A Review on Technologies for the Use of CO2 as a Working Fluid in Refrigeration and Power Cycles

The use of carbon dioxide as a working fluid has been the subject of extensive studies in recent years, particularly in the field of refrigeration where it is at the heart of research to replace CFC and HCFC. Its thermodynamic properties make it a fluid of choice in the efficient use of energy at low and medium temperatures in engine cycles. However, the performance of transcritical CO2 cycles weakens under high temperature and pressure conditions, especially in refrigeration systems;On the other hand, this disadvantage becomes rather interesting in engine cycles where CO2 can be used as an alternative to the organic working fluid in small and medium-sized electrical systems for low quality or waste heat sources. In order to improve the performance of systems operating with CO2 in the field of refrigeration and electricity production, research has made it possible to develop several concepts, of which this article deals with a review of the state of the art, followed by analyzes in-depth and critical of the various developments to the most recent modifications in these fields. Detailed discussions on the performance and technical characteristics of the different evolutions are also highlighted as well as the factors affecting the overall performance of the systems studied. Finally, perspectives on the future development of the use of CO2 in these different cycles are presented.

FLUID INDUCED HYDRAULIC SYSTEM VIBRATIONOF POWERED SUPPORT

Fluid and solid interaction analysis of hydraulic support under the coming pressure of roof rocks was presented. The mathematical model of the system was proposed and numerical studies by the character line method were carried out.

Drag characteristics of power law fluids on an upstream moving surface

The specific problem to be considered here concerns the boundary layer problem of a non-Newtonian fluid on a flat plate in length, whose surface has a constant velocity opposite in the direction to that of the mainstream with Uw 〉〉 U∞, or alternatively when the plate surface velocity is kept fixed but the stream speed is reduced to zero. A theoretical analysis for a boundary layer flow is made and the self-similar equation is determined. Solutions are presented numerically for special power index and the associated transfer behavior is discussed.

Characteristics of Convection Heat Transfer in Power⁃Law Fluid Saturated Porous Media Channel

Considering Brinkman⁃Forchheimer extended Darcy flow and local thermal non⁃equilibrium effect,a general model of forced convection with viscous dissipation in power⁃law fluid saturated porous media channel was established.The dimensionless temperature profiles and Nusselt number were numerically solved using the classical fourth⁃order Runge Kutta method under a constant heat flux boundary condition.The conclusion showed that the fluid⁃solid temperature distributions were significantly affected by dimensionless Bi,k,Da,Br,and F,and the effects of power⁃law indexes on convection heat transfer characteristics were also non⁃negligible.

The Sixth International Conference on Fluid Power Transmission and Control(ICFP'2005)

Date: April 12-15, 2005 Venue: Zhejiang University, Hangzhou, P. R. China Organized by Institute of Mechatronic Control Engineering, Zhejiang University

OBTAINING THE CRITICAL DRAW RATIO OF DRAW RESONANCE IN MELT SPINNING FOR POWER LAW POLYMER FLUIDS

A direct difference method has been developed for Non-Newtonian power law fluids to solve the simultaneous non-linear partial differential equations of melt spinning, and to determine the critical draw ratio for draw resonance. The results show that for shear thin fluids, the logarithm of the critical draw ratio has a well defined linear relationship with the power index for isothermal and uniform tension melt spinning. When the power index approaches zero, the critical draw ratio points at unity, indicating no melt spinning can be processed stably for such fluids. For shear thick fluids, the critical draw ratio increases in a more rapid way with increasing the power index.

Similarity solutions for non-Newtonian power-law fluid flow

The problem of the boundary layer flow of power law non-Newtonian fluids with a novel boundary condition is studied. The existence and uniqueness of the solutions are examined, which are found to depend on the curvature of the solutions for different values of the power law index n. It is established with the aid of the Picard-Lindelof theorem that the nonlinear boundary value problem has a unique solution in the global domain for all values of the power law index n but with certain conditions on the curva- ture of the solutions. This is done after a suitable transformation of the dependent and independent variables. For 0 〈 n ≤ 1, the solution has a positive curvature, while for n 〉 1, the solution has a negative or zero curvature on some part of the global domain. Some solutions are presented graphically to illustrate the results and the behaviors of the solutions.

SOLUTION OF THE RAYLEIGH PROBLEM FOR A POWER-LAW NON-NEWTONIAN CONDUCTING FLUID VIA GROUP METHOD

An investigation is made of the magnetic Rayleigh problem where a semi_infinite plate is given an impulsive motion and thereafter moves with constant velocity in a non_Newtonian power law fluid of infinite extent. The solution of this highly non_linear problem is obtained by means of the transformation group theoretic approach. The one_parameter group transformation reduces the number of independent variables by one and the governing partial differential equation with the boundary conditions reduce to an ordinary differential equation with the appropriate boundary conditions. Effect of the some parameters on the velocity u(y,t) has been studied and the results are plotted.

Approximate analytical solutions and approximate value of skin friction coeffcient for boundary layer of power law fluids

This paper presents a theoretical analysis for laminar boundary layer flow in a power law non-Newtonian fluids. The Adomian analytical decomposition technique is presented and an approximate analytical solution is obtained. The approximate analytical solution can be expressed in terms of a rapid convergent power series with easily computable terms. Reliability and efficiency of the approximate solution are verified by comparing with numerical solutions in the literature. Moreover, the approximate solution can be successfully applied to provide values for the skin friction coefficient of the laminar boundary layer flow in power law non-Newtonian fluids.

Fully Developed Turbulence of Power⁃Law Fluids in Circular Pipe Based on Large Eddy Simulation

In this study,Large eddy simulation(LES)of the fully developed turbulence of power⁃law fluids in a circular pipe was performed using the dynamic subgrid⁃scale model.Under a specific Reynolds number,the flow information of three fluids with a range of power⁃law indexes was obtained.The trends of the mean axial velocity and the normalized apparent viscosity were analyzed.Simulation results show that shearing⁃thinning fluid displayed more noticeable non⁃Newtonian characteristics than shear⁃thickening fluid.The predicted friction factors were approximately equal to the Dodge and Metzner correlation and Gomes correlation.The peak values of root mean squares(RMS)and Reynolds stress increased as the power⁃law index increased.The turbulence statistics(skewness and flatness)from the wall to the pipe center were calculated.From the calculated results,the velocity fluctuation near the wall had strong intermittent and asymmetry.As demonstrated by the contours of the normalized instantaneous axial velocity and viscosity,the turbulence was more developed as the power⁃law index increased.It is concluded that the LES is feasible to predict the turbulence of pipe flow under higher Reynolds numbers.

New design solutions for low-power energy production in water pipe systems

This study is the result of ongoing research for a European Union 7th Framework Program Project regarding energy converters for very low heads, and aims to analyze optimization of new cost-effective hydraulic turbine designs for possible implementation in water supply systems （WSSs） or in other pressurized water pipe infrastructures, such as irrigation, wastewater, or drainage systems. A new methodology is presented based on a theoretical, technical and economic analysis. Viability studies focused on small power values for different pipe systems were investigated. Detailed analyses of alternative typical volumetric energy converters were conducted on the basis of mathematical and physical fundamentals as well as computational fluid dynamics （CFD） associated with the interaction between the flow conditions and the system operation. Important constraints （e.g., size, stability, efficiency, and continuous steady flow conditions） can be identified and a search for alternative rotary yolumetric converters is being conducted. As promising cost-effective solutions for the coming years, adapted rotor-dynamic turbomachines and non-conventional axial propeller devices were analyzed based on the basic principles of pumps operating as turbines, as well as through an extensive comparison between simulations and experimental tests.

AN INVESTIGATION ON INTERNAL THERMAL FLOW OF NON-NEWTONIAN FLUID

In the present paper an unsteady thermal flow of non-Newtonian fluid is investigated which is of the flow into axisymmetric mould cavity. In the second part an unsteady thermal flow of upper-convected Maxwell fluid is studied. For the flow into mould cavity the constitutive equation of power-law fluid is used as a Theological model of polymer fluid. The apparent viscosity is considered as a function of shear rate and temperature. A characteristic viscosity is introduced in order to avoid the nonlinearity due to the temperature dependence of the apparent viscosity. As the viscosity of the fluid is relatively high the flow of the thermal fluid can be considered as a flow of fully developed velocity field. However, the temperature field of the fluid flow is considered as an unsteady one. The governing equations are constitutive equation, momentum equation of steady flow and energy conservation equation of non-steady form. The present system of equations has been solved numerically by the splitting difference method. The numerical results show that the splitting difference method is suitable for the 2D problem of non-Newtonian fluid. The present application of the splitting diffference method is at first developed by us for non-Newtonian case. For the unsteady flow in the tube the finite difference scheme is given which leads to a tridiagonal system of equations.

Unsteady Rotative Flow of Non-Newtonian Fluid in an Annular Pipe

This paper .Studies power law no-Newtonian fluid rotative flow. in an annularpipe. The governing equation is nonlinear one, we linearized the governing equationby assuming that partial factor is at state. With Laplace transform we obtain ananalytical solution of the problem In the paper several groups of curves are given.these curves reflect the temporal change law and. spatial distribution of fluid velocity.In addition.we study the effection of power law index on the flow field the resultindicates that when the power law index n < l. the flow velocity is highly sensitive tothe index. and this fact is importanl in related engineering decisions.

Review: Prediction of Unexpected Fluid-Induced Vibration in Pipeline Network

This review considers unexpected destructive disasters involving fluid power plants, such as nuclear electric power plants and fluid power plants. It specifically addresses the possibility of fluid vibration induced in a pipeline network of such a plant. The authors investigate the flow oscillation induced within a T-junction for laminar steady flow at a Reynolds number less than 103 and clarify that there is a periodic fluid oscillation with a constant Strouhal number independent of several flow conditions. Generally, a nuclear electric power plant is constructed using straight pipes, elbows, and T-junctions. Indeed, a T-Junction is a basic fluid element of a pipeline network. The flow in a fluid power plant is turbulent. There are peculiar flow phenomena that occur at high Reynolds numbers, which are also seen in other flow situations;e.g., Kaman vortices are observed around a circular cylinder in low Reynolds numbers, around structures like bridges and downstream of islands in oceans. Although the flow situation of a T-junction and elbow in a fluid power plant, such as the fluid suddenly changing its flow direction is turbulent flow, the authors mention the possibility of the fluid-induced vibration of a pipeline network.

U型减摇水舱的流体动力特性分析及控制系统设计

船舶的减摇控制一直是船舶领域的重要研究方向,减摇水舱利用水舱液体的重力产生抗摇动力,提高船舶的稳定性。常见的减摇水舱包括主动式减摇水舱和被动式减摇水舱2种,被动式减摇水舱没有控制系统,只能借助舱内水体的惯性进行减摇;主动式减摇水舱具备舱内水泵控制系统,可根据外界环境特征,控制舱内水体的运动,具有更好的减摇效果。主动式减摇和被动式减摇水舱的结构以U型结构为主,本文研究主动式U型水舱的流体动力学性能和控制系统,详细介绍了控制系统构成和仿真过程。

基于热-流耦合模型的动力电池液冷系统冷却性能研究

构建了动力电池液冷系统的热-流耦合数值模型,其中冷却液流动过程采用一维非等温管道流方程计算。基于此模型,研究了不同运行参数对液冷系统冷却性能的影响规律。结果表明,当冷却液流量增大时,其功耗增大,但电池均温性提高;当冷却液进口温度升高时,系统泵功增加,但车载制冷系统功耗降低、电池均温性提高;当液冷系统停止温度升高时,其功耗降低,但启停次数呈增加趋势。上述模型对电池液冷系统的设计和优化具有重要意义。

液压能源管路系统振动主动控制的理论研究

对飞机液压能源管路系统的振动问题进行了探讨 .提出一种基于振动主动控制 (VAC)技术对飞机液压能源管路系统进行消振的方法 ,在手段上采用压电 压电致伸技术 ,以压电陶瓷 (PZT)作为作动器 ,具有驱动力大、响应频率高和体积小等优点 ;控制方法上采用参数寻优的控制策略 ,它能始终能根据外界干扰因素的变化来调整控制参数 .经过理论分析和仿真验证 ,证明其具有良好的自适应性和鲁棒性 。

PHEV电池包热管理系统设计优化与仿真分析

为实现电池包热管理系统低能耗和高效率散热的目的,文章通过流体动力学(CFD)仿真及实验对某插电式混合动力汽车(PHEV)乘用车电池包热管理系统进行优化研究。电池包热管理系统采用液冷散热,流场压力损失设计目标值为27kPa。初始方案中,流场压力损失实测值约为60 kPa,CFD仿真分析表明,液冷系统流场进出口是产生压力损失的主要部件;采用增大进出口管径的方法对液冷系统进行优化,仿真和实验结果表明,优化后的液冷系统压力损失减小至26 kPa左右;液冷系统流场优化后,对电池包散热特性进行仿真和实验分析,结果表明,在67.6 kW工况下电池包最高温度为53.2℃,低于目标值55℃。综合分析可以得出结论,优化后的电池包液冷系统各项指标达到目标状态。

脉宽调制流体位置控制系统稳定性的研究

在分析自然采样、双沿调制模拟式脉宽调制器的基础上,找出了由其组成的脉宽调制流体位置控制系统的特殊性,提出了系统稳定的必要条件.在由三通气动高速开关阀和差动气缸组成的脉宽调制高压气动位置控制系统上进行了实验研究。

流体空间管道布置过程研究及软件实现

对流体传动及控制系统空间管道布置过程进行全面分析，找出了空间管道设计所面临的问题，提出在微机上可行的解决办法，介绍软件的设计方法及所形成的软件的功能。