关于热传导问题的研究

所谓的导热还可以将其称之为热传导,这也就是说物体的各个部门没有相对位移或者是各个不同的物体直接接触的时候借助于分子机或者原子机自由电子等这些微观粒子热运动从而实施的一种传递热量的现象,导热属于物质的一种属性,那么导热过程能够发生在气体、液体、固体中.     

Thermal performance of perforated plate matrix heat exchangers with effects from outer wall and flow channel geometry

The performance of high effectiveness (high NTU) perforated plate matrix heat exchangers (MHEs) is dependent on the geometry of the flow channels, as well as the longitudinal heat conduction through the outer walls. The effect of the above factors on the performance of MHEs is investigated in this paper numerically. The results obtained with the present model are validated with our own experimental results as well as those in the literature. The results show a strong influence of longitudinal heat conduction through the outer wall on the performance of MHEs. A parametric study has been carried out to arrive at the optimum flow channel geometry under given operating conditions.     

Current conduction mechanism of MIS devices using multidimensional minimization system program

The present work presents an evaluation approach which enables the in-depth analysis of current–voltage (I–V) characteristics of MIS devices to determine their current transport mechanisms using a multidimensional minimization system program.Exemplarily, the current transport mechanisms were determined for a TiN/SiO₂/p-Si MOS and a TaN/HfSiO/SiO₂/p-Si MIS structure by fitting the analytical expressions for different current transport mechanisms to experimental I–V data in a wide range of applied biases and temperatures. The considered mechanisms for the investigated samples include temperature dependent Fowler–Nordheim (FN) tunneling and Poole–Frenkel (PF) emission as well as ohmic conduction. The presented approach can easily be extended to account for additional mechanisms such as trap assisted tunneling (TAT) if relevant for different samples. In contrast to typical extraction procedures which determine current conduction mechanism parameters sequentially, in this work, the adjustable fit parameters are extracted in a single operation using the Levenberg–Marquardt algorithm (Nash, 1990) to obtain a least-square fit of the model to measured I–V characteristics. Thus, simultaneously occurring current mechanisms can properly be evaluated which allows to determine the fraction of each conduction mechanism quantitatively for each voltage.     

Optimization of N2/Ar gas flow ratio for the realization of nitrogen-doped p-type ZnCdO thin films synthesized by RF magnetron sputtering

Nitrogen doped ZnCdO films [ZCO:N] have been grown on quartz substrates by radio frequency (RF) reactive magnetron sputtering technique, and the effect of the ratio of nitrogen to argon gas flow [N₂:Ar] on their electrical, microstructure and optical properties were investigated by Hall effect, energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscope (TEM), optical absorbance and photoluminescence (PL) measurements. The results indicate that all the ZCO:N films are of hexagonal wurtzite structure with highly (002) preferential orientation. As the N₂:Ar increases from 0:1 to 4:1, the absorption edge for the samples exhibits blue shift. Hall effect measurement results indicate that the N₂:Ar exerts an immense influence on the p-type conduction conversion for ZCO:N film. It is found that ZCO:N film deposited at the N₂:Ar of 1:2 shows the optimal p-type behavior, which has a carrier concentration of 1.10×10¹⁷ cm⁻³, a mobility of 3.28 cm²V⁻¹s⁻¹ and a resistivity of 17.3 Ω cm. Compared with the other samples, ZCO:N film fabricated at the relatively lower N₂:Ar possesses the superior crystal quality, luminescent and electrical properties. Additionally, a possible mechanism of p-type conduction for ZCO:N film was discussed in this work.     

Impedance Studies of La2Mo2-xSnxO（9-δ） Oxide Ion Conductors

A series of compounds La₂Mo_2-xSn_xO（9-δ）（x=0-0.3） have been synthesized by solid-state reaction technique.Materials have been characterized by XRD,SEM,DSC and impedance study.In the temperature regime 520℃-590℃,the specimens with x ≤ 0.05 have the conductivity higher than La2Mo2O9.Conductivity of Sn-doped compound decreases consistently with increasing Sn-doping,compared to the undoped compound both below and above phase transition,barring the specimens with x ≤ 0.05,where conductivity values remains almost same as that of undoped specimen in high temperature region.In the intermediate temperature regime（520℃-590℃）,the conductivity of doped compounds increases for x ≤ 0.05 as compared to parent compound.Also,there is no indication of phase stabilization with Sn-doping in this compound even with the highest doping level,x=0.3.Electric modulus analysis suggests that thermally activated oxygen ion hopping mechanism is responsible for the conduction in Sn-doped compound.     

Metallic conduction behavior in selenium-hyperdoped silicon

Hall measurements at 80–300 K are performed on crystalline silicon doped with selenium exceeding the equilibrium solid solubility limit using ion implantation combined with furnace annealing. The temperature dependence of free carrier density and sheet conductivity of the Se doping layer changes with implantation dose. Metallic conduction behavior is well observed in the sample doped with selenium to be 7.4×10²⁰/cm³. The overlapping between Se impurity states below Si conduction band might give a microscopic explanation.     

不同热源下一维晶格的量子热传输特性

运用发展的Ford-Kac-Mazur方法,研究了一维谐振和非谐振晶格与不同热源相接触时的热传输特性.研究表明,对于一维谐振晶格系统,不同噪声热源条件下,边界受热源的特征影响较大,远离边界的位置存在局域稳态平衡;而对于非谐振晶格系统,选择不同的热源直接导致了连接两热源之间的晶格体系的热传输能力不同.     

活塞式压缩机变工况热力学分析

建立了活塞式压缩机变工况下的绝热吸气和等温排气模型 ,讨论了模型的瞬时压力、瞬时压力比、排气量、质量流量、抽气时间、充气时间、最低抽气压力、最高充气压力及指示功率等工作参数 ,并推导了相应的计算公式。通过分析计算 ,指出变工况操作时 ,活塞式压缩机的功率将在某一时刻达到最大值。因工作介质假设为理想气体 ,导致理论与实际出现偏差。在工程实践中 ,可根据实际气体的临界状态参数 ,查取其压缩性系数 ,计入实际气体的状态方程中 ,并将过程指数换成实际气体的容积绝热指数 ,这样就可把结论用于实践以解决工程问题。     

Heat Transfer during Multiple Jet Impingement on the Top Surface of Hot Rolled Steel Strip

Using a unique pilot facility a series of tests were conducted using three top jets to simulate the heat transfer that occurs during run‐out table (ROT) cooling. Steel samples instrumented with internal thermocouples were tested on this facility and the effect of top jet configuration (nozzle spacing of 40 to 115mm), and water flow rate (15 and 30 1/min) were quantified using moving plate samples. The multiple top jet work indicated that heat transfer across the plate width varies significantly and is high directly under the nozzle but decreases rapidly away from the nozzle in the interaction region. As cooling progresses a much larger wetted region occurs and more uniform cooling is experienced across the plate. Multiple jet cooling experiments have also confirmed that nozzle spacing does have an effect on heat transfer. This effect is predominate in the interaction region where closer nozzle spacing leads to enhanced and more uniform heat transfer in the lateral direction across the plate width away from the nozzle. As expected higher water flow rates led to higher heat transfer both under the nozzle and in the interaction region.