The effects of element direction and intersection angle of adjacent Q-type inserts on the laminar flow and heat transfer

• The heat transfer and laminar flow in Q type static mixers are investigated.
• The effects of Reynolds number and insert arrangements are evaluated.
• The effect of hydraulic diameter is incorporated into the performance plot.
• The results are also analyzed from the view point of field synergy principle.

Three dimensional numerical studies were performed for laminar heat transfer and fluid flow characteristics of circular tubes equipped with two Q types of RL- and RR-series inserts. The simulation results of axial velocity distribution in Q-type static mixer (QSM) have a good agreement with the experimental results from the literature using water as working fluid. The effects of Reynolds number, element direction and intersection angle of adjacent Q-type inserts on the heat transfer are evaluated in the range of Re = 20–100 under uniform heat tube wall temperature conditions. The friction factor decreases with the increase of Re, and the deviations of friction factor in RL-QSM with different intersection angles are within 1% when the sum of two angles is equal to 180°. The product of friction factor and Re in QSM linearly increases with an increase in Re, and it is 3.5–10.7 times higher than predicted by empirical theory for tubes without inserts. Taking the effect of hydraulic diameter into account, a modified performance evaluation plot is generated. The ratios of heat transfer rate in QSM to that in smooth tube are larger than 1 and the maxima approach 3.4 under the identical pumping power constraint. The heat transfer augmentation is attained by the swirl flow formation induced by the Q-type inserts and tube wall. Based on the numerical results, synergies between velocity field and temperature field have been investigated through field synergy principle.