Friction characteristics for water-ethylene glycol mixture flow in horizontal tubes with new type of helically fins

doi:10.11949/j.issn.0438-1157.20151514

Abstract

Abstract:

An experiment setup was built for investigating single-phase adiabatic flow characteristics of internal helical-rib roughness. The friction characteristics for 15% (by volume) water-ethylene glycol mixture flow in three internal finned tubes (two types of new developed internal helical-fins) and a smooth tube were obtained. The parameters of test tubes are nominal inside diameters (22 mm and 16 mm), numbers of fins (60 and 38), helix angles (45° and 60°) and fin height to inside diameter ratios (0.022 and 0.053). The lengths of the internal helical-rib tubes in test section were 2643 mm and 2945 mm, respectively. The Prandtl number varied from 13.9 to 23.2 and the Reynolds number ranged from 4000 to 33000. The smooth-tube results were compared to the Filonenko equation with satisfactory agreement. The experimental results of different length and same type multi-start internal helically-finned tubes also showed that the entrance effect on the friction factor in the multi-start internal helically-finned tube increased with the increase of Re. Especially for Re>20000, the criterion that entrance effect can be ignored when l_o/d_i>60 (l_o—length in test section, d_i—inside diameter) was not suitable for the multi-start internal helically-finned tube. All the three helically-finned tubes results indicated that there was a critical Re, Re_cr, a function of geometric variables of internal helically fins. The friction factor achieved the maximum when Re=Re_cr and for 4000<Re<Re_cr. The earlier friction factor correlations could not be in good agreement with experimental data. Much efforts should be done to enlarge the application range of the earlier empirical formula. Also, for 4000<Re<Re_cr, the variation tendency of friction factors in multi-start internal helically-finned tubes were greatly different from those in equivalent roughness tubes used in the Nikuradse experiment. The difference between resistance mechanisms of internal helically-finned tube and artificial equivalent roughness tube was analyzed and deserved more attention.

Key words: internal helically-finned tube, friction factor, ethylene glycol, entrance effect, experiment, flow, simulation, numerical analysis

摘要：

建立了水平管内绝热流动阻力特性试验系统,试验研究了乙二醇溶液在两种新型多头内螺纹管内的流动特性。试验中,乙二醇体积分数为15%,两种试验管公称内径为22 mm与16 mm、螺纹头数为60头与38头、螺旋升角为45°与60°、相对粗糙高为0.022与0.053,测试段长度分别为2643 mm与2945 mm,Pr范围13.9～23.2,Re范围4000～33000。结果表明:多头内螺纹管阻力系数达到极大值之前的变化趋势与均匀粗糙管显著不同,而且无法通过既有多头内螺纹管经验模型准确描述;多头内螺纹管内达到阻力系数极大值的分界点Re为内肋结构参数的函数;入口效应对内螺纹管阻力系数的影响随Re增加而增大,传统的判别入口段可忽略的判据(l/d_i>60)并不适用于多头内螺纹管,尤其是在Re>20000的工况;既有多头内螺纹管经验模型适用工况条件有待进一步拓宽,多头内螺纹结构流动阻力的作用机制、阻力系数出现极大值的分界点的变化规律有待进一步试验探索。

关键词: 内螺纹管, 阻力系数, 乙二醇, 入口效应, 试验, 流动, 模拟, 数值分析

CLC Number:

TK124

ZHANG Jili, WANG Yonghui, MA Zhixian, CHEN Jingdong. Friction characteristics for water-ethylene glycol mixture flow in horizontal tubes with new type of helically fins[J]. CIESC Journal, 2016, 67(5): 1762-1770.

张吉礼, 王永辉, 马志先, 陈敬东. 乙二醇溶液水平新型多头内螺纹管内流阻特性[J]. 化工学报, 2016, 67(5): 1762-1770.

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