平板微热管式相变蓄热装置蓄放热特性研究

本文提出一种基于平板微热管阵列的低温相变蓄热装置。该装置以平板微热管阵列为核心传热元件,以月桂酸为相变蓄热材料。搭建实验测试系统对该相变蓄热器在不同空气流量和进口温度的工况下进行蓄放热试验,对蓄放热过程中平板微热管阵列的均温性能、蓄热器内部的温度变化及蓄放热功率进行了实验研究及分析。结果表明;微热管阵列组件在蓄热、放热过程中表现出良好的均温性,工作高效且稳定;相变蓄热装置的实际蓄放热性能优良,平均蓄热、放热功率分别为418 W和353 W。     

新型平板热管相变换热器储放能过程的研究

将新型平板热管作为换热元件引入相变蓄热系统,研制了一套新型的平板热管式相变蓄热换热器。蓄热换热器采用石蜡作为蓄热材料,对其蓄、放热过程进行了实验研究,得到了不同时刻换热器内石蜡温度分布。改变供、取热流体温度,分析了流体入口温度对换热器蓄放热过程的影响,分析了新型平板热管在蓄放热过程的均温性能以及换热器的蓄放热效率。结果表明,新型平板热管相变换热器蓄、放热效果良好。     

平板微热管阵列式太阳能空气集热-蓄热一体化装置换热特性研究

本文基于平板微热管阵列技术,提出了一种太阳能空气集热、蓄热一体化装置,阐明了该装置的结构和工作原理。本装置以平板微热管阵列为关键热输送部件,采用52#石蜡作为相变储热材料,搭建了该一体化装置性能研究试验系统,对该装置蓄热器内部石蜡温度变化、蓄放热效率及蓄放热功率进行了实验研究和分析。结果表明:太阳能集热蓄热一体化装置可高效稳定运行,实测集/蓄、放热性能优良,测试工况下平均蓄/放热效率为59%/91.6%,平均蓄/放热功率为393 W/344 W。     

水平圆柱相变单元蓄放热动态特性研究

通过实验和数值方法研究了水平圆柱蓄热单元蓄、放热过程中换热特性的共性和差异,分析了壁面温度在高于/低于相变温度10 K的间隙性周期热边界条件下,蓄放热单元的热动态特性。结果表明,在相变起始阶段,蓄、放热过程主要以导热换热方式为主;随着蓄放热过程的进行,蓄热过程的换热方式转变为以自然对流主导,放热过程则仍以导热主导。在本文所研究的等温差等时长的间歇交替蓄-放热循环中,由于蓄热融化速率大于放热凝固速率,会出现由不稳定状态发展到周期稳定状态的演变过程;在周期稳定工况下,蓄放热单元会在完全液相到液固两相共存间交替变化。     

相变介质填充床斜温层蓄热罐蓄放热联合循环运行特性实验

蓄热装置的应用有利于热电联产机组获得更大的调峰裕度,在传统热水单罐中增加相变储热介质可以大幅提升蓄热罐的储能密度。以石蜡作为相变材料,制备成相变球并以填充床的形式布置在蓄热罐内。通过实验研究其循环蓄放热过程中的运行特性,以蓄放热截止温度、蓄放热流量为变量,分析不同运行工况对各循环的所需时间、罐内温度场、容量利用率等参数的影响。实验结果表明:循环蓄放热过程具有稳定的"收敛"特性,蓄放热截止温度对"收敛"速度等参数具有重要影响,而蓄放热流量的增大有利于缩短"收敛"所用时间,但较大的流量会导致蓄放热容量利用率的下降。     

相变蓄热体的热工特性数值模拟

为了深入研究蓄热式换热器的蓄放能效果,提出了采用具有相变材料的蓄热体强化蓄放热,通过gambit软件建立了三维蓄热体相变传热过程的物理模型和数学模型,利用fluent软件模拟了具有相变材料的蓄热体与具有变截面管强化的蓄热体传热,得到了两者蓄放热过程温度场分布。根据模拟结果分析了相变材料及缩放结构对蓄热体蓄放热效果的影响,为优化设计蓄热式换热器提供了理论参考。     

电加热式平板微热管阵列相变蓄热器蓄放热性能研究

本文提出了一种基于相变蓄热技术和平板微热管阵列技术的电加热式蓄热器,阐明了该装置的结构形式和工作原理,并对其单独蓄/放热与同时蓄/放热过程的热特性进行了研究。该新型电蓄热器采用12支带有百叶窗翅片的平板微热管阵列作为传热元件,蓄热器内填充18 kg的67#工业石蜡。蓄热工况采用不同加热功率(0.2～2.0 kW)对该电蓄热器进行加热,放热时控制放热流体体积流量(20～120 m³/h)和放热流体温度(15～27?C)进行放热。实验结果表明：在不同的运行模式下,该新型电蓄热器运行高效稳定,在单独蓄放模式下,测试结果显示装置的蓄、放热效率可达到99%和89%。     

蓄热换热与有害气体分解的实验研究

采用蜂窝陶瓷蓄热换热器实现高温烟气与空气的高效换热,实验研究了蓄放热时间对高温温度场均匀性的影响, 探讨了蓄热周期对烟气和空气进出口温度特性的影响,利用燃烧产物实现了四氟化炭高温分解。     

相变蓄冷换热器的优化设计

针对某间歇剧烈放热的设备,设计了一套某带相变蓄冷换热器的泵驱两相环路热控系统,并对相变蓄冷换热器进行优化设计。经过比较,拟采用石蜡与膨胀石墨的混合物为相变材料(PCM),在大大提高材料热导率时,又可保持较大的相变潜热。为了提高换热效率,应尽量避免PCM的融化距离过深,同时应优先减小外管壁与PCM间的接触热阻。相变蓄冷换热器的最优管间距与蓄冷时间、冷凝传热系数和接触表面传热系数等因素密切相关,本相变蓄冷器的最优管间距选为30 mm.通过动态模拟,可以得到相变蓄热换热器内不同时间的温度分布,确认所设计的相变蓄冷换热器可以满足要求,并为储液器的设计提供了相变蓄热换热器内不同时间的空泡率。     

移动式间隔蓄热器的蓄放热特性分析

通过FLUENT软件对不同布置方式的蓄热器进行数值模拟,结果表明,采用间隔式蓄热器会使蓄热器的材料温度更高,前中期蓄放热速率更快;但存在很明显的区域不均匀的现象:具体表现为中心区域要较其他区域反应速率更快,温升明显更高.从模拟结果来看,此种布置方法虽然一定程度上节省了余热资源,但由于区域反应的不平衡,致使总反应时间滞后.将模拟所得到的数据整理结合云图分析出现"类死区现象的原因",并在此基础上进行优化.具体优化方法主要有两个方面:改变肋片的几何构型、改变肋片的布置方式;另一方面在蓄热器的边璧区域使用导热系数更高的蓄热材料.通过对优化后蓄热器的蓄放热速率与优化前相比,发现蓄热器中出现的"类死区"的区域在优化后蓄放热性能均得到了很大的增强,蓄放热总时间分别减少了19.4％.     

热声发动机用加热器的设计与实验验证

热声发动机利用热声效应将热能转换为机械能,热能由核心部件加热器提供。加热器在热声发动机的能量传递和转化过程中起着举足轻重的作用。针对热声发动机的工作特点,介绍了一种采用时均流对流换热公式进行热声发动机用加热器设计的方法。基于该方法,设计了一种新型热声发动机用电加热器,并应用于自行研制的太型多功能行波热声发动机试验台。设计计算和实验结果表明,该加热器能够充分满足热声发动机的加热要求。本文对以振荡流体为特征的换热器设计具有一定参考价值。     

Experimental study on the heat transfer characteristics of a new type flat micro heat pipe heat exchanger with latent heat thermal energy storage

An experimental energy storage system has been designed using a new type flat micro heat pipe heat exchanger that incorporates a moderate-temperature phase change material paraffin with a melting point of 58°C. The basic structure, working principles, and design concept are discussed. The heat transfer process during the charging and discharging of the heat exchanger under various operating conditions has been experimentally investigated. Results show that the performance of the new type flat micro heat pipe was steady and efficient during charging and discharging. The average thermal storage power and absorption efficiency have been determined to be approximately 537 W and 92.5%, respectively.     

Spiral phase-change material for enhancing natural circulation solar water heater: An experimental study

This article studies the use of spiral phase-change material as an energy storage to improve the performance of a domestic solar water heater. The heating and cooling tests have been conducted for the vertical and horizontal position of the phase-change material in the water heater tank. The vertical position phase-change material yields better results than horizontal position. The charging energy and system thermal efficiencies of the tank are increased up to 20% and 12%, respectively, when the phase-change material is kept vertically. Also, it is observed that better heat transfer coefficient between water and phase-change material and upgraded thermal stratification during the cooling tests.     

热管式相变蓄热换热器储/放能过程中传热特性的实验研究

将热管作为换热元件应用于相变蓄热系统中,研制了一套热管式相变蓄热换热器。采用石蜡作为蓄热材料,对其储、放能过程即内部石蜡的融化与凝固过程进行了实验研究。测定了储、放能过程中不同时刻换热器内石蜡的温度分布; 改变供、取热流体参数,分析了供/取热流体的入口温度与流量对换热器储/放能过程的影响;分析了储、放能过程中能量随时间的变化情况。结果表明,热管在本换热器内极好地发挥了换热元件的作用,换热器运行状况良好,各项功能均能较好地实现。     

Investigation of Thermal Performance of Perforated Finned Heat Exchangers

In this study, the thermal performance of perforated finned heat exchangers with angle of rotation θ was experimentally investigated. Six-millimeter-diameter holes that were opened on each circular fin on a heating tube have a potential to reduce the thickness of the boundary layer that is formed on the circular fins placed on the heating tube, thus increasing heat transfer through convection in this area. The experiments were carried out at six different angular locations to determine the best angular location. In addition, a perforated finned heater was compared with an imperforate finned heater. For the finned heater at 60°, the effectiveness is 18% higher and the pressure drop is 1.16% lower than other angular positions. In this respect, it can be concluded that the best angular position is 60°. In addition, results show an increase in effectiveness with an increasing number of transfer units.     

基于多物理场的TFC磁头热传导机理及其影响因素仿真研究

为了利用微尺度热效应的热致飞高控制(TFC)磁头技术实现磁头飞行高度的精确控制,分析了工作状态下TFC滑块在多物理场综合作用下所呈现出来的传热特性及其主要影响因素,考虑了磁头磁盘间超薄气膜的稀薄效应,建立滑块导热、空气轴承表面传热、气膜流动等模型,利用有限元法,对磁头热变形作用机理及热传导特性对滑块动力学特性影响进行了仿真研究,结果表明,建立的传热模型及对雷诺方程的修正适用于求解磁头磁盘界面气膜传热问题和磁头滑块的动力学问题;影响滑块热力学性能的因素主要可以归结为加热器高度、热生成率以及材料的传热系数;空气轴承力及工作表面热变形的双重作用决定了滑块飞行高度的改变.仿真结果为磁头滑块加热器的设计及空气轴承动力学特性分析提供了依据.     

新型平板热管式太阳能集热技术

利用二维微通道阵列平板热管,提出了全新平板式太阳能集热技术及其热水系统,测试了平板微热管基本性能,将其应用于平板太阳能热水器,研制成功了新型平板热管式太阳能热水器,测试了热水器性能,其逐时最高效率为87.82%,日平均效率高达65.98%,且不受时域和地域限制,并具有成本低、抗冻、承压、紧凑、轻巧、不结垢等优点,整体性能优越,应用前景极其广阔。     

Mechanism of electric energy production in galvanic and concentration cells

The mechanism of electric energy production in galvanic and concentration cells, which is based on considering the reaction of separate ions, is described. The production electric energy via useful work in concentration and galvanic cells is considered at constant temperature and pressure by analogy to the Van’t Hoff equilibrium box (VHEB) on a molecular level. It is shown that the reaction heat dissipates in a thermostat (or in the environment) and does not participate in electric energy production. The only source of useful work is the thermal thermostat energy (that of the environment). The second law of thermodynamics is satisfied because the useful work arising from cooling of the environment is accompanied by a decrease in the volume of reagents and an increase in the volume of products. Electric energy arises indirectly via heat exchange with a thermostat according to the scheme reaction heat → thermal thermostat energy → useful work → electric energy. Execution of useful work due to thermal thermostat energy provides electric charging of electrodes whose discharging is followed by electric energy release.     

Energy and Entropy Analyses of a Pilot-Scale Dual Heating HDH Desalination System

This study focuses on energy and entropy analysis to theoretically investigate the performance of a pilot scale dual heated humidification-dehumidification (HDH) desalination system. Two cases of HDH systems are considered in the analysis. The first case is a dual heated (DH) cycle consisting of 1.59 kW air heater and 1.42 kW water heater with a heat rate ratio of 0.89 (CAOW-DH-I). Whereas the second case is a dual heated HDH cycle comprising of 1.59 kW air heater and 2.82 kW water heater with a heat rate ratio of 1.77 (CAOW-DH-II). As a first step, mathematical code was developed based on heat and mass transfer and entropy generation within the major components of the system. The code was validated against the experimental data obtained from a pilot scale HDH system and was found to be in a good agreement with the experimental results. Theoretical results revealed that there is an optimal mass flowrate ratio at which GOR is maximized, and entropy generation is minimized. Furthermore, the degree of irreversibility within the humidifier component is low and approaches zero, while the specific entropy generation within other components are relatively high and are of the same order of magnitude. Entropy analysis also showed that the dual heated system with heat rate ratio greater than unity is better than the one with heat rate ratio less than unity.     

Heat transfer and friction characteristics of solar air heater duct having protruded roughness geometry on absorber plate

Protruded roughness geometry is generally considered to be simple, an innovative and economic technique for improving thermal performance of solar air heater. Experimental investigation has been carried to study the effect of different shapes, position, and height of protrusions on heat transfer and friction characteristics of solar air heater duct for the range of parameters. Correlations for Nusselt number and friction factor have been brought out from the experimental data which can be further used for evaluating performance of solar air heater having the considered roughness geometry.