Innovative Air Drying Process

Innovative Air Drying Process for
Air Conditioning Systems and
Other Dehumidification Applications

Our new process of using capillary condensation and then osmosis through a semi-permeable membrane to dry air is considerably more efficient than the current method of dehumidification, which has been used since 1902.  The old system squanders a large amount of energy by cooling air down to the dew point to get water vapor to condense and drip off refrigerated coils.  It then heats the air back up to a comfortable temperature.  Our transformative process avoids wasting energy to cool and reheat the air!

osmosisThink about water in a glass; the water rides up the sides of the glass because of surface tension.  If the water were in a straw, the surface energy would cause it to rise up even higher because there is more surface in a given volume of straw.  If the straw were one thousandth of the diameter of a human hair (nanometer size), at moderate humidity, the water vapor would come right out of the air and condense in the straw.  That phenomenon is called capillary condensation, and it has been known for over 100 years.  We can see it happening in different kinds of small spaces in one figure that looks like 3 mini-test tubes and another that shows two different sizes of small particles, where condensation happens between the particles.

So we can fill some straws with condensed water.  How do we get the water out of the straws?  If one end of the straws is placed in salt water, and the hydrated salt ions are too big to fit in the straws, then the water comes out of the straws into the salt solution.  That phenomenon is called osmosis and it has been known for well over 200 years.

If our ‘straws’ are pores in a membrane (think of a piece of Saran wrap), then all we need is a membrane with nanometer size pores floating on a salt solution.  We then pass humid air over the membrane and the humidity is reduced by having some of the water vapor condense by capillary condensation and move through the very thin membrane into the salt solution.  Our first experiments tested the effectiveness of this process in a simple apparatus.  A glass container, filled to the top with salt solution, is covered with a membrane.  A narrow tube attached to the side of the container extends up above the container.  Humid air is blown across the top of the container and the rate of removal of water from the air is measured by the change in liquid level in the tube. The membranes we tested were some of those used commercially for water purification.