Taking inspiration from the capillary forces harnessed by mangrove trees to secure water, engineers at Virginia Polytechnic Institute and State University designed a “synthetic tree” to increase the efficiency of solar steam generation for water harvesting.

The synthetic tree consists of a 19-tube array structure that is covered by a nanoporous ceramic disk designed to function as the leaf. Each plastic tube, imitating the xylem conduits of trees, is 6 cm high with an inner diameter of 3.175 mm. The operating principle replaces capillary action with transpiration, a more efficient mechanism by which plants suck up water through hollow vessels made from xylem tissue. As the water warms, it releases as vapor through pores on the underside of leaves. Transpiration can pump water up insulating tubes of any desired height.

The design detailed in Applied Physics Letters enables the evaporating interface to thermally separate from the bulk water in the tank, so the evaporator does not dry out. Water evaporating from the disk is replenished by suction, which continuously pumps more water from a bottom tank up the tube array. The system was demonstrated to harvest three times more water than using a bulk reservoir alone.

“We expect our tree-based solar steam generator will be of interest for applications in underground water extraction and purification,” said researcher Jonathan Boreyko. “The ultimate goal is to achieve a suction pressure strong enough to pull ocean water through a salt-excluding filter without requiring a mechanical pump, analogous to how mangrove trees are able to grow in ocean water.”

The synthetic tree technology adds to the arsenal of solar-driven water production technologies, including a seawater desalination system and a solar energy-absorbing hydrogel membrane.