燃煤锅炉吹灰过程的熵产分析

电站燃煤锅炉运行中对受热面进行吹灰,要经历一系列不可逆过程,出现各种熵产,从热力学第二定律出发,分析电站锅炉吹灰过程的熵产,建立了吹灰蒸汽减压熵产、吹灰蒸汽混合熵产、吹灰蒸汽传热熵产、吹灰蒸汽排烟熵产以及吹灰器电机熵产的计算模型.利用某台燃煤锅炉的现场数据进行了实例计算,结果表明:同一个受热面吹灰所产牛的各种熵产在数值...     

轴流风机动叶异常对风机内熵产影响的数值模拟

采用Fluent软件对OB-84型轴流风机动叶安装角异常情况进行数值模拟,并用熵产理论研究和分析了风机动叶安装角异常前后的熵产分布特征．结果表明：湍流耗散为风机熵产的主要来源,动叶区和导叶区的熵产率较高,集流器区和扩压区的熵产率很小,但动叶区、导叶区和扩压区的总熵产处于同一数量级．叶片偏离程度对风机熵产有不同程度的影响,除异常叶片安装角偏离值△β±10°外,风机内的熵产均高于正常值,且熵产随△β增大而提高,但当△β〉30°时,△β对风机内熵产的影响有所减弱;同向偏离时,在异常叶片下游形成影响多流道的高熵产带,而反向偏离时的高熵产率区仅呈现零散分布;在相同偏离程度下,同向偏离对熵产的影响大于反向偏离．     

螺旋翅片管束换热过程的熵产分析

对不同翅片间距Sf、管束横向节距St和管束纵向节距Sl的9组螺旋翅片管束的换热和流动过程进行了试验研究.分析了换热过程的熵产,研究了雷诺数(RP)、翅片间距、管束横向节距和管束纵向节距对管束换热熵产数NsH、流动熵产数NsF和总熵产数Ns的影响.结果表明:对不同布置方式的管束,随着Re的增加,NsH迅速减小,NsF逐渐增加,Ns先减小后增加;翅片间距对NsH影响较小,在高Re下,翅片间距增大时,NsF和Ns均明显降低;横向节距对NsH几乎没影响,但随着横向节距的增加,NsF和Ns均明显降低;管束纵向节距对NsH、NsF和Ns的影响都很小.     

电站锅炉运行中换热器传热熵产的试验研究

建立了换热器传热熵产的理论模型,然后利用采集的某火电厂实时运行数据计算得出锅炉运行中换热器的传热熵产变化曲线,并分析了负荷变化和负荷稳定过程中影响其熵产变化的因素,最终提出了可以利用传热熵产监测受热面清洁状况进而开发基于熵产最小理论的吹灰优化新策略的理念.     

电站锅炉换热器传热熵产影响因素的试验研究

首先建立了换热器传热熵产的理论模型,然后利用采集的某火电厂实时运行数据计算得出锅炉运行中换热器的传热熵产变化曲线,并分析了负荷变化和负荷稳定过程中影响其熵产变化的因素,最终提出了可以利用传热熵产监测受热面清洁状况进而开发基于熵产最小理论的吹灰优化新策略的理念.     

火焰参数对辐射图像法不同测温模型的影响

对火焰温度分布的实时测量能够了解燃烧过程、验证燃烧机理、预防工业事故、优化燃烧设备。图像法测温在工业现场的火焰三维温度测量上有明显的优势,但通常均考虑火焰为均匀折射率介质,给测温结果带来了不可避免的误差。本文建立了梯度折射率介质下火焰的辐射成像模型和图像法测温模型,验证了方法的正确性,分析了火焰尺寸对成像的影响及炭黑颗粒浓度对温度场重建的影响。得出随着火焰尺寸的增大,图像强度随火焰尺寸出现先增大后减小的趋势,梯度介质模型与均匀介质模型的差异逐渐增大,随着炭黑颗粒浓度的增加,两种模型的重建精度逐渐下降。     

系统参数对超临界水冷堆子通道熵产影响分析

利用流体力学计算软件CFX,采用结构化网格,研究系统参数如系统压力、热流密度以及质量流率对超临界水冷堆堆芯子通道内熵产行为的影响。湍流模型选择SSG雷诺应力模型,近壁面采用加强壁面处理方法。研究结果表明:系统压力对子通道熵产的影响有限,而热流密度和质量流率的影响则更为显著。随着热流密度的升高,传热对熵产的贡献增大,子通道内主流熵产增加;随着质量流率的升高,流体摩擦阻力对熵产的贡献增大,子通道内主流熵产减少。为了从热力学角度综合评估系统参数对主流熵产行为的影响,引入无量纲熵产数,进一步获得合理的热流密度和质量流率的系统参数设计方案,为超临界水冷反应堆的概念设计提供一定的理论指导。     

偏振对辐射传递计算精度的影响

偏振是散射光的重要特征之一,而标量辐射传输方程中不包含有偏振信息。当考虑散射光的偏振或者是有高精度要求时,需用矢量辐射传输方程。利用求解矢量辐射传输方程的双层迭代解法,针对两种均匀介质中单色偏振辐射传输的一维平行平板模型,分析了偏振对辐射强度和热流计算结果的影响。计算结果表明,若不考虑偏振,在反照率较大、光学薄、有镜反射表面的一维介质中辐射强度的最大相对误差可以达到10％左右;在反照率较大、光学厚、有平行光源入射的一维介质中辐射强度的最大相对误差可以达到6％～7％左右。而不考虑偏振时对热流的计算结果的影响并不大。     

PMS协同介质阻挡放电对污泥水解及厌氧产酸效果的影响

鉴于强化污泥水解对于改善厌氧产酸效果的重要作用,在分析介质阻挡放电(DBD)、过一硫酸盐(PMS)单独破解污泥的反应参数及结果后,将两者进行联合,探讨联合反应后污泥水解及厌氧产酸效果的变化。结果表明,DBD放电或PMS单独处理对于污泥水解效果有限,当两者联合后,污泥的水解效果显著提高,说明PMS能被放电活化从而产生协同作用,其最佳反应条件为放电电压11kV、频率10kHz、时间20min、PMS投加量n(HSO_5~-)=1.0mmol/gTS;HO·、SO_4~-·为参与反应的重要活性物质;剩余污泥经预处理后能显著提高厌氧发酵系统中挥发酸的产量,并促进多碳酸向乙酸转化。     

内衬管对U型辐射管表面温度分布的影响

通过FLUENT软件,对U型辐射管内的燃烧与传热过程进行了三维数值模拟。研究了内衬管相对位置对辐射管表面温度分布以及烟气中污染物含量的影响。结果表明:当内衬管相对燃烧室距离40～60 mm时,管内燃烧与传热情况较好;烟气中NO的含量与内衬管位置无明显关系。     

Entropy flow,entropy generation,exergy flux,and optimal absorbing temperature in radiative transfer between parallel plates

Taking nonequilibrium radiative heat transfer between two surfaces as an example, the nonequilibrium thermodynamics of radiation is studied and discussed. The formulas of entropy flow, entropy generation, exergy flux, and optimal temperature of absorbing surface for maximum exergy output are derived. The result is a contribution to the thermodynamic analysis and optimization of solar energy utilization and can be applied in more complex radiative heat transfer cases.     

SLA (Second-law analysis) of transient radiative transfer processes

This paper concerns a SLA (second-law analysis) of transient radiative heat transfer in an absorbing, emitting and scattering medium. Based on Planck’s definition of radiative entropy, transient radiative entropy transfer equation and local radiative entropy generation in semitransparent media with uniform refractive index are derived. Transient radiative exergy transfer equation and local radiative exergy destruction are also derived based on Candau’s definition of radiative exergy. The analytical results are consistent with the Gouy–Stodola theorem of classical thermodynamics. As an application concerning transient radiative transfer, exergy destruction of diffuse pulse radiation in a semitransparent slab is studied. The transient radiative transfer equation is solved using the discontinuous finite element based discrete ordinates equation. Transient radiative exergy destruction is calculated by a post-processing procedure.     

Influence of conjugate heat transfer on the minimization of entropy generation for forced convective flow through parallel plate channel filled with porous material

A fluid–solid conjugate heat transfer model is developed to analyze the characteristics of entropy generation for forced convective steady hydrodynamically fully developed laminar flow of a Newtonian fluid through a parallel plate channel filled with porous material by modulating the following parameters: substrate thickness, the ratio of thermal conductivity of wall to fluid, Biot number, the axial temperature gradient in the fluid, and Peclet number. The exteriors of both the walls are subjected to the thermal boundary conditions of the third kind. The mass and Brinkman momentum conservation equations in the fluidic domain and the coupled energy conservation in both the solid and fluidic domain are solved analytically using the local thermodynamic equilibrium model, so as to derive closed-form expressions for the velocity in the fluid and the temperature both in the fluid and solid walls in terms of relevant parameters. Suitable combinations of influencing factors, namely the geometric parameters of the system, fluid, flow, and substrate properties are identified for which global entropy generation rate is minimized. The findings may be helpful in the design of thermal systems frequently used in diverse engineering applications having heat transfer in the solid wall being a crucial parameter.     

Effect of gas radiation on radiative heat transfer in urban street canyon model

In this paper, we describe the results of numerical simulation of radiative heat transfer between the human body and an urban street canyon (building walls, pavement, and the sky) in the presence of participating non‐gray gas mixtures consisting of H₂O and CO₂. The ambient temperature in typical summer conditions and the concentration of gas mixtures during summer in Tokyo were assumed. Further, the parallel infinite plane model and simple urban street canyon model were used. The results show that the participating gas significantly affects the infrared radiation field in an urban street canyon. The radiation flux emitted by the participating gas is approximately 35% of the total radiation flux incident on the human body surface. This causes a homogenization of the infrared radiation field surrounding the human body. Gas radiation plays an important role in the heat transfer between the human body and the environment under hot and humid summer conditions. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20258     

传热与流动系统熵产生的研究与进展

本文综述了熵产分析在传热与流动系统的研究与进展,包括对流传热传质、基本流动传热、换热器、热能贮存系统、绝热层布置等方面的研究与进展。     

MHD conjugate heat transfer and entropy generation analysis of MWCNT/water nanofluid in a partially heated divided medium

The aim of this article is to conduct the lattice Boltzmann simulation of the magnetohydrodynamic (MHD) natural conjugate heat transfer in an apportioned cavity loaded with a multiwalled carbon nanotube/water nanofluid. The divided cavity is, to some extent, heated and cooled at the upright walls, whereas the horizontal walls are adiabatic. The nanofluid properties are evaluated on the basis of experimental correlations. The parameters ranges in the study are as follows: nanoparticles' volume fraction (%): 0 ≤ ? ≤ 0.5, temperature (°C): T = 27, Rayleigh number (Ra): 10³ ≤ Ra ≤ 10⁵, Hartmann number (Ha): 0 ≤ Ha ≤ 90, and the magnetic field inclination angle (γ): 0 ≤ γ ≤ π/2. The current outcomes are observed to be in great concurrence with the numerical results introduced in the literature. The impacts of the aforesaid parameters on local and average heat transfer, entropy generation, and Bejan number (Be) are explored and discussed. Indeed, the transfer of heat increases linearly with ? for a low Ra. As Ra increases, the average Nusselt number decreases for a high value of ?. The increase of nanoparticles' volume fraction leads to a reduction in the entropy generation and an increase in the Bejan number for a high Ra, but at low Ra, these functions remain constant. As the Ha increases, the transfer of heat and the entropy generation decreases, whereas there is an increase in Be. The transfer of heat, total entropy generation, and the Be depends strongly on the direction of the magnetic field. The increase of heater and cooler size has a great influence on the transfer of heat, entropy generation, and Be.     

Entropy generation minimization and nonlinear heat transport in MHD flow of a couple stress nanofluid through an inclined permeable channel with a porous medium,thermal radiation and slip

Irreversible losses and heat transport in a magnetohydrodynamic flow of a viscous, steady, incompressible, and fully developed couple stress Al₂O₃–water nanofluid through a sloping permeable wall channel with porous medium and under the effect of radiation heat flux and slip were analyzed. The fundamental equations were solved numerically by using Runge-Kutta together with the shooting technique and the results were in qualitative agreement with an exact solution obtained for a limit case. The impacts of couple stress, Darcy number, solid nanoparticle concentrations, conduction-radiation parameter, Hartmann number and hydrodynamic slip on flow, temperature, heat transport, and entropy production were examined. It was possible to achieve values of minimum entropy production not yet reported in previous studies. In this way, optimal values of couple stress and slip were obtained. The heat transport was also explored and optimal values of slip flow and conduction-radiation parameter with maximum heat transfer were found. Finally, in addition to the alumina, the distributions of velocity, temperature, and entropy generation in TiO₂–water and Cu–water were presented for different solid nanoparticle concentrations. It was obtained that the local entropy of TiO₂–water was lower than Cu–water and Al₂O₃–water in the channel bottom region while it was greater in the upper region.     

H形对流传热脉管的熵产率最小构形优化

针对H形对流传热脉管,以脉管区域面积和通道总表面积为约束,在线热流密度恒定时,基于熵产生最小化进行了构形优化,给出了无量纲总熵产量和无量纲单位传热负荷的总熵产率与脉管组合级数、无量纲质量流量和无量纲泵功率的完整解析关系式及优化算例.结果表明:给定通道总表面积与文献中给定通道总体积约束的优化结果是不同的;无量纲单位传热负...