多股流换热器的数学建模与精确数学控制

本文以平行流多股流换热器为研究对象,考虑了多股流换热器在换热过程中存在的多种影响因素,根据其复杂的传热机理建立了数学模型,并通过数值计算,获得了准确的结果.该模型的建立为多股流换热器的精确数学控制奠定了理论基础,同时为多股流换热器的性能分析,结构优化及运行优化提供了理论依据.     

多股流板翅式换热器温度交叉的数值分析

以平行多股流板翅式换热器为研究对象,给出了考虑翅片旁通作用的多股流板翅式换热器流体和翅片的能量方程。在改变多股流板翅式换热器各通道的流体参数、流动方式及换热器的结构参数等情况下,对能量方程进行数值求解,获得了各通道的流体温度分布情况及相邻通道的流体温度差,并分析了流体参数、流动方式和结构参数的变化对相邻通道流体温度交叉的影响。     

换热器动态过程中的定常输出

为了使换热器在动态过程中保持目标出口参数的恒定，从整体系统考虑建立了换热器动态过程的数学模型，采用I．aplace变换及其逆变换推导了换热器出口温度响应的分析解，并在一个或者多个进口参数阶跃变化的情况下，推导了两股流换热器和多股流换热器的调节方法．结果表明：在动态过程中，通过对换热器进口参数的调节可以精确地控制换热器出口参数，保证换热器的稳定和安全运行．     

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。     

自组织能力对多股流换热器运行和控制影响的研究

在考虑多场（如温度场，温差场和速度场等）相互作用和相互影响的基础上，对多股流换热器从一个稳态过渡到另一个稳态的自组织能力进行了分析。目标流体出口温度的响应时间和敏感性，在温度控制系统中是很重要的两个参数，因此本文分析了评估上述指标的多股流换热器自组织能力及其对控制和运行的影响。     

有机工质低温余热发电系统多目标优化设计

针对现有有机朗肯循环单目标优化设计的局限性,从热力性、经济性等多方面对有机工质低温余热发电系统进行多目标优化设计.以系统效率最大和总投资费用最小为目标函数,选取透平进口温度、透平进口压力、余热锅炉节点温差、接近点温差和冷凝器端差等5个关键热力参数作为决策变量,利用非支配解排序遗传算法(NSGA-II)分别对采用R123、R245fa和异丁烷的有机工质余热发电系统进行多目标优化,获得不同工质的多目标优化的最优解集(Pareto最优前沿),并采用理想点辅助法从最优解集中选择出最优解及相应的系统最佳热力参数组合.结果表明:在给定余热条件下,从热力性能和经济性两方面考虑,R245fa是最优的有机工质,从多目标优化的最优解集中选择出的最佳效率为10.37%,最小总投资费用为455.84万元.     

多股流换热器自动最优控制过程的模拟

为了模拟多股流换热器自动控制过程，应用特别适用于“多输入．多输出”系统的状态空间方法。该方法的调节依据是状态参数的反馈，状态参数不仅包括输出参数，还包括输出参数变化的速度和加速度及高阶导数等。利用实验所得的动态特性，导出了多股流换热器的状态方程和输出方程，并用动态规划方法对其自动最优控制过程进行了模拟。给出了一个四股流换热器自动最优控制过程模拟实例。结果表明：状态空间方法和动态规划方法可有效地应用于多股流换热器的最优反馈控制设计。图4表2参8     

管翅式换热器遗传算法优化

管翅式换热器作为一种高效的换热设备,提升其换热效率和降低投资成本显得至关重要。通过单目标遗传算法(GA)和多目标非支配排序遗传算法(NSGA-Ⅱ)对管翅式换热器进行优化设计,设置翅片高度、翅片间距、管长、横向管数和纵向管数5个自变量的合理设计范围,单目标优化选用换热器效率、压降熵产和最大收益3个目标函数,根据热力学第一、二定律以及经济分析进行目标优化,比较三者的优化结果从而得到最佳优化目标函数,以及在特定运行条件下换热器的最佳设计方案,其中运行净利润能直接反应出换热器效益;多目标采用单目标优化中换热器传热效率和总投入为目标函数,进一步验证优化的合理性和经济性。     

管壳式换热器折流部件优化研究进展

为了提高管壳式换热器的能源利用率,换热器强化传热的研究得到广泛关注。本文从强化传热原理、结构改进和设计优化等三方面对换热器折流部件的优化改进研究进行了分析和总结。其中,强化传热原理主要包括不同折流板通过改变流场的特性影响换热器性能;结构改进包括分段挡板、折流孔板和螺旋挡板的优化进展以及与单弓挡板的对比研究;设计优化包括利用各种新型算法对换热器结构参数的优化和成本的控制。针对管壳式换热器折流部件的强化传热问题,提出了非连续螺旋挡板的研究和结合多目标优化设计的结构改进是未来的重点研究方向。     

多股流换热器动态过程场协同分析

建立了多股流板翅式换热器动态数学模型,通过换热器入口温度及流量阶跃的改变,模拟过渡过程中温度场的动态响应,利用温差场均匀性因子对多股流换热器过渡过程动态特性进行了评价,通过分析内部温度场与速度场的协同关系,揭示温差场在动态过程中的变化特征.将温差场均匀性因子与过渡时间结合,建立了自组织能力系数,并对多股流换热器控制品质进行了分析.多股流换热器在流量阶跃时,温差场均匀性因子平缓迁移,而温度阶跃时变化剧烈且存有极值.多股流换热器自组织系数越大,越易达到新的热平衡.     

Inverse problem and variation method to optimize cascade heat exchange network in central heating system

Urban heating in northern China accounts for 40％ of total building energy usage.In central heating systems,heat is often transfened from heat source to users by the heat network where several heat exchangers arc installed at heat source,substations and terminals respectively.For given overall heating capacity and heat source temperarure,increasing the terminal fluid temperature is an effective way to improve the thermal performance of such cascade heat exchange network for energy saving.In this paper,the mathematical optimization model of the cascade heat exchange network with three-stage heat exchangers in series is established.Aim at maximizing the cold fluid temperature for given hot fluid temperature and overall heating capacity,the optimal heat exchange area distribution and the medium fluids' flow rates are determined through inverse problem and variation method.The preliminary results show that the heat exchange areas should be distributed equally for each heat exchanger.It also indicates that in order to improve the thernmal performance of the whole system,more heat exchange areas should be allocated to the heat exchanger where flow rate difference between two fluids is relatively small.This work is important for guiding the optimization design of practical cascade heating systems.     

传热传质过程和设备的有限时间热力学优化

1前言能源的短缺与高效利用问题是当代世界各国面临的重大社会问题之一。随着世界人口和经济的迅速增长,能源的消耗急剧地增加,并导致能源的严重短缺。因此,研究充分、高效利用现有能源的方式成为我们目前的重要任务。蒸馏作为全球范围内耗能量最大的工业,引起了很多工程界和物     

蚁群算法在换热网络优化中的应用

提出将蚁群算法应用于换热网络优化中,按照相等的能量份额将各股热流体分解成能量集合,热流体能量通过换热器在与冷流体换热的过程中得到分配,换热器单元面积得到相应地调整．能量分配过程中换热网络得到优化,从而使年综合费用减少的换热器面积不断积累,最终形成了一个最优的换热网络结构．通过具体算例验证了该方法的可行性和有效性,最终优化的结果证明该方法具有较强的全局搜索能力,能够应用于复杂换热网络的优化问题中．     

蜡油加氢装置换热网络分析与优化

洛阳石化蜡油加氢装置由反应、分馏、富氢气体脱硫、热回收和产汽系统以及装置公用工程部分等组成,设计年加工能力220×104t/a,以减压蜡油、焦化蜡油和脱沥青混合油为原料,采用抚顺石油化工研究院开发的FFHT蜡油加氢处理工艺技术,催化剂采用FF-18型,主要生产低硫含量的精制蜡油,同时副产少量石脑油和柴油,富氢气体经脱硫后送至制氢装置作原料.利用换热网络优化软件PINCH2.0,对蜡油加氢装置换热网络进行模拟,得出现行工艺条件下换热网络最小冷却公用工程和最小加热公用工程用量,提出以现行换热网络的操作工艺为基础,停运分馏塔进料加热炉,提高反应进料加热炉热负荷,在不增加装置换热网络换热器换热面积前提下,充分利用装置现有换热器换热面积余量,增大换热器的换热负荷.实施换热网络优化方案后,降低蜡油加氢装置耗能105.5kg标油/h,年运行时间以8400h计算,年实现节能886.2t标油,标油价格按照3600元/t计算,年实现经济效益319万元;装置进料量按照295t/h计算,则降低装置综合能耗0.358kg标油/t原料.     

Finite time thermodynamics study and exergetic analysis of ammonia–water absorption systems

This paper presents an optimization study of a single stage absorption machine operating with an ammonia–water mixture under steady state conditions. The power in the evaporator, the temperatures of the external fluids entering the four external heat exchangers as well as the effectiveness of these heat exchangers and the efficiency of the pump are assumed fixed. The results include the minimum value of the total thermal conductance UA_tot as well as the corresponding mean internal temperatures, overall irreversibility and exergetic efficiency for a range of values of the coefficient of performance (COP). They show the existence of three optimum values of the COP: the first minimises UA_tot, the second minimises the overall irreversibility and the third maximises the exergetic efficiency. They also show that these three COP values are lower than the maximum COP which corresponds to the convergence of the internal and external temperatures towards a common value. The influence of various parameters on the minimum thermal conductance of the heat exchangers and on the corresponding exergy efficiency has also been evaluated. From an exergetic viewpoint it is interesting to reduce the temperature at the desorber and at the evaporator and to raise the values of that parameter at the condenser and the absorber. However these changes must be accompanied by an important increase in the total UA if it is desired to conserve a constant COP. The internal heat exchangers between the working fluid and the solution improve both the overall exergy efficiency and the coefficient of performance of the absorption apparatus.     

Effect of fluid property variations on the effectiveness of a cryogenic heat exchanger

Cryogenic heat exchangers are commonly used for industrial processes, such as air separation and natural gas liquefaction. Generally, the performance of heat exchangers is analyzed adopting constant properties for the working fluid. But, in cryogenic heat exchangers, fluids reach their critical states with significant variations in their properties. The current work is based on the effect of fluid property variations in the performance analysis of a two-fluid countercurrent cryogenic heat exchanger subject to ambient heat in a leak. Finite element method–subdomain method is used to conduct the performance analysis. The effect of fluid property variations is analyzed considering effectiveness, ∈, as the performance parameter. The percentage deviation in the effectiveness value on considering fluid property variation is determined. The relationship between effectiveness ∈ and the number of transfer units (NTUs) is obtained by plotting the ∈-NTU curve by varying the mass flow rate of the fluid flow. A maximum deviation of 16.108% in the effectiveness and 58.734% in the hot fluid exit temperature is obtained by considering fluid property variation.     

Studies on pumping power in terms of pressure drop and heat transfer characteristics of compact plate-fin heat exchangers—A review

Renewable energy sources like solar energy, wind energy, etc. are profusely available without any limitation. Heat exchanger is a device to transfer the energy from one fluid to other fluid for many applications in buildings, industries and automotives. The optimum design of heat exchanger for minimum pumping power (i.e., minimum pressure drop) and efficient heat transfer is a great challenge in terms of energy savings point of view. This review focuses on the research and developments of compact offset and wavy plate-fin heat exchangers. The review is summarized under three major sections. They are offset fin characteristics, wavy fin characteristics and non-uniformity of the inlet fluid flow. The various research aspects relating to internal single phase flow studied in offset and wavy fins by the researchers are compared and summarized. Further, the works done on the non-uniformity of this fluid flow at the inlet of the compact heat exchangers are addressed and the methods available to minimize these effects are compared.     

Effects of Distributor Configuration on Flow Maldistribution in Plate-Fin Heat Exchangers

In this paper, an original concept of a design that adds a complementary fluid cavity in the distributor is presented. The experimental investigation of the effects of distributor configuration parameter on the fluid flow maldistribution in the plate-fin heat exchanger is completed. The correlation of the dimensionless flow maldistribution parameter and the Reynolds number is obtained under different distributor configuration parameters. The experimental studies prove that the performance of flow distribution in heat exchangers can be effectively improved by the optimum design of the distributor's configuration parameter. The ratio of the maximum velocity and the minimum velocity in the channels of the plate-fin heat exchanger can drop from 2.57–3.66 to 2.08–2.81 for various Reynolds numbers. The conclusions are of great significance on the optimum structure design of the plate-fin heat exchangers and can effectively improve the performance of the heat exchangers.     

Cooling load density characteristics of an endoreversible variable‐temperature heat reservoir air refrigerator

The performance optimization of an endoreversible air refrigerator with variable‐temperature heat reservoirs is carried out by taking the cooling load density, i.e. the ratio of cooling load density to the maximum specific volume in the cycle, as the optimization objective in this paper. The analytical relations of cooling load, cooling load density and coefficient of performance are derived with the heat resistance losses in the hot‐ and cold‐side heat exchangers. The maximum cooling load density optimization is performed by searching the optimum pressure ratio of the compressor, the optimum distribution of heat conductance of the hot‐ and cold‐side heat exchangers for the fixed total heat exchanger inventory, and the heat capacity rate matching between the working fluid and the heat reservoirs. The influences of some design parameters, including the heat capacitance rate of the working fluid, the inlet temperature ratio of heat reservoirs and the total heat exchanger inventory on the maximum cooling load density, the optimum heat conductance distribution, the optimum pressure ratio and the heat capacity rate matching between the working fluid and the heat reservoirs are provided by numerical examples. The refrigeration plant design with optimization leads to a smaller size including the compressor, expander and the hot‐ and cold‐side heat exchangers. Copyright © 2002 John Wiley & Sons, Ltd.     

An analysis of the heat transfer rate and efficiency of TE (thermoelectric) cooling systems

The heat transfer rate and efficiency of TE (thermoelectric) cooling systems were investigated. The emphasis of the present study is focused on the use of large-scale TE refrigerators for air conditioning applications. A one-dimensional heat transfer analysis was performed to determine the cooling power and electricity consumption of the TE elements. The constant-property results are in good agreement with the variable-property solutions for TE materials and temperatures typical for air conditioning applications. A heat transfer analysis was also carried out for TE refrigerators equipped with a heat exchanger. Both parallel- and counter-flow heat exchangers were considered. Fluid temperature variations of these two flow arrangements were found to be quite different, but the efficiencies and cold fluid exit temperatures differed only slightly when a uniform current was used for all TE elements. If the length of the heat exchanger exceeds an optimal value, the cold fluid temperature begins to rise and the efficiency drops for both parallel- and counter-flow arrangements. The second law of thermodynamics was applied to the optimization of TE refrigerators operating between two constant-temperature reservoirs and between two flowing fluids. It was found that if a TE cooling system incorporates a heat exchanger, a nonuniform current distribution should be used to achieve the maximum efficiency and the lowest cold fluid temperature. The optimization results for TE refrigerators operating between two constant-temperature reservoirs are not applicable to TE cooling systems between two flowing fluids. The most energy-efficient current distribution for the parallel-flow arrangement is the one which increase in the direction of the cold fluid.