A Liquid Crystal “Heat Switch”∗

∗U.S. Patent Number 4.515.206.

Abstract

A novel method of controlling heat flow from a surface is discussed. The method employs a nematic liquid crystal. A convective motion of the liquid crystal can be induced by subjecting it to either an AC or DC electric field. If the liquid crystal is used to transfer heat between two surfaces, the heat transfer rate can be controlled by varying the electric field strength. It is shown that the heat transfer rate through a thin layer of the liquid crystal can be increased by 25 limes when an electric field is present. This paper briefly discusses the physical phenomena that induce the convective motion in the liquid crystal due to the electric field. Experiments to determine the effects of field strength and gap distance on the enhancement of the heat transfer rate are discussed. An abrupt change in the rate of increase of the heat transfer rate with increasing voltage was found and is believed to be caused by a change in the fluid flow structure. This “heat switch” may find applications in aerospace and electronics cooling situations in which heat must be removed from a surface periodically while at other times the surface must remain insulated.

Notes

∗U.S. Patent Number 4.515.206.