Residence time distribution and heat transfer in circular pipe fitted with longitudinal rectangular wings

Numerical simulations are used to analyze the heat and mass transfer in a circular pipe fitted with longitudinal rectangular vortex generators for Reynolds number between 7500 and 15,000 based on the pipe diameter. The aim of the present study is to test and quantify the mixing efficiency of a new solution able to avoid the bypass region that exists in the center of the high efficiency vortex static mixer (HEV), and also to enhance the heat transfer without increasing the pressure losses. The rectangular wings used here generate each a streamwise counter-rotating vortex pair sweeping the volume of the mixer and act as internal agitator on the flow. The particle dispersion is investigated by analyzing Poincaré sections and by studying the residence time distribution (RTD). The two approaches show much better mass transfer performance and better mixing homogeneity for the new wings arrangement. The heat transfer is also investigated and it is shown that the thermal enhancement factor in the new arrangement is much greater than that of the conventional systems used in the industry. When compared to the HEV heat exchangers it is shown that the thermal enhancement in the present configuration reaches about 40% relative to the classic HEV and 15% relative to the reversed HEV.