三分仓回转式空气预热器传热的数值解法

根据回转式空气预热器的工作机理,通过理论分析,把金属蓄热元件视为某一假想的流体,将非稳态传热与金属蓄热元件的机械运动等同于稳态换热过程,采用控制容积法建立了回转式空气预热器的流体动力学传热微分方程组与对应的差分方程组,详细给出了数值解法的计算过程,并以某220 MW锅炉机组的三分仓冷、热分段回转式空气预热器为例,结合实际运行参数进行了校核热力计算.结果表明:该数值解法合理、收敛快且具有合理的计算精度,可以得到空气预热器运行中金属蓄热元件、烟气与空气的温度分布;经与实际运行参数校核,与设计工况参数较吻合.     

基于XR修正的回转式空气预热器换热效率计算方法

依据逆流换热器换热理论模型,基于换热器无因次变量效能、传热单元数和热容量比之间的关系,对回转式空气预热器换热过程进行分析,提出基于XR修正的回转式空气预热器换热效率计算方法。根据某600 MW机组的空气预热器的设计参数及运行数据,利用该计算方法求解得到实际运行工况换热效率。并对该空气预热器进行了蓄热元件更换、密封间隙调整等改造,对改造前后实际运行工况换热效率进行计算。结果表明：未修正的换热效率与XR有较强的相关性,修正后的换热效率离散程度降低,更能反映空气预热器本身的换热能力。不进行修正情况下,改造前、后的平均换热效率分别为67.6%和67.4%,与设计值69.7%有较大的差距,不能体现出空气预热器改造的效果。通过XR修正,改造后的平均换热效率69.3%与设计值69.7%基本相当,高于改造前的平均换热效率,基本达到改造预期效果。该计算方法可更准确的评价空气预热器的实际性能及改造效果。     

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.     

Energy‐saving evaluation of a thermosyphon heat recovery unit for an air‐conditioning system

The energy‐saving effect and economic benefits of a thermosyphon heat recovery unit installed in a shopping mall are investigated. To evaluate the thermal performance of the heat recovery unit in a season, a seasonal temperature effectiveness is advanced, and its calculation formula is deduced referring to the calculation method of seasonal energy efficiency ratio (SEER) for an air conditioner. The annual operating energy‐saving effect of the unit is analyzed by using the seasonal temperature effectiveness while the static economic evaluation method is applied for the economic benefits analysis of the unit. The analysis results indicate the seasonal temperature effectiveness of the unit is 66.08% in the winter and 55.43% in the summer. The energy‐saving effect of the unit is quite remarkable, and the payback time is about 2.65 years. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21049     

直吹式制粉系统与空气预热器的质量能量平衡关系分析

1前言在现代煤粉锅炉中,制粉系统是锅炉设备最重要的辅助系统之一。直吹式制粉系统与锅炉设备的联系尤为密切,直吹式制粉系统的运行条件不但影响进入锅炉炉膛的热量大小和燃料进入炉膛的着火燃烧条件,而且还会影响流经空气预热器的空气量和出口热空气温度,导致空气预热器在尾部     

三维内肋管管式空气预热器的设计与可行性研究

采用强化传热性能优良的新型三维内肋管与传统热能力强、漏风系数小的热管双级布置的方案对300MW电站锅炉机组空气预热器进行了优化设计和可行性研究。空气预热器总的漏风系数设计值为5％,加热一、二次风的上级三维内肋管卧式空气预热器的布置空间分别为螺纹管空气预热器的64．46％和47．87％,相应的受热面积为42．61％和37．32％,这有效地解决了回转式空气预热器漏系大,以及一航管式空气预热器体积庞大、难以布置的问题。     

Numerical Modeling of Fin Heat Exchanger in Application to Cold Storage

The fin-and-tube heat exchanger are extensively used in refrigeration systems applied to cold storage. The performance of the heat exchanger affects the efficiency of the refrigeration system. Prediction of temperature, humidity, as well as velocity distribution in a cold storage chamber requires accurate prediction of operation of the finned air cooler. The operation of the air cooler unit is usually taken into account in modeling of operation of the cold storage chambers, but with very simplified geometry and physics. On the other hand numerical investigations of the heat exchangers are focused on thermal performance mostly in order to improve the overall heat transfer coefficient or to optimize its geometry. Results of numerical modeling using the computational fluid dynamics software ANSYS FLUENT of fin-and-tube air cooler applied on a cold storage chamber is presented in the paper. Two different approaches were used: the dual cell model, and porous media conditions. Numerical predictions of air temperature as well as air velocity at the air cooler outlet were also validated on the basis of the own experimental data.     

Design and characterization of a cylindrical,water‐cooled heat sink for thermoelectric air‐conditioners

Thermoelectric air‐conditioners (TEACs) are becoming much concerned due to their many advantages, but the low COPs limit their broad applications. The two key factors to raise the COPs of TEACs are both the improvement of thermoelectric materials and the optimum design of hot side heat sinks. This paper provides a thermoelectric air‐conditioning system with a water‐cooled sleeve heat sink in the hot side of the thermoelectric pellets, and compares the overall heat transfer rates q_t, the total heat resistances R_t between the water‐cooled and air‐cooled heat sinks as well as the optimum fin length, the optimum fluid flow velocity and the optimum fin gap distance. The simulation results show that the overall heat transfer rate of water‐cooled heat sink is more than 20 times that of air‐cooled heat sink under the other same circumstances, as a result of the improvement of heat sink, the optimum COP of the thermoelectric air‐conditioning system with the water‐cooled heat sink proximately doubles that with the air‐cooled heat sink. This novel system could be simply installed and applied all the year round for cooling in summer and heating in winter. Copyright © 2005 John Wiley & Sons, Ltd.     

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 heat pipe is determined according to the flat interface model. With the same initial conditions, the comparisons between variable conductance heat-pipe air preheater and regular heat pipe air preheater has been analyzed and tested in terms of heat pipe wall temperature, heat transfer surface area and outlet fluid temperatures. Based on the real industrial applications, it has been confirmed that the variable conductance heat pipe air preheater has excellent performance of anti-corrosion and anti-ash-deposition especially at the variable working condition and the sulfur coal (5%-6% mass fraction of sulfur) condition.     

Analysis of two‐dimensional heat and moisture transfer during drying of spherical objects

This paper deals with the numerical and analytical modelling of two‐dimensional heat and moisture transfer during drying of a spherical object. Drying is considered to be a process of simultaneous heat and moisture transfer whereby moisture is vapourized by means of a drying fluid (e.g. air), as it passes over a moist object. Numerical modelling of two‐dimensional heat and moisture transfer during drying of a spherical object is carried out using an explicit finite‐difference approach. Temperature and moisture distributions inside the object are determined by using the developed computer code. Moreover, the results predicted from the present model are compared with the experimental data available in the literature and a considerably high agreement is found. Copyright © 2003 John Wiley & Sons, Ltd.     

Numerical study of heat transfer enhancement and fluid flow with inline common‐flow‐down vortex generators in a plate‐fin heat exchanger

Three‐dimensional numerical simulations are performed on a plate‐fin heat exchanger (with triangular fins as inserts between the plates) to evaluate the laminar heat transfer and fluid flow characteristics with longitudinal vortex generators (LVGs). The effect with an inline rectangular winglet pair (RWP) with a common‐flow‐down (CFD) configuration is studied. The numerical results indicate that the application of inline LVGs effectively enhances the heat transfer of the channel. The heat transfer further increases with the increase in the Reynolds number from 200 to 500 and angle of attack from β = 15° to 22.5°. The computations are also performed to find the best location for the second RWP. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20414     

火电厂空气预热器旁路余热利用系统经济性分析

为实现对某电厂空气预热器旁路烟气余热利用系统的经济性综合评价,针对采用空气预热器旁路的机组提出了一种锅炉效率检测和计算方法,将空气预热器旁路传递的烟气热量作为锅炉热损失的一部分,确立了一套以试验检测为基础,结合理论推导计算的评价方法,定量分析了空气预热器旁路余热利用系统运行对锅炉效率、汽轮机热耗和厂用电率的影响,并开展...     

Exergy analysis on the irreversibility of rotary air preheater in thermal power plant

Energy recovery devices can have a substantial impact on process efficiency and their relevance to the problem of conservation of energy resources is generally recognized to be beyond dispute. One type of such a device, which is commonly used in thermal power plants and air conditioning systems, is the rotary air preheater. A major disadvantage of the rotary air preheater is that there is an unavoidable leakage due to carry over and pressure difference. There are gas streams involved in the heat transfer and mixing processes. There are also irreversibilities, or exergy destruction, due to mixing, pressure losses and temperature gradients. Therefore, the purpose of this research paper is based from the second law of thermodynamics, which is to build up the relationship between the efficiency of the thermal power plant and the total process of irreversibility in the rotary air preheater using exergy analysis. For this, the effects of the variation of the principal design parameters on the rotary air preheater efficiency, the exergy efficiency, and the efficiency of the thermal power plant are examined by changing a number of parameters of rotary air preheater. Furthermore, some conclusions are reached and recommendations are made so as to give insight on designing some optimal parameters.     

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。     

Solutal Dispersion and Viscous Dissipation Effects on Non‐Darcy Free Convection Over a Cone in Power‐Law Fluids

The effects of viscous dissipation and solutal dispersion on free convection about an isothermal vertical cone with a fixed apex half angle, pointing downwards in a power‐law fluid‐saturated non‐Darcy porous medium are analyzed. The governing partial differential equations are transformed into partial differential equations using non‐similarity transformation. The resulting equations are solved numerically using an accurate local non‐similarity method. The accuracy of the numerical results is validated by a quantitative comparison of the heat and mass transfer rates with previously published results for a special case and the results are found to be in good agreement. The effects of viscous dissipation, solutal dispersion, and/or buoyancy ratio on the velocity, temperature, and concentration field as well as on the heat and mass transfer rates are illustrated, by insisting on the comparison between pseudo‐plastic, dilatant, and Newtonian fluids. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(5): 476–488, 2014; Published online 11 November 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21095     

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...     

Experimental and numerical study on charging processes of an ice‐on‐coil thermal energy storage system

In this study, an external melt ice‐on‐coil thermal storage was studied and tested over various inlet conditions of secondary fluid—glycol solution—flow rate and temperature in charging process. Experiments were conducted to investigate the effect of inlet conditions of secondary fluid and validate the numerical model predictions on ice‐on‐coil thermal energy storage system. The total thermal storage energy and the heat transfer rate in the system were investigated in the range of 10 l min ^?1?V??60 l min ^?1. A new numerical model based on temperature transforming method for phase change material (PCM) described by Faghri was developed to solve the problem of the system consisting of governing equations for the heat transfer fluid, pipe wall and PCM. Numerical simulations were performed to investigate the effect of working conditions of secondary fluid and these were compared with the experimental results. The numerical results verified with experimental investigation show that the stored energy rises with increasing flow rate a decreasing tendency. It is also observed that the inlet temperature of the fluid has more influence on energy storage quantity than flow rate. Copyright © 2006 John Wiley & Sons, Ltd.     

Operational aspects of adsorption air‐conditioner used in diesel locomotive

A locomotive cabin adsorption air‐conditioner has been equipped in #DF4B‐2369 locomotive; and has been successfully run for 2 years. It is powered by waste heat from the exhaust of the diesel engine. The influence on heat transfer is described by the equivalent heat transfer coefficient or thermal resistance of components inside the adsorber. The variation of adsorption capacity is expressed by a non‐equilibrium adsorption function. The dynamic heat transfer process of adsorption air‐conditioning system is treated with the lumped parameter method. Some typical running experimental results are present. The diesel engine rotating speed and locomotive speed influenced on the refrigeration system are discussed. The maximum mean refrigeration power is regarded as an objective function. Based on experiments and theoretical analysis, the running characteristics of the air‐conditioning system are optimized. Some techniques of performance improvement are suggested as well. Copyright © 2006 John Wiley & Sons, Ltd.     

Thermo‐economic Optimization of Gas Turbine Power Plant with Details in Intercooler

In this paper a gas turbine power plant with intercooler is modeled and optimized. The intercooler is modeled in details using the ε ? NTU method. Air compressor pressure ratio, compressor isentropic efficiency, gas turbine isentropic efficiency, turbine inlet temperature, cooling capacity of the absorption chiller, recuperator effectiveness as well as eight parameters for configuration of the intercooler are selected as design variables. Multi‐objective genetic algorithm is applied to optimize the total cost rate and total cycle efficiency simultaneously. Two plants including an intercooler and with/without air preheater are studied separately. It is observed that the air compressor pressure ratio in the HP compressor is higher than the LP compressor in both cases and its differences are higher for a plant without an air preheater. Actually the air compressor pressure ratio is found to be about 8.5% lower than the ideal value and 9.5% higher than the ideal value in the LP compressor and HP compressor, respectively, in the case with an air preheater. Moreover, a correlation for intercooler pressure drop in terms of its effectiveness was derived in the optimum situation for each case. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(8): 704–723, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21051     

Shape optimization of steady‐state heat‐conduction fields considering temperature dependency of thermal conductivity coefficient

This paper presents a numerical analysis method for shape optimization of domains with steady‐state heat‐conduction fields considering the temperature dependence of the thermal conductivity coefficient. In this paper, we formulate two shape optimization problems, namely, maximization of thermal dissipation on heat transfer boundaries and minimization of heat‐conduction fields. The shape gradient functions for these shape optimization problems are derived theoretically using the Lagrange multiplier method and formulae of the material derivative. Reshaping is accomplished using the traction method proposed as a solution to the shape optimization problems. The proposed method is validated from the results of two‐dimensional numerical analysis. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20374