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.

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。

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。

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℃。

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。

基于保温隔热建筑墙体的相变混凝土热物理性能研究

以双层相变混凝土墙体为模型,通过测量比热容和导热系数以及升温曲线,研究相变混凝土墙体热物理性能,并结合COMSOL数值模拟的方法验证其节能潜力。结果表明,相变材料的掺入能降低混凝土的导热系数,并在相变温度区间大幅提高其比热容;高温火灾情况下,相变混凝土墙体升温速率远低于普通墙体;其对室内温度的自主调节能力也有大幅提升,在夏季可使室内最高温度降低2.7℃,日均节能率23.6%;冬季可使室内最低温度升高2.6℃,日均节能率36.6%;并推迟最高或最低温度的到来时间。

冻融循环下相变混凝土剪力墙抗震性能研究

该文通过建立相变储能混凝土冻融损伤本构模型,获取受损后混凝土重要性能参数,并将其代入剪力墙计算模型,进行墙体抗震性能分析.结果表明:添加相变材料对混凝土剪力墙的承载能力和刚度略有折减,但提高了墙体的变形能力;相变材料减轻了冻融循环对混凝土强度的影响,使得冻融循环后相变混凝土剪力墙的承载能力和刚度高于普通混凝土剪力墙,展现出良好的延性和耗能能力.

MWCNTs-水合盐复合相变材料的蓄热性能研究

研究CH_(3)COONa·3H_(2)O(SAT)/Na_(2)HPO_(4)·12H_(2)O(DSP)共晶盐的相变过程,分析亲水碳纳米管(HCNTs)对共晶盐热性能的优化效果。结果表明:SAT/DSP质量比为9∶1时共晶盐循环稳定性最好,且过冷度仅为2.5℃;随着HCNTs掺量提高,复合材料的热导率呈线性增长趋势,最高达到1.29 W/(m·K),较未加HCNTs时提升了182.89%,蓄热密度呈线性下降趋势,最多降低了5.59%。最后对各组HCNTs/SAT/DSP复合相变材料(CPCM)进行200次固-液循环,结果表明各组材料的循环稳定性良好,具备实际应用价值。

空气层厚度及送风量对相变特朗勃墙性能的影响

关注华东地区的冬季寒冷气候条件下,相变特朗勃墙体的传热蓄热特性。以济南地区为例,建立相变特朗勃墙体流动及传热数学模型,并利用有限元方法进行求解。通过分析空气层厚度以及空气层入口处送风量的变化探究其对特朗勃相变墙体传热及蓄热性能的影响。数值结果表明,与传统特朗勃墙体相比,改变墙体内部的空气层厚度可使送风速度及温度的均匀度发生变化,空气通道的厚度为100 mm时室内送风温度最高。送风量的变化影响空气的分布均匀性及空气与周围墙体的对流换热,送风量为35 m^(3)/(m^(2)h)时温度分布均匀且室内获得热量最大。

纳米流体强制对流过程中充填相变材料的三角形弹性壁通气腔内的相变动力学

本文研究了在层流状态下纳米流体强制对流时三角形弹性壁通气腔内的相变过程动力学。采用有限元方法探讨了雷诺数(Re)、柯西数(Ca)和腔口尺寸对流场和相变动力学的影响。研究发现,Re、Ca和腔口尺寸的变化对进气道下流动再循环和相变动力学有一定的影响。当Re从100增加到200时,相变时间(TF)先缩短后延长。在Re=100时,混合纳米流体相变速度快,相变时间降低约26%。当Ca为最大值时,相变时间减少了12.5%。腔口尺寸对相变有负面影响,而腔口尺寸的增大使相变时间增加了19%。

室外温度周期性变化下带有防晒墙的PCM外墙的动态传热特性

为了有效反映相变材料在带有防晒墙的建筑中的节能效用,将防晒墙与相变墙体组合形成二维墙体传热模型,基于enthalpy-porosity法,通过数值模拟分析讨论了室外空气温度随时间正弦变化的条件下相变材料的相变温度和相变材料层的空间位置对外墙动态传热特性的影响。研究结果表明,相较于不含相变材料层的普通墙体,相变墙体内表面温度变化的波动范围更小,时间滞后更强。当相变材料的相变温度区间更靠近室外空气温度的平均值时,使用相变材料对改善室内环境的舒适性更好;而扩大相变材料的相变温度区间间隔,使得相变材料在相变过程中处于糊状区的时间变长,对室内环境舒适性不利。