Temperature field analysis of tangential clearance leakage flow for scroll compressor based on fuzzy ridgelet finite element method

To improve the computing precision and efficiency of temperature field analysis in tangential clearance of scroll compressor, the ridgelet finite element method is combined with fuzzy finite element method to construct the fuzzy ridgelet finite element method of analyzing temperature field in tangential clearance. First, the related research progresses on heat transfer of scroll compressor, wavelet finite element method, and fuzzy finite element method are summarized. Second, the leakage flow model of tangential clearance in scroll compressor is studied in depth. Third, the heat transfer model of leakage flow in tangential clearance of scroll compressor is established, and then the fuzzy ridgelet finite element model is constructed, the fuzzy finite element model is transformed to the random model based on information entropy, the corresponding calculating procedure is designed. Finally, the simulation analysis is performed based on fuzzy finite element method, fuzzy Daubechies wavelet finite element method, and the fuzzy ridgelet finite element model, respectively, comparing analysis between simulation and test results shows that the fuzzy ridgelet finite element method has best computing effectiveness on temperature field analysis of tangential clearance of scroll compressor. In addition, the tangential clearance temperature of scroll compressor with and without water cooling has been analyzed based on the fuzzy ridgelet finite element method, and the results show that the water cooling system can reduce the temperature in tangential clearance greatly.     

Study on heat transfer of leakage flow in tooth tip clearance for single screw compressor based on fuzzy contourlet finite element method

Heat transfer of leakage flow in tip clearance will reduce the working performance, and therefore it is necessary to study it in depth. To improve the computing effectiveness of heat transfer of leakage flow in the tooth tip clearance of the single-screw compressor, the fuzzy contourlet finite element model is constructed by combining the contourlet finite element method and fuzzy finite element method. First, the related research progresses are summarized. Second, heat transfer model of leakage flow in the tip clearance of single-screw compressor is constructed. Third, the fuzzy contourlet wavelet finite element model is established. Finally, heat transfer simulation of leakage flow in the tip clearance of single-screw compressor is performed, and the variables with fuzziness are chosen, which are transformed to random variables based on information entropy theory. The comparing analysis among simulation analysis and test results is performed, and results show that the contourlet finite element method has highest computing precision and efficiency. In addition, the temperature of leakage flow in the tip clearance (L1) is also obtained, and results show that the fuzzy contourlet wavelet finite element method can effectively obtain the temperature distribution rules with fuzziness.     

Study on heat transfer of ground heat exchanger based on wedgelet finite element method

In order to maximize the economic benefit of ground source heat pump system, it is necessary to grasp the heat transfer rules of ground heat exchanger, the wedgelet finite element method is applied in analyzing heat transfer process of ground heat exchanger. First, existing researches on heat transfer analysis of ground heat exchanger and wavelet finite element method have been summarized. Second, the basic characteristics of wedgelet function are studied. Third, the wedgelet finite element model of analyzing heat transfer rules of ground heat exchanger is constructed using wedgelet function as interpolation function. Finally, the heat transfer simulation analysis of vertical U-type ground heat exchanger is carried out, and results show that the wedgelet finite element has higher precision and efficiency, and the effect of main affecting factors on heat transfer rules of ground heat exchanger is obtained.     

Research on the performance of water-injection twin screw compressor

Due to the development of the automotive fuel cell systems, the study on water-injection twin screw compressor has been aroused again. Twin screw compressors with water injection can be used to supply the clean compressed air for the Proton Exchange Membrane (PEM) fuel cell systems. In this research, a thermodynamic model of the working process of water-injection twin screw compressor was established based on the equations of conservation of mass and energy. The effects of internal leakage and air–water heat transfer were taken into account simultaneously in the present mathematical model. The experiments of the performance of a prototype compressor operating under various conditions were conducted to verify the model. The results show that the predictions of the model are in reasonable agreement with the experimental data.     

Method for modifying convective heat transfer coefficients used in the thermal simulation of a feed drive system based on the response surface methodology

ABSTRACT

This paper presents a method based on response surface methodology (RSM) to calculate the convective heat transfer coefficients (CHTCs) of a feed drive system. First, the temperature values at thermal-critical points and ball screw thermal elongation of a feed drive system were obtained by experimental and finite element (FE) methods. Second, the relationship between the CHTCs and simulated temperature values was established using RSM, and the CHTCs were calculated using the designed 25 tests. Finally, the effectiveness of the proposed method was proved using steady-state and transient-state simulation of the feed drive system.     

交流特高压杆塔基础混凝土温升研究

针对特高压线路杆塔基础故障散流时引起混凝土温升问题,基于热力学有限元分析理论构造杆塔基础模型块,在比较ANSYS软件仿真和试验结果的基础上确立了混凝土发热仿真分析的可行性和有效性。对典型垂直四塔基单桩特高压杆塔基础散流情况下混凝土最大温升计算表明,杆塔基础混凝土的热稳定性能得到保证。     

FINITE ELEMENT ANALYSIS OF COUPLED HEAT. MASS,AND PRESSURE TRANSFER IN POROUS BIOMATERIALS

Abstract

The finite element method was used to solve Luikov's system of partial differential equations for neat, mass, and pressure transfer in capillary porous bodies. The finite element predictions were validated by comparing with exact solutions and the analytical results given by Mikhailov and Shishedjiev [1]. An application of the finite element method to the drying of wood (spruce) and a comparison based on an eigenvalue solution for simultaneous heat and mass transfer [2] are also provided. This technique was applied to study the coupled transport process in a silicon gel. The simulation indicated that the results obtained from the heat, mass, and pressure transfer model showed a marked difference from the results obtained by the heat and mass transfer model.     

Heat pump system utilizing produced water in oil fields

As the alternative to the heating furnace for crude oil heating, a heat pump system utilizing produced water, a main byproduct, in oil fields was proposed and the thermodynamic model of the system was established. A particular compression process with inner evaporative spray water cooling was applied in the screw compressor and an analysis method for the variable-mass compression process was introduced. The simulation results showed that the efficiency of the screw compressor, the temperature of produced water and the temperature difference in flash process are key parameters affecting the system performance. The energy cost of the heat pump system was compared to that of the heating furnace, revealing that the heat pump system with EER, 4.67, would save over 20% energy cost as compared with the heating furnace. Thus, the heat pump system was energy saving, money saving and environmentally benign.     

Computational and experimental study of nanosecond laser ablation of crystalline silicon

In this paper, a numerical model of nanosecond laser ablation of crystalline silicon has been established. Based on the highly nonlinear model of heat transfer and phase change in crystalline silicon after absorbing laser light, heat transfer equation is solved by using finite element method implemented in ANSYS. The simulation of ablation depth of crystalline silicon is obtained under different conditions of laser fluence and pulse overlap. Comparing with the ablation morphology obtained from SEM observations, the computational results and experimental data show good agreement.     

高温条件下接触热阻的数值模拟与试验研究

接触热阻是衡量接触界面间传热效率的重要指标之一。利用ANSYS有限元软件对高温条件下高温合金GH4169界面间的接触热阻进行了研究。通过光学显微镜获得高温合金表面的真实形貌,并在ANSYS有限元软件中重建其表面模型,基于结构力学理论对接触界面微观结构的弹塑性变形进行模拟,以及传热学分析获得接触界面间的接触热阻值。研究了界面温度与接触压力对接触热阻的影响,同时考虑了高温条件下接触界面间辐射换热的影响,最后利用试验测试装置进行验证。结果表明：理论模拟与试验测试的结果两者之间的最大误差为12.6%,高温合金界面间的接触热阻随着界面温度和接触压力的增加而减小;接触界面温差随着界面温度的增加出现先增大后减小的趋势。     

Thermal energy storage in the ground: Comparative analysis of heat transfer modeling using U-tubes and boreholes

Large scale thermal energy storage for solar heating applications can be accomplished in the ground through the installation of an array of vertical heat exchange boreholes or U-tubes. Simulation modeling of the storage subsystem and its integration with the total system is essential for design and performance evaluation. Although U-tube storage design is especially attractive in clay soils and preferable to boreholes in many geological conditions, only a borehole simulation model is currently available, validated, and integrated into a system simulation model. This article presents a comparative analysis of the heat transfer from boreholes and U-tubes using analytical solutions, finite element modeling, and the available simulation model. The analysis is used to support the development of a methodology by which the heat transfer of any U-tube configuration can be modeled by appropriately specifying parameters in the borehole storage simulation model. The borehole model can then be used to model the storage subsystem integrated within a total system simulation model.     

考虑沸腾换热的内燃机流固耦合传热分析

某发动机在开发过程中缸套顶部出现机油结焦现象.为分析原因,建立了该发动机缸盖缸体整机耦合传热模型,通过CFD三维仿真获得冷却水侧及缸内燃气侧的温度和对流换热系数分布,并映射至对应结构分析边界单元,建立了整机结构传热分析的边界条件;同时基于BDL单相流沸腾换热模型编写相关子程序考虑了沸腾换热的影响,求解分析了该发动机试验状态下的温度场,并进行了优化.计算表明,结焦现象发生区域温度明显高于机油碳化温度,同时沸腾换热对局部关键高热区影响可达15℃以上.为验证分析结果,分别测量了原方案和优化方案缸套顶部缸间温度,结果表明,考虑沸腾换热后缸间温度计算值与实测数据非常接近,采用优化方案后缸套顶部机油结焦问题得到排除.     

Estimation of Temperature Fields in Local Tissues During Intracavitary Hyperthermia

INTRODUCTIONAsthefifththerapyforcancerfollowingoperativemethodsoftreatment,radiotherapy,chemotherapyandimmunizationtherapythyperthermiatreatmenthasbeengenerallyusedinclinicaltreatmentofcancerrecelltyears.Theprimaryobjectforanyhyperthermiatreatmentsys...     

Streamline upwind numerical simulation of two-dimensional confined impinging slot jets

In the present paper, flow and heat transfer characteristics of confined impinging slot jets have been numerically investigated using a SIMPLE-based segregated streamline upwind Petrov-Galerkin finite element method. For laminar jets, it is shown that the skin friction coefficient approaches the grid-independent Galerkin solution and that the present simulation induces negligible false diffusion in the flow field. For turbulent jets, the k-ω turbulence model is adopted. The streamwise mean velocity and the heat transfer coefficient respectively agree very well with existing experimental data within limited ranges of parameters.     

Hydromagnetic effect on mixed convection in a lid-driven cavity with sinusoidal corrugated bottom surface

The present numerical simulation is conducted to analyze the mixed convection flow and heat transfer in a lid-driven cavity with sinusoidal wavy bottom surface in presence of transverse magnetic field. The enclosure is saturated with electrically conducting fluid. The cavity vertical walls are insulated while the wavy bottom surface is maintained at a uniform temperature higher than the top lid. In addition, the transport equations are solved by using the finite element formulation based on the Galerkin method of weighted residuals. The implications of Reynolds number (Re), Hartmann number (Ha) and number of undulations (λ) on the flow structure and heat transfer characteristics are investigated in detail while, Prandtl number (Pr) and Rayleigh number (Ra) are considered fixed. The trend of the local heat transfer is found to follow a wavy pattern. The results of this investigation illustrate that the average Nusselt number (Nu) at the heated surface increases with an increase of the number of waves as well as the Reynolds number, while decreases with increasing Hartmann number.     

基于有限元方法的溴化锂降膜吸收传热传质的数值研究

吸收器是吸收式制冷系统的重要部件.溴化锂溶液的降膜吸收是吸收器中最常见的传质传热形式之一.通过对溴化锂溶液在降膜吸收过程中传质和传热特性的分析,使用基于有限元法的COMSOL Multiphysics软件,建立了溴化锂溶液和水蒸汽降膜吸收的物理数学模型,计算了液膜内部温度和质量分数的分布、界面处传质通量、界面处传热通量...     

增压器压气机叶轮低周疲劳强度有限元计算分析

作为涡轮增压器的核心零件,压气机叶轮主要失效模式是低周疲劳破坏。为了获得某新设计压气机叶轮的低周疲劳极限强度,确定叶轮低周疲劳试验转速,应用ANSYS有限元软件,主要考虑离心应力,采用周期循环模型、选用20节点等参单元计算方法、对该叶轮进行了强度计算和分析-得到了该叶轮的应力-转速曲线,为叶轮低周疲劳试验提供了理论依据。     

Effect of magnetic field on g-jitter induced convection and solute striation during solidification in space

A 2-D finite element model is presented for the melt growth of single crystals in a microgravity environment with a superimposed DC magnetic field. The model is developed using deforming finite element methodology and predicts steady and transient convective flows, heat transfer, solute distribution, and solidification interface morphology associated with the melt growth of single crystals in microgravity with and without an applied magnetic field. Numerical simulations were carried out for a wide range of parameters including idealized microgravity condition, synthesized g-jitter and real g-jitter data taken by on-board accelerometers during space flights. The results reveal that the time varying g-jitter disturbances, although small in magnitude, cause an appreciable convective flow in the liquid pool, which in turn produces detrimental effects during the space processing of single crystal growth. An applied magnetic field of appropriate strength, superimposed on the microgravity, can be very effective in suppressing the deleterious effects resulting from g-jitter disturbances.     

Finite element modeling of coating formation and transient heat transfer in the electric arc spray process

The electric arc sprayed coating can be described as a superposition of Gaussian profile particles whose overlapping depends on the movement of spray gun. The heat transfer behavior during the deposition has a significant influence on the performance of the process. In this paper, simulation of the coating formation and analysis of the transient heat transfer were performed based on a newly developed finite element model, in which the dynamic stochastic multiple particles deposition characteristic of the process was taken into account. In order to investigate the effects of the kinematics and dimensional aspects on the coating/substrate temperature distribution, a traditional layer-by-layer finite element model without consideration of gun movement and particles Gaussian profile was also performed as a comparison. The stochastic deposition model provided a more objective result of the transient heat transfer of the coating/substrate than that of the layer-by-layer model, especially the severely inhomogeneous temperature distribution characteristics in different locations and spraying conditions. Finally, the molding results were experimentally compared with the temperature measurements on the coating surface and substrate back face using an infrared thermal imaging video camera, which shows that most of the modeling findings are consistent with that of the experiment.     

Improving the efficiency of the numerical modelling of built environment earth-contact heat transfers

This paper reports on a method which has been developed to improve the efficiency of the numerical simulation of built environment earth-contact heat transfers. This method modifies a numerical method by incorporating elements of the response factor method. Additionally, this paper reports on the use of extrapolation techniques to further speed up one stage of the simulation. Essentially, the method requires that a numerical technique be initially used to generate a certain number of simulated hours for use as a time-series by the response factor element of the method. This first (‘pre-processing’) part of the procedure takes a certain time and this time can be significantly reduced by means of the extrapolation techniques described in the paper. However, assuming that the earth-contact domain remains unchanged from then on, this ‘pre-processing’ does not need to repeated, and every subsequent simulation that is performed to calculate the effect on the earth-contact heat transfer of changing another parameter (i.e. during a parametric analysis) takes only a few seconds. Reductions in run-time for these successive simulations are of the order of 1000 times faster than the full finite volume technique whilst still retaining the flexibility and accuracy of this method.