Volume 20: Pages 521-526, 2007

Oscillating Temperature Pump for Water

Kern E. Kenyon ¹

¹4632 North Lane, Del Mar, California 92014‐4134 U.S.A.

A simple idea for a water pump is proposed based on the thermal expansion of water at moderate temperatures and the assumed nonexpansion of the tube that is filled with water. When an oscillating heat source is applied to the outside of the tube walls, and the tube is oriented vertically, a slow net upward water flow will occur in the tube provided one‐way valves are fitted to each end of the tube and the bottom end of the tube is submerged in a water reservoir. The upper valve only lets water out and the lower valve only lets water in; they operate independently of each other. A continuous oscillation of temperature at the tube occurs between two extremes. For a temperature difference between extremes of 10°C, centered about an average temperature of 20°C, taking place over a period of 20 h, the net flow rate out the top of a 1‐m‐long tube is calculated to be 0.1 mm/h (instantaneous speeds can be much larger). This net flow rate is predicted to decrease to zero as the average temperature of the oscillation decreases to 0°C since the thermal expansion coefficient for water goes monotonically to zero near the freezing point. One potential application of the model pump is to increase our understanding of what forces cause fluids to rise up inside plants against gravity in the warmer seasons and to rise more slowly or to not rise at all in the coldest season at mid to high latitudes.

Keywords: botany, xylem flow, model pump

Received: April 13, 2004; Published Online: October 7, 2009