扭曲椭圆管换热器壳程强化传热的数值研究

基于扭曲椭圆管的换热器是一种新型的新风系统换热器,针对扭曲椭圆管及其应用特点,设计了两种不同结构参数的新风系统换热器。应用FLUENT软件,在夏季工况下对两种不同结构参数的新风系统换热器壳程进行模拟分析,并通过与实验数据的对比,验证计算模型的可靠性。结果显示在相同体积流量下,随着壳程开孔面积的增大,对流换热系数h不断减小,压降Δp不断减小,综合性能系数h/Δp1/3变化不明显;随着螺距的减小,对流换热系数h不断增大,压降Δp不断增大,综合性能系数h/Δp1/3也不断增大;流场分析显示,扭曲椭圆管换热器壳程流道内,呈现出明显沿着扭曲椭圆管壁面的螺旋流,使得空气在流道内充分扰动,增强换热效果。     

有机酸清洗剂去除换热设备污垢实验研究

以A、B、C三种有机酸清洗剂为研究对象,筛选出性能较好的清洗剂并优化其清洗工艺参数,结果表明,清洗剂C与水的体积比为1∶20、清洗温度为20~40℃、清洗时间为1 h时,除垢率达97%,且对碳钢和不锈钢的腐蚀率为三种清洗剂中最低,满足化学清洗对腐蚀率的要求.在此基础上,建立动态除垢实验装置考察实际清洗效果,结果表明,清洗剂C实际清洗效果较好,除垢后清洗试件在管程流速分别为0.5、0.7、0.9、1.1 m·s-1时,传热系数分别提高6.01%、6.98%、6.93%、9.04%.     

不同宽度扭带传热与阻力特性试验研究

本文对管内扭带旋流装置在不同扭带宽度下的传热与阻力进行了试验研究,并得到了传热与阻力拟合式。     

Heat Exchanger Fouling in Phosphoric Acid Evaporators

Multistage shell and tube evaporators are frequently used in phosphoric acid plants to increase the concentration of dilute phosphoric acid to 52–55 wt% P₂O_5. The concentrated phosphoric acid solution is supersaturated with respect to calcium sulfate. As a result, part of the calcium sulfate in the liquor deposits on the heat exchanger tube walls. Because the thermal conductivity of these scales is very low, thin deposits can create a significant resistance to heat transfer. Therefore, regular cleaning of heat exchangers is required, frequently at shorter than biweekly intervals. As the major costs in modern phosphoric acid plants are the cost of energy, a thorough understanding of the fouling kinetics and of the effects of various operational parameters on the behavior of calcium sulfate is required to improve operation and design of the shell and tube heat exchangers, which are extensively used. In this investigation, a large set of heat exchanger data was collected from shell and tube heat exchangers of the phosphoric acid plant of the Razi Petrochemical Complex in Iran, and the fouling deposits were analyzed with respect to appearance and composition. The overall heat transfer coefficients and fouling resistances were evaluated at different times, and a kinetic model for the crystallization fouling was developed. It is shown that the crystallization rate constant obeys an Arrhenius relationship with an activation energy of 57 kJ/mol. The average absolute error of 12.4% shows that the predictions of the suggested model are in good agreement with the original plant data.     

Experimental Investigation on Thermo-Hydraulic Performance of Heat Exchanger Tube with Solid and Perforated Circular Disk Along with Twisted Tape Insert

Heat transfer enhancement in heat exchanger by using passive approach has become a very versatile area of research for the researchers. Although very significant results has been achieved in the thermal performance of heat exchangers, especially in the range of lower Reynolds number, but still these passive approaches of heat transfer enhancement is not effective for the range of higher Reynolds number. In the present work the effect of ‘perforated circular disk turbulators with and without twisted tape’, on heat transfer, friction factor and thermal performance of heat exchanger is evaluated experimentally. The different geometrical parameters used for the experiment include fixed diameter ratio (0. 8), pitch ratios (1, 2, and 3), perforation index (0%, 8%, 16%, and 24%), fixed twist ratio (2) and fixed width ratio (0.4). The experiment is done in the range of Reynolds number lying from 6,500 to 26,500. On the basis of experimental observation, there is 2.2–3.54 times improvement in heat transfer and around 1.18–1.64 times improvement in thermal performance factor over smooth tube heat exchanger.     

Heat Transfer and Flow Resistance Characteristics of Helical Baffle Heat Exchangers with Twisted Oval Tube

To overcome the defect of the significant increase in pressure drop when the heat transfer performance of helical baffle heat exchanger is improved,a novel heli...     

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。     

管内插入扭带及螺旋线圈的传热与阻力特性实验研究

实验研究了以空气为工质的管内插入扭带与螺旋线圈的传热与阻力特性,在3000相似文献   

Real Time Fouling Diagnosis and Heat Exchanger Performance

The issue of fouling in preheat trains of crude oil distillation units in Petrobras's refineries is a major concern—especially now, as heavier Brazilian crudes with higher asphaltene content are being refined. As the efficiency of the preheat train plays an important role in the energy consumption of a distillation unit, its performance must be tracked as precisely as possible in order to identify operational problems. This work describes an online heat exchanger performance evaluation system based on rigorous simulation of the equipment in order to predict both the operational and clean overall heat transfer coefficient. A real-time comparison between these two values indicates the actual performance of the heat exchanger and of the preheat train. The use of a rigorous process simulator (Petrox from Petrobras) together with a rigorous calculation of the global heat transfer coefficient (using the program Xist from HTRI) allows one to consider aspects that are not usually taken into account in this kind of evaluation. These aspects include crude vaporization after the desalters and variations of crude and products composition with the distillation unit run. The system is being implemented at the biggest Petrobras refinery (360,000 bpd) in a 25 heat exchanger preheat train.     

Measuring Local Crystallization Fouling in a Double-Pipe Heat Exchanger

Abstract

Although fouling is a problem varying in space and time, sizing and assessment of a process apparatus is almost always based on one single integral fouling resistance value. Furthermore, the integral fluid dynamic behavior, e.g. the development of time-dependent pressure drop in a heat exchanger, can be influenced by local constrictions. While it is generally possible to determine the time dependency of the integral fouling behavior, local differences are not taken into consideration at present. Therefore, this paper introduces a metrological, an incremental and a segmental approach to study the local development of crystallization fouling by calcium sulfate in a countercurrent double-pipe heat exchanger. The consecutive approaches allow for thermal, volumetric, gravimetric, and optical fouling investigations, aiming to examine the axial distribution of deposit as well as local differences in the deposit morphology. All methods provided congruent results and local fouling could be described properly. An almost clean surface at the colder end of the heat exchanger and an exponential increase of deposit thickness were observed towards the hot end. Hence, the section near to the hot water inlet turned out to be a key area with regards to increasing fouling mass and structural changes of the layer.     

Experimental Investigation of Microbial Fouling and Heat Mass Transfer Characteristics on Ni-P Modified Surface of Heat Exchanger

Fouling deposition problem on heat transfer surface is widely distributed in the field of energy and chemical industry,and microbial fouling is a common fouling type in heat exchanger.In this article,the surface modification was used for inhibiting or mitigating the microbial fouling deposition on heat exchange surface.Firstly,the experimental system for real-time monitoring the fouling deposition process was built,and then the Ni-P modified surface was prepared.Further,the slime forming bacteria(SFB)microbial fouling characteristics and corresponding influencing factors on Ni-P modified surface were investigated experimentally.The results indicated that Ni-P modified surface had an excellent fouling inhibition property.Comparing with carbon steel,Ni-P modified surface reduced the fouling heat resistance by 80%.Accordingly,the influencing factors of microbial fouling deposition including temperature,flow rate and microbial concentrations were discussed.With cooling water temperature increasing given in the experiment arrangement,the microbial fouling resistance was increased first and then decreased,while with bacteria concentration and flow rate increasing,the fouling resistance was increased and decreased separately.The work can provide experimental reference for the fouling inhibition surface development and fouling inhibition mechanism study.     

Detection of Fouling in a Cross-Flow Heat Exchanger Using Wavelets

Detection of fouling in a heat exchanger experiencing perfect steady-state conditions is not very difficult. But the challenge is to detect fouling when all inputs (inlet temperature of the fluids and the mass flow rates) are simultaneously varying. In this paper it has been considered that the mass flow rates can vary in a ratio of 2, and that the inlet temperatures can vary by about ±20%. This first approach is dedicated to show the feasibility of using the wavelet transform. It has been considered that getting simulated data is the best way. In fact, it is then possible to introduce an arbitrary fouling factor. Thus, in the first part of the paper the model of the heat exchanger is presented. It is developed using Simulink. The validation is carried out on an electrical heater, for which it is possible to find an analytical solution for transient states. It is also shown that steady states are accurately computed over a large range of the number of transfer units and heat capacity rate ratios. Then a brief overview of the wavelet transform is given. Then basic examples show that the wavelet transform can help to find the trend of time series. It is then applied to the analysis of the “wavelet-transformed” effectiveness of the heat exchanger. This analysis is carried out on a sliding observation window (to be able to detect fouling on-line). It is shown that fouling is detected at a very early stage.     

Fouling of Heat Exchanger Surface: Measurement and Diagnosis

Fouling in heat exchange equipment results in a significant energy toss by increasing heat transfer resistance and fluid frictional resistance. This paper deals with an effective way to monitor fouling and describes a potentially useful diagnostic approach for discriminating different types of deposit in situ. Information regarding deposit type would be useful in selecting an appropriate treatment procedure. Some cautions regarding the indiscriminate use of fouling factor or fouling resistance are also discussed.     

烟气换热器堵灰原因及解决办法

介绍了数家电厂GGH堵灰情况，总结出GGH堵灰的主要原因，并且提出了对策。     

板式换热器颗粒污垢特性的实验研究

以纳米氧化镁颗粒溶液为实验工质,进行了板式换热器颗粒污垢特性的实验研究,分析了颗粒质量浓度、颗粒粒径、流速和低温介质温度对颗粒污垢热阻的影响.结果表明:板式换热器颗粒污垢无明显诱导期存在,结垢速率和污垢热阻渐进值均随颗粒质量浓度的增大而增大,且增大幅度逐渐减小;颗粒粒径对污垢热阻的影响较明显,在相同质量浓度下,颗粒粒径越小,结垢速率越快,且污垢热阻越大;流速对污垢热阻的影响较为复杂,高流速下的结垢速率略大于低流速下,且高流速下达到稳定时的污垢热阻渐进值小于低流速下;低温介质温度对颗粒污垢热阻的影响不明显.     

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。     

Study of the Effect of Fin-and-Tube Heat Exchanger Fouling on its Structural Performance

This paper presents the thermal and structural analysis of high temperature fin-and-tube heat exchanger. Water flowing in tubular space and flue-gas flowing in the intertubular space, were considered as working fluids. The effect of limescale fouling on thermal and structural performance of heat exchanger was studied. The analysis considered an industrial heat exchanger, which failure occur from time to time. The expert inspection, after the failure indicated the existence of fouling layer within the heat exchanger tubes. In order to understand the reasons of heat exchanger failure, a detailed fluid flow analysis (both in the tubular and intertubular spaces) was performed. The analysis indicated that the silicate limescale fouling layer with thermal conductivity of 0.35 W/(mK) and thickness up to 1.5 mm existing in the tube, may increase the tube wall temperature even more than 150°C. The study also includes the impact of outer tube wall surface fouling with thickness of 0.2 mm and heat transfer coefficient of 2 W/(mK). As a result, the compressible stresses may increase over three times compared to the situation where the tube wall fouling does not exist.     

紧凑高效型水平管束降膜蒸发换热器的实验研究

在大气压条件下使用单列和3列叉排光滑管和滚压强化换热管紧凑管束进行了水降膜蒸发换热实验,确认了滚压管在中,低热负荷范围内能够增强换热系数3～4倍,有很好的沸腾强化换热性能。管间距及液膜溅射损失对蒸发换热特性影响很小。同时也考察了单列和3列管束换热特性闯的差异。实验发现这种差异在低雷诺数区域时更加明显。