相变微胶囊悬浮液强制对流换热实验研究

提出了一种可以同时作为储能介质与传热流体的新型相变微胶囊悬浮液(MPCS),设计和搭建试验台,分别在层流和湍流条件下在等热流密度的光滑圆管中对MPCS进行了强制对流换热实验,研究了悬浮液浓度、流量、泵送功率和加热速率对其流动及传热特性的影响。结果表明:对于质量分数为5%的MPCS,当微胶囊中相变材料分别处于固体、固体-液体和液体状态时,对应的努塞尔数平均增大了23.9%、20.5%和9.1%;与纯水相比,MPCS作为在热力系统应用的传热流体可以实现强化传热,但是需要在传热实验中控制好相变过程才能使MPCS的传热性能优于水。     

圆管内相变微胶囊悬浮液换热特性实验研究

实验研究了质量浓度为2%和5%的相变微胶囊悬浮液在等热流加热圆管内的对流换热特性,结果表明:相变微胶囊颗粒的加入明显增强了溶液的冷却效果,有效降低了管道壁面温度,并且悬浮液浓度越高,管道壁面温度越低;相变微胶囊悬浮液使管道入口段的局部努塞尔数明显增大,但随着流程进行,对流换热增强的幅度减弱;和水相比,浓度2%的相变微胶囊悬浮液的平均努塞尔数提高11%,悬浮液具有较好的强化换热效果;但浓度5%的悬浮液的平均努塞尔数低于水,这是由于5%的悬浮液粘度增加明显,悬浮液的高粘度和低导热率减缓了圆管中心处微胶囊颗粒的吸热相变,降低了5%悬浮液的强化换热效果。     

杂化壳相变微胶囊的制备与热性能研究

采用原位聚合法以石蜡为储热芯材、二氧化钛和壳聚糖的杂化壳体为壁材、石墨烯微片（GNP）作导热填料制备一种结构稳定的防泄漏相变微胶囊。采用电镜扫描（SEM）、傅里叶红外光谱（FTIR）、热重分析法（TGA）、差示扫描量热法（DSC）和导热系数测试仪研究不同芯壳比、GNP填充量对微胶囊的微观结构、表面官能团、热稳定性、相变性能和导热性能的影响。结果表明：制得微胶囊的结构致密防泄漏性能良好，微胶囊相变潜热最高达到134.78 J/g，对应包覆率为75.51%,GNP的加入使微胶囊的导热系数提高261.5%。     

TiO_2纳米颗粒对相变悬浮液流变和导热系数特性影响研究

通过实验方法研究了掺入TiO2纳米颗粒的相变悬浮液粘性和导热系数。研究表明,当纳米颗粒浓度不超过5%时,悬浮液仍可被视为牛顿流体,悬浮液的粘性随纳米颗粒浓度增加以非线性方式增加;当纳米质量颗粒浓度为5%时,相变悬浮液的粘性提高约23%。纳米颗粒的加入能够显著提高相变悬浮液的导热系数,当纳米颗粒质量浓度为5%时,相变悬浮液导热系数提高约7%。当纳米颗粒浓度较低时,纳米颗粒对相变悬浮液导热系数的提高幅度要高于对水的提高幅度。文中从不同方面分析了使用这种新型悬浮液作为传热工质的优势。     

微胶囊相变悬浮液在空调系统中的应用前景

介绍了一种功能性热流体—微胶囊相变悬浮液,它的浓度为15%时,载冷能力是水的两倍多;处于湍流时,表现出非牛顿流体的特性,流动阻力小于水;浓度为20%时,层流对流换热的修正努塞尔数Nuc是单相流体的2~3倍,传热性能远优于单相流体。因此,微胶囊相变悬浮液应用于空调系统可大幅度提高换热器的传热性能和空调系统的运行效率,达到节能的效果。     

圆管内对流换热过程中潜热型功能流体流动阻力特性的实验研究

实验研究了由正十四烷和尿素甲醛树脂制成的相变微胶囊和水混合制成的潜热型功能流体在流过恒热流圆管进行对流换热时的流动阻力特性,获得了压降随流速的变化关系、摩擦阻力系数和表观黏度随R e的变化关系。并在同样条件下用单相水进行了对比实验。相变微胶囊的加入导致流体流动阻力较单相流体有显著增大。管路中扰动件导致单相流体的流动阻力特性在低R e条件下呈湍流特征;功能流体则呈不同规律,扰动仅导致流动阻力进一步增大,而流动阻力特性仍呈层流特征。     

纳米铜/微胶囊复合体系相变过程及传热特性

针对相变材料的微胶囊化过低的导热性能限制了其大规模应用,通过将具有优良导热性能的纳米铜粉末(CNPs)填充在微米级相变微胶囊颗粒间,构建CNPs质量分数1.0%～8.0%的复合相变体系,研究复合体系相变过程和相变传热特性。研究结果表明,相比于微胶囊相变材料,复合相变体系有效导热系数随CNPs含量增加而提高,有效热扩散系数、相变速率与相变焓值随CNPs含量增加而先减小后增大,且有效热扩散系数与相变速率变化趋势基本保持一致,均在CNPs质量含量1.0%时出现增长的转变,且在CNPs质量含量低于3.0%时两者的数值均低于微胶囊相变材料,而复合体系相变温度则不受CNPs影响。     

SiO2纳米流体强化换热的实验和仿真研究

为研究纳米流体稳定性并增强换热机理,在乙二醇/去离子水基液中,采用原液化学生长法制备了不同质量浓度（1%,2%,3%,4%和5%）的氧化硅-乙二醇/水纳米流体,通过Zeta电位测量和透射扫描电镜实验表征纳米流体的稳定性。实验测量并研究了温度和质量浓度对纳米流体的导热系数和粘度的影响。依据实测结果,利用格子玻尔兹曼方法对圆管内纳米流体的流动与换热特性进行数值模拟研究。结果表明：二氧化硅颗粒在基液中具有良好的稳定性;纳米流体的导热系数随温度和质量浓度的提高而增大;纳米流体的加入可以显著提高基液的对流换热系数,当质量浓度为5%时对流换热系数的提高幅度可达到25.5%。     

等热流圆管内相变微胶囊悬浮液层流换热实验研究

用基液代替水来配置微胶囊相变悬浮液,并对实验数据的准确性进行了检验。在等热流密度环境下对管道内的该悬浮液进行加热实验,对相变微胶囊悬浮液的质量分数、St、入口过冷度、粒径和Re等因素影响强化换热的效果进行了分析。结果显示影响微胶囊相变悬浮液管内层流换热最主要的因素是微胶囊的质量分数和St。     

Numerical simulations on performance enhancement of a cross-flow latent thermal energy storage heat exchanger

基于列管式换热器具有传热面积大、结构紧凑、操作弹性大等优点,使其在相变储能领域具有广阔的应用前景。本文建立一种新型列管式相变蓄热器模型,在不考虑自然对流的情况下,利用Fluent软件对相变蓄热器进行二维储热过程的数值模拟。本文主要研究斯蒂芬数、雷诺数、列管排列方式、肋片数以及相变材料的导热系数对熔化过程的影响,并对熔化过程中固液分界面的移动规律进行了分析。模拟结果表明,内肋片强化换热效果明显,特别是对应用低导热系数相变材料[导热系数小于1 W/(m·K)]的列管式蓄热器,相对于无肋片结构,加入肋片（N_fn=2）可缩短熔化时间52.6%。     

Thermal and rheological properties of microencapsulated phase change materials

The use of microencapsulated phase change materials (MPCMs) is one of the most efficient ways of storing thermal energy. When the microencapsulated phase change material (MPCM) is dispersed into the carrier fluid, microencapsulated phase change slurry (MPCS) is prepared. Due to the relatively large surface area to volume MPCM and its large apparent specific heat during the phase change period, better heat transfer performance can be achieved. Therefore, MPCS can be used as both the energy storage and heat transfer media.This paper studies the thermal and rheological properties of a series of prepared MPCS. In the experiment: MPCS fabricated by dispersing MPCM into water with an appropriate amount of surfactant. The mass ratio of MPCM to water and surfactant was 10:90:1, 25:75:1, 35:65:1 in prepared MPCS samples, respectively. Then the thermal conductivity and specific heat of MPCS were measured by the Hot Disk. The melting/crystallizing temperature and fusion heat/crystallization heat of the phase change materials were obtained from a DSC (differential scanning calorimetry) during the heating/cooling process. Physical properties, such as viscosity, diameter and its size distribution of MPCS were investigated by a rheometer and a particle characterization system. Meanwhile, the chemical structure of the sample was analyzed using Fourier Transformed Infrared spectroscopy (FTIR).The results showed that the thermal conductivity and the specific heat of MPCS decreased with particle concentration for the temperatures below the melting point. Overall, the MPCS can be considered as Newtonian fluid within the test region (shear rate >200 s^?1 and mass fraction <0.35). The viscosity is higher for bigger particle slurries. The findings of the work lead to the conclusion that the present work suggested that MPCMs can be used in “passive” applications or in combination with active cooling systems; and it also provided a new understanding for fabricating microencapsulated phase change slurry, it is for sure that to have a better potential for energy storage. Accordingly, it has demonstrated that the MPCS fabricated in the current research are suitable for potential application as heat transfer media in the thermal energy storage.     

正交各向异性相变材料的无网格法传热模型及应用

利用无网格迦辽金(EFG)法建立正交各向异性相变材料的传热计算模型,基于该模型编程完成各向异性材料太阳能相变蓄热水箱和管壳式相变蓄热单元的相变传热分析,并探讨热导率因子和材料方向角对复合材料相变传热特性的影响.研究表明:在相同节点布置下EFG法的温度场和相界面计算精度均高于有限元法,EFG法在动态相界面追踪方面具有明显...     

相变贮热管管内强化传热的数值研究

以管壳式相变换热器为例,研究了肋片对增强贮热管管内传热的影响。建立了内部设置肋片的贮热管放热过程的数理模型,分析比较了不同的肋片参数,如肋片布置密度、长度及厚度等因素对贮热管放热效果的影响,并通过瞬态传热过程的计算,确定了与多种肋片布置方式所对应的相变贮热管的有效导热系数。     

Review on the low melting point alloys for thermal energy storage and heat transfer applications

低熔点合金具有导热系数高,储能密度大,使用温度范围广,性能稳定等特点,是一种潜在的宽温域传热工质和中低温相变储热材料.结合低熔点合金的相变温度,相变潜热,热导率及相变稳定性等热物理性能,综述了低熔点合金相变储热材料的研究进展;介绍了液态低熔点合金传热材料的蒸汽压,表面张力,黏度及比热容等性能,以及低熔点合金在高温下与容器材料的相容性;对低熔点合金传热储热材料的下一步研究进行了展望.     

An overview of phase change material slurries: MPCS and CHS

Phase change material slurries (PCS) can serve as both the heat transfer fluids and energy storage media, consequently, they are potentially applicable to the thermal systems, e.g., the secondary refrigeration and air conditioning loops, so as to improve the energy efficiency and to reduce the quantity of refrigerant used in the system. The design of the system using PCS needs the quantitative information about the thermal and fluidic behaviors of PCS. Here we provide an overview of the characteristics of two big groups of PCS, namely microencapsulated phase change material slurry (MPCS) and semi-clathrate hydrate slurry (CHS). The focuses are placed on the flow and heat transfer features and thermal properties, such as specific heat, viscosity and thermal conductivity. The suitable materials for making PCS are also discussed and compared based on the available data in the literature, and some examples of the applications of PCS are summarized as well.     

带相变蓄热小型热泵冷凝热回收性能实验研究

通过实验初步研究了采用光管螺旋相变蓄热器替代传统水蓄热器的小型家用热泵冷凝热回收系统的性能,对相变蓄热和水蓄热的冷凝热回收过程进行了对比实验,分析并得到了两类冷凝热回收系统的性能参数及综合能效系数。实验数据表明:与水蓄热系统相比,光管螺旋相变蓄热器体积减小,并且系统运行较传统水蓄热工况下更加平稳,但存在传热效果较差、热回收率低的缺点,回收率仅为15%,系统综合能效系数2.9。可知,相变蓄热器的内部结构对系统综合能效系数影响很大。     

A review on effect of phase change material encapsulation on the thermal performance of a system

This paper presents a detailed review of effect of phase change material (PCM) encapsulation on the performance of a thermal energy storage system (TESS). The key encapsulation parameters, namely, encapsulation size, shell thickness, shell material and encapsulation geometry have been investigated thoroughly. It was observed that the core-to-coating ratio plays an important role in deciding the thermal and structural stability of the encapsulated PCM. An increased core-to-coating ratio results in a weak encapsulation, whereas, the amount of PCM and hence the heat storage capacity decreases with a decreased core-to-coating ratio. Thermal conductivity of shell material found to have a significant influence on the heat exchange between the PCM and heat transfer fluid (HTF). This paper also reviews the solidification and melting characteristics of the PCM and the effect of various encapsulation parameters on the phase change behavior. It was observed that a higher thermal conductivity of shell material, a lower shell size and high temperature of HTF results in rapid melting of the encapsulated PCM. Conduction and natural convection found to be dominant during solidification and melt processes, respectively. A significant enhancement in heat transfer was observed with microencapsulated phase change slurry (MPCS) due to direct surface contact between the encapsulated PCM and the HTF. It was reported that the pressure drop and viscosity increases substantially with increase in volumetric concentration of the microcapsules.     

Laminar Flow Forced Convection Heat Transfer Behavior of a Phase Change Material Fluid in Finned Tubes

The heat transfer behavior of phase change material fluid (PCM) under laminar flow conditions in circular tubes and internally longitudinal finned tubes was studied. An effective specific heat technique was used to model the phase change process. Heat transfer results for a smooth circular tube with PCM fluid were obtained under hydrodynamically and thermally fully developed conditions. Results for the finned tube were obtained using the H2 and T boundary conditions. It was determined that the Nusselt number was strongly dependent on the Stefan number, fin thermal conductivity value, and height of the fins.     

蓄热式管壳换热器传热特性研究

针对热电联产机组供热期发电负荷受供热量限制,机组调峰能力下降、电力系统弃风弃光现象严重的问题,设计了一种新型蓄热式管壳换热器.利用相变材料蓄/放热过程中温度接近恒定、释放潜热量大等优点,选取石蜡为相交材料,换热器相交区作为换热单元,采用控制变量法,针对传热流体流速、相变材料导热系数及相变层厚度等关键因素,对换热单元的蓄...