库温及换热温差对顶排管换热性能的影响

为分析顶排管的换热性能,对12组工况分别进行试验研究。结果表明:在相同库温环境下,顶排管的制冷量随着换热温差的增大而增大,换热温差为10℃时比换热温差为5℃和7℃时的传热系数要高。由于库体漏热和顶排管结霜等客观因素的影响,传热系数从总体来看变化并不大,均在7.57～7.91 W/(m~2·K)范围内。     

地埋管虹吸换热井技术研究

分析现有地源热泵系统的原理及构成,提出地埋管虹吸换热井系统的地源热泵新技术,利用多孔的渗水套管加虹吸管取代地埋管井的封闭式套管,根据虹吸原理通过设置在虹吸井内潜水循环泵实现系统循环。并对地埋管虹吸换热井系统与其他地下水地源热泵系统进行对比分析,指出地埋管虹吸换热井系统具有打井数量少、换热温差大、一次投资及运行费用相对较低的优点。     

两相热虹吸循环动量模型评价

两相热虹吸管在工业领域应用广泛,其内部工质的流动模拟是热虹吸管设计的主要因素。然而在模拟过程中,存在着两相流模型适用范围有限而自然循环模拟精度要求高的矛盾,因此有必要根据热虹吸特性对现有两相流动量模型进行适用性评价。建立了稳态两相热虹吸循环模型,结合不同工质(水、R113和R600a)的两相热虹吸循环实验数据,分别对4种均相流动量模型和24种分相流动量模型组合(4种分相流摩阻压降模型和6种截面含气率模型组合)进行了计算比较,发现Lorkhart-Martinelli摩阻压降模型结合Tom截面含气率模型的模拟精度最高。利用此模型分析两相热虹吸循环内工质的流动特征,证实了质量流速随着热流密度的增大先增大后减小的规律,并从内部分布参数变化角度给出了新的解释。     

模拟界面换热系数和密度对热溶质对流影响

为了能够更好地控制凝固过程热和溶质的传输,以二元合金为例,研究了在单边散热条件下,不同界面换热系数和密度对热溶质对流的影响.研究表明:当材料密度一定时,随着界面换热系数的提高,沿散热方向上的温度梯度增大,热溶质对流的效果增强;当界面换热系数为1 000 W/(m2·K)时,在凝固初期铸件底部出现涡流现象;在界面换热系数不变的情况下,随着材料密度的增加,铸件内液体金属的热溶质对流效应减弱.     

利用永磁体的室温磁制冷机性能研究

介绍了利用1.5 T永磁体驱动,氦气作为换热流体,采用主动式磁回热器的室温磁制冷机的实验研究情况.在现有实验装置下,通过调节气体压力与循环频率,高低温端最大达到了10.7K的温差,研究结果为室温磁制冷机的设计以及进一步发展提供了参考.     

基于LNG冷能利用的半导体温差发电性能试验研究

为了研究半导体温差发电在应用于LNG相关传感器监测所需供电方面的潜力,首先在半导体温差发电基本模型的基础上计算出不同热端温度下的最大发电功率和效率曲线,结果显示当热端温度低于220 K时几乎没有功率输出。然后基于天然气汽化与温差发电相结合的场景,设计了一种用于LNG冷能利用的换热器结构,仿真结果显示:壁面温度为140 K时换热器的换热能力为6.608 kW。最后,为了探究半导体温差发电在低温下的发电性能,基于所设计的换热器搭建了一套用于冷能利用的半导体温差试验系统,试验结果显示半导体温差发电系统最大发电量可达到9.33 W。     

蒸发式冷凝器顺流式和逆流式换热性能实验

对蒸发式冷凝器顺流式和逆流式两种不同方式的换热性能进行实验研究。搭建了蒸发式冷凝器换热性能实验台,分别在顺流式和逆流式条件下,对冷凝器喷淋密度和迎面风速对换热性能的影响进行理论和实验研究。结果表明:随着迎面风速的提高,喷淋密度增大,在顺流和逆流条件下,总换热系数均呈现上升的趋势,最后达到一个最大值,逆流式条件下的换热性能高于顺流式;在迎面风速为3.28 m/s,喷淋密度为0.057 kg/(m·s)条件下,顺流式的总传热系数最大为616 W/(m2·K),逆流式总传热系数可达到628 W/(m2·K)。在相同条件下,逆流式的传质系数及能效比EER均优于顺流式。     

低温热虹吸管传热性能的初步研究

作为一种高效传热方式,低温热管可望在空间探索、超导磁体冷却等方面获得广泛应用.介绍了低温热虹吸管的设计过程,实验分析了低温热虹吸管的工质质量、倾斜角度对低温热虹吸管传热性能的影响.研制的低温热虹吸管平均传热能力达2 W/K.     

采用多通道直冷板的两相循环冷却系统实验研究

本文搭建了以R1233zd(E)为工质的多通道直冷板两相循环冷却系统,并在冷凝温度为10、15、20 ℃,质量通量147~882 kg/(m2?s),热流密度7.73~39.75 kW/m2工况下对系统热力学循环和冷却性能进行实验研究。实验结果表明：质量通量上升,出口制冷剂焓值降低,热流密度上升,蒸发压力与出口制冷剂焓值升高。不同热流密度下冷板壁面温度随质量通量的变化趋势有所不同：当热流密度为7.73 kW/m2时,制冷剂质量通量由147 kg/(m2?s)增至735 kg/(m2?s),最大温差由2.9 K降至1.6 K;当热流密度为39.75 kW/m2时,最大温差由3.6 K增至5.2 K。不同质量通量下,换热系数随热流密度增加有不同幅度的升高：质量通量为147 kg/(m2?s)时,换热系数由1 843 W/(m2?K)增至4 528 W/(m2?K);而质量通量为588 kg/(m2?s)时,在相同条件下换热系数由1 536 W/(m2?K)增至3 569 W/(m2?K)。     

大冷量GM制冷机可插拔结构设计及实验验证

在高温超导电缆低温系统中采用GM制冷机可插拔结构,可实现在系统不停机条件下整机的简易更换及拆卸维修。对可插拔结构的低温系统进行设计并分析计算漏热,以提高真空低温环境下系统的传热性能,减小制冷机与待冷却物体间的传热温差。通过实验研究了不同制冷温度以及不同预紧力矩的条件下传热温差的变化,探究了在接触面添加铟片对传热性能的提升作用。实验结果表明,70 K温区固定加载255 W热负载条件下,随着预紧力矩的增加,传热温差逐渐减小,在力矩为10 N·m时,温差仅为0.82 K。在预紧力矩较小时,添加铟片对降低传热温差有比较明显的效果,铟片厚度的影响相对较小。     

单面波浪平板脉动热管的传热性能

对一种单面波浪平板脉动热管的传热性能进行了实验研究,分析在空气强制对流冷却条件下充液率、加热功率、倾角等因素对其传热性能的影响。研究结果表明,除0°倾角外,脉动热管的最佳充液率为20%～30%,倾斜角度对脉动热管传热性能的影响很小,但90°时相对最好。脉动热管在0°放置时其传热性能较差,在低充液率的情况下甚至丧失脉动效果,主要是工质回流不畅的原因,与平板脉动热管的槽道设计有很大关系。此外低加热功率时热管传热性能存在波动,有时甚至不能启动。     

Heat transfer from Ni–W tapes in liquid nitrogen at different orientations in the field of gravity

Ni–W tapes of the micrometric thickness are considered as the basis for the cost-effective manufacturing of coated conductors – the 2nd generation of high-temperature superconductor (HTS). Many HTS applications involve widely-available and inexpensive liquid nitrogen. The transition from superconducting to normal state may however occurs due to unexpected temperature fluctuations. In this case Ni–W tape is significantly heated by electrical current propagating through it. The amount of heat transferred from the tape to coolant is defined by heat transfer from the surface of tape to liquid nitrogen. The heat transfer, in turn, is strongly dependent on the tape orientation in the field of gravity. The present paper reports the experimental results on the heat transfer from Ni–W tape to a pool of liquid nitrogen. The heat transfer coefficients are quantified for three subsequent heat transfer regimes: natural convection of liquid nitrogen, nucleate boiling regime and film boiling. The dependence of heat transfer coefficient on inclination angle of the tape from vertical are experimentally clarified for each regime. The expression for the heat transfer coefficient at different inclination angles is derived for the case of nucleate boiling.     

166.6 MHz超导腔加强筋结构的多物理场耦合仿真

高能同步辐射光源加速器的166.6 MHz超导腔采用4.5K饱和液氦浸泡冷却,其内导体与小束管之间设计有加强筋以改善超导的应力分布,加强筋会影响气泡排出,气泡聚集过多会降低液氦冷却效果,有引发失超的风险.使用Fluent、Hfss软件对超导腔内导体附近的流场进行了流动/传热/电磁多物理场耦合仿真,研究了加强筋顶部开孔设...     

Effect of number of turns and configurations on the heat transfer performance of helium cryogenic pulsating heat pipe

The pulsating heat pipe (PHP) is a potential alternative to highly conductive metals such as copper for long distance heat transfer. Effective thermal conductivity and heat transfer capacity of a PHP are two of the most critical factors for practical applications. In this paper, a helium based PHP, which consists of 48 parallel tubing sections, was developed. The lengths of the evaporator, adiabatic and condenser sections are 50 mm, 100 mm and 50 mm respectively. The condenser section was thermally anchored to a Gifford-McMahon cryocooler (GM cryocooler) with a cooling capacity of 1.5 W at 4.2 K. A maximum effective thermal conductivity of 12330 W/m∙K was obtained when 1.1 W heat was applied to the evaporator section at a fill ratio of 70.5%. With the same geometric parameters and operational parameters, the effect of the number of turns on the heat transfer performance was figured out by comparing the 48-turn PHP with an 8-turn PHP. The results show that the temperature difference between the evaporator and condenser sections of the 48-turn PHP is much smaller than that of the 8-turn PHP. The dry-out temperature response, effective thermal conductivity and heat transfer capacity of them are obtained and analyzed. Furthermore, two configurations of the 48-turn PHP, a parallel configuration and a series configuration, are defined. An optimum configuration is proposed and makes a reference to the design of a cryogenic PHP for applications.     

Radiative and conductive heat transfer in a 4-K helium phase separator with minimum heat loss

Improvements in simulation and practice for the heat load of a helium phase separator are discussed. The separator cryostat (volume 100 L, cooling capacity 1.5 W at 4.2 K) re-condenses and stores liquid helium. An additional radiation shield was designed to minimize the radiative heat transfer and to decrease the heat conduction. The experimental results indicate that the heat load of the separator was decreased from 5.56 W to 1.555 W, a gain about 4 W of heat load, which is an improvement by 72%. Liquid helium (50 L) was stored in the separator stably for more than 90 h. Software implementing the finite-element method (FEM) was used to predict the temperature distribution of pipe fittings and the separator heat load with or without the additional radiation shield. The results of these simulations show that the temperatures of the pipe fittings were significantly decreased in the separator with additional radiation shields. For the heat load, the trends of simulation and experimental results were similar. This work provides a simple and effective method to minimize the radiation heat load of a separator. In this paper, we discuss in detail the improvements of the model, the experimental setup and the results of comparisons between experiments and simulations.     

Film condensation heat transfer of helium in a vertical tube

Helium was condensed on the wall of a vertical copper tube (14 mm in diameter, 32 mm long) in the experimental range: vapour temperature in the tube ? 4.1–5.0 K; heat flux ? 0.5–86 mW cm^?2; temperature differences across a liquid film ? 0.01–1.3 K ;film Reynolds numbers ? 3–380.It was found that the heat flux increased linearly with the film temperature difference, yielding a constant heat transfer coefficient of about 0.065 W cm^?2 K^?1. The discrepancy between the experimental results and the laminar condensation theory is also considered.     

Non-stationary helium heat transfer

This Paper presents the results of an experimental investigation of heat transfer to helium in stationary conditions, in conditions of increase and decrease of heat power at various rates and with pulse heating. Heat transfer both from a free surface and in a coaxial gap of 0.5 mm was studied. The experiments were carried out within the range of liquid saturation temperatures from 1.94 to 4.23 K. The values of the heat loads in a pulse were ≈1.5 – 15 times the steady-state value of the critical heat flux for helium nucleate boiling. It has been shown that transient thermal processes may have higher heat transfer coefficients compared with steady-state conditions. The most pronounced effect is observed under pulse heating conditions.     

倾斜角度对封闭方腔内液体自然对流的影响

在多种倾斜角度下,对封闭腔内液体进行了数值模拟。重点分析了Ra数变化和倾斜角度对对流传热的影响。研究表明：随着Ra数的增大,换热由热传导为主转化为对流换热为主;倾斜角度对Nu数的变化影响很大,并且当倾斜角度处于90o～135o时,Nu数可以达到最大值。     

Experimentelle Untersuchung der thermischen Konvektion in einem geneigten Spalt

The liquid flow behaviour in a small vertical gap with a heated and a cooled sidewall was studied experimentally in a former work as far as heat and mass transfer are concerned (Heiland et al. in Heat Mass Transf 43:863?C870, 2007). Following this, a study of thermal convection in a narrow cavity with variable inclination angle has been performed with a liquid crystal tracer technique for flow visualization. Velocity and temperature fields of the flow have been measured. Amongst other things the results show that from an inclination angle of approximately 5^°?C15^° on a drastic change of the velocity and temperature field topology occurs, which qualitatively will not change any more when further increasing the inclination angle up to 90^°.     

The cryogenic system for ITER CC superconducting conductor test facility

This paper describes the cryogenic system of the International Thermonuclear Experimental Reactor (ITER) Correction Coils (CC) test facility, which consists of a 500 W/4.5 K helium refrigerator, a 50 kA superconducting transformer cryostat (STC) and a background field magnet cryostat (BFMC). The 500 W/4.5 K helium refrigerator synchronously produces both the liquid helium (LHe) and supercritical helium (SHe). The background field magnet and the primary coil of the superconducting transformer (PCST) are cooled down by immersing into 4.2 K LHe. The secondary Cable-In-Conduit Conductor (CICC) coil of the superconducting transformer (SCST), superconducting joints and the testing sample of ITER CC are cooled down by forced-flow supercritical helium. During the commissioning experiment, all the superconducting coils were successfully translated into superconducting state. The background field magnet was fully cooled by immersing it into 4.2 K LHe and generated a maximal background magnetic field of 6.96 T; the temperature of transformer coils and current leads was reduced to 4.3 K; the inlet temperature of SHe loop was 5.6 K, which can meet the cooling requirements of CIC-Conductor and joint boxes. It is noted that a novel heat cut-off device for High Temperature Superconducting (HTS) binary current leads was introduced to reduce the heat losses of transformer cryostat.