Experimental study on the flow and heat transfer behavior of polymer solutions in the closed liquid ring vacuum pump system

Abstract

The closed liquid ring vacuum pump system, which mainly includes the liquid ring vacuum pump and the heat exchanger, is widely used for gas pumping in various industries. In this paper, the energy saving effect in the liquid ring vacuum pump and the flow and heat transfer behavior in the shell-and-tube heat exchanger are investigated for aqueous solutions of rigid xanthan gum (XG) and flexible Polyacrylamide (PAM), and the effects of the concentration, Reynolds number, polymer conformation and flow geometry on the flow behavior of polymer solutions are studied. Results show that, despite the significant differences in molecular conformation and rheological properties between XG and PAM, the similar energy saving rate, about 1.5 ∼ 17.5%, is obtained in the liquid ring vacuum pump. However, in the shell-and-tube heat exchanger, XG solutions exhibit the more obvious pressure drop enhancement and heat transfer reduction than that of PAM solutions for the same concentration. Furthermore, due to the polymer shear degradation, the shaft power in the liquid ring vacuum pump decreases first and then stabilizes, conversely, the flow resistance decreases and the flow rate increases in the heat exchanger. The great difference in the flow condition between the intense rotating gas–liquid two-phase flow field and the gentle liquid pipe flow causes the different flow behavior for XG and PAM solutions.