脉动热管水平及小倾角条件下的传热性能

为了研究脉动热管放置方式对其传热性能的影响,以超纯水作为工质,对水平及倾角为30°放置的脉动热管的传热性能进行研究,用壁面温度振荡性能和传热热阻来描述其传热能力。在不同的放置条件下,着重分析不同加热功率和充液率(35%,50%,70%)对其传热性能的影响。研究表明：水平放置时,充液率为35%和50%时脉动热管不能启动,充液率70%时可以启动运行;脉动热管在运行时存在临界热量输入值,倾角为30°时,临界值为60 W,但水平放置条件下临界值为90 W;水平放置下的脉动热管传热热阻在不同加热功率下,显著高于倾角为30°的情况;倾角为30°,充液率为35%时的脉动热管适合在低加热功率范围运行,此时传热热阻要低于充液率为50%的情况,但传热范围很窄,传热极限低;30°倾角时,与充液率35%和50%相比,高充液率70%的脉动热管整体传热性能最优。     

单回路紫铜_水脉动热管传热性能的实验研究

实验研究了单回路紫铜—水脉动热管在水冷方式和定传热功率时,冷却水流量、倾角、管径和充液率4种因素对热管传热性能,包括管壁测点温度、冷热段均温、传热温差、传热热阻和温度振幅的影响规律,得到提高传热性能的一些措施。结果显示:水平放置的单回路脉动热管无法启动;30°以上倾角管内可产生振荡,增加倾角可降低传热热阻;定加热功率下,冷却水流量存在最佳值,过大和过小都会增加传热热阻;在脉动热管允许管径范围内,增加管径可大大降低传热热阻;相同传热功率时,30%充液率热管的传热热阻明显低于70%充液率管;小而均匀的壁温振荡比大幅锯齿状振荡时的传热性能好。     

常规工况下多弯头数脉动热管运行性能的实验研究

设计了两组内径1和2 mm的40个弯头细铜管组成的脉动热管,通过开启或关闭管路中的一个阀门,可以得到闭式或开式两种回路形式,分别采用R123、水及酒精为工作介质,充液率从15%变化至95%,安装角度可任意调节.通过实验,分析比较了管内径、工质种类及充液率、加热角度以及回路形式等多弯头数脉动热管在常规工况下启动及传热性能的影响.     

环路型脉动热管的工质流动和传热特性实验研究

建立了部分可视化的环路型铜-乙醇脉动热管试验台,研究了充液率、倾斜角度、环路数目等因素对脉动热管传热性能的影响。结果表明:不能形成脉动效应时工质的流型是间歇振动,形成脉动效应时工质的流型是弹状流或环状流;最佳倾角为70°~90,°最佳充液率在50%左右;热阻随着环路数目的增加而减小。     

单回路脉动热管传热特性研究

试验研究了单回路紫铜-水脉动热管在3种充液率下的传热性能,理论分析了不同加热功率和充液率下工质的干度、流速、显热和潜热及其份额的变化特性。结果显示:较小传热功率时,减小充液率或增大加热功率会提高热管的传热性能;而较高传热功率时,充液率和加热功率对热管的传热性能影响较小。增加传热功率或减小充液率,会提高管内工质的流速及流量,提高热管的潜热传热量及潜热传热份额;显热量随加热功率和充液率的增加而增大。     

脉动热管运行可视化及传热与流动特性的实验研究

对脉动热管的运行进行了可视化实验 ,在不同的充灌率、倾角、截面形状、加热量条件下对脉动热管的运行进行了测试 ,实验结果表明 :脉动热管是一种十分有效的散热技术 ;脉动热管存在传热极限 ;在最佳充灌率 (5 0 % )和最佳倾角 (5 0°)下运行的脉动热管传热极限最高 ,高热流密度下的传热热阻最低 ;当热流密度较小时 ,三角形通道的脉动热管要优于正方形通道的脉动热管 ,但当热流密度较大时 ,通道形状对热阻和单位截面传热极限影响不大 ;通道大小对热管的热性能影响很小     

热管置入式墙体传热优化研究

提出一种新型被动式太阳能利用技术——热管置入式墙体。通过理论分析和实验测试对其传热性能进行优化研究,考察热管管径、蒸发段长度比、充液率等因素对热管置入式墙体传热性能的影响。研究表明,平均等效传热系数与热管外径近似成线性关系,在热管置入式墙体结构允许的条件下宜选用较大管径,蒸发段长度比的最佳范围为67%~80%;重力热管充液率对热管置入式墙体等效传热系数的影响显著,最佳充液率范围为30%~40%。     

分离型热管单管回路传热特性实验研究

分离型热管作为高效的非能动传热元件,在工业领域得到了广泛的应用。本研究以氨为工质,对分离型热管单管回路开展了实验研究,主要探讨了热源温度与充液率对热管传热性能的影响。实验结果表明:外界热源温度越高,管内工作温度越高,热管换热量越大;氨的沸腾换热系数随外界热流密度增大而增大,实验条件下,最高可达到7 000 W/(m2·K);水平冷凝管壁存在周向温差;在不同的工况下,分离式热管都存在一个最佳充液率,且在一定范围内随着外界热负荷的升高而增大。     

脉动热管传热性能的实验研究

对脉动热管的运行进行了可视化实验,分析了影响脉动热管运行性能的因素,并且在不同的充液率、传热量和不凝性气体含量的条件下,对脉动热管的运行进行了测试,实验结果表明:脉动热管的整体热阻受充液率、传热量、不凝性气体的影响,存在最佳的充液率,在一定的条件下脉动热管的运行达到最佳。     

倾角对复合中空热管传热性能的影响

为了研究倾角对复合中空热管传热性能的影响,建立了复合中空热管传热性能实验装置,对相同充液比(33％)不同倾角(分别为60°、75°、90°)和不同工质(分别为纯水和无水乙醇)复合中空热管的传热性能进行了实验研究.研究结果表明:对于充液比为33％,工质为纯水和无水乙醇的复合中空热管,倾角为90°时传热性能最佳.实验研究为复合中空热管换热器的工业应用提供基础.     

显热储热材料的制备及性能研究

采用水泥作为材料的胶凝剂,添加热容、热导率大的物质作为骨料来制备混凝土储热材料。研究表明:当铝酸盐水泥含量为10%时,材料的抗压、抗折强度能满足工业需求;材料的比热容随温度的升高先增大,在500℃时达到最大,后随着温度的升高反而降低;材料的热导率随着石墨粉含量的增加几乎成直线上升,当石墨含量为5%时材料的热导率大于1.7W/(m·K)。     

On the steady‐state modelling of a two‐stage evaporator system

We develop and validate against experimental measurements a steady‐state two‐stage flooded refrigerant evaporator model for a heat pump drying system. A prototype two‐stage heat pump dryer test facility was designed, built and instrumented to provide the required measurements for the validation of the model. Repeatability and data quality tests were conducted to evaluate the accuracy of measurements. Experimental data could be reproduced to within ±6.5 per cent of replicated air and refrigerant side measurements for the same evaporator's air inlet conditions while the discrepancy of energy balance at the air‐side and refrigerant‐side was observed to be within ±8.9 per cent. The two‐stage evaporator model predicted the air‐side total heat and latent heat transfer of the two‐stage evaporator to within (?6.3 per cent, 7.6 per cent) and (?11.5 per cent, 9.5 per cent), respectively. On the refrigerant‐side, the model enabled the calculation of the degree of superheat to within (?10.6 per cent, 1.7 per cent). The model has shown that there is significant improvement in the heat recovered from a two‐stage evaporator system compared to a single evaporator system. In addition, the model demonstrated that the improvement in total heat recovery could be as high as 40 per cent over its base‐value when the latent to total load at the two‐stage evaporator is increased. Copyright © 2001 John Wiley & Sons, Ltd.     

间歇式热处理炉传热计算与分析

建立了台车式热处理炉炉膛传热数学模型和辐射换热器工作模型，分析了换热器的传热特性（空气预热温度、壁温、传热系数）随炉况的变化。结果表明，辐射换热器的传热特性随炉子的升温及保温过程变化而波动很大，因而对炉子的热工性能产生了影响。     

国内分离式热管概况与热环研究的小结及展望

本文对我国分离式热管技术的研究进行了简要概况,针对工程中热源在上,冷源在下及冷热源相距较远时的热量传递问题,在分析了一般分离式热管及“水回路”等技术的基础上,对一种新型分离式热管－泵或风机驱动的动力型分离式热管（简称热环）的研究进行了小结和展望。     

Quantification of the European industrial heat demand by branch and temperature level

We present the first comprehensive estimate of the final energy demand for heat in all EU28 member states for the reference year 2012, differentiated by temperature levels, comparing two different approaches. Two different calculation approaches based on different data sets yielded estimates of the total final energy demand for heat in the EU28 of 8150 PJ and 8518 PJ in 2012, respectively. Approach 1 distinguishes between three different process heat (PH) temperature levels and results in final energy demand for heat <100°C: 2077 PJ, 100–400°C: 2214 PJ and >400°C: 3859 PJ. The second approach distinguishes between low temperature space heat and hot water (<100°C: 1161 PJ) and four different PH temperature levels with a resulting energy demand of <100°C: 1027 PJ, 100–500°C: 1785 PJ, 500–1000°C: 1679 PJ and >1000°C: 2865 PJ. The high share of high‐temperature heat illustrates the limits to the potential decarbonisation of industrial thermal processes with renewable energy sources such as (non‐concentrating) solar thermal, geothermal or environmental heat. Therefore specific information on required temperature levels is of the essence. This, in turn, points out the relevance of renewable electricity and synthetic fuels based on renewable power for a significant reduction of CO₂ emissions from the industry sector in Europe. Considering current data quality, it is recommended to develop a consistent, comprehensive methodology to significantly improve the data basis on industrial heat demand. Copyright © 2015 John Wiley & Sons, Ltd.     

地源热泵竖直埋管的有限长线热源模型

对地热换热器竖直埋管的非稳态传热模型进行了分析讨论。采用虚拟热源和格林函数法给出了半无限大介质中有限长线热源产生的非稳态温度场的解析解表达式。与稳态温度场的解进行比较,讨论了温度场达到名义上的“稳态”所需的时间,同时对于达到稳态时的温度场也进行了分析,指出了现行教科书中关于该问题的错误,提出了稳态时两个地热换热器孔壁代表性温度的定义,并对两者进行了比较,进而给出了可供工程应用的简化计算公式,并对两者进行了比较,进而给出了可供工程应用的简化计算公式。基于以上分析,进一步讨论了全年冷热负荷不平衡对地热换热器长期性能的影响。     

Augmentation of heat transfer through passive techniques

The thermal performance of energy preservation systems is greatly improved by increasing miniaturization and boosting. These are imaginative (or Promethean) techniques to enhance heat transfer. Enhancement methods of heat transfer draw great attention in front of the industrial sector because of their ability to provide energy savings and raise the economic efficiency of thermal systems. Three techniques these methods are categorized; those are active, passive, and compound. Different types of components are used in passive methods because of the transfer/working fluid flow path to the enhancement of the heat transfer rate. In this article, the subject of the review was the passive heat transfer enhancement methods including inserts (conical strips, winglets, twisted tapes, baffles), porous materials, coil/helical/spiral tubes, rough surfaces (corrugated/ribbed surfaces), extended surfaces (fins) and nanofluids (mono and hybrid nanofluid). Recent passive heat transfer enhancement techniques are studied in this article as they are cost-effective and reliable, and also comparably passive methods do not need any extra power to promote the energy conversion systems' thermal efficiency than active methods. In the passive approaches, various components are applied to the heat transfer/working fluid flow path to improve the heat transfer rate. The passive heat transfer enhancement methods studied in this article include inserts (twisted tapes, conical strips, baffles, winglets), extended surfaces (fins), porous materials, coil/helical/spiral tubes, rough surfaces (corrugated/ribbed surfaces), and nanofluids (mono and hybrid nanofluid). From the pioneers' research work, it is clear that a lower twist ratio and lower pitch, lesser winglet angles can provide more heat transfer rate and a little bit more friction factor. In the case of nanofluids, a little bit of pumping power is enhanced. Finally, heat transfer enhancement is compared with the thermal performance factor, which is more than unity.     

城市住宅及企业集中供热浅析

随着住宅商品化进程的进一步加快 ,以及供热商品化意识的普及 ,人们对集中供热提出了更高的要求 ,在利用其它手段诸如空调、电暖气等设施取暖的同时对集中供热进行开发     

Heat-spreading analysis of a heat sink base embedded with a heat pipe

A simplified model predicting the heat transfer performance of a heat sink base with a high thermal conductivity was developed. Numerical analysis was performed using the commercial software FLUENT. The investigation indicates that for heat sink bases with a high effective thermal conductivity, such as the base embedded with a typical heat pipe, the entire heat sink can be modeled as a flat plate with a uniform temperature and an effective convection heat transfer coefficient. This simplified model can be used to determine the heat transfer performance of a heat sink embedded with a typical heat pipe or vapor chamber.     

Experimental investigation of heat transfer enhancement using impingement of multiple water jets

The problem of cooling electronic components has become a subject of special interest in recent years due to the increasing capacity and rapidly decreasing size of electronic components. Direct contact cooling using multiple jet impingement is considered the most effective method. The heat transfer problem is complex and a better understanding of the jet impingement method is essential for the proper application of this method for electronic cooling. Investigations were carried out using an electrically heated test plate. Heat flux in the range of 25 to $200 \ \hbox{W/cm}^{2}$ , which is a typical requirement for cooling high power electronic components was dissipated using 0.5‐mm diameter water jets arranged in a 7×7 array with a pitch of 3 mm. Temperature difference between the test plate and water was within $30 \ ^{\circ}\hbox{C}$ . Tests were performed in the flow rate range of 22 to 40 ml/min, resulting in a Reynolds number range of 1100 to 1750. Results show a significant increase in the heat transfer coefficient or Nusselt number with an increase in heat flux. The effect of the flow rate or Reynolds number on the heat transfer coefficient is found to be negligible. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20291