Experimental Research on Flow Maldistribution in Plate-Fin Heat Exchangers

The flow maldistribution and the effect of different inlet configuration on the flow distribution in platefin heat exchangers were studied experimentally. It is found that the flow maldistribution is serious because of the defects of inlet configurations, while the inlet configuration and Reynolds number are the main factors affecting the flow distribution. The improved inlet configurations, which are the header with a two-stage distributing configuration and the guide vane with a fluid complementary cavity were proposed and tested in this paper. The experimental results show that the improved inlet configurations can effectively improve the performance of flow distribution in heat exchangers.

PIV Investigations of Flow Patterns in the Entrance Configuration of Plate-fin Heat Exchanger

Flow characteristics in the entrance of plate-fin heat exchanger have been investigated by means of particle image velocimetry (PIV). The flow field was measured using the two-frame cross-correlation technique. Streamline and velocity contour graphs at different cross-sections were obtained in the experiment. The experimental results indicate that flow maldistribution in the conventional header is very serious, while the improved header configuration with punched baffle can effectively improve the uniformity. The flow maldistribution parameter in plate-fin heat exchanger has been reduced from 1.21 to 0.21, and the ratio of the maximum velocity to the minimum is reduced from 23.2 to 1.8 by install-ing the punched baffle. The results suggest room for the optimum design of plate-fin heat exchanger.

Performance Evaluation Methods for Multi-stream Plate-Fin Heat Exchanger

Mathematical model of cross type multi-stream plate-fin heat exchanger is established.Meanwhile,mean square error of accumulative heat load is normalized by dimensionless,and the equations of temperature-difference uniformity factor are improved.Evaluation factors above and performance of heat exchanger are compared and analyzed by taking aircraft three-stream condenser as an example.The results demonstrate that the mean square error of accumulative heat load is common result of total heat load and excess heat load between passages.So it can be influenced by passage arrangement,flow inlet parameters as well as flow patterns.Dimensionless parameter of mean square error of accumulative heat load can reflect the influence of passage arrangement to heat exchange performance and will not change dramatically with the variation of flow inlet parameters and flow patterns.Temperature-difference uniformity factor is influenced by passage arrangement and flow patterns.It remains basically unchanged under a certain range of flow inlet parameters.

Optimal design of the first stage of the platefin heat exchanger for the EAST cryogenic system

The size of the heat exchanger is an important factor determining the dimensions of the cold box in helium cryogenic systems. In this paper, a counter-flow multi-stream plate-fin heat exchanger is optimized by means of a spatial interpolation method coupled with a hybrid genetic algorithm.Compared with empirical correlations, this spatial interpolation algorithm based on a kriging model can be adopted to more precisely predict the Colburn heat transfer factors and Fanning friction factors of offset-strip fins. Moreover, strict computational fluid dynamics simulations can be carried out to predict the heat transfer and friction performance in the absence of reliable experimental data. Within the constraints of heat exchange requirements, maximum allowable pressure drop, existing manufacturing techniques and structural strength, a mathematical model of an optimized design with discrete and continuous variables based on a hybrid genetic algorithm is established in order to minimize the volume. The results show that for the first-stage heat exchanger in the EAST refrigerator, the structural size could be decreased from the original2.200？×？0.600？×？0.627（m^3） to the optimized 1.854？×？0.420？×？0.340（m3）, with a large reduction in volume. The current work demonstrates that the proposed method could be a useful tool to achieve optimization in an actual engineering project during the practical design process.

Numerical simulation of heat transfer and flow of cooling air in triangular wavy fin channels

Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.

Exertional heat illness risk factors and physiological responses of youth football players

Objective:To determine which intrinsic and extrinsic exertional heat illness(EHI)risk factors exist in youth American football players and observe perceptual and physiological responses of players during events(games and practices).Methods:Cross-sectional cohort study observing 63 youth football players,varying in position.Independent variables were league(weightrestricted(WR,n=27)and age-restricted(AR,n=36))and event type.Dependent variables were anthropometrics,work-to-rest ratio,and wet bulb globe temperature.Descriptive variables included preparticipation examination and uniform configuration.A subset of 16 players participated in physiological variables(heart rate and gastrointestinal temperature).Data collection occurred on 7 AR and 8 WR nonconsecutive practices and the first 3 games of the season.Results:Mean values for anthropometric variables were higher(p<0.05)in the AR league than the WR league.Work time(χ^2(1,111)=4.232;p=0.039)and rest time(χ^2(1,111)=43.41;p<0.001)were significantly greater for games,but ratios were significantly higher for practices(χ^2(1,111)=40.62;p<0.001).The majority of events(77%)observed were in black and red flag wet bulb globe temperature risk categories.A total of 57%of the players had a preparticipation examination,and up to 82%of events observed were in full uniforms.Individual gastrointestinal temperature and heart rate responses ranged widely and no players reached critical thresholds.Conclusion:Extrinsic(disproportionate work ratios,environmental conditions)and intrinsic(higher body mass index)EHI risk factors exist in youth football.Certain risk factors may be influenced by event and league type.National youth football organizations need to create thorough guidelines that address EHI risk factors for local leagues to adopt.

Computer Implementation of the Passage Arrangement for Plate-Fin Heat Exchangers According to Local Balance Principle

A two-step method for stacking arrangement of passages in multistream plate-fin heat exchanger is proposed. The first step (predict step) is to initialize the arrangement according to a local-balance principle, and the second step (correct step) is to resadust the arrangement according to the results of differential computation of the temperature distribution. The computer implementation process of the local balance principle is described in detail and three examples are illustrated to show the feasibility of this principle. A subroutine program is provided to facilitate the reader to adopt this principle.

CFD-Based Optimization of a Diesel Engine Waste Heat Recycle System

A dedicated heat exchanger model is introduced for the optimization of heavy-duty diesel engines.The model is a prerequisite for the execution of CFD simulations,which are used to improve waste heat recovery in these systems.Several optimization methods coupled with different types of working fluids are compared in terms of exergy efficiency and heat exchanger complicity.The three considered optimization methods all lead to significant improvements in the R245fa and R1233zd systems with a comparatively low evaporation temperature.The optimal R245fa system has the highest efficiency increase(77.49%).The cyclopentane system displays the highest efficiency among the optimized ORC(Organic Rankine Cycle)systems,yet achieved by using a much heavier evaporator HEC(Heat Exchanging Core).In contrast,the 96.84%efficiency increase for the optimized R1233zd is achieved with only 68.96%evaporator weight.

Flow mechanism and heat transfer enhancement in longitudinal-flow tube bundle of shell-and-tube heat exchanger

The flow disturbance and heat transfer mechanism in the tube bundle of rod baffle shell-and-tube heat exchanger were analyzed, on the basis of which and combined with the concept of heat transfer enhancement in the core flow, a new type of shell-and-tube heat exchanger with combination of rod and van type spoiler was designed. Corresponding mathematical and physical models on the shell side about the new type heat exchanger were established, and fluid flow and heat transfer characteristics were numerically analyzed. The simulation results showed that heat transfer coefficient of the new type of heat exchanger approximated to that of rod baffle heat exchanger, but flow pressure drop was much less than the latter, indicating that comprehensive performance of the former is superior to that of the latter. Compared with rod baffle heat exchanger, heat transfer coefficient of the heat exchanger under investigation is higher under same pressure drop, especially under the high Reynolds numbers.

极地钻井液冷却用板式换热器设计及换热性能模拟研究

在极地开展冰下基岩取心钻探,对研究冰下地质构造、揭示冰盖演化历史、评估未来气候变化等均有重要的意义。在极地冰下基岩钻探过程中,钻井液在孔底循环后温度可能升高至0℃以上,进而在上返过程中融化冰孔孔壁,导致井壁失稳,甚至引发卡钻事故。为此,有必要研发极地钻井液冷却系统,在地表将钻井液冷却至较低的温度后再注入孔内,进而使钻井液在循环过程中始终保持在0℃以下。换热器是钻井液冷却系统的核心部件。本文选用板式换热器做为钻井液的换热部件,采用平均温差法确定了板式换热器的换热面积和基本参数,然后使用COMSOL Multiphysics 6.0软件对板式换热器的换热性能进行了数值模拟。研究结果表明,该换热器可将钻井液冷却至-4~-3℃;此外,模拟结果表明,钻井液的出口温度随载冷剂注入温度的降低和载冷剂流量的增大而降低;钻井液的类型对换热器的换热性能有较大影响,而换热板片的材质对换热器的换热效果影响不大。

国内外露点间接蒸发冷却技术研究最新进展

通过对露点间接蒸发冷却基本原理,露点蒸发冷却模型特点,相关试验研究的成果以及露点蒸发冷却空调机组的实际商业化产品的介绍,论述了国内外露点蒸发冷却技术研究的最新进展。相关研究表明,露点蒸发冷却技术在制冷空调、建筑节能领域有着巨大的应用前景。

高空抽芯作业车设计

论述了新型换热器高空抽芯作业车的结构原理。将计算结构力学的矩阵分析法用于换热器抽芯作业车主体金属结构的力学分析与计算 ,编制了该空间桁架的计算程序 ,校核了主体金属结构的强度、刚度和稳定性。高空抽芯作业车集起重、抽芯和行走三大功能于一体 。

搅拌摩擦焊核心区温度在线检测方法

提出了基于热图像的搅拌摩擦焊核心区温度检测方法,通过建立轴肩边缘焊材表面辐射度与电压的映射关系、热图像灰度与电压的映射关系,推导出轴肩边缘焊材表面温度与热图像灰度的关系.结合辐射热交换原理,得到了轴肩边缘焊材表面温度与核心区温度的关系,并求解得到搅拌摩擦焊核心区温度.实验对比验证了所建测温模型的正确性与可行性.

大型热交换器装芯抽芯机设计

大型热交换器装芯抽芯机是影响热交换器的装配及检修效率的重要设备,国内目前使用的热交换器装配检修设备较为落后。大型热交换器装芯抽芯机的步进移动装置是重要组成部分,也是热交换器装芯抽芯机设计和制造的关键。针对国内外热交换器装芯抽芯机存在的技术缺陷和不足,制订了新的热交换器装芯抽芯机设计方案。通过调研和类比设计法确定了其主体结构。该装置结构新颖、性能稳定可靠、安全性高、作业效率高,改变了长期依赖吊车配合装芯抽芯作业的局面。

冻土区天然气水合物钻井泥浆冷却系统设计及关键参数计算

泥浆冷却技术是天然气水合物钻探的关键技术之一,低温泥浆可以抑制天然气水合物在钻进和提钻过程中分解,有利于钻获水合物实物样品。新型天然气水合物钻井泥浆冷却系统主要包括载冷剂制冷器、翅片管式换热器、温度监测与记录和防冻装置4部分。制冷机组采用变频启动,减小了野外施工中配套发电机的功率,大幅度降低油料消耗;翅片管式换热器中泥浆与载冷剂对流换热,换热面积大,换热效率高;温度监测与记录装置对4个关键节点的温度进行监测和记录,同时防冻装置可防止泥浆在换热器中结冰堵塞,影响正常使用。运用传热学和流体力学理论对泥浆与载冷剂对流换热过程进行计算,在满足制冷要求的前提下,换热器换热面积是10.58 m2,管路压力损失为0.34 MPa。

内插螺旋弹簧换热管核心流强化传热特性研究

采用FLUENT模拟计算及实验这两种方法,对内插不同圈径螺旋弹簧换热管在核心流区域的传热特性进行了研究,综合分析了内插螺旋弹簧圈径大小对管内速度场、温度场及对核心流强化传热效果的影响。结果显示,在管内核心流区域插入不同圈径螺旋弹簧具有显著的强化传热作用,增加幅度为5%~20%;管内核心流区域插入螺旋弹簧的强化传热效果与插入弹簧的圈径大小以及流体状态有关,存在一个内插螺旋弹簧的最优值。

液力缓速器全流道式制动流场数值计算方法研究

现有关于液力缓速器制动流场数值计算方法的研究均忽略了换热芯子的流阻压降作用,导致计算边界条件设置不准确的问题。为此,基于三维扫描还原的模型重建技术,考虑换热芯子的流阻压降作用,采取全流道式选取方案,选用RNG双方程模型与基于压力的PISO求解算法,运用CFD技术对VOITH公司VR120液力缓速器制动流场进行全流道式数值计算,获得制动力矩与转速特性曲线,并使用流场压力云图对换热芯子的流阻压降作用进行验证分析。结果表明:制动力矩随着转速的升高呈现二次方增长趋势;换热芯子的流阻压降作用显著,是不可忽略的流场边界条件,全流道式数值计算方法是必要的。

新型换热器抽芯机主体金属结构设计

换热器抽芯机是影响换热器检修效率和检修时间的重要设备。我国目前所用换热器抽芯设备尚十分落后，严重影响了石油、化工企业的经济效 益。换热器 抽芯机主体金属结构是换 热器抽芯机最重要组成部分，也是换热器抽芯机设计与制造的关 键。针对 国际、国内换热器抽芯设备的 落后状况及现有换热器抽芯机所存在的技术缺陷，拟定了新型换热器抽芯机的设计方案。通过调研和类比设计法确定了换热器抽芯机主体金属结构和空间桁架的截面型式及立柱、腹杆的几何参数。又根据结构力学的矩阵位移法，利用计算机高级语言编制了该主体金属结构的 Ｃ Ａ Ｄ 程序，具有一定的通用性， 能方便、快捷地计算出立柱和腹杆的内力，进而精确校核了主体金属结构的强度。

新型换热器高空抽芯作业车的设计方案

针对我国换热器抽芯设备的落后状况 ,提出了新型换热器高空抽芯作业车的设计方案。论述了这种作业车的基本结构、工作原理和技术指标。运用结构力学的矩阵分析法和计算机对抽芯作业车主体金属结构做了力学分析与计算 ,进而校核主体金属结构的强度、刚度和稳定性。设计将作业车的起重、抽芯和行走三大功能集于一体 ,控制系统采用电液联合控制 ,工作台能自动升降 ,自动抽芯 ,抽芯速度快 ,改变了以往依赖吊车配合作业的落后局面。这种作业车的研制对提高我国石油及石化行业设备检修效率 ,缩短检修时间 。

复合钎焊铝箔技术在汽车热交换器生产中的应用

采用以Al-Mn合金为芯材,双面包覆厚度为10%的Al-Si合金钎料,采用热轧工艺轧制复合而成的复合钎焊铝箔具有优异的综合性能,质量比铜箔制的同类产品约轻40%,具有十分广阔的应用前景。