聚丙烯酸酯玻璃化转移温度QSPR的研究

对聚丙烯酸酯的定量构性关系(QSPR)研究具有重要意义.采用分子电性作用失量(MEIV)表征聚丙烯酸酯的分子结构,运用多元线性回归(MLR)建立定量结构玻璃化转移温度相关(QSPR)模型,同时采用逐步回归结合统计检测筛选模型变量,建立了22个聚丙烯酸酯玻璃化转移温度(T_g)与其结构间的多元线性回归方程.另外采用内部及外部双重验证的办法深入分析和检验模型的稳定性.建模的复相关系数(R_(cum))、留一法(LOO)交互校验复相关系数(R_(CV))和外部样本校验复相关系数(Q_(cxt))分别为0.982、0.971和0.922.表明用MEIV对聚丙烯酸酯分子结构信息表达较好,所建QSPR模型的稳定性和预测能力良好.

基于地表参数变化的延河流域地表温度时空演变分析

地表温度是地表能量平衡与陆面过程的重要参数,与地表参数变化关系密切。该文以黄土高原的延河流域为例,基于2015年、2018年和2020年Landsat OLI/TIRS影像,在利用大气校正法反演地表温度的基础上,提取影像归一化建筑指数(normalized difference built-up index,NDBI)、归一化植被指数(normalized differential vegetation index,NDVI)和归一化水汽指数(normalized difference moisture index,NDMI),分析地表温度与地表参数和土地利用类型的关系,以及地表温度时空变化特征。结果表明,地表温度的反演值与验证值在2015年、2018年和2020年的相关系数分别达0.569,0.675和0.632,均大于0.5,具有一定的准确性和可行性。从地表温度时空变化特征上看,低温区、次中温区、次高温区面积有所减少,而中温区面积增长较大,高温区面积略有增长,地表温度有向中、高温增长的趋势;从与土地利用类型的关系来看,下垫面覆盖类型的地表温度均呈现为水域<林地<草地<耕地<建设用地;从与地表参数的定量关系来看,延河流域地表温度变化与地表参数变化存在显著相关性,NDBI与地表温度变化呈正相关性,NDVI和NDMI与地表温度变化呈负相关性;从与地理环境因素的关系来看,地表温度随着海拔的升高而降低。在不同坡度上地表温度也体现差异性,其中平坡地表温度最高,坡度越陡温度越低。不同坡向地表温度具有显著差异,其中阳坡地表温度明显大于阴坡地表温度。研究结果可为复杂地区的地表水热环境研究提供参考。

架空输电线路用低弧垂特种导线

随着我国国民经济的快速增长,对用电需求急剧增长,输电线路要求向大电流、超高压方向发展。同时我国线路走廊比较狭窄,另外在近城区以及旅游景点、跨越江河等地区,均对线路弧垂有严格要求。本文介绍几种低弧垂架空特种导线。

Design of heat exchanger network based on entransy theory

The heat exchanger network(HEN) synthesis problem based on entransy theory is analyzed. According to the characteristics of entransy representation of thermal potential energy, the entransy dissipation represents the irreversibility of the heat transfer process, the temperature difference determines the entransy dissipation, and four HEN design steps based on entransy theory are put forward. The present study shows how it is possible to set energy targets based on entransy and achieve them with a network of heat exchangers by an example of heat exchanger network design for four streams. In order to verify the correctness of the heat exchanger networks design method based on entransy theory, the synthesis of the HEN for the diesel hydrogenation unit is studied. Using the heat exchange networks design method based on entransy theory, the HEN obtained is consistent with energy targets. The entransy transfer efficiency of HEN based on entransy theory is 92.29%, higher than the entransy transfer efficiency of the maximum heat recovery network based on pinch technology.

Heat Transfer in Nucleate Pool Boiling of Binary and Ternary Refrigerant Mixtures

Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditions at 0.9MPa. Compared to pure components, both binary and ternary mixtures showed lower heat transfer coefficients.This deterioration was more pronounced as heat flux was increased. Experimental data were compared with some empirical and semi-empirical correlations available in literature. For binary mixture, the accuracy of the correlations varied considerably with mixtures and the heat flux. Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Thome. For ternary mixture, the boiling range of binary mixture composed by the pure fluids with the lowest and the medium boiling points, and their concentration difference had important effects on boiling heat transfer coefficients.

A device for fluorescence temperature measurement based on fast fourier transform

A sapphire fiber thermal probe with Cr^3＋ ion-doped end was grown using the laser heated pedestal method. The fluorescence thermal probe offers advantages of compact structure, high performance and the ability to sustain high temperature from the room temperature to 450℃. Based on the fast fourier transform （FFT）, the fluorescence lifetime is obtained from the tangent function of the phase angle of the first non-zeroth item of FFT result. Compared with other traditional fitting methods, our method has advantages such as fast speed, high accuracy and being free from the influence of the base signal. The standard deviation of FFT method is about half of that method. In addition, since the FFT method is immunity to analysis can be skipped. of the Prony method and close to the one of the Marquardt the background noise of the signal, the background noise

The Pressure Gradient Elastic Wave： Energy Transfer Process for Compressible Fluids with Pressure Gradient

The temperature separation was discovered inside the short vortex chamber （H/D = 0.18）. Experiments revealed that the highest temperature of the periphery was 465 ℃, and the lowest temperature of the central zone was -45 ℃ （the compressed air was pumped into the chamber at room temperature）. The objective of this paper is to proof that this temperature separation effect cannot be explained by conventional heat transfer processes. To explain this phenomenon, the concept of PGEW （Pressure Gradient Elastic Waves） is proposed. PGEW are kind of elastic waves, which operate in compressible fluids with pressure gradients and density fluctuations. The result of PGEW propagation is a heat transfer from area of low pressure to high pressure zone. The physical model of a gas in a strong field of mass forces is proposed to substantiate the PGEW existence. This physical model is intended for the construction of a theory of PGEW. Understanding the processes associated with the PGEW permits the possibility of creating new devices for energy saving and low potential heat utilization, which have unique properties.

间隙型增容导线在扩容线路上的应用

间隙型增容导线是耐热铝合金导线的一种。它的高强度钢芯和合金铝股之间的特殊结构,使其耐受运行温度高达210℃。它的载流比常规同截面的钢芯铝绞线高几乎两倍,弧垂也较小。通过110kV步畔线更换间隙型增容导线工程的案例分析,它的实践应用经验可为同类案例的处理提供借鉴参考。

Heat transfer of nanofluidics in hydrophilic pores: Insights from molecular dynamics simulations

Nanofluidics in hydrophilic nanopores is a common issue in many natural and industrial processes. Among all,the mass transport of nanofluidics is most concerned. Besides that, the heat transfer of a fluid flow in nano or micro channels is always considered with adding nanoparticles into the flow, so as to enhance the heat transfer by convection between the fluid and the surface. However, for some applications with around 1 nm channels such as nano filtration or erosion of rocks, there should be no nanoparticles included. Hence, it is necessary to figure out the heat transfer mechanism in the single phase nanofluidics. Via non-equilibrium molecular dynamics simulations, we revealed the heat transfer inside nanofluidics and the one between fluid and walls by setting simulation into extremely harsh condition. It was found that the heat was conducted by molecular motion without temperature gradient in the area of low viscous heat, while it was transferred to the walls by increasing the temperature of fluids. If the condition back to normal, it was found that the viscous heat of nanofluidics could be easily removed by the fluid-wall temperature drop of less than 1 K.

Relationship between the parent charge transfer gap and maximum transition temperature in cuprates

One of the biggest puzzles concerning the cup- rate high temperature superconductors is what determines the maximum transition temperature （Tc,max）, which varies from less than 30 to above 130 K in different compounds. Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,max than the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size （ACT）, indicating a clear anticorrelation between AcT and Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high To mechanism from doped Mott insulator perspective.

Turbulent Convective Heat Transfer of Methane at Supercritical Pressure in a Helical Coiled Tube

The heat transfer of methane at supercritical pressure in a helically coiled tube was numerically investigated using the Reynolds Stress Model under constant wall temperature. The effects of mass flux （G）, inlet pressure （Pin） and buoyancy force on the heat transfer behaviors were discussed in detail. Results show that the light fluid with higher temperature appears near the inner wall of the helically coiled tube. When the bulk temperature is less than or approach to the pscudocritical temperature （Tpc）, the combined effects of buoyancy force and centrifugal force make heavy fluid with lower temperature appear near the outer-right of the helically coiled tube. Beyond the Tpc, the heavy fluid with lower temperature moves from the outer-right region to the outer region owing to the centrifugal force. The buoyancy force caused by density variation, which can be characterized by Gr/Re3 and Gr/Re2.7, enhances the heat transfer coefficient （h） when the bulk temperature is less than or near the T~, and the h expe- riences oscillation due to the buoyancy force. The oscillation is reduced progressively with the increase of G. Moreover, h reaches its peak value near the Tpv. Higher G could improve the heat transfer performance in the whole temperature range. The peak value ofh depends on Pin. A new correlation was proposed for methane at su- percritical pressure convective heat transfer in the helical tube, which shows a good agreement with the present simulated results.

Design and heat transfer analysis of a compound multi-layer insulations for use in high temperature cylinder thermal protection systems

Thermal protection systems are very essential for high temperature thermal conductivity measurement system to reduce the heat loss to environment at the range of 600-1800 K. A compound multi-layer insulations structure which composed of inner carbon fibrous materials and outer alternately arranged alumina fibrous materials and high reflectivity foils is proposed for use in high temperature cylinder thermal protection systems. A coupled conductive and radiation governing equations is presented for heat transfer analysis of the structure. The finite volume method and the discrete ordinate method are used to solve the goveming equations. The optimization structure of the compound multi-layer insulations is investigated by considering the pressure of the gas, the density of the carbon fibrous materials, the density of the alumina fibrous materials, the number of reflective foil layers and the emissivity of reflective foils. The results show that the compound structure has the best thermal insulation performance when the pressure of the gas is below 0.01 kPa, the density of carbon fibrous materials is 180 kg m^-3, the density of alumina fibrous materials is 256 kg m^-3 and the number of reflective foil layers is 39. In addition, the thermal insulation performance is much better when the emissivity of reflective foils is lower.

Study of Cycle Output Improvement by Work-Fluid Including Phase Change Material

This paper deals with the output improvement of heating and cooling cycle by using the work-fluid including phase change material.The experimental study is carried out by heat exchange between work-fluid and heat transfer surface.The work-fluid is flown to a high temperature or a low temperature heat transfer surface from the narrow path.In order to increase the amount of the heat transmission,a trace of Diethylether(boiling point 34.8 ℃),as a phase change material(PCM),is added to the work-fluid.The parameters of the experiment are additive amount of PCM,the rotational speed of the displacer piston and the temperature of heat transfer surface.It is clarified that the increasing of engine cycle output is brought by the PCM addition.The effect of PCM addition is evaluated by output ratio which is defined from the experimental cycle output data.The requirements for acquiring the increasing effect of output by adding PCM are clarified.

Heat Transfer and Entropy Generation Analysis of an Intermediate Heat Exchanger in ADS

The intermediate heat exchanger for enhancement heat transfer is the important equipment in the usage of nuclear energy. In the present work, heat transfer and entropy generation of an intermediate heat exchanger(IHX) in the accelerator driven subcritical system(ADS) are investigated experimentally. The variation of entropy generation number with performance parameters of the IHX is analyzed, and effects of inlet conditions of the IHX on entropy generation number and heat transfer are discussed. Compared with the results at two working conditions of the constant mass flow rates of liquid lead-bismuth eutectic(LBE) and helium gas, the total pumping power all tends to reduce with the decreasing entropy generation number, but the variations of the effectiveness, number of transfer units and thermal capacity rate ratio are inconsistent, and need to analyze respectively. With the increasing inlet mass flow rate or LBE inlet temperature, the entropy generation number increases and the heat transfer is enhanced, while the opposite trend occurs with the increasing helium gas inlet temperature. The further study is necessary for obtaining the optimized operation parameters of the IHX to minimize entropy generation and enhance heat transfer.

Analysis and Application of Variable Conductance Heat Pipe Air Preheater

The heat transfer analysis of variable conductance heat pipe air preheater was carried out. The temperature trans-fer matrix was obtained for the air preheater that comprises several discrete heat transfer units with same or different heat transfer surface area in a parallel or counter flow mode. By using the temperature transfer matrix, the outlet fluid temperatures could be easily calculated for a given air preheater and inlet fluid temperatures. The active length of condenser in a variable conductance heat pipe is determined according to the flat interface model. With the same initial conditions, the comparisons between variable conductance heat-pipe air preheater and regular heat pipe air preheater has been analyzed and tested in terms of heat pipe wall temperature, heat transfer surface area and outlet fluid temperatures. Based on the real industrial applications, it has been confirmed that the variable conductance heat pipe air preheater has excellent performance of anti-corrosion and anti-ash-deposition especially at the variable working condition and the sulfur coal (5%-6% mass fraction of sulfur) condition.

Excess heat capacity in glass-forming liquid systems containing molecules

Excess heat capacities at glass transition temperature in two types of glass-forming systems of [xNaNO3(1x)KNO3]60·[Ca(NO3)2]40(0x1) and Ca(NO3)2yH2O(4y13) are studied.In the former system,with the replacement of K + cation with Na + cation,the excess heat capacity is around 65.1 J mol-1·K-1,while the excess increases by 38.9 J mol-1·K-1 upon one molar H2O content in latter system.A quantitative description to the excess heat capacity is built up with the thermal effects of atomic and molecular translational motion in liquids.The results might offer a further understanding to the glass transition.

Reducing the climate shift in a new coupled model

Climate drift refers to spurious long-term changes that may be inherent in coupled models when external forcing factors are fixed. Understanding the sources of this drift and tuning the drift are crucial for obtaining reasonable simulations from coupled models. To prepare for the upcoming Coupled Model Intercomparison Project Phase 6, a new coupled model has been constructed based on the Community Earth System Model and the Grid-point Atmospheric Model of IAP LASG version 2. However, the surface temperature predicted by the new model is too underestimated, and this underestimation is caused by a type of climate drift, i.e., ‘‘initial shock.'' This study analyzes the source of the cold surface temperature from the perspective of energy balance and attempts to reduce the surface temperature drift by tuning the relative humidity threshold for low cloud.

Performance of Copper Calorimeter for Heat Transfer Measurement in High Enthalpy Shock Tunnel

Copper calorimeter, based on a calorimetric principle, offers a solution for heat transfer measurement in high enthalpy situation, especially in the erosive flow of high enthalpy shock tunnels. In this study, we numerically investigated the measuring performance of copper calorimeters. Non-ideal effects, such as heat loss to the insulator around and replacement of the average temperature of the copper element by the junction temperature, were discussed in detail. The influences of copper element thickness, copper/constantan wires thickness and sensor diameter were also estimated, with the aim to provide theoretical guidance for the design of copper calorimeter. In addition, corresponding experiments in JF10 high enthalpy shock tunnel were carried out against the data of coaxial thermocouples for verification. Results showed that the non-ideal thermal environment of a copper calorimeter(heat exchange with its surroundings) would result in a smaller measuring heat flux comparing to the one actually loaded; proper thickness of copper element matching the effective test time of shock tunnel was suggested. Besides, preliminary experimental results with corrections showed reasonable agreement with the heat flux of thermocouples, with an average deviation of 8%. Over all, this gauge developed extends and supplements the high enthalpy shock tunnel heat transfer measurements made by other techniques.

Controlling synthesis and host sensitized Eu^(3+) emissions of K_5Gd_9F_(32) and GdF_3

By controlling the reactant ratios, hydrothermal time, hydrothermal temperatures, p H values of the prepared solutions, and the concentrations of K3C6H5O7·2H2O, 1 mol% Eu3+ doped cubic phase of K5Gd9F32 and/or orthorhombic phase of Gd F3 micro/nanocrystals have been synthesized based on a hydrothermal method. For comparison, the sample was also synthesized by a co-precipitation method. The samples were characterized by X-ray diffraction(XRD) patterns, field emission scanning electron microscopy(FE-SEM) images, energy-dispersive spectroscopy(EDS) spectra, and photoluminescence(PL) excitation and emission spectra. By host Gd3+ sensitizing, the Eu3+ presents relatively strong emissions. The energy transfers from host Gd3+ to doping Eu3+ are observed in all the samples and the energy transfer plays an important role in the emission of Eu3+. Acting as a probe, the Eu3+ presents its distinct optical properties in the samples.