Convective heat and mass transfer effects in three-dimensional flow of Maxwell fluid over a stretching surface with heat source

Heat and mass transfer effects in three-dimensional flow of Maxwell fluid over a stretching surface were addressed.Analysis was performed in the presence of internal heat generation/absorption. Concentration and thermal buoyancy effects were accounted. Convective boundary conditions for heat and mass transfer analysis were explored. Series solutions of the resulting problem were developed. Effects of mixed convection, internal heat generation/absorption parameter and Biot numbers on the dimensionless velocity, temperature and concentration distributions were illustrated graphically. Numerical values of local Nusselt and Sherwood numbers were obtained and analyzed for all the physical parameters. It is found that both thermal and concentration boundary layer thicknesses are decreasing functions of stretching ratio. Variations of mixed convection parameter and concentration buoyancy parameter on the velocity profiles and associated boundary layer thicknesses are enhanced. Velocity profiles and temperature increase in the case of internal heat generation while they reduce for heat absorption. Heat transfer Biot number increases the thermal boundary layer thickness and temperature. Also concentration and its associated boundary layer are enhanced with an increase in mass transfer Biot number. The local Nusselt and Sherwood numbers have quite similar behaviors for increasing values of mixed convection parameter, concentration buoyancy parameter and Deborah number.     

Convective heat transfer and flow characteristics of Cu-water nanofluid

An experimental system is built to investigate convective heat transfer and flow characteristics of the nanofluid in a tube. Both the convective heat transfer coefficient and friction factor of Cu-water nanofluid for the laminar and turbulent flow are measured. The effects of such factors as the volume fraction of suspended nanoparticles and the Reynolds number on the heat transfer and flow characteristics are discussed in detail. The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid and show that the friction factor of the sample nanofluid with the low volume fraction of nanoparticles is almost not changed. Compared with the base fluid, for example, the convective heat transfer coefficient is increased about 60% for the nanofluid with 2.0 vol% Cu nanoparticles at the same Reynolds number. Considering the factors affecting the convective heat transfer coefficient of the nanofluid, a new convective heat transfer correl     

Similarity solutions for the mixed convection flow over a vertical plate with thermal radiation

The steady laminar boundary layer flow adjacent to a vertical plate with prescribed surface temperature immersed in an incompressible viscous fluid,where the effect of thermal radiation was taken into consideration,was investigated.The governing partial differential equations were transformed into a system of ordinary differential equations using similarity transformation,before being solved numerically by the shooting method.Both assisting and opposing buoyant flows were considered.It is found that dual...     

Dual solutions of MHD stagnation point flow and heat transfer over a stretching/shrinking sheet with generalized slip condition

An analysis was made to study the steady momentum and heat transfer characteristics of a viscous electrically conducting fluid near a stagnation point due to a stretching/shrinking sheet in the presence of a transverse magnetic field and generalized slip condition. Two flow problems corresponding to the planar and axisymmetric stretching/shrinking sheet were considered. By means of similarity transformations, the obtained resultant nonlinear ordinary differential equations were solved numerically using a shooting method for dual solutions of velocity and temperature profiles. Some important physical features of the flow and heat transfer in terms of the fluid velocity, the temperature distribution, the skin friction coefficient and the local Nusselt number for various values of the controlling governing parameters like velocity slip parameter, critical shear rate, magnetic field, ratio of stretching/shrinking rate to external flow rate and Prandtl number were analyzed and discussed. An increase of the critical shear rate decreases the fluid velocity whereas the local Nusselt number increases. The comparison of the present numerical results with the existing literature in a limiting case is given and found to be in an excellent agreement.     

Flow of Burgers' fluid over an inclined stretching sheet with heat and mass transfer

Effects of heat and mass transfer in the flow of Burgers fluid over an inclined sheet are discussed. Problems formulation and relevant analysis are given in the presence of thermal radiation and non-uniform heat source/sink. Thermal conductivity is taken temperature dependent. The nonlinear partial differential equations are simplified using boundary layer approximations. The resultant nonlinear ordinary differential equations are solved for the series solutions. The convergence of series solutions is obtained by plotting theη-curves for the velocity, temperature and concentration fields. Results of this work describe the role of different physical parameters involved in the problem. The Deborah numbers corresponding to relaxation time(β1 and β2) and angle of inclination(α) decrease the fluid velocity and concentration field. Concentration field decays as Deborah numbers corresponding to retardation time(β3) and mixed convection parameter(G) increase. Large values of heat generation/absorption parameters A/B, and the temperature distribution across the boundary layer increase. Numerical values of local Nusselt number,-θ′(0), and local Sherwood number,-f′(0), are computed and analyzed. It is found that θ′(0) increases with an increase in β3.     

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.     

退火钢卷辐射换热及对流换热的讨论

主要研究罩式炉退火钢卷在退火过程中,对流热流及辐射热流的变化情况及其影响因素,由此得到退火过程的不同阶段对流热和辐射热的大小比较,以判断在计算过程中,忽略辐射热流是否合理。计算得出,到退火加热中期,钢卷通过对流获得总热量是通过辐射获得的总热量的35倍,到保温中期,这两个量仅相差9倍,且退火保温时间越长,二者差距越小。     

纳米流体流动传热性能的实验与模拟研究

为了研究高温冷却条件下,γ-Al2O3-PG90纳米流体作为冷却介质在一车用机油冷却器内的流动传热性能,采用三维k-ε湍流模型,应用块结构网格生成技巧,融合流固耦合研究方法和薄壳导热模型数值模拟了纳米流体的性能,进行了基液与纳米流体的性能对比计算,分析了纳米粒子体积分数对性能的影响,考察了纳米流体物性预测模型的普适性,并研究了将纳米流体视为单相流体进行性能分析的可行性,通过实验测试得到了性能数据.研究发现:与基液相比,纳米流体强化换热效果明显,流动阻力有所增加,随着纳米粒子体积分数的增加,传热性能提高,流动阻力增加,说明该物性预测模型不能普适,当纳米粒子体积分数大于3%时,将纳米流体视为单相流体的性能研究结果与实验数据偏差较大,可能原因是单相流体流动无法反映较多的粒子之间的相互作用.     

Peristaltic flow with convective mass condition and thermal radiation

The primary objective of present investigation is to introduce the novel aspects of convective mass condition and thermal radiation in the peristaltic transport of fluid. Magnetohydrodynamic(MHD) fluid was considered in a symmetric channel. Heat and mass transfer characteristics were analyzed in the presence of Soret and Dufour effects, and the results were presented via two forms of thermal radiation. The temperature, concentration and pressure rise per wavelength were examined. It is observed that the velocity slip and magnetic field parameters have opposite effects on the pressure rise per wavelength. Temperature of fluid is a decreasing function of the radiation parameter. Further, the temperature of fluid decreases by increasing the heat transfer Biot number. It is notified that the heat transfer rate at the wall is a decreasing function of radiation parameter.     

Convective heat transfer enhancement of laminar flow of latent functionally thermal fluid in a circular tube with constant heat flux: internal heat source model and its application

Latent functionally thermal fluid is a kind of new two-phase fluid, in which phase change material is microencapsulated and suspended in a conventional single-phase heat transfer fluid (fig. 1). Such a slurry is of much larger apparent specific heat than conventional single-phase fluids during the phase change period, which enhances the heat transfer rate between the fluid and the tube wall. The flow rate and pump power required can be reduced evidently by using the slurries …     

Characteristics of radiation and convection heat transfer in indirect near-infrared-ray heating chamber

Numerical study was performed to evaluate the characteristics of combined heat transfer of radiation,conduction and convection in indirect near infrared ray (NIR) heating chamber.The effects of important design parameters such as the shape of heat absorbing cylinder and heat releasing fin on the pressure drop and heat transfer coefficient were analyzed with different Reynolds numbers.The Reynolds numbers were varied from 103 to 3×106,which was defined based on the hydraulic diameter of the heat absorbing cy...     

On the combined heat transfer of natural convection, radiation and conduction in the non-gray semitransparent thermal fibrous insulation

Non-gray semitransparent fibrous insulation hasbroad application in high-temperature industry, such asthe TPS ( thermal protection systems) of reusablelaunch vehicles. A metallic thermal protection systemgenerally consists of a metallic shell panel partit…     

Convective heat transfer for incompressible laminar gas flow in micropassage with constant wall temperature

Theoretical investigations have been performed on the convective heat transfer for incompressible laminar flow of gases through microtube and parallel-plates micropassages with constant wall temperature. Considering the change in thermal conductivity and viscosity of gas in wall adjacent region from the kinetic theory, mathematical models are built for both of the micropassages. The dimension-less temperature distribution and the corresponding heat transfer characteristics are simulated numerically, and the results discussed briefly.     

Slip flow and variable properties of viscoelastic fluid past a stretching surface embedded in a porous medium with heat generation

This study examines theoretically and computationally the non-Newtonian boundary layer flow and heat transfer for a viscoelastic fluid over a stretching continuous sheet embedded in a porous medium with variable fluid properties, slip velocity, and internal heat generation/absorption. The flow in boundary layer is considered to be generated solely by the stretching of the sheet adjacent to porous medium with boundary wall slip condition. Highly nonlinear momentum and thermal boundary layer equations governing the flow and heat transfer are reduced to set of nonlinear ordinary differential equations by appropriate transformation. The resulting ODEs are successfully solved numerically with the help of shooting method. Graphical results are shown for non-dimensional velocities and temperature. The effects of heat generation/absorption parameter, the porous parameter, the viscoelastic parameter, velocity slip parameter, variable thermal conductivity and the Prandtl number on the flow and temperature profiles are presented. Moreover, the local skin-friction coefficient and Nusselt number are presented. Comparison of numerical results is made with the earlier published results under limiting cases.     

碳纳米流体特性及其在重力热管内的传热

采用阿拉伯胶辅助分散法制备了一种新型的纳米流体--碳纳米管 水纳米流体,并以其为工质在以铜为管壳的一种新型重力热管内进行了传热实验研究.制备和实验结果表明,碳纳米管 水纳米流体的导热系数比基液水约增加了30％～50％,导热能力明显增强;这种纳米流体黏度低,流动性好,制备过程简单,可用于大规模生产;纳米流体重力热管加热段沸腾换热弱化了纳米流体的稳定性对热管传热性能的影响,实现了纳米流体与重力热管的优势互补;以该纳米流体为工质的重力热管的内热阻比水小,并且随着传输功率的提高,热管总热阻逐渐减小,传热性能逐渐提高.     

水平肋片管在自然对流换热条件下表面温度的测定

实测了水平肋片管在自然对流换热条件下圆管表面温度在圆周方向上的分布。实验表明,用半圆周中点的温度可以近似代替圆周表面的平均温度。     

多通道自适应陷波滤波器组设计及性能分析

通过对多个单频自适应陷波滤波器的组合,得到了多通道自适应陷波滤波器,推导了其并联和级联结构的传递函数,分析了单通道、并行多通道和串行多通道3种滤波器的工作特性,并比较了它们的滤波性能.仿真结果表明,多通道自适应陷波滤波器既可有效抑制宽带噪声,又可同时完成对多个不同频率正弦波的提取;增设陷波通道可以去除正弦干扰,避免包络波动.另外,串行多通道陷波滤波器更适合单通道接收的情况,而并行多通道陷波滤波器则适用于多通道接收的场合,具有较大的实用价值.     

旋转圆筒表面传热和传质特性实验研究

为研究旋转圆筒表面对流传热和传质特性,用微型热偶式测温和测湿探头对旋转圆筒表面的温度场和浓度场分布进行了测试.实验结果表明,旋转圆筒表面对流传热和传质特性之间存在着较好的类比性.旋转对纯传热边界层局部努塞尔数的影响规律与对传质边界层局部舍伍得数的影响规律相似;对平均努塞尔数和平均舍伍得数的影响规律也相似.当旋转雷诺数小于临界雷诺数时,旋转对平均努塞尔数和平均舍伍得数几乎没有影响,当大于临界雷诺数时,随旋转雷诺数的增大平均努塞尔数和平均舍伍得数也增大.     

存在垂直加热时的矩形池内热毛细对流的数值模拟

为了了解垂直加热对矩形浅液池内稳态热毛细对流的影响,利用有限容积法进行了二维直接数值模拟,液池左、右壁分别维持恒定温度Th和Tc,且ThTc,底部被加热,自由表面存在散热,液池宽深比为(20~30),流体为1cSt硅油。结果表明,随着底部加热热流密度的增大,矩形液池内的流动会由单胞或多胞流动转化为旋转方向相反的非对称双胞流动,流动转化过程的临界热流密度随Marangoni数和Biot数的增加而增大,随液池宽深比的增加而减小,液池内的最高温度会随Marangoni数和宽深比的增大而减小。