Thermally Developing Forced Convection of Non-Newtonian Fluids Inside Elliptical Ducts

Laminar-forced convection inside tubes of various cross-section shapes is of interest in the design of a low Reynolds number heat exchanger apparatus. Heat transfer to thermally developing, hydrodynamically developed forced convection inside tubes of simple geometries such as a circular tube, parallel plate, or annular duct has been well studied in the literature and documented in various books, but for elliptical duct there are not much work done. The main assumptions used in this work are a non-Newtonian fluid, laminar flow, constant physical properties, and negligible axial heat diffusion (high Peclet number). Most of the previous research in elliptical ducts deal mainly with aspects of fully developed laminar flow forced convection, such as velocity profile, maximum velocity, pressure drop, and heat transfer quantities. In this work, we examine heat transfer in a hydrodynamically developed, thermally developing laminar forced convection flow of fluid inside an elliptical tube under a second kind of a boundary condition. To solve the thermally developing problem, we use the generalized integral transform technique (GITT), also known as Sturm-Liouville transform. Actually, such an integral transform is a generalization of the finite Fourier transform, where the sine and cosine functions are replaced by more general sets of orthogonal functions. The axes are algebraically transformed from the Cartesian coordinate system to the elliptical coordinate system in order to avoid the irregular shape of the elliptical duct wall. The GITT is then applied to transform and solve the problem and to obtain the once unknown temperature field. Afterward, it is possible to compute and present the quantities of practical interest, such as the bulk fluid temperature, the local Nusselt number, and the average Nusselt number for various cross-section aspect ratios.     

Performance of Microchannel Heat Sinks with Newtonian and Non-Newtonian Fluids

In this paper, the flow behavior and heat transfer performance of a microchannel heat sink is examined. Microchannel heat sink is a heat exchanger that is used to control the temperature of electronic devices with high heat flux capacity. A comprehensive thermal model for a microchannel should include a three-dimensional conduction analysis in the solid parts, followed by an extensive three-dimensional developing flow in the fluid region. The heat transfer analysis in the transition region of the fluid section is a crucial matter. Hydrodynamic and thermal entrance lengths are two important parameters, among others, which are studied in the solution. To examine the potential of using a non-Newtonian fluid, the power law model was used for both Newtonian and non-Newtonian fluids. The numerical solution of the problem was based on a finite difference approach using a control volume with staggered grid system. The SIMPLE algorithm was applied to the problem, and convection terms were estimated using QUICK method. A comparison of the Newtonian and non-Newtonian results showed that for shear thinning fluids, the pressure drop could reduce up to 45%, while for shear thickening fluids, it can increase up to 48%. The same comparison for the Nusselt number showed about a 160% increase with shear thinning fluids and a 43% decrease with shear thickening fluids. The thermal resistance at a Reynolds number of 50 will reduce approximately 25% with shear thinning fluids and will increase approximately 5% with shear thickening fluids. At higher values of the Reynolds number, the changes in the value of the thermal resistance are more pronounced.     

Forced Convection Heat Transfer to Power-Law Non-Newtonian Fluids Inside Triangular Ducts

A hybrid analytical-numerical approach based on the Generalized Integral Transform Technique is employed to simulate the laminar forced convection (hydrodynamically fully developed and thermally developing laminar flow) of power-law non-Newtonian fluids inside ducts with arbitrary shaped cross-sections. The analysis is illustrated through consideration of both right angularly and isosceles triangular ducts subjected to constant wall temperature as thermal boundary condition. Reference results for quantities of practical interest such as dimensionless average temperature and Nusselt numbers within the thermal entry region were produced for different values of power-law index and apex angles. Finally, critical comparisons are performed with results available in the literature for direct numerical and approximate approaches.     

Parallel Finite Volume Method Simulation of Three-Dimensional Fluid Flow and Convective Heat Transfer for Viscoplastic Non-Newtonian Fluids

Three-dimensional fluid mechanics and heat transfer for viscoplastic flows are described by finite volume method, FVM. The open multi-processing approach has been implemented to parallelize the numerical code. Results for the elapsed times, speed-ups and efficiencies are presented. The code was used to describe the natural convection (Ra = 10⁴; 10⁶) and the lid-driven cavity (Re = 100; 1000) processes with Bingham, Casson and Herschel–Bulkley fluids (Bn = 0.01; 1.0). Results describing isotherms, velocity distributions and streamtraces, as a function of Ra, Re, Pr and Bn numbers are shown. The grid size analysis shows that different sizes are required to obtain precise results for Nusselt number and friction factor.     

Confined Flow and Heat Transfer Phenomena of Non-Newtonian Shear-Thinning Fluids Across a Pair of Tandem Triangular Bluff Bodies

Extensive numerical computations for the confined flow and heat transfer of shear-thinning fluids over two long tandem triangular bluff bodies are performed for Reynolds number (Re) = 1–40, power-law index (n) = 0.2–1, and gap ratio (S/B) = 1–4 for a fixed blockage ratio and Prandtl number of 25% and 50, respectively. The values of critical Re are obtained for each of the two triangular cylinders for all S/B and n. Augmentation in heat transfer for the two tandem triangular cylinders is calculated with respect to both S/B and n.     

Investigation of Vapor-liquid Ejector with Organic Working Fluids

The vapor-liquid ejector is a simply flow device and driven by thermal energy. In this paper, a modified mathematical model of the vapor-liquid ejector is proposed, and the validation shows good agreements with the experimental data. A study is carried out with six organic working fluids, namely R1233 zd(E), R1336 mzz(Z), R236 ea, R245 ca, R245 fa and R365 mfc. The influences of the entrainment ratio, the area ratio, the superheating at the vapor nozzle inlet, the subcooling at the liquid nozzle inlet, and the pressures at these inlets on the pressure lifting are parametrically investigated. An increase in the subcooling leads to the great increasing of pressure lifting and the superheating has slight effect on the pressure lifting, whereas others have the opposite tendency. The studies of the pressures and temperatures at the typical locations inside the vapor-liquid ejector are further conducted by using R1336 mzz(Z). The results show that the above parameters have great influence on these pressures and temperatures inside except that the pressures are insignificantly impacted by the superheating, and the temperatures are negligibly affected by the area ratio. R1336 mzz(Z) is recommended as a good working fluid for the vapor-liquid ejector.     

Natural Convection Heat Transfer and Entropy Generation in a Porous Trapezoidal Enclosure Saturated with Power-Law Non-Newtonian Fluids

Abstract

In the present study, natural convection heat transfer and its associated entropy generation in a porous trapezoidal enclosure saturated with a power-law non-Newtonian fluid has been numerically investigated. Horizontal walls of the enclosure are assumed to be adiabatic while the side walls are considered to be kept at a constant temperature. A continuum-based approach is adapted here to model the fluid flow through porous media and the Darcy’s law is modified to account for non-Newtonian rheological behavior of the fluid. The obtained governing equations are discretized using the finite volume method and a detailed parametric study is undertaken to account for the effects of various relevant parameters of the problem on the heat transfer and entropy generation rates. It was shown that the impact of the power-law index on both entropy generation and heat transfer significantly intensifies in a convection-dominated flow regime inside the enclosure, especially for a shear thinning liquid. Moreover, heat transfer rate and entropy generation increase as the sidewall angle is elevated.     

Stability for a Transmission Problem in Thermoelasticity with Second Sound

We consider a semilinear transmission problem for a coupling of an elastic and a thermoelastic material. The heat conduction is modeled by Cattaneo's law removing the physical paradox of infinite propagation speed of signals. The damped, totally hyperbolic system is shown to be exponentially stable, and the existence of a global attractor is shown.     

An Equation of State for Fluids by Applying the Tower-Well Potential Model

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First and Second Law Analysis for the MHD Flow of Two Immiscible Couple Stress Fluids between Two Parallel Plates

This paper aims to analyze the heat transfer by the first and second laws of thermodynamics for the flow of two immiscible couple stress fluids inside a horizontal channel under the action of an imposed transverse magnetic field. The plates of the channel are maintained at constant and different temperatures higher than that of the fluid. The flow region consists of two zones, the flow of the heavier fluid taking place in the lower zone. No slip condition is taken on the plates and continuity of velocity, vorticity, shear stress, couple stress, temperature, and heat flux are imposed at the interface. The velocity and temperature distributions are derived analytically and these are used to compute the dimensionless expressions for the entropy generation number and Bejan number. The results are presented graphically. It is observed that the imposed magnetic field reduces the entropy production rate near the plates.     

太阳能驱动有机朗肯循环的工质比较

针对太阳能热水和其它低品位热能的动力利用,研究了工作在100℃供热温度和30℃冷凝温度之间的有机朗肯循环工质的优化选择,以满足较高的循环效率、较大的机械能输出、较小的排气量需求等要求。工质模型采用RKS状态方程,针对R22在-30～95℃温度区间内,计算结果与ASHRAE20-2005数据比较,除液相密度外,其它的热力学参数计算绝对误差小于5%,满足工程模拟要求。利用RKS模型,文中分析了19种有机工质的动力循环参数,发现工质R11的热力学性能系数最高。结合GWP和ODP环境指标,发现R142b、Rc318与R600适合于低温朗肯循环。     

燃料乙醇电雾化

运用显微摄像,配以计算机图像采集,摄取了大量画面,从乙醇电雾化物理过程的变化,得到其液体碎裂现象,不同于离心力、气动力、撞击力的液体碎裂。在库伦力的作用下,其液体拉成丝,它的直径不断拉细,直径拉到某定值,而后细丝断裂为长度几乎相等的圆柱,收缩成直径变化不大的液滴群,即单分散的液滴雾。     

A Numerical Method for Simulation of Incompressible Three-Dimensional Newtonian and Non-Newtonian Flows

Three-dimensional Newtonian and non-Newtonian flows are found in numerous engineering applications. Simulation of this class of problems requires robust mathematical and computational modeling. The main goal of this article is to propose a unified numerical methodology for solving three-dimensional, laminar, incompressible Newtonian and non-Newtonian steady flows. A second-order, fully implicit finite-difference approximation is used to discretize the governing equations in a collocated mesh, in which Jacobian matrices are derived to account for distinct constitutive relations for Newtonian and non-Newtonian fluids. The strategy also uses a Euler implicit pseudo-transient time stepping aiming at steady-state solutions. Examples illustrating Newtonian and non-Newtonian (polymer melts) fluid flow in 3-D geometries are discussed.     

基于改进布谷鸟算法的电力系统最优潮流计算

针对电力系统最优潮流问题,提出一种融入量子计算和混沌局部搜索策略的改进布谷鸟算法(QCCS),即对布谷鸟算法的个体进行量子位编码,通过叠加态的量子位实现多样化种群,并在算法每次迭代的优化值附近进行混沌局部搜索进而增加布谷鸟算法的局部搜索能力,同时采用量子门变换使每个个体朝最优个体进化,从而提高算法的寻优能力。最后以IEEE 118节点系统的最优潮流计算问题为例,应用QCCS进行仿真计算。通过与其他方法(PSO、GA、CS)计算结果进行对比分析,验证了QCCS算法求解电力系统最优潮流问题的有效性,从而为电力系统最优潮流(OPF)问题的求解提供了一种新方法。     

An Experimental Investigation on the Chemical Stability of Selected Formation and Determination of the Proper Type of Water-Base Drilling Fluids. Part 2. Test Results

The objective of this study was to select the proper drilling fluid type and composition for drilling stable holes through the problems of the selected formations. This study was performed on shale samples taken from 10 wells in which hole instability was encountered to various extents during drilling the Germav formation. Both ionic and polymer inhibitions were utilized in formulating the proper drilling for the Germav formation. Ionic inhibition was obtained using KCl and NaCl. Polyanionic polymer (Pac-L) was used for providing the polymer encapsulation. Experimental results indicated that KCl is superior to NaCl in providing ionic inhibition. Both salts lowered the interaction between the drilling fluid and Germav formation, but better results were obtained with KCl. Minimum salt concentration up to 15% yields more inhibitive environment. Polymer inhibition tests indicated that minimum Pac-L concentration required for maintaining the polymer inhibition was about 2 lb/bbl for both systems. In conclusion, KCl/encapsulating polymer system seems to be the most proper water: base drilling fluid available for Germav formation achieving the required wellbore stability. The fluid loss and suspending properties of the proposed system must be controlled using the modified starch and XC polymer.     

Computational Study of Convective Transport in a Coating Applicator for a Non-Newtonian Fluid

Convective transport in an optical fiber coating applicator and die system has been simulated for a non-Newtonian fluid. Low-density polyethylene (LDPE) is employed for the numerical analysis, though ultraviolet (UV) curable acrylates are more commonly used, because of a lack of property information for acrylates and similar behavior of these two materials. The equations governing fluid flow and heat transfer are transformed to obtain flow in a cylindrical domain. A numerical scheme similar to the SIMPLE algorithm is developed and employed with a nonuniform grid. Variable fluid properties are employed because of the strong dependence of these on the temperature. In contrast to the isothermal case, streamlines for the non-Newtonian fluid are found to be quite different for various fiber speeds. The temperature level in the applicator is much higher for the Newtonian case, due to the larger fluid viscosity and associated viscous dissipation. The shear near the fiber is found to be lower for the Newtonian fluid. As expected, the effects become larger with increasing fiber speed. A fairly high temperature rise is observed in the die, regardless of fiber speed. This study focuses on the computational modeling of non-Newtonian effects during the coating process, and several interesting and important features, as compared to the Newtonian case, are observed.     

计入非牛顿效应的曲轴轴承的混合润滑分析

分析了剪切变薄的非牛顿流变学特性和两表面都具有的纵向、横向和各向同性粗糙度对动载有限宽径向滑动轴承性能的综合影响。 Ｃｈｒｉｓｔｅｎｓｅｎ 的粗糙表面流体动力润滑的随机模型和 Ｇｒｅｅｎｗ ｏｏｄ Ｔｒｉｐｐ 接触压力的计算模型用于处理粗糙问题,并考虑了磨合对粗糙高度分布的影响。幂律流体模型用来表征剪切变薄的流变学特征,质量守恒的油膜破裂算法用于雷诺方程的求解。计算结果表明,粗糙度总是减小最小名义油膜厚度,并使油膜压力在接触区剧烈振荡,其幅值大于光滑表面时周期内的最大名义油膜压力。名义最小油膜厚度在纵向粗糙时最大,横向粗糙时最小。粗糙纹理相同时,相同粗糙结构下的名义最小油膜厚度在牛顿流体时大于不同粗糙结构时的相应值,在非牛顿流体情况下,结论相反。混合润滑的轴承性能受粗糙纹理和结构、幂律指数、轴承几何结构、轴颈质量及运行工况的综合影响。     

柴油机燃用LPG的高原特性实验研究

在高原环境条件下,针对柴油机燃用LPG的经济性,动力性和排放排性进行了研究,柴油机掺烧LPG后,在一定的掺烧比下,动力性有所提高,经济性有所改善,碳煤排放降低幅放较大,但发动机振动和大,噪声和排温升高,试验结果为在高原地区推广应用PLG／柴油双燃料发动机提供了依据。