Experimental Investigation of a Rectangular Airlift Pump

Hydraulic performance of an airlift pump having a rectangular cross-section 20？mm × 80？mm was investigated through an experimental program. The pump was operated at six different submergence ratios and the liquid flow rate was measured at various flowrates of air injected. The effectiveness of the pump, defined as the ratio of the mass of liquid pumped to the mass of air injected, was determined as a function of the mass of air injected for different submergence ratios. Results obtained were compared with those for circular airlift pumps using an analytical model for circular pumps. Effectiveness of the rectangular airlift pump was observed to be comparable to that of the circular pumps. Hydraulic performance of the rectangular airlift pump investigated was then described by a set of semilogarithmic empirical equations. 1. Introduction Airlift pumps have been used since the beginning of the 20th century. They are simple devices in which liquid enters from one end, and a mixture of air and liquid discharges from the other end. Air is injected near the inlet. Almost without exception, the riser section of airlift pumps has been vertical pipes with circular cross-sections. As discussed by Parker [1], the air injector system for these pumps is in the form of an air jacket in which several small holes are drilled radially through the pipe and air is supplied to them from a surrounding manifold. Figure 1 shows the side view of the rectangular airlift pump used in this study. It is similar to pumps with circular section except that air is injected through a perforated pipe placed in the inlet section. Figure 1: Model airlift pump with rectangular cross-section. Fran？ois et al. [2] have described the two-phase flow that takes place in the vertical section of the pump as (i) bubble flow that occurs when dispersed small air bubbles flow upward with the liquid; (ii) slug flow characterized by large air bubbles; (iii) churn flow which is similar to slug flow but with a more chaotic and disordered flow pattern; (iv) annular flow where the liquid phase flows upward as a film along the pipe wall, and the gas phase flows as a separate phase in the center of the pipe. Initially, a detailed analysis of the flow in airlift pumps was not made for several decades. In general, the liquid flowrate in the pump was described by empirical correlations. It was known, however, by Pickert [3] that for each submergence ratio (ratio of the depth of the submerged portion of the pump, , to the total pump height, ), the quantity of liquid pumped first increased rapidly with increased