Analysis and Application of Variable Conductance Heat Pipe Air Preheater

The heat transfer analysis of variable conductance heat pipe air preheater was carried out. The temperature trans-fer matrix was obtained for the air preheater that comprises several discrete heat transfer units with same or different heat transfer surface area in a parallel or counter flow mode. By using the temperature transfer matrix, the outlet fluid temperatures could be easily calculated for a given air preheater and inlet fluid temperatures. The active length of condenser in a variable conductance he...     

回转式空气预热器运行特性影响规律的研究

针对三分仓回转式空气预热器的自身特点,建立其传热模型和传热方程式来进行计算,通过对不同物性传热元件进行计算,发现对于回转式空气预热器,材质物性对传热特性的影响不大,但受热面污染会使回转式空气预热器空气出口温度及受热面壁温下降。     

三维变形管与三维内肋管在管式空气预热器上的应用研究

本研究对比分析了三维内肋管及三维变形管的结构特点和强化传热机理,在相同工况下,揭示了光滑圆管、三维内肋管及三维变形管用于管式空气预热器时的传热性能和流动阻力性能,三维内肋管和三维变形管传热性能均优于光滑圆管,三维变形管管内传热系数和流动阻力系数随短长轴B/A的减小而增大,三维内肋管可增加每米肋数、肋宽和肋高以强化传热效果,但流体流动阻力也将增加,低Re下,三维变形管管内综合传热性能优于三维内肋管,三维变形管管外自支撑而防止管束振动的特点可以实现在管内外的冷热流体纯逆流动,提出一种传热温差高的逆流三维变空间管式空气预热器,在相同工况条件下,空气预热器重量减轻,体积减小约65%,节省大量的生产和运输成本以及安装空间,三维变形管空气预热器在烟气余热利用中具有推广应用价值。     

1000MW火电机组安装的三分仓和四分仓空气预热器的性能比对试验

空气预热器尺寸随着机组容量的增加逐渐增大,而空气预热器尺寸的增大会使得空气预热器出口烟温偏差增加,加之排烟温度整体不高,会使得部分区域温度低于烟气酸露点,在环保压力越来越大的背景下,机组出现堵灰的几率也随之增加,影响机组运行的安全运行。本文通过对比某电厂两台1000MW机组中具有几乎相同尺寸和换热面积的的三分仓和四分仓的空气预热器运行经济性和安全性数据,突出了四分仓空气预热器在两方面具有的优势。     

Three‐dimensional modeling method for heat exchange of rotary air preheater in coal‐fired power plant

A numerical modeling method based on a 3‐D heat transfer model and duct models for a dual‐sectional rotary air preheater have been developed in this paper. Owing to different boundary conditions for the heat transfer model obtained by modeling and calculation of the ducts, this method is capable of calculating the 3‐D metal and fluid temperature fields at different radial locations in the rotary air preheater along the rotor height as well as the rotating period, and furthermore, it can calculate temperature and flow field inside the flow passage as well. A case study with a dual‐sectional rotary air preheater of a typical 300 MW_e unit used as the research object is presented in this paper. The calculation results accord well with those obtained by verified numerical methods in published literature. The difference between the calculated and the measured outlet fluid temperature of the rotary air preheater is smaller than 3 °C. The numerical modeling method presented in this paper is proved to have high precision and is beneficial for the secure and economic operation of a rotary air preheater as well as the whole unit. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20325     

结构参数对电厂翅片管散热器动态特性的影响

散热器经常处于变化的工作条件中,研究散热器的动态特性有助于改善间接空冷系统的安全和经济运行,而散热器的结构参数会影响其动态特性。根据能量守恒建立了散热器空气、管壁和循环水的热平衡偏微分方程,采用改进欧拉法对偏微分方程组进行求解。以迎面风速阶跃变化为典型工况,研究了换热面积、换热系数和工质体积对散热器动态特性的影响。结果如下:当空气侧换热面积增加时,散热器换热量增大,两个稳态之间的空气出口温度差值不变,循环水出口温度差值增加,空气侧响应时间增加,循环水侧响应时间不变。当循环水侧换热面积增加时,散热器换热量增大,两个稳态之间的空气和循环水出口温度差值不变,空气侧和循环水侧的响应时间也不变。换热系数变化时,散热器动态过程的变化规律与换热面积变化时类似。空气侧工质体积变化对散热器动态特性没有影响。循环水侧工质体积增大会使得动态响应时间变长。     

充气热管空气预热器的设计分析及应用

对充气热管空气预热器的结构进行分析和应用介绍,采用平界面模型,确定充气热管冷却段的有效长度。在原始参数相同的条件下,对充气和不充气的热管换热器进行试验,分析热管最低控制工作温度、排烟温度和换热面积之间的差异。工业试验和实际应用结果表明：在变工况和高硫煤(5％-7％)的条件下采用充气热管空气预热器具有十分优良的防腐蚀和防积灰的性能。     

热管空气预热器设计、运行中的几个问题

热管空气预热器结构紧凑,布置方便,换热效果好,但在运行中往往出现热管失效,低温腐蚀、积灰、漏风等问题。究其原因,主要是设计不合理和使用不当造成的。充分考虑实际需要,正确选定各种参数,合理组合工艺路线,完善计量和检测手段,是保证热管空气预热器长寿命、高效、稳定运行的关键。     

电站锅炉热管空气预热器优化设计数学模型

本文提出电站锅炉热管式空气预热器优化设计的数学模型,将预热器最低管子壁温的控制条件引入约束函数失量;对最优化技术在热管空气预热器设计中应用的方法特点作了说明,并给出一个计算实例。     

The influence of secondary refrigerant air chiller U-bends on fluid temperature profile and downstream heat transfer for laminar flow conditions

This paper describes numerical investigations, using computational fluid dynamics, conducted to examine the heat transfer mechanisms by which air-chiller U-bends cause enhanced downstream internal convection, where single phase secondary refrigerants under laminar conditions are employed as the heat exchanger fluid. The numerical model, created using FLUENT, consists of a single heat exchanger tube pass incorporating an inlet pipe, a U-bend and an outlet pipe. The model was validated using experimental data from the literature. Numerical investigations indicate that within the U-bend, secondary flows partially invert temperature profiles resulting in a significant localised decrease in average fluid temperature at the pipe surface. As a result, downstream heat transfer enhancement is observed, the magnitude of which can exceed that typical of a pipe combined entry condition in some circumstances by greater than 20% for up to 20 pipe diameters downstream. Heat transfer enhancement was found to increase with increasing U-bend radius, but to decrease with increasing heat exchanger pipe radius and internal Reynolds number. A simple technique based on quantification of the degree of temperature inversion at the U-bend is proposed which provides a mechanism by which heat transfer enhancement can be estimated.     

开放式热管中温太阳能空气集热装置的试验研究

设计一种使用简化CPC(非追踪式复合抛物线聚光板)集热板和新型开放式热管组合的全真空玻璃集热管中温太阳能空气集热装置。每个集热单元包括一个简化CPC集热板,一根全真空玻璃集热管,在玻璃集热管内安装一个铜管和外部的一个蒸汽包连接构成一个开放式热管结构。蒸汽包内安装螺旋换热管加热通过换热管的流动空气工质。分别使用水和CuO纳米流体作为热管工质,以空气作为集热工质,对热管式中温空气集热器的传热特性进行了实验研究。分析了不同工作压力、不同工质及纳米流体质量分数对热管集热传热特性的影响,详细比较了热管水工质和纳米流体工质在集热传热性能上的优劣。试验结果表明:本系统只使用2根玻璃集热管构成集热器,空气最大出口温度在夏天可达到200℃,在冬天可接近160℃,系统平均集热效率达到0.4以上,整个系统表现了良好的中温集热特性。以纳米流体为工质的热管热阻比以水为工质时平均降低了20%左右     

电站锅炉应用热管式空气预热器的利弊分析

对部分电站锅炉应用热管预热器实际运行的调查研究以及２００ＭＷ燃煤锅炉低温管式空气预热器改热管预热器的各种可实施方案的热力计算结果表明,     

A numerical model for the analyses of heat transfer and leakages in a rotary air preheater

Air preheaters make a considerable contribution to the improved overall efficiency of fossil-fuel-fired power plants. In this study we used a combination of fluid dynamics and a newly developed three-dimensional numerical model for heat transfer as the basis for a theoretical analysis of a rotary air preheater. The model enables studies of the flue-gas flow through the preheater and the adjoining channels as well as the regenerative heat transfer and the resulting temperature distribution in the matrix of the preheater. Special attention was focused on the influences of leakages on the flue-gas parameters in the preheater. The numerical analysis and the experimental results showed an obvious dependence of the flue-gas parameters on various seal settings. Based on the results a method for online monitoring of the tightness of the radial seals is proposed.     

螺纹管空气预热器在有机热载体炉上的应用及其设计

介绍了空气预热器的作用机理、螺纹管空气预热器在有机热载体炉系统中的应用及其具体结构设计。     

Numerical Investigation of Heat Transfer Performance of Rectangularly Coiled Pipes

A numerical simulation was conducted to investigate convective heat transfer from small and compact coiled pipes heat exchangers using computational fluid dynamics (CFD) software Fluent V6. One fluid (air) moves over the coiled pipe while a second fluid (refrigerant R141B) at different temperature flows through the pipe. The studied heat exchanger is composed with bends and straight tubes. Calculations were done for two cases with different outside flow arrangements. The simulation results showed remarkable differences in the flow characteristics and heat transfer rate of different single tubes of the entire heat exchangers. The temperature distribution and heat transfer are mainly influenced by temperature gradient, backflow conditions, exterior flow velocity, and surface area. The results also show the effect of the bends on the flow in straight tubes and vice-versa.     

Research,development and industrial application of heat pipe technology in China

This paper introduces some typical cases of industrial applications, which include the equipment for the waste heat recovery and the industrial process equipment. Carbon steel–water heat pipe technology, applied to air preheater and waste heat boiler, has been successfully used in many fields, such as waste heat recovery, energy conservation and environmental protection. Liquid metal high-temperature heat pipe technology has been extensively employed in the process equipment, for example, high-temperature hot air generators and heat extractors. Heat pipe technology also finds its use in chemical reactors including ammonia converters. The success of applications is founded on the basis of fundamental research of heat pipe technology, which includes the theoretical and experimental researches on the vapor–liquid two-phase flow and heat transfer inside the heat pipe, the heat transfer limits of heat pipes, the heat transfer enhancement with heat pipes, and researches on the material compatibility and life tests of heat pipes. Hi-efficient heat pipe heat and mass transfer equipment is going to play a more and more important role in the various industrial fields.     

中深层地热地埋管实际运行影响因素研究

为研究中深层地热地埋管运行的影响因素,分析西咸新区中深层地热地埋管供暖系统的长期运行结果,并结合关中地区地质数据,建立深度为2510 m的中深层地埋管换热器全尺寸模型,采用数值模拟法研究实际岩层分布下地埋管的运行、结构和材料因素对其取热能力的影响。结果表明,西咸新区某项目1号地埋管和2号地埋管两个地埋管,其平均取热功率均在310 kW以上,具有优良的取热能力。地埋管进水温度随季节变化明显,并引起用户侧负荷及热泵回水温度的波动。在结构方面,随内管径由63 mm增至125 mm,平均出口水温和换热功率分别降低1.9%和4.8%,但内管径过小将影响内管运行的安全性,综合安全和换热两方面因素,最佳内管径应选取ϕ110 × 10mm规格;随外管径由168.3 mm增至244.5 mm,平均出口水温和换热功率分别增加3.5%和9%,综合成本和换热两方面因素,最佳外管径应选取ϕ 177.8 × 19 mm规格;在运行方面,地埋管出口水温随着流量的增加而减小,换热功率随着流量增加而增加;出口水温随着进水温度的升高而上升,换热功率也随之减小。在材料方面,减小内管导热系数和增加固井材料导热系数均能增加地埋管出口水温和换热功率,考虑换热功率变化和成本因素,在工程中导热系数为0.42 W/（m∙K）的内管和导热系数为3 W/（m∙K）左右的固井材料。     

地道风系统地埋管管径对出口空气温度的影响研究

构建了空气与地道壁面换热理论模型,用于计算地埋管出口空气温度,通过正交模拟分析了地埋管管径、长度以及进口风速对地埋管出口空气温度的影响,并与数值模拟结果进行对比.结果 表明:地埋管管径极差值最大,可达20.4 m,是地埋管出口空气温度的主要影响因素,地埋管长度和进口风速为次要因素;随着管径的增大,出口空气温度随之升高;...     

IMPROVEMENT IN PERFORMANCE OF COOL-THERMAL DISCHARGE SYSTEMS FROM ICE MELTING WITH PRODUCING CHILLED AIR UNDER CONSTANT HEAT FLUX AND EXTERNAL REFLUXES

The effects of recycle at the ends on the heat transfer through two parallel plates with one side heated and the other side insulated in cool-thermal discharge systems by melting ice have been studied to produce chilled air under constant heat flux at the free liquid surface. The mathematical formulation was derived from an analysis of the heat transfer coupled with a moving boundary to estimate the required air mass flow rate by direct contact of air with melting ice. The numerical results show that the recycle can enhance the heat transfer rate, and thus lower outlet chilled air temperature during on-peak daytime hours, represented graphically and compared with that in an open duct of the same working dimensions without recycle. Three examples of inlet air temperatures with specified discharge fluxes are discussed. The effect of recycle on the enhancement of heat transfer efficiency is also delineated.     

Design of A Single Tube Fuel Oil Preheater

This article presents design analysis of a fuel oil preheater. The preheater is a concentric tube heat exchanger where the fuel oil is on the tube-side and the heating medium flows in the annular space. Two situations were addressed in this study. In the first case, an analytical model was developed where the required heat exchanger length, diameter and the fluid velocity were determined for a given heat transfer duty and for an allowable pressure loss. A detailed study was conducted by individually varying parameters such as pressure loss, preheater discharge temperature, and mass flow rate of the fuel oil. In each instance their influence on the predicted design of the heat exchanger was investigated. In the second case, an optimization strategy was proposed for a certain heat transfer duty. The heat exchanger dimensions and the fluid flow rate were selected such that the annual operating cost of the heat exchanger was minimized. In addition, a detailed study was conducted to understand the total annual operating cost as a function of the fuel oil outlet temperature and the fuel oil mass flow rate.