共查询到20条相似文献,搜索用时 511 毫秒
1.
2.
3.
4.
本文建立了DY—1003型电液调速器的数学模型,通过计算机进行了大量的仿真计算,较为全面地分析了各可调参数的变化与调速系统稳定性和动态性能的相互关系,以及非线性因素对系统的影响,并通过实机试验验证了理论分析的结果。 相似文献
6.
本文根据弹性力学关于应力函数与翘曲函数的基本理论,应用有限元法与有限差分法对非圆截面柱体抗扭断面系数的计算提出了较为完善的方法.首先用有限元法通过应力函数求解;再用有限元法通过翘曲函数求解,最后用有限差分法通过应力函数求解.对这几种方法进行了比较. 相似文献
7.
发展了一种能够较为准确预测跨音速多级轴流压气机气动性能的准一维数学模型。该模型基于欧拉方程外加源项的方法,可对多级轴流压气机的气动性能进行数值模拟。方程中的源项用于表示叶片、壁面摩擦以及流道面积变化对气流的影响,可以通过求解叶片排的进出口速度三角形求得。通过对跨音速压气机内部复杂的三维流动现象进行了简化,发展了合适的损失系数和落后角模型用来计算得到叶片排出口参数。对两种不同的多级跨音速压气机进行了数值模拟并与实验结果进行了对比,验证了本模型能够较为准确地模拟出跨音速轴流压气机的气动性能,但计算的精确度还需要根据不同的压气机类型对经验公式的系数进行优化。发展的模型根据压气机简单的几何尺寸就能对其气动性能做出较为准确的预测,这在压气机的预设计以及优化阶段有着重要的指导作用。 相似文献
8.
本文主要讨论Honeywell PKS系统与Tricon PLC之间通过Modbus协议进行实时通讯的开发与应用,介绍了Modbus协议的特点,对两系统的结构、硬件配置和软件组态方面作了较为详细的说明. 相似文献
9.
10.
通过计算流体动力学(CFD)模拟计算分析某实际工程设计阶段的充盐策略参数,对储罐内熔盐温度和储罐壁面温度的影响,通过分析模拟结果后确定在项目具体实施阶段采用预热系统及电加热器系统配合的充盐策略.通过将此充盐策略用于实际商业项目第1次充盐过程,效果良好,储罐整体温度较为均匀,同时也发现在第1次充盐过程中储罐基础存在较为明... 相似文献
11.
Extended surfaces mostly aim to improve the heat transfer upon increasing the area of heat transfer. In this paper, the influence of using fins on flow behaviors and the heat transfer of the shell and tube heat exchanger has been investigated. In this regard, the present results are verified with available experimental data in the literature for a helical tube without fins. The effects of fin density (fin per inch), its height, and material have been studied on the heat transfer rate. In addition, the effects of radial pitch and the number of coil loops are studied. The results indicate that implementing extended surfaces significantly increases the heat transfer rate. The increase of fin density from 8 to 12 and the height from 11.5 to 13.5 mm enhances heat transfer up to 48% and 43% depending on Dean number, respectively. The rise of coil pitch augments the overall heat transfer, and it is more efficient at lower Dean numbers. The predicted results also show that the fin material does not have any significant effect on heat transfer. 相似文献
12.
13.
Kemal Ermis 《国际能源研究杂志》2008,32(6):581-594
This paper focuses on the heat transfer analysis of compact heat exchangers through artificial neural network (ANN). The ANN analysis includes heat transfer coefficient, pressure drop and Nusselt number in the compact heat exchangers by using available experimental results in a case study. In this study, data sets are established in 15 different test channel configurations. A feed‐forward back‐propagation algorithm is used in the learning process and testing the network. The learning process is applied to correlate the heat transfer analysis for different ratios of rib spacing and height, various Reynolds numbers, different inlet–outlet temperatures, heat transfer areas and hydraulic diameters. Various hidden numbers of the network are trained for the best prediction of the heat transfer analysis. Heat transfer coefficient, pressure drop and Nusselt number values are predicted by the network algorithm. The results are then compared with the experimental results of the case. The trained ANN results perform well in predicting the heat transfer coefficient, pressure drop and Nusselt number with an average absolute mean relative error of less than 6% compared with the experimental results for staggered cylindrical ribbed and staggered triangular ribbed of test channels in the case study. The ANN approach is found to be a suitable method for heat transfer analysis in compact heat exchangers. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
14.
对竖直上升管内超临界压力下航空煤油的传热特性进行了实验研究。分析了不同质量流量、热流密度、压力和进口温度对超临界压力下航空煤油传热特性的影响。实验结果表明,提高质量流量或进口温度均使煤油传热效果变好。而热流密度对流体传热的影响主要在于改变了流体和壁面温度,热流密度越大,传热系数越高。压力对煤油传热影响不大,一般情况下,提高压力会恶化传热。超临界状态下,煤油物性变化很大,因此对煤油的传输和热力学性质的准确计算是研究超临界压力下传热现象的关键。利用拓展的对比态法来计算煤油的密度和传输特性,如黏度、热导率等。给出了煤油在超临界压力下的传热关联式,其计算值和实验值吻合良好。 相似文献
15.
16.
利用三维数值模拟的方法对带有3种异形纵向涡发生器的H型翅片椭圆管换热器的空气侧流动传热特性进行研究。基于H型翅片椭圆管束,讨论了在不同雷诺数下,纵向涡发生器的摆放位置、摆放攻角和形状对空气侧流动传热的影响。研究表明:纵向涡发生器能够将高能量的流体引向流速较低的壁面区域,使冷热流体之间的混合加剧,增强流体的湍流动能,进而达到强化传热的效果;与无纵向涡发生器的管束相比,带纵向涡发生器管束的传热效果有明显的提高;当纵向涡发生器后置时,换热器的传热效果最优;在雷诺数相同,攻角为30°时,流体的传热性能和阻力特性均达到最优;相同攻角摆放时,椭圆角矩形发生器的传热性能和阻力因子均优于其他两种形式的发生器。研究结果为烟气余热回收系统换热器传热性能强化提供理论依据。 相似文献
17.
Numerical simulation of fluid flow and heat transfer in a microchannel heat sink with offset fan-shaped reentrant cavities in sidewall 总被引:1,自引:0,他引:1
Lei ChaiGuodong Xia Mingzheng ZhouJian Li 《International Communications in Heat and Mass Transfer》2011,38(5):577-584
The paper is focused on the investigation of fluid flow and heat transfer characteristics in a microchannel heat sink with offset fan-shaped reentrant cavities in sidewall. In contrast to the new microchannel heat sink, the corresponding conventional rectangular microchannel heat sink is chosen. The computational fluid dynamics is used to simulate the flow and heat transfer in the heat sinks. The steady, laminar flow and heat transfer equations are solved in a finite-volume method. The SIMPLEX method is used for the computations. The effects of flow rate and heat flux on pressure drop and heat transfer are presented. The results indicate that the microchannel heat sink with offset fan-shaped reentrant cavities in sidewall improved heat transfer performance with an acceptable pressure drop. The fluid flow and heat transfer mechanism of the new microchannel heat sink can attribute to the interaction of the increased heat transfer surface area, the redeveloping of the hydraulic and thermal boundary layers, the jet and throttling effects and the slipping over the reentrant cavities. The increased heat transfer surface area and the periodic thermal developing flow are responsible for the significant heat transfer enhancement. The jet and throttling effects enhance heat transfer, simultaneously increasing pressure drop. The slipping over the reentrant cavities reduces pressure drop, but drastically decreases heat transfer. 相似文献
18.
The present work reports the influence of pressure and bed temperature on particle‐to‐wall heat transfer in a pressurized circulating fluidized bed (PCFB). The particle convection heat transfer plays a dominant role in determining the bed‐to‐wall heat transfer coefficient. So far, no information is reported on the effect of pressure and bed temperature on particle‐to‐wall heat transfer in a PCFB in the published literature. The present investigation reports some information in this direction. The effect of system pressure and bed temperature are investigated to study their influence on cluster and particle heat transfer. The particle convection heat transfer coefficient increases with system pressure and bed temperature due to higher cluster thermal conductivity. The increase in particle concentration (suspension density) results in greater cluster solid fraction and also the particle concentration near the wall is enhanced. This results in higher cluster and particle convection heat transfer between the bed and the wall. Higher particle convection heat transfer coefficient results in enhanced heat transfer between the bed and the wall. The results will also help to understand the bed‐to‐wall heat transfer mechanism in a better way in a PCFB. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
19.
20.
目前,燃煤锅炉三维CFD数值模拟中对炉膛水冷壁传热分布的预测大都基于给定的壁面温度边界条件。然而,此方法无法体现锅炉运行状态对壁面传热与壁温分布的影响。提出了一种基于锅炉烟气侧放热与汽水侧吸热间热平衡关系的壁面传热计算方法,并重点讨论了壁面传热系数的物理意义及取值方法。研究发现,壁面传热系数基本由壁面结渣状态决定,因此可根据壁面渣层的传热系数确定。本文方法将影响壁面传热的关键因素合理地体现在计算过程中,同时在模型复杂性与工程适用性之间保持了合理的平衡。采用此方法对一台320 MW锅炉的燃烧与传热分布进行了数值模拟,水冷壁吸热量的预测结果与锅炉运行数据吻合良好。 相似文献