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板翅式换热器导流片结构参数对其导流性能的影响 总被引:11,自引:6,他引:5
由于板翅式换热器结构的复杂性,存在着内部流动速度分布的不均匀性,从而引起其换热效率下降,影响了换热器的整体效能.引起流动速度分布不均匀的因素是多方面的,针对不同导流片结构参数(h/H)对导流片导流性能的影响进行了深入研究,发现导流片结构参数对换热器内部流动速度分布不均匀性的影响主要表现在总管流动方向上,通过改变板翅式换热器导流片的结构参数可有效地改善换热器内部物流在总管流动方向上的分配情况,从而有效地改善换热器内部流动速度的分布.研究结果对板翅式换热器的优化设计具有重要意义. 相似文献
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本文提示了换热网络优化综合的两步法.第一步为应用夹点设计法(PD法),在给定的最优夹点传热温差的基础上,综合出一初始的优化网络.本文通过对夹点概念的理论分析,推导出求取最优夹点温差的解析式.计算实例表明,利用此解析式求取最优夹点温差值具有计算简便、准确的优点.第二步为在第一步所获得的初始优化网络的基础上,建立换热网络优化综合非线性规划数学模型,其目标函数为投资和年操作费用,其约束条件为各换热器及分流器、混合器的物料平衡、热量平衡、传热方程等等.应用逐次二次规划法优化软件VMCON进行求解.计算实例表明:经过非线性规划法优化所得的换热网络,其费用比仅由第一步所获得的初始优化网络下降14%,比由其它调优方法所改进的换热网络也要好.为了工程上使用的方便,将上述方法开发成一换热网络自动综合积成软件,该软件包括:1.扩展表格程序.该程序将换热网络综合问题的原始数据和综合结果通过此表格输入或输出.2.3DPLOT绘图程序.它可将冷、热物流匹配关系以图形方式绘出.3.换热网络综合程序.该程序应用夹点设计法对给定的冷、热物流进行网络综合,产生一初始优化网络.4.换热网络模拟程序.对已知结构及尺寸的换热网络进行模拟计算.5.标准换热器数据库.它包括若干标准换热器的尺寸和性能等数据.并 相似文献
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管壳式换热器壳侧湍流流动与换热的三维数值模拟 总被引:6,自引:1,他引:5
综合应用体积多孔度、表面渗透度和分布阻力方法建立了适用于准连续介质的N-S修正控制方程.用改进的k-ε模型考虑管束对湍流的产生和耗散的影响,用壁面函数法处理壳壁和折流板的壁面效应, 对一管壳式换热器的壳侧湍流流动与换热进行了三维数值模拟.对计算结果进行了归纳,并与换热器冷态实验、前人的研究结果进行了对比分析,从而证明了该方法能更有效地模拟管壳式换热器壳侧的流动特性,压降实验数据和计算结果符合良好. 相似文献
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奚治政 《硫磷设计与粉体工程》2003,(5):20-23
如何提高换热器的传热系数K、提高气液热交换气体走管程的给热系数α,是换热器技术进步的一大课题。介绍了内展翅片管的结构及管程流体给热系数的计算方法,并以60kt/a环己酮工程中烷三塔塔顶气体冷凝的换热流程为例,对比了选用管壳式换热器与内展翅片管换热器的计算结果。认为选用内展翅片管换热器在技术指标和经济上都是有利的。 相似文献
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基于粒子群算法的内外翅片管换热器优化 总被引:3,自引:0,他引:3
粒子群优化算法(Particle Swarm Optimization,简称PSO)是一种新型的优化算法,今把PSO应用于内外翅片管换热器的结构尺寸优化,建立了物理数学模型,开发了C 程序.把体积作为优化目标函数,以换热面积和压降作为约束条件,对管子横向间距、纵向间距、管排数、外翅片间距、换热器在与热气流垂直方向的长度进行了优化,并与利用遗传算法的文献结果对比:在相同的设计参数和相同的优化变量搜索范围条件下,体积减小9.5%,重量减轻16%,优化计算时间减小一个量级,PSO应用于换热器优化设计优于遗传算法. 相似文献
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采用CFX软件Fluent模拟了用于低温余热回收的重力热管内的相变情况及充液率、热管长度比、管中心距对热管换热器传热性能的影响。模拟结果显示,水量一定时,加热段与冷凝段长度相同的热管在不同充液率条件下的传热特性,高充液率的传热能力优于低充液率的传热能力,适宜的充液率为60%~70%。当充液率一定时,加热段的长度小于冷凝段的长度有利于热管传热。当充液率及管长一定时,热管换热器的传热系数随管中心距的增大而减小。将热管换热器数值模拟的总传热系数与理论计算的结果进行对比,实现了特定体系热管换热器的结构优化。 相似文献
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D. MUNZ R. T. BUBSEY J. L. SHANNON Jr. 《Journal of the American Ceramic Society》1980,63(5-6):300-305
Fracture toughness of a sintered A12 O3 was determined with four-point-bend specimens having either straight-through or chevron notches. For the straight-through notched specimens, measured K Ic decreased with decreasing notch width. For the smallest notch width (66 μm) K Ic = 3.42±0.13 MN m−¾ . For specimens with chevron notches, a crack initiates and extends from the tip of the notch under increasing load. K Ic is calculated from the maximum load without measuring crack length, under the assumption that the derivative of the compliance is the same as that for a specimen with a straight-through crack. A refined calculation accounts for the truncated chevron crack shape at maximum load using Bluhm's slice model. For the chevronnotch configuration, a value of K Ic = 3.49±0.11 MN m−¾ was measured, which appears to be independent of the initial notch length a 0 (distance from the crack mouth to the tip of the triangular notch). An effect of a 1 (length of the chevron notch at the surface) on K Ic was observed, independent of whether the calculation of K Ic was based on the straight-through crack assumption or on the slice model. 相似文献
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为研究包覆方式对片状发射药燃烧性能的影响,建立了不同包覆方式下多层片状发射药的物理模型,并推导了形状函数和燃气生成猛度表达式,利用Matlab软件对不同的宽厚比、长厚比及多层结构的片状发射药进行了数值计算;制备了不同长厚比的片状变燃速发射药,并进行了密闭爆发器实验。结果表明,四面包覆和全包覆可以很好地消除临界宽厚比对片状发射药燃烧性能的影响;与两面包覆的片状发射药相比,四面包覆和全包覆的片状发射药能够延缓内层药减面燃烧的时间,其燃气生成猛度的阶跃程度分别提高了1.17%和1.23%,呈现出良好的燃烧渐增性。 相似文献
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Thermal degradation of polyurethane samples was studied by a thermogravimetric method. The effect of soft-segment length and soft-segment concentration on activation energy of the degradation process was measured. Three methods of calculation gave activation energies at different stages of the very complex weight loss process. It was shown that at initial stages of the weight loss the process was dominated by hard-segment degradation. Activation energy of the whole process calculated by the Ozawa–Flynn method did not offer clear insight into the structure–stability relationship of polyurethanes. The second method showed that activation energy of the initial stage of degradation increased with decrease in hard-segment length. The Flynn method of calculating activation energy produced fairly constant activation energy of the first 40% degradation, at around 150 kJ/mol, for polymers in the C series. Generally, calculation of kinetic parameters of a complex degradation process as in polyurethanes gives results that are not easy to interpret. It has been shown qualitatively that polymers with higher soft-segment concentration display lower initial weight loss and higher onset temperatures of degradation. © 1994 John Wiley & Sons, Inc. 相似文献
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《Journal of Adhesion Science and Technology》2013,27(2):259-267
In various kinds of orthopedic or dental prostheses, adequate fixation of prosthetic components to the host bone represents a great challenge. The short- and long-term fixation stabilities of the implants are often provided by the use of posts. In this work, a cylindrical steel post inserted in a predrilled High Density Polyethylene (HDPE) cylinder with an initial interference fit was used as a model to analyze the contribution of post fixation to the initial stability of Total Knee Arthroplasty (TKA) tibial component. To characterize the ability of the steel post/HDPE cylinder interface for transferring mechanical load, pull-out tests were carried out on the model post fixation for different initial interference fits and implantation lengths. Experimental ultimate pull-out force was found to increase in a quasi-linear fashion with increase in the interference fit or the implantation length. On the basis of Coulomb friction at the post/HDPE interface, an analytical model has been developed for the analysis of the experimental ultimate pull-out force results. For the ranges of initial interference fit and implantation length considered, the analytical model was fitted to the experimental results by adjusting the friction coefficient. The mean value of the friction coefficient obtained was 0.043. Finite element simulation was also carried out for the pull-out test using the ABAQUS program. It was found that the finite element simulation describes well the experimental ultimate pull-out forces than the analytical calculation. 相似文献
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Finite difference numerical solutions have been obtained to the Navier-Stokes equations for entry-region flow in a falling liquid film issuing from a slot. The iterative method developed does not neglect surface tension forces, however the effect of surface tension on the film acceleration is shown to be small. The results show a smooth transition between the initial velocity profile and the final fully-developed profile. The starting length, defined as the distance required for the surface velocity to reach 95% of its final value, is on the order of 20 times the initial film thickness and increases with Reynolds number. A comparison of the calculations with available experimental data shows fair agreement. 相似文献
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天然气压缩因子在天然气工程计算中具有重要的地位,其计算方法有多种,其中就包括由美国燃气协会提出的基于气体组成来计算压缩因子的AGA8-92DC方程。根据GB/T 17747.2-2011标准所给出的AGA8-92DC方法计算过程,用Visual Basic6.0 program编写了计算程序。为了验证程序的正确性,分别将程序计算值与GB/T 17747.2标准提供的计算值和含碳贫气气样实测值进行了对比,且获得了较小的计算误差。由计算值与实测值的对比结果可知,通过Visual Basic6.0 program所编写的AGA8-92DC方法计算程序而得到的计算结果能够满足工程上的要求;对于中高压含碳贫气,AGA8-92DC方法具有较高的计算准确度;当气体温度升高时,AGA8-92DC方法的计算误差将有所减小。 相似文献