波纹板式空气预热器内流动换热过程的数值模拟

对波纹板式空气预热器内换热与流动过程进行数值模拟,分析了波纹板片的结构特征、波纹倾角β、波纹高度H、波纹节距以及板间距对空气预热器性能的影响.结果表明:当波纹倾角和波纹高度增大时,换热性能提高但是压降增大,在β=45°、H=10mm时换热性能最优;波纹间距的改变对换热性能影响较小,但板间距的影响较为明显,综合考虑换热器的紧凑性,选用较小板间距能达到较好的换热效果.     

疏水表面对微通道换热和压降性能的影响

通过搭建的微通道两相沸腾流换热实验台,利用高速摄像仪拍摄其工质两相流流型,研究了接触角分别为48.2°、140°的普通微通道和疏水微通道的压降特性、换热性能,并结合工质流型图阐述其变化规律机理。实验采用的微通道尺寸为0.55 mm×0.55 mm×80 mm,工质质量流量范围为1983～3636 kg/(m~2·s),两相流进口干度为0～0.45。研究结果表明,疏水微通道的压降在所有实验干度区间均显著大于普通微通道的压降,在低干度区间,疏水微通道的换热性能高于普通微通道的换热性能。     

人字形波纹板传热与阻力特性的数值模拟和试验研究

对板式低温多效海水淡化技术中的人字形波纹板式换热器进行了单相流换热试验和数值模拟,试验结果表明其换热系数较高,在低Re数下就能达到3000 W/(m~2·K)以上。通过建立三维模型,运用CFD软件对人字形波纹板内部的传热及阻力特性进行数值模拟,研究了波纹倾角β、波高h和波纹间距λ对人字板传热以及流动阻力的影响,模拟结果与试验值误差都在15%以内。数值模拟结果表明,波纹倾角从30°增大到60°,传热因子j约提高60%,继续增大波纹倾角,传热因子反而降低,摩擦因子f随着波纹倾角的增大而增大;波高从3 mm增大到6 mm,传热因子j约提高5%,但摩擦因子f增大1倍;波纹间距从5 mm增大到20 mm,传热因子j约降低30%,但同时摩擦因子f降低70%。建议板式低温多效海水淡化系统的板型参数:波纹倾角60°,波高3~4 mm,波纹间距15~20 mm。     

两种波纹通道内周期性充分发展对流换热的数值研究

应用数值方法研究了流体在正弦型和三角型两种波纹通道内周期性充分发展的层流流动与换热特性，分析了恒壁温条件下，雷诺数Re对流动与换热性能的影响，并对两种通道的摩擦阻力系数厂与努谢尔特数Nu分别进行了比较。结果表明：两种通道流动阻力的相对大小因雷诺数Re的大小而异；正弦型波纹通道的换热速率比三角型通道的换热速率大，因此换热器通道表面的选择应综合考虑。     

波纹通道板间距对通道内流动与换热影响的数值研究

应用数值模拟方法，分析了流体在不同板间距的正弦型波纹通道内，周期性充分发展的稳态层流流动与换热的特性；探讨了板间距对流动与换热的影响，并对其综合性能进行评估。结果表明：在Re相同的条件下，通道内所形成旋涡的尺寸随相对间距A／H(波长／间距)的减小而增大。     

垂直矩形窄通道流动沸腾换热特性实验研究

流动沸腾换热是典型的两相流问题。窄通道与常规通道相比较,其流动沸腾换热系数有较大提高,换热机理也更加复杂。针对截面为250 mm×5 mm的竖直矩形窄缝通道,在低压、入口温度过冷、不同质量流速及加热功率密度的条件下,对水流动沸腾换热特性进行实验研究。通过实验分析可知:入口温度27～60℃、质量流速2.22～3.49 kg/(m2.s)及加热功率密度0～12 kW/m2对饱和沸腾起始点和过冷段长度有重要影响;高的空泡份额和通道结构的限制使汽液两相流动不稳定而影响换热系数,换热系数随着功率的增大而减小,流体进入完全对流沸腾阶段;由于实验段通道顶部结构的限制,干度的增加不会出现干涸点,换热不会得到恶化,换热系数随着功率的增大基本不变。     

除湿条件下波纹通道内对流传热传质的数值研究

通过数值计算对紧凑换热器一种波纹翅片通道内除湿条件下周期性充分发展的对流传热传质情况进行数值研究。计算采用曲线坐标系下压力与速度耦合的SIMPLER算法,湿空气流动Re数的范围为100～1100,Pr数为0.71,Sc数为0.61。讨论了不同波纹高度、波纹间距对阻力与换热的影响,给出了不同Re数下的浓度场,并对动量、传热及传质进行了定量比较分析。计算结果表明,整体Nu数及fRe数随着波纹高度的增加或波纹间距的减小而增加;浓度随着Re数的增加沿着流动方向迅速降低;计算能较好的满足Chilton-Colburn相似,表明传热特性均可类推到传质特性中去。     

基于正交试验的涡流发生器传热特性结构数值分析

为进一步提高管壳式换热器壳程换热效率,设计了一种布置于壳程肋片上的仿生鸟喙式涡流发生器。采用ANSYS FLUENT软件结合田口正交试验模拟了矩形通道中鸟喙式涡流发生器的传热特性,分析了纵向高度、斜截角度、迎流攻角、入口距离、流向间距5种结构参数对强化传热和综合热性能的贡献率及最佳结构组合。流动通道为长方体,其长、宽、高分别为1 600,240和40 mm,温度为286.86 K的空气流体从入口以1.491~3.195 m/s的速度流入,通道底部为337.048 K的恒温换热面。结果表明：纵向高度对于强化换热特性的贡献率最高,达到4744%,最强换热效果组合的换热因子较空矩形通道提高了185.71%;迎流攻角对于综合热性能的贡献率最高,达到了总占比的31.35%,利用正交试验分析得到的最强组合较空通道的综合热性能提高了47.82%     

高低板式换热器板片的换热特性分析及优化

为了强化船用板式换热器换热,对曲折形波纹板式换热器进行优化设计。采用数值模拟的方法,研究了曲折形波纹板不同波纹倾角、波纹高度下的流动换热特性。研究结果表明:曲折形波纹板内部流体的Nu数和阻力特性随着波纹倾角β的增大而增加,随着波纹高度a的增加而减小。通过优化得到的波纹板波纹角度为β=40°,纵向波高比a为0.4,与原曲折波纹板相比,同一流速下,新板片的换热性能提高了15.4%,阻力系数升高了16.2%,综合性能参数与原板片相比提高了22.3%。研究结果对船用换热设备的设计及优化奠定了理论基础。     

纵向涡发生器几何参数对微通道流动传热特性的影响研究

为增强微通道的流动和换热特性,对微通道结合纵向涡发生器进行了数值模拟,分析不同雷诺数下纵向涡发生器的长度、横向间隙对微通道流动与换热性能指标的影响。结果表明:在进口速度为0.5～2 m/s时,雷诺数的增加会引起微通道内的换热性能增强,摩擦因子减小及综合传热性减小;涡发生器长度对换热影响较小,但增加涡发生器长度会引起阻力增加,横向间距对阻力影响较小,但增加横向间距会引起换热性能提高;涡发生器长度为0.30～0.40 mm时综合因子为0.94～1.21,横向间隙为0.1～0.5 mm时综合因子为0.88～1.17;纵向涡发生器长度为0.3 mm和横向间隙为0.5 mm时,有利于综合传热性能的提高。在低雷诺数时微通道结合纵向涡发生器的强化传热和综合传热因子要比高雷诺数时好。     

余热回收用热管及热管式换热器的研究

简要介绍了热管及热管式换热器的工作原理,热管式换热器在工业余热回收中的应用,以及热管式换热器运行过程中防止积灰和低温腐蚀等问题的有效措施。     

管壳式换热器的换热管强化传热技术浅述

介绍了管壳式换热器的换热管强化传热技术,分析了各自的原理、优缺点及推荐的使用场合。采用节能技术的换热器不仅提高了能源的利用率,而且减少了金属材料的消耗,对化工行业提高经济效益具有重要意义。     

Stream-Symmetry of Heat Exchangers and Heat Exchanger Assemblies

Sufficient conditions are given for a heat exchanger or an assembly of heat exchangers to be invariant under the interchange of the two fluids. Analysis of this symmetry is performed on tht basis of geometrical or topological properties of the exchanger, and no prior knowledge of the exchanger solution is required. The 1-2 and 1-4 TEMA E, the split-flow TEMA G, and the divided-flow TEMA J shell-and-tube exchangers are discussed as examples. A t tent ion is drawn to possible erroneous interpretations of published F-charts for stream-unsymmetric eases.     

Heat Pipe Finned Heat Exchanger for Heat Recovery: Experimental Results and Modeling

This paper presents an experimental and theoretical analysis of a 6-row horizontal microfin Heat Pipe Finned Heat Exchanger (HPFHE) used for energy recovery purposes inside an air conditioning unit. The experimental campaign investigated both the summer and the winter conditions for European countries by varying the operating conditions at the inlet of the HPFHE. New experimental tests are presented for the identification of low – global warming potential refrigerants, environmental friendly substitutes of the more traditional HFC134a. The results showed the interesting heat transfer capabilities of HFC152a as an alternative HPFHE working fluid. A simulation model previously developed by present authors was validated against the new experimental data collected and then used to simulate the thermal performance of the HPFHE under different operating test conditions, in order to assess the potentiality of seasonal energy savings with HFC152a.     

热管及其换热器在烟气余热回收中的应用

简要介绍了热管技术,并分析了其传热机理。热管换热器具有许多独特的优点,已经获得了广泛的工业应用,应用主要集中在中低温余热资源回收利用方面,应完善高温热管,以拓宽热管换热器在高温余热资源中的应用。     

椭圆热管传热与阻力性能分析

为解决圆形热管换热器换热效率低、积灰和腐蚀严重的问题,应用椭圆管束进行了改造。通过实例分析计算,效果显著：在相同折合速度下,椭圆热管换热器的传热系数明显高于圆形热管换热器;在相同总压降下,椭圆热管换热器的传热系数也比圆形热管换热器高得多;无论在烟气侧,还是在空气侧,同一速度下椭圆热管换热器的流阻损失明显下降．下降幅度达80％左右。提出了进一步改善积灰和腐蚀的措施。     

具有热阻_热漏和内不可逆性的联合热机性能

建立一类存在热阻、热漏和内不可逆性的定常态流联合热机循环模型,并研究其性能优化,导出功率、效率优化关系,最大功率及其相应效率,和最大效率及其相应功率。     

从节能蓝海的独孤求败到行业隐形冠军——记亚太电效系统(珠海)有限公司十年发展历程

我国电力供应短缺催生了全民节电意识的觉醒,节电业迅速兴起成为近年来我国经济领域不容忽视的新生力量.但我国节电行业也正面临着从技术到市场全面的竞争升级问题.     

Fluid Flow Distribution and Heat Transfer in Plate-Fin Heat Exchangers

Single-phase and two-phase flow distribution in plate-fin heat exchangers and the influence of nonuniform fluid flow distribution on the thermal performance of such heat exchangers were experimentally investigated. The experimental results show that flow maldistribution can be a serious problem in plate-fin heat exchangers because of nonoptimized header configurations. The uneven distribution of two-phase flow in plate-fin heat exchangers is more pronounced than that of single-phase flow. It is shown that the uneven distributions result in a significant deterioration of the heat transfer performance. The relationship between the flow maldistribution characteristics and the resulting loss in heat exchanger effectiveness has been studied in this work. Certain improved header configurations with perforated plates were proposed in order to solve the maldistribution problem. It was found that the new header configurations could effectively improve the thermal performance of plate-fin heat exchangers. By changing the header configuration, the degree of flow and temperature nonuniformity in the plate-fin heat exchanger was reduced to 16.8% and 74.8%, respectively, under the main test condition.     

Heat Transfer and Exergy Analysis of a Spiral Heat Exchanger

The heat transfer effectiveness of a countercurrent spiral heat exchanger is expressed as a function of number of transfer units, ratio of flow capacity rates, number of spiral turns, and dimensionless start-point angle of spiral (dimensionless angular angle of the start point of a spiral curve constituting the solid wall of the heat exchanger). The heat transfer effectiveness is weakly dependent on the dimensionless start-point angle of spiral, but moderately increases with the number of spiral turns. As the number of spiral turns is larger than 20, the heat transfer effectiveness of the spiral heat exchanger approaches that of a counterflow heat exchanger. The heat transfer effectiveness of the spiral heat exchanger has a maximum. The optimum number of transfer units at the maximum heat transfer effectiveness increases with the number of spiral turns, whereas it increases with a decrease of the ratio of flow capacity rates. In the second-law analysis, an optimum hot flow-to-cold flow capacity-rate ratio is found. For obtaining a large net recovered exergy rate, the spiral heat exchanger needs to possess a large number of transfer units (greater than 2.0) and operate at a near balanced-flow condition. In addition, a small consumed mechanical power is demanded.