Heat Transfer Characteristics in a Double-Pipe Heat Exchanger Equipped with Coiled Circular Wires

An experimental investigation has been carried out to study the enhancement in heat transfer coefficient by inserting coiled wire around the outer surface of the inner tube of the double-pipe heat exchanger. Insulated wires, with a circular cross-section of 2 mm diameter, forming a coil of different pitches (p = 6, 12, and 20 mm), were used as turbulators. The investigation is performed for turbulent water flow in a double-pipe heat exchanger with cold water in the annulus space for both parallel and counter flows. The experiments were performed for Reynolds numbers ranging from 4,000 to 14,000. The experimental results reveal that the use of coiled circular wires leads to a considerable increase in heat transfer coefficients compared with a smooth wall tube for both parallel and counter water flows. The mean Nusselt number increases with Reynolds number and pitch. The convective heat transfer coefficient for a turbulent water flow increases for all coiled wire pitches, with the highest enhancement of about 450% for counter flow and 400% for the parallel flow. New correlations for mean relative Nusselt numbers at different coiled wire pitches are provided.     

An Experimental Investigation of Forced Convection Heat Transfer from a Coiled Heat Exchanger Embedded in a Packed Bed

Forced convection heat transfer from a helically coiled heat exchanger embedded in a packed bed of spherical glass particles was investigated experimentally. With dry air at ambient pressure and temperature as a flowing fluid, the effect of particle size, helically coiled heat exchanger diameter, and position was studied for a wide range of Reynolds numbers. It was found that the particle diameter, the helically coiled heat exchanger diameter and position, and the air velocity are of great influence on the convective heat transfer between the helically coiled heat exchanger and air. Results indicated that the heat transfer coefficient increased with increasing the air velocity, increasing helically coiled heat exchanger diameter, and decreasing the particle size. The highest heat transfer coefficients were obtained with the packed-bed particle size of 16 mm and heat exchanger coil diameter of 9.525 mm (1/4 inch) at a Reynolds number range of 1,536 to 4,134 for all used coil positions in the conducted tests. A dimensionless correlation was proposed for Nusselt number as a function of Reynolds number, particle size, coil size, and coil position.     

Evaluation of Nusselt number and effectiveness for a vertical shell-coiled tube heat exchanger with air bubble injection into shell side

Air bubble injection was employed to increase the heat transfer rate (Nusselt number) of a vertical shell and coiled tube heat exchanger in this article. Hot and cold water flowed into the coil side and shell side of heat exchanger, respectively, and air bubbles were injected inside the shell side of heat exchanger via a memorable method. Bubbles' vertical movement due to buoyancy forcing through the heat exchanger can enhance the heat transfer rate by mixing the thermal boundary layer, increasing the turbulence level of the fluid flow and increasing the shell-side fluid Reynolds number.     

超大拓展表面三维微肋管换热器的对流换热及抗积灰特性研究

工业烟气含尘的特点易导致换热器积灰,进而制约烟气余热的高效回收。本文针对一种具有超大拓展表面的三维微肋管换热器的对流换热与积灰特性进行了研究。首先,对比研究了光管与三维微肋管的对流换热特性;接着,基于所建立的积灰数值模型,探究了三维微肋管的积灰特性,并揭示了烟气流速与飞灰粒径对其积灰特性的影响规律。结果表明,相对于传统光管,三维微肋管的换热面积可增大约2.9倍;换热性能平均能提高16%;积灰后渐进污垢热阻最大能减小70%;同时,清灰周期更长,运行经济性更佳。综合而言,三维微肋管相比传统光管,在增强换热的同时,还能有效减轻积灰,因此可作为高效的抗积灰传热元件,应用于含尘烟气的余热回收场合。     

Pressure drop,heat transfer and performance of a helically coiled tubular exchanger

Experiments have been conducted, and correlations are developed for the pressure drop and heat transfer coefficient for the tube and shell sides of a helical coil heat exchanger. In the tube side, the laminar friction factor and Nusselt numbers are represented as functions of Re√d/D, whereas in turbulent flow the results are correlated with Re·(d/D)². The pressure drop and heat transfer values for the shell side are found to follow the classical Blasius and Dittus-Boelter type relations, while a strong dependence on the coil to tube diameter ratio is detected. The performance of the exchanger has been tested not only as simulated experimental exchanger but also as a waste heat recovery device for a 60 HP gas turbine. Excellent corroboration of the effectiveness-NTU relation has been observed between the simulation and in situ experiments.     

乳品行业低温余热回收系统性能分析

针对乳品行业排风风量大但品位低的特点,本文提出利用排风余热代替蒸汽来预热干燥空气的余热回收系统.在构建预热器、回热器和主加热器等部件热量流模型的基础上,建立了不包含中间节点参数的系统整体热量流模型.结合某奶粉厂运行数据对模型进行求解,结果表明,该系统将排风温度由90℃降低到42.58℃.在给定热负荷下,通过匹配中间回路...     

热管式吸附床制冷性能的实验研究

利用高效热管作为吸附床的传热部件,有效地提高了船用柴油机废气的热量回收。本文将热管式吸附床与传统的壳管式吸附床进行了性能对比。同时,选择氯化钙-氨作为吸附工质对,通过实验测定解吸、吸附过程的变化情况。本文的研究结果表明,采用热管式吸附床使得初始解吸和吸附速率有明显提高,从而有效缩短解吸和吸附周期,并能有效提高系统的SCP和COP。     

微管换热器流动与传热的实验研究

本文对自制微管换热器的流动与传热性能进行了实验研究。提出了微细圆管换热器管内单相强制对流换热努摩尔数准则式,并与已有相关文献提出的关联式做了对比,结果表明:微管管内换热系数比常规尺度计算公式预测值要高,同时本文分析了微细管内的压力降、摩擦阻力系数f随雷诺数的关系。研究表明微管管内压降、摩擦系数都比常规尺度预测值要高。     

ELECTROHYDRODYNAMIC ENHANCEMENT OF HEAT TRANSFER IN A SHELL-AND TUBE HEAT EXCHANGER

Enhancement of heat transfer in a heat exchanger via a DC corona discharge was studied experimentally using a single-tube shell-and-tube heat exchanger. Air was the working fluid in both the tube and shell sides. Excitation of the tube side was via a single wire electrode, while that of the shell side was via four rod electrodes oriented symmetrically at 90^° intervals. Three series of experiments were performed: (1) excitation of the tube side only, (2) excitation of the shell side only, and (3) simultaneous excitation of the tube and shell sides. Both heat transfer and pressure drop measurements were performed, with Reynolds number and electric field potential as parametric quantities in the tube and shell sides. It was found that highest enhancements take place when the tube and shell sides are excited simultaneously, yielding a 322% increase in the overall heat transfer coefficient. Study of the heat transfer enhancements per unit pumping power indicates that for the range of parameters studied, the technique is most efficient at moderate Reynolds numbers and at electrode potentials in the midrange between threshold and sparkover limits.     

波纹板式空冷器阻力与传热特性实验研究

在可改变风量和热水流量的实验条件下,对波纹板式空冷器的阻力与传热特性进行实验研究。得到了空气侧的阻力降关联式以及两侧的对流换热系数关联式,其适用于热水雷诺数在2000-8000之间、空气雷诺数在2000-10000之间。在相同工况下,比较了波纹板式、光管式和翅片管式空冷器的性能指标,结果表明:迎面风速在2.45-4.1 m/s之间,波纹板式空冷器传热系数达到100-160 W/m2/℃;约比光管式提高70%,但只有以管束外表面为基准的翅片管式传热系数的六分之一;板式空冷器单位体积换热量约是翅片管式空冷器的1.5倍,是光管式的15倍;板式空冷器单位功耗换热量约是光管式空冷器的5.5倍,而翅片管式空冷器与光管式空冷器则相差不大。     

低品位烟气余热回收换热器热力学分析

低品位烟气余热回收过程存在冷凝现象,烟气的放热过程分为显热、潜热两部分。冷凝时,局部热流率和熵产率明显增大;增加水蒸气质量分数、冷却水质量流量和降低烟气入口温度都会导致烟气提前冷凝;存在最优冷却水质量流量使得热回收过程熵产数最小。另外,提出热回收效率评价烟气热回收程度,该指标受冷凝的影响很大。随着烟气中蒸汽质量分数的增加,冷凝过程的影响明显增强,因此,在低品位烟气的全热回收中必须考虑潜热的影响。     

Study on Heat Transfer Performance of Skin Heat Exchanger

Cooling technology is facing new challenges with the increase of electronic equipment power onboard aircraft. The traditional heat sink based on high-altitude bleed air does not satisfy this increase of cooling demands. In this article, an air/air-type skin heat exchanger is studied for cooling aircraft electronic equipment. It uses outside high-altitude cold air rather than bleed air as a heat sink. This cooling technology can effectively remove the heat load of high-power electronic devices without greatly increasing aircraft performance penalty. To assess its high-altitude heat transfer performance, an experimental prototype was designed and made. Some experiments were conducted on a ground experimental test. The heat transfer criteria formulas were obtained for both the side air in the skin heat exchanger and its convective heat transfer coefficients. Based on these experimental analyses, the heat transfer performances of the skin heat exchanger in a high-altitude cruise condition are deduced when it is assumed to be installed at an unfavorable position and a favorable position, separately. This work tries to provide a technical support for its future onboard application.     

斜向流换热器壳程流场均匀化研究

传统弓形折流板换热器壳程流体横向流动时存在流动阻力和传热死区大等缺点。为克服上述不足,研究开发了一种新型高效节能的斜向流管壳式换热器,采用导向型折流栅替代传统弓形折流板,倾斜流道内流体斜向冲刷换热管束。考察和对比了斜向流换热器和弓形折流板换热器壳程主流区的流体流速分布和变化规律,证实了导向型折流栅具有显著的控涡均化壳程流场和提高壳程流体整体流速的作用,有助于减小壳程压降,增大有效换热面积,为管壳式换热器结构改良提供了参考依据。     

Evaluation of a Thermosyphon Heat Pipe Operation and Application in a Waste Heat Recovery System

Efficient and economical utilization of industrial waste heat would result in reduced energy use and thereby contribute to reduction of greenhouse gas emissions to the atmosphere. Two-phase thermosyphon technology has demonstrated the potential capability for waste heat recovery, but it has not been yet utilized in large-scale industrial applications. As a part of an industrial project, various types of thermosyphon heat pipes have been designed and tested for extraction of waste heat and process control in aluminum industry. This article presents the heat and mass transfer model, developed to provide a fast and accurate simulation tool for industrial application of thermosyphon heat pipe technology for waste heat utilization. The mathematical model considers the energy, momentum, and mass transfer equations, in their one-dimensional form, to predict output parameters of the thermosyphon and enable parametric and sensitivity analysis. The mathematical model structure is set up in a way that the least numerical cost and time is spent while the model accuracy is kept at acceptable level for the defined application. To provide experimental data for validation of the simulation model, the proposed thermosyphon was tested experimentally using a test set-up instrumented for this purpose. The simulation results are found to be in good agreement with the experimental data. The developed model and code are viable to be used as a simple and fast tool for modeling, design, and optimization of the thermosyphon as an element in a heat recovery module.     

吸附制冷用吸附单元管设计和传热传质性能研究

本文介绍了一种具有较好传热传质性能的吸附式制冷用吸附单元管,该吸附单元管直接用烟气加热、空气冷却, 可以用于沸石等高温吸附剂。该吸附单元管在加热／冷却流体侧和吸附剂侧均设了翅片,吸附剂内部的传热尺度不大于 2．5 mm,最大传质尺度不大于11 mm。通过数值计算和由吸附单元管组合而成的吸附床的性能初步试验,证明该结构形式的吸附单元管具有优良的传热传质性能。     

周向重叠三分螺旋折流板换热器壳侧性能试验研究

对倾斜角为20°、24°、28°和32°的单头以及32°的双头周向重叠三分螺旋折流板换热器和弓形折流板换热器的传热和压降性能进行了测试,换热器采用公共壳体和可更换管芯结构。采用壳侧轴向雷诺数和轴向欧拉数分别作为反映壳侧流量和阻力系数的无因次参数。试验结果显示在试验范围内周向重叠三分螺旋折流板换热器壳侧换热系数、壳侧压降和综合性能指标都随着倾斜角增大而减小;倾斜角20°方案的性能指标最佳,其平均壳侧努塞尔数和轴向欧拉数与弓形折流板方案的数值之比分别为1.123和0.45;双头螺旋折流板方案的换热系数和压降都大于同样倾斜角的单头螺旋折流板方案,但两者的综合性能较接近。     

含不凝气体时煤油在水平管束外的冷凝

采用实验的方法,研究了在较宽的不凝气体含量范围内,煤油蒸汽在不同几何结构的螺旋扁管管束外的冷凝换热现象,得出了螺旋扁管的几何结构对冷凝换热的影响规律,并与同样条件下的光管管束的冷凝换热进行了分析比较。     

螺旋折流片强化壳侧传热的四管模型数值模拟

针对螺旋折流片管壳式换热器的正方形布管方式,建立了相间套螺旋折流片的四管数学物理模型,利用FLUENT软件对该模型的流动与传热情况进行了数值模拟;并与光滑通道中及单管螺旋折流片模型的流动和传热结果进行了对比.结果显示旋向相反的相邻螺旋折流片所诱导的两股旋流通过相互作用可提高通道内流体流速,并有效地形成对相邻传热管外的斜向冲刷,这对于减薄边界层,促进近壁流体与主流区流体的动量和质量交换进而强化传热有明显的作用,算例显示其传热系数可比相同尺寸的光管通道中的情形提高约44%～57%.     

Performance Analysis and Optimization of a Series Heat Exchangers Organic Rankine Cycle Utilizing Multi-Heat Sources from a Marine Diesel Engine

Organic Rankine Cycle (ORC) is an effective way to recycle waste heat sources of a marine diesel engine. The aim of the present paper is to analyze and optimize the thermoeconomic performance of a Series Heat Exchangers ORC (SHEORC) for recovering energy from jacket water, scavenge air, and exhaust gas. The three sources are combined into three groups of jacket water (JW)→exhaust gas (EG), scavenge air (SA)→exhaust gas, and jacket water→scavenge air→exhaust gas. The influence of fluid mass flow rate, evaporation pressure, and heat source recovery proportion on the thermal performance and economic performance of SHEORC was studied. A single-objective optimization with power output as the objective and multi-objective optimization with exergy efficiency and levelized cost of energy (LCOE) as the objectives are carried out. The analysis results show that in jacket water→exhaust gas and jacket water→scavenge air→exhaust gas source combination, there is an optimal heat recovery proportion through which the SHEORC could obtain the best performance. The optimization results showed that R245ca has the best performance in thermoeconomic performance in all three source combinations. With scavenge air→exhaust, the power output, exergy efficiency, and LCOE are 354.19 kW, 59.02%, and 0.1150 $/kWh, respectively. Integrating the jacket water into the SA→EG group would not increase the power output, but would decrease the LCOE.     

列管式换热器强化传热研究及发展

简述了列管式换热器强化传热技术的进展及发展方向,管程强化传热采用螺纹管、横纹管、波纹管、缩放管、管内插入物、三维内肋管、翘片管等传热元件,壳程强化传热采用板式支撑、折流插式支撑、空心环支撑、管子自支撑等管束支撑结构。指出了列管式换热器研究中存在的不足。指出了今后的发展方向,为列管式换热器的研究和应用提供理论参考。