PETER MEANS FOR VIRGINIA TECH
Testing then literally moved to the field . In the open fields of Virginia Tech ’ s Kentland Farm , then-undergraduate Brandon Hart built roofed structures to prevent rainfall from impacting findings . Under these coverings , fog harps were placed side-by-side with three different mesh harvesters : one with wire diameters equivalent to the harp , one with a wire size more optimal to harvesting , and one using Raschel mesh — a mesh made of flat-panel ribbons in v-shaped arrays between horizontal supports . This v-shaped mesh is currently the most popular among fog harvesting sites around the world .
Whereas heavy fog conditions were used in the lab , the actual fog conditions surrounding Virginia Tech are generally much lighter . As field tests began , Boreyko and Kennedy were skeptical that the available fog would provide the feedback they needed to do adequate testing . They were pleasantly surprised .
As fog began rolling over the hills of the New River Valley , the fog harps always showed results . In thin fog , the collection pipes of the mesh collectors were completely devoid of drips . Even as fog density increased , the harps continued outperforming their companions . Depending on the density of the fog , this ranged from twice as much output to almost 20 times .
Bringing together lab studies and field data , researchers determined that collection potential is the result of multiple factors . Greatest among these is the size of collectable water droplets between mesh and harp . To be harvested in both cases , water must be caught on the mesh or harp as air passes through , traveling downward into collection points by gravity . Fog harps use only vertical wires , creating an unimpeded path for mobile drops . Mesh collectors , by contrast , have both horizontal and vertical construction , and water droplets must be significantly larger to cross the horizontal pieces . In field tests , mesh collectors routinely require droplets reaching a size roughly 100 times larger than those on harps before descending . Water that never drops will simply evaporate and cannot be collected .
“ We already knew that in heavy fog , we can get at least two times as much water ,” said Boreyko . “ But realizing in our field tests that we can get up to 20 times more water on average in a moderate fog gives us hope we can dramatically enhance the breadth of regions where fog harvesting is a viable tool for getting decentralized , fresh water .”
Full publication of the field tests have been accepted by Advanced Sustainable Systems , written by lead author Weiwei Shi .
Close-up of fog harvesting .
VIRGINIA TECH MECHANICAL ENGINEERING ANNUAL REPORT • 2019-2020 • RESEARCH 35