channel walls. These are discussed one by one in depth and detail through graphical illustrations. Special attention has been given to the effects of convective boundary conditions. The results show that for Bi1≠Bi2, there exists a critical value of Brinkman number Brc at which the temperatures of both the walls become equal. And, for Bi1>Bi2 and Br>Brc, the temperature of the cold wall exceeds the temperature of hot wall.

Novel wavelet-homotopy Galerkin technique for analysis of lid-driven cavity flow and heat transfer with non-uniform boundary conditions

In this paper, a brand-new wavelet-homotopy Galerkin technique is developed to solve nonlinear ordinary or partial differential equations. Before this investigation,few studies have been done for handling nonlinear problems with non-uniform boundary conditions by means of the wavelet Galerkin technique, especially in the field of fluid mechanics and heat transfer. The lid-driven cavity flow and heat transfer are illustrated as a typical example to verify the validity and correctness of this proposed technique. The cavity is subject to the upper and lower walls’ motions in the same or opposite directions.The inclined angle of the square cavity is from 0 to π/2. Four different modes including uniform, linear, exponential, and sinusoidal heating are considered on the top and bottom walls, respectively, while the left and right walls are thermally isolated and stationary.A parametric analysis of heating distribution between upper and lower walls including the amplitude ratio from 0 to 1 and the phase deviation from 0 to 2π is conducted. The governing equations are non-dimensionalized in terms of the stream function-vorticity formulation and the temperature distribution function and then solved analytically subject to various boundary conditions. Comparisons with previous publications are given,showing high efficiency and great feasibility of the proposed technique.

Similarity Solutions for Laminar Boundary Layer Flow of Darcian Fluid over Horizontal Plate with a Convective Boundary Condition

This paper considers the problem of hydrodynamics and thermal boundary layers of Darcy flow over horizontal surface embedded in a porous medium. The solutions of such problems for the cases of uniform surface temperature and variable surface temperature have been studied and analysed in many papers. This paper, however, attempts to find similarity solutions for the Darcy flow problem with a convective boundary condition at the plate surface. It is found that the solution is possible when the heat transfer coefficient is proportional to x–2/3. The numerical solutions thus obtained are analyzed for a range of values of the parameter characterizing the hot fluid convection process. Analytical expressions are provided for local surface heat flux and total surface heat transfer rate while the flow variables are discussed graphically.

Fourth-Order Compact Formulation for the Resolution of Heat Transfer in Natural Convection of Water-Cu Nanofluid in a Square Cavity with a Sinusoidal Boundary Thermal Condition

In the present work, we numerically study the laminar natural convection of a nanofluid confined in a square cavity. The vertical walls are assumed to be insulated, non-conducting, and impermeable to mass transfer. The horizontal walls are differentially heated, and the low is maintained at hot condition (sinusoidal) when the high one is cold. The objective of this work is to develop a new height accurate method for solving heat transfer equations. The new method is a Fourth Order Compact (F.O.C). This work aims to show the interest of the method and understand the effect of the presence of nanofluids in closed square systems on the natural convection mechanism. The numerical simulations are performed for Prandtl number ( ), the Rayleigh numbers varying between and for different volume fractions varies between 0% and 10% for the nanofluid (water + Cu).

Effects of viscous dissipation and Joule heating on the Couette and Poiseuille flows of a Jeffrey fluid with slip boundary conditions

In this article,we have presented the exact solutions of the Couette,Poiseuille and generalized Couette flows of an incompressible magnetohydrodynamic Jeffrey fluid between parallel plates through homogeneous porous medium.The effects of slip boundary conditions and heat transfer are considered.Viscous dissipation,radiation and Joule heating are also considered in the energy equation.The governing equations of the Jeffrey fluid flow are modeled in Cartesian coordinate system.Analytical solutions for the velocity and temperature the velocity and temperature profiles are studied and the results are presented through graphs.It Temperature behaves as a decreasing function due to the impact of Hartmann number,non-Newtonian parameter and slip parameter in all noted problems.

Unsteady boundary layer flow and heat transfer over an exponentially shrinking sheet with suction in a copper-water nanofluid

An analysis of unsteady boundary layer flow and heat transfer over an exponentially shrinking porous sheet filled with a copper-water nanofluid is presented.Water is treated as a base fluid.In the investigation,non-uniform mass suction through the porous sheet is considered.Using Keller-box method the transformed equations are solved numerically.The results of skin friction coefficient,the local Nusselt number as well as the velocity and temperature profiles are presented for different flow parameters.The results showed that the dual non-similar solutions exist only when certain amount of mass suction is applied through the porous sheet for various unsteady parameters and nanoparticle volume fractions.The ranges of suction where dual non-similar solution exists,become larger when values of unsteady parameter as well as nanoparticle volume fraction increase.So,due to unsteadiness of flow dynamics and the presence of nanoparticles in flow field,the requirement of mass suction for existence of solution of boundary layer flow past an exponentially shrinking sheet is less.Furthermore,the velocity boundary layer thickness decreases and thermal boundary layer thickness increases with increasing of nanoparticle volume fraction in both non-similar solutions.Whereas,for stronger mass suction,the velocity boundary layer thickness becomes thinner for the first solution and the effect is opposite in the case of second solution.The temperature inside the boundary layer increases with nanoparticle volume fraction and decreases with mass suction.So,for the unsteadiness and for the presence of nanoparticles,the flow separation is delayed to some extent.

Boundary Layer Flow of an Unsteady Dusty Fluid and Heat Transfer Over a Stretching Sheet with Non-Uniform Heat Source/Sink

An analysis has been carried out to study the effect of hydrodynamic laminar boundary layer flow and heat transfer of a dusty fluid over an unsteady stretching surface in the presence of non-uniform heat source/sink. Heat transfer characteristics are examined for two different kinds of boundary conditions, namely 1) variable wall temperature and 2) variable heat flux. The governing partial differential equations are transformed to system of ordinary differential equations. These equations are solved numerically by applying RKF-45 method. The effects of various physical parameters such as magnetic parameter, dust interaction parameter, number density, Prandtl number, Eckert number, heat source/sink parameter and unsteadiness parameter on velocity and temperature profiles are studied.

Unsteady Boundary Layer Flow and Heat Transfer Due to a Stretching Sheet by Quasilinearization Technique

In this paper, the problem of unsteady laminar boundary-layer flow and heat transfer of a viscous income-pressible fluid over stretching sheet is studied numerically. The unsteadiness in the flow and temperature is caused by the time-dependent stretching velocity and surface temperature. A similarity transformation is used to reduce the governing boundary-layer equations to couple higher order non-linear ordinary differential equations. These equations are numerically solved using quasi-linearization technique. The effect of the governing parameters unsteadiness parameter and Prandtl number on velocity and temperature profile is discussed. Besides the numerical results for the local skin friction coefficient and local Nusselt number are presented. The computed results are compared with previously reported work.

Computational fluid dynamics simulation of friction stir welding:A comparative study on different frictional boundary conditions

Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.

Comparative Numerical Analysis of Heat and Mass Transfer Characteristics in Sisko Al_(2)O_(3)-Eg and TiO_(2)-Eg Fluids on a Stretched Surface

In the current research,a thorough examination unfolds concerning the attributes of magnetohydrodynamic(MHD)boundary layer flow and heat transfer inherent to nanoliquids derived from Sisko Al_(2)O_(3)-Eg and TiO_(2)-Eg compositions.Such nanoliquids are subjected to an extending surface.Consideration is duly given to slip boundary conditions,as well as the effects stemming from variable viscosity and variable thermal conductivity.The analytical approach applied involves the application of suitable similarity transformations.These conversions serve to transform the initial set of complex nonlinear partial differential equations into a more manageable assembly of ordinary differential equations.Through the utilization of the FEM,these reformulated equations are solved,considering the specified boundary conditions.The outcomes attained are graphically depicted by means of plots and tables.These visual aids facilitate a comprehensive exploration of how diverse parameters exert influence over the distributions of velocity,temperature,and concentration.Furthermore,detailed scrutiny is directed towards the fluctuations characterizing pivotal parameters,viz.,Nusselt number,skin-friction coefficient,and Sherwood number.It is identified that the Nusselt number showcases a diminishing trend coinciding with increasing values of the volume fraction parameter(φ).This trend remains consistent regardless of whether the nanoliquid under consideration is Al_(2)O_(3)-Eg or TiO_(2)-Eg based.In contrast,both the skin-friction coefficient and Sherwood number assume lower values as the volume fraction parameter(φ)escalates.This pattern remains congruent across both classifications of nanoliquids.The findings of the study impart valuable insights into the complex interplay governing the characteristics of HMT pertaining to Sisko Al_(2)O_(3)-Eg and TiO_(2)-Eg nanoliquids along an extending surface.

MHD EYRING-PRANDTL FLUID FLOW WITH CONVECTIVE BOUNDARY CONDITIONS IN SMALL INTESTINES

In this paper, we have discussed the food movement in stomach with thermal bound- ary conditions. Eyring-Prandtl fluid model is considered. Formulation of the considered phenomena have been developed for both fixed and moving frame of references. Regular perturbation is used to find the solution of stream function, temperature profile and pressure gradient. Analysis has been carried out for velocity, ＂stream function, temper- ature, pressure gradient and heat transfer＂. Appearance of pressure gradient is quite complicated so to get the expression for pressure rise we have used numerical integra- tion. It is perceived that the velocity close to the channel walls is not same in outlook of the Eyrin^Prandtl fluid parameter taken as fl and Hartman number M. The velocity decreases by increasing β and M.

Freezing of Water in a Slab with Boundary Conditions of the Third Kind

Predictions for freezing heat transfer in a slab with convective boundary conditions at the cold surfaceare obtained from heat balance integral approximations, which consider conduction as the only modeof heat transfer in both the solid and liquid and consider durations of precooling and freezing in theheat transfer process. The thermal penetration dimensionless parameter or is presented to distinguishtwO cases of freezing, and analytical results for α≥ 1 are given in this paper. An experimental investigation on freezing of water is reported for comparison with the one-dimensional conduction model toshow that experimental modeling for freezing heat transfer with convective boundary conditions usingPeltter devices is feasible. The comparison also demonstrated that the freezing rate in this case wasdecreased by natural convection in the liquid just as freezing with boundary conditions of the first kindand phase change approximately proceeds linearly with time rather than with square root of time atthe initiation of freezing.

Heat transfer model for microwave hot in-place recycling of asphalt pavements

In order to solve for temperature fields in microwave heating for recycling asphalt mixtures, a two-dimensional heat transfer model for the asphalt mixtures within the heating range is built based on the theory of unsteady heat conduction. Four onedimensional heat transfer models are established for the asphalt mixtures outside the heating range, which are simplified into four half-infinite solids. The intensity of the radiation electric field is calculated through experiment by using heating water loads. It is suggested that the mathematical model of boundary conditions can be established in two ways, which are theoretical deduction and experimental reverse. The actual temperature field is achieved by fitting temperatures of different positions collected in the heating experiment. The simulant temperature field, which is solved with the Matlab PDE toolbox, is in good agreement with the actual temperature field. The results indicate that the proposed models have high precision and can be directly used to calculate the temperature distribution of asphalt pavements.

Mixed convective heat and mass transfer analysis for peristaltic transport in an asymmetric channel with Soret and Dufour effects

The present investigation addresses the simultaneous effects of heat and mass transfer in the mixed convection peristaltic flow of viscous fluid in an asymmetric channel. The channel walls exhibit the convective boundary conditions. In addition, the effects due to Soret and Dufour are taken into consideration. Resulting problems are solved for the series solutions. Numerical values of heat and mass transfer rates are displayed and studied. Results indicate that the concentration and temperature of the fluid increase whereas the mass transfer rate at the wall decreases with increase of the mass transfer Biot number. Furthermore, it is observed that the temperature decreases with the increase of the heat transfer Biot number.

Heat Transfer in Helical Coil Heat Exchanger

The research paper tends to review the effectiveness of helical coil in heat exchangers (HCHE). Heat exchanger is a device used in transferring thermal energy between two or more fluids or solid interfaces and a fluid, in solid particulates and a fluid at different temperatures and thermal contact. The author has concisely discussed the helical coil in heat exchanger at different shapes and conditions and compared the HCHE with straight tubes heat exchangers, and the factors affecting the performance and effectiveness of the helical coil heat exchanger such as the curvature ratio, and other heat exchangers. The author demonstrated that the HCHE provided more excellent heat transfer performance and effectiveness than straight tubes and other heat exchangers because of secondary flow development inside the helical tube, and heat transfer coefficient increased with an increase in the curvature ratio of HCHE for the same flow rates. The secondary flow and mass flow rates, advantages and disadvantages have also been reviewed. The authors back their findings with available theories. Suitable fluid should be searched for high efficiency in the helical coil.

NATURE OF THE SURFACE HEAT TRANSFER FLUCTUATION IN A HYPERSONIC SEPARATED TURBULENT FLOW

This paper presents the results of an experimental study of the unsteady nature of a hypersonic sepa- rated turbulent flow.The nominal test conditions were a freestream Mach number of 7.8 and a unit Reynolds number of 3.5x10^7/m.The separated flow was generated using finite span forward facing steps.An array of flush mounted high spatial resolution and fast response platinum film resistance thermometers was used to make mul- ti-channel measurements of the fluctuating surface heat trtansfer within the separated flow.Conditional sampling ana- lysis of the signals shows that the root of separation shock wave consists of a series of compression wave extending over a streamwise length about one half of the incoming boundary layer thickness.The compression waves con- verge into a single leading shock beyond the boundary layer.The shock structure is unsteady and undergoes large-scale motion in the streamwise direction.The length scale of the motion is about 22 percent of the upstream influence length of the separation shock wave.There exists a wide band of frequency of oscillations of the shock system.Most of the frequencies are in the range of 1-3 kHz.The heat transfer fluctuates intermittently between the undisturbed level and the disturbed level within the range of motion of the separation shock wave.This inter mittent phenomenon is considered as the consequence of the large-scale shock system oscillations.Downstream of the range of shock wave motion there is a separated region where the flow experiences continuous compression and no intermittency phenomenon is observed.

Effects of radiation and heat source/sink on unsteady MHD boundary layer flow and heat transfer over a shrinking sheet with suction/injection

In this paper,an investigation is made to study the effects of radiation and heat source/sink on the unsteady boundary layerflow and heat transfer past a shrinking sheet with suction/injection.Theflow is permeated by an externally applied magneticfield normal to the plane offlow.The self-similar equations correspond-ing to the velocity and temperaturefields are obtained,and then solved numerically byfinite difference method using quasilinearization technique.The study reveals that the momentum boundary layer thickness increases with increasing unsteadiness and decreases with magneticfield.The thermal boundary layer thickness decreases with Prandtl number,radiation parameter and heat sink parameter,but it increases with heat source parameter.Moreover,increasing unsteadiness,magneticfield strength,radiation and heat sink strength boost the heat transfer.

第三类加热边界条件下超临界正癸烷的流动换热和热裂解特性研究

为深入理解不同类型热边界条件下碳氢燃料流动换热和裂解特性,对第三类加热边界条件下圆通道内超临界正癸烷的流动换热和热裂解特性开展了数值研究,并与等热流和等壁温加热条件下的结果进行了对比。结果表明:管内对流换热热阻的沿程变化和管道内外温差的缩小会造成不均匀的壁面热流分布和壁温分布。通过将第三类加热边界条件下的结果与等热流加热条件下的结果进行对比发现,第三类加热条件下换热恶化程度更低,最高壁面温度由1 219 K降低到1 175 K;与等壁温加热条件下的结果相比,第三类加热条件下壁面热流密度变化规律相似但变化范围和幅度更小,在加热段后半段,其转化率和压降均低于等壁温加热条件,出口处两种条件下的转化率相差约4%。

引入风流热流耦合特性的智能通风系统状态重构参数修正

为精准定量重构时间序列下实际矿井通风系统状态,以实时反映风网运行特征,基于实际矿井中风流的空气动力耦合热力流动特征,提出了时空特征下风流状态属性变化式,以井下网络和通风动力参数作为修正指标,以动态风流状态属性为修正变量,提出了通风系统状态重构参数点修正模型。为表述通风系统的动态连续运行状态,在点修正基础上引入连续时间特征,构建状态重构参数区间映射修正模型,以求解出时间序列下的系统状态重构参数波动区间来完成精准状态重构。为验证修正模型可靠性,以常村煤矿为工程对象进行状态重构,结果验证了井下风流的动态热流耦合特征及提出的风流状态属性变化式的可靠性,得出了状态重构参数波动区间,达到了实时准确构建风网运行状态的目的,有效提高了后续风网实时解算和控风决策的本质精度。

电磁场暴露中实验动物的热剂量学研究

本文开展了电磁暴露下实验动物的热剂量学特征研究。基于生物热方程和数字化三维大鼠模型建立了电磁剂量和热剂量仿真环境,评估了比吸收率、代谢率和边界条件对温度分布及变化的影响。结果表明:核心温升随全身平均比吸收率(WBASAR)增加而增加;在WBASAR值为4 W/kg的电磁波照射下,中脑和睾丸因趋肤效应具有较高的比吸收率值,导致器官组织的温升明显高于核心温升;在WBASAR值为0.4 W/kg的电磁波照射下,代谢和外界环境突变引起的浅层器官温度变化可达到1℃,远高于核心温升值。在实验评估中,头部和睾丸等靶器官是关键的热剂量评估对象;在实验设计中,需合理规范实验条件,降低代谢率和热边界条件对热剂量的影响。本研究为生物电磁学实验设计及效应研究提供热剂量学评估基础。