Abstract:

Non-Newtonian fluids play a key role in chemistry, food, materials, and other fields. They usually have low heat transfer performance due to the high apparent viscosity. The blade-type static mixers have distinctive technical characteristics in chemical process intensification as a kind of efficient heat transfer enhanced equipment. The flow and heat transfer characteristics of non-Newtonian fluids in Kenics (KSM) and Lightnin static mixers (LSM) were compared. The effects of volume flow rate, aspect ratio and solution concentration on the flow and heat transfer of carboxy-methyl cellulose (CMC) power-law fluids were analyzed. The results showed that the higher volume flow rate of CMC solution contributed to the higher heat transfer coefficient and pressure drop. The static mixing elements significantly enhanced the heat transfer coefficient and pressure drop, and the influence of Lightnin was more obvious. The aspect ratio of the elements and the concentration of the CMC solution also affected the fluid flow and heat transfer. The heat transfer performance was improved with the decreasing aspect ratio, while the comprehensive heat transfer performance coefficient (PEC) decreased because the influence of increased friction coefficient was dominated. The increase of solution concentration gradually weakened the heat transfer capacity and significantly increased the pressure drop thus the comprehensive heat transfer performance decreased. It was concluded that the KSM with aspect ratio of 3.0 had the highest PEC which was 2.114 when the volume flow rate was 4.5×10^-4m³/s and the solution concentration was 0.374%.

Key words: non-Newtonian fluids, static mixer, heat transfer, comprehensive heat transfer performance coefficient, numerical simulation

摘要：

非牛顿流体在化学、食品和材料等领域具有关键作用，但高表观黏度使其通常具有低传热特性。叶片式静态混合器作为一种高效的传热强化设备，在化工过程强化中具有鲜明的技术特色。本文针对非牛顿流体在Kenics静态混合器（KSM）和Lightnin静态混合器（LSM）内的流动和传热特性进行了比较研究。重点分析了体积流量、元件长径比及流体浓度等参数对羧甲基纤维素（CMC）幂律流体的流动及传热影响。结果表明，在相同工况下，随着CMC溶液的体积流量增大，管道内的换热系数和压降均增大。静态混合元件的插入使得换热系数和压降显著提高且Lightnin元件产生的影响更明显。元件长径比和CMC溶液浓度影响流体在管道内的流动和换热。随着长径比的减小，传热性能得到提高，但其增大的阻力系数影响占据主导地位，综合换热性能系数（PEC）降低。溶液浓度的增大使得管道换热能力逐步削弱，并对管道内压降的提升有显著影响，综合换热性能降低。总结得出，在体积流量为4.5×10^-4m³/s，质量分数为0.374%、长径比为3.0时，KSM的PEC最大为2.114。

关键词: 非牛顿流体, 静态混合器, 传热, 综合换热性能系数, 数值模拟