The Kinetic Water Pump

SOLAR-POWERED KINETIC PUMP

(To download a Microsoft Word version of this document, click here)

Written by Dr. Melvin L. Prueitt, Principal Investigator

Introduction

There is need for efficient and simple high-pressure solar-powered pumps that impel seawater or brackish water into reverse osmosis (RO) systems to produce fresh water. Solar dish or trough collectors can produce steam to drive a turbine that drives a high-pressure seawater pump. For systems operating from a single dish, small steam turbines typically have efficiencies of 25% or less. With the turbine connected to a gearbox and the pump, which have efficiencies of about 85% each, the overall efficiency of the system is about 18%.

Steam or other working fluid can be used as a high-pressure gas to pump water directly by simply having a vertical cylinder filled with the water and then admitting the steam into the top of the pipe, as shown in Figure 1. (A number of patents have been granted on this and similar pumps). The steam forces the liquid out the bottom. After the water is flushed, the three-way steam valve turns off the steam from the boiler and switches the exhaust steam into a condenser to be condensed to a liquid and returned to the boiler. After the pressure is released, the cylinder is re-filled with water, and the cycle is repeated. This would make a very simple pump that could use solar energy to heat the boiler. It could be used to pump high-pressure salt water into an RO cylinder to desalinate the water.

Figure 1. Prior art direct steam-powered pump, which is inefficient.

The main problem with this system is that the steam is at constant pressure as it forces the liquid out of the cylinder, and the heat energy in the steam is not used. After the water is pumped out the bottom, the steam is released in a free expansion. Petichakis in his U.S. Patent 5,865,086 disclosed such a system. Its efficiency is only about 8%. If the gas could be allowed to expand adiabatically in the pump cylinder, it could do more work as it cools in the expansion. But the pressure would immediately drop below the required pressure required by the RO unit, and the pumping action would cease.

Another problem with the pump shown in Figure 1 is that the steam condenses on the walls and the water surface, and this represents a loss of energy.

Introduction | Part 1 | Part 2 | Part 3 | Part 4