The air-lift pump

The liquid feed line is known as the submergence limb and the line carrying the aerated mixture as the rising main. The ratio of the submergence hg) to the total height of rising main above the air injection point (hr + hg) is known as the submergence ratio. 

If a mass Gi of liquid is raised through a net height hr by a mass Ga of air in unit time, the net rate of energy transfer to the liquid is Gighr. If the pressure of the entering air is P, the work done by the air in expanding isothermally to atmospheric pressure Pa is given by  

The mass of air required to pump unit mass of liquid is, therefore, given by  

If all losses in the operation of the pump were neglected, the pressure at the point of introduction of the compressed air would be equal to atmospheric pressure together with the pressure due to the column of liquid of height hs, the vertical distance between the liquid level in the suction tank, and the air inlet point. Therefore  

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A gas-liquid mixture will have a lower density than the liquid alone. Therefore, if in a U-tube one limb contains liquid and the other a liquid-gas mixture, the equilibrium height in the second limb will be higher than in the first. If two-phase mixture is discharged at a height less than the equilibrium height, a continuous flow of liquid will take place from the first to the second limb, provided that a continuous feed of liquid and gas is maintained. This principle is used in the design of the air lift pump described in Chapter 8. 

The principal flow patterns are shown in Figure 5.1. In general, the flow pattern map (Figure 5.2) is also applicable to vertical flow. Further reference to flow of gas- liquid mixtures in vertical pipes is made in Section 8.4.1 with reference to the operation of the air-lift pump. 

There are a number of important applications of the air-lift pump in the process industries due to its simplicity. It is particularly useful for handling radioactive materials as there are no mechanical parts in contact with the fluid, and the pump will operate virtually indefinitely without the need for maintenance which can prove very difficult when handling radioactive liquids. 

An improved perfusion unit. Perfusion units of earlier design used air-lift pumps operated by reduced pressure to circulate the aqueous solution. Such units are often used in banks of about ten and were difficult to adjust so that all of them circulated solution at the same rate. With this design, which uses compressed air, the air-lift pumps are easily adjusted and more positive in action. The solution can be readily sampled without dismantling the components. Additives to the solution can be introduced without disturbing the flow setting (Fig. A. 10). 

Harris, E.G. (1895). Theory of the air-lift pump. Journal of the Franklin Institute 140(1) 32-52. Harris, E.G. (1903). Theory of centrifugal pumps and fans Analysis of their action, with suggestions for designers. Trans. ASCE 51 166-252. 

Engineering Experiment Station, Bulletin 82. University of Wisconsin Madison WI. Ward, C.N., Kessler, L.H. (1924). Experimental study of the air-lift pumps and application of results to design. Engineering Series 9, Bulletin 1265. University of Wisconsin Madison. 

Stepanoff, A.J. (1929). Thermodynamic theory of the air-lift pump. Trans. ASME 51(5) 49-55. 

However, I can t call Professor Peterson. He s dead. I wouldn t call him anyway. I know what he would say "Lieberman, the analogy between the air lift pump and draft in a fired heater is obvious to the perceptive mind, which apparently excludes you."... 

In Fig. 1.1, the pressure at point A will be greater than the pressure at point B. It s true that the height of liquid in the riser tube is double the height of water in the tank. But because of the bubbles of air in the riser tube, the density of the mixed phase fluid in the riser is small compared to the density of water. The pressure difference between points A and point B is called the "air lift pump driving force." Water flows from an area of higher hydrostatic head pressure (at A) to an area of less hydrostatic head pressure (at B). Using more air, reduces the density in the riser tube. This lowers the pressure at point B. The... 

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