矩形微槽道结构与平板微热管传热特性研究

为研究矩形槽道深度对平板微热管传热特性的影响,根据ANSYS(有限元)软件瞬态热仿真结果进行结构设计,利用MEMS(微电子机械系统)干法刻蚀工艺分别制作了不同深度的等宽和不等宽矩形槽道平板微热管。采用乙醇液体工质并在加热功率恒定的条件下,分析了不同充液率的平板微热管轴向温度分布及其等效导热系数。研究结果表明:在加热功率为3.1 W的条件下,槽道深度为220μm的矩形槽道微热管比槽道深度为180μm的矩形槽道微热管传热性能提高近60%,不等宽矩形槽道微热管的轴向温差为25℃左右,要优于等宽矩形槽道微热管的45℃。由此得到微槽道的深度越深,微热管传热性能越佳;不等宽槽道微热管的传热性能优于等宽槽道微热管。     

地源热泵系统非平衡冷热负荷运行特性研究

建立地埋管传热模型和系统能耗模型,对非平衡冷热负荷条件下地源热泵系统运行特性进行模拟计算。当建筑空调冷负荷大于热负荷,且供冷时间较长时,地源热泵系统从冬季初始运行,到达夏季时段,地温比夏季初始运行低,更加有利于夏季地源热泵系统节能。地源热泵系统运行7a后,采取夏季和冬季初始运行两种方案的地埋管钻孔壁年平均温度与土壤初始温度相比,分别上升3.10和5.12℃,导致机组耗功率逐年增加,应考虑采用复合式地源热泵系统间歇运行或增设地埋管设置分区运行策略,平衡土壤传热量。     

基于日光温室墙体蓄热需求的弯曲微热管阵列传热特性试验

为了提升日光温室墙体的蓄放热性能,以长度为750 mm的平板微热管阵列为例,探究不同弯曲半径、弯曲角度对微热管阵列传热特性的影响,并将弯曲后的微热管阵列应用于日光温室。结果表明：弯曲和平直的微热管阵列均具有较好的均温性和较高的导热系数,与平直热管相比,经过2次90°弯曲的热管表面温度升高;相同加热功率时,随着弯曲半径增加,微热管阵列轴向温度下降;弯曲半径为30～40 mm的微热管阵列满足日光温室蓄热墙体的蓄放热需求,平均等效导热系数达300 816 W/(m·℃);将弯曲的微热管阵列应用于日光温室墙体,与普通温室墙体相比,平均蓄热速率与放热速率分别提高12.4%和15.6%,微热管阵列能够有效提升温室墙体的蓄放热性能。     

开式热管传热特性的实验研究

对新型换热元件开式热管的传热特怀进行了实验研究，结果表明开式热管存在两个传热转折点。其实际工作的最佳范围应在两个传热转折点之间。本文给工度经、小孔直径及小孔位置变化工式热管传热能力的实验结果。为合理设计开式热管理提供了参考实验数据。     

热管式冰蓄冷空调的运行特性及分析

文中论述了热管在冰蓄冷中应用的原理与特点，扩展了热管的应用范围，分析了热管式蓄冰系统的动态特性，建立了相应的物理模型，该模型可为热管式蓄冰系统的设计提供理论依据。     

弯曲微热管阵列传热性能的实验研究

微热管阵列是一种导热能力较强的元件,具有接触面积大、热输运能力强和承压能力强的特点。将750 mm长的微热管阵列分别弯曲成"L"形和"乙"字形,测试其在热源温度为45℃条件下的响应时间及轴向均温性,并与平直微热管阵列对比,分析弯曲对微热管阵列传热性能的影响。结果表明:弯曲会使微热管阵列响应时间滞后,"L"形、"乙"字形1号和"乙"字形2号微热管阵列响应时间约为120 s,较平直微热管阵列滞后80 s;弯曲微热管阵列两端温差随弯道数的增加而增大,随弯曲角度的增大而增大,"L"形和"乙"字形1号微热管阵列蒸发段与冷凝段温差分别为0.76℃、1.61℃,较平直微热管阵列大11.76%、106.41%;"乙"字形2号微热管阵列两端温差为1.70℃,比"乙"字形1号微热管阵列两端温差大10.84%。     

弯折和倾角对微槽道扁平热管传热特性的影响

研究了弯折和顺重力倾角对具有梯形微槽道的铝—丙酮扁平热管传热特性的影响,搭建了可变重力倾角热管传热性能实验台,在冷凝段采用第三类边界条件下进行测试。结果表明,顺重力倾角可显著提高热管传热极限,30°及以上的倾角可使传热极限从40 W左右提高至90 W以上,同时热阻在高热流时达到0.1 K/W的低位。弯折可有效降低热阻,30°弯折可使热阻整体降低23.6%以上,从而提高等效导热系数,在高热流和小倾角下效果更佳,最大等效导热系数可达1.47×10⁴ W/(m·K)。在热管设计与应用时,合适的弯折和倾角可帮助提高热管传热性能。     

分离式热管蒸发段传热特性的研究

在研究分离式热管蒸发段流动特性的基础上,对其传热特性进行了系统的试验研究和理论分析,首先分析了核态沸腾传热区及飞溅降膜传热区的换热原理;根据数据回归整理了核态沸腾传热区和飞溅降膜传热区的换热系数无量纲准则关系式,与试验数据吻合较好;并将它们与其它关系式进行了比较,得出了有用的结论,其结果为分离式热管的研究及工程应用提供了理论依据。     

微热管阵列平板太阳集热器的数值模拟与优化

介绍一种全新的平板式太阳集热器,该集热器应用微热管阵列作为集热元件,具有成本低、抗冻、承压、不易结垢、易与建筑一体化等优点。对其瞬时热性能进行的实验研究表明,该集热器瞬时效率曲线的截距达83.1%,斜率为-4.77。建立了微热管阵列平板太阳集热器的CFD模型,对集热器内部流体流动与换热进行数值模拟,模拟结果与实验结果吻合较好,从而验证了模型的可靠性。采用CFD模型对集热器干式接触式换热器进行优化,结果表明,该集热器循环水的最佳流量为0.1~0.2 kg/(m2·s),水流量较低时,采用直内肋管可适当提高集热效率,随着流量的增加,管内加肋对集热器性能的提高影响不大。     

超临界变压运行锅炉垂直上升内螺纹管的传热特性

在压力为10～28 MPa、质量流速为500～1 220 kg/(m2·s)、热负荷为140～400kW/m2的工况范围内,在试验台上进行了直径38.1 mm、厚度7.5 mm垂直上升内螺纹管的传热特性研究.结果表明:在亚临界压力区,内螺纹管的旋流作用使内螺纹管具有明显的传热强化效果;随着压力的升高,特别是在近临界压力区,由于汽-液比体积的差值减小,内螺纹管的旋流作用降低,所以强化传热效果降低.在超临界压力区,管内流体属于单相流体,当管中心处工质温度与贴壁处工质温度均低于拟临界温度时,管中心工质与管内贴壁处工质之间的比体积相差很小,使得内螺纹管的旋流作用降低,管壁温度升高较快,传热恶化;当管中心工质温度低于拟临界温度、而贴壁处工质温度高于拟临界温度时,两处工质之间的比体积差增大,使得内螺纹管的旋流作用增强,传热强化,壁温降低.     

开启式重力热管传热特性的实验研究

对φ38 mm×3 mm,长1 600 mm的开启式碳钢-水重力热管进行了传热性能的实验研究.实验为0.02～0.8 MPa,2.5～9.6 kW.对负压下开启武重力热管的传热性能首次进行了研究,发现负压与正压的传热规律相似,但传热性能较正压差.实验结果表明,开启式热管具有较好的传热特性,性能稳定,可作为高温烟气余热锅炉的传热部件.根据实验数据回归了开启式重力热管沸腾换热系数实验关联式,可用于工程实际.     

热管在采油中的热力学特性研究

热管在采油中的应用,主要应用在井筒中.井筒重力热管是利用热管将油藏自身能量即井底热量传递到井筒上部,在无需外加动力条件下实现对井筒近井口流体加热,改善井口流体温度分布,防止近井口结蜡和絮凝,从而降低采油成本.为了研究井筒重力热管的传热性能和工作过程,进而改进和优化重力热管的传热性能,运用Visual Basic进行模拟计算.基于理论研究,证明热管起到了均衡流体温度场的作用.在此基础上,原油与地层传热系数反应了原油向地层散热的能力,该系数与井口油温基本呈线性关系;原油与热管传热系数对原有温度的降低有一定局限性;对于长径比较大的热管,热流密度不大的情况下,会出现携带极限,可通过计算得到验证.     

An Experimental Study on the Performance of a Stainless Steel-Water Loop Heat Pipe under Natural Cooling Condition简

Aiming to improve the thermal characteristics of modern electronics, we experimentally study the performance of a stainless steel/water loop heat pipe （LHP） under natural cooling condition. The LHP heat transfer performance, including start-up performance, temperature oscillation and total thermal resistance at different heat loads and with different incline angles have been investigated systematically. Experimental results show that at an optimal heat load （i.e. 60 W） and with the LHP being inclined 60~ to the horizontal plane, the total thermal resistance is lowered to be -0.24 K/W, and the temperature of evaporator could be controlled steadily at around 90~C.     

Effect of amount of fluid charge in thermal performance of loop heat pipe

Loop heat pipes (LHPs) are two‐phase thermal control system, which works only by heat from its cooling target. In order to utilize the LHPs in various fields, it is required to be smaller, more reliable, and higher in performance. In the present study, a miniature LHP has been fabricated, and the effect of the amount of working fluid charged on thermal performance of the LHPs has been investigated. Tests were conducted including start‐up, and power step up, as function of the amount of working fluid. The test results showed that under‐charging the working fluid caused start‐up failure, while over‐charging the working fluid made the LHP less stable. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20306     

An Experimental Investigation of Thermal Performance of a Polymer‐Based Flat Heat Pipe

A polymer‐based flat heat pipe (PFHP) was fabricated. The heat transfer performance was measured and analyzed when deionized (DI) water and acetone were used as the working fluid, separately. Input power ranging from 2.8 W to 14.2 W was provided to the evaporator section while the device was at different filling ratios. Experimental results revealed that, when the polymer‐based flat heat pipe was laid in a horizontal position, the thermal resistance (1.02 K/W) was much smaller than that (4.6 K/W) of a copper plate with the same thickness at the thermal power of 10.3 W and the value decreased as the tilt angle changed from 0° to 90°.     

Study on heat transfer characteristics of reservoir embedded loop heat pipe (Influence of condenser cooling method on heat transfer characteristics)

As heat generation in satellites increases, securing sufficient radiator panel area is an important problem. Deployable radiators, whose radiator panels are deployed post‐launch in space to increase the effective radiator panel area of the satellite, is becoming an important thermal control technology. A reservoir embedded loop heat pipe (RELHP) is applied to the deployable radiator for a thermal transport device. This paper presents the heat transport dynamic characteristics of a RELHP using a radiant cooling condenser and liquid forced convection cooling condenser by an experimental study. It was found that heat leak into the liquid line, flexible line, and reservoir increases the length of the sub‐cooling region in the condenser. In the case of the radiant cooling condenser, the sub‐cooling region length is shorter than that of a liquid forced convection cooling condenser. Furthermore, vapor temperature is mainly decided by the radiation capacity of the radiator panel, because liquid temperature returned into the evaporator rises with an increase in radiator panel temperature. In addition, time length from start‐up until steady state is greater than the liquid forced convection cooling condenser case, because the radiator panel has a large heat capacity. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20229     

Heat transport characteristics of flexible looped heat pipe under micro‐gravity condition

This paper presents the heat transport performance of a flexible looped heat pipe (FLHP) with the working fluid of ammonium under micro‐gravity condition. The evaporator of the FLHP has two coaxial wicks. The outer wick is made of PTFE with 1.2µm pore diameter and the inner one is made of polyethylene with 12µm pore diameter. The inside surface of the inner wick is axially grooved. The core of the inner wick is used as liquid reservoir so that reliability of the operation can be enhanced. The experiment revealed that the FLHP performed normally under micro‐gravity condition and had the predicted capillary limit. The FLHP showed good temperature control ability and was like a VCHP in the range of 150 to 240 W heat transfer rate. Liquid behavior observed in the visual module ensured the normal operation of the second wick and inner axial grooves under micro‐gravity condition. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(5): 381–390, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10092     

水基纳米流体在铜丝平板热管中的应用

对使用三种水基纳米流体作为工质的铜丝平板热管的传热特性进行了实验研究.使用的纳米流体分别是平均粒径20 nm的Cu纳米颗粒、平均粒径50 nm的Cu纳米颗粒和平均粒径50 nm的CuO纳米颗粒的水基悬浮液(简称水基20 nm Cu、50 nm Cu、50 nm CuO纳米流体),着重分析了纳米流体种类,纳米颗粒质量分数、运行温度或工作压力对热管传热特性的影响.研究结果表明,使用纳米流体作为工质可以显著提高热管的传热特性;在不同运行温度条件下,不同的纳米流体均在质量分数1.0％时具有最佳传热效果;纳米流体是一种适用于铜丝平板热管的新型工质.     

Experimental investigations on operating characteristics of a closed loop pulsating heat pipe

The operating mechanism of the pulsating heat pipe (PHP) is not well understood and the present technology cannot predict required design parameters for a given task. The aim of research work presented in this paper is to better understand the operation regimes of the PHP through experimental investigations. A series of experiments were conducted on a closed loop PHP with 5 turns made of copper capillary tube of 2 mm in inner diameter. Two different working fluids viz. ethanol and acetone were employed. The operating characteristics were studied for the variation of heat input, filling ratio (FR) and inclination angle of the tested device. The results strongly demonstrate the effect of the filling ratio of the working fluid on the operational stability and heat transfer capability of the device. Important insight into the operational characteristics of PHP has been obtained.     

The correlation between the number of fins and the discharge time for a finned heat pipe latent heat storage system

The concept of a solar energy heat pipe latent heat storage system is presented. In order to assure large charging and discharging rates, finned heat pipes are used to transfer heat to and from the phase-change material (paraffin in this case). The evolution of the solid - liquid interface is studied by considering the radial heat transfer (due to the heat pipe wall) and the angular one (due to the fin). Two mathematical models, corresponding to exponential, respectively polynomial functions describing the fin temperature profile are presented and the results are compared. The two models allow the evaluation of the discharge time of the storage unit for a certain number of fins for a single heat pipe. When the discharge time has a fixed value, the methods presented in the paper allow to conclude whether the number of fins is sufficiently large to assure the complete solidification of the phase-change material.