Dimerization of defect fullerenes and the orientational phase transition in oxidized C60 fullerite

Oxidized fullerite was obtained by heating a fullerite sample intercalated with oxygen, (O2)0.44C60, up to 300 degrees C. Orientational phase transitions in the oxidized fullerite are studied using differential scanning calorimetry (DSC) and have been found to possess a specific enthalpy whose value is lower by 25% than in the initial (O2)0.44C60 sample. In order to find possible reasons for hindrance to the buckyball rotations, we performed optimizations of defect buckyball fullerenes C60-n with different distributions of vacancies along with the dimers C60-n-C60-n and C60-C60-n for n = 1-4 using density functional theory with generalized gradient approximation. We found that the dimerization energy ranges from 1.07 eV (C58-C58) to 6.56 eV (C56-C56) and from 1.81 eV (C60-C58) to 4.29 eV (C60-C56), respectively. The formation of such dimers, which could in addition interact with defect buckyball cages and form larger aggregates, is to be related to the lowering of the orientational transition enthalpy.     

Low temperature heat release,sound velocity and attenuation,specific heat and thermal conductivity in polymers

We have measured the long time (t = 5 to 200 h) heat release of Polymethylmethacrylate (PMMA) and Polystyrene (PS) at 70 mK T 300 mK. After cooling from a charging temperature of 80 K the heat release in PMMA shows a t^–1 dependence in the measured time and temperature ranges in agreement with the tunneling model. In contrast, for PS we observe strong deviations from at ^–1 dependence and a factor of ten smaller heat release than in PMMA in apparent contradiction to specific heat and thermal conductivity data for PS. To compare the heat release with other low temperature properties and to verify the consistency of the tunneling model we have measured also the acoustical properties (sound velocity and attentuation), the specific heat and the thermal conductivity of PMMA and PS in the temperature range 70mKT 100 mK, 70mKT200 mK and 0.3 KT4K, respectively. We show that the anomalous time dependence of the heat release of PS is due to the thermally activated relaxation of energy states with excitation energies above 15 K.     

Photo‐Induced Polymerization and Stress Effects in Fullerite C60

Abstract

Modifications of the structure and hardness of fullerite C₆₀ crystals under stresses generated during photo‐induced polymerization are investigated.     

Experimental investigation of the surface temperature and water retention effects on the frosting performance of a compact microchannel heat exchanger for heat pump systems

Frost formation on a louvered fin microchannel heat exchanger was experimentally investigated in this paper with the aim of determining the dominant factors affecting the time of frosting and frost growth rate. A novel methodology was developed to measure frost thickness and frost weight at intervals during the frosting period. Frost mass and thickness growth rates, corresponding coil heat transfer, capacity degradations and air pressure drop are measured and discussed. The experimental data showed that at a given air dry bulb temperature, the fin surface temperature and air humidity are the primary parameters that influence the frost growth rates. Water retention and air velocity had a secondary impact on the frosting performance. From digital images of the frost growth it was observed that frost does not nucleate from the water droplets retained in between fins but it developed from the leading edges of the fins.     

空分设备换热系统的设计及温差选取

简介一般空分设备换热系统的设计软件环境,阐述空分设备换热与制冷系统的流路组织和换热系统的设计温差选取,提出空分设备换热系统节能降耗的措施。     

Investigation on capacity matching in liquid desiccant and heat pump hybrid air-conditioning systems

Liquid desiccant and heat pump (LDHP) hybrid air-conditioning system provides a promising independent air dehumidification solution. Capacity matching among the four major heat and mass transfer components, i.e. dehumidifier, regenerator, evaporator and condenser, is essentially important for energy efficiency of the hybrid system. In this paper, the configuration of the hybrid system is firstly studied. Novel matching indices are proposed to evaluate the matching effect. The results show that a LDHP hybrid system with double-condenser, one solution-cooled and one air-cooled, is a feasible configuration for achieving capacity matching. To achieve dynamic capacity matching under real changing operating conditions, the effects of three critical operating variables, including solution flow rate, revolution of the compressor and air flow rate in the air-cooled condenser, on capacity matching and energy performance are studied. Simulation results show that dynamic capacity matching can only be achieved by regulating these three operating variables simultaneously.     

空分设备主换热器热端温差的控制及意义

减小主换热器热端温差是减少空分设备冷损,进而降低空分设备运行能耗的关键因素。叙述了武钢氧气公司30000 m3/h空分设备和60000 m3/h空分设备主换热器热端温差的控制方法,分析了两种控制方式的优缺点,并阐述了减小热端温差进而减少热交换不完全冷损的意义。     

Effect of transverse velocity and temperature gradients on sound attenuation in straight annular ducts

Abstract

In this paper, the effects of transverse mean velocity and temperature gradients on the acoustic propagation in a straight annular duct are studied so as to be the basis of further analyzing the sound propagation in nonuniform annular ducts. The wave equation governing this acoustic field is a difficult eigenvalue problem. The eigenvalue is solved by an IMSL package which is proposed to find suitable initial guess. By using the initial guess, in addition to the iterative process, the final results have been found. The results are proved to be of good accuracy by comparing with published data, and the errors are under 2.0%. From this paper we also find that, under the influence of the unsymmetric boundary condition, the attenuations of the axial symmetric radial mode are different from other modes, and this property of the former mode can not be expected by ray acoustic arguments, on the other hand, the attenuations of the lowest mode and the spinning modes can be expected.     

火焰燃烧区域空气声速与温度关系的实验研究

为使声学方法能对火焰温度进行精确测量,实验研究了火焰燃烧区域中空气声速与温度的关系。首先对非火焰气体环境中的声速与温度进行测量,然后在此基础上对不同燃料燃烧的火焰区域进行声速测量实验,并结合热电偶测得火焰温度,进而得到火焰中空气声速与温度的关系。结果表明:在固定距离下,与室温空气环境相比,高温烟气环境会使声波的传播时间减小,火焰环境会使声波的传播时间变长;在非火焰区域,空气声速与温度的关系符合理想气体中声速与温度的关系;在火焰燃烧区域,空气声速与温度关系偏离理想气体的声速与温度方程,与按照理想气体计算的声速结果相比,实际声速测量值偏小;对于同种燃料的火焰,随着火焰温度升高会出现空气中的声速减小的现象。     

Brillouin scattering measurements of the temperature dependence of sound velocity and acoustic absorption in simple alcohols

A scanning Fabry–Perot interferometer was used to measure Brillouin spectra of methanol, isopropanol and a 95% ethanol–water mixture for temperatures ranging between 285?K and 320?K. The Brillouin frequency shifts and linewidths were used to calculate the velocities and absorption coefficients of hypersonic acoustic waves in these liquids. The temperature dependence of sound speed and acoustic attenuation was determined. For all three materials, both sound velocity and absorption coefficient decreased with temperature.     

Hydrogenation-induced variation in crystal structure and heat capacity of magnetic regenerative material Er3Ni

In order to analyze the influence of hydrogenation on magnetic regenerative material Er₃Ni, the structures of Er₃Ni and its hydrides Er₃NiH_x are tested by X-ray diffraction (XRD), and their magnetic properties and heat capacities are measured by a magnetic property measurement system (MPMS) and by a physical property measurement system (PPMS), respectively. The results show that different crystal structures can be formed by the hydrogenation at 293 K, while the Er₃NiH_x does not go through magnetic transition above 2 K. The Er₃NiH_x exhibits different specific heat features with that of original compound Er₃Ni, which could be attributed to the absence of magnetic transition and other effects caused by hydrogenation. The insertion of hydrogen atoms can lead to a larger specific heat than that of Er₃Ni in some certain temperature range.     

Ammonia in low capacity refrigeration and heat pump systems

Ammonia has been used as refrigerant in large vapour compression systems continuously since the beginning of the era of refrigeration. In small systems, it has hardly been used at all since the introduction of the halogenated hydrocarbons around 1930. Lately, with the search for alternatives with less influence on global warming, the use of ammonia in small systems has come into focus again.In the present paper, the work done at the Royal Institute of Technology (KTH) with the aim of developing a prototype of a domestic water to water heat pump with a heating capacity of 9 kW is presented. It has been shown that such a system can be designed to operate with about 100 g of ammonia.Crucial problems in the development of the direct expansion system were to arrange for oil return, and to achieve good heat transfer in the evaporator. These problems were solved by use of an oil which is soluble in ammonia.The main obstacle for introducing this technology commercially is the limited supply of components. Particularly, there are no hermetic or semi-hermetic compressors for ammonia available in this size range.     

Q235与400MPa超级钢焊接热影响区晶粒尺寸的预测对比

应用有限元方法建立了低碳钢与超级钢焊接温度场数学模型,分别对5mm厚低碳钢板和超级钢板等离子焊温度场和热循环进行了模拟和时比分析;利用模拟得到的热影响区热循环曲线,根据晶粒长大动力学原理分别对其热影响区晶粒尺寸进行预测。预测结果表明,低碳钢热影响区晶粒尺寸远大于超级钢热影响区晶粒。     

Capacity control in ground source heat pump systems part II: Comparative analysis between on/off controlled and variable capacity systems

In the present paper, as the second part of two, modeling and simulation was carried out for a Ground Source Heat Pump (GSHP) system in the presence of all the most important interacting sub-systems such as building, ground heat source, electrical auxiliary heater, and the heat pump unit in order to make a fair and comprehensive comparison between the annual performance of on/off controlled and variable capacity systems. The annual modeling showed that dimensioning of the on/off controlled GSHP based on the peak heat demand of the building plays a significant role when the two control strategies are compared: if the on/off controlled GSHP is dimensioned to cover only 55% of the peak heat demand of the building, the electrical auxiliary, which then covers about 10% of the annual heating demand of the building, makes the SPF of the on/off controlled GSHP to be lower than the one of the variable speed system. On the contrary, when the on/off controlled system is dimensioned to cover more than 65% of the building’s peak heat demand, i.e. more than 95% of the annual heat demand of the building, there is no considerable difference between the SPFs of the on/off controlled and variable capacity systems.     

Correction of logarithmic mean temperature difference in a compact brazed plate evaporator assuming heat flux governed flow boiling heat transfer coefficient

The heat transfer in heat exchangers is commonly calculated using the concept of Logarithmic Mean Temperature Difference (LMTD). As is well known this approach is only valid for counter-current and co-current heat exchanger configurations. For other configurations, corrections for the deviation from pure counter-current are introduced. From any standard text book in heat transfer it may be found that the LMTD approach may also be used if condensation and evaporation occurs in the heat exchanger. The purpose of the present paper is to investigate if the LMTD approach can be used in a compact brazed plate evaporator. It will be shown through integration of the governing equations that the LMTD approach indeed may be used for practical cases, even though deviations occur at small logarithmic mean temperature differences. The article presents suggestions on the correction factor (F) needed under some simplified assumptions in a compact brazed plate heat exchanger operating as an evaporator for heat pump and refrigeration applications.     

Wall and fluid inlet temperature effect on heat transfer in incompressible laminar oscillating flows

This paper deals with the problem of oscillating flows occurring in devices such as Stirling or thermoacoustic engines and refrigerators. Since the global governing equations cannot be solved, the authors propose to introduce a few simplifications; the most simplifying reduction is that the fluid is assumed to be incompressible. However, specific attention is paid to describing the flow characteristics that's why the Lagrangian formalism which allows the individual study of each fluid particle is adopted. Thereby each particle contribution to global thermal effects can be evaluated and the gas temperature profiles along the exchanger can be computed. Various situations are presented including the case of a non-uniform temperature at the wall and a phase lag between pressure and temperature at the fluid entrance. The efficiency of the wall to fluid thermal exchange is analyzed. The authors show that this exchange depends upon two important parameters: the geometric ratio between the exchanger length and the particle oscillating displacement, and a thermal parameter “β”, governing the temperature profiles and related to the Prandtl number, the operating frequency and the phase lag between the instantaneous heat flux and the wall to fluid temperature difference.     

湖南某地表水源热泵水温调查与扩容方案分析

对湖南某湖水源热泵系统的水温进行多点连续监测并对监测数据进行分析,提出几种空调扩容方案,并分析各方案的优劣与可行性,其中多冷热源方案在一定程度上能够起到为空调系统增效的作用。在进行类似地表水源热泵系统扩容改造时,本文的实测数据与扩容方案可作为参考与借鉴。     

空分主换热器温差分析的计算与分析

简述了Praxair 2 0 0 0 0m3/h内压缩流程空分设备主换热器的流程和参数 ,利用数字计算机软件Maehcad7 0计算并作出了主换热器内部的传热温差分布曲线图 ,分析以主换热器内的温差分布情况 ,最后简单讨论了传热温差与不可逆损失的关系。     

Low temperature (< 100 °C) deposited P-type cuprous oxide thin films: Importance of controlled oxygen and deposition energy

With the emergence of transparent electronics, there has been considerable advancement in n-type transparent semiconducting oxide (TSO) materials, such as ZnO, InGaZnO, and InSnO. Comparatively, the availability of p-type TSO materials is more scarce and the available materials are less mature. The development of p-type semiconductors is one of the key technologies needed to push transparent electronics and systems to the next frontier, particularly for implementing p-n junctions for solar cells and p-type transistors for complementary logic/circuits applications. Cuprous oxide (Cu₂O) is one of the most promising candidates for p-type TSO materials. This paper reports the deposition of Cu₂O thin films without substrate heating using a high deposition rate reactive sputtering technique, called high target utilisation sputtering (HiTUS). This technique allows independent control of the remote plasma density and the ion energy, thus providing finer control of the film properties and microstructure as well as reducing film stress. The effect of deposition parameters, including oxygen flow rate, plasma power and target power, on the properties of Cu₂O films are reported. It is known from previously published work that the formation of pure Cu₂O film is often difficult, due to the more ready formation or co-formation of cupric oxide (CuO). From our investigation, we established two key concurrent criteria needed for attaining Cu₂O thin films (as opposed to CuO or mixed phase CuO/Cu₂O films). First, the oxygen flow rate must be kept low to avoid over-oxidation of Cu₂O to CuO and to ensure a non-oxidised/non-poisoned metallic copper target in the reactive sputtering environment. Secondly, the energy of the sputtered copper species must be kept low as higher reaction energy tends to favour the formation of CuO. The unique design of the HiTUS system enables the provision of a high density of low energy sputtered copper radicals/ions, and when combined with a controlled amount of oxygen, can produce good quality p-type transparent Cu₂O films with electrical resistivity ranging from 10² to 10⁴ Ω-cm, hole mobility of 1-10 cm²/V-s, and optical band-gap of 2.0-2.6 eV. These material properties make this low temperature deposited HiTUS Cu₂O film suitable for fabrication of p-type metal oxide thin film transistors. Furthermore, the capability to deposit Cu₂O films with low film stress at low temperatures on plastic substrates renders this approach favourable for fabrication of flexible p-n junction solar cells.     

Low temperature Si:C co-flow and hybrid process using Si3H8/Cl2

In this paper we demonstrate a Si₃H₈/SiH₃CH₃/PH₃/Cl₂ based co-flow process and a “hybrid” co-flow process with interruptions of the deposition. The motivation for the work stems from the desire to improve manufacturability through higher growth rates and higher etch rates commensurate with the drive to lower thermal budgets of integration of Complementary Metal Oxide Semiconductor and memory platforms. For high volume manufacturing, high selective epitaxial growth rates are necessary for enhanced throughput and low cost of ownership. Both high growth rate and low temperatures enable sufficiently high substitutional carbon levels [C]_sub in dilute Si:C alloys. The hydride deposition gases Si₃H₈, SiH₃CH₃ and PH₃ and the etch gas Cl₂ were kept separate in the pressurized gas supply lines and injected separately into the reaction chamber thus avoiding premature chemical reactions. The importance and the role of a suitable inert carrier gas are emphasized.