考虑污垢时换热器热力学性能的评价

在分析污垢对换热器传热性能影响的基础上,在考虑污垢时采用Ｙｏｎｇ损率这一指标对换热器的热力学性能进行了评价,讨论了传热数和冷热流体热容量率比对其性能的影响,并把结果与不考虑污垢时的情况进行了比较,得到了一些有益的结论。     

基于周期流模型的螺旋板换热器流动换热特性数值模拟

为了研究螺旋板换热器结构对其性能的影响,为换热器设计提供指导,采用周期流模型对螺旋板换热器流动传热性能进行数值模拟,结果表明:周期流模型适用于螺旋板换热器的流动传热问题;定距柱通过强化对流传热以及冲击换热提高换热器的传热性能;定距柱间距增大或板间距减小会降低换热器传热性能,减小压损;减小流向间距或板间距降低综合性能;横向间距、板间距增大或流向间距减小可提高换热器经济性;换热器传热和压损对横向间距的变化最敏感,而板间距对综合性能影响最大;流向间距对换热器性能影响不明显。     

热管换热器的计算机辅助设计

热管是一种新型的传热元件,由热管组成的热管换热器具有传热效率高、结构紧凑、流体阻损小、有利于控制露点腐蚀等优点。这种换热器在利用热能、回收废热、节约原料、降低成本、以及一些特殊用途上(如散热)取得了显著的经济效益。随着应用市场的逐步打开,市场竞争也日趋激烈。为了适应市场需求、更为了能在时间上和技术上占领竞争的优势,针对     

导热油在单叶型空心桨叶换热器中的层流换热特性

采用数值模拟方法计算了导热油在单叶型空心桨叶换热器中的层流换热特性,并与实心桨叶换热器进行了比较。计算结果表明,空心桨叶换热器的导热油压降、传热率、总传热系数和总熵产率均显著高于实心桨叶换热器;对于空心桨叶换热器,流动孔直径和数量对导热油压降影响较大,但对传热率影响有限;在总熵产率组成,传热熵产率占主要部分。物料换热系数和总传热系数组合结果可用于桨叶换热器设计。     

一种监测换热器污垢的新方法

在考虑污垢对换热器传热性能影响的基础上,提出换热器当量总污垢热阻和污垢函数的概念,并给出换热器当量总污垢热阻的监测方法,讨论了换热流型、传热有效度ε和冷热流体热容量率比R对换热器当量总污垢热阻的影响。     

土壤蓄冷与释冷过程的能量分析

在对土壤蓄冷系统冷量损失过程分析的基础上,提出了地下埋管换热器垫层冷量损失与温差传热冷量损失的概念,并建立了垫层冷量损失和温差传热冷量损失的计算模型;为衡量系统在运行期间地下埋管换热器管束系统的运行效率,建立了埋管换热器管束系统的平均释冷率模型。通过理论研究与模拟计算,分析了土壤初始温度、埋管间距及管束结构对土壤蓄冷系统冷量损失的影响,指出了土壤蓄冷系统冷量损失随土壤初始温度及埋管间距之间的变化规律,为土壤蓄冷系统地下埋管换热器的优化设计提供理论依据。     

熔盐-气体换热器传热性能的实验研究

利用搭建的熔盐换热器传热性能实验系统,对一台熔盐-气体换热器试件进行硝酸盐-空气、硝酸盐-氦气两组传热特性实验,并采用修正的威尔逊法分离相应的管程和壳程对流换热系数。实验分析表明:实验系统能够可靠地完成熔盐-气体换热器换热性能的测试实验;熔盐-气体换热器的传热性能受气侧传热能力的影响,采用传热能力强的气体介质和强化传热措施可提高熔盐-气体换热器的性能;Gnielinski公式同样适用于熔盐在光滑圆管内过渡和湍流流动传热的计算。     

湍流_传递方程及其应用

导出了湍流火用传递方程组 ,依此研究了壁面常热流对流换热管的火用传递 ,计算了由于粘性耗散、径向和轴向导热引起的火用损率分布。通过对单位体积总火用损率的计算表明 ,单位体积总火用损率是换热管几何参数和边界条件的多元函数 ,对于给定的几何参数 ,存在使单位体积总火用损率最小的边界条件 ,反之亦然。该结论对优化设计换热器及对给定边界条件的换热器优化选取具有一定的指导意义。     

基于火积理论的螺旋折流板换热器的优化结构分析

为了比较平面螺旋折流板换热器和折面螺旋折流板换热器的传热和阻力性能,应用了换热器常用评价标准PEC准则和火积理论对两种换热器实验结果进行了分析,同时采用火积耗散极值原理对两种换热器的传热火积耗散率、阻力火积耗散率以及总火积耗散率进行了对比。结果表明:火积耗散理论分析换热器性能的结果与传统换热器评价标准PEC准则相符,说明了火积耗散理论的可靠性;折面螺旋折流板换热器的综合性能得到了有效的改进,火积耗散率也均优于原始结构,表明折面螺旋折流板换热器的性能得到较大改善;两种换热器传热火积耗散率值要远远大于阻力火积耗散率,约为阻力火积耗散率的一千余倍,说明传热损失为换热器的主要不可逆损失。     

湍流Ｙou传递方程及其应用

导出了湍流Ｙou传递方程 ，依此研究了壁面常热流以对流换热管的Ｙou传递，计算了由于粘性耗散、径向和轴同导热引起的Ｙou损率分布。通过对单体积总Ｙou损率的计算表明，单位体积总Ｙou损率是抑热管几何参数和边界条件的多元函数，对于给定的几何参数，存在使单位体积总Ｙou损率最小的边界条件，反之亦然。该结论对优化设计换热器及对给定边界条件的换热器优化选取具有一定的指导意义。     

A Correction Factor-Based General Thermal Resistance Formula for Heat Exchanger Design and Performance Analysis

Methods for the analysis of heat exchangers with various flow arrangements modeling, design, and performance are essential for heat transfer system modeling and its integration with other energy system models. This paper proposes the use of the linear-transfer law for the heat exchanger design and performance analysis as a function of the thermal resistance related to the ratio of a linear temperature difference to the total heat transfer rate. Additionally, we derived a correction factor that represents the influence of the flow arrangement on the heat transfer performance by the effective thermal conductance, as a function of correction factor, heat transfer coefficient, and surface area. Based on the effective thermal conductance, we propose the hot-end NTU and cold-end NTU for deriving a standardized and general thermal resistance formula for different types of heat exchangers by the combination of the correction factor with linear-transfer law. Moreover, for parallel-flow, cross-flow, and 1-2 Tubular Exchanger Manufacturers Association(TEMA) E shell-and-tube heat exchangers, we derived and obtained alternative correction factor expressions without introducing any temperatures. Two cases about heat exchanger design and performance analysis show that the calculation processes using the correction factor-based general thermal resistance are straightforward without any iteration and the calculation results are accurate. Finally, the experimental validation shows that the general thermal resistance formula is appropriate for analyzing the heat transfer performance. That is, the correction factor-based general thermal resistance formula provides a standardized model for heat exchanger analysis and heat transfer/integrated energy system modeling using the heat current method.     

两种用于HCPV/T的水冷换热器传热特性的对比实验研究

本文对两种适用于高倍聚光发电供热（HCPV/T）系统的多槽道和微通道水冷换热器进行了实验研究。利用模拟热源模拟了HCPV/T系统中光伏电池工作时的热流密度,分别研究了流量、壁面温度和输入电压对两种换热器传热特性的影响,并利用传热学理论对两种换热器的特点进行分析,获得了两种换热器努赛尔数Nu与雷诺数Re的拟合经验公式。实验结果表明,微通道换热器在低流量下有较强的换热能力,但在高流量下,换热能力无法随流量增大继续提高;多槽道换热器在低流量下换热能力不佳,但在高流量下仍可随流量增大继续提高。     

A General Matrix Approach to Model Steady-State Performance of Cross-Flow Heat Exchangers

A steady-state performance model of multirow multipass cross-flow tubular heat exchangers is developed. The proposed matrix approach uses the concepts of local effectiveness, energy balance, and number of transfer units (NTU) applied to every pass/row in the cross-flow heat exchanger to predict thermal performance. The method can predict the total effectiveness of assemblies of heat exchangers. Several circuiting configurations, such as overall counter-cross-flow, overall parallel cross-flow, and fluids in parallel in one of the streams, were considered. Predictions of the steady heat transfer performance of selected multirow multipass cross-flow heat exchangers are obtained by applying the general matrix approach. The heat exchanger geometries selected for the comparative study represent common cross-flow heat exchanger configurations used in industry. For these heat exchangers the overall heat exchanger effectiveness values were computed for various capacity rate ratios and NTU values. The validity of the matrix approach was then verified by comparing the resulting predictions with those obtained using the P-NTU approach and the Domingos method for the selected complex cross-flow heat exchanger configurations.     

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.     

Fluid temperature and velocity effect on fouling

A wide variety of industrial processes involve the transfer of heat energy between fluids in process equipment. As a result of this energy exchange unwanted deposits accumulate on the process surfaces causing a resistance to energy transfer. These deposits reduce the heat recovery and can restrict fluid flow in the exchanger by narrowing the flow area. Prevention and control of fouling is costly and time consuming. In many situations, fouling can be reduced but not necessarily eliminated. Fouling is a major unresolved problem in heat transfer.In general, the heat exchangers evaluated in this study were exposed to untreated lake water for typical conditions. After the prescribed time period the exchangers were taken off line and evaluated. Conclusions and observations regarding fouling of brazed heat exchangers, exposed to once-through lake water, are presented here. Transient observations and photographs of the exchanger surfaces are given. Results are presented that compare these heat exchangers to test plates, also exposed to lake water. The progressive change of surface appearance with increasing immersion times is presented.     

提高地能利用的强化传热试验研究

以太阳辐射积聚大量能量和冷热良性循环蓄集巨大能量的地下是一个庞大的可再生能源库，也是一项可充分利用的自然能量资源。该文介绍了在地源热泵系统中开展的地下100m和200m竖直井闭式循环传热的研究工作，提出利用地下螺旋芯管束新方法，加强旋流流动，提高地下换热能力。试验表明，在放热和吸热过程中，传热均得到显著提高。所提出的可控制间歇过程，将充分发挥换热井的换热能力，实现最少的井数布置，保证良好的地源热泵机组运行工况。     

Optimum design of double pipe heat exchanger

Heat exchangers are used in industrial processes to recover heat between two process fluids. Although the necessary equations for heat transfer and the pressure drop in a double pipe heat exchanger are available, using these equations the optimization of the system cost is laborious. In this paper the optimal design of the exchanger has been formulated as a geometric programming with a single degree of difficulty. The solution of the problem yields the optimum values of inner pipe diameter, outer pipe diameter and utility flow rate to be used for a double pipe heat exchanger of a given length, when a specified flow rate of process stream is to be treated for a given inlet to outlet temperature.     

Performance analysis of heat exchangers of an existing naphtha hydrotreating plant: A case study

This paper presents the performance evaluation of heat exchangers of an existing naphtha hydrotreating (NHT) plant. Originally, the NHT plant consisted of six plain tube heat exchangers connected in series. During plant revamps operation, three plain tubes were replaced with the three twisted tube heat exchangers. In this study, the heat exchangers data were collected from the plant before and after installation of the three twisted tube heat exchangers. The data were then analyzed to see the effects of the twisted tube configuration on fouling of heat exchangers and heat transfer. The analysis of the data showed that the twisted tube heat exchangers caused reduction in fouling resistance of tubes and increased the heat transfer. Also, the replacement of the three shells and tube type heat exchangers by the twisted tubes resulted in an increase of feed flow rate by about 7.85%. An economic analysis showed that the simple payback period for the twisted tube heat exchangers is 2.12 years. It can be concluded that considerable benefits in terms of energy and cost savings can be realized through the application of this innovative twisted tube heat exchanger technology in existing or new chemical plants.     

Advanced Micro-Heat Exchangers for High Heat Flux

Three micro-heat exchangers for use in a liquid cooling system with a long offset strip, short offset strip, and chevron flow path based on the traditional heat transfer enhancement concepts were designed and tested. A straight channel heat exchanger was also made for comparison. The liquid crystal thermography method described by Lin and Yang (2005) was used to observe the flow and temperature distributions in the micro-heat exchangers. The test results show that the chevron channel heat exchanger provides the lowest thermal resistance. However, its pressure drop is also the highest, approximately five times higher than that for other three heat exchangers. The offset strip heat exchangers provide better thermal performance than does the straight channel heat exchanger. The performance of the heat exchanger with the shorter strip is better than that of heat exchanger with longer strip. From the above results, all of the three micro-heat exchangers with conventional heat transfer enhancement showed less thermal resistance than the straight channel heat exchanger. The conventional heat transfer techniques may be effectively applied in the high-flux micro-heat exchanger design.     

Numerical model and effectiveness correlations for a run-around heat recovery system with combined counter and cross flow exchangers

A two-dimensional steady-state numerical model is developed to study the heat transfer in a run-around heat recovery system with two exchangers each with a combination of counter and cross (counter/cross) flow between parallel plates or membranes. A finite difference method is used to solve the steady-state equations of continuity, momentum and heat transfer. The simulated values for the effectiveness of each counter/cross flow heat exchanger and the overall run-around system are used to develop effectiveness correlations which agree within ±2% of the simulated effectiveness of individual heat exchangers and overall system. It is shown that the effectiveness of this new run-around heat exchanger (RAHE) falls between the effectiveness of similar run-around systems with either two cross-flow exchangers or two counter-flow exchangers. For a given total surface area of the exchangers, the highest overall sensible effectiveness is achieved with exchangers which have a small exchanger aspect ratio and relatively small solution flow inlet and outlet lengths.