MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

3.1.2.2 Displacement MethodAs mentioned in Chapter 1, the displacement method of liftingwater was discovered by Heron. Air is withdrawn from a container whichallows water to flow into it. Aia is then forced back into the container,displacing the water and forcing it up a discharge pipe.Since the development of the eductor air-lift methods, displacementtypeinstallations have rarely been used for irrigation and drainagepurposes. They require much more plumbing and have several check valvesand switches (e.g., the regulator) which must be maintained. However,two recent developments have found new applicationsair-liftprinciple.for the displacementThe current "energy shortage" has created an incentive for thedevelopment of water lifters which can utilize natural energy. Amongthem is the solar water pump designed by D. P. Rr_o and K. S. Rao at theBirla Institute in Pilani, India. They have developed two types ofsystems--aircooled and water cooled.In the water cooled arrangment shown in Figure 3.31, the systemconsists of a solar collector, flash tank, and cocling tank located aboveground, and a pair of water tanks located in the water source. Waterenters these water tanks by an inlet check valve under atmosphericpressure. A working fluid--pentane orsome other petroleum Zraction-- flowsby gravity from the flash tank into the solar collector where it vaporizesat about 3S" -4O'C. It then flows through the flash tank and in% one ofthe water tanks. As in the penumatic-operated displacement container, thisvapor will create a pressure within the tank sufficient to push the waterup a discharge pipe. The water being discharged from the one tank passesthrough the coolingtank and condenses the vapor in the other water tank.