Heat transfer and parametric studies of an encapsulated phase change material based cool thermal energy storage system

This work investigates the transient behaviour of a phase change material based cool thermal energy storage (CTES) system comprised of a cylindrical storage tank filled with encapsulated phase change materials (PCMs) in spherical container integrated with an ethylene glycol chiller plant. A simulation program was developed to evaluate the temperature histories of the heat transfer fluid (HTF) and the phase change material at any axial location during the charging period. The results of the model were validated by comparison with experimental results of temperature profiles of HTF and PCM. The model was also used to investigate the effect of porosity, Stanton number, Stefan number and Peclet number on CTES system performance. The results showed that increase in porosity contributes to a higher rate of energy storage. However, for a given geometry and heat transfer coefficient, the mass of PCM charged in the unit decreases as the increase in porosity. The St number as well as the Ste number is also influential in the performance of the unit. The model is a convenient and more suitable method to determine the heat transfer characteristics of CTES system. The results reported are much useful for designing CTES system.

Cool storage time of phase change wallboard room in summer

More and more attention was paid to phase change energy storage in air conditioning domain and construction energy conservation,and became the focus of the international research. Through the test and analysis of the parameters of the indoor thermal property in phase change wallboard room and ordinary room,the effects of using phase change wallboards on indoor temperature in summer and air conditioning are obtained. The combination of construct enclosure and phase change materials can stabilize indoor temperature,improve indoor thermal comfort,reduce the frequency of the operation of air conditioning facility,cut the initial investment and operation expense,and meanwhile play an practical role in "the power balancing between the peak period and the valley period" policy. Through the experiment and the test of the effects exerted by phase change wallboard room and ordinary room on the indoor thermal environment,it is obtained that the phase change wallboard can reduce the fluctuation range of indoor temperature and the heat flow from the outside into indoor environment in summer. According to the study,it is found that the effect of cool-storing for 5 h is obvious. Through the analysis of the phase change wallboard without air conditioning in daytime,it is obtained that the frequency of the operation of air conditioning in phase change wallboard room is smaller than that in the ordinary room,which can prolong the lifetime of the facility and reduce operation expense.

Performance analysis of thermal storage unit with possible nano enhanced phase change material in building cooling applications

The heat transfer performance of the phase change materials used in free cooling and air conditioning applications is low,due to the poor thermal conductivity of the materials.The recent phenomenal advancement in nano technology provides an opportunity for an appreciable enhancement in the thermal conductivity of the phase change materials.In order to explore the possibilities of using nano technology for various applications,a detailed parametric study is carried out,to analyse the heat transfer enhancement potential with the thermal conductivity of the conventional phase change materials and nano enhanced phase change materials under various flow conditions of the heat transfer fluid.Initially,the theoretical equation,used to determine the time for outward cylindrical solidification of the phase change material,is validated with the experimental results.It is inferred from the parametric studies,that for paraffinic phase change materials with air as the heat transfer fluid,the first step should be to increase the heat transfer coefficient to the maximum extent,before making any attempt to increase the thermal conductivity of the phase change materials,with the addition of nano particles.When water is used as the phase change material,the addition of nano particles is recommended to achieve better heat transfer,when a liquid is used as the heat transfer fluid.

Thermal properties in phase change wallboard room based on air conditioning cold storage

By comparing the thermal performance parameters of an ordinary wall room with a phase change wall (PCW) room,the effect of phase change wallboard on the fluctuation of temperature in air-conditioning room in summer was studied. And PCW room and an ordinary wall room,which are cooled by air-conditioner,were built up. Differential scanning calorimetry (DSC) was used to test the temperature field and heat flow fluctuation in these rooms. Through analyzing the data tested,it is found that the mean temperature of PCW is lower than that of ordinary wall room by 1-2 ℃,and PCW can lower the heat flow by 4.6 W/m2. Combining phase change material to building envelope can lower the indoor temperature,make the room thermal comfortable,and cut down the turn-on-and-off frequency of air-conditioner,the primary investment and operating costs. It alleviates urgent need of the electric power. Building envelope which contains phase change wallboard can improve the indoor thermal environment,and decrease energy consumption in buildings. Phase change wallboard can make impressive effect on energy efficiency of buildings.

Experimental Study on Preparation of Natural Gas Hydrate by Crystallization

In this paper, the saturated solution crystallization method is proposed to promote the formation of hydrate by means of the known similarities between the hydrate formation process and the crystallization process. In this method,adding the second phase crystals was used to replace the spontaneous formation of hydrate crystal nuclei to form hydrate.The effects of saturated Na_2SO_4, MgSO_4, NH_4HCO_3 and CuSO_4 solutions on the formation rates of natural gas hydrate and gas storage capacity were investigated. The results showed that the saturated solution had an influence on the hydrate formation process. Under the given experimental conditions, the saturated Na_2SO_4 solution showed a highest increase in the hydrate formation rate, and the average hydrate formation rate in its presence was 11.8 times higher than that obtained in the deionized water. Moreover, the largest formation rate of gas hydrates observed in the saturated Na_2SO_4 solution was 386 times bigger than that in the deionized water, and the gas storage capacity increased by 10 times. In addition, the average hydrate formation rate in the saturated Mg SO_4 solution was faster than that in water by 20 times. The largest formation rate of gas hydrates in the saturated MgSO_4 solution was 165 times faster than that obtained in the deionized water, and the gas storage capacity increased by 6.2 times. The saturated NH_4HCO_3 and saturated CuSO_4 solutions also influenced the formation process of hydrate. Therefore, the crystallization method of saturated solution can be used to achieve a highefficiency preparation of natural gas hydrates, which provides theoretical guidance for the storage of natural gas in the form of hydrate.

Mesoporous molecular sieve confined phase change materials with high absorption,enhanced thermal conductivity,and cooling energy charging/discharging capacity

The biggest challenge for organic phase change materials(PCMs)used in cold energy storage is to maintain high heat storage capacity while reducing the leakage risk of PCMs during the phase transition process.This is crucial for expanding their applications in the more demanding cold storage field.In this study,novel formstable low-temperature composite PCMs are prepared with mesoporous materials,namely SBA-15 and CMK-3(which are prepared using the template method),as supporting matrices and dodecane as the PCM.Owing to the combined effects of capillary forces within mesoporous materials and interactions among dodecane molecules,both dodecane/SBA-15 and dodecane/CMK-3 exhibit outstanding shape stability and thermal cycling stability even after 200 heating/cooling cycles.In comparison to those of dodecane/SBA-15,dodecane/CMK-3 exhibits superior cold storage performance and higher thermal conductivity.Specifically,the phase transition temperature of dodecane/CMK-3 is-8.81℃ with a latent heat of 122.4 J·g^(-1).Additionally,it has a thermal conductivity of 1.21 W·m^(-1)·K^(-1),which is 9.45 times that of dodecane alone.All these highlight its significant potential for applications in the area of cold energy storage.

基于TRNSYS的主动式建筑相变蓄冷空调系统模拟

以夏热冬冷地区的办公建筑为例,利用瞬态系统仿真程序(transient system simulation program, TRNSYS)构建主动式相变蓄能地板模块,建立了主动式相变蓄能地板空调系统和常规风机盘管加新风空调系统的仿真模型,对其节能性和经济性进行模拟计算.以典型日和供冷季晚间蓄冷运行工况为条件,研究冷冻水温对主动式相变蓄能地板的蓄释能特性、室温波动与热泵制冷系数的影响.结果表明:夜间相变蓄冷工况下,在满足每平方米冷负荷为74.78 W情况下,9℃为最佳供水水温;采取晚间低电价时段间歇运行蓄冷热泵的方案,能够有效提高热泵运行时的制冷系数,并降低运行费用;主动式相变蓄能地板空调系统供冷季的能耗相比于常规风机盘管加新风空调系统减少30.5%,运行费用减少44.24%,夏季制冷综合能效比达到了2.38.

新型迷你通道-相变热沉实验研究

电子元件的集成化、微型化等特点加剧了芯片的热问题,基于相变材料的被动式冷却技术已无法满足功率波动的高功率电子设备的需求。本文将相变技术与主动冷却技术相结合,提出了一种用于风冷散热的新型迷你通道-相变热沉结构。该结构改善了相变材料导热性能差的问题,也解决了相变材料熔化后泄漏的问题。通过实验测试了不同热流密度、不同风速对其热控性能的影响,总结了热沉的蓄放热特性,并与未填充相变材料热沉的热控性能进行了对比。实验中热流密度变化范围为1.81~3.47 W/cm^(2),风速变化范围为0~4 m/s。研究表明:热流密度的增大和风速的降低均会导致热沉温控时间的缩短。2 m/s风速足以满足热流密度小于2.91 W/cm^(2)的芯片散热需求,4 m/s风速可以在热流密度为3.47 W/cm^(2)的情况下将热沉底面温度维持在70℃。与未填充相变材料热沉相比,本研究提出的热沉可以起到延长温控时长,降低稳态温度的作用。此外,风扇的开启可以有效缩短热沉的冷却时间,对于间歇性工作的电子设备具有重要的应用意义。研究结果可为迷你通道-相变热沉在实践中的应用提供参考依据。

基于圆柱封装单元的水合盐相变储热填充床的储释特性实验研究

水合盐相变储热技术具有储热密度高、成本低等优势,在清洁供暖中具有广阔应用前景。本研究设计并搭建了以三水合乙酸钠作为储热材料,以圆柱形相变材料封装单元作为基础单元的填充床相变储热装置。通过实验研究填充床储热装置的运行特性,研究了流量和储热温度对装置的储释热用时、出口温度、热效率及储热密度的影响。实验结果表明:提高储热温度和增大流量可缩短储热用时、提升热效率和储热密度。储热装置的热效率可达94.73%,储能密度可达71.77 kW·h/m^(3)。

无机水合盐相变储能材料性能优化及应用进展

无机水合盐类相变储能材料因具有储能密度高、无毒、经济等明显优势而受到广泛关注。对无机水合盐的研究有望提高可再生能源的利用效率,缓解能源危机。然而此类材料存在固有缺陷,包括相分离严重、过冷度高、热导率低等,阻碍了其应用。文章以无机水合盐的热物理性质为出发点,详细介绍了无机水合盐类相变储能材料的相变行为、导热性、过冷现象以及相分离等特征。针对其缺陷,总结了近年来性能优化的两大常用策略为与多孔材料复合和微胶囊化,并根据其特性,讨论了无机水合盐在太阳能热能储存和光电转换、建筑节能、储冷等方面的实际应用。

基于相变蓄冷的核电厂主控室非能动冷却系统

为提高现有核电厂主控室紧急可居留系统的蓄冷能力及热舒适性水平,提出了基于定形相变蓄冷材料的核电厂主控室非能动冷却系统。基于主控室热负荷分布情况,该冷却系统在主控室顶板与吊顶之间、内墙面、地板底面及循环风道内,针对性地布置相应的含有定形相变材料的非能动冷却装置,进而实现事故工况下对主控室温度的精确控制。该非能动冷却系统无需引入额外冷源和管道,可靠性强,同时不破坏主体结构,且可灵活布置,解决了现有主控室非能动热阱时间余量小、热舒适性差的问题。

乳酸钙复合相变蓄冷材料的制备及性能研究

为满足葡萄微冻贮藏保鲜温度的要求,研制了一种以乳酸钙水溶液为主储能剂,氯化铵水溶液为降温剂,高吸水树脂为增稠剂的复合相变蓄冷材料,测试蓄冷材料的相变温度、相变潜热、腐蚀性、导热性和稳定性。结果表明:当乳酸钙质量分数为1%,氯化铵质量分数为1%,高吸水树脂质量分数为2.2%时,复合相变蓄冷材料Onset温度为-4.45℃,相变潜热为300.8 J/g,导热系数为4.671 W/(m.K)。铜和铁在相变蓄冷材料中基本无腐蚀,复合相变蓄冷材料经过50次冻融循环后,性能稳定。

一种蓄冷式飞机地面空调车的设计及实验研究

为了减少机场终端碳排放,机场将逐步减少柴油发电供冷设备的使用。设计了一种供风温度15℃,供风风量2750 m ^(3)/h,供风压力45 kPa的蓄冷式飞机地面空调车并进行实验。系统采用6℃相变蓄冷材料,设计制冷负荷为45 kW,蓄冷量为18.3 kW·h,能够满足80 kW的供冷需求。实验结果表明,蓄冷式飞机地面空调车短时间内最大供冷负荷达105 kW,满足飞机机载电子设备的用冷需求。蓄冷式飞机地面空调车在供冷间歇时段将冷量储存在相变蓄冷模块中,在供冷时段释冷,使机场供冷时段的部分冷负荷均摊到间歇时段,降低机场整体供冷时段的电负荷,有效减少机场电路铺设和配电改造的成本。

相变蓄冷材料研究进展

相变蓄冷材料具有储能密度高、相变温度可控、循环稳定性强的优点,成为目前最有发展前景的储能方式。文章对现有的相变蓄冷材料进行了分类,总结了不同类型材料的优缺点,重点介绍了国内外学者在固-液相变方面的研究进展,罗列了各种材料的热物性和化学特性,对其在医疗冷链、建筑制冷、生鲜冷冻等具体应用中的研究进行了阐述。在此基础上,针对目前相变蓄冷材料存在的导热率低、腐蚀性强、易泄漏和过冷度大等问题,文章提出相应的解决方案并阐述改善机理,对相变蓄冷材料的未来发展进行了展望。

R134a 气体水合物蓄冷实验研究

以Ｒ１３４ａ为工质，对温－压相图进行了校核，对水合物的生成和融解进行了观察，对正丁醇含量对水合物的影响进行实验研究，确定Ｒ１３４ａ作为气体水合物蓄冷工质的可行性。

气体水合物相变热研究进展

气体水合物作为一种特殊的相变材料,在形成与分解过程中会发生相态改变并伴随着相变热的变化。本文从气体水合物相变热的测定和应用两个方面对气体水合物相变热的研究现状进行了综述。对比分析了两种确定气体水合物相变热的方法,两种方法分别为差示扫描量热仪(DSC)实验直接测定法和基于相平衡的Clausius-Clapeyron方程间接计算法。综述了气体水合物相变热的应用研究现状,尤其是在空调蓄冷技术中的应用,其中气体水合物空调蓄冷技术从蓄冷工质和蓄冷装置两个方面进行了阐述。指出了气体水合物相变热应用研究中的重点和难点,为气体水合物相变热应用的进一步发展提供参考。

HFC134a/HCFC141b混合气体水合物相平衡特性

In this study, the phase-equilibrium property of the mixed gas hydrate formed by an-other pair of CFC alternatives HFC152a/HCFC141b was measured under a constant volume condition. The phase diagrams of mixed gas hydrates and their characteristics were fur-ther studied, and the phase-equilibrium property of mixed gas hydrates comparing to that of simple gas hydrates was depicted and discussed. The experimental result reveals that HFC134a/HCFC141b mixed gas hydrate has a non-azeotropic melting property, which is different from that of HFC152a/HCFC141b[4]. The melt and freeze points are quite close because the decomposition temperatures of HFC134a and HCFC141b simple gas hydrates have small difference.

Na_2SO_4·10H_2O复合相变储冷体系的热力学性质

目的 研究制备相变温度在 5～ 1 0℃之间的新型空调储冷材料 .方法 测定以Na2 SO4· 1 0 H2 O为主要成分的低共熔混合体系的相变温度随组成变化的关系 ,确定适宜配方 .研究抑制过冷和相分层现象的方法 .结果 由质量分数为 80 %的 Na2 SO4· 1 0 H2 O、2 %～ 8%的 KCl、5 %～ 1 0 %NH4Cl和 1 %～ 5 %( NH4) 2 SO4组成的低共熔水合盐体系的相变温度降至 9～ 1 0℃ .结论 加入无机盐 KCl,NH4Cl,( NH4) 2 SO4或 Na Cl可降低 Na2 SO4.1 0 H2 O的相变温度 .加入成核剂和增稠剂是解决过冷和相分层的有效方法 .

低温纳米复合相变蓄冷材料热物性研究

低温相变蓄冷的关键是蓄冷材料的开发。本文针对啤酒工艺对冷源温度的要求,选择BaCl_2共晶盐水溶液:勾相变蓄冷材料基液,在基液中添加粒径为20nm的TiO_2纳米粒子,形成具有蓄冷功能的纳米复合材料。对其热物性如导热系数、相变潜热、相变温度、过冷度及粘度进行了实验测量和分析。结果表明,在TiO_2纳米粒子的质量分数为1%的情况下,纳米复合蓄冷材料的导热系数比基液提高了11.28%,过冷度从3.97℃降为1.21℃,同时粘度增加了21.7%,相变潜热略有降低。

夏季昼夜温差较大地区相变墙蓄冷可行性分析

目的把相变储能技术应用在夏季昼夜温差较大地区,使相变墙夜间通过通风蓄冷,调节室内温度.方法从降低建筑能耗和利用可再生能源的角度出发,选取癸酸(CA)、月桂酸(LA)两种有机混合物作为相变材料,将建筑材料浸入有机相变材料中制成一种新型复合储能构件.对气象数据以及相变材料进行了分析和实验测试.结果通过测试可知选取的有机混合物的相变温度为18.491～24.262℃,符合室内舒适温度范围.通过对气象数据以及对相变材料的实验测试分析可知,昼夜温差较大地区夏季可以应用相变储能墙板实现夜间通风蓄冷,白天吸收室内多余的热量,调节室内温度,提高室内的舒适性.结论相变墙板的应用使室内和室外之间的热流波动幅度减弱,外扰作用时间被延迟,从而可以降低建筑物供暖、空调系统的设计负荷,达到节能的目的.