非稳态法测定冷库围护结构传热系数的应用研究

冷库围护结构的传热系数是冷库热工性能的一个重要参数，国内外关于围护结构传热系数的测定主要有两种方法；稳态法和非稳态法，生产现场的测试无法满足稳态法所要求的条件，本文用非稳态法中的积分法，首次提出在测试过程中用变Q法以缩短试验周期，提高试验效率。     

低温试验箱隔热层传热特性的实验研究

研究了1台在给定时间内达到-30 ℃的低温型试验用小型制冷低温试验箱,该试验箱配有全自动的微机控制系统能完成各项试验的数据记录.主要针对低温箱围护结构(隔热层)在降温阶段非稳态传热特性进行了实验研究.通过试验数据分析,对隔热层在降温过程的一维大平板非稳态传热问题进行了内部温度场随时间变化关系的的讨论,同时对低温箱隔热层随时间变化的放热量进行了数据拟合并得出了简化公式,为这类有特殊要求的制冷装置在节能节材方面的设计提供了的一定的参考数据.     

两级热泵活塞式压缩机模型研究

采用稳态仿真的方法对双级压缩热泵系统的压缩机部件建立模型,并建立中间冷却器模型。由于在低温丁况下试验,模型建立考虑了压缩机和环境的换热。通过建立试验台,采集试验数据并与仿真结果进行比较。结果表明,稳态仿真能够良好地反映系统运行中的参数变化。     

对由多台螺杆压缩机组成的配组式双级压缩系统制冷量及电机功率的分析

本文对某低温冷库制冷系统中的由多台螺杆压缩机组成的配组式双级压缩方式的制冷量及低压级、高压级压缩机电机功率的选配合理性作一下分析。并结合该工程实例，与螺杆压缩机采用经济器用于低温工况时的情况作了比较。     

中空玻璃传热系数测定结果的不确定度评定

采用CD-8080型双试样导热系数测定仪按GB/T 22476—2008《中空玻璃稳态U值（传热系数）的计算及测定》中的防护热板法对某结构为6mm透明普通玻璃+12mm空气层+6mm透明普通玻璃的中空玻璃的稳态传热系数进行了测定,并依据JJF 1059-1999《测量不确定度评定与表示》对试验过程中影响测定结果的各不确定度分量进行了评定。结果表明:该中空玻璃的稳态传热系数为U=（2.8±0.2）W·m^-2·K^-1,包含因子k=2;其中,由标准板标定,确定加热单元计量部分平均热流量引入的不确定度为影响中空玻璃稳态传热系数测定结果准确度的主要因素,由温度测量引入的不确定度其次,由数值修约引入的不确定度最小。     

非稳态法测量环境试验箱体的传热特性参数

本文依据传热的基本原理 ,针对具有空气冷却和加热功能的环境试验箱围护结构隔热层的传热特性参数———传热系数和蓄热系数 ,用非稳态测量方法进行了比较试验。提出一种较为实用的测量方法 :它是利用隔热箱内升、降温变温过程中所建立的箱体内外侧传热方程的近似解并结合实验数据的处理而形成的一种现场测量方法     

稳态及非稳态传热条件下膨胀珍珠岩绝热性能的研究

在低温系统工作过程中,绝热材料随工作过程的变化和外界温度的波动交替工作在稳态和非稳态两种传热情况下,绝热材料在非稳态传热条件下的绝热性能对低温系统的影响极为重要。本文以常用低温保温材料膨胀珍珠岩（珠光砂）为研究对象,实验测量了在稳态和非稳态传热条件下的导热性能,热扩散性能及其随温度的变化规律,并对两种传热条件下的绝热特性进行了分析和研究,为工程应用提供可靠的依据,也为低温绝热方案的选择及优化设计提供参考资料。     

两种CPU散热器换热特性的数值研究

对整体平直翅片与分段开缝平直翅片两种不同结构的CPU散热器，在不同加热功率和不同风速下的散热特性进行了数值模拟。采用商业软件FLUENT6．0进行计算，结果显示：对流换热表面传热系数和热阻主要与风速有关，与加热功率关系不大，对流换热表面传热系数的计算结果和实验数据趋势一致。在低风速下，加热功率对这两种散热器压降的影响也不大。采取数值模拟的方法对CPU散热器进行研究是实验方法的可靠补充，计算所得的结果有助于分析CPU散热器的换热过程，并可为电子设备的设计和改进提供参考。     

立式低温绝热气瓶颈管传热的数值模拟与试验分析

对自然排放条件下颈管的共轭传热模型和稳态导热模型进行数值模拟,模拟结果显示两种模型的颈管壁面温度分布规律一致。通过液氮蒸发法的试验对导热模型的模拟方法进行验证,试验结果略低于数值模拟结果,但与共轭传热模型和稳态导热模型吻合程度良好。稳态导热模型的误差略大于共轭传热模型,但对低温气瓶颈部计算选择稳态导热模型精度已经足够,且方法简单。     

BEPCⅡ电流引线低温端温度非稳态变化理论计算

介绍一种计算电流引线低温端温度非稳态变化的理论计算方法,并将计算结果与大型CFD软件包Fluent6.0的模拟结果进行比较,两者符合良好.采用该方法分析了稳态时的氦气流量对非稳态电流引线冷端温升速度的影响.     

确定金属型铸造界面传热系数方法的研究

铸造凝固过程数值模拟中通常用界面传热系数表示热阻的影响,在诸多影响模拟精度的因素中,该系数起主导作用。为提高模拟精度,以ANSYS软件为平台,在测温试验的基础上,考虑铸件与铸型的不同接触位置以及不同界面传热系数对模拟结果的影响,采用0.618黄金分割法选取了该系数;应用最小二乘法建立起界面传热系数与时间关系的数学模型,并对金属型铸造凝固过程的温度场进行了模拟,将模拟结果与试验结果做了对比分析,得到了合理的温度分布。研究的结果为获得精确的界面传热系数提供了一种研究方法。     

Correlation of time dependent recovery from film boiling heat transfer in He II

A correlation is presented that describes the behaviour of time dependent recovery from film boiling in He II. In a one dimensional heat transfer experiment, the recovery time from the film boiling once heat generation stops is observed to be a function of the energy applied to the heater during film boiling. This correlation has a power law dependence which can be physically understood in terms of heat capacity of the heat transfer sample and the film boiling heat transfer coefficient. A direct comparison of experimental data with the analysis is achieved by adjusting the value of the transient film boiling heat transfer coefficient. Data can be predicted to within 20% for recovery under SVP conditions. The results are somewhat less certain for data taken in subcooled He II.     

A numerical study on heat transfer of the nanofluid flow inside helical tube through the two-phase method

In this study, a new numerical investigation was carried out to study the heat transfer characteristics of nanofluid flow inside a copper helical tube under constant heat flux. A nanofluid with different particle weight concentrations of 0.5%, 1.0%, and 2.0% was used. The effects of different parameters such as Reynolds number, nanofluid particle concentration, and constant heat fluxes (1500 and 3800?W/m²) on heat transfer coefficient were studied. For validation, Nusselt number and convection heat transfer coefficient obtained from the numerical model was compared with the experimental results. Also, to verify the accuracy of the method, grid independency was studied for each heat flux. The observations showed that the heat transfer coefficient increased by using nanofluid instead of base fluid. In addition, the convection heat transfer coefficient performance improved by increasing the nanoparticles’ concentration. The results from the numerical simulation compared with the experimental data showed that this new numerical method has high accuracy and could correctly predict the heat transfer behavior of nanofluids with different weight particle concentrations under constant heat flux.     

Identification of materials in a hyperbolic annular fin for a given temperature requirement

This article deals with the prediction of parameters in an annular hyperbolic fin with temperature-dependent thermal conductivity. Three parameters such as thermal conductivity, variable conductivity coefficient and the surface heat transfer coefficient have been predicted for satisfying a prescribed temperature distribution on the surface of fin. This is achieved by a hybrid differential evolution-nonlinear programming optimization method. The effect of random measurement errors is also considered. It is observed from the present inverse analysis that many feasible materials exist satisfying the given temperature distribution, thereby providing engineering flexibility in selecting any material from the available choices. For a given material, this is possible by regulating the surface heat transfer coefficient.     

Experimental study on heat transfer and rheological characteristics of hybrid nanofluids for cooling applications

The enhancement of heat transfer and rheological behaviour of hybrid nanofluids (HyNF) flowing through the tubular heat exchanger system were experimentally analysed. In this study, the effects of Nusselt number, Peclet number, Reynolds number, heat transfer coefficient and pressure drop were investigated for various volume concentrations of copper-titania hybrid nanocomposite (HyNC). The experiments were performed for various HyNC volume concentrations in the base fluid (cold water) ranging from 0.1% to 1.0%. The experimental results showed that the convective heat transfer coefficient of the HyNF increased by 59.3% for the particular volume concentration of 0.7% of HyNC. The friction factor and pressure drop of HyNF for 1.0% volume concentration were expected to be 0.8% and 5.4%, respectively. This implies for experiencing penalty in the pumping capacity. The experimental measurements, on the other hand, were validated using a newly developed correlation. For all the volume concentrations of HyNF, the deviation obtained for the experimental data and the prediction was observed to be +8% and ?8%, respectively. The present correlation has been found to be in good agreement with the experimental data, which can be helpful in predicting the heat transfer characteristics of the HyNF.     

Model for transient behavior of pulse tube cryocooler

This article describes an investigation of the transient behavior of a small (2.0 W at 85 K) pulse tube cryocooler operating at 120 Hz with an average pressure of 3.5 MPa, capable of relatively fast cool-down from ambient to about 60 K. In a series of experiments, the cold end temperature was measured as a function of time in a complete cool-down and subsequent warm-up cycle, with no heat load and different quantities of excess mass at the cold end. A transient heat transfer model was developed, that considers the effects of the cooling power extracted at the cold end and that of the heat gain at the warm end on the cool-down time. The heat gain factor was calculated from warm-up data, and found to be approximately the same for all experiments. Using the same model with cool-down data enables a determination of both the gross and net cooling power as functions of time, but more importantly – as functions of the cold end temperature. An expression was derived for the cold end temperature as a function of time for any amount of excess mass, including zero. The cool-down time of the “lean” cryocooler (with no excess mass) was found to be less than 50 s.This cool-down/warm-up method for evaluating the cooling power of a cryocooler seems simpler than steady-state experiments with a heater simulating load at the cold end. Use of the heat transfer model with data from one or two good experiments conducted in the above manner, can yield both the gross and net cooling powers of a cryocooler as functions of the cold end temperature, and allow the determination of cool-down time with any amount of excess thermal mass. While the net cooling power during cool-down differs somewhat from that under steady-state operation, the former can serve as a good measure for the latter.     

冻干机冷阱传热性能实验研究

对影响冻干机冷阱传热性能的两个因素(冷阱盘管壁面温度和结霜厚度)进行了实验研究。实验研究表明冷阱壁面温度越低则冷阱捕集效率越高；随着霜层厚度的不断增加，传热性能将不断下降。对影响冷阱传热的另一个因素-真空度，进行了理论分析，认为随着冷阱真空度的提高，换热强度不断降低，直至可以不考虑换热。     

Investigation of turbulent heat transfer and nanofluid flow in a double pipe heat exchanger

In present study, heat transfer and turbulent flow of water/alumina nanofluid in a parallel as well as counter flow double pipe heat exchanger have been investigated. The governing equations have been solved using an in-house FORTRAN code, based on finite volume method. Single-phase and standard k-ε models have been used for nanofluid and turbulent modeling, respectively. The internal fluid has been considered as hot fluid (nanofluid) and the external fluid, cold fluid (base fluid). The effects of nanoparticles volume fraction, flow direction and Reynolds number on base fluid, nanofluid and wall temperatures, thermal efficiency, Nusselt number and convection heat transfer coefficient have been studied. The results indicated that increasing the nanoparticles volume fraction or Reynolds number causes enhancement of Nusselt number and convection heat transfer coefficient. Maximum rate of average Nusselt number and thermal efficiency enhancement are 32.7% and 30%, respectively. Also, by nanoparticles volume fraction increment, the outlet temperature of fluid and wall temperature increase. Study the minimum temperature in the solid wall of heat exchangers, it can be observed that the minimum temperature in counter flow has significantly reduced, compared to parallel flow. However, by increasing Reynolds number, the slope of thermal efficiency enhancement of heat exchanger gradually tends to a constant amount. This behavior is more obvious in parallel flow heat exchangers. Therefore, using of counter flow heat exchangers is recommended in higher Reynolds numbers.     

翅片管空气冷却器换热系数模型

以管内介质有相变的翅片管空气冷却器为研究对象,采用量纲分析、泛函分析等方法,构建了一个合理的翅片管空气冷却器换热系数关联式。以氨泵供液型空气冷却器为实验研究对象,设计了结构参数、迎面风速、库温、驱动温差和供液倍率等多因素、多水平的实验方案,并采用校准箱法测得不同测点下的换热系数值。采用测试数据并以关联式为目标函数,通过非线性拟合方法建立了适用于氨泵供液空气冷却器换热系数计算的关联式。关联式计算值与实测值相对误差在±10%之间,且分项管内换热系数大于管外换热系数,符合空气冷却器换热系数分布的一般规律,证明了换热关联式是合理准确的。在氨泵供液空气冷却器常用设计点,关联式计算值约为设计经验值1.11~1.30倍,这表明采用关联式设计该类型空气冷却器可节约11%~30%的换热面积,提高了经济效益。