Onset of Benard-Marangoni Ferroconvection with Internal Heat Generation

The effect of internal heat generation on the onset of Benard-Marangoni convection in a horizontal ferrofluid layer heated from below in the presence of a uniform vertical magnetic field is studied. The lower boundary is rigid and the upper free boundary is assumed to be flat and undeformable. Both the boundaries are considered to be perfectly insulated to temperature perturbations and the resulting eigenvalue problem is solved numerically using the Galerkin technique as well as analytically by regular perturbation technique with wave number as a perturbation parameter. It is observed that the analytical results agree well with those obtained numerically. It is noted that the combined effect of magnetic Rayleigh number and dimensionless internal heat source strength is to reinforce together and to hasten the onset of Benard-Marangoni ferroconvection compared to their presence in isolation. In addition, the nonlinearity of fluid magnetization is found to have no influence on the criterion for the onset of ferroconvection. Some existing results are reproduced as particular cases from the present study.     

热电热泵换热面积最优分配

考虑实际多热电堆热泵,在总传热面积一定的条件下,研究最优供热率、供热系数时传热面积的最优分配,并分析了各种参数对最优性能的影响,所得结果对实际热电热泵性能分析与优化有一定的指导作用.     

Specific Heat of Solid Helium

No Heading Recent torsional oscillator measurements of solid ⁴He in Vycor glass suggest the existence of a supersolid state of matter below 175mK. We have obtained preliminary data of the specific heat of solid helium down to 80mK. No sharp feature at the onset temperature is observable to within 1%. We are currently working towards extending our measurement to lower temperatures.PACS numbers: 67.40.–w, 67.80.–s, 67.80.Mg.     

多联式热泵驱动热管复合供热装置的实验研究

本文提出多联式热泵驱动热管的新型供热循环方式。该方式的特征是采用空气源热泵直接驱动串联式热管散热器供热。为验证该供热方式可行性,本文基于额定功率为2.5 k W的压缩机和9台热管散热器搭建了实验台,在不同工况下进行测试。测试结果表明:新型供热装置启动速度较快,当室外温度为-10℃时,系统运行36 min时,热管散热器表面温度即可达到45℃。热管散热器温度均匀性好,除1#、9#散热器存在过冷、过热现象外,其余散热器之间温差约为1℃。同时系统传热温差小,并能在除霜工况下正常运行。     

The Study of Heat Flux Measurement for Heat Transfer during Condensation at Pipe Surfaces

Technical Physics Letters - For the first time, heat transfer during condensation has been studied using gradient heat flux measurement. The applicability of the new method has been tested on a...     

相变蓄热型空气源热泵系统的模拟

为提高空气源热泵系统的低温适应性,将相变蓄热技术与空气源热泵结合,实现白天蓄热、夜晚放热的运行模式。本文通过模拟研究了相变蓄热型空气源热泵系统的蓄放热特性和应用多级相变材料对系统的影响。结果表明：系统蓄热量随时间线性增大,380 min时达到18.94 kW·h,平均COP为2.51;系统放热量先随时间线性增大,随后增大速率有所减缓,180 min时达到13.58 kW·h。放热过程进口水温为35℃时,系统经过6次蓄放热循环后达到稳定运行状态,蓄放热效率为99.06%。相比单级PCM,应用三级PCM的系统蓄热时间缩短9.60%,COP提高3.97%,总■效率提高4.84%,其中降低过冷区PCM熔点对提高系统性能起到关键作用。     

Heat conduction equation in fractional-order derivatives

Based on the heat conduction equation in fractional-order derivatives, the influence of the nonlocality of the heat conduction equation in time and space on temperature distribution in media with fractal structure is investigated. The cases of an infinite and semibounded straight line are considered.     

换热器（火/用）“分析计算和（火/用）焓图表示

本文分析了换热器传热过程中的(火用)损失,给出了换热器(火用)损失的计算公式,采用(火用)分析方法,给出了换热器效率的计算公式,并且对换热器传热过程在(火用)焓图上进行了图示。     

基于插值与神经网络的包装薄膜热封参数分析

目的研究塑料薄膜热封工艺中热封参数之间的非线性关系,建立一种可用于自动包装机热封过程的数学模型。方法通过实验采集样本数据,并用附加动量法训练BP神经网络,建立热封参数之间的非线性数学模型,最后通过神经网络预测热封时间,并采用插值算法建立目标热封强度下热封温度和热封时间之间的多项式数学模型。结果通过插值算法与神经网络的结合运用,较为精确地描述了热封温度和热封时间之间的数学关系,插值函数实现了神经网络模型的简化,两者误差较小。结论通过文中方法确定了包装材料热封参数之间的非线性关系,将其用于热封包装设备,可提高设备的智能化程度。     

A Preliminary Heat Capacity Measurement of 3He in Aerogel near its Superfluid Transition

We report simultaneous heat capacity and torsional oscillator measurement of ³ He in aerogel near the superfluid transition. The heat capacity has a peak at the temperature T_c where the torsional oscillator shows the onset of superfluid decoupling. The coincidence of these signatures suggests that ³ He in aerogel does undergo a true thermodynamic transition.     

芯片封装均温板壳体的传热特性研究

高热流密度、微型化芯片的发展使传统金属材料的热扩散能力受限.本文设计加工了一款具有微针筋的均温板,应用于芯片封装壳体,实验研究了充液率、芯片尺寸、散热器运行参数(水流量、温度)对均温板壳体(VC IHS)传热性能的影响,并与同工况条件下芯片封装金属铜壳体(Cu IHS)的传热性能进行对比.结果表明:VC IHS的充液率...     

Isochoric Heat Capacity and Cluster Structure of Simple Liquid

The formation process of the short-range order and the liquid itself in the critical region is described in terms of a cluster model. The “exploding” formation of dimeric clusters marks the onset. The estimation of cluster size on a vapor–liquid equilibrium curve is proposed. The X-ray diffraction analysis for argon on the saturation line and the observed correlation between the temperature dependences of number of particles in the cluster and the isochoric heat capacity of simple liquids validate the model.     

微通道换热器结霜特性及换热性能实验研究

结霜是制约微通道换热器在制冷及空调系统应用的主要因素之一。针对微通道换热器结霜问题,本文基于相变驱动力分析了结霜机理,观察了不同环境因素下冷表面霜层生长形貌,并实验研究了湿空气温度、含湿量、气流速度及冷却液温度对微通道换热器结霜特性及换热性能的影响。结果表明:湿空气含湿量及气流速度是影响微通道换热器结霜的主要因素,结霜时间为15 min,含湿量为5.75 g/(kg干空气)工况下,换热器表面结霜量比含湿量为3.58 g/(kg干空气)时提高了63.87%;气流速度为2.5 m/s工况下,换热器表面结霜量比气流速度为1 m/s时增加了55.4%。随着结霜时间的增长,湿空气温度、冷却液温度越低,含湿量、气流速度越大,换热量下降趋势越明显。     

定形相变蓄热单元周期性释热实验分析

针对相变蓄热材料实际应用中的周期性释热情况,本文采用响应面法设计实验方案,对一种基于圆环形赤藻糖醇/膨胀石墨复合相变材料的间接式蓄热器进行周期性释热实验.利用蓄热材料的释热量、释热动力、有效能利用率对蓄热单元的释热性能进行分析.结果表明:当间歇时间为20 min,材料累计释热时间为40 min,总释热功率、斯蒂芬数、火...     

管壳式换热器换热管的传热强化

本文介绍管壳式换热器的传热节能元件-换热管的强化传热技术,指出传热技术发展新途径。简述典型强化换热管的构造、性能,分析换热管强化传热机理。     

不同传热方式下温度传感器动态特性研究

为了研究传热方式对温度传感器动态特性的影响,通过时间常数理论推导分析传热方式与温度传感器动态特性的关系,并对不同传热方式下温度传感器的动态特性进行分析。分别建立对流传热和辐射传热方式下温度传感器的传热模型,采用油浴法和脉冲激光法对热电偶时间常数进行测试。测试结果表明:该热电偶在对流传热和辐射传热方式下的时间常数测试值分别为1.2s和6.2s,可以看出传热方式直接影响温度传感器的动态特性,最后通过时间常数测试值与理论计算值的比较,验证了传热模型的合理性。     

包装材料EPE热封工艺的实验研究与分析

目的研究EPE包装袋的热封质量与热封参数(电热丝直径、热封时间、热封压力)的关系,分析弹性包装材料热封过程的特性。方法通过观察显微封口形貌,比较不同参数下的热封强度,研究热封参数对珍珠棉热封强度的影响,并分析其原因。结果在热封1.0 mm珍珠棉过程中使用直径为0.8 mm电热丝,热封压力为0.2 MPa,热封时间为2 s时,热封质量最好、效率较高。结论弹性材料的可压缩性导致封切压力对热封强度的影响随电热丝直径的增加而明显增加,弹性材料的回弹特性使电热丝直径以及热封时间对其热封缺陷产生更加显著的直接影响。     

Criterion for quantum turbulence onset after rectangular heat pulse in superfluid helium

On the basis of transient heat transfer measurements of the film boiling onset time in a He II bath, a criterion correlated to the bath temperature and pressure for quantum turbulence onset after a rectangular heat pulse in superfluid helium is shown. Using the criterion parameter α it is possible to determine the time τ needed to initiate quantum turbulence in the He II bath after a rectangular heat pulse. It is found that the criterion value in a He II bath is much smaller than that for He II confined in small channels. A strong pressure effect is also exhibited.     

Heat transfer in floating insulations for open cryogenic liquid containers

A transient heat transfer analysis of floating insulations in open cryogenic liquid containers is presented. The results are obtained in terms of three dimensionless parameters and are correlated to give the values of the cool down time, the total heat in-leak during cool down, the heat of sensible cooling of insulation and the steady state values of the temperature and heat flux at the exposed surface, as functions of the three parameters. The analysis facilitates the determination of the optimum insulation thickness for a given storage time. The utility of the analysis is demonstrated with a practical example of liquid nitrogen storage using expanded polystyrene beads as floating insulation.     

空气源热泵除霜研究

空气源热泵的结霜问题已经成为影响空气源热泵机组可靠性的关键,提出了解决问题的三个方法:延缓结霜、除霜方法改进和除霜控制技术。增加风量、改进换热器形式等可以有效延缓结霜,并降低结霜的程度;采用蓄能除霜法可以减少除霜时间,室内恢复供热更快;模糊控制等控制方式可以使除霜更加智能化,从而达到良好的除霜效果。