Forced Convective Heat Transfer in a Porous Plate Channel

INTRODUCTIONHeattransferenllancen1enttechniquesplayaveryimportantroleintllermalcontroltechnologies1lsedwithnlicroelectronicchips,powerfullasermirrors,aerospacecraft,thermalnuclearfusion,etc.Itiswidelyrecognizedthattl1eheattransfercanbein-creasedbyil1creasingthesurfaceareaincontactwiththecoolant.TuckermanandPease[1,2]pointedoutthatforlaminarflowinconfinedchannels,theheattransfercoefficientisinverselyproportionaltothewidthofthechannelsincethelimitingNusseltnum-berisconsta11t.Theybuiltawate…     

迪恩涡强化传热技术的初步实验研究

对迪恩涡的强化传热作用进行了初步的实验研究,发现在迪恩涡的作用下,90°弯管的传热系数明显高于直管;弯管的阻力损失在层流区略高于直管,但是在过渡区之后便开始低于直管的阻力损失。迪恩涡强化传热技术在提高传热系数、降低阻力损失方面有着极大的潜力,是一种节能的强化传热技术。     

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     

内展翅片换热器在压缩空气系统中的应用分析

通过实验数据分析以及实际工程案例,对内展翅片换热器在压缩空气系统的相同工况下采用光管换热器和外翅片换热器的换热效果及阻力特性进行了比较。结果表明,内展翅片换热器不仅具有较好的强化传热效果,而且单位压降损耗低,节能效果显著。     

相变微胶囊功能流体相变区间的影响因素和变化趋势分析

相变微胶囊功能流体所具有的相变区间是影响其强化传热效应和工程应用价值的主要因素。采用双流体数学模型通过数值模拟发现:在层流条件下,双流体模型能够很好地模拟颗粒相体积分数、管径和R e对相变区间的影响。功能流体的相变段长度和总吸热量都随着这三个因素的增大而显著增大。同时相变段长度还取决于入口温度和边界条件等因素。以直链烷烃为相变材料的功能流体在相变段的蓄热能力相近。但在同R e下,功能流体的相变段长度和总吸热量都随着囊芯材料相变温度的升高而减小。入口温度是影响相变材料熔化速度的重要因素。相变段的长度、总温升和总吸热量与流体入口过冷度都呈线性关系。在第一类边界条件下,相变段长度与壁面过热度呈指数为负的幂指数关系,而相变段总温升和总吸热量都随壁面过热度的增大而增大。     

Parametric Evaluation of Heat Recovery Steam Generator (HRSG)

Thermal efficiency of a combined cycle power plant depends strongly on a heat recovery steam generator (HRSG), which is the link between the gas turbine‐based topping cycle and steam turbine‐based bottoming cycle. This work is based upon the design of physical parameters of a HRSG. In this article, the physical parameters of a HRSG have been considered to study their implications on HRSG design by comparing the existing plant design with an optimized plant design. Thermodynamic analysis of HRSG for the two designs gives important outcomes which are useful for power plant designers. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21106     

热风炉提高风温的几点浅见

综述了热风炉提高风温的主要途径：采用空煤气预热和高效能陶瓷燃烧器技术提高理论燃烧温度和拱顶温度;增大单位体积格砖的换热面积和采用均匀配气技术加强蓄热室内的热交换;同时在热风炉的不同部位选用不同材质的耐火材料,实现良好的保温效果;在此基础上适当缩短送风周期时间,并采用合理的操作制度。适当评价了各种技术对提高风温的效果。     

Study on high performance evaporator with micro‐grooves (Measurement of capillary force in a single groove and modeling of heat and mass transfer)

A micro‐grooved evaporator is composed of µm‐wide grooves on a heat transfer plate in which the inter‐line regions at the liquid–vapor meniscus of coolant become identifiable. The high‐heat performance of the evaporator is realized by this inter‐line region (ILR) where the liquid thin film reduces the thermal resistance on the heat transfer surface. In this report, we propose a numerical simulation model of heat and mass transfer in a single groove to predict its capillary force and heat flux. The capillary force performance (capillary‐rise length in a groove) of a single groove was measured for samples of varying width, superheat, and inclination. The performance was found to be a maximum at a specific groove width of 200–400 µm, which is in good agreement with the predicted results calculated by the proposed model. For a better prediction of capillary‐rise length, the effective capillary force and the effective flow resistance were considered. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20257     

太阳能平板型吸附床强化传热的分析

通过对太阳能平板型吸附床内温度分布的计算,分析了吸附床中嵌入金属助片和吸附剂（活性炭）中掺入铜粉等提高其导热系数的强化传热 方法的效果,认为当肋片的间距在6cm左右或增大吸附剂的导热系数到0．4－0.6W/(m.℃）时,吸附床内厚度方向的温度分布近乎直线,温度梯度较小,同时,胁片的热容对吸附床的整体温度的提高有很大影响。     

Numerical simulation of heat transfer enhancement in wavy microchannel heat sink

In this paper, heat transfer and water flow characteristics in wavy microchannel heat sink (WMCHS) with rectangular cross-section with various wavy amplitudes ranged from 125 to 500 μm is numerically investigated. This investigation covers Reynolds number in the range of 100 to 1000. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite-volume method (FVM). The water flow field and heat transfer phenomena inside the heated wavy microchannels is simulated and the results are compared with the straight microchannels. The effect of using a wavy flow channel on the MCHS thermal performance, the pressure drop, the friction factor, and wall shear stress is reported in this article. It is found that the heat transfer performance of the wavy microchannels is much better than the straight microchannels with the same cross-section. The pressure drop penalty of the wavy microchannels is much smaller than the heat transfer enhancement achievement. Both friction factor and wall shear stress are increased proportionally as the amplitude of wavy microchannels increased.     

Heat and fluid flow characteristics inside differentially heated square enclosures with single and multiple sliding walls

Fluid flow and heat transfer characteristics of differentially heated lid driven cavities are numerically modeled and analyzed in the present study. One‐, two‐, and four‐sided lid driven cavity configurations are considered with the vertical walls being maintained at different temperatures and the horizontal walls being thermally insulated. Eight different cavity configurations are considered depending on the direction of wall motion. The Prandtl number Pr is taken to be 0.7, the Grashof number is taken to be 10⁴, while two values for the Richardson number Ri are considered, 0.1 and 10. It is found that both the Richardson number and the cavity configuration affect the heat and fluid flow characteristics in the cavity. It is concluded that for Ri=0.1, a four‐sided driven cavity configuration with all walls rotating in the same direction would triple the value of the average Nusselt number at the cold wall when compared to a one‐sided driven cavity configuration. However, for Ri=10, the cavity configuration has minimal effect and all eight cases result in an average Nusselt number value at the cold wall ranging between 1.3 and 1.9. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/htj.20264     

Enhancement in Evaporative Effectiveness of an Evaporative Tubular Heat Dissipator Using Experimental Design Approach

An experimental investigation of evaporative effectiveness and mass transfer coefficient on a bundle of tubes of an evaporative tubular heat dissipator is presented. Based on the experiments, correlations of evaporative effectiveness and mass transfer coefficient are derived using multiple regression analysis. A statistical model is developed to correlate the operating variables using design of experiment approach by selecting central composite design of a response surface methodology. Results shown in this article indicate that as the cooling film flow rate increases, evaporative effectiveness and mass transfer coefficient increases provided that the air flow rate is constant which is flowing from underneath the tubes of the evaporative tubular heat dissipator. Derived correlations are helpful in improvement of the design of heat transfer devices and many other engineering applications. Consideration of relative humidity of upstreaming air as one of the operating variables leads to the contribution to heat and mass transfer study of evaporative tubular heat dissipators in the present investigation.     

水平光管内R410A与R134a流动冷凝换热特性的对比研究

为研究R410A与R134a在水平光管内的冷凝换热特性,在管内冷凝换热试验台上进行冷凝试验,分析质量流量、冷凝温度、测试水雷诺数Re、管径和制冷剂物性对换热系数和压降的影响。研究表明:换热系数、压降均随着质量流量的增加而变大,随冷凝温度的升高而减小,换热系数随测试水雷诺数Re的增加而减小,而测试水雷诺数Re对压降的影响相对较小;尽管R410A的换热系数随管径的减小而增大,而管径对R134a换热系数的影响并不显著,R134a与R410A的压降均随管径的减小而增大;单位压降换热系数随质量流量的增加而减小; Cavallini et al.关联式可较好预测R410A与R134a在光管内换热系数,而Shah关联式只能用于预测R134a的换热系数。     

高温梯度锯齿表面液滴运动特性

利用铝片制备了不同高度、倾角由小到大连续变化的梯度锯齿表面,采用高速摄影技术对高温梯度锯齿表面自推进液滴的运动行为进行了探讨,并和常规锯齿进行了比较。结果发现:液滴可以在一定温度梯度锯齿表面发生由锯齿倾角小的方向往倾角大的方向的定向运动,并且运动的加速度和锯齿高度以及锯齿表面温度有关;随着锯齿高度的增加,液滴运动的平均加速度呈逐渐减小的趋势;而随着锯齿表面温度的增高,液滴的平均加速度则经历从减小到增大的两个阶段。     

内展翅片换热器应用在压缩空气系统中的节能效益分析

文中通过实验数据分析以及实际工程案例,就内展翅片换热器在压缩空气系统的相同工况下,采用光管换热器和外翅片换热器的换热效果及阻力特性进行了比较,结果表明,内展翅片换热器不仅具有较好的强化传热效果,而且单位压降损耗低,节能效果显著。