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在自行设计的无焰燃烧系统中探究了生物质气化燃气无焰燃烧的温度场、污染物排放等特性,研究预热温度(950 K、1 000 K、1 050 K、1 100 K)、当量比(0.45、0.60、0.75、0.90)、不可燃成分组成(BGG1~4)对燃烧特性的影响,并找到最优运行参数.结果表明,生物质气化燃气无焰燃烧时具有传统燃料类似的均匀温度场和低污染排放,但是整体温度更低,污染物排放更低.预热温度、不可燃成分、当量比等因素由高到低影响燃烧的热效应.最优的运行参数为:预热温度1 100 K,当量比0.9;不可燃成分组成BGG1为60%N2+5%CO2. 相似文献
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现有获取热能的主要方法是在燃烧室中将有机燃料燃烧 ,燃烧时的温度高达 170 0℃。为了实现燃料在环保方面清洁燃烧 ,必须把温度降到 85 0~ 90 0℃ ,这对于应用通常方法完成气体燃料的均相燃烧过程来说 ,是无法实现的。提出的催化法与传统的燃烧方法相比有以下优越性 :燃烧效率高 ;不产生对人体健康有害的 CO和 NOX 气体 ;煤气与空气可以组成任何比例成分的混合物。介绍了一些非传统性的应用触媒使烃煤气氧化的方法 ,包括三种形式的加热元件、应用系统和热交换计算方法。图 4表 1参 10应用触媒催化法使烃(碳氢化合物)煤气氧化而获取热量@… 相似文献
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针对单个碳颗粒在静止气氛中的燃烧过程,进行了包括详细的物理和化学模型在内的瞬态数值模拟。研究了粒径收缩、初始粒径(50~200μm)、环境氧气的体积分数(9%~21%)和气相温度(1 200~1 600 K)对燃烧过程的影响。结果表明:碳粒燃烧过程中,碳粒表面温度先逐渐升高后迅速下降至环境温度,峰值温度出现在碳粒半径为35~45μm的范围内;碳粒收缩过程符合d2定律,推导得到的碳粒单位面积燃烧速率?与粒径rs的反比例关系式可用于对碳粒燃烧速率的预测计算;碳粒燃烧过程的特征值只取决于当前的颗粒直径,与其先前的演变过程无关;碳粒粒径越小,温度越低,化学动力学对燃烧过程的控制能力越强;初始碳粒半径相同时,升高气相温度或环境氧气的体积分数不会改变燃烧过程特征值的基本变化趋势,燃烧速率和碳粒表面温度均随气相温度或环境氧气体积分数的增大而增大,其中气相温度升高会导致碳粒表面温度达到峰值时的粒径减小。 相似文献
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利用1 MW循环流化床试验台进行了石煤和烟煤的混燃试验,对燃烧过程中炉膛温度、燃烧效率、成灰特性的数据进行了分析,结果表明石煤与烟煤混燃稳定,燃烧效率较高,灰渣的粒度特性有利于灰渣的综合应用,可为石煤的综合利用技术提供依据。 相似文献
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在平面扩散火焰煤粉燃烧实验系统上采用光纤光谱仪和CMOS相机分别测量了不同燃烧气氛(O_2/N_2、O_2/CO_2)、热协流温度(1 473~1 873 K)和氧气体积分数(5%~20%)下烟煤煤粉燃烧火焰的辐射光谱和火焰图像,获得了不同燃烧条件下煤粉颗粒温度沿程分布和燃烧特性。结果表明:在O_2/N_2或O_2/CO_2气氛下,随着热协流温度和氧气体积分数的降低,火焰颜色由亮黄色逐渐转变为暗红色,煤粉颗粒温度降低;随着热协流氧气体积分数的下降,煤粉颗粒温度波动系数减小了37%,颗粒温度分布更均匀;与O_2/N_2气氛相比,O_2/CO_2气氛下煤粉火焰光强减弱,煤粉着火距离增加,煤粉颗粒的平均温度降低了24~103 K,颗粒温度波动系数最大减小了24%。 相似文献
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三、膜式富氧化燃烧系统的节能分析1 富氧燃烧的节能效果采用富氧空气燃烧时,与普通空气比较,最大的特点是单位燃料所需要的空气量减少。对同一固体燃料(含 C:80%、H:5%、O:3%,硫不计)的计算表明:每公斤燃料燃烧所需的30%富氧空气理论量为普通空气量的70%,由此,可有下列两种效果:(1)火焰温度升高在基准温度为0℃下及理论空气量下完全燃烧,并且完全没有热损失时的理论绝热燃烧温度 t_(ad)与理论排气量 V_0成反比:t_(ad)=H/(V_0C_(pm)) (4)但是,实际上燃烧室内的燃烧温度 t相似文献
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将天然气催化燃烧炉窑应用到琉璃烧制中。并在催化燃烧过程中始终保持2.0的过量空气系数,通过合理调节空气和天然气的流量值,使得炉窑内温度缓慢达到900℃左右。研究表明:炉窑内温度分布满足烧制要求,且当达到稳定催化燃烧时,排放烟气中甲烷和NO_x、CO等污染物含量均为1 mg/m~3左右,甲烷几乎完全燃烧且污染物达到近零排放,说明天然气催化燃烧炉窑适合琉璃烧制,且具有节能环保的特性。 相似文献
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循环流化床锅炉动态运行特性模型研究 总被引:1,自引:0,他引:1
循环流化床锅炉由于其高效、低污染、燃料适应性强等优点 ,在热电行业内得到广泛的应用。其燃烧系统是一个分布参数、非线性、实变、多变量紧密耦合的对象。通过建立包括燃烧系统和汽水系统在内的总体数学模型 ,对 1台 2 2 0t/h循环流化床锅炉的动态特性进行了仿真计算。仿真结果表明 ,燃烧系统耦合性强 ,给煤量和送风量对床层温度和蒸汽温度都有明显影响 ;滞后时间大 ,燃料加入后 ,经较长的时间才会影响到主汽温度和床层温度的变化。研究结果为循环流化床锅炉燃烧控制系统设计和优化提供基础 ,为从根本上解决循环流化床锅炉燃烧控制系统自动投入率低的问题创造条件。 相似文献
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木基和竹基生物质燃料燃烧动力学特性研究 总被引:1,自引:0,他引:1
《可再生能源》2015,(10)
选用木基和竹基生物质燃料进行燃烧热重实验,分段推断其燃烧反应机理及拟合计算动力学参数,探究燃烧动力学特性随温度变化规律。结果表明:木基生物质燃料着火温度、燃尽温度、挥发分析出燃烧最大速率及其对应温度均低于竹基生物质燃料,焦炭燃烧阶段前者的燃烧速率大于后者;木基生物质燃料挥发分析出燃烧初期(260~280℃)和过渡阶段(360~440℃)燃烧反应机理为三维扩散机理(G11),挥发分析出燃烧及焦炭燃烧最大速率前后的机理函数不相一致,竹基生物质燃料整个燃烧反应过程可用同一机理函数描述。挥发分析出燃烧阶段,木基生物质燃料活化能随温度按"增加-下降-增加-下降"变化,竹基生物质燃料则先增加至峰值后下降。 相似文献
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《International Communications in Heat and Mass Transfer》1999,26(5):669-678
An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effects of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distribution is carried out using a finite element method. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in fluid flow. Using these models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance variations are quite significant in some typical applications. 相似文献
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Heat conduction appears in almost all natural and industrial processes. In the current study, a two‐dimensional heat conduction equation with different complex Dirichlet boundary conditions has been studied. An analytical solution for the temperature distribution and gradient is derived using the homotopy perturbation method (HPM). Unlike most of previous studies in the field of analytical solution with homotopy‐based methods which investigate the ODEs, we focus on the partial differential equation (PDE). Employing the Taylor series, the gained series has been converted to an exact expression describing the temperature distribution in the computational domain. Problems were also solved numerically employing the finite element method (FEM). Analytical and numerical results were compared with each other and excellent agreement was obtained. The present investigation shows the effectiveness of the HPM for the solution of PDEs and represents an exact solution for a practical problem. The mathematical procedure proves that the present mathematical method is much simpler than other analytical techniques due to using a combination of homotopy analysis and classic perturbation method. The current mathematical solution can be used in further analytical and numerical surveys as well as related natural and industrial applications even with complex boundary conditions as a simple accurate technique. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20292 相似文献
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Y.P. Du Z.G. Qu C.Y. Zhao W.Q. Tao 《International Journal of Heat and Mass Transfer》2010,53(21-22):4899-4907
The two equation numerical model has been applied for parallel flow double-pipe heat exchanger filled with open cell metal foams. The model fully considered solid–fluid conjugated heat transfer process coupling heat conduction and convection in open cell metal foam solid matrix, interface wall and fluid in both inner and annular space in heat exchanger. The non-Darcy effect and the wall thickness are also taken into account. The interface wall heat flux distribution along the axial direction is predicted. The numerical model is firstly verified and then the influences of solid heat conductivity, metal foam porosity, pore density, relative heat conductivity and inner tube radius of the heat exchanger on dimensionless temperature distribution and heat transfer performance of heat exchanger are numerically studied. It is revealed that the proposed numerical model can effectively display the real physical heat transfer process in the double pipe heat exchanger. It is expected to provide useful information for the design of metal foam filled heat exchanger. 相似文献
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Jan Taler Piotr Dzierwa Magdalena Jaremkiewicz Karol Kaczmarski Marcin Trojan 《热应力杂志》2019,42(6):698-724
AbstractTwo methods for monitoring the thermal stresses in pressure components of thermal power plants are presented. In the first method, the transient temperature distribution in the pressure component is determined by measuring the transient wall temperature at several points located on the outer insulated surface of the component. The transient temperature distribution in the pressure component, including the temperature of the inner surface is determined from the solution of the inverse heat conduction problem (IHCP). In the first method, there is no need to know the temperature of the fluid and the heat transfer coefficient. In the second method, thermal stresses in a pressure component with a complicated shape are computed using the finite element method (FEM) based on experimentally estimated fluid temperature and known heat transfer coefficient. A new thermometer with good dynamic properties has been developed and applied in practice, providing a much more accurate measurement of the temperature of the flowing fluid in comparison with standard thermometers. The heat transfer coefficient on the inner surface of a pressure element can be determined from the empirical relationships available in the literature. A numerical-experimental method of determination of the transient heat transfer coefficient based on the solution of the 3D-inverse heat conduction problem has also been proposed. The heat transfer coefficient on the internal surface of a pressure element is determined based on an experimentally determined local transient temperature distribution on the external surface of the element or the basis of wall temperature measurement at six points located near the internal surface if fluid temperature changes are fast. Examples of determining thermal and pressure stresses in the thick-walled horizontal superheater header and the horizontal header of the steam cooler in a power boiler with the use of real measurement data are presented. 相似文献
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Fouling is one of the main problems of heat transfer which can be described as the accumulation on the heat exchanger tubes, i.e.; ash deposits on the heat exchanger unit of the boiler. A decrease in heat transfer rate by this deposition causes loss in system efficiency and leads to increasing in operating and maintenance costs. This problem concerns with the coupling among conduction heat transfer mode between solid of different types, conjugate heat transfer at the interface of solid and fluid, and the conduction/convection heat transfer mode in the fluid which can not be solved analytically. In this paper, fouling effect on heat transfer around a cylinder in cross flow has been studied numerically by using conjugate heat transfer approach. Unlike other numerical techniques in existing literatures, an unstructured control volume finite element method (CVFEM) has been developed in this present work. The study deals with laminar flow where the Reynolds number is limited in the range that the flow field over the cylinder is laminar and steady. We concern the fouling shape as an eccentric annulus with constant thermal properties. The local heat transfer coefficient, temperature distribution and mean heat transfer coefficient along the fouling surface are given for concentric and eccentric cases. From the results, we have found that the heat transfer rate of cross-flow heat exchanger depends on the eccentricity and thermal conductivity ratio between the fouling material and fluid. The effect of eccentric is dominant in the region near the front stagnation point due to high temperature and velocity gradients. The mean Nusselt number varies in asymptotic fashion with the thermal conductivity ratio. Fluid Prandtl number has a prominent effect on the distribution of local Nusselt number and the temperature along the fouling surface. 相似文献
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In this article, we first propose the novel semi‐analytical technique—modified Adomian decomposition method (MADM)—for a closed‐form solution of the nonlinear heat transfer equation of convex profile with singularity where all thermal parameters are functions of temperature. The longitudinal convex fin is subjected to different boiling regimes, which are defined by particular values of n (power index) of heat transfer coefficient. The energy balance equation of the convex fin with several temperature‐dependent properties are solved separately using the MADM and the spectral quasi‐linearization method. Using the values obtained from the direct heat transfer method, the unknown parameters of the profile, such as thermal conductivity, surface emissivity, heat generation number, conduction‐convection parameter, and radiation‐conduction parameter are inversely predicted by an inverse heat transfer analysis using the simplex search method. The effect of the measurement error and the number of measurement points has been presented. It is found that present measurement points and reconstruction of the exact temperature distribution of the convex fin are fairly in good agreement. 相似文献
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A method for the measurement of local convective heat transfer coefficients from the outside of a heat-transferring wall has been developed. This method is contact-free and fluid independent, employing radiant heating by laser or halogen spotlights and an IR camera for surface temperature measurements; it allows for the rapid evaluation of the heat transfer coefficient distribution of sizable heat exchanger areas. The technique relies first on experimental data of the phase lag of the outer surface temperature response to periodic heating, and second on a simplified numerical model of the heat exchanger wall to compute the local heat transfer coefficients from the processed data. The IR temperature data processing includes an algorithm for temperature drift compensation, phase synchronization between the periodic heat flux and the measured temperatures, and Single Frequency Discrete Fourier Transformations. The ill-posed inverse heat conduction problem of deriving a surface map of heat transfer coefficients from the phase-lag data is solved with a complex number finite-difference method applied to the heat exchanger wall. The relation between the local and the mean heat transfer coefficients is illuminated, calculation procedures based on the thermal boundary conditions are given. The results from measurements on a plate heat exchanger are presented, along with measurements conducted on pipe flow for validation. The results show high-resolution surface maps of the heat transfer coefficients for a chevron-type plate for three turbulent Reynolds numbers, including a promising approach of visualizing the flow field of the entire plate. The area-integrated values agree well with literature data. CFD calculations with an SST and an EASM–RSM were carried out on a section of a PHE channel. A comparison with the measured data indicates the shortcomings of even advanced turbulence models for the prediction of heat transfer coefficients but confirms the advantages of EASM–RSM in complex flows. 相似文献
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《International Communications in Heat and Mass Transfer》2006,33(3):391-400
One of the newest analytical methods to solve the nonlinear heat transfer equations is using both homotopy and perturbation methods in equations. Here, homotopy–perturbation method is applied to solve heat transfer problems with high nonlinearity order. The origin of using this method is the difficulties and limitations of perturbation or homotopy. It has been attempted to show the capabilities and wide-range applications of the homotopy–perturbation method in comparison with the previous ones in solving heat transfer problems. In this research, homotopy–perturbation method is used to solve an unsteady nonlinear convective-radiative equation and a nonlinear convective-radiative conduction equation containing two small parameters of ε1 and ε2. 相似文献