泡沫金属强化石蜡相变蓄热过程可视化实验

相变材料的低热导率是限制潜热蓄热广泛应用的重要原因。将相变材料石蜡真空条件下注入到泡沫金属铜内制备泡沫金属铜-石蜡复合相变材料,通过铜的高热导率及高孔隙材料的大面体比来强化相变换热过程。采用DSC示差扫描量热法对石蜡进行热物性测量获得准确的石蜡相变温度及相变潜热。以管壳式相变蓄热结构为对象,提取对称结构进行可视化设计,对比纯石蜡及泡沫金属铜-石蜡复合材料在相同运行条件下的相变过程,追踪二者熔化过程的相界面位置随时间的演化过程并布置热电偶准确测量材料内部的温度分布。结果显示加入泡沫金属后的复合材料的内部温差明显减小,温度分布均匀,蓄热热通量显著增大,有效缩短相变时间并缓解了自然对流造成的顶部过热和底部不熔化现象。     

石蜡与石蜡/膨胀石墨熔化性能的实验研究

为改善相变储能过程中石蜡(PA)的熔化性能,向PA中添加少量膨胀石墨(EG)制备了4种配比的石蜡/膨胀石墨复合相变材料(PA-EG)。通过热物性分析筛选出合适配比的PA-EG,并对其和PA在水平管壳式相变储能单元中的熔化过程进行了实验研究。根据相变材料的温度场变化以及加权法计算得到的熔化分数变化,对比分析了添加EG前后PA的熔化性能,并探究了加热温度对相变材料熔化性能的影响。结果表明,PA-EG3的热导率比PA高了7倍,且两者的相变温度和潜热相差不大。PA-EG3熔化过程中的自然对流效应弱于PA,但是较高的热导率能够显著改善相变储能单元中下部的熔化,使得其整体熔化速度快于PA。当加热温度为80℃时,PA-EG3的熔化过程比PA缩短了78.16%。此外,降低加热温度会使PA和PA-EG3的完全熔化时间都显著增加,但相同条件下PA-EG3的增加幅度更小。     

Crystallinity,thermal diffusivity,and electrical conductivity of carbon black filled polyamide 46

Polyamide 46 (PA 46) with carbon black (CB) has been subjected to a heat treatment. Crystallinity, specific heat capacity, crystalline melting peak temperature, thermal diffusivity, and electrical conductivity were measured. The crystallinity increases with duration of thermal treatment. The maximum value is dependent on the filler fraction. A lower CB content leads to a higher crystallinity at maximum tempering time. The crystalline melting peak temperature increases with decreasing filler fraction and duration of thermal treatment due to different crystal types and/or diverging geometric forms of the crystals. Thermal diffusivity and electrical conductivity act positively proportional to each other and increase with CB content and tempering time. The thermal diffusivity decreases with increasing temperature. The volume resistance of PA 46 is lowered by heat treatment. By CB addition in combination with a tempering process, the PA 46 can be transferred into a conductor. CB is moved by PA 46 crystals into amorphous regions forming conductive pathways. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48882.     

用于储热新型低熔点二元无机盐特性研究

通过对熔盐的热物性分析,研究一种新型低熔点熔盐进行储热,能够有效解决传统燃煤供暖所产生的环境污染等诸多问题。熔盐材料由于高温下的稳定性好、成本低及导电性能良好等特点成为了与新能源结合的研究热点。由于常用的二元混合熔盐熔点约为221 ℃,而供暖系统传热介质温度较低,高熔点熔盐对于供暖系统并不适用,所以开发熔点较低的熔盐用于供暖系统成为了研究热点。通过试验测试的方法对熔盐混合配比进行调整,开发了熔点较低的新型熔盐,并通过大温差储能供暖系统中的应用进行了有效性验证。     

Crystal structure, melting behaviour and equilibrium melting point of star polyesters with crystallisable poly(ε-caprolactone) arms

Star polymers consisting of poly(ε-caprolactone), PCL, attached to third generation dendrimer, hyperbranched and dendron cores have been studied by differential scanning calorimetry and wide-angle X-ray scattering. The degree of polymerisation of the PCL arms of the star polymers ranged from 14 to 81. The crystal unit cell was the same for the star polymers as for their linear PCL analogues. The star polymers showed a lower degree of crystallinity than the linear PCL, suggesting that the dendritic cores imposed restriction on PCL crystallisation. Slow heating of rapidly cooled samples led to crystal rearrangement—a gradual increase in melting point with decreasing heating rate and recrystallisation followed by additional high temperature melting. The tendency for crystal rearrangement was less pronounced in star polymers based on dendrimer or hyperbranched cores, suggesting that the dendritic cores constitute an obstacle to crystal rearrangement. The star polymers showed higher equilibrium melting points than the linear PCL analogues. It is suggested that covalent attachment of the PCL arms to the dendritic core reduced the positional freedom and the entropy of the melt with respect to that of linear PCL.     

Effect of thermal conductivity and heat transfer on crystallization,structure, and morphology of polypropylene containing different fillers

The crystallization behavior, structure, and morphology developed was investigated for polypropylene containing different fillers such as silica, calcium carbonate, talc, mica, graphite, etc. by using compression‐molded samples prepared at several cooling rates. It was observed that the crystallinity obtained for any given composition depended on the thermal conductivity of the filler and the PP composite containing it as well as the cooling rate to which it was subjected. These composites exhibited skin‐core type of morphology and the skin layer thickness was found to depend not only on the cooling rate but also on the type of filler, its thermal conductivity, etc. These various experimental findings were discussed in light of the phenomenological model described in our earlier work, which correlates thermal conductivity and degree of crystallinity for various compositions of PP containing additives. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 615–623, 2004     

翅片重力热管传热性能实验研究

热管是一种利用工质相变传热,具有传热温差小、热响应速度快、换热量大等优点的传热元件。为研究翅片重力热管的传热性能,实验测试了翅片重力热管与平板重力热管（铝-丙酮工质）的传热性能,比较了其瞬态热响应速率,获得了翅片与平板重力热管在蒸发段不同电功率稳定加热条件下表面温度沿高度方向的变化规律,计算了平板热管的等效热导率,并与铝板测量结果进行了对比。结果表明：重力热管传热速度快、表面均温效果好,热导率随功率的增大先升高后降低,整体上热导率高达纯铝的84~258倍,翅片热管相比于平板热管具有更好的均温性和散热效果,在建筑供暖、车载电池散热、余热利用等领域具有广泛的应用前景。     

Improved mathematical modeling for the sheet reheat phase during thermoforming

In any thermoforming process, plastic sheet heating is the most important phase as it is responsible for final part quality as well as overall process efficiency and productivity. The goal of the study reported here was to improve existing mathematical models to accurately predict the temperature profile inside a heated sheet, where the model could be used to better control the overall thermoforming process. A mathematical model with temperature dependent, variable sheet material properties including density, thermal diffusivity, specific heat, and thermal conductivity was developed and validated against experimental data. Models with constant and variable plastic sheet properties were created, simulated, and compared in Matlab. The models were validated by experiments which obtained temperature profiles at different depths within a plastic sheet by inserting thermocouples and recording temperatures. Further, the effect of sheet color on heating was investigated by considering two extreme cases: white (transparent) and black (opaque) colored sheets, and the effect of oven air temperature and velocity on sheet heating was also investigated. Results indicated that a variable properties model was needed to control sheet reheating especially with narrow forming windows, and that the heating profiles required for colored and noncolored sheets were very different. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

周向非均匀加热水平圆管内超临界正癸烷换热特性

针对超燃冲压发动机再生冷却热防护问题,开展了顶部加热和底部加热水平圆管内超临界压力正癸烷换热的模拟研究。探究了两种加热模式下的换热特征和换热差别,阐述了通道外表面热通量、质量流速、运行压力及通道热导率对换热的影响机制。实现了周向平均换热的预测。结果表明：两种加热模式下的浮升力作用不同,通道内壁面周向呈现了不同的管壁温度和热通量分布情况。顶部加热时随周向角增大传热恶化逐渐减弱,底部加热时二次流更强,周向始终存在传热恶化问题。高温流体拟膜态热阻是传热恶化的原因。采用高热导率通道、增加运行压力、降低热质比可以缩小周向壁温和热通量差别。提出的关联式能合理预测周向平均换热情况,满足热防护设计的工程应用。     

Thermal Conductivity of PNIPAm Hydrogels and Heat Management as Smart Windows

Though thermoresponsive lower critical solution temperature (LCST) hydrogels have attracted intense attention to be applied in smart windows, less efforts are paid on the LCST effect on the heat transfer process. Herein, the research mainly focuses on heat transfer process of thermoresponsive PNIPAm hydrogels. It is the first time reported that LCST behaviors can decrease thermal conductivity upon heating process. To be utilized as a smart window, thermal conduction flux is investigated yet the thermal conduction energy occupies little to manage the thermal transfer process in a model house. It is found that radiation thermal transfer predominates the heat transfer process for PNIPAm-based smart windows. These results are meaningful to provide basic data for energy transfer in using thermoresponsive hydrogels.     

石墨烯增强复合相变储能材料的热学性能研究

以铁尾矿多孔陶瓷为载体,通过自发浸渗法成功制备出了添加石墨烯的复合相变储能材料,并对该材料热学性能及稳定性进行测试。结果表明：通过改变载体孔隙率,可以制得导热系数为0.41～0.59 W/(m·K)、潜热为69～120 kJ/kg、热学稳定性良好的导热增强复合相变储能材料。通过拟合,复合相变储能材料的导热系数与多孔载体的孔隙率呈线性关系,且经100次热循环后材料熔化潜热和导热系数分别降低了3.2%和16.7%。本研究为固废铁尾矿在蓄热、储能领域的应用提供了新思路。     

Role of heat transfer and thermal conductivity in the crystallization behavior of polypropylene‐containing additives: A phenomenological model

The thermal conductivity of a filler and the thermal conductivity of a composite made from that filler influence the heat‐transfer process during melt processing. The heat‐transfer process from the melt to the mold wall becomes an important factor in developing the skin–core morphology. These aspects were examined in this study. The thermal conductivity of polypropylene–filler composites was estimated with a standard model for various fillers such as calcium carbonate, talc, silica, wollastonite, mica, and carbon fibers. The rate of cooling under given conditions, including the melting temperature, mold wall temperature, mass of the composite, and filler content, was estimated with standard heat‐transfer equations. The time to attain the crystallization temperature for polypropylene was evaluated with a regression method with differential temperature steps. The crystallization curves were experimentally determined for the different fillers, and from them, the induction period for the onset of crystallization was estimated. These observations were correlated with the expected trends from the aforementioned formalism. The excellent fit of the curves showed that in all these cases, the thermal conductivity of the filler and composite played a dominant role in controlling the onset of the crystallization process. However, the nucleation effects became important in the later stages after the crystallization temperature was attained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2994–2999, 2003     

热处理对PPS结晶度的影响分析

利用差示扫描量热仪研究了不同温度热处理对聚苯硫醚(PPS)树脂的结晶度影响。结果表明,在玻璃化转变温度与熔融温度之间,PPS树脂的结晶度随热处理温度的升高呈先增大、后稳定、再减小的趋势,相对结晶度最大值为65.36%,最小值为46.14%。这是由于PPS分子活性、分子链的热氧交联反应随热处理温度的不同具有不同的表现形式,这些因素会直接影响PPS聚合物的晶核形成和晶体生长,进而影响PPS的结晶度。     

Miscibility,melting, and crystallization behavior of poly(hydroxybutyrate) and poly(D,L‐lactic acid) blends

Melting behavior and crystal morphology of poly(3‐hydroxybutyrate)‐poly(D ,L ‐lactic acid) (PHB‐RPLA) blends with various compositions have been investigated by modulated temperature differential scanning calorimetry (mt‐DSC), polarized optical thermomicroscopy (POTM), modulated force thermomechanometry (mf‐TM), and small angle X‐ray scattering (SAXS). Thermal properties were investigated after fast cooling crystallization treatment. Multiple melting peak behavior was observed for all polymers. mt‐DSC data revealed that PHB‐RPLA blends undergo melting‐recrystallization‐remelting during heating, as evidenced by exothermic peaks in the nonreversing heat capacity. A decrease in degree of crystallinity due to significant melt‐recrystallization was observed for blends. PHB‐RPLA showed different crystal morphologies for various compositions. POTM results showed that the crystallization rates and sizes of spherulites were significantly reduced as RPLA content increased. mf‐TM results confirmed miscibility of these two polymers. SAXS data provided evidence of lamella thickness of blends, which increased with increasing RPLA content. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

脂肪酸低熔混合物的制备及强化传热研究

利用差示扫描量热仪测定了羊蜡酸-棕榈酸二元混合物的热性能,确定其低熔混合物配比,并采用激光导热仪分析了添加微米级导热填料对提高该低熔混合物作为相变材料(PCM)的导热性的效果。结果表明,将20质量份数的改性SiC粉加入100份PCM中,其导热率增加100%且相容性较好,而添加同量的α-Al2O3粉和玻璃粉,其导热率分别提高66%和44%。DSC热性能分析表明,填料的使用会使PCM的熔点增加3～5℃,但随着添加量的增加熔点基本保持不变,而熔融焓则会随着添加剂量的增加而递减。以上结果表明,对导热率提高效果最明显的是改性SiC粉。     

绝缘导热Si_3N_4/LLDPE复合材料的研制

用粉末法制备了Si3N4增强线型低密度聚乙烯(LLDPE)导热材料,研究了填料Si3N4对LLDPE熔融温度、结晶度、热导率、电绝缘性能及力学性能的影响.结果表明,加入Si3N4粒子,提高了LLDPE的熔融温度和结晶度;当w(Si3N4)为30%时,体系热导率达基体的6～7倍,热导率随Si3N4粒径的减小而增大,此时体系仍然具有较高电阻率及良好的介电性能,但力学性能明显下降.     

The measurement of the crystallinity of polymers by DSC

The procedures adopted and the inherent assumptions made in the measurement of crystallinity of polymers by differential scanning calorimetry (DSC) are reviewed. The inherent problem in all DSC measurements is concurrent recrystallisation and melting of the polymer sample on heating to the melting point and the variation of the enthalpies of crystallisation and melting, heat capacities and degree of crystallinity with temperature. A First Law procedure is suggested which involves heating the sample between two set temperatures, T₁ and T₂. T₁ is selected by the requirement that the degree of crystallinity of the sample should not change either with temperature or time, and be representative of the sample during its use. T₁ is taken to be ambient or just above the glass transition temperature. T₂ is taken to be just above the observed last trace of crystallinity. Integrating the observed specific heat difference between the sample and the completely amorphous material during these two temperature ranges determined the residual enthalpy of fusion at T₁. Problems are noted in the use of this procedure in that the specific heat of the liquid should not be arbitrarily chosen since this leads to systematic errors in the heat of crystallisation.The degrees of crystallinity of metallocene polyethylene (m-PE) and polyethylene terephthalate (PET) measured by this procedure have been compared with values measured by density, determined at room temperature.     

石墨烯导热高分子复合材料的制备、性能与机理

石墨烯是一种具有超大的比表面积、良好的热和化学稳定性、超高的热导率以及易于化学修饰的蜂窝状单层碳材料,已作为填料广泛应用于导热高分子复合材料领域。近年来石墨烯导热高分子材料的研究重点是改善石墨烯在聚合物基体中的界面相容性和分散性能。阐述了近年来石墨烯导热高分子复合材料的制备方法及其热性能,并重点对石墨烯导热高分子复合材料的导热机理进行综述,同时结合研究现状对石墨烯导热高分子复合材料的研究方向进行展望。     

Chemical recycling of polymer composites induced by selective variable frequency microwave heating

The application of variable frequency microwave (VFM) heating to achieve rapid thermal depolymerization of polymer composites is reported for the first time. The thermal and chemical influence of composite additives on polymer decomposition has been studied for a set of chemically recyclable polymers, including polyphthalaldehyde, polypropylene carbonate, two polyhydroxyalkanoates, and nylon 6. Carbon-based additives, specifically nanocarbon particles, were used as effective microwave absorbers to controllably degrade the surrounding polymer matrix into valuable, monomeric compounds. Depolymerization and byproduct confirmation were quantified by gel permeation chromatography and nuclear magnetic resonance spectroscopy. Synergistic effects can be leveraged from pre-treating composite samples to further reduce the total microwave energy required to depolymerize composite samples. This study establishes the use of VFM heating for chemical recycling of polymer composites that can be leveraged toward a plastic circular economy.     

半芳香族耐热性共聚酰胺的合成及性能

以癸二胺、己二胺和对苯二甲酸为主要原料,通过一步熔融缩聚法合成了半芳香族共聚酰胺聚对苯二甲酰癸二胺/己二胺(PA10T/6T),采用核磁共振碳谱确认了其结构。在此基础上,通过差示扫描量热仪、X射线衍射仪和热重分析仪对其熔融温度、结晶温度、晶体生长方式、结晶活化能、结晶度以及热稳定性进行了测试分析研究。结果显示,PA10T/6T具有较宽的加工窗口,当PA6T链段的物质的量分数达到10%,30%和50%时,PA10T/6T熔融温度较PA10T分别下降了10.97,37.41,7.8℃;PA6T链段的引入并没有改变聚合物的晶体生长方式且对聚合物的热稳定性没有明显影响;随着PA6T链段含量的增加,聚合物的结晶温度、熔融温度、结晶活化能的绝对值以及结晶度均呈先降低后升高的趋势,这是聚合物分子链结构和聚合物晶体完整性综合影响的结果。