An Unsteady Oscillatory Flow of Generalized Casson Fluid with Heat and Mass Transfer: A Comparative Fractional Model

It is of high interest to study laminar flow with mass and heat transfer phenomena that occur in a viscoelastic fluid taken over a vertical plate due to its importance in many technological processes and its increased industrial applications. Because of its wide range of applications, this study aims at evaluating the solutions corresponding to Casson fluids’ oscillating flow using fractional-derivatives. As it has a combined mass-heat transfer effect, we considered the fluid flow upon an oscillatory infinite vertical-plate. Furthermore, we used two new fractional approaches of fractional derivatives, named AB (Atangana–Baleanu) and CF (Caputo–Fabrizio), on dimensionless governing equations and then we compared their results. The Laplace transformation technique is used to get the most accurate solutions of oscillating motion of any generalized Casson fluid because of the Cosine oscillation passed over the infinite vertical-plate. We obtained and analyzed the distribution of concentration, expressions for the velocity-field and the temperature graphically, using various parameters of interest. We also analyzed the Nusselt number and the skin friction due to their important engineering usage.     

Heat Transfer in a Micropolar Fluid along a Non-linear Stretching Sheet with a Temperature-Dependent Viscosity and Variable Surface Temperature

In this paper, heat transfer characteristics of a two-dimensional steady hydromagnetic natural convection flow of a micropolar fluid passed a non-linear stretching sheet taking into account the effects of a temperature-dependent viscosity and variable wall temperature are studied numerically for local similarity solutions by applying the Nachtsheim-Swigert iteration method. The results corresponding to the dimensionless temperature profiles and the local rate of heat transfer are displayed graphically for important material parameters. The results show that in modeling the thermal boundary layer flow with a temperature-dependent viscosity, consideration of the Prandtl number as a constant within the boundary layer produces unrealistic results and therefore it must be treated as a variable rather than a constant within the boundary layer. The results also show that the local rate of heat transfer strongly depends on the non-linear stretching index and temperature index.     

Effects of Combined Heat and Mass Transfer on Entropy Generation due to MHD Nanofluid Flow over a Rotating Frame

The current investigation aims to explore the combined effects of heat and mass transfer on free convection of Sodium alginate-Fe3O4 based Brinkmann type nanofluid flow over a vertical rotating frame. The Tiwari and Das nanofluid model is employed to examine the effects of dimensionless numbers, including Grashof, Eckert, and Schmidt numbers and governing parameters like solid volume fraction of nanoparticles, Hall current, magnetic field, viscous dissipation, and the chemical reaction on the physical quantities. The dimensionless nonlinear partial differential equations are solved using a finite difference method known as Runge-Kutta Fehlberg (RKF-45) method. The variation of dimensionless velocity, temperature, concentration, skin friction, heat, and mass transfer rate, as well as for entropy generation and Bejan number with governing parameters, are presented graphically and are provided in tabular form. The results reveal that the Nusselt number increases with an increase in the solid volume fraction of nanoparticles. Furthermore, the rate of entropy generation and Bejan number depends upon the magnetic field and the Eckert number.     

A Fractal-Fractional Model for the MHD Flow of Casson Fluid in a Channel

An emerging definition of the fractal-fractional operator has been used in this study for the modeling of Casson fluid flow. The magnetohydrodynamics flow of Casson fluid has cogent in a channel where the motion of the upper plate generates the flow while the lower plate is at a static position. The proposed model is non-dimensionalized using the Pi-Buckingham theorem to reduce the complexity in solving the model and computation time. The non-dimensional fractal-fractional model with the power-law kernel has been solved through the Laplace transform technique. The Mathcad software has been used for illustration of the influence of various parameters, i.e., Hartman number, fractal, fractional, and Casson fluid parameters on the velocity of fluid flow. Through graphs and tables, the results have been implemented and it is shown that the boundary conditions are fully satisfied. The results reveal that the flow velocity is decreasing with the increasing values of the Hartman number and is increasing with the increasing values of the Casson fluid parameter. The findings of the fractal-fractional model have elucidated that the memory effect of the flow model has higher quality than the simple fractional and classical models. Furthermore, to show the validity of the obtained closed-form solutions, special cases have been obtained which are in agreement with the already published solutions.     

Wide-Range Model of Mixture for Chemically Reacting Nonideal Gases and Composite Plasma

A mixture model is constructed for dense chemically reacting gases and dense chemically active nonideal composite plasma. Investigations are performed of the contribution made by the interactions of free heavy particles (charged and neutral) into the thermodynamic functions of gases and plasma in different regions of the phase diagram, where bound states may arise. The excluded phase volume, accessible for classical motion of free atoms, is included by introducing the Hill pseudopotential. A wide-range calculation is performed of the thermodynamic parameters of various substances and mixtures, and a comparison is made with the experimental data and the theoretical results of other researchers.     

蜂窝板换热器内部流动传热特性研究

建立了蜂窝板换热器湍流流动的物理数学模型,并应用数值分析方法模拟了蜂窝板换热器的三维流动传热过程;分析了不同雷诺数下通道内流动阻力和换热性能及其随雷诺数的变化规律,并与相同当量直径的平行平板通道的流动换热性能进行了对比。结果表明,蜂窝板换热器在换热系数提高的同时流动阻力也增大了,在雷诺数Re=3000~15000的范围内,其传热努塞尔数比平行平板增大了0.93~2.12倍,阻力系数增大了2.24~2.35倍。最后从场协同理论的角度分析了蜂窝板强化传热的机理。     

钨极氩弧点焊熔池中流体流动及传热过程的数值模拟

本文建立了一个描述钨极氩弧点焊熔池中流体动力学状态及传热过程的数值分析模型。该模型考虑到了熔池传热过程的瞬时特点、熔池界面的移动以及电磁力、自然对流和表面张力梯度的综合影响;揭示了熔池内部电磁力场、流场和温度场相互作用的规律;采用了流函数—涡度法以及全隐式差分格式。根据该模型得出的数值分析结果与实验值吻合程度良好。     

点波板式换热器内流体流动换热及压降特性的实验研究

介绍了丹佛斯提出并开发的点波板式换热器。分别通过单相水-水换热测试和制冷剂(R410A)-水蒸发换热测试,实验研究了点波板式换热器与传统人字波板式换热器的传热及流动性能。结果表明,新型点波钎焊板式换热器,作为单相换热装置,具有较好的传热和流动性能。与传统的人字波板式换热器相比,较大雷诺数下,点波板式换热器强化传热20%以上,沿程阻力因子降低为传统结构的1/4左右。同时,作为蒸发器,在相似的制冷剂流动特征下,点波板式换热器比人字波板式换热器具有更好的流动和传热性能,这些性能优势,随着制冷剂流动特征的加强将变得更为明显。     

Heat Transfer in Meshed Metallic Materials with Interchannel Transpiration and Two-Dimensional Intermesh Flow of a Heat-Transfer Fluid

Some experimental data on the heat transfer in different meshed metallic materials with interchannel heat-transfer fluid transpiration and two-dimensional intermesh flow are presented. It is established that the thermal conductivity of a wire mesh material and the relative pathway, intermesh velocity, and thermophysical properties of a heat-transfer fluid has an effect on the heat transfer in meshed metallic materials with the two-dimensional flow of a single-phase heat-transfer fluid.     

固定电弧脉冲TIG焊接熔池流体流动与传热模型

在浮力、电磁力和表面张力梯度共同作用下对固定电弧脉冲ＴＩＧ焊接熔池中的流体流动与传热的动态过程建立了数学模型。在控制方程组强烈耦合的情况下，将处理导热问题边界条件的附加源项法应用于处理动量边界条件，同时采用交替方向隐式迭代法及双块修正技术，使求解非稳态控制方程组的迭代收敛速度大为提高。计算结果展示了脉冲ＴＩＧ焊接过程中，随着焊接电流的周期性变化，熔池流场与热场的周期性变化规律以及熔池形成的动态发展过程。根据该模型得出的计算结果与试验测定结果吻合程度良好。     

TIG焊接熔池表面变形对流场与热场的影响

利用流体力学理论和变分法原理,根据熔池本身重力、电弧压力和表面张力之间的动态平衡,推导出了 TIG 焊接熔池表面变形的计算公式。建立了熔池表面存在变形的流场与热场的数学模型。采用 SIMPLER 方法对不锈钢试件焊接熔池内的流场与热场进行了数值分析。焊接工艺试验表明,该模型计算的熔池成形与实验值吻合良好。     

Unsteady Natural Convection Fluid Flow in a Vertical Microchannel under the Effect of the Dual-Phase-Lag Heat-Conduction Model

The unsteady hydrodynamics and thermal behavior of fluid flow in an open-ended vertical parallel-plate microchannel are investigated semi-analytically under the effect of the dual-phase-lag heat conduction model. The model that combines both the continuum approach and the possibility of slip at the boundary is adopted in the study. The effects of the Knudsen number Kn, the thermal relaxation time τ _q , and the thermal retardation time τ _T on the microchannel hydrodynamics and thermal behavior are investigated using the dual-phase-lag and hyperbolic-heat-conduction models. It is found that as Kn increases the slip in the hydrodynamic and thermal boundary condition increases. Also, the slip in the hydrodynamic behavior increases as τ _T and τ _q decrease, but the effect of τ _T and τ _q on the slip of the thermal behavior is insignificant.