Abstract:

Static mixer is a kind of efficient and energy-saving mixing equipment with broad applications in chemical engineering and environmental protection. The unique morphological structures of natural organisms provide rich inspiration for the design of high-efficiency equipment. The three-twisted conch static mixing element has been designed, which was inspired by the spiral shape of the conch. The enhanced heat transfer performance of the three-twisted conch static mixer (TCSM) and the reverse three-twisted conch static mixer (RTCSM) were evaluated and compared. In the constant heat flux heat transfer experiments, pressure drop (Δp), Fanning friction factor (f), and Z-factor were used to evaluate the performance of energy consumption. Meanwhile, Nusselt number (Nu), convective heat transfer coefficient (h), and preference evaluation criterion (PEC) were utilized to evaluate the enhanced heat transfer performance of different mixers at Reynolds numbers (Re_t) ranging from 2640 to 11450. The results indicate that compared with the empty tube, the h of the Kenics static mixer (KSM), TCSM, and RTCSM are enhanced by 22.15%—40.53%, 10.83%—27.34%, and 33.29%—50.30%, respectively. The PEC of the RTCSM is higher than that of TCSM and KSM by 9.41%—28.99% and 4.94%—13.29%, respectively. Additionally, the power spectral density (PSD) and scaling exponent (ϕ) of the pressure signal time series at the inlet and outlet of different mixers were analyzed. The results indicate that due to the large-scale macroscopic motion of the liquid phase, the PSD strength of KSM is greater than that of TCSM and RTCSM in the low-frequency range. Concurrently, the ϕ of RTCSM is lower than others, which indicates that RTCSM generates more small-scale vortices and dissipation leading to a higher energy proportion of the high-frequency range. The maximum Lyapunov exponent (λ) of RTCSM at the outlet is larger than the λ of TCSM and KSM, indicating that the fluid exhibits stronger chaotic characteristics after flowing through RTCSM.

Key words: static mixer, heat transfer, turbulent flow, PEC, power spectral density, largest Lyapunov exponent

摘要：

基于绿色仿生学理念，依据海螺的外形特点设计了一种三旋海螺型静态混合元件。在进口空管段Re_t=2640~11450的恒热通量传热实验中，采用压降（Δp）、范宁摩擦因数（f）和Z因子评价了Kenics型静态混合器（KSM）、正向三旋海螺型静态混合器（three-twisted conch static mixer，TCSM）和反向三旋海螺型静态混合器（reverse three-twisted conch static mixer，RTCSM）的能耗。基于Nusselt数（Nu）、对流传热系数（h）和综合传热系数（PEC）评价三种混合器的强化传热特性。结果表明，KSM、TCSM和RTCSM的h与空管相比分别提高22.15%~40.53%、10.83%~27.34%和33.29%~50.30%，RTCSM的PEC分别比TCSM和KSM增加9.41%~28.99%和4.94%~13.29%。此外，通过功率谱密度（PSD）和标度指数（ϕ）表征不同混合器进出口压力信号的湍流脉动特征，发现RTCSM能够产生更多的小尺度涡进而强化传热。出口处RTCSM的最大Lyapunov指数（λ）大于TCSM和KSM的λ，表明流体流经RTCSM后呈现更强的混沌特性。

关键词: 静态混合器, 传热, 湍流, PEC, 功率谱密度, 最大Lyapunov指数