A Lie-Group Adaptive Method to Identify Spatial-Dependence Heat Conductivity Coefficients

We consider an inverse problem for numerically estimating a spatial-dependence heat conductivity α(x) in T _t (x, t) = ?[α(x)T _x ]/? x + h(x, t), 0 < t < t _f , 0 < x < ?; α(x) is assumed to be a continuous function of x, and α(?) is given. An iterative Lie-group adaptive method (LGAM) is developed, which can be used to find α(x) at the spatially discretized locations x _i , requiring only a few measured temperature data at a final time t _f as a target to select a suitable value of the parameter r ∈ [0, 1] appearing in the present method. The new method has three advantages in that no a priori information of the heat conductivity function is required, only a few extra data are measured, and it is robust againt noise. The accuracy and efficiency of the present method are confirmed by comparing the estimated results with some exact solutions.     

一种基于低品位热源的LNG冷能回收低温动力系统

在分析LNG物理冷Yong的基础上,提出了一种基于低品位热源的LNG冷能回收低温动力系统,并对影响系统循环效率的相关参数进行了研究。结果表明,在较低的热源温度下,系统的热效率和烟效率可以达到30％以上;对影响循环的主要参数分析表明,二次冷煤的冷凝温度及膨胀机进口压力对循环的效率影响很大。随着冷凝温度的降低及膨胀机进口压力的提高,循环热效率、Yong效率都将有所提高。     

控制容积平衡法在一维、稳态且含内热源导热微分方程中的应用

首先采用区域离散方法A和区域离散方法B分别划分计算网格节点,然后采用控制容积平衡法对某一维、稳态且含内热源导热微分方程进行了数值求解,并与其解析解（精确解）进行了比较.计算结果表明：控制容积平衡法物理意义明确,数值求解精度高,且随网格划分节点数的增加计算精度进一步提高;对于这两种网格划分方法,其网格节点处的离散方程推导均简单明了,且都具有统一的形式,因此对计算节点数增加的情况具有很大的适应性,有利于计算机编程实现.     

On the Accuracy of a Finite-Difference Method for Parabolic Partial Differential Equations with Discontinuous Boundary Conditions

Although the numerical solution of parabolic partial differential equations (PDEs) is widely documented, the effect of discontinuous boundary conditions on numerical accuracy is not. This article employs the Keller box finite-difference method to study the effect of such discontinuities when solving the linear one-demensional transient heat equation. We demonstrate that this formally second-order-accurate scheme can lose accuracy, but that an analytical understanding of the behavior of the solution helps in providing an accuracy-restoring formulation. Benchmark computations are presented that will provide guidance in the numerical solution of nonlinear parabolic PDEs for which there are no closed-form analytical solutions.     

基于机组负荷-压力动态模型的燃煤发热量实时计算方法

煤质变化剧烈是当前影响火力发电机组稳定运行的一个主要因素.针对此问题,提出一种基于机组负荷一压力动态模型的燃料发热量实时计算方法.首先建立机组负荷一压力之间简化的非线性动态模型,然后根据机组设计参数和扰动实验获得的数据,推导出燃料发热量的计算公式,利用调节级后压力、汽包压力、给煤量等实时计算燃料发热量.实验表明,该方法得到的燃料发热量具有动态响应速度快、稳定性好、准确度高的优点,具有很好的工程实用价值.     

A Study of Two-Step Heat Conduction in Laser Heating Using the Hybrid Differential Transform Method

This article presents a numerical approach using the hybrid differential transform/finite-difference method to study heat transfer in a thin film exposed to ultrashort-pulsed lasers based on the hyperbolic two-step model. The governing equations are transformed from the time domain into the spectrum domain using the differential transform method and then discretized in the space domain by the finite-difference method. The numerical solutions are obtained through a recursive process. The results show that even though the electron/lattice temperature is at equilibrium at only a couple hundred degrees, the maximum electron temperature can reach as high as several thousand degrees.     

Oscillation of Linear Ordinary Differential Equations: On a Theorem of A. Grigoriev

We give a simplified proof and an improvement of a recent theorem of A. Grigoriev, placing an upper bound for the number of roots of linear combinations of solutions of systems of linear equations with polynomial or rational coefficients. To Yulij Sergeevich Ilyashenko on his 60th birthday. 2000 Mathematics Subject Classification. 34C08, 34C10, 34M10. Gershon Kekst professorial chair in Mathematics.     

基于价值工程的热机设备选型方法分析及实践

目的  传统设计工程中,热机辅机设备设计选型存在两种倾向,一是以功能为先,忽视成本;二是以低成本为准,忽略部分功能的重要性。这两种选型方式都存在一定的缺陷,不能实现功能与成本的统筹,不能获取收益最大化。随着行业发展,设计工程热机设备选型越来越重视性价比,即以合理的成本实现最佳的功能。 方法  将价值工程理论应用于热机设备选型,通过价值系数公式,统一考虑功能与成本,实现热机设备选型方案的最优选择。 结果  结合实际案列,文章论证了价值工程理论应用于热机设备选型的可行性。 结论  为后续电厂在设计设备选型过程中实现设备的功能与成本统一论证提供了一种可行方法。     

A three-region conduction-controlled rewetting analysis by the Heat Balance Integral Method

Conduction-controlled rewetting of two-dimensional objects is analyzed by the Heat Balance Integral Method (HBIM) considering three distinct regions: a dry region ahead of wet front, the sputtering region immediately behind the wet front and a continuous film region further upstream. The HBIM yields solutions for wet front velocity, sputtering length and temperature field with respect to wet front. Employing this method, it is seen that heat transfer mechanism is dependent upon two temperature parameters. One of them characterizes the initial wall temperature while the other specifies the range of temperature for sputtering region. Additionally, the mechanism of heat transfer is found to be dependent on two Biot numbers comprising a convective heat transfer in the wet region and a boiling heat transfer in the sputtering region. The present solution exactly matches with the one-dimensional analysis of K.H. Sun, G.E. Dix, C.L. Tien [Cooling of a very hot vertical surface by falling liquid film, ASME J. Heat Transf. 96 (1974) 126–131] for low Biot numbers. Good agreement with experimental results is also observed.     

Thermal Stresses Induced by a Variable Heat Source in a Rectangle and Variable Pressure at Its Boundary by Finite Fourier Transform

This paper deals with the two-dimensional, non-homogeneous boundary value problem for static, isotropic and thermoelastic material occupying an infinitely long cylinder with a rectangular cross-section. The cylinder is surrounded by a given temperature and subjected to variable pressures at its boundaries. We deal with static, uncoupled, linear thermoelasticity. The equations of heat conduction and mechanical problem are considered separately. The technique of the finite Fourier transform is used for the solution. The thermoelastic behavior, due to an internal heat generation within the domain, is discussed. The results for displacement and stresses have been computed from the Airy stress function and are illustrated graphically.     

Optimal Homotopy Asymptotic Solutions for Nonlinear Ordinary Differential Equations Arising in Flow and Heat Transfer due to Nonlinear Stretching Sheet

Optimal homotopy asymptotic method (OHAM) is used to obtain solutions for nonlinear ordinary differential equations (ODEs) arising in fluid flow and heat transfer at a nonlinear stretching sheet. The solutions for skin friction and temperature gradient for some special cases are tabulated and compared with the available numerical results in the literature. Moreover, OHAM is found to be very easy to use and the technique could be used for solving coupled nonlinear systems of ordinary differential equations arising in science and engineering.     

基于蒙特卡洛法的单室火灾热辐射计算

根据CFAST软件模拟简单房间着火后热烟气层温度及高度的变化情况,采用蒙特卡洛法计算热烟气层对房间地板面及地板中心1m2面积上的平均热辐射通量.计算时,分别假设烟气层的辐射能力集中于热烟气层的下表面,或烟气层为温度均匀的灰体,结果表明两种假设的计算结果相近.根据两种假设计算出的地板面上的热辐射通量,预测出室内发生轰燃的时间分别是640s和700s,与CFAST软件的预测结果665s相近.评估中引入热辐射对人体的伤害判据,其结果也可以用来估算安全疏散时间.     

用渐近分析法研究蜂窝蓄热体温度分布

1前言在冶金、机械和石化工业锻造炉、均热炉、连续加热炉、热处理炉、钢包烘烤炉、辐射管和熔铝炉上应用的高温空气燃烧(High Temperature Air Combustion,Hi-TAC)[1],具有热效率高、低NOx排放和燃烧放热均匀等特点。大多数的HiTAC应用了蜂窝蓄热系统[2]。温度变化和温度效率(     

A comprehensive analysis of conduction-controlled rewetting by the Heat Balance Integral Method

A two region conduction-controlled rewetting model of hot vertical surfaces with a constant wet side heat transfer coefficient and negligible heat transfer from dry side is solved by the Heat Balance Integral Method (HBIM). The HBIM yields a simple closed form solution for rewetting velocity and temperature distribution in both dry and wet regions for given Biot numbers. Using this method it has been possible to derive a unified relationship for one-dimensional object and two-dimensional slab and rod. The effect of convection is expressed by an effective Biot number whose exact value depends on the geometry and process parameters. The solutions are found to be exactly the same as reported by Duffey and Porthouse [R.B. Duffey, D.T.C Porthouse, The physics of rewetting in water reactor emergency core cooling, Nucl. Eng. Des. 25 (1973) 379–394], Thompson [T.S. Thompson, An analysis of the wet-side heat transfer coefficient during rewetting of a hot dry patch, Nucl. Eng. Des. 22 (1972) 212–224] and Sun et al. [K.H. Sun, G.E. Dix, C.L. Tien, Cooling of a very hot vertical surface by falling liquid film, ASME J. Heat Transfer 96 (1974) 126–131; K.H. Sun, G.E. Dix, C.L. Tien, Effect of precursory cooling on falling-film rewetting, ASME J. Heat Transfer 97 (1974) 360–365]. Good agreement with experimental results is also observed.     

Performance Analysis of a Combined Absorption Refrigeration-Liquid Desiccant Dehumidification THIC System Driven by Low-Grade Heat Source

Traditional condensing air-conditioning systems consume large amounts of energy in hot and humid areas,and it is difficult to achieve simultaneous control of temperature and humidity.A combined absorption refrigeration(AR) and liquid desiccant dehumidification(LDD) air-conditioning system based on cascade utilization of low-grade heat source is proposed.The system can realize independent control of temperature and humidity and carry out profound recovery of low-grade heat sources.Under the desig...     

中低温热源干燥系统的设计及试验

为解决工农业干燥过程中存在的干燥效率低、能耗高等问题,同时充分利用生产过程中产生的中低品位热能,设计了一种可控温湿度的中低温热源干燥系统,干燥系统由加热系统、排湿换气系统、温湿度控制系统和干燥室组成。介绍了其干燥工艺,分析了其运行性能和能耗情况,通过试验数据分析发现该干燥系统气流温度和速度分布均匀、能耗低,系统在整个干燥过程中的干燥速率为0.122 kg/(kg∙h),整个过程的能耗因子为391.2 kJ/kg。系统适用于以地热能和工业余热等中低温热能为热源的工农业干燥过程。     

地表水水源热泵输配系统优化模型的研究

以输配能耗最小为目标,室内舒适和建筑节能相关要求为约束条件,利用MATLAB的优化工具箱,对地表水水源热泵输配系统的优化模型进行研究,确定影响地表水水源热泵输配系统能耗的主要因素。应用此方法对水源热泵实验系统进行了应用分析,得到了系统随负荷率变化的冷却水和冷冻水变流量优化运行方案。对于大部分时间处于部分负荷运行的系统,优化运行比定流量运行可减少能耗10%以上。该优化模型能方便地应用于实际工程,为输配系统的设计和运行提供最佳参数,实现随负荷变化的流量调控,从而有效降低水源水输配能耗,提高系统能效。     

Thermal Efficiency Optimization of a Ground Source Heat Pump System by Assistant Preheating/Precooling: A Case Study on a Heating-Load Dominated Building

Operation strategies of Ground Source Heat Pump System(GSHPS) such as continuous or intermittent approaches have been extensively studied. In this work, a novel strategy was proposed to maximize the energy efficiency of GSHPS. In this approach, the buildings was first air-conditioned by the preheating/precooling mode and the rest thermal load was covered by the heat pump(HP) mode. The system performance can then be optimized by considering the combination of these two operating modes. A case stu...     

燃用中低热值煤气时燃气轮机的压气机与透平的重新匹配

一般的燃气轮机是按燃用天然气等高热值燃料来设计的，当燃用中低热值煤气时，燃料流量显著增加，导致压气机与透平的流量差别增大，需要调整压气机或透平的通流面积来重新匹配。由于调整通流面积，燃料变化引起燃气热力性质的变化和透平进口燃敢温度的可能调整，需计算重新匹配后的压比。     

Natural Convection in a Square Enclosure with a Square Heat Source at Different Horizontal and Diagonal Eccentricities

The present article aims to extend a previous numerical study on the natural convection process in a square enclosure with a vertical eccentric square heat source (cylinder) [1]. Here, we investigated buoyancy-induced convective flow and heat transfer for horizontal and diagonal eccentric displacement in a square cylinder. Numerical studies are performed for Rayleigh numbers in the range 10³–10⁶, using our recently developed flexible forcing IB–thermal lattice Boltzmann method scheme [1 S. M. Dash, T. S. Lee, and H. Huang Natural Convection from an Eccentric Square Cylinder Using a Novel Flexible Forcing Ib-Lbm Method, Numer. Heat Transfer, Part A: Appl., vol. 65, pp. 531–555, 2013.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]]. Detailed analysis of isotherms, streamlines, and Nusselt number distribution as functions of Rayleigh number and eccentricity is provided in this paper.