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新型管内插入物——立交盘强化传热的实验与模拟 总被引:1,自引:3,他引:1
对装有新型强化传热管内插入物-立交盘的管路压降与传热情况进行了实验研究,并利用计算流体力学方法模拟了结构参数变化对传热及压降的影响。实验方面,通过不同黏度的测量物系,测定了Reynolds数为2×10-4~4×104时装有立交盘管路的压降,得到了摩擦系数与Reynolds数的关系曲线,并拟合了关联式,结果表明相同条件下装有立交盘的管路其压降为空管的7~40倍。其次,利用蒸气加热麦芽糖浆的传热实验,测量了水平放置与垂直放置条件下空管与装有立交盘时管路传热情况,拟合了相应的传热关联式,结果表明爬流条件下水平放置时传热强化倍数为2~3.5倍,垂直放置时传热强化倍数为2.5~4倍。最后,采用计算流体力学的方法,利用Fluent软件对立交盘的传热及流动过程进行了模拟研究,考察了结构参数变化对传热及压降的影响,整合了内外流道直径比及长径比对传热及压降的影响关联式,为立交盘的优化设计提供了理论依据。 相似文献
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工业的发展、节能及新能源开发等都迫切需要装备尺寸小、重量轻和容量大的换热器。要达到这一要求,必须采用强化传热技术增强换热器中的换热工况。围绕着强化传热,国内外进行了不少研究,文献[1]对此作了比较详细的报道。本文研究的是用一种新的、比较简单的方法进行强化传热,即在管间插入强化元件以提高传热效率。1试验原理与装置简介流体流动时,在紧靠壁面的一薄层内呈滞流状况,流速很低。滞流层的存在,使这一层流体得不到充分混合,传热系数降低;同时,由于流体具有粘性,流动时具有内摩擦,这是流动阻力产生的根源。如果能破坏… 相似文献
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对水力直径分别为0.72 mm的矩形扁材多孔管和0.86 mm的圆形扁材多孔管中单相流体换热特性以及流动压降进行了实验研究.流体Re小于500时,随着热通量的增大,Nu减小;随着Re的增大,热通量对Nu的影响减小,Nu趋于一致.实验结果显示,这些变化是由于入口段效应和共轭效应相互制约的结果.圆形扁材多孔管的Nu高于矩形扁材多孔管的Nu.对于乙醇溶液,低热阻时,入口温度越高,压降随热阻的增大降低的斜率越小,随着热阻值的增大,压降降低速率减小趋于平缓.对水、酒精和丙酮进行了单相对流换热的研究.通过比较发现,3种流体的换热特性并不相同,而且差别很大.在同一热通量和入口温度条件下,相同Re,乙醇的Nu最大,丙酮次之,水的Nu最小.同时测试了不同乙醇浓度水溶液的换热特性,发现随着乙醇浓度的增大,溶液的Nu由基本保持不变到随着Re的增大而增大,并且乙醇浓度越大相邻浓度间的Nu差别越大,出现以上现象的理论原因还有待进一步的研究. 相似文献
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管内插入螺旋线圈强化传热的研究 总被引:4,自引:0,他引:4
<正> 一、引言 节能与节材以及提高经济效益的需要促进了强化传热研究的蓬勃开展,强化传热追求的目标,其一为在给定传热量的情况下,不仅希望新设计的热交换器的体积尽可能地小而同时能减少输送流体所需的功率。此外,对已有的换热器希望提高其容量或者减少传热温差以便利用低温热源。通过传热方 相似文献
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The experimental results of single‐phase flow heat transfer and pressure drop experiments in the turbulent flow regime in a spirally ribbed tube and a smooth tube are presented in this paper. The ribbed tube has an outside diameter of 22 mm and an inside diameter of 11 mm (an equivalent inside diameter of 11.6 mm) and the smooth tube has an outside diameter of 19 mm and an inside diameter of 15 mm. Both tubes were uniformly heated by passing an electrical current along the tubes with a heated length of 2500 mm. The working fluids are water and kerosene, respectively. The experimental Reynolds number is in the range of 104–5 · 104 for water and is in the range of 104–2.2 · 104 for kerosene. The experimental results of the ribbed tube are compared with those of the smooth tube. The heat transfer coefficients of the ribbed tube are 1.2–1.6 fold greater than those in the smooth tube and the pressure drop in the ribbed tube is also increased by a factor of 1.4–1.7 as compared with those in the smooth tube for water. The corresponding values for kerosene are 2–2.7 and 1.5–2, respectively. The heat‐transfer enhancement characteristics of the ribbed tube are assessed. This tube is especially suitable for augmenting single‐phase flow heat transfer of kerosene. Correlations for the heat transfer and the pressure drop for the spirally ribbed tube are proposed, according to the experimental data. 相似文献
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在垂直受热通道中气液两相流的传热是一种从单相流、泡状流、弹状流、搅拌流直至环状流的各种流型的气、液两相复杂传热。本文采用了特制的实验研究设备,以水及其蒸汽为介质,研究了各种流型的传热特性及其影响因素(进料质量流速、热通量以及干度等),探讨了成膜条件,并用J.C.Chen双机理传热模型计算、分析了在不同情况下各机理对传热所起的作用。 相似文献
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针对粘稠液体传热系数很低这一现象,开发了MC新型强化传热扰动元件。该元件以圆环作为基本扰动部件,在一个横截面上将若干个小圆环以不同方式组合成一个单元,形成圆弧网格型或球网格型.圆环与管子内壁紧密接触,单元节距可以改变构成不同线密度。以1%CMC水溶液作为粘性介质对节距为24、40、60、80、160及400~40 mm变密度六种元件进行实验研究。在Ae<100,Pr数为5~1300m范围内,管内传热膜系数较光管增加4~6倍,摩擦因子为光管的10~20倍。因此可以认为MC型元件是一种低阻高效的传热强化元件。并从流体力学基本原理对强化机理进行了分析。 相似文献
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Heat transfer augmentation and entropy generation were investigated for a helically coiled tube with internal longitudinal fins. The Nusselt number, friction factor, thermal‐hydraulic performance ratio, and augmentation entropy generation number were calculated and analyzed. The results indicated that the internal longitudinal fins enhance the secondary flows and increase the temperature gradient near the tube wall, which in turn increase the heat transfer. It was found that the helically coiled tube with internal longitudinal fins provides the best integrated performance over the range of computed Dean numbers. The Nusselt number rised by 20–35 % with a corresponding 27–56 % increase of the friction factor. The computed results indicated that augmentation entropy generation numbers are approximately changed between 0.012 to 0.132 levels, i.e., the novel helically coiled tube with internal longitudinal fins is more efficient than that without internal fins. 相似文献
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锯齿型螺旋翅片管束传热特性实验研究与传热关联式评价 总被引:2,自引:0,他引:2
对一种锯齿型螺旋翅片管束的传热特性进行了系统的实验研究,基于实验结果提出了该管束的换热关联式,并与现有的相关关联式进行对比分析。研究发现,当纵向管排数小于4时,管束换热的Nu随管束的增加而增大,而当管排数不小于4时,管排数对管束换热的Nu影响不显著。现有的关联式之间差异较大,评估关联式应综合考虑关联式预测值与实验值的偏差和关联式预测值与实验值随雷诺数变化趋势。 相似文献
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恒热流直管中纳米流体对流传热的实验研究(英文) 总被引:1,自引:0,他引:1
In this work, the laminar convective heat transfer performance and the pressure drop of water-based nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles flowing through a straight circular tube were experimen-tally investigated. The experimental results showed that addition of small amounts of nano-sized Al2O3 and TiO2 particles to de-ionized water increased heat transfer coefficients considerably, while the SiO2 nanofluids showed the opposite behavior attracting the authors’ interests. An average of 16%and 8.2%increase in heat transfer coefficient were observed with the average of 28%and 15%penalty in pressure drop for Al2O3 and TiO2 nanofluids. 相似文献