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为了研究波节管换热器的热应力和阻力特性,对具有相同管长和传热面积的波节管换热器和直管换热器进行了对比实验,分析了不同温差下的轴向应力和不同雷诺数下的管程、壳程的阻力损失。结果发现:与直管换热器相比,波节管换热器具有很好的轴向热补偿性能,在相同的实验条件下,其轴向作用力和轴向热应力均比较小,适合应用于大传热温差场合;波节管换热器的阻力损失高于直管换热器,但在低雷诺数时阻力损失相差不大,且具有较高的传热系数。 相似文献
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在上引式流态化气力输送试验台上,对3种不同角度分支管进行输送试验,分析管路分流处局部阻力损失的变化规律,并拟合分支管局部阻力特性方程;同时以试验所得参数为基础,采用fluent软件对分支管段分流情况进行数值模拟。研究结果显示,分支管局部阻力损失随管道内固气比和表观气速的增大而增大,当表观气速为8 m/s时达到了输送系统的沉积速度;误差分析表明所得拟合方程有较高准确性;模拟结果显示在管道分流处湍流现象明显并有较大的漩涡出现,且分支角度越大,湍流和漩涡现象越明显。 相似文献
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通过模拟试验的方法,对直起片管换热器的传热,阻力特性进行了模拟试验研究,得出了丰相应几何条件下管外对流换热系数及磨擦系数的准则方程,并与热管换热器综合性能试验台上直翅片热管余热管余热锅炉所测量的数据相比较,结果表明,在模拟条件下试验得到的准则方程是可靠的。 相似文献
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<正> 引言 螺旋槽管是一种优良的换热元件.许多学者对其换热强化机理比较一致的看法是:一方面由于螺旋槽的引导作用使得近壁处流体发生旋转,加强了径向扰动;另一方面,发生了绕流脱体,形成了回流区,在再附点处换热最强.同时由于流体的旋转和脱体使得摩擦阻力较大地增大.流体在管内流动过程很复杂,对螺旋槽管的研究基本上是以实验为主的数据拟合,有的学者虽对其进行了数学分析并建立了相应的关联式,但不能表征出流体在管内旋转和脱体的实际流动情况,因此不能对二者的相互耦合进行定性或定量的分析.本文以流体在螺旋槽管内的流态为基础,以期建立能够反映其流动特性的阻力和换热计算公式. 相似文献
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旨在研究螺旋椭圆管式换热器管内流动换热性能。借助CFD数值模拟方法分析了流体入口角度θ和椭圆截面长短轴之比a/b对螺旋椭圆管式换热器管内流动和换热的影响,并且利用综合传热增强因子PEC评价了换热器的综合换热性能。结果表明:螺旋椭圆管内存在二次流,导致螺旋椭圆管截面内温度梯度和速度梯度径向分布不均;在研究范围内,θ增大,努塞尔数Nu增加,摩擦系数f提高,综合换热性能增加;θ>45°时,螺旋椭圆管综合换热性能优于螺旋圆管。θ一定时,a/b越大,综合换热性能越好。通过对多种不同结构的螺旋椭圆管进行多工况数值模拟后,修正了现有的准则关联式,提高了准则关联式的准确度。 相似文献
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In the industrial application of ethylene pyrolysis tubular heating furnace, the fluid transferred from horizontal to rotary flow by adding twisted slices internals, which increased the tangential velocity and strengthened the flushing effect on the tube wall, so as to achieve the purpose of enhancing heat transfer. Based on the second generation of twisted slices, the structure was improved, and RNG k?ε turbulence model was used to simulate the flow details inside the furnace tube. The longitudinal vorticity structure, resistance coefficient, Nusselt number Nu, comprehensive heat transfer coefficient PEC and the coupling coordination between velocity vector field and temperature gradient field in different twisted slice structures were compared and analyzed. The results showed that the structure with "slit" openings along the wall can reduce the loss of flow resistance while increased the strength of fluid swirl. The resistance coefficient of twisted slices with opening structure of 7 mm length, 2 mm width and 2 mm interval was 93.75% of the first generation and 8.67% more than the second generation, but the comprehensive heat transfer coefficient was 1.56% higher than that of the second generation and 1.29 times of the smooth tube. It can be considered that the optimized structure improved the stability of longitudinal vortex structure as well as strengthened the coupling between flow and heat transfer. Besides, along the central opening of the slices, the resistance coefficient at the twisted slices increased, resulting in larger local losses. 相似文献
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J. T. Rogers 《加拿大化工杂志》1981,59(2):213-222
Knowledge of falling film flow and heat transfer characteristics on horizontal tubes is required in the assessment of certain CANDU reactor accident sequences for those CANDU reactors which use moderator dump as one of the shut-down mechanisms. In these reactors, subsequent cooling of the calandria tubes is provided by falling films produced by sprays. This paper describes an analysis of falling film flow and heat transfer characteristics on horizontal tubes using integral methods. The application of the results to an assessment of the stability of the films on the calandria tubes following a loss-of-coolant accident with impaired emergency coolant injection flow is discussed. 相似文献
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采用实验方法对比制冷剂R410A在3根强化管和1根光滑管内的换热和压降特性。所有的三维双侧强化管均通过高压分层轧制制成,其立体化内表面结构分别是旋涡状凸起和船型凹坑与花瓣纹背景图案的叠加。通过热平衡分析,实验热损失小于5%。保持制冷剂侧流量不变的情况下,改变水侧的质量流率,可以通过Wilson图解法计算每个管型的水侧传热系数。经热阻模型计算,1EHT-1的管内单相换热性能最佳,3EHT次之,1EHT-2最弱。3根强化管的蒸发和冷凝换热实验结果差距较大,不锈钢的低热导率对凸起/凹坑区域的温度分布影响是主要原因。 相似文献
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Based on finite volume method, the pressure drop and heat transfer characteristics of one smooth tube and ten different axisymmetric corrugated tubes, including two with uniform corrugation and eight with non-uniform corrugation, have been studied. A physical model of the corrugated tube was built, then the numerical simulation of the model was carried out and the numerical simulation results were compared with the empirical formula.The results show that: the friction factor decreases with the increase of Reynolds number ranging from 6000 to 57000, the value of which in the corrugated tubes with non-uniform corrugation(tube 03–10) are smaller than those with uniform corrugation(tube 01–02). The geometry parameters of tube(01) have advantages on the heat transfer enhancement in low Reynolds number flow region(from 6000 to 13000) and tube(07–08)have advantages on the heat transfer enhancement in high Reynolds number flow region(from 13000 to 57000). The vortex, existed in each area between two adjacent corrugations called second flow region, is the root of the enhancement on heat transfer in the corrugated tubes. The effectiveness factor decreases with the increasing of Reynolds number and the performances of the corrugated tubes with pitch of 12.5 mm have advantages than these of 10 mm under the same corrugation geometric parameter. 相似文献
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旋流板分离器的结构对三维流场的影响 总被引:1,自引:0,他引:1
引言 旋流式分离器种类很多[1-4],其中浙江大学发明的旋流板在传质和双相分离过程中均得到广泛应用[5-9].旋流板分离器是利用导向叶片使气体做旋转运动,从而产生离心力,达到气液或气固分离的目的. 相似文献
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The statistical parameters of Taylor bubbles in cryogenic slug flow along glass tube were studied experimentally for various inclination angles θ (0°–60° from the vertical direction) and four tube inner diameters D (14, 18, 25 and 32 mm) by using high speed digital camera. The distributions and mean values of initial formation position, and the length and velocity of Taylor bubbles along the tube at various inclination angles were obtained. Initial position of Taylor bubbles increases as tube inner diameter increases and the effect of tube diameter on Taylor bubble initial position becomes more obvious at θ ≥ 30°. Taylor bubble length shows an allometric decreasing trend with the increasing of tube inner diameter. The influence of inclination angle and axial position on the length and velocity of Taylor bubble in cryogenic slug flow agrees qualitatively with conventional air–water system. The maximum mean velocity of Taylor bubble occurs at 30° ≤ θ ≤ 45° and the minimum mean length of Taylor bubble occurs at 0° ≤ θ ≤ 20°. The Mean length of Taylor bubble increases along the tube for x/D ≤ 60. © 2011 Canadian Society for Chemical Engineering 相似文献
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针对一种新型的非对称外凸式波节管(ACT)换热元件,基于三维RST模型对其进行了数值模拟研究。通过与传统的对称型外凸式波节管(SCT)分析比较,考察了两者流动及传热特性的区别。为了验证雷诺应力模型(RST)在研究波节管结构时的可靠性,比较了现有波纹壁面中直接数值模拟(DNS)与RST模型在同一条件下的计算结果。通过对比发现,RST模型得出的包括速度场、压力系数等计算结果与DNS所得出的结果基本吻合。随后对外凸型的流动及传热机理进行了深入探讨。结果表明,与传统的SCT相比,ACT提高综合传热性能最多能够提高32.3%。 相似文献