Enhancing Heat Transfer and Energy Storage Performance of Shell-and-Tube Latent Heat Thermal Energy Storage Unit with Unequal-Length Fins

Previous studies in literatures adequately emphasized that inserting fins into phase change material is among the most promising techniques to augment thermal performance of shell-and-tube latent heat thermal energy storage unit.In this study,the novel unequal-length fins are designed from the perspective of synergistic benefits of heat transfer and energy storage performance,and the effects of arrangement,number and total length of unequal-length fins are numerically investigated.Results show t...     

Seasonal Storage of Thermal Energy with Radiatively Heated Storage Walls

It is shown by calculations that if a highly effective translucent insulating material were available a storage system with energy collecting walls could be constructed. Conditions are derived under which the thermal losses in midwinter are compensated by radiative gains. Thus effective longterm storage becomes possible. Several variations of this principle are considered in detail: a cubic storage system, a storage element incorporated into the roof of a building and an earth storage system. It is demonstrated that with an overall heat transfer coefficient of 0.2 W/m²K a water tank of 50 to 100 m³ is sufficient for the thermal energy needs of a single family dwelling.     

Patterns of Fluid Flow in a Shell-and-Tube Heat Exchanger

The oil-lampblack technique was employed to reveal the patterns of fluid flow in a shell-and-tube heat exchanger. Flow patterns were visualized adjacent to the shell wall, to the baffle plates, and to each tube of the array. From the flow patterns adjacent to the shell, three recirculation zones were identified. The patterns adjacent to the baffles were similar to those for cross flow over a tube bank, with curvature-related deviations near the shell. The flow patterns adjacent to the tubes showed, typically, a stagnation line/circumferential flow system on the upstream face of each tube and a recirculation tone dominating the tee side. Turn-related deviations from these patterns were in evidence at the window region.     

Numerical Analysis on a Latent Thermal Energy Storage System with Phase Change Materials and Aluminum Foam

Abstract

A latent heat thermal energy storage system with phase change material (PCM) is numerically studied. To enhance the heat transfer inside the system, a highly conductive metal foam is employed with ceramic nanoparticles. The latter method of enhancement leads to a new class of material called Nano-PCM. The system under investigation is a 70-L tank filled up with pure PCM or Nano-PCM and several pipes are situated where the heat transfer fluid (HTF) flows. The pipe surfaces are assumed at constant temperature above the PCM melting temperature to simulate the heat transfer from the HTF. The enthalpy-porosity theory is applied to simulate the PCM phase change, while the porous media formulation is assumed to describe the metal foam behavior. The nano-PCM is modeled with single-phase model where the properties are the weighted-average between the fluid base and the nanoparticles. The simulations are accomplished for charging-discharging process at different porosities and nanoparticle concentration. The results are given in term of average melting fraction evolution, average temperature as function of time, average stored energy. The metal foam significantly improves the heat transfer between PCM and HTF respect to the addition of nanoparticles, reducing the charging and discharging time more than one order of magnitude.     

脉冲液体射流泵能量平衡的数值研究

运用能量平衡分析原理,根据脉冲液体射流泵主要流动部件的能量损失压力比公式,利用脉冲液体射流泵性能数值计算模块,对脉冲液体射流泵能量平衡进行了数值研究,分析了主要流动部件的能量损失变化及其对脉冲液体射流泵性能的影响,并与恒定液体射流泵的能量损失压力比、性能及效率进行了对比。结果表明,脉冲射流是提高射流泵传能、传质效率的有效途径。     

Thermal Performance of a Phase Change Material‐Based Latent Heat Thermal Storage Unit

An experimental analysis is presented to establish the thermal performance of a latent heat thermal storage (LHTS) unit. Paraffin is used as the phase change material (PCM) on the shell side of the shell and tube‐type LHTS unit while water is used as the heat transfer fluid (HTF) flowing through the inner tube. The fluid inlet temperature and the mass flow rate of HTF are varied and the temperature distribution of paraffin in the shell side is measured along the radial and axial direction during melting and solidification process. The total melting time is established for different mass flow rates and fluid inlet temperature of HTF. The motion of the solid–liquid interface of the PCM with time along axial and radial direction of the test unit is critically evaluated. The experimental results indicate that the melting front moves from top to bottom along the axial direction while the solidification front moves only in the radial direction. The total melting time of PCM increases as the mass flow rate and inlet temperature of HTF decreases. A correlation is proposed for the dimensionless melting time in terms of Reynolds number and Stefan number of HTF. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21120     

组合相变材料储热的实验研究

分析了在同一储热系统中采用两种或两种以上相变材料的特点,介绍了用于组合相变材料储热研究的实验装置,给出了四种相变材料水平柱状储热单元储热系统的初步测试结果,并对其进行了讨论。     

偏心管翅式相变储热单元性能强化的模拟

对管翅式相变储热单元进行了二维非稳态模拟研究。在考虑自然对流与外管传热的情况下对比研究了同心管翅、偏心管翅以及翅片接触外管三种储热单元的传热特性。考虑了内管壁温度、外管材料、翅片厚度对储热性能的影响。结果表明,与采用同心管翅时相比,由于自然对流的影响,偏心管翅储热单元有效削弱了固-液界面分布不均匀现象,完全融化时间减少了29.3%,而当翅片接触金属外管时,通过翅片的传热外管温度迅速升高,增大了换热面积,完全融化时间减少了近49.3%。可见,翅片接触外管储热单元不仅削弱了自然对流引起固-液界面分布不均匀现象,而且利用了外管的传热,强化了储热换热性能。     

Numerical Study of Laminar Natural Convection in a Side-Heated Trapezoidal Cavity at Various Inclined Heated Sidewalls

Steady natural convection of air flow in a two-dimensional side-heated trapezoidal room was investigated numerically using a non-orthogonal, collocated finite-volume grid system. The considered geometry has an inclined left heated sidewall, a vertical right cooled sidewall, and two insulated horizontal upper and lower walls. Computations are performed for seven values of the heated sloping wall angle, three different values of aspect ratio, and five Rayleigh number values. Results are displayed in terms of streamlines, isotherms, and both local and average Nusselt number values. The principal result of this work is the great dependence of the flow fields and the heat transfer on the inclination angle, the aspect ratio, and the Rayleigh number. A correlation between the average Nusselt number, Rayleigh number, heated sloping wall angle, and aspect ratio is proposed.     

A Comparison Study of Sensible and Latent Thermal Energy Storage Systems for Concentrating Solar Power Applications

Thermal energy storage (TES) provides a key opportunity to reduce the cost of concentrating solar power generation. In this article transient heat transfer performance and operational characteristics of sensible TES systems (made of liquid solar salt) and latent TES systems (made of sodium nitrate undergoing liquid-solid phase change), all enclosed in vertical annuli, are numerically simulated. The results show that the latent TES systems can operate with a much higher energy density than the sensible TES systems, and that compact latent TES systems are capable of offering both high energy density and a satisfactory charging/discharging rate.     

Effect of Laminar and Turbulent Buoyancy-Driven Flows on Thermal Energy Storage using Supercritical Fluids

Efficient heat transfer to storage fluid is required for the desirable operation of thermal energy storage systems. Most of the fluid candidates for supercritical thermal storage have poor thermal conductivity; therefore, conduction does not provide sufficient heat transfer. The current study concerns a supercritical thermal energy storage system consisting of horizontal tubes filled with a storage fluid in its supercritical state. The results of this study show that the heat transfer to the supercritical fluid is dominated by laminar and turbulent natural convection. The buoyancy-driven flow inside the storage tubes enhances the heat transfer and dramatically reduces the charge time.     

CFD Modeling of the Charging and Discharging of a Shell-and-Tube Latent Heat Storage System for High-Temperature Applications

In this study, a validated CFD model was employed for the simulation of the charging and discharging processes in a long shell-and-tube latent heat storage system suitable for high-temperature applications, such as solar thermal power generation. A shell-and-tube enclosure, having a height of 0.92 m and shell inner radius of 0.0325 m, was simulated. The results indicated that the effect of natural convection cannot be neglected during charging. The heat transfer rate during discharging, which is primarily dictated by conduction, is lower than that during the charging process and thus the design of such systems must be based on the discharging process. Models that neglect the effect of convection during discharging can predict the amount of heat discharged with a maximum discrepancy of 6%     

连铸中间罐内流场和温度场数值模拟研究

以本钢连铸中间罐为研究对象,通过建立罐内钢液的流动的数学模型,计算出六流T型中间罐内钢液的流动状况和温度分布情况,其结果表明:在罐内中间流与边流之间钢液流速和温度分布是存在差异的.因此,确定了有利于发挥中间罐冶金功能的控流方案,为连铸稳定生产获得合格坯提供了理论依据.     

Comparison of Thermal Performance between Annular Fins and Longitudinal Fins in Latent Heat Storage Unit

As a simple and effective method of heat transfer enhancement,fins are widely used in latent heat storage systems.However,the choice of annular fins and longitudinal fins has always been controversial.In this paper,the melting process of phase change material(PCM) in annular fins and longitudinal fins latent heat storage units with the same volume is numerically simulated.To ensure the same thermal penetration,three-dimensional spaces occupied with fins are specially controlled to be the same.Co...     

Latent Thermal Storage for Solar Cooling Applications: Materials Characterization and Numerical Optimization of Finned Storage Configurations

ABSTRACT

The present paper presents the development of a thermal energy storage system for application with non-concentrating solar plants using phase change materials (PCMs). The outcomes of an experimental analysis on commercial PCMs and laboratory-grade chemical compounds suitable for latent heat storages in a temperature range of 80–100°C is presented, with main focus on to the enthalpy and the cycle stability of the materials. Particularly, a first evaluation of possible degradation mechanisms in hydrated salts was investigated by means of nuclear magnetic resonance spectroscopy. The best performing materials have been implemented in a numerical model, based on the enthalpy method, used for the design of a thermal storage system. The configuration of the system, starting from a simple shell-and-tube layout, has been optimized by inserting asymmetric fin-and-tubes and the results with two selected materials have been compared. The analysis has shown that the most promising materials are the commercial ones belonging to the classes of paraffinic materials and hydrated salts and that, with the designed configuration, it is possible to store up to 200 kJ/m³ and get a peak power during discharge of about 1.5 kW.     

显热/潜热复合储能材料的研究

描述了Na2CO3-BaCo3/MgO和Na2SO4/SiO2这两种无机盐／陶瓷体显热／潜热复合储能材料的配方、制备工艺和热性能研究结果,讨论了无机盐在多孔陶瓷体微结构内的容积份额与成型压力,烧结温度,升温速度,保温时间以及不同的添加剂的朴素关系,测试结果表明,研制材料的性能达到了预期的结果,给出了可行的配方和制备工艺。     

压缩空气储能系统与火电机组的耦合方案研究

针对火电机组的灵活改造,提出一种压缩空气储能系统与火电机组的耦合方案,利用Ebsilon软件进行系统建模,将热耗率和能量利用系数作为评价参数.结果 表明:最佳方案为储能阶段从凝结水泵出口抽取凝结水,其吸收压缩热后被送回至除氧器;释能阶段取少量5号抽汽,其加热高压空气后被送回至5号低加疏水冷却器;通过改变膨胀机入口空气温...     

Numerical Analysis of Phase Change Material Characteristics Used in a Thermal Energy Storage Device

In this study, a numerical analysis is performed to investigate the freezing process of phase change materials (PCM) in a predesigned thermal energy storage (TES) device. This TES device is integrated with a milk storage cooling cycle operating under predefined practical conditions. Using this cooling unit, 100 litres of milk is kept cool at 4°C for 48 hours before it is collected. A 2-D model of the TES device is developed in COMSOL Multiphysics to analyze the phase change performance of water-based PCMs. The variations of thermal properties with temperature during the phase change are considered in the analysis. The model is used for exploring the solidification process of PCMs inside the TES device. Temperature variations with time, ice formation, and the impacts of boundary conditions are investigated in detail. Water PCM shows better characteristics in the solidification process in comparison to eutectic PCMs, which is mainly due to the differences between phase change temperatures of the PCMs.     

Numerical Modeling of Fluid Flow and Thermal Behavior of Different Nanofluids on a Rotating Disk

The thermal and velocity profiles of various nanofluid systems on a rotating disk are simulated. Finite difference method, the orthogonal collocation method, and the differential quadrature method (DQM) of numerical approaches are used to solve the governing equations and are compared to determine the faster and more accurate solution procedure. Five nanoparticles Al, Al₂O₃, Cu, CuO, and TiO₂ solved in three base fluids water, ethylene glycol, and engine oil are considered to be used on the disk at different volume fractions. A new general algorithm is presented for solving equations of a rotating‐disk problem quickly and accurately and it is found that the DQM method is the best approach for this numerical simulation. Heat transfer performance of a rotating disk would be much better enhanced with water based Al nanofluid. A wide range of results for different base–fluid combinations with nanoparticles is presented with untransformed 3D results and effects of the variation of different parameters provides comprehensive insight and prevents inaccurate deductions.