Validation and Scalability – Bench Tests

Subsequent experiments were performed using a larger apparatus in which shallow trays were filled with a salt solution and each covered with a membrane.  Trays were arranged in a cafeteria style with narrow spaces between the trays for air flow over the membranes.  Air was blown over the membranes and then through an exhaust manifold.  An anemometer was used to measure air flow and humidistats were placed upstream and downstream of the trays to measure temperature and humidity.  A circulating pump was used to move the salt solution through the trays from inlet to outlet manifolds.

Tests were performed on arrays of trays and on single trays with various spacing and air flow.  A single tray, for example, covered with a membrane of 0.13 square meters reduced relative humidity of an air stream flowing at 15 cfm (0.4 cubic meters per minute) by 7%.  At 20 cfm, the relative humidity was reduced by 5%.  An array of 12 of these trays (occupying a volume of less than 0.02 cubic meters) would remove about 0.5 liters/hr of water from a humid air stream.  Reducing volumetric flow rates results in increased relative humidity reduction.  However, capillary condensation with current membranes is limited by pore size and relative humidity is generally not reduced below 65-70%.

A mathematical model of the transport of air and removal of water vapor at membrane surfaces has been developed to help to optimize the design of the system.  The tray system is but one of many potential configurations.