Just as ionic rain can irrigate a forest of nanotubes, ionic winds can cool the surface of chips. Harnessing ionic winds to accelerate charged air between high-voltage electrodes can enhance a chip's heat-transfer coefficient by 250 percent, according to Purdue University (West Lafayette, Ind.). Its chip-sized ionic wind engine prototype, funded by Intel Corp., works by overcoming the "no-slip" effect that ordinarily keeps the air molecules nearest the chip surface relatively stationary. The ionic wind engine prototype consists of two high-voltage electrodes positioned on either side of a chip's backside. By putting a thousand voltage potential between the electrodes, air molecules become charged and an ionic wind is generated between them across the surface of the chip. Ordinarily the "no-slip" effect in air flow keeps the air molecules closest to a surface increasingly stationary, thereby inhibiting thermal transfer. However, if ionic wind engines could be integrated in arrays on the backside of chips, then normal cooling fans would become more than double their efficiency because air near the surface of chips would no longer be stationary.