流化床-煤粉复合燃烧锅炉的炉膛传热计算方法

针对流化床－煤粉复合燃烧锅炉的特点,在综合考虑流化床、火焰和受热面之间换热的基础上,推导了流化床－煤粉复合燃烧锅炉炉膛传热计算的基本方程,得到了复合燃烧锅炉炉膛传热计算的零维模型半径验法。以某７５ｔ／ｈ树皮流化床－煤粉复合燃烧锅炉为例,进行了炉膛传热计算。图１表６参５     

有压相变新型水火管热水锅炉

有压相变新型水火管热水锅炉,可做到锅炉受热面水侧不结垢、无固体杂物附着,烟气侧不积灰;可保证锅炉运行时不产生爆管、管板开裂和锅壳下部鼓包等不安全事故,并使锅炉出力和热效率长期不变。     

应用相变换热技术对65t/h循环流化床锅炉节能改造

为了解决安徽国祯生物质发电有限责任公司65 t/h循环流化床锅炉由于安装运行使用时间较长,造成的受热面传热效率降低,实际排烟温度高达160℃,锅炉排烟损失增加和引风机电耗增加等问题。根据用户要求和现场的实际条件并结合该锅炉自身的特点,提出了在锅炉尾部安装相变换热系统的改造方案,使排烟温度降低至120℃,增加了受热面的传热效率,降低了锅炉的排烟损失。在避免受热面低温腐蚀的同时保证低温烟气余热得到有效、安全的回收。     

锅炉受热面管泄漏分析及预防

锅炉受热面管泄漏是影响电厂安全稳定运行的重要因素。以某电厂运行生产过程中发生的受热面管泄漏为例,通过分析引起锅炉受热面管泄漏的原因,并结合相关知识,提出针对性的预防措施,经过实际运行检验,有效地控制了受热面泄漏事故的发生,从而保障了锅炉的安全稳定运行。     

工业锅炉实用除垢技术

锅炉受热面外部的烟垢和受热面内部的水垢,我们称之为污垢。实践证明,在许多情况下,锅炉设备运行的经济性和可靠性取决于受热面的污垢量和清除它的可能性。工业锅炉数量约占我国锅炉总量的96％以上。定期除垢是确保锅炉安全经济运行的方式之一。因此,去除锅炉受热面污垢是锅炉运行中的一项经常和重要的任务。通常,一台新安装的锅炉刚投人运行时,人们会看到锅炉上汽快,排烟温度低,     

600MW超临界机组的复合相变换热器仿真研究

为了分析复合相变换热器的性能,以山西兴能600 MW机组为研究对象,建立了复合相变换热器系统的数学模型,同时构建其仿真模型,并将其集成到该600 MW供热机组仿真系统中。利用该仿真系统,通过是否投入相变换热器系统分析了该系统对火电机组运行特性的影响;通过阀门扰动实验和降负荷过程研究了相变换热器系统的动态特性。结果表明,复合相变换热器技术是在保证受热面不结露的前提下降低排烟温度,"最大幅度"进行有效地降温节能、提高热效率和防腐能力。     

锅炉受热面高温腐蚀及预防措施

针对大坝发电公司2号炉和4号炉在运行中锅炉受热面管材腐蚀的问题,通过对2号炉和4号炉在运行中产生高温硫化腐蚀的过程进行分析,阐述了锅炉产生高温硫腐蚀的机理,提出锅炉受热面预防高温硫腐蚀的方法。分析结果表明：高温硫化腐蚀是燃煤锅炉受热面管材腐蚀的主要原因。     

生物质循环流化床锅炉尾部受热面积灰分析及处理

针对某生物质电厂直燃锅炉尾部受热面严重灰渣沉积情况,结合该电厂生物质原料特性和生物质锅炉运行工况,对生物质直燃锅炉受热面灰渣形成机理及灰渣沉积的影响因素进行分析,明确了在生物质燃料特性和锅炉燃烧方式不变的情况下,受热面灰渣沉积的必然性。结合生物质直燃锅炉实际运行情况,提出通过优化受热面布置和改进烟道结构等措施来解决尾部受热面灰渣沉积积堵问题,并在某生物质直燃锅炉发电厂的优化改进中取得良好效果。     

CG-35/5.30-MX锅炉改造及运行情况

介绍我厂两台CG－35／5．30－MX循环流化床锅炉,由于设计、选型等原因,致使锅炉出力低、能耗高、受热面磨损快、运行可靠性差,经过一年多时间不断调试、改造,认真分析原因后决定将循环流化床锅炉造成低烟速、加理管的低倍率CG－35／5．30－MXD鼓泡型循环锅炉,并介绍改造后运行情况。     

SZL8-1.57-AⅡ 锅炉的综合改进

ＳＺＬ８－１．５７－ＡⅡ锅炉的综合改进江苏省泰兴市磷肥厂沙德宏１概述ＳＺＬ８－１．５７－ＡⅡ锅炉是一种链条炉排的双锅筒纵置组装式水管锅炉，锅筒布置在锅炉中心线上，上锅筒的前部与两侧水冷壁管组成炉膛辐射受热面，后部与下锅筒之间由弯曲管子组成对流受热面。...     

Studies on a two-staged micro-combustor for a micro-reformer integrated with a micro-evaporator

A new micro-combustor configuration for a micro fuel-cell reformer integrated with a micro-evaporator is studied experimentally and computationally. The micro-combustor as a heat source is designed for a 10–15 W micro-reformer using the steam reforming method. In order to satisfy the primary requirements for designing a micro-combustor integrated with a micro-evaporator, i.e., stable burning in a small confinement and maximum heat transfer through a wall, the present micro-combustor is a simply cylinder, which is easy to fabricate, but is two-staged (expanding downstream) to control ignition and stable burning. The aspect ratio and wall thickness of the micro-combustor substantially affect ignition and thermal characteristics. For optimized design conditions, a pre-mixed micro-flame is easily ignited in the expanded second-stage combustor, moves into the smaller first-stage combustor, and finally is stabilized therein. The measured and predicted temperature distributions across the micro-combustor walls indicate that heat generated in the micro-combustor is well transferred. Thus, the present micro-combustor configuration can be applied to practical micro-reformers integrated with a micro-evaporator for use with fuel cells.     

Matching of a DC motor to a photovoltaic generator using a step-upconverter with a current-locked loop

A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop     

Using a fin with a parabolic concentrator

The consequences of using a fin collector in focusing solar collectors is examined and is found to have merits.     

Natural convection of a non-Newtonian fluid about a horizontal cylinder and a sphere in a porous medium

The problem of natural convection of a non-Newtonian fluid about a horizontal isothermal cylinder and an isothermal sphere in the porous medium is considered. The present study is based on the boundary layer approximation and only suitable for a high Rayleigh number. Similarity solutions are obtained by using the fourth order Runge-Kutta method. The effects of the wall temperature T_W and the new power-law index n on the characteristics of heat transfer are discussed.     

Bioconvection in a squeezing flow of a micropolar fluid in a horizontal channel

The bioconvection flow of an incompressible micropolar fluid containing microorganisms between two infinite stretchable parallel plates is considered. A mathematical model, with a fully coupled nonlinear system of equations describing the total mass, momentum, thermal energy, mass diffusion, and microorganisms is presented. The governing equations are reduced to a set of nonlinear ordinary differential equations with the help of suitable transformations. The resulting nonlinear ordinary differential equations are linearized using successive linearization method, and the resulting system of linear equations is solved using the Chebyshev collocation method. The detailed analysis illustrating the influences of various physical parameters, such as the micropolar coupling number, squeezing parameter, the bioconvection Schmidt number, Prandtl numbers, Lewis number, and bioconvection Peclet number on the velocity, microrotation, temperature, concentration and motile microorganism distributions, skin friction coefficient, Nusselt number, Sherwood number, and density number of motile microorganism, is examined. The influence of the squeezing parameter is to increase the dimensionless velocities and temperature and to decrease the local Nusselt number and local Sherwood number. The density number of motile microorganism is decreasing with squeezing parameter, bioconvection Lewis number, bioconvection Peclet number, and bioconvection Schmidt number.     

Coupling a two-temperature model and a one-temperature model at a fluid-porous interface

We study a convective heat transfer problem in a fluid-porous domain in the case of the local thermal non-equilibrium assumption (LTNE). The issue of this study is to determine appropriate boundary conditions to model heat transfer, while using models with a different number of equations: a two-temperature model in the homogeneous porous region versus a one-temperature model in the free region. To proceed, a two-step up-scaling approach is used, which has the particularity to provide closed jump relations depending on intrinsic characteristic of the interface. Thus, the use of jump or continuity conditions depend only on the interface location inside the fluid-porous transition region. The pertinence of the approach is illustrated on a 2D convective heat transfer problem considering a solid heat source in the porous medium.     

Comparative analysis of a Sisko nanofluid over a stretching cylinder through a porous medium

The present article examines the Sisko nanofluid flow and heat transfer through a porous medium due to a stretching cylinder using Buongiorno's model for nanofluids. Suitable similarity transformations are used to transform the governing boundary layer equations of fluid flow into nonlinear ordinary differential equations. The finite difference method is used to solve coupled nonlinear differential equations with MATLAB software. The impact of different parameters viz., the Sisko material parameter, porosity parameter, curvature parameter, thermophoresis parameter, and Brownian diffusion parameter on the velocity and temperature distribution are presented graphically. Moreover, the effect of the involved parameters on the heat transfer rate is also studied and presented through table values. It is noticed from the numerical values that the porosity parameter reduces the velocity while enhancing the temperature. The curvature parameter enhances the velocity throughout the fluid regime and reduces the temperature near the surface while enhancing the temperature far away from the surface. The study reveals that the thermophoresis and Brownian diffusion parameters that characterize the nanofluid flow reduce the wall heat transfer rate, while the curvature parameter enhances it. This investigation of wall heating/cooling has essential applications in solar porous water absorber systems, chemical engineering, metallurgy, material processing, and so forth.     

Exploration of heat transfer effect in a magnetohydrodynamics flow of a micropolar fluid between a porous and a nonporous disk

An analysis is carried out for the flow characteristics of a conducting micropolar fluid. The fluid was passed in between two parallel disks of infinite radii. The novelty of the study is to consider one of the disks as porous and the other one as nonporous, and the external magnetic field is applied along the transverse direction of the flow. The flow phenomena for the polar fluid characterized by the magnetic effect in conjunction with the temperature equation reduce to a set of coupled nonlinear ordinary differential equations using the requisite transformations and nondimensionalization. An analytical approach such as the variation parameter method is employed to tackle the system efficiently. To emphasize the effect of various physical parameters contributing to the flow phenomena, that is, non-zero tangential slip, Reynolds number, Prandtl number, magnetic parameter, and material parameter on the flow profiles of axial and radial velocities, the microrotation and temperature profiles are presented graphically. To validate the simulated results, a comparison with established results is made, and it is concluded that both are in good correlation.     

Evaporating characteristics of a microlayer under a bubble

Using the Hallinan‐Ervin model, the flow and evaporation in a bubble microlayer were theoretically analyzed, and the dryout characteristics and Staub's criterion were discussed in detail. It was revealed that the critical dryout radius is associated with the wettability of the heated surface, and that the dominant role for microlayer evaporation is disjoining pressure, not surface tension gradient. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 456–462, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10052