冷冻靶降温过程的数值分析

利用CFD软件的传热和Boussinesq模型分析了系统的传热规律,研究了不同降温方式影响靶丸冷冻过程中的温度分布,得到了慢速降温中降温速率对温度分布的影响,并研究了阶梯降温技术对靶丸温度场的影响。结果发现:阶梯降温中,靶丸外表面最大温差的最大振幅值由降温段的降温速率和时间决定;当降温耗时与稳定段耗时之比大于2.3可使得靶丸外表面最大温差获得最小振幅值。     

低温靶封口膜上铝镀层开裂对靶丸及冰层的影响分析

针对低温靶封口膜上铝镀层开裂现象,使用实验方法和CFD仿真方法研究了其对冰层均匀性和靶丸温度场均匀性的影响。通过实验方法确认了封口膜铝镀层开裂的原因是填充气体压力过高。通过CFD模拟方法对比了三种不同的开裂位置。结果表明,低温靶封口膜铝镀层开裂会使靶丸温度场均匀性变差,从而导致冰层均匀性恶化;为避免铝镀层开裂,应控制封口膜内外压差,对实验用靶来说应控制在10 kPa以内;实验中填充气体压力过高引起的铝镀层破裂方式应为整体开裂;封口膜中心区域铝膜开裂对靶丸温度场均匀性的影响最小,外围开裂影响最大。     

背光成像技术在DT冷冻靶研制中的应用

主要介绍了背光成像实验样机的组成及工作原理,讨论了各光学部件的选择,在原理型样机建成后,获得了玻璃微球靶高质量的背光图像,通过对背光影像的光路图分析与测量(测量精度达到1μm),掌握了靶球DT冰层厚度的计算方法;初步建立了靶球二维内外表面粗糙度分析方法;通过设计模拟实验,获得了冰层在微球靶丸内均匀分布后清晰的背光影像.运用实验结果来模拟冷冻靶球DT燃料行为是非常重要的,它将为点火靶的设计和特殊表面粗糙度靶球的制备提供强大的支撑.     

EAST内冷屏降温过程瞬态温度场和热应力分析

基于EAST内冷屏降温过程的安全问题,验证目前50K控制温差的合理性。运用有限元软件ANSYS计算了降温过程中冷氦流在50K进出口温差下内冷屏的温度场和热应力分布,以及总应力的大小,计算结果表明当前的控制参数是合理的。     

香蕉冻干过程中有效导热系数实验研究

为实现对冻干工艺的精准热控制,提高冻干产品品质,本文以香蕉为研究对象,利用稳态热流法研究了在真空环境下压强(10、30、50 Pa)和干燥温度(-20、-30℃)对香蕉切块整个冻干过程中有效导热系数的影响。借助微CT扫描,观察分析了香蕉内部的升华过程,深入探讨了冻干过程孔隙率和有效导热系数的关系。结果表明:当压强由10 Pa增至50 Pa,对应的有效导热系数由0.036 W/(m·K)增至0.072 W/(m·K);升华干燥温度由-30℃增至-20℃,对应的有效导热系数由0.084 W/(m·K)降至0.058 W/(m·K);微CT在冻干过程(30 Pa,-20℃)中,升华界面逐渐向切块中心移动,孔隙率由最初的0.059增至0.252,对应的有效导热系数由0.695 W/(m·K)减小至0.123 W/(m·K)。     

接触热阻对导热系数测量准确度的影响

测量固体材料的导热系数时,测温误差是影响其测量准确度的主要因素之一。本文仅对其中接触热阻引起的附加温差等问题作一论述,并提出提高测量准确度的改进措施。一、接触热阻引起的附加温差导热系数的测试方法很多,若按物体内温度的变化状态,可分为稳态法和非稳态法两种,它们都是建立在热传导理论的基础上,很     

靶丸装配位置偏差对靶丸表面温度均匀性的影响

为了研究靶丸装配对惯性约束核聚变间接驱动靶系统中靶丸表面温度场的影响,建立了三维冷冻靶系统数值计算模型,利用CFD软件的传热和Boussinesq模型分析了系统的传热规律,并对靶丸装配中可能产生的装配偏差的影响进行了探究。结果表明:靶丸在水平方向上的装配位置偏差会对靶丸表面温度场分布产生极大的影响,而在竖直方向上的装配位置偏差影响相对较小。在竖直方向上看,向上偏移的位置偏差相对于向下偏移的位置偏差对靶丸温度均匀性的影响会较大。     

液相剥离法制备石墨烯及在导热硅橡胶中的应用

采用高速剪切机液相剥离法,在胆酸钠的水溶液中将鳞片石墨剥离,离心得到石墨烯分散液。AFM、TEM、Raman表征结果发现,剥离出的石墨烯厚度小于4层,尺寸大约在2~3μm,高质量缺陷少(I_D/I_G≈0.15)。将石墨烯分散液冷冻干燥后与银粉共同添加到硅橡胶中,制备出导热硅橡胶。利用稳态热流法测试导热硅橡胶的导热系数发现,当添加3vol%石墨烯时,复合材料的导热系数由未添加石墨烯时的4.900 W/(m·K)提高到12.367 W/(m·K)。综上所述,通过液相剥离法成功制备出缺陷较少的少层石墨烯,能够与银粉协同提高导热硅橡胶的导热系数。     

冷板内共晶溶液冻结过程数值模拟

冷板充冷时,共晶溶液降温、冻结过程中温度场不均匀,从而延长了其总体冻结时间.用焓法建立了蒸发盘管外共晶溶液冻结过程的二维导热数学模型,在二维柱面坐标下用控制容积法对导热控制方程进行离散化处理,并对共晶溶液的降温、冻结过程进行数值计算,指出可以通过调整蒸发盘管的布置方式,使冷板内共晶溶液温度场尽可能均匀、完成冻结的时间接近,从而缩短充冷时间,达到节能的目的.     

沥青路面导热系数测试及其对路面温度场影响的模拟

沥青路面温度场是沥青路面车辙计算和沥青混合料粘弹性分析的重要参数,路面温度场的精确预估涉及到面层各层材料热物理参数的精确测试,因此沥青混合料热物理参数的准确测试变得越来越重要.基于对测试结果重现性和可比性的考虑,采用瞬态热线法进行沥青混合料导热系数的测试,选取几种有代表性的混合料进行了导热系数测试,分析了影响导热系数的因素.基于ABAQUS模拟计算路面温度场分布,通过改变路面上、中、下面层的导热系数,计算路面温度场分布变化的情形,对计算结果的分析发现,上面层导热系数对面层温度场分布的影响更显著,可以预期通过改变上面层导热系数能达到主动改善沥青路面工作温度的目的.     

低温风洞电动推杆热防护结构设计及传热分析

为解决低温风洞中电动推杆的热防护问题,设计了使其能够在低温风洞高温工况(323 K)和低温工况(110 K)下正常工作的热防护结构。采用数值模拟方法校核了热防护结构强度及刚度,分析了电机发热功率,冷却气体流量和加热片加热功率等因素对推杆元件温度的影响。结果表明:低温风洞内压力达到极值0.35 MPa时,由厚度5 mm,材料S30408不锈钢制成的圆筒形热防护结构最大变形量为0.397 mm,最大应力为160.62 MPa;冷却气体流量大于等于0.005 kg/s时,高温和低温工况下电机最高温度均不大于418 K的允许工作温度;当加热功率达到500 W时,缸杆端部各考察截面温度均高于263 K;在高温工况和加热功率为500 W的低温工况下,冷却气体流量为0.005 5kg/s时,缸体、缸杆均能维持在263—313 K的工作温度,且高温工况最大温升与温差分别为3.62、2.81 K,低温工况最大温降与温差分别为4.94、6.82 K,满足温度稳定性与均匀性要求。     

超低温温区热连接方式试验研究

为验证超低温温区不同热连接方式对深冷辐射源的降温影响程度,搭建了超低温温区真空热试验系统,对三种型式的热连接件的超低温导热特性进行了试验.结果表明:40K以下高纯铜与铝呈现出极好的超低温导热特性;在结构允许的前提下,可通过增大热连接件导热截面积、缩短导热路径、降低热连接件热容的方式来降低冷屏降温时间;同时可通过采用柔性...     

Fundamental study of adhesion of ice to cooling solid surface (Discussion on influence of copper oxide layer on ice adhesion force)

In many situations, ice often adheres to a cooling solid surface, frequently causing serious accidents. It is critical to clarify the mechanism of ice adhesion to the cooling surface in order to prevent ice adhesion. In a past study, the shearing stresses of two kinds of test plates with a copper surface having the higher thermal conductivity were measured. The shearing stress corresponds to ice adhesion force. Both shearing stresses were significantly different; however, the cause remains unclear.Therefore, the present study focuses on an oxide layer as the main factor causing the difference of both shearing stresses; the influence of the oxide layer formed on shearing stress was discussed. And in the removal and reformation processes of the oxide layer, the time variation of the shearing stress was clarified. Moreover, the relationship between the state of the copper surface and the shearing stress was also clarified by surface analysis.     

低温容器隔热结构的分析

讨论了在干冰温度以下工作的低温容器的隔热,提出了双层隔热结构型式。用热阻分析的方法对隔热材料不出现冷缩、外壳不出现凝露的温度条件进行分析,导出了两种隔热材料的厚度关系、隔热结构最小热阻和限定单位漏热量时热阻的计算式。     

Thermal conductivity of ME771 glass-epoxy laminate from millikelvin temperatures to 4 K

Permaglas ME771 is a glass-epoxy laminate which is suitable for use at cryogenic temperatures. We have measured the thermal conductivity of a sample of this material between 64 mK and 4.2 K in the direction parallel to the reinforcing fibres, enabling us to make a comparison with the better known material G-10CR. The thermal conductivity follows the form that would be expected for such a material, and is similar to that of G-10CR, which has a similar (room temperature) tensile strength. We comment on some confusion that has arisen over the difference between G-10CR, a material specifically produced for cryogenic use, and G-10, the more common equivalent.     

一种新型复合相变材料导热性能的实验研究

针对相变材料在实际应用过程中交替存在升温液化和降温固化的复杂传热过程,采用JW-Ⅲ建筑材料热流计式导热仪,分别对升温和降温过程中处于固态、混合态、液态的新型复合相变材料导热性能进行了测试和分析。研究结果表明,复合相变材料在加热和冷却过程中的导热系数随温度的变化存在明显的规律性差异,导热系数在混合态时差值达到20%;升温过程中,复合相变材料在混合态和液态时的导热系数值相差不大,但与固态时相比有明显减小;降温过程中,在液-固相变的过程中导热系数随温度减小而增大,有利于加速相变材料的固化。     

无碳化物贝氏体钢渗碳后的深冷处理

采用热磁分析、显微硬度分析与直读光谱分析等相结合的方法,对无碳化物贝氏体钢进行渗碳后的深冷处理工艺优化。结果表明:无碳化物贝氏体钢在1193K渗碳空冷后,测试有效硬化层样品的热磁曲线,可以得到有效硬化层的深冷处理温度宜低于134K。经123K深冷处理和463K回火,有效硬化层残留奥氏体含量约为12.2%(质量分数)。通过深冷处理使渗碳钢近表面层得到显著硬化,再经低温回火使近表面层硬度均达到810HV_(1.0)左右,渗碳钢的硬度梯度分布趋于合理。     

Phase change material for the thermal protection of ice cream during storage and transportation

Ice cream is a very temperature sensitive product and temperature variations during the storage and distribution steps may result in a reduction of quality. It is possible to improve the ice cream storage and transportation conditions by using an additional packaging with a low thermal diffusivity. This paper studies a phase change material (PCM) packaging and compares its performance to a polystyrene packaging configuration. The impact on temperature fluctuations and ice crystal size distribution was characterized experimentally during long term storage and temperature abuse. The results show that the use of an additional PCM packaging has a significant impact on the final quality of the product by keeping ice cream temperature stable and close to the phase change temperature of the PCM material. These results were compared with the insulation material results and discussed, showing that a material with a buffering heat capacity can be more efficient to reduce temperature fluctuations than a low conductivity material, and that the same results can be usually obtained with a much thinner layer of material.     

Research of thermal response simulation and mold structure optimization for rapid heat cycle molding processes, respectively, with steam heating and electric heating

The dynamic mold temperature control system is the key of rapid heat cycle molding (RHCM) technology because it significantly affects the stability of the process, productivity and the quality of the final polymer part. For this reason, the approaches and techniques for dynamic mold temperature control were discussed in this study and two different dynamic mold temperature control methods, respectively, with steam heating and electric heating were found to be very feasible in mass production. The methods and principles of mold design for the two RHCM technologies were also discussed and then several different kinds of mold structures were designed. By constructing the corresponding thermal response analytical models for these RHCM molds, the temperature responses of the molding systems in the heating and cooling process of RHCM were simulated and studied. The effects of the mold design parameters such as the insulation layer between mold plate and mold inert, and mold material, on thermal response efficiency and temperature uniformity of the two RHCM processes were analyzed based on the simulation results. The results show that the insulation layer can increase the upper limit temperature of RHCM with steam heating and improve the heating speed of RHCM with electric heating. It can also greatly decrease the energy consumption of the two RHCM processes. The heating efficiency of RHCM with steam heating can be effectively improved by increasing the thermal conductivity of the cavity/core material, while the situation is diametrically opposite for RHCM with electric heating. Therefore, we acquired an optimized mold design principle and method for RHCM with steam heating and electric heating, respectively. Finally, a new electric heating mold with a cooling plate was proposed to enhance the cooling efficiency. The thermal response of this new electric heating mold was also simulated. The simulation results show that the cooling plate can significantly improve the cooling and heating efficiency.     

Study on the Principle Mechanisms of Heat Transfer for Cryogenic Insulations: Especially Accounting for the Temperature-Dependent Deposition–Evacuation of the Filling Gas (Self-Evacuating Systems)

This study concentrates on the principles of heat transfer within cryogenic insulation systems, especially accounting for self-evacuating systems (deposition–evacuation of the filling gas). These principles allow the extrapolation to other temperatures, gases and other materials with the input of only a few experimentally derived or carefully estimated material properties. The type of gas (e.g. air or \(\hbox {CO}_{2}\)) within the porous insulation material dominates the behaviour of the effective thermal conductivity during the cooldown of the cryogenic application. This is due to the specific temperature-dependent saturation gas pressure which determines the contribution of the gas conductivity. The selected material classes include powders, fibrous insulations, foams, aerogels and multilayer insulations in the temperature range of 20 K to 300 K. Novel within this study is an analytical function for the total and the mean thermal conductivity with respect to the temperature, type of gas, external pressure and material class of the insulation. Furthermore, the integral mean value of the thermal conductivity, the so-called mean thermal conductivity, is calculated for a mechanically evacuated insulation material and an insulation material evacuated by deposition–evacuation of the filling gas, respectively. This enables a comparison of the total thermal conductivity of cryogenic insulation materials and their applicability for a self-evacuating cryogenic insulation system.