新型环保制冷剂氟化醚类物质的热力学分析

本文筛选了可能作为替代制冷剂的氟化醚类（ＨＦＥｓ）纯物质和混合物,然后对这些工质的制冷循环性能进行了热力学分析。分析结果表明：在醚类纯质及混合物中 ｃ－ＨＦＥ２１６、 ＨＦＥ１４３ａ、 ｃ－Ｅ２－２１６、 ｃ－ＨＦＥ２１６／ＨＦＥ１４３ａ和ｃ－ＨＦＥ２１６／ｃ－Ｅ２－２１６适合替代 ＣＦＣ１２和 ＨＦＣ１３４ａ ; ＨＦＥ１２５适合替代 ＣＦＣ１１５; ＨＦＥ１３４、 ＨＦＥ２４５ｃｂ β和 ＨＦＥ１４３／ＨＦＥ３１－１０适合替代 ＣＦＣ１１４ ; ＨＦＥ３３８ｍｆ、 ＨＦＥ２４５ｆａ、 ＨＦＥ１４３、 ＨＰＥ２６３ｆｂ、 ＨＦＥ２３６ｅａ／ＨＰＥ２４５ｆａ和 ＨＦＥ２３６ｅａ／ＨＦＥ１４３有望成为ＣＦＣ１１的替代物。     

高效传热管内凝结换热性能及阻力性能的实验研究

本文以ＨＦＣ１３４ａ和ＨＣＦＣ２２为工质对光管及两种不同槽型的强化传热管（ＤＡＥ－２管与ＤＡＥＣ管）的水平管内凝结换热进行了对比实验研究、研究发现,ＤＡＥ－２管平均换热系数比光管提高了１４０％～１７０％,而单位长度阻力损失增加了５０％～１００％,ＤＡＥＣ管平均换热系数比光管提高了１６０％～２００％,同时单位长度阻力损失增加了７０％～１３０％。此外,本文给出了ＤＡＥ－２管和ＤＡＥＣ管平均换热系数及阻力损失的计算关联式,可用于冷凝器设计。     

二元致冷剂气体水合物相平衡计算

本文在测定 ＨＦＣ１５２ａ／ＨＣＦＣ１４１ｂ和 ＨＦＣ１３４ａ／ＨＣＦＣ１４１ｂ 二元气体水合物相平衡数据的基础上［３］,建立二元混合气体水合物计算模型和方法。利用 Ｗｉｌｓｏｎ活度系数理论和Ｌａｎｇｍｕｉｒ等温吸附理论建立了水合物相各组成的逸度计算模型,并依据水合物中客体分子的逸度平衡条件进行了混合水合物的相平衡计算。计算结果正确地表征混合气体水合物相平衡特性,并与实验数据较精确吻合。     

碳氢化合物与R152a的混合物替代R12的理论研究

碳氢化合物与Ｒ１５２ａ的混合物替代Ｒ１２的理论研究吴之春，马一太，吕灿仁，陈东（天津大学热能研究所天津３０００７２）关键词：碳氢化合物，制冷系统，混合替代工质一、引言随着ＣＦＣ替代工质研究的不断深入，人们逐步发现Ｒ１２的替代物Ｒ１３４ａ存在着许多不足...     

多元混合工质及纯质的PVTx实验研究

多元混合工质及纯质的ＰＶＴｘ实验研究王怀信，高志明，马一太，刘靖，赵凤亭（天津大学热能研究所天津３０００７２）关键词代用工质，ＰＶＴｘ特性以ＨＣＦＣ２２、ＨＣＦＣ１２４及ＨＦＣ１５２ａ为组元的混合工质是ＣＦＣ１２有希望的灌注式替代物。其中ＨＣＦＣ１２...     

HFC—32饱和液粘度的试验研究

ＨＦＣ—３２饱和液粘度的试验研究孙立群，朱明善，韩礼钟，林兆庄（清华大学热能工程系北京１０００８４）关键词粘度，替代物，热物性，ＨＦＣ—３２１试验装置及试验原理本文所采用的毛细管法试验装置参见图１［１］。根据哈根—泊肃叶（Ｈａｇｅｎ－Ｐｏｉｓｅｕｉｌ...     

水平管内环状流动核态沸腾换热模型

本文在已有的池和外掠平板核态沸腾机理研究的基础上,提出了系统的水平管内饱和流 动核态沸腾理论,建立了水平管内环状流下流动核态沸腾换热的组合模型,并对该模型进行了简化 和数值求解。最后,将计算结果与ＨＦＣ－１３４ａ实验数据进行了比较;结果表明二者一致性较好。     

模拟分析R134a和R12在汽车空调“两器”中的换热

模拟分析Ｒ１３４ａ和Ｒ１２在汽车空调“两器”中的换热史琳，付屹东，韩礼钟，朱明善（清华大学热能工程系北京１０００８４）关键词汽车空调；模拟；Ｒ１３４ａ；热物性１前言Ｒ１３４ａ是目前国际上公认的汽车空调冷剂Ｒ１２的替代物［１］。当汽车空调采用Ｒ１３４ａ...     

Tl2Ba2Ca2Cu3Oy大块超导体的磁化和钉扎势

研究了Ｔｌ２Ｂａ２Ｃａ２Ｃｕ３Ｏｙ大块超导体的磁化和磁通钉扎势。由ＺＦＣ磁化测量发现，在远低于Ｔｃ的温度发生２Ｄ－３Ｄ转变。由磁驰豫确定的磁通钉扎势Ｕｐ与磁场之间遵守Ｕｐ∝Ｈ＾－α，且α≈１，在Ｈ＜Ｈｃ１磁场范围内，弱连接超导体的钉扎势则遵守Ｕｐ∝ｅｘｐ［－Ｈ／Ａ］关系，且Ａ＝６０。     

氧化硅包敷对铁黄脱水过程的影响

本文采用ＤＴＡ、ＴＧ、ＨＴＸＴＤ和ＴＥＭ研究了ＳｉＯ２包敷ａ－ＦｅＯＯＨ粒子的脱水过程。从ＤＴＡ和ＴＧ曲线算得的动力学参数表明，ＳｉＯ２包敷ａ－ＦｅＯＯＨ粒子的脱水过程近似为一级反应，其活化能大于未处理的ａ－ＦｅＯＯＨ粒子的活化能。     

壁面对纳米管轴向导热影响的MD模拟与分析

纳米管是一种有着广泛应用前景的纳米材料,作为初步研究,本文采用非平衡分子动力学模拟方法和LJ势函数研究了氩结构纳米管的轴向热导率随着纳米管的温度、厚度和长度的变化,并对结果进行了分析。研究表明:在温度为12-60K的范围内,纳米管的轴向导热率随着温度的升高先上升,然后很快下降,再比较缓慢下降。氩纳米管的轴向导热率随着壁厚的增加先是基本不变,然后出现一个极大值。本文分析了产生极值的原因。     

Lattice thermal conductivity of polyvinyl acetate at low temperatures

The lattice thermal conductivity of a non-crystalline polymer has been studied at low temperatures in the frame of the density fluctuation model by calculating the total lattice thermal conductivity of polyvinyl acetate in the temperature range 0.1–4K as an example and a very good agreement has been reported between the calculated and the experimental values of the lattice thermal conductivity in the entire temperature range of study. It is also found that at low temperatures, the lattice thermal resistivity of a non-crystalline polymer is mainly due to scattering of phonons by empty spaces.     

Thermal conductivity of NbSe3

The thermal conductivity, κ, of NbSe₃ has been measured by novel self-heating techniques that allowed the electric field dependence of κ to also be measured. Measurements were made from 35 K to room temperature. Above the charge density wave transitions, the phonon thermal conductivity is 4–7 times the electron thermal conductivity, and it rises smoothly below the transitions, indicating that phonon-phonon scattering predominates. Phonon mean free parths have been estimated at 187 A° at 60 K and 60 A° at 150 K. No clear anomalies were observed at the phase transitions, giving upper limits to changes in the phonon mean free path. No field dependence of κ was observed.     

软质聚氨酯泡沫塑料的低温热导率

讨论了软质聚氨酯泡沫塑料对流判据的低温传热机理.根据软质聚氨酯泡沫塑料结构简图,将各种参数和低温数据带入对流判据公式,得到对流判据L的计算结果.计算了软质聚氨酯泡沫塑料的低温热导率.为了与计算的低温热导率比较,采用测试硬质泡沫塑料热导率的稳态热流双试样保护热板装置,测试了软质聚氨酯泡沫塑料的低温热导率,最后给出了低温热导率与温度关系曲线.根据试验,讨论了低温热导率的影响因素如温度、密度、吸水率等.     

Molecular dynamics simulation of decomposition and thermal conductivity of methane hydrate in porous media

The hydrate has characteristics of low thermal conductivity and temperature sensitivity. To further analysis the mechanism of thermal conductivity and provide method for the exploitation, transportation and utilization of hydrate, the effect of decomposition and thermal conductivity of methane hydrate in porous media has been studied by using the molecular dynamics simulation. In this study, the simulation is carried out under the condition of temperature 253.15 K-273.15 K and pressure 1 MPa. The results show that the thermal conductivity of methane hydrate increases with the increase of temperature and has a faster growth near freezing. With the addition of porous media, the thermal conductivity of the methane hydrate improves significantly. The methane hydrate-porous media system also has the characteristics of vitreous body.With the decrease of the pore size of the porous media, thermal conductivity of the system increases gradually at the same temperature. It can be ascertained that the porous media of different pore sizes have strengthened the role of the thermal conductivity of hydrates.     

稠密气体中的输运现象和方位势氩的粘滞率和热导率

建议用推广的恩斯柯克方程(14),讨论稠密气体中的输运现象。指出空间关联函数Y(r)可以从状态方程的维里展开求得。文中给出了计算方位势稠密气体的粘滞率和热导率的公式以及计算关联函数的方法。用得到的结果,计算了温度为173K和348K的氩的粘滞率和温度为183K和348K的氩的热导率。在高密度区,计算结果与实验测定的符合程度,较之现有理论,有明显的改进。 关键词：     

Effect of dispersion on the phonon focusing and anisotropy of thermal conductivity of silicon single crystals in the boundary scattering regime

The effect of dispersion on the focusing of thermal phonons and on the thermal conductivity of silicon single crystals in the boundary scattering regime has been investigated. Analysis of the spectra of acoustic modes obtained for silicon single crystals from inelastic neutron scattering data has demonstrated that, upon transition from long-wavelength phonons to short-wavelength phonons, the directions of their focusing change. With an increase in temperature, this leads to a change in the anisotropy of thermal conductivity of phonons with different polarizations and, consequently, to a change in the anisotropy of the total thermal conductivity. Analysis of the temperature dependence of the thermal conductivity has revealed that the presence of extended flattened sections in the spectrum of short-wavelength transverse phonons indicates anomalously low values of the group velocity and, accordingly, a significant decrease in the contribution from these phonons to the thermal conductivity with increasing temperature. The contribution from longitudinal phonons to the thermal conductivity also significantly increases even at temperatures higher than 110 K and becomes dominant.     

Homotopy perturbation method for fin efficiency of convective straight fins with temperature-dependent thermal conductivity

In this Letter, the homotopy perturbation method (HPM) has been used to evaluate the efficiency of straight fins with temperature-dependent thermal conductivity and to determine the temperature distribution within the fin. The fin efficiency of the straight fins with temperature-dependent thermal conductivity has been obtained as a function of thermo-geometric fin parameter and the thermal conductivity parameter describing the variation of the thermal conductivity. The results reveal that homotopy perturbation method is very effective and simple. The resulting correlation equations can assist thermal design engineers for designing of straight fins with temperature-dependent thermal conductivity.     

Contribution of thermal radiation in measurements of thermal conductivity of sandstone

The effective thermal conductivity of sandstone at high pressures of up to 400 MPa and temperatures of 273–523 K has been studied. It has been shown that the degree of crystallization of rock-forming minerals substantially influences the temperature and pressure dependences of the thermal conductivity. The contribution of the radiation heat transfer in measurements of the thermal conductivity of sandstone at various temperatures has been analyzed taking into account the reflection and attenuation of the thermal radiation. The results of measuring the reflection and absorption spectra of the thermal radiation have been presented.     

碳纳米管热传导的分子动力学模拟研究

采用改进的经验键序作用势描述碳原子间的相互作用,应用分子动力学方法和Green-Kubo函数计算了碳纳米管的热导率.在模拟中,使用了重叠计算的方法来计算热流相关函数,大大减少了模拟步数.计算结果表明,碳纳米管的热导率以原子间作用力相互做功所引起的热流形式为主;热导率的值随着直径的增加而减小;在室温下,热导率的值随着温度的增加而增加,达到室温后逐渐收敛于定值.计算的单壁碳纳米管热导率在1000W/mK至4000W/mK之间,计算结果与实验结果基本符合. 关键词： 分子动力学 碳纳米管 热导率