Numerical Investigation of the Thermal Behavior of a System with a Partition Wall Incorporating a Phase Change Material

The work deals with the thermal behavior of a conventional partition wall incorporating a phase change material(PCM).The wall separates two environments with different thermal properties.The first one is conditioned,while the adjacent space is characterized by a temperature that changes sinusoidally in time.The effect of the PCM is assessed through a comparative analysis of the cases with and without PCM.The performances are evaluated in terms of dimensionless energy stored within the wall,comfort temperature and variations of these quantities as a function of the amount of PCM and its emplacement.

Numerical Study on the Combined Use of Corten Steel and Phase Change Materials in Container-Type Houses

A study is presented on the feasibility of an approach based on the combination of Phase Change Materials(PCM)with metal walls in container-type houses.This line of research finds its motivations in recent trends in the energy and building sectors about energy consumption reduction.Another important objective concerns possible improvements in the comfort provided by such houses during the summer period.The results obtained through numerical solution of the governing equations accounting for heat transfer and latent heat effects associated with the PCM show that the indoor temperature can be reduced with a varying degree of success depending on the considered conditions.

Preparation of Palygorskite-based Phase Change Composites for Thermal Energy Storage and Their Applications in Trombe Walls

Palygorskite/paraffin phase-change composites were prepared by the combination of purified palygorskite clay and sliced paraffin. Then, this composite was used in the Trombe wall to improve its energy storage ability. Further, its energy storage ability was compared to that of ordinary concrete wall through contrastive test. The experiments show that palygorskite clay is a type of clay mineral with strong adsorption ability, and the purity of natural palygorskite clay can reach up to 97.1% after certain purification processes. Paraffin is well adsorbed by palygorskite, and the test results show that the optimal adsorption ratio is palygorskite： paraffin = 2：1（mass ratio）. Palygorskite/paraffin phase change composites can be obtained by using palygorskite as the adsorbing medium to adsorb paraffin. The composite materials exhibit good heat storage（release） performance, which can store heat with increasing environment temperature and release heat with decreasing temperature. This property not only increases the inertia to environment temperature change, but also promotes the energy migration in different time and space, thus achieving a certain energy-saving effect. The application of palygorskite/paraffin phase change composite materials to the Trombe wall can significantly reduce the fluctuation of indoor temperature and enhance the thermal inertia of indoor environment. From the aspect of energy storage effect, the Trombe wall fabricated using PCMs is significantly superior to the concrete wall with the same thickness.

Designing an Automatic Control System for the Improved Functioning of a Solar Wall with Phase Change Material (PCM)

Solar walls constitute an important green architectural feature that positively contributes to energy saving in buildings. Different configurations may be proposed, such as, solar wall with Phase Change Material (PCM), composite solar wall, photovoltaic solar wall, zigzag solar wall, and solar hybrid wall. Being environmentally friendly, these passive solar components can provide thermal comfort and help save energy. Their disadvantages include principally unpredictable heat transfer, heat losses by night for some systems or inverse thermo-siphon phenomenon. Appropriate energy management techniques can be used to control and optimize the performances of solar walls. An experimental study for energy management of a PCM based solar wall is described in this paper. The experimental results show the effectiveness of the proposed automatic control system in regulating the capture of solar energy.

Thermal comfort in a building with Trombe wall integrated with phase change materials in hot summer and cold winter region without air conditioning

Trombe wall and phase change materials(PCMs)are two effective ways to regulate indoor thermal comfort.However,Trombe wall surfers from overheating in summer and PCMs suffer from low heat transfer rate caused by the limited thermal conductivity.To compensate the shortcomings of the two methods,this paper proposed a Trombe wall system integrated with PCMs.Based on a light-weight building envelope in Changsha,China,the thermal comfort of 10 kinds of Trombe wall systems with PCMs with a melting temperature of 18-28℃ were studied.Taking the integrated indoor discomfort duration(I_(D)),integrated indoor discomfort degree-hour(I_(DH)),indoor air temperature(T_(in)),PCM liquid fraction(γ)and heat flux across wall(q)as evaluation indexes,the indoor thermal comfort was assessed in hot summer and cold winter region.Results show that the Trombe wall helped PCMs complete the phase change process effectively.Trombe wall with PCM25 next to the wall inner surface possessed the lowest annual I_(D) and I_(DH),as 2877 h and 12,974℃·h,respectively.Compared with the values in a traditional building,the I_(D) and I_(DH) were reduced by 7.01% and 14.14%.In order to give full play to the heat storage and heat release of the Trombe wall with PCMs,PCMs with phase change temperature 7℃ lower than the peak ambient temperature in summer or 8℃ higher than the winter night temperature was recommended according to regional climate conditions.

相变墙体应用于办公建筑的多目标优化设计

以寒冷地区某办公建筑为例,基于TRNSYS建立了相变材料应用于建筑南外墙内侧的仿真模型,利用jEPlus+EA平台的NSGA-Ⅱ算法对建筑冷、热负荷进行了多目标优化设计,应用乌托邦点法对帕累托前沿解集进行了均衡决策,并对优化方案的相变时间和节能率进行了分析。结果表明:寒冷地区典型办公建筑合理的相变温度范围为17~25℃;以南外墙内侧采用相变材料的房间为计算基准的年均节能率可达7.2%,建筑冷、热负荷可分别减小7.78%、6.04%;最优解方案对于建筑热负荷的增益更高。

双层定型相变墙体在合肥地区传热特性的数值模拟

为探究双层相变墙体所使用的相变材料在不同季节下的相变表现,以合肥地区夏、冬两季室外温度数据为背景,基于Fluent焓-孔隙率法,对普通墙体和双层相变墙体的传热过程进行仿真计算。结果表明,在夏季工况下,外相变板的相变温度为36℃的相变墙体综合表现更好,墙体内表面热流密度与普通墙体相比降低了20.53%,平均延迟时间约为普通墙体的1.8倍。在冬季工况下,内相变板的相变温度为14℃的相变墙体内表面温度波幅较平缓,墙体内表面热流密度与普通墙体相比降低了16.25%,它的衰减倍数约为普通墙体的1.2倍。在合肥地区,使用相变温度为36℃的外相变层和相变温度为14℃的内相变层的墙体在制冷、采暖期单位面积可降低热/冷负荷分别为1.86 W、3.75 W,该种墙体具有很好的节能效果和经济效益。

针对夏热冬冷地区的新型承载蓄热超结构墙体力学性能与温控效能研究

相变蓄热墙体能够有效降低室外温度波动对内墙面温度的干扰,提升室内热环境的稳定性并降低建筑能耗.由于冬夏季气象条件的差异,相变材料(phase change material,PCM)熔点的选择成为影响墙体热工性能的重要因素.为了实现蓄热墙体冬夏两季的高效利用,该研究构建了新型承载蓄热超结构墙体数值模型,对墙体力学性能进行检验,并模拟了冬季典型日和夏季典型日空气对流换热下墙体传热特性.结果表明,新型承载蓄热超结构墙体的力学性能满足工程应用需求,同时相较普通墙体具有良好的传热特性.其中,熔点为20℃的墙体在冬季热工性能最好,峰值相变率达到0.30,且内壁面最大温度波动为5.8℃,在夏季工况中,熔点为30℃的墙体具有较高的相变利用率为0.48,熔点为24℃的墙体内壁面温度波动最小.最后,综合考虑相变利用率和衰减倍数,获得了夏热冬冷地区最佳相变墙体熔点为24℃.

石蜡@碳酸钙相变微胶囊在海藻纤维中的应用研究

使用石蜡作为相变的基础材料、碳酸钙为壁材,采用自组装法制备功能良好的相变微胶囊,后与海藻酸钠共混后经湿法纺丝制备具有调温功能的海藻纤维。文章通过对微胶囊制备过程中芯壁质量比、搅拌速率、乳化剂类型及配比等工艺参数优化设计,使用扫描电子显微镜、傅里叶红外光谱仪研究了微胶囊的表面形貌和结构,热重分析仪、差示扫描量热仪、红外热成像仪等分析了微胶囊和调温纤维的热性能。结果表明,当微胶囊芯壁质量比为1︰1、反应转速为1000 r/min、乳化剂为Span80+Tween80(1︰2)时,可得到粒径均匀、形貌良好、具有优异热性能的相变微胶囊;将其与4%的海藻酸钠、2%的PVA混合得到纺丝原液,经湿法纺丝可制备出良好调温功能的海藻纤维。

多壁碳纳米管/水纳米流体的蓄冷特性研究

目的探究多壁碳纳米管的浓度、管径以及超声声强对纳米流体的蓄冷特性和换热性能的影响规律。方法将5~12 nm、10~20 nm、20~30 nm 3种不同管径的多壁碳纳米管和质量分数为0.05%~0.2%的多壁碳纳米管分别制备成不同的纳米流体样品,并搭建试验台对样品进行蓄冷实验。结果在质量分数从0.05%变为0.2%时,纳米流体的平均过冷度减小了0.7℃,管径由20~30 nm变至5~12 nm时,平均过冷度下降了64.3%;1级超声声强使传热能力提高了5.3%,而4级超声声强使传热能力提高了7.8%。结论研究表明,多壁碳纳米管浓度的增加及管径的减小,可使纳米流体的换热能力增大,过冷度减小,超声声强对多壁碳纳米管/水纳米流体有强化传热作用。

相变壁材微球对固井水泥浆性能影响与调控机制

【目的】当前在含水合物地层固井用相变微球低热水泥浆设计时,未充分考虑相变微球粒径及质量分数对水泥浆性能的影响,导致水泥浆性能降低和成本增加,从而引发一系列固井质量问题,因此,分析相变微球对固井水泥浆性能影响及调控机制尤为关键。【方法】为排除相变芯材储热效应的干扰,以自制的多级粒径相变壁材微球为研究对象,研究壁材微球粒径和质量分数对水泥浆性能的影响,建立了不同水化龄期水泥浆的Dinger-Funk方程(DFE)模型,揭示了壁材微球对固井水泥浆性能的调控机理。【结果和结论】结果表明:(1)相较于质量分数,微球粒径对固井水泥浆流动性能和力学性能影响更大,在进行相变微球低热固井水泥浆设计时,需重视微球粒径对固井水泥浆性能的影响。(2)微球质量分数增大对水泥浆体系存在2种不同的效应,一方面是堆积密度增大导致的水泥石力学强度提升以及水泥浆流动性能减弱效应,另一方面是微球引入本身强度缺陷导致的水泥石强度下降效应,这2种效应的主导地位取决于微球的质量分数和粒径,其中质量分数对两种效应起决定性作用,当质量分数较小时,堆积密度上升效应占主导,当质量分数超过4%时,强度缺陷效应占主导,2种效应共同作用下,水泥石单轴抗压强度呈现先上升后下降的趋势。(3)最紧密堆积DFE模型与水泥浆流动性能和力学性能有较强的相关性,当固井水泥浆DFE模型处于较优状态时,通常意味着该体系具有较好的流动性和力学性能。研究结果为热敏地层低热相变微球固井水泥浆设计提供有益参考。

气动嵌管式相变墙体动态传热特性实验与数值模拟研究

将建筑围护结构与相变材料相结合被认为是减少建筑运行能耗的有效技术之一.为了解决静态储能墙体无法同时提高释冷、蓄冷速度的缺点,提出一种气动嵌管式的动态相变墙体,通过实验测试以及采用动网格技术建立并验证其数值模型,再将该模型与静态储能墙体在释冷、蓄冷方面的热工性能进行对比分析.计算结果表明,数值模拟与实验结果内表面温度平均相对误差为0.59%,内表面热流密度平均相对误差为3.55%;在释冷方面,气动嵌管式相变墙体较PCM-O墙体相变材料液化时间延长了4.167 h,累计向室内传递热量减少了32%;在蓄冷方面,气动嵌管式相变墙体较PCM-I墙体相变材料固化时间总体提高了65.8%,内表面热流密度下降速率提高了69.9%,可显著提升昼夜相变材料的融化和凝固效率.

新型动态保温相变Trombe墙体热性能的实验研究

通过测试一间有一面是相变材料另一面是保温材料的新型动态Trombe墙体的房屋全尺寸模型,对该墙体的热性能进行实验研究。以墙体和房间的空气温度以及通过墙体的热流量和气流速率来评估其性能。结果表明:在相变过程中,温度变化相对平缓;墙体从玻璃获得的热量占其获得总热量的26.2%,且利用其储存的90.1%的热量对房间进行加热;在相变材料放热期间,该墙体可降低室内温度的分层且房间中部的温度至少比室外温度高3.2℃。

一种双碳节能相变储热材料制备及在高层建筑中的应用

以十二水磷酸氢二钠(DHPD)为主要原料制备了相变储热材料(DCAPM),并制作相变储热墙板,用于高层建筑。对相变储热材料的基础性能进行测试,并对相变储热墙板在高层建筑的应用效果进行研究。试验结果表明,多壁碳纳米管用量为1%制备的相变储热材料性能最佳,此时相变温度和相变潜热分别为35.27℃和218.52 J/g,过冷度约为0.8℃,储热时间和放热时间分别为1975 s和1284 s,完全热分解后,质量损失率为61.47%,经过50次循环后,DCAPM相变材料的储热性能并未受到影响,表现出良好的综合性能。将相变储热墙板用于高层建筑,使得室内温度保持在相对舒适的状态。

再生建材在装配式建筑应用中的导热性能数据模拟研究

为降低建筑能耗、促进绿色发展,试验以28#石蜡和硬脂酸钠作为相变材料,制备了一种分层插入式的相变墙体,对其传热性能进行研究。并通过BIM技术,对相变墙体在装配式建筑中的应用进行模拟。结果表明,相变墙体基本无渗透现象,加热面温度变化与普通墙体一致。相变墙体的平均升温速率和平均降温速率分别是0.04、0.01℃/min,导热系数λ为0.138 W/(m·K),均远小于普通墙体。BIM表明,相变墙体在装配式建筑中的计算机模拟数据与实际试验结果基本一致,该模型准确性较高。试验制备的相变墙体可以延缓室内温度变化,起到节能效果。

Investigation of heat transfer of a building wall in the presence of phase change material(PCM)

The energy consumption in buildings for heating,ventilation,and air-conditioning is increasing with the in-creasing demand for thermal comfort.Thermal energy storage with phase change material(PCM)has attracted growing attention for its role in achieving energy conservation in buildings with thermal comfort.This paper investigates the effect of PCM on the heat transfer rate in a building wall and the role of PCM on the indoor thermal comfort of the building.Two models of building wall fragments were developed for the experimental study.In one model,tests were conducted for different positions of the PCM layer in the building wall to identify the optimal position of the PCM layer inside the wall.In another model,tests were carried out integrating PCM,air gap,and other conventional building materials(brickbat and sand),one at a time,to investigate the role of PCM on the heat transfer rate in the building wall fragment.The results show that placing the PCM layer closer to the heat source gives a low-temperature gain of the cold water bath(indoor state)as compared with the PCM layer near the heat sink.With PCM,the temperature rise of the cold water bath(indoor state)of the building wall fragment was the lowest,and the slope of the temperature rise of the cold water bath becomes steadier with time i.e.,fewer temperature fluctuations.There was a significant time delay for the cold water bath to reach a given temperature.The heat required for a unit degree increase in the temperature of the cold water bath was higher and the peak heat flux of the wall was lower relative to the other building materials.

Molecular Dynamics Study on the Mechanism of Nanoparticle Phase Change Caused by Collision with Wall Surface

The collision between the nanoparticle and wall surface is supposed to cause the escape of nanoparticle molecules which indicates the potential phase change of the nanoparticle.It is significant to understand the mechanism of the collision process involved with phase change for applications of nanoparticles in energy and mass transfer.In this study,the collision process between nanoparticle made of monatomic argon molecule and wall surface made of nickel metal crystal is simulated by molecular dynamics method.The travelling behavior and energy transformation of escaped molecules are respectively analyzed.The effects of the intermolecular force and initial temperature on the collision process are further discussed.The results show that the nanoparticle can be accelerated by the wall surface with the intermolecular force and finally collide with it.The molecules escape from the nanoparticle either by bouncing off the wall surface or the intermolecular energy exchange with the energy transformation between the potential energy and kinetic energy.The molecules far from the nanoparticle center are more likely to escape,while the velocity distributions of the escaped molecules follow the Maxwell distribution.More escaped molecules,namely higher phase change potential,are observed with lower intermolecular force and higher initial temperature.As a fundamental study on nanoparticle phase change in the vicinity of wall surface,the present investigation will be helpful for further study on the heat transfer characteristics and phase change mechanisms of nanoparticles.

相变墙体柔性用能预冷策略优化与敏感性分析

建筑柔性用能对削减空调负荷的峰谷差具有重要意义。相变墙体采用预冷策略可以有效降低高峰负荷,然而预冷可能会增加总能耗。因此,有必要对其柔性用能和能耗特征进行综合研究分析。以长沙的办公建筑为例,建立相变墙体的传热模型并采用实验数据进行对比验证,在此基础上,研究不同预冷策略下相变墙体夏季的柔性潜力,并对影响柔性的相变参数进行敏感性分析。结果表明:当预冷温度为23℃,预冷时长为4 h时,相变墙体能在总能耗降低2.6%的情况下使高峰期的总冷负荷降低85.4%。另外,相变材料的相变温度对柔性的影响最大,其次是位置、密度、相变潜热、厚度、相变范围,而导热系数和比热容对柔性的影响很小。该研究可为相变墙体的应用提供参考。

相变墙体构造对室内热稳定性影响分析

由于相变材料的合理利用,能够有效提高建筑的室内热稳定性,降低建筑物的能源消耗;不同的相变墙体构造,其室内热稳定性也不同。为研究徐州冬季工况下适宜的相变墙体构造,通过ANSYS workbench软件,针对3种不同构造的相变墙体,模拟了其传热过程,并对室内外表面温度进行了分析。结果表明:徐州冬季工况时,内侧相变墙体内表面最低温度升高了0.35℃,相较于外侧和夹心相变墙体,提升幅度明显,同时,内侧相变墙体内表面温度的波幅也明显降低,内侧相变墙体对室内温度的调节作用明显,冬季工况下室内热稳定性最优。

相变材料选用及储能墙体节能研究进展

相变材料由于相变温度恒定、储能效果好、稳定性好等特征,在建筑墙体中的应用越来越多。介绍了相变材料的分类及建筑用相变材料的选择原则,分析了影响相变墙体节能效果的因素,总结了相变储能墙体构件形式及特征,并对相变墙体在建筑中的应用节能效果进行了综合对比分析。结果表明,相变墙体的节能效果受到诸多因素的影响,包括相变材料自身特性、气候、墙体形式及材料经济性等。因此需要综合衡量才能得到相变材料在墙体中的最佳应用方式,使相变墙体的节能性能最优化。通过综合布局可以有效地发挥相变材料的高储能性,从而达到降低建筑能耗、提高室内热舒适性的目的。