共查询到18条相似文献,搜索用时 843 毫秒
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为了研究螺旋形扭带阻力与传热特性,选取了不同宽度(6、7和8 mm)的3种扭率(2.0、3.0、4.0)、3种螺距比(1.5、2.0、2.5)的参数组合下共27根螺旋形扭带插入换热管内进行实验.实验结果表明,插入螺旋形扭带后换热管内流动阻力和传热效果都有明显提高.通过对实验数据的多元线性回归分析,建立了相应的阻力系数和努赛尔数关联式.并且由强化传热综合性能评价分析,在实验雷诺数范围内得出强化传热综合性能评价因子φ=1.063~1.587,证明了实验研究的扭带具有强化传热的应用价值. 相似文献
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螺旋槽管与折流栅组合的高效水冷器的传热和阻力特性与其管、壳程的结构因素密切相关,本文就螺旋槽管槽深对水冷器管、壳程传热与阻力特性的影响进行了实验研究.结果表明:壳程流速变化对水冷器传热系数的影响更加明显,即壳侧热阻相对较大,强化传热应以强化壳侧换热为主要目标;螺旋槽管槽深对水冷器传热系数的影响很大,应在实际工程设计中确保实际槽深符合设计要求;槽深越深,管壳程阻力也相应增加,即传热的强化是以阻力增加为代价.根据实验结果还得到了不同结构水冷器的管、壳程换热与阻力计算关联式. 相似文献
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采用大涡模拟对底面为凹槽的矩形通道内湍流流动与传热特性进行了研究,为验证所采用数值方法的准确性与可靠性,将平直矩形通道内模拟结果与文献中的直接数值模拟结果进行了比较,换热面Nusselt数与采用Dittus-Boelter公式计算所得Nu进行了比较,计算误差小于5%。以凹槽表面为底面的矩形通道的数值模拟结果表明:通道底面的凹槽结构改变了凹槽表面处流动结构,不同的凹槽高度和长度对流动阻力和换热效果的影响不同,在特定的几何参数下,与平直矩形通道相比,凹槽表面时均Nusselt数提高了近50.5%,时均摩擦阻力系数减小了近35.17%,综合系数增加了73.89%。通道内的流动结构显示:凹槽表面附近存在流体垂直流向壁面区域,在垂直流动区域内流体出现前、后分流,分流位置处Nusselt数增加明显,摩擦阻力系数没有明显增加,其综合流动特性最好。 相似文献
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摘要对某公司换热器的运行情况。采用旋液流态化技术设计了模拟试验方案。首先在φ57mm×3.5mm×2000mmPVC管内进行旋液流态化清洗试验,然后在碳钢管上内置不同螺距的钢丝螺旋线进行流体阻力测试,并进行旋液流态化与空管的对比传热试验。结果表明:旋液流态化技术清洗管道中人工污垢只需时间145s,没有发生粒子沉积和堵塞的现象,安全可靠性好;旋液流态化流体阻力△p随着Re的增大而增大,摩擦系数随着Re的增大而减小,流体总阻力48.7kPa低于供水压力,总传热系数平均提高幅度13.3%,强化传热效果好。 相似文献
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Stable TiO2-water nanofluids are prepared by a two-step method, stabilities of nanofluids are investigated by precipitation method and transmittance method respectively, and thermal conductivities and viscosities are also measured. An experimental system for studying the heat transfer enhancement of nanofluids is established, and heat transfer and flow characteristics of TiO2-water nanofluids in heat exchanger systems with a triangular tube and circular tube are experimentally studied. The effects of nanoparticle mass fractions (ω=0.1 wt%-0.5 wt%) and Reynolds numbers (Re=800-10000) on the heat transfer and flow performances of nanofluids are analyzed. Fitting formulas for Nusselt number and resistance coefficient of nanofluids in a triangular tube are put forward based on the experimental data. The comprehensive performances of nanofluids in a triangular tube are investigated. It is found that nanofluids in a triangular tube can significantly improve the heat transfer performance at the cost of a small increase in resistance coefficient compared with that in a circular tube, especially the resistance coefficients are almost the same between different nanoparticle mass fractions at turbulent flow. It is also found that the comprehensive evaluation index η decreases with Reynolds number at laminar flow but a critical maximum value appears at turbulent flow. 相似文献
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The distributions of thermal resistance in viscous sublayer,buffer region and turbulent core region,local flow resistance and local heat transfer characteristics at different locations downstream of the twisted-tape element were numerically studied in a converging-diverging tube inserted with spaced twisted-tape element by analyzing the attenuation of self-sustaining swirl flow.The results showed that the local performance was poor as thermal resistance was too concentrated in its distribution for a particular region.The more uniform the distribution of thermal resistance,the better the local performance.The local performance reached its best when the fluid just left the spaced twisted-tape,in which the flow resistance dropped substantially but the enhancement of heat transfer was still significant.The self-sustaining flow was maintained at a long distance.The best performance was at the length of 36.85 times the diameter,increasing by 6.8% compared with a converging-diverging tube. 相似文献
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介绍了粗糙管换热器中沿传热管轴向间隔分置旋流片的两区协同强化传热方法。旋流片使流体产生螺旋流,螺旋流在离开旋流片之后依靠自身的运动惯性保持一定距离的自旋流,对管道近壁区与中心区产生互动的协同传热强化。此外,该方法也可用于管间,除了对管间管束的机械支撑外,旋流片也可使管间流体产生自旋运动,实现壳程流体的两区协同传热强化。对现有工业系统的换热器技术升级、实现节能降耗意义重大。 相似文献