碳纳米复合相变材料熔化传热的理论分析

针对传统相变材料导热系数低的缺点,将高导热碳纳米材料添加到相变材料基体中可强化其相变传热.对碳纳米复合相变材料熔化传热过程进行理论分析,研究碳纳米材料导热系数、添加体积比以及材料形状对熔化传热的影响.研究表明:提高碳纳米材料的添加体积比,相变材料熔化速度随之增大;碳纳米材料的形状对复合相变材料熔化传热性能有显著影响;在高导热系数范围内,碳纳米材料导热系数变化对复合相变材料熔化传热性能的提升影响甚微.     

基于相变材料的锂离子电池热管理

相变材料被动式冷却利用相变材料相变时温度基本保持不变吸收或放出热量的特性,对电池组进行热管理。该冷却方式具有寄生功耗低、温度均匀性好、吸收或释放热量多等特点。但由于相变材料导热系数普遍较低,难以满足电动汽车在高电流密度工况下的电池热管理要求,从而限制了相变材料在电池热管理中的进一步应用。如何有效地提高相变材料的导热系数,同时保证其储热能力和化学稳定性,成为了研究相变材料电池热管理系统的关键问题。通过强化传热措施包括添加导热颗粒、金属翅片、泡沫金属和膨胀石墨可提高相变材料的导热系数。总结了四种强化相变材料传热的措施的研究进展,并概述了其传热措施的影响因素和强化传热效果。     

太阳能相变炕影响因素分析及热工性能模拟

本文设计了一种太阳能热水供热与相变蓄热组合的热炕供热系统,为提高蓄热炕的热响应,配置了高导热复合相变材料,利用数值模拟对炕体单元进行三维非稳态瞬态传热模拟。通过控制变量法,对太阳能相变蓄热炕的相变材料导热系数、相变温度、相变潜热等炕体热工特性影响因素进行模拟分析,得出:相变材料导热系数、供水温度、相变潜热对相变炕的热响应时间影响显著,且相变潜热决定放热时长,相变温度、相变温度范围对相变炕的垫面温度有明显影响。最后,以十二水磷酸氢二钠复合相变材料作为炕体的蓄热材料,对炕体进行蓄放热模拟设计,发现垫面温度昼间可达到17.1 ℃,夜间可达到30.3 ℃,可以很好地满足居民的热舒适要求。     

石蜡/膨胀石墨复合相变材料耦合热管电池热管理性能研究

为了改善相变材料用于电池热管理导热率较低的问题,制备了不同含量的石蜡(paraffin, PA)-膨胀石墨(expanded graphite, EG)复合相变材料,在相变储能单元中使用PA-EG复合相变材料包裹热源并耦合热管增强其散热能力。使用方形发热源模拟高密度能量电池充放电时的发热,在不同发热功率下探究不同EG含量的PA-EG复合相变材料耦合热管的热管理性能。实验结果表明：发热功率较低时,各相变材料热管理性能相当,发热功率较高时,更高的EG含量将带来更高的导热率以及更好的热管理效果。在EG含量为5%时,PA-EG复合相变材料导热率可提高至纯石蜡的6.36倍,实验中最大降温幅度可达7.6%,相变储能单元中温差峰值为纯石蜡散热系统温差峰值的37.7%。当EG含量较低时,PA-EG复合相变材料未熔融时呈现固态,导热率呈现各向同性,但当PA熔融后,PA-EG复合相变材料总体呈现液态,出现较强的自然对流换热,将导致储能单元内温度分布不均,容易导致电池表面温度不均产生应力,因此EG含量不宜低于5%。     

纳米TiO2 /石蜡复合乳状液相变材料的 制备与传热性能

蓄冷空调性能及制冷系数与相变材料密切相关.将石蜡复合乳状液作为分散介质,以纳米TiO_2粒子作为导热载体,采用低能乳化工艺微乳液转相法,制备出纳米TiO_2/石蜡复合乳状液相变材料,并对其分散稳定性、导热系数和蓄-放热循环稳定性进行了分析.研究结果表明:纳米TiO_2/石蜡复合乳状液相变材料的导热系数相对于纯石蜡乳状液的导热系数有明显提高,当纳米TiO_2粒子质量分数为0.15%时,纳米TiO_2/石蜡复合乳状液相变材料的导热系数比纯石蜡乳状液的导热系数提高了117.95%;TiO_2/石蜡乳状液固-液相变热循环过程中并无明显温度平台,而且其蓄-放热循环稳定性很好.该纳米TiO_2/石蜡复合乳状液相变材料有望应用于蓄冷空调,以提高蓄冷空调性能及制冷系数.     

内蒙古西部超低能耗草原民居相变墙体调温节能性研究

内蒙古西部草原民居冬季室内热环境质量普遍较差,采暖能耗高,而相变材料具有优异的热工特性。探索研究在外墙中加入石蜡基相变材料改善草原民居冬季室内热舒适性和降低采暖能耗的可行性,分析在临河地区冬季典型气象条件下,墙体材质、相变材料层厚度、对流换热系数和相变潜热对内壁面温度响应和节能性的影响。结果表明:不同墙体材质的导热系数影响墙体热性能,随着导热系数减小,温度衰减倍数增加,内壁面热稳定性提升;随着相变层厚度的增加,墙体保温性能不断增强;墙体内壁面温度波幅随对流换热系数的增大而增加;随着相变潜热的增大,对提升冬季室内热环境和减少采暖能耗方面有一定作用,但其效果有限。研究结果为内蒙古西部草原民居非透明围护结构的节能设计提供参考依据。     

太阳能热发电复合相变蓄热材料的实验研究

针对相变材料无机盐KNO3/NaNO3(摩尔比50/50)导热系数低,影响了蓄热系统充放热过程传热效率,制备了适用于太阳能热发电系统的无机盐/膨胀石墨复合相变材料,对复合相变材料的微观结构和热物性进行了分析,并搭建充放热测试平台对相变材料分别进行了热性能研究。结果表明:复合相变材料中的无机盐均匀分布在膨胀石墨中,其相变潜热与基于复合材料中无机盐质量分数的计算值相当,添加膨胀石墨后相变材料的导热系数得到了改善;在充热过程中纯无机盐的换热方式以自然对流为主,同一蓄热单元内沿轴向上下位置温差较大,不同蓄热单元内相同位置完成充热过程所需时间从上到下依次增加,而对于无机盐/膨胀石墨复合相变材料(质量比90/10)充热过程以导热为主;与纯无机盐不同,同一蓄热单元内沿轴向上下位置温度变化趋势基本一致,不同蓄热单元相同位置完成充热过程所需时间几乎没有差别。添加膨胀石墨后,相变材料的充热过程所需时间减少较小,而放热过程所需时间减少约45%,传热介质流量的变化对复合相变材料充/放热过程影响较小。     

基于分形的多孔介质复合相变材料的储热特性

本文利用膨胀石墨和纳米颗粒来强化相变储热系统的传热性能。在膨胀石墨基体中填充含纳米颗粒的相变材料,用焓-孔隙度法模拟材料的相变过程。针对不规则的膨胀石墨孔隙结构,用三维W-M分形函数修正膨胀石墨孔隙率波动,以研究不同的孔隙率和有效导热系数比对固态显热蓄热阶段相变材料熔融速率的影响。在液态显热蓄热阶段时探讨膨胀石墨孔隙率以及纳米颗粒体积分数对相变储热系统中对流传热的影响。研究结果表明,分形分布的孔隙结构能有效地抑制纳米颗粒的自由运动从而降低了纳米颗粒的局部团聚的可能性,所以利用三维W-M分形函数修正的膨胀石墨比采用平均孔隙率能更好地模拟相变材料的熔融速率。在固态显热蓄热阶段,膨胀石墨孔隙率为0.8的相变材料熔融速率比孔隙率为0.85和0.9显著增加,另外,膨胀石墨与纳米颗粒-相变材料的有效导热系数比为100的熔融速率也明显比有效导热系数比为80和60的快。当相变材料处于液态显热蓄热阶段时,其在膨胀石墨孔隙中产生对流,对流传热速率随着膨胀石墨的孔隙率增大而增大,纳米颗粒体积分数的增加也会提高对流传热速率。     

相变蓄热材料导热系数对太阳能通风墙性能的影响

通过对相变蓄热型太阳能烟囱模型通风蓄放热变化过程的计算,分析比较不同相变蓄热墙导热系数对太阳能烟囱性能的影响.计算结果表明:吸热板最大表面温度随着相变蓄热墙导热系数的增大越接近相变蓄热墙的相变温度;蓄热阶段,入口平均风速随着相变蓄热墙导热系数的增大而减小;放热阶段,入口平均风速随着相变蓄热墙导热系数的增大反而越大;相变蓄热墙导热系数越大,蓄热型太阳能烟囱系统16 h的累计通风量越高,但在导热系数增大到0.66 W·(m·K)^-1后,再增大材料导热系数,累计通风量几乎不再增加.     

载流体导热性能对相变微胶囊悬浮液层流传热特性的影响

以低熔点液态金属为载流体的相变微胶囊悬浮液（MEPCM-LM）作为散热工质,是解决高热流密度芯片散热的一种新的技术手段。针对以低熔点液态镓作为载流体的相变微胶囊悬浮液,考虑轴向导热的影响,采用等效比热法对相变微胶囊悬浮液在等热流密度圆管内的层流传热特性进行数值模拟,并与以水为载流体的相变微胶囊悬浮液（MEPCM-W）的传热能力进行比较。结果表明：对于MEPCM-LM悬浮液,轴向导热主要在热入口段产生较大影响,且随x/r0减小而增大;Peb0数越小,轴向导热的影响越大;轴向导热促进了悬浮液中相变颗粒的相变吸热,对换热的强化效果更显著。相较于MEPCM-W悬浮液,MEPCM-LM悬浮液相变更快,对流换热系数更高,可采用更短的流道而获得较大的传热能力。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

橡胶颗粒沥青混合料低温抗裂性试验研究

以AC-13级配为基础,将橡胶颗粒代替部分集料掺入混合料中,以低温弯曲试验为评价方法对不同橡胶颗粒掺量下沥青混合料的低温抗裂性进行研究,并引入应变能密度值对混合料的低温抗裂性进行综合评价.试验结果表明:橡胶颗粒沥青混合料试件的破坏微应变均超过2 300,满足冬寒区的技术指标;无论是否掺加橡胶颗粒,随着温度的下降,沥青混合料破坏时的最大弯拉强度增大,弯拉应变降低,劲度模量增大;弯曲应变能密度在胶粒掺量为1%左右时具有较大的弯曲应变能密度值,此时橡胶颗粒沥青混合料具有较好的低温抗裂性.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-