汽轮机转子热应力在线监测模型研究

从轴对称导热微分方程出发,根据汽轮机转子的特点,对转子模型进行简化,推导出汽轮机实心转子温度分布和热应力理论计算公式。此模型不仅可以用作实心汽轮机转子热应力理论分析、疲劳寿命计算,更方便用于转子在线监测,为汽轮机的安全启停和状态检修提供依据。     

Numerical simulation using boundary element method of the mechanism to enhance heat transport by solitary wave on falling thin liquid films

A boundary element method has been developed for analysing heat transport phenomena in solitary wave on falling thin liquid films at high Reynolds numbers.The divergence theorem is applied to the non-linear convective volume integral of the boundary element formulation with the pressure penalty function.Consequently,velocity and temperature gradients are dliminated.and the complete formulation is written in terms of velocity and temperature,This provides considerable reduction is storage and computational requirements while improving accuracy.The non-linear equation systems of boundary element discretization are solved by the quasi-Nweton iterative scheme with Broyden‘s update.The streamline maps and the temperature distributions in solitary wave and wavy film flow have been obtained,and the variations of Nusselt numbers along the wall-liquid interface are also given.There are large cross-flow velocities and S-shape temperature distributions in the recirculating region of solitary wave.This special flow and thermal process can be a mechanism to enhance heat transport.     

Numerical analysis for heat shield ablation law in transpiration cooling system

The transpiration cooling control system of the thermal protective shield with surface ablation is a nonlinear control system of distributed parameter with moving boundary.As far as the boundary conditions the third king and a one-dimensional incompressible coolant flow under constant transpiration mass flux are concerned,this paper transforms the definite solution problem into the second-type Volterra integral equations,and applies them directly to compute the shield ablation law.Investigation of the system‘s control by transpiration mass flux,ablation amount and ablation velocity varying with time,time of the ablation‘s beginning and ending,etc.,are presented.     

Fuzzy cascade control based on control''s history for superheated temperature

To address the characteristics of the large delay and uncertainty of superheated temperature, a new cascade control system is presented based on control’s history. Based on the analysis of the control objects’ dynamic characteristics, historical control information (substituting for the deviation change rate) is used as the basis for decision-making of the fuzzy control. Therefore, the changing trend of the controlled variable can be accurately reflected. Furthermore, a proportional component is introduced, the advantages of PID and fuzzy controllers are integrated, and the structure weaknesses of conventional fuzzy controllers are overcome. Simulation shows that this control method can effectively reduce the adverse impact of the delay on control effects and, therefore, exhibit strong adaptability by comparing the superheated temperature control system by this controller with PID and conventional fuzzy controllers. Translated from Proceeding of the CSEE, 2005, 25(10): 89–93 [译自:中国电机工程学报]     

Une méthode caractérisant l’influence réciproque entre parois: application aux échanges thermiques dans une cavité rotor–statorA method characterising the respective influence of the heated walls: application to the heat transfer in a rotor–stator cavity

This paper presents a heat transfer analysis for a turbulent flow in a rotor–stator system. A method based on the use of thermal influence coefficients is developed in order to determine wall heat transfer. This method is applied to an enclosed rotor–stator system as well as to an air-cooled rotor–stator system with centrifugal or centripetal injection. The comparison between numerical simulations and predicted heat fluxes shows small discrepancies. Then, the influence of the heated wall temperature on the other walls is discussed.     

An analytic solution of one-dimensional steady-state Pennes’ bioheat transfer equation in cylindrical coordinates

Based on the Pennes’ bioheat transfer equation, a simplified one-dimensional bioheat transfer model of the cylindrical living tissues in the steady state has been set up for application in limb and whole body heat transfer studies, and by using the Bessel’s equation, its corresponding analytic solution has been derived in this paper. With the obtained analytic solution, the effects of the thermal conductivity, the blood perfusion, the metabolic heat generation, and the coefficient of heat transfer on the temperature distribution in living tissues are analyzed. The results show that the derived analytic solution is useful to easily and accurately study the thermal behavior of the biological system, and can be extended to such applications as parameter measurement, temperature field reconstruction and clinical treatment.     

Experimental Investigation of Transient Heat Transferin the Once-Through Boiler Water Separator

INTRODUCTI0NWaterseparat0risanimportantthickwallc0mpo-nentof600MWsupercriticalpressureboiler.Itsmainfunctionist0ensurethattheevap0rator,superheater,reheaterandeconomizert0becooledfullyandoper-atesafelyduringstart-up.Itisfittedatthe0utletofevaPorator.Whentheb0ilerloadislessthan35%MCR(boilermaJximumc0ntinuousevaporation),sub-cooledwaterorwatersteammixturefromtheevap-orator0fupperc0mbustioncharnberenterstangen-tiallyinthewaterseparator.Thesteam,separatedbycentrifugalforceandgravity,flowsi…     

Dynamic characteristics of molten droplets and hot particles falling in liquid pool

The dynamic characteristics of molten droplets and hot particles at the very beginning of their fall into coolant pools are presented. The falling course of a single droplet or a single hot particle was recorded by a high-speed camera and a curve of velocity vs. time was obtained. Emphasis was placed on the effects of the droplet’s size and temperature, the coolant’s temperature and properties, and the droplet’s physical properties on the moving behavior. The results for the all cases showed that the velocity of a falling droplet/particle decreased rapidly but rebounded shortly, at the beginning of droplet/particle falling in the coolant. Following such a V-shaped evolution in velocity, the droplet/particle slows down gradually to a comparatively steady velocity. An increase in either coolant temperature or droplet temperature results in a larger velocity variation in the “J-region”, but a smaller deceleration when it moves out of the “J-region”. The elevated volatility of a coolant leads to a steeper deceleration in the “J-region” and beyond. The bigger size of a particle leads to a greater velocity variation in the “J-region” and terminal velocity. A high melting point and thermal conductivity as well as lower heat capacity contribute to dramatic variation in the “J-region” and low terminal velocity.     

Air-borne noise of thermal module and system for notebook personal computers:experimental study

Thermal performance is the most important issue to be considered when a thermal module is designed for a notebook personal computer (PC). Because the fan causes air-borne noise and affects the user’s comfort, the acoustic characteristics of the module attract more attention. Experiments were conducted to study the noise sources, the noise characteristic and the main factors influencing the noise level. The difference between the air-borne noise of the thermal module and the whole computer system was analyzed and its propagating characteristics were derived. The influence of I/O ports on the air-borne noise was also studied experimentally. __________ Translated from Journal of Shanghai Jiaotong University, 2007, 41(3): 465–468 [译自: 上海交通大学学报]     

Heat transfer in a reaction–diffusion system with a moving heat source

A general formulation is presented for a moving boundary problem in which heat is generated at the boundary due to an exothermic reaction involving a species which diffuses into a dispersed phase from an external medium of finite volume. The speed of the moving boundary is prescribed based on the solution of the mass diffusion problem and an analysis is presented of the thermal dynamics of the system. The set of equations describing heat transport leads to a Green’s function type problem with time dependent boundary conditions and the Galerkin finite element method is employed to develop a numerical solution. Transformations are introduced to freeze the moving boundary and partition the domain for ease of computation, and an iterative scheme is defined to satisfy the heat flux jump boundary condition and match the temperature field across the moving boundary. The numerical results are used to set the limits of applicability of an analytical perturbation solution. Essential aspects of thermal dynamics in the system are described and parametric regions resulting in a local temperature hot spot are delineated. Computed contour plots describing thermal evolution are presented for different combinations of parameter values. These may be of utility in the prediction of thermal development, for control and avoidance of hot spot formation, and in physical parameter estimation.     

Numerical prediction of turbulent flow and heat transfer with phase change in crystallizer of inverse casting

horoductionInverse casting is a technique for Producing nearnet-shape cast strips. T'he main idea of this technique isdeveloped from a successful inveshgation['], in which ithas been Proved that the inverse cashng teclmiquewould be applicable to produce the steel strip with aabackness of 0.5-3 nun, with a good material prOPertyand with a lower energy consumption in contrast withconventional conhnuous cashng process. The POssibilitytO p~ce composite strips is also one of the mostattrachve pro…     

Analysis of the Impact of Nonlinear Heat Transfer Laws on Temperature Distribution in Irradiated Biological Tissues: Mathematical Models and Optimal Controls

In this paper, we consider nonlinear control problems governed by some generalized transient bioheat transfer-type models with the nonlinear Robin boundary conditions. The control estimates the blood perfusion rate, the heat transfer parameter, the distributed energy source terms, and the heat flux due to the evaporation, which affect the effects of thermal physical properties on the transient temperature of biological tissues. The result can be very beneficial for thermal diagnostics in medical practices, for example, for laser surgery, photo and thermotherapy for regional hyperthermia often used in treatment of cancer. First, the mathematical models are introduced and the existence, uniqueness, and regularity of a solution of the state equation are proved as well as the stability and maximum principle under extra assumptions. Afterwards, the optimal control problem is formulated in order to control the online temperature given by radiometric measurement. We prove that an optimal solution exists and obtain necessary optimality conditions. Some strategy for numerical realization based on the adjoint variables are provided.      

Frequency control of singularly perturbed forced duffing’s oscillator

We analyze the dynamics of the forced singularly perturbed differential equation of Duffing’s type. We explain the appearance of the large frequency nonlinear oscillations of the solutions. It is shown that the frequency can be controlled by a small parameter at the highest derivative. We give some generalizations of results obtained recently by B. S. Wua, W. P. Suna, and C. W. Lim. Analytical approximations to the double-well Duffing oscillator in large amplitude oscillations (see J. Sound Vibration 307 (2007), Nos. 3–5, 953–960). A new method for an analysis of the nonlinear oscillations which is based on the dynamic change of coordinates is proposed.     

A novel approach to accelerate attainment of thermal steady state in coupled thermomechanical analysis of machining

A novel approach for obtaining the steady state temperature distribution of cutting tools involves reducing the specific heat capacity of the cutting tool by a scale factor and carrying out a short duration single step thermomechanical analysis. Reduction of the specific heat causes the thermal time constant of the tool to be reduced by the same scale factor, making it closer to the mechanical time constant required for stabilization of the chip geometry, and enables rapid attainment of mechanical and thermal steady state conditions. As expected, FEA results show that the steady state temperature distribution achieved by the reduced specific heat approach is exact. Results obtained from a single step simulation of the first 1200 μs of cutting, using this approach, are found to be more accurate than those obtained using the time consuming multistep analysis approach used to date. Rapid attainment of an accurate steady state temperature distribution permits tool wear rate to be calculated accurately using tool wear models. This enables tracking of changes in tool geometry due to wear over time, and resulting changes in the machining process and quality of parts produced. It is also shown that this approach is essential for accurate simulation of processes such as saw-tooth chip formation, where the ‘steady state’ involves local periodic thermomechanical changes, and leads to accurate thermomechanical results so long as the specific heat of the local region experiencing significant thermal oscillations is not scaled. An estimate for the size of this boundary layer, related to the wavelength of the thermal waves, is also given. The reduced specific heat approach can be used in many other applications involving a range of phenomena coupled with temperature, where the thermal changes are the most sluggish and take the most time to reach steady state.     

Calculation and analysis of sub/supercritical methanol preheating tube for continuous production of biodiesel via supercritical methanol transesterification

Biodiesel is an important renewable energy. Supercritical methanol transesterification for biodiesel has recently been concerned because of its obvious advantages. The tubular reactor is an ideal reactor for continuous preparation of biodiesel via supercritical methanol transesterification. A methanol preheating tube is necessary for the tubular reaction system because the reaction temperature for supercritical methanol transesterification is usually 520―600K. Therefore, in the range of 298―600K, changes of the density, isobaric capacity, viscosity and thermal conductivity of sub/supercritical methanol with temperature are first discussed. Then on the basis of these thermophysical properties, an integration method is adopted for the design of sub/supercritical methanol preheating tube when methanol is preheated from 298K to 600K at 16MPa and the influencing factors on the length of the preheating tube are also studied. The computational results show that the Reynolds number Re and the local convection heat-transfer coefficient α of sub/supercritical methanol flowing in ф6mm×1.5mm preheating tube change drastically with temperature. For the local overall heat transfer coefficient K and the average overall heat transfer coefficient K_m, temperature also has an important influence on them when the inlet velocity of methanol is lower than 0.5m/s. But when the inlet velocity of methanol is higher than 0.5m/s, K and K_m almost keep invariable with temperature. Additionally, both the outlet temperature and the inlet velocity of methanol are the key affecting factors for the length of the preheating tube, especially when the outlet temperature is over the critical temperature of methanol. At the same time, the increase of tin bath’s temperature can shorten the required length of the preheating tube. At the inlet flow rate of 0.5m/s, the required length of the preheating tube is 2.0m when methanol is preheated from 298K to 590K at 16MPa with keeping the tin bath’s temperature 620K, which is in good agreement with the experimental results.     

A computational method for determining segmental and overall geothermal gradients and geothermal heat flow values

A new computational method is presented which calculates geothermal heat flow values and geothermal gradients with more precision than permitted by previously published techniques. The data required are: geothermal temperature at a known depth, mean surface temperature, the rock types in the stratigraphic column and the thermal resistivity values for the different types of rocks. This method is valuable in areas that have no measured gradient values. Basic equation used was the Fourier heat transfer equation where is heat flux in μcal/(cm² s), ρ_i is thermal resistivity (°C s cm/μcal) and ∂T/∂x is the x component of the temperature gradient (°C/cm). The thermal resistivity was allowed to vary linearly with temperature ρ_i = ρ_i^o [1 + K_i (T − 30)] where ρ_i is thermal resistivity of the lithographic segment «iå at a temperature T, ρ_i^o is thermal resistivity at 30°C and K_i is the temperature coefficient of thermal resistivity. The procedure consisted of integrating the combined equation for heat flux in terms of temperature dependent resistivity.Two iterative solutions were used to simplify the calculations: exact and approximate. The heat flux for each well was assumed to be 1.0 HFU and segmental temperatures were calculated from the bottom (arbitrarily) up, until a surface temperature was obtained. The calculated surface temperature could then be compared with the mean surface temperature (MST). Correction in the heat flux value was made until the calculated surface temperature and MST agreed. An analysis of three deep Appalachian test wells was made and the results showed the critical importance of lithographic ordering and the temperature dependence of thermal resistivity upon calculated geothermal quantities.     

Thermoelastic vibration analysis of functionally graded skew plate using nonlinear finite element method

Numerical investigation of nonlinear free vibration of functionally graded skew (FGS) plate in the thermal environment is presented. The mathematical model is proposed for the first time based on higher order shear deformation theory in conjunction with Green–Lagrange-type geometric nonlinearity for the FGS plate subjected to a thermal load. The material properties are considered to be temperature dependent and are graded along the thickness direction as per simple power law of distribution in terms of volume fraction of the constituent phase. The governing algebraic equations are derived using Hamilton’s principle, and the solutions are obtained using the direct iterative method. The proposed finite element model has discretized into an eight-noded quadratic serendipity elements. To validate the model, the obtained results are compared with the available literature. The influence of volume fraction index, skew angle, temperature change, aspect ratio, side–thickness ratio, and boundary conditions on the linear and nonlinear frequency of skew functionally graded material plate is examined and discussed in detail.     

Average temperature of the rotor of high-speed rotating heat exchanger during the period of thermal start-up

The paper presents results of the calculations of the average temperature variations of model rotor of a high-speed rotating heat exchanger in the course of thermal start up. A model rotor adopted for the calculations has a porous structure formed by radially oriented ducts of a constant circular cross-section. The scope of this paper covers numerical calculations of temperature distribution in the material of the rotor versus its rotational speed, temperature difference of the gases at the inlet, and types of the rotor material. With the use of these results, graphs are elaborated representing the dependence of the rotor’s dimensionless temperature on the Fourier number, with the Biot number used as a parameter.     

基于加热弱光纤阵列分布式测量技术的大坝渗流监测新方法

新型弱光纤阵列分布式测量技术是大坝渗流监测的新技术。根据弱光纤光栅测温原理、对流传热方程组和牛顿冷却公式,推导出热光纤渗流监测理论公式。设计了基于加热弱光纤监测渗流的圆筒模型试验,通过光纤周围温度场与渗流场的耦合关系,间接获得圆筒模型的渗流状态。试验结果表明,温度边界层是影响温度场和渗流场的重要因素,渗流水温度对温度边界层影响较大;渗流量与温差ΔT的线性度高;渗流流速u在0.02~0.08cm/s时与ΔT/θ(θ为光纤测量温度与渗流水温度之差)拟合关系式的各项系数与理论推导公式相近。     

Effects of thermocline on performance of underwater glider’s power system propelled by ocean thermal energy

The thermal glider’s changeable volume produces propelling force to power the glider’s descending and ascending through the thermocline. The different depth, thickness, and intensity of the thermocline at different seasons and locations affect the working processes of the glider’s power system. Based on the enthalpy method, a mathematical model of the underwater glider’s power system was established and the time efficiency of operation was introduced, so that the effects of different thermoclines on the underwater glider’s power system were analyzed theoretically. The simulation result shows that the thermocline affects the transition time of the phase change processes of working fluids within the thermal engine tubes. There exist the threshold values of the thermocline’s depth and upper thickness for the power system’s operation. A depth or upper thickness of the thermocline less than the corresponding threshold leads the power system to work abnormally. To keep the power system working efficiently, a glider must be kept in warm surface water for a certain period before it moves through cold water, so that the time efficiency of operation is reduced. A less time efficiency of operation is unfavorable to the thermal glider to penetrate through the ocean currents.