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汽包水位是确定锅炉是否安全稳定运行的重要参数之一,建立汽包水位的动态模型并进行仿真,对研究锅炉的动态特性和确定控制策略具有重要意义.在分析已有文献对汽包建模和仿真方法的基础上,从汽包变工况下水位变化的机理出发,通过对汽包内工质相变过程进行更为合理的假设和简化,建立了汽包水位动态模型.利用所建模型对汽包的动态特性进行了仿真研究,结果不但证实了模型的有效性,并且可以满足更大范围的动态仿真要求,可以为各类汽包建模仿真做参考. 相似文献
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基于模糊自适应PID的锅炉汽包水位智能控制系统 总被引:1,自引:0,他引:1
针对锅炉汽包水位经常受到负荷变化、进出水速度、水质等诸多因素的影响,具有时滞、非线性等特性,设计了以误差e及误差变化率ec为输入,PID控制器的KP、KI、KD为输出的二输入三输出的模糊自适应PID控制器,目的是为了改善PID控制的参数整定困难、适应差的缺点。并通过仿真进行了验证,结果表明锅炉汽包水位控制系统不论是在负荷变化较小的情况下,还是在负荷剧烈变化的运行工况下,都可以实现水位的平稳调节,水位始终保持在规定的波动范围之内。 相似文献
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锅炉汽包满水、缺水事故是长期困扰火力发电厂安全的重大事故之一.保持汽包水位在正常范围内是锅炉运行的一项重要的安全性指标。由于负荷、燃烧工况及给水流量的变化.汽包水位会经常变化,而水位过高或急剧波动会引起蒸汽品质恶化和带水.造成过热器管内表面结盐,严重时导致汽机水冲击;水位过低会引起排污失效,炉内加药进入蒸汽,甚至引起下降管带汽,影响炉水循环工况,造成炉管大面积爆破。 相似文献
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平原感潮河网区水流计算复杂,边界条件需考虑入江口潮位的影响,同时流域内闸坝调度工况对水流运动状态影响显著,是区域防洪调度中亟需解决的问题之一。以秦淮河流域为例,利用Landsat遥感技术提取了流域下垫面因素,建立了丘陵—平原产汇流模型,考虑了秦淮河入江口的潮位关系和流域内水库、闸门的调度情况,利用河网水动力学模型模拟计算了流域内各重要节点的水位过程。结果表明,本文模型对较大暴雨洪水年份1991、2003、2007年洪水的模拟能力较好,主要断面最高水位模拟误差均控制在0.15m以内。 相似文献
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《中外能源》2016,(9)
锦西石化公司5×104m3/h(标准状态)制氢装置有一台转化气锅炉和一台废热锅炉,共用一个汽包,汽包液位采用三冲量调节控制系统。锅炉汽包水位越高,汽水分离的空间越小。水位过高会严重影响汽水分离效果,造成蒸汽带水影响过热段运行;水位过低会造成锅炉水循环的破坏,影响锅炉运行,容易使水全部汽化烧坏锅炉甚至爆炸。汽包液位波动还会影响汽包连续排污系统,最终使蒸汽品质恶化。为了克服给水压力扰动的现象,将给水流量和蒸汽流量信号都引入汽包液位调节系统,汽包液位是被控变量,是主冲量信号,蒸汽流量和给水流量是辅助冲量信号。工业应用结果表明,汽包液位控制在50%~60%,优于工艺卡指标;过热蒸汽的Na+含量和Si O2含量均达到工艺指标,使余热锅炉系统的稳定性和可靠性得到提高,取得了较好的效果。 相似文献
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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 相似文献
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《International Communications in Heat and Mass Transfer》1988,15(5):605-614
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 TW and the new power-law index n on the characteristics of heat transfer are discussed. 相似文献
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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. 相似文献
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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 相似文献
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Solidification of a liquid about a cylindrical pipe 总被引:1,自引:0,他引:1
Graham E. Beli 《International Journal of Heat and Mass Transfer》1979,22(12):1681-1686
The temperature distribution and the rate of removal of heat by a coolant are predicted for the process of solidification of a liquid about a cold, isothermal pipe. The heat balance integral method incorporating spacial sub-division is used. It is found that acceptable results can be obtained by using only a small number of sub-divisions together with a piece-wise, linear profile. Furthermore, the results illustrate that the sensitivity which is normally associated with the heat balance integral method is overcome. 相似文献
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Rahim Y.H.A. Osheba S.M. Alyan M.A.A.S. Al-Ohaly A.A. 《Energy Conversion, IEEE Transaction on》1988,3(3):458-464
A preliminary study on the transient behavior of a superconducting turbo-alternator in a typical multimachine system is described. The study covers the effect of conventional controllers, power-system stabilizers and phase advance networks. The open-loop response of the system is compared to the response when the superconducting alternator is replaced by its conventional counterpart 相似文献
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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. 相似文献
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Hydrothermal Behavior of a Ferrofluid in a Corrugated Channel in the Presence of a Magnetic Field
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In this paper, results of applying a non‐uniform magnetic field on a dilute ferrofluid (water and 3% vol. Fe3O4) flow in a corrugated channel under a constant heat flux boundary condition have been reported. The thermal behavior of the flow is investigated numerically using a two‐phase mixture model and control volume technique. It is concluded that using a magnetic field with a negative gradient on a nanofluid flow in corrugated channels can be proposed as a suitable method to achieve higher heat transfer performance and augment the heat transfer coefficient and also reduces the wall temperature. This method can lead to the design of more compact heat exchangers. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(1): 80–92, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21060 相似文献
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A homogeneous planar photoconverter (PC) of a new type based on a multi-junction n-p-p +-n-p-p +-...-n-p-p + semiconductor structure was proposed. This semiconductor structure is a cascade PC consisting of several exposed PCs connected in series, with the light passing through the previous semiconductor layers. A theory was worked out, and the limiting values of photoelectric and energy characteristics of high-voltage devices that convert monochromatic and solar light were developed. These values include optimum values of the thickness and the number of the PCs applied onto the base PC, spectral selectivity, voltage-current characteristics, and performance. The no-load voltage rises practically in a linear fashion when the number of cells in the cascade increases. With an optimum number of cells, the peak performance values reach their peaks and considerably exceed the performance of the base PC, especially at a low carrier collection coefficient in the base PC. 相似文献