电动汽车热泵系统中易燃制冷剂R290的燃烧特性

研究了制冷剂R290在电动汽车热泵空调系统潜在泄漏过程中的燃烧特性,通过实验得到了不同泄漏温度和体积流量下R290的燃烧特性,并与制冷剂R134a进行对比。实验表明:R290在低温下更难点燃,而在高泄漏体积流量下和高泄漏温度下会发生喷射火焰的吹灭现象,且当泄漏温度在30~60℃之间时,泄漏体积流量的增大会提高其燃烧强度。R290制冷剂气体温度越高,其火焰燃烧强度越大,燃烧火焰越细,火焰心高度越低;R290制冷剂气体的体积流量越大,火焰燃烧区域越大,火焰高度越低,热辐射通量越大。     

生化模型化合物的热化学研究 Ⅰ. L( )-天冬氨酸和L( )-谷氨酸在水中的低浓度溶解焓

本文报道利用参考温升测定牛顿冷却常数K值,适于在常量环境恒温潜水式反应量热计中测定温升只有10~(-3)～10~(-4)℃的较小热量。在浓度为10~(-3)～10~(-4)mol/kg时测定了L( )一天冬氨酸和L( )-谷氨酸在水中的积分溶解焓。在实验偏差范围内,没有观察到溶解焓对浓度的依赖关系。ΔH_s(298.15K)分别为25.8±0.6和25.7±0.4kJ/mol.偏差为平均值标准偏差的两倍。这两种氨基酸分子中由于差一个亚甲基而引起的水中摩尔积分溶解焓差并不明显。     

(n-C18H37NH3)2MCl4热容的测定

在差示扫描量热仪(DSC仪)上, 采用扫描热焓法测定物质的热容, 实验精度达到±1%左右. 在190-410 K温度区间内, 测定了四氯合金属酸(Ⅱ)正十八铵(n-C_(18)H_(37)NH_3)_2MCl_4(M=Mn和Zn; 简称C_(18)M)的热容. 同时测定了C_(18)M的固-固相变焓和相变熵. 本文报导了C_(18)M每隔5 K的热力学函数.     

熔融NaCaF3、Na2CaF4和Na3CaF5的分子动力学模拟

通过分子动力学模拟，研究了熔盐溶液NaCaF_3、Na_2CaF_4和Na_4CaF_5体系，模拟表明，三种二元混合系的径向分布函数十分接近．由模拟所得到的摩尔混合焓很好地与实验值一致．混合焓与Na~+离子势阱深度之间表现出很好的线性关系．模拟表明，在Na_2CaF_4体系中，即NaF-CaF_2二元系处于低共熔混合组分比NaF:CaF_2＝2:1时，Na~+，Ca~(2+)和F~-离子的自扩散系数出现很大的反常．     

木糖醇玻璃焓松弛的量热分析

为了考察木糖醇的玻璃化转变和焓松弛行为,寻求碳链长度对线性多元醇玻璃化转变和焓松弛行为的影响,利用差示扫描量热(DSC)技术测定了不同降温速率下木糖醇在玻璃化转变温度(Tg)前后的比热容(Cp),通过曲线拟合获得了TNM(Tool-Narayanaswamy-Moynihan)模型参数,并和其他多元醇类已有研究结果进行对照.结果表明,尽管TNM模型可以很好地重现不同降温速率体系的实验比热容数据,但模型参数并不是材料常数,而是和热历史有关,不同的降温速率对应不同的模型参数.指前因子(A)、非线性参数(x)和非指数参数(β)均随着降温速率的增加而降低,松弛活化焓(△h*)的变化趋势刚好相反.几种线性多元醇玻璃化转变和TNM模型参数的对照表明,玻璃化转变温度,松弛活化焓和动力学脆度(m)都随着烷基碳链长度的增加而增加.虽然非线性参数、非指数参数随碳链长度的增加有降低的趋势,但木糖醇展现出反常变化的情形.     

(XN)4R4簇合物的结构与化学键

用密度泛函理论,在B3LYP/6-311G水平上,对(XN)4R4 (X=C,Si,Ge;R=H,CH3,NH2,OH)及合成的先驱化合物(XN)2R2进行几何构型、电子结构、振动频率和化学反应焓变等进行了研究.结果表明,(RCN)4比(CNR)4更稳定.所有簇合物的零点能EZP值,R=H时最小,R=CH3时最大,R配位原子依次为C、N和O时,EZP值逐渐减小.     

聚己内酯-天然骨粉生物医用复合材料的制备和性能

采用熔融共混法制备了不同天然骨粉含量的聚己内酯-天然骨粉（PCL-BP）生物医用复合材料,并通过力学实验、表面亲水性分析、差示扫描量热分析和热重分析对复合材料的性能进行了表征。结果表明：随着天然骨粉含量的增加,复合材料的拉伸和弯曲强度先增加后降低,其表面亲水性得以改善。此外,复合材料的结晶温度升高,熔融焓降低,热稳定性...     

不同质量流量下正癸烷的裂解换热特性

碳氢燃料裂解吸热反应是超燃冲压发动机实现主动冷却所利用的重要手段。为探究不同燃油流量下冷却通道中的裂解换热特性,本文通过设置不同质量流量,不同出口温度探究了正癸烷的热沉、转化率、壁面温度以及结焦情况,确定了正癸烷在不同质量流量下的裂解换热特性。结果表明正癸烷在高温时化学反应对停留时间的影响减弱,停留时间对化学反应的影响得到增强。正癸烷的气相产物分布随着质量流量变化而变化,烷烃含量随质量流量增大而减少,烯烃含量随质量流量增大而增加。发现了低流量高出口温度情况下正癸烷的裂解强化换热现象,发生裂解强化换热时壁温会显著下降。同时通过裂解残液的色谱分析,得到了结焦反应迅速增强的温度与流量。     

甘氨酸在氯化钾水溶液中的稀释焓

利用瑞典LKB-2277生物活性检测仪测定了298．15K时甘氨酸在不同浓度的氯化钾水溶液中的稀释焓,根据McMilkm-Mayer理论计算了甘氨酸在不同浓度的氯化钾水溶液中的同系焓相互作用系数．结果表明,甘氨酸在氯化钾水溶液中的焓对相互作用系数h2均为负值,并且随着氯化钾浓度的增加,h2的绝对值逐渐减小。     

我国测定的铟原子量新值首次被采用为国际标准

1991年北京大学化学系教授张青莲和青海盐湖研究所副研究员肖应凯使用一台英制VG354型固体源热电离质谱仪,并收集国内外五种铟试剂,纯制硝酸铟溶液。在钽带上涂样2μg In,加磷酸烘干。加热电流为1.5A时,得稳定的115In离子发射,其流强达3×1011A。每种样品涂样5次,每次测100个同位素丰度比R113/115数据,自动记录平均值及标准偏差。测得所有样品的平均R113/115=0.044804±0.000055（2SD）。在实验中,严格要求各项专业技术细节,包括排除同量素干扰等问题。研究报告见张青莲、肖应凯:“铟的原子量”,《中国化学快报》,卷2,407—410页,1991。     

Heat of Terpolymerization

Abstract

A novel correlation for predicting the heat of terpolymerization from the binary data is proposed. This correlation is applicable to the ternary system with monomers which obey the Q-e scheme. The heat of terpolymerization for the ternary system methyl methacrylate-styrene-acrylonitrile is calculated from binary data.     

Heat Transfer Enhancement on the Adsorber of Adsorption Heat Pump

Three methods for improving the heat transfer of the adsorber have been developed in this paper. First, an electrically conductive polyaniline was applied for enhancing the thermal conductivity of adsorbent bed. A thermally conductive composite of polyaniline and adsorbent was prepared by chemical oxidative in situ polymerization of aniline onto the surface of adsorbent particles. A thin thermal conducting net on the surface of the adsorbent particles was grown. The experimental results indicated that the thermal conductivity of this composite could be increased to approximately 4 times that of the raw adsorbent. Second, the adsorbent bed was shaped by a compressing process. This process can reduce the thermal resistance among the adsorbent particles and the contact thermal resistance between the adsorbent bed and the heat exchanger. The thermal conductivity of the shaped adsorbent bed itself from the tests can be increased 30% when the density of the solid adsorbent bed is 1.5 times that of its original density. Furthermore, the adsorption capacity of the above treated adsorbent did not decrease obviously. Third, a proper design of adsorber has been introduced and analyzed. Further tests of this design will be conducted soon.     

Heat capacities of perfluoropolyethers

The heat capacities at constant pressure of liquid perfluoropolyethers with different chain structures were determined above the glass transition temperature up to 480 K by means of differential scanning calorimetry (DSC). The group contributions of the  O , CF₂ , and  CF(CF₃) were calculated as a function of the temperature. Anomalous behavior of ethereal oxygen in a perfluorinated chain, as previously found for group contributions to the glass transition and to the vaporization energy, was observed also for heat capacity where the oxygen contribution is consistently lower for perfluorinated polyoxides in comparison to the hydrogenated homologous. The jump in c_p at the glass transition follows a regular behavior in the sense that ΔC_p/beadmole is within the average range found by Wunderlich for the majority of polymers. Moreover, data obtained in the present work allow the prediction of c_p of perfluoropolyethers of whatever structure between T_g and 480 K. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2073–2082, 1997     

Heat capacity of fluoropolymers

The heat capacities of poly(vinyl fluoride), poly(vinylidene fluoride), and polytrifluoroethylene have been measured between 80 and 340°K. The results can be expressed as the sum of two terms: the optical contribution calculated from the vibrational band assignments in the literature and the acoustical contribution calculated according to the Tarasov continuum model. Combining our data with those for polyethylene and polytetrafluoroethylene, it is concluded that the force constant for one-dimensional intrachain interaction is approximately constant for all polymers with carbon backbones. The force constant for three-dimensional interchain interaction is one order of magnitude smaller than the one-dimensional force constant, and decreases when the hydrogen atoms in polyethylene are replaced by fluorine atoms. The thermodynamic functions for the three polymers have been evaluated. Glass transitions at 228°K and 305°K have been found in poly(vinylidene fluoride) and polytrifluoroethylene, respectively.     

Heat capacity of cheese

The heat capacity of several samples of hard cheese, semi-hard cheese and soft cheese was determined by conventional differential scanning calorimetry (DSC) and by temperature modulated DSC. Additionally, the gross composition of the cheeses was analysed, and equations from the literature were used to calculate the heat capacity therefrom. Both analytical methods were suitable to determine the heat capacity of the cheese samples whereas only one out of three equations proposed for the calculation of the heat capacity of foods from composition data led to results which were comparable with analytical data. As the equation coefficients for particular constituents are responsible for the deviations in the calculated heat capacities the differences between calculated and measured values increase with a decreasing moisture content of the cheeses.     

Heat Resistance of Polyamidobenzimidazoles

Thermal degradation of polymers based on polyamidobenzimidazoles was studied in relation to the monomeric units structure and mole fraction of the initial monomers.     

Heat inhibited reactions

Acyl transfer from p-nitrophenyl trimethylacetate to hydrogen peroxide in millimolar aqueous solutions of an amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer slows down as the temperature is raised due to partitioning of the hydrophobic ester into heat-induced micelles.     

Heat shield materials

Some properties and applications in the aerospace industry of high-temperature whiskers (SiC, Si₃N₄, AlN) and fibers (SiO₂, A1₂O₃) are described