HEAT EXCHANGER FOR IN-GROUND HEAT STORAGE

The first phase of a research project using undisturbed soil for sensible heat storage is described. A laboratory scale model of a heat exchange system was constructed and tested. Thermal charging and recovery rates, modes of heat transport and transient temperature conditions, as well as over-all heat storage performance of the unit are given. The experimental results are compared with predictions of a numerical model based on mass and heat transport. A prototype field installation has been constructed and preliminary results are presented.     

SIMULATION OF HYDRATION/DEHYDRATION OF CaO/Ca(OH)2 CHEMICAL HEAT PUMP REACTOR FOR COLD/HOT HEAT GENERATION

ABSTRACT

A chemical heat pump (CHP) utilizes reversible reactions involving significant endothermic and exothermic heats of reaction in order to develop a heat pump effect by storing and releasing energy while transforming it from chemical to thermal energy and vice versa. In this paper, we present a mathematical model and its numerical solution for the heat and mass transport phenomena occurring in the reactant particle bed of the CHP for heat storage and cold/hot heat generation based on the CaO/Ca(OH)₂ reversible hydration/dehydration reaction

Transient conservation equations of mass and energy transport including chemical kinetics are solved numerically subject to appropriate boundary and initial conditions to examine the influence of the mass transfer resistance on the overall performance of this CHP configuration. These results are presented and discussed with the aim of enhancing the CHP performance in next generation reactor designs.     

结晶垢结垢过程的传热传质模型

通过对结晶垢结垢过程传热传质机理的分析,证明了垢层表面温度随时间的变化会对结垢过程产生重大影响.据此提出了考虑垢层表面温度变化的描述结垢过程的传热传质模型.对恒壁温和恒热流条件下的结垢过程进行了详尽的分析和讨论.结果表明,对恒壁温情况必须考虑垢层表面温度随时间的变化,这一变化是导致结垢过程渐近特性的重要原因之一;而对恒热流情况,垢层表面温度随时间的变化很小,可以忽略它所带来的对结垢过程的影响.与实验数据比较表明,模型预测是正确可靠的.     

A STUDY ON THE SOLIDIFICATION HEAT TRANSFER CHARACTERISTICS OF HEAT STORAGE SYSTEM UTILIZING THE PCM

This study is concerned with the solidification heat transfer characteristics of phase change energy storage system. The heat transfer characteristics experiment for the solidification of PCM is performed on the PCM cylindrical heat exchanger with six fins. Experimental results are compared with the theory to investigate the appropriateness of heat conduction equation of PCM and the effect of coolant inlet temperature and flowrate on the total solidification time of PCM are investigated.

Experimental results are in good accordance with the theory and they show that heat transmission enthalpy model is sufficient for the analysis of solidification heat transfer characteristics of PCM. The total solidification time of PCM in two dimensional finned PCM cylinder is shortened 5-6 times than that of PCM in one dimensional PCM cylinder. The total solidification Fourier number is correlated with Biot number and Stefan number as following.     

HEAT AND MASS TRANSFER WITH MULTIPLE PARTICLE INTERACTIONS PART I. DROPLET EVAPORATION

A generalized treatment of heat and/or mass transport between an assemblage of particles and a surrounding continuum is presented. The unsteady state diffusive transport is shown to depend on the size and positions of the particles, and the rate processes are found to be radically different from single particle rates because of particle interactions. A three dimensional model has been developed to predict global concentration or temperature distributions by treating the particles as point sources or sinks. The conditions for which particles can be treated as isolated or as interactive members of a group are established, and correction factors are presented from which multiple particle mass transfer rates can be calculated from single isolated particle mass transfer rates. For finite assemblages the correction factors are shown to be in close agreement with results computed previously using the method of images.     

HEAT AND MASS TRANSFER WITH MULTIPLE PARTICLE INTERACTIONS PART I. DROPLET EVAPORATION

A generalized treatment of heat and/or mass transport between an assemblage of particles and a surrounding continuum is presented. The unsteady state diffusive transport is shown to depend on the size and positions of the particles, and the rate processes are found to be radically different from single particle rates because of particle interactions. A three dimensional model has been developed to predict global concentration or temperature distributions by treating the particles as point sources or sinks. The conditions for which particles can be treated as isolated or as interactive members of a group are established, and correction factors are presented from which multiple particle mass transfer rates can be calculated from single isolated particle mass transfer rates. For finite assemblages the correction factors are shown to be in close agreement with results computed previously using the method of images.     

Optimization of the heat plant of district energy systems

This paper presents a scheme to achieve structural and operational optimization for the heat plant in a district energy system. A district energy system consists of energy suppliers and consumers, district heating pipelines and heat storage facilities in a region. Production and consumption of energy and transport of energy as well as storage of heat are taken into account in the model. The problem is formulated as a mixed integer linear programming (MILP) problem where the objective is to minimize the overall cost of the district energy system. Evaluation of the energy production cost is based on the daily operation for every season at the plant located at Suseo in Seoul, Korea. From the results of numerical simulations we can see that the district energy system is well approximated by the proposed model, and that the energy efficiency is improved by the application of the optimal operation conditions provided by the proposed model.     

CERAMIC HEAT PIPES FOR HIGH TEMPERATURE HEAT RECOVERY

Difficulties in finding metal or protected metal components that exhibit both strength and corrosion resistance at high temperature have severely restricted the application of effective heat recovery techniques to process heat furnaces. A potential method of overcoming this restriction is to use heat pipes fabricated from ceramic materials to construct counterflow recuperators. A development program has been initiated to demonstrate the technical and eventually the economical feasibility of ceramic heat pipes and ceramic heat pipe recuperators. The prime candidate for heat pipe construction is SiC. Closed-end tubes of this material have been prepared by chemical vapor deposition (CVD). These tubes were lined internally with tungsten by a subsequent CVD operation, partially filled with sodium, and sealed by brazing a tungsten-lined SiC plug into the open end with a palladium-cobalt alloy.

Heat pipes constructed in this manner have been successfully operated in vacuum at temperatures of 1225 K and in air at a temperature of 1125 K. The heat source used initially for the air testing was an induction heated metallic sleeve in thermal contact with the test unit. Subsequent testing has shown that a silicon carbide heat pipe can be successfully operated with natural gas burners providing the input heat. Methods of fabricating and testing these devices are described.     

ANALYSIS OF HEAT AND MASS TRANSFER DURING DRYING OF PAPER/BOARD

A mathematical model has been successfully developed to study the heat and mass transfer process during paper drying. This model takes into account the consective transfer of vapor and liquid apart from the known transport mechanisms of capillary flow of liquid, diffusion, vaporization-condensation, and heat conduction. The partial differential equations describing temperature, saturation and pressure change within the web during drying with associated boimdary conditions and initial conditions were solved using finite difference method. The model predictions show that during the drying process the web can be conveniently divided into three different zones, namely dry zone, wet zone and an intermediate zone. The movement of liquid and vapor in opposite directions in the intermediate zone is similar to the action of a heat pipe. Also, as drying proceeds the location of the intermediate zone and hence the heat pipe advances progressively through the thickness of the web.     

泡沫金属在熔盐相变蓄热中的强化传热特性

搭建了熔盐蓄热特性实验平台,开展相变蓄热过程传热特性实验研究。建立了蓄热容器二维轴对称、瞬态固液相变数学模型,相变过程模拟采用Solidfication & melting模型,相变区域采用Boussinesq近似,对比了纯硝酸盐蓄热工况和填加泡沫金属后蓄热工况数值模拟结果。采用实验与数值模拟相结合的方法,重点分析了泡沫金属对熔盐蓄热过程的强化传热作用。结果表明,填加泡沫金属能够有效提高熔盐换热速率,泡沫金属孔隙率越小强化蓄热效果越显著。泡沫铜的热导率较高,相对于泡沫镍和泡沫铝有更好的强化传热效果,蓄热速率是纯硝酸盐蓄热的1.6倍。在相变蓄热后期自然对流换热占主导地位,此时泡沫金属会抑制自然对流。同时,填加的泡沫金属越靠近容器中心位置,对自然对流抑制作用越强,蓄热性能越差。     

ANALYSIS OF HEAT AND MASS TRANSFER DURING DRYING OF PAPER/BOARD

ABSTRACT

A mathematical model has been successfully developed to study the heat and mass transfer process during paper drying. This model takes into account the consective transfer of vapor and liquid apart from the known transport mechanisms of capillary flow of liquid, diffusion, vaporization-condensation, and heat conduction. The partial differential equations describing temperature, saturation and pressure change within the web during drying with associated boimdary conditions and initial conditions were solved using finite difference method. The model predictions show that during the drying process the web can be conveniently divided into three different zones, namely dry zone, wet zone and an intermediate zone. The movement of liquid and vapor in opposite directions in the intermediate zone is similar to the action of a heat pipe. Also, as drying proceeds the location of the intermediate zone and hence the heat pipe advances progressively through the thickness of the web.     

PROPOSAL FOR A NOVEL CHEMICAL HEAT PUMP DRYER

A new chemical heat pump (CHP) system for ecofriendly effective utilization of thermal energy in drying is proposed from the viewpoints of energy saving and environmental impact. CHPs can store thermal energy in the form of chemical energy by an endothermic reaction and release it at various temperature levels for heat demands by exo/endothermic reactions. CHPs have potential for heat recovery and dehumidification in the drying process by heat storage and high/law temperature heat release. In this study, we estimate the potential of the CHP application to drying systems for industrial use. Some combined systems of CHPs and dryers are proposed as chemical heat pump dryers (CHPD). The potential for commercialization of CHPDs is discussed.     

A 2-D MICROSCOPIC SIMULATION OF HEAT AND MASS TRANSPORT IN DRY SNOW

The problem of acid deposition and its effects on the environment is receiving increasing attention in North America and Europe. The interaction between

seasonal snowcovers and deposited pollutants is of particular importance because a snowpack accumulates and stores pollutants which can ultimately be released in a rapid pulse with the first melt water in the springtime. As a direct result of an impurity pulse, water quality degrades with deleterious effects on the local environment and aquatic biological species. The timing and severity of an inpurity pulse is dependent upon the redistribution of pollutants in a snowpack which is attributed to a process known as temperature gradient metamorphism.

This work investigates the influence of geometry, density and temperature on the coupled heat and mass transport in idealized, two dimensional ice lattice cells. Mass flux, concentration and temperature distributions, as well as effective diffusion coefficients and thermal conductivities are presented as functions of temperature, geometry, and density. A finite element model of the coupled, heat and mass transport is used to analyze the problem on a microscopic scale in two dimensions. Deforming meshes are used to simulate the growth/decay process which occurs over time in an ice lattice pore.     

DYNAMICS OF LATENT HEAT STORAGE IN FIXED BEDS A NON-LINEAR EQUILIBRIUM MODEL—THE ANALOGY WITH CHROMATOGRAPHY

This paper investigates theoretically the dynamics of a latent heat storage system consisting of a fixed bed operating close to thermal equilibrium with a percolating fluid. The model used is an idealized one, which emphasizes the role of the heat capacity factor, but neglects heat transfer resistances, losses, and hydrodynamic non-idealities. The approach is shown to resemble that used classicaly in non-linear adsorption, and analogous concepts, such as shock waves and dispersive waves are introduced. The shapes and propagation characteristics of the temperature profiles generated during loading and unloading of the bed are discussed, for various fusible materials, operating temperatures, initial and boundary conditions, and flow direction. The non-linear dependence of the enthalpy of the storage material on temperature is shown to play a central role in determining the qualitative features of these profiles. The aims of the article are mainly qualitative, conceptual and didactic.     

PROPOSAL FOR A NOVEL CHEMICAL HEAT PUMP DRYER

ABSTRACT

A new chemical heat pump (CHP) system for ecofriendly effective utilization of thermal energy in drying is proposed from the viewpoints of energy saving and environmental impact. CHPs can store thermal energy in the form of chemical energy by an endothermic reaction and release it at various temperature levels for heat demands by exo/endothermic reactions. CHPs have potential for heat recovery and dehumidification in the drying process by heat storage and high/law temperature heat release. In this study, we estimate the potential of the CHP application to drying systems for industrial use. Some combined systems of CHPs and dryers are proposed as chemical heat pump dryers (CHPD). The potential for commercialization of CHPDs is discussed.     

新型两相闭式热虹吸管的传热性能

本文设计了一种新型结构的两相闭式热虹吸管(重力热管),通过可视化研究和传热性能研究,探索了新型结构热管中充液率、操作温度及传热量对传热性能的影响。提出了新型热管的流体流动的物理模型,并得到实验验证。结果表明,本文所提出的新型结构热管操作稳定,传热性能良好,临界热通量高。     

管壳式换热器壳侧湍流流动与换热的三维数值模拟

综合应用体积多孔度、表面渗透度和分布阻力方法建立了适用于准连续介质的N-S修正控制方程.用改进的k-ε模型考虑管束对湍流的产生和耗散的影响,用壁面函数法处理壳壁和折流板的壁面效应, 对一管壳式换热器的壳侧湍流流动与换热进行了三维数值模拟.对计算结果进行了归纳,并与换热器冷态实验、前人的研究结果进行了对比分析,从而证明了该方法能更有效地模拟管壳式换热器壳侧的流动特性,压降实验数据和计算结果符合良好.     

DYNAMICS OF LATENT HEAT STORAGE IN FIXED BEDS A NON-LINEAR EQUILIBRIUM MODEL—THE ANALOGY WITH CHROMATOGRAPHY

This paper investigates theoretically the dynamics of a latent heat storage system consisting of a fixed bed operating close to thermal equilibrium with a percolating fluid. The model used is an idealized one, which emphasizes the role of the heat capacity factor, but neglects heat transfer resistances, losses, and hydrodynamic non-idealities. The approach is shown to resemble that used classicaly in non-linear adsorption, and analogous concepts, such as shock waves and dispersive waves are introduced. The shapes and propagation characteristics of the temperature profiles generated during loading and unloading of the bed are discussed, for various fusible materials, operating temperatures, initial and boundary conditions, and flow direction. The non-linear dependence of the enthalpy of the storage material on temperature is shown to play a central role in determining the qualitative features of these profiles. The aims of the article are mainly qualitative, conceptual and didactic.     

求解相变传热问题的等效热容法

采用等效热容法求解伴有相变过程的瞬态热传导问题.在整个区域建立统一的能量方程,将分区域求解问题化为整个区域的非线性问题处理.给出了解决相变温度为单一温度或者相变温度区间很小时产生的数值奇异问题的方法.用热焓判据判断单元是否发生相变,并考虑了固液两相材料物性参数的变化,相变界面位置按线性插值计算.算例表明,等效热容法求解相变传热问题,程序简单,计算效率高,相变界面位置计算准确.     

IDENTIFICATION OF MATHEMATICAL MODEL COEFFICIENTS IN THE ANALYSIS OF THE HEAT AND MASS TRANSPORT IN WOOD

A method based on the concept of solving inverse heat and mass transport problems was proposed to identify wood physical properties, with the use of empirical data, a mathematical model corresponding to the direct problem, and an optimization procedure. The computer software was developed to solve transient, three-dimensional, quasi-linear direct and inverse problems of heat and mass transport in wood as an anisotropic body together with initial and boundary conditions of any kind. The software was adapted to data parallel processing environment of high performance computers. Identification of thermal conductivity was performed for beech wood in three principal anatomic directions, and accuracy of temperature distribution predictions was significantly increased (the global relative error of prediction was reduced to 1.0 - 1.9%).