Transient Response of a Serpentine Finned-Tube Cross-Flow Heat Exchanger to a Step Change in Inlet Temperature

Abstract

An analysis of the thermal response of a finned-tube, liquid-to-gas cross-flow heat exchanger due to a step change in the liquid inlet temperature is performed. Closed-form solutions for the liquid and gas temperatures as functions of space and time are obtained via the Laplace transform technique for both small and large arguments of the modified Bessel function of the first kind. Using four physically important dimensionless parameters, the response of the liquid and average gas outlet temperatures are studied and presented in the time domain. The analysts is extended to a single-row serpentine coil geometry by accounting for U-tube bends. Using a typical heat exchanger geometry, the effects of the tube bends are shown to be significant. Relevant applications include automotive and HVAC heat exchangers and systems.     

Mathematical Model for Predicting the Heat Transfer Characteristics of a Helical-Coiled,Crimped, Spiral,Finned-Tube Heat Exchanger

This paper is a continuation of the authors’ previous work. Theoretical and experimental studies of the heat transfer characteristics of a helical-coiled, crimped, spiral, finned-tube heat exchanger in dry surface conditions are presented. The test section is a helical-coiled, finned-tube heat exchanger. The coil unit is composed of four concentric helical-coiled tubes of different diameters. All tubes are constructed by bending straight copper tube into seven layers of helical coil. Aluminum crimped spiral fins, with an outer diameter of 28.25 mm and a thickness of 0.5 mm, are connected around the tube. Hot water is used as a working fluid for the tube side, while ambient air is used for the shell side. The test runs are done at air mass flow rates ranging between 0.04 and 0.13 kg/s. The water mass flow rates are between 0.2 and 0.4 kg/s. The water temperatures are between 40 and 50°C. A mathematical model is developed and the simulation results show reasonable agreement with the experimental data.     

常减压换热网络的优化改进和优化控制

对结构已定或正在运行的常减压换热网络,在操作夹点附近设置旁路,通过对旁路流量的优化控制,使换热网络在某些过程物流的流量、温度发生变化时,换热网络的换热仍能满足工艺上的换热要求,公用工程能量消耗在现有的换热设备的基础上接近最小公用工程消耗量。     

应用遗传算法优化设计紧凑式换热器

应用遗传算法对锯齿型板翅式换热器的结构进行了优化设计.以预定的传热量、两侧压降、体积等设计要求为适应度函数,通过对设计变量构成的种群个体进行适应度评估以及选择、交叉、变异等遗传操作,得到符合设计约束的换热器最优结构参数(如翅高、翅长、间距,以及长、宽、高等).此外,对10次计算得到的设计参数进行了统计分析.结果表明:相关结构参数的不确定度很小,应用遗传算法可以快速方便地对紧凑式换热器的几何结构参数作出符合设计要求的选择.     

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。     

Performance Optimization of Co-current Gas-to-Gas Micro Heat Exchanger Considering Radiation

Optimization of a parallel flow gas-to-gas tubular micro heat exchanger with hot core and cold annulus fluid is numerically analyzed, considering the beneficial role of surface radiation. Operating and geometric parameters are varied for fixed overall mass flow rate and temperature of cold core fluid, to study the effects on the following performance parameters: heat transferred to annulus fluid, logarithmic mean temperature difference, effectiveness, and volumetric heat transfer coefficient. The micro heat exchanger is optimized for high heat transfer to annulus fluid and volumetric heat transfer coefficient, for different operating and geometric conditions. Optimization for high volumetric heat transfer coefficient maximizes the micro heat exchanger effectiveness, heat transferred and improves logarithmic mean temperature difference.     

换热器网络优化研究进展

本文阐述了国内外换热器网络研究的最新进展,详细比较了研究换热器网络的两种不同的方法,还对换热器网络的动态特性研究做了简要介绍。作者认为：把窄点理论和混合整数非线性优化应用在其它动力系统如：制冷、空调、热泵、热电联产等,并对这些系统的节能也有一定的帮助。最后指出了换热器网络研究的发展方向。     

应用遗传算法优化设计管壳式换热器

两级管壳式换热器优化设计是一个有约束非线性规划问题,目前还没有方法能够保证寻找到该问题的全局最优解.传统的转动坐标轴直接搜索可行方向法(DSFD方法)可以获得该问题的局部最优解,但该最优解对初始点的依赖性很大,需要多次尝试寻找"全局"最优解.应用遗传算法对两级管壳式换热器进行优化设计,优化结果与DSFD方法优化结果对比表明,遗传算法更易于寻找"全局"最优解,提高优化过程的效率.     

Optimization Design of Refuse-Incinerating Power Plant With Air-Cooled Heat Exchanger

As a newly developed industry, refuse incinerating power plants with air-cooled heat exchanger (ACHE) systems benefit both environment and energy savings. Since the exhaust steam of power plant is cooled in the atmosphere, the pressure of the exhaust steam fluctuates with variation of air temperature. As a result, the generated electric power of a power plant with an ACHE system is considerably influenced by meteorological conditions in the region where this type of power plant is built. The present work studies three different designs of a refuse-incinerating power plant with ACHE for a real project. Under the local meteorological conditions, the overall flow and temperature fields of the air in the whole power plant, especially around the air-cooled heat exchanger, are numerically investigated with the commercial computational fluid dynamics (CFD) code FLUENT and the feasibility of the project is then evaluated. In addition, a comparison of these three designs is also provided, including the performance of the exchangers and the fans, the collocation of the exhaust gas pipe, and the costs of the ACHE system.     

基于粒子群优化算法的板式换热器优化设计

从板式换热器的结构出发,通过对板式换热器中的流程组合数和冷热流体流速优化分析,得出板式换热器最优结构参数的数学模型,并且结合实例,运用粒子群算法对其进行求解,最终得到更为合适的流程组合数和流体流速,使设计的板式换热器更经济,效率更高。     

Condensing Heat Exchanger

The paper shows a method of designing a heat exchanger recovering heat from the condensation of water vapour contained in flue gases. A heat exchanger condenses water vapour and SO2 （sulphur dioxide） in the presence of inert gases （CO2, CO, N2, O2） contained in flue gases. A mathematical model and a sample design of a heat exchanger were presented. The heat exchange is capable of recovering from a dozen or so to several dozen percent of heat from flue gases escaping into the atmosphere. A second advantage of the heat exchanger is the possibility to reduce the emissions of SO2 considerably. Depending on the parameters, it can be even a sevenfold reduction in the emissions. The main mathematical tool used for designing the condensing heat exchanger is the Colburn-Hougen method. The authors omitted that part of the method which requires iterative calculations. The Mollier diagram was used instead.     

冰级船板式换热器流动传热分析及结构优化

采用数值模拟方法研究换热板结构对冰晶两相流换热机制和流动特性的影响。研究结果表明:波纹倾角β=60°、波纹深度h=4 mm、波纹间距λ=12 mm为所研究的换热器适用于海水-冰晶两相流的最佳值。利用宽通道对其进行结构优化设计,并采用相关试验数据验证。结果表明:宽通道间距为16 mm时,换热强度最大,流动阻力较小,可有效防止冰晶堵塞板内沟槽,且此时的换热效果和流动特性最佳,适合极地工况下冰晶两相流流动换热。     

Prediction and Measurement of Apparent Heat Transfer Coefficient by Condensation in Finned-Tube Heat Exchangers

The apparent heat transfer coefficient by condensation in finned-tube heat exchangers is determined experimentally and numerically in this paper. The film method is used to predict the partial or total condensation of the water vapor contained in the humid air over the smooth or finned tube-heat recuperators. Based on this method, a computer code is developed here. The mathematical formulation is validated by our experimental results, using tube bundles in staggered and aligned arrangements. The determination of the fin portion, which functions in wet regime, is carried out by the prediction of thermal field over a circular fin. The condensation of the water vapor contained in the humid air is done preferentially with the last rows of the heat exchanger. The heat flux is predicted in a range of 20% and 5% in wet and dry regimes, respectively. The apparent heat transfer coefficient by condensation can exceed 10 times the value of the air-side heat transfer coefficient in dry regime.     

基于耗散理论的螺旋板式换热器多目标优化设计

在理论的基础上,分析了螺旋板式换热器运行过程中,传热和压降引起的耗散数与冷流体出口温度和冷、热流体的流速的关系。利用多目标遗传算法,以传热和压降引起的耗散数最小为目标,对流体出口温度和冷、热流体的流速的组合进行了优化。给出了优化实例,根据优化解对优化效果进行了评价,指出采用优化解对换热器进行设计,可以减少流体流动的压降减少水泵用能,而且可以减少传热单元数、降低设备的投资和运行费用,提高换热器的经济性。     

Thermal-Hydraulic-Structural Analysis and Design Optimization for Micron-Sized Printed Circuit Heat Exchanger

The Printed Circuit Heat Exchanger(PCHE) is one of the most promising heat exchangers for Synergetic Air-breathing and Rocket Engine(SABRE). To reduce pressure drop and improve compactness, the micron-sized PCHE made up of rectangular channels of tens of microns in size, is used in SABRE. In present work, we focus on thermal-hydraulic-structural characteristics of micron-sized PCHE by conducting three-dimensional(3-D) numerical simulation. Helium and hydrogen are employed as the working fluids and the Stainless Steel 316(SS316) as the solid substrate. The thermal-hydraulic performance of the micron-sized PCHE is discussed by using the commercial Computational Fluid Dynamics(CFD) software of Fluent. ANSYSMechanical is also employed to simulate stress field of representative PCHE channels. The mechanical stress induced by pressure loading and the thermal stress induced by temperature gradient are found to be equally important sources of stress. To improve comprehensive performances of micron-sized PCHE, two types of channel arrangements and different channel aspect ratios are studied. The double banking is of higher thermal-hydraulic performance compared to the single banking while the stress performance is identical for the two modes. Meanwhile, the effect of channel aspect ratio is investigated by comparing thermal-hydraulic characteristics and structural stress of the model. The rectangular channel with w/h=2 achieves the most balanced stress characteristic and higher thermal-hydraulic performance.     

一种割裂耦合关系的换热网络优化方法

在用强制进化随机游走算法优化换热网络时,优化后期由于换热单元之间存在耦合关系,换热网络结构已基本稳定,难以新增加或者消去换热单元,因此结构变异较为缓慢。为了促进结构变异,提出了一种割裂结构耦合关系的高效优化方法。该方法基于耦合关系随机消去换热单元,使得匹配已稳定的冷热流股重新获得一定的换热潜能,从而具有匹配新换热单元的潜力,快速寻找到更多匹配方式。通过20SP和15SP算例进行有效性验证,分别取得1 395 461 $和5 115 557 $的年综合费用,表明割裂结构耦合关系的方法能进一步促进结构进化,增强算法的全局搜索能力。     

A New Nodes-Based Model for Optimization of Heat Exchanger Network Synthesis

Searching the global optimal value in heat exchanger network synthesis(HENS) becomes more difficult along with the increasing scale of cases. In structural optimization model, such as stage-wise superstructure, solution domain can be enlarged by adding the stages of network, which would involve multiple integer and continuous variables in optimization and result in a decreasing computational efficiency. Thus, a new nodes-based model with stream splits is proposed, which can promote the quality of result and decrease time consumption at the same time. The characteristic of this model is that it changes the matching mode of heat exchangers by setting the number of nodes on streams to quantify the positions of heat exchangers. The proposed nodes-based model has more flexibility in generating and eliminating the heat exchangers and strong ductility in exploring the solution domain. The random walk with compulsive evolution is modified for enhancing its searching ability and applying modified random walk algorithm with compulsive evolution(RWCE) into the new proposed model. The obtained results of Case 1, Case 2 and Case 3 are superior to those reported in the literature, which decreases 106 USD·a~(–1), 1253 USD·a~(–1), 23 444 USD·a~(–1), respectively, verifying the robust effectiveness of this new model in solving HENS problem.     

The RODbaffle Heat Exchanger

The RODbaffle exchanger offers a solution to the vexing problem of tube failures in shell-and-tube exchangers resulting from tube vibration. Additional benefits are good heat transfer rates, low pressure drop, and lower fouling rates. The ratio of heat transfer rate to pressure drop can be more than double that of the conventional plate-type baffle in a comparable application.     

炼油厂脱前原油换热网络的设备优化

利用夹点技术对某炼油厂脱前原油换热网络进行了改造。与原换热网络相比，换热网络的换热设备数目减少了4个，使设备数达到最优化，从而节省了设备的投资。     

改进的遗传算法在换热网络综合优化中的应用研究

通过对遗传算法和模拟退火算法进行深入研究,建立了改进的遗传算法--遗传模拟退火算法,并通过换热网络综合优化的实例进行计算验证,结果表明,该算法切实可行.