High power ultrasonic generators (or even audio frequency) cause cavitation, this is not boiling in the same sense as happens when you heat water.
The pressure wave from the sound source drops the pressure in a region so microscopic bubbles expand, or with high enough intensities pulls the liquid
apart forming a pocket of vacuum. In either case the liquid does evaporate into the low pressure bubble, which removes some energy from the adjacent
fluid. But the pressure wave soon reverses, collapsing the bubbles with the generation of heat. The bulk liquid does not cool down, indeed it heats
up from the energy being pushed into it.
Humidifies don't 'boil' the bulk water through cavitation, they atomise the surface of it. This can be done by flowing a film of water across a
vibrating sheet which disperses the water as very fine droplets. Alternatively they can use enough energy to do the same thing at the surface of bulk
water. If you wish you can think of it as cavitation happening at the water's surface, but it's not boiling into vapour but being broken into
droplets.
These droplets evaporate as they diffuse into the surrounding atmosphere, which does generate cooling. However this cooling occurs where the mist of
droplets evaporates, not in the bulk liquid.
Again, the energy for these effects comes from the sonic energy pushed into the liquid, not from the liquid's basic thermal energy. The fluid heats
up from the sound energy being shoved into it,
The high voltage in CRT displays generally comes from the flyback circuit, meaning it's tied to the horizontal deflection. The HV section is tuned to
work optimally at that frequency, and generally is designed to produce only a very low current; as a safety feature many designs will shut down if too
much current is drawn.
The excitation frequency and output impedance of the voltage source must be matched to the transducer used. Wrong frequency means little or no
output, and possible damage to the signal source. Wrong impedance means the same thing, if the transducer needs high voltage then too low drive
voltage means weak output; too high drive voltage means excessive current draw with damage to driver and/or transducer a distinct possibility.
http://www.kronjaeger.com/hv/hv/src/fly/index.html
You've not discussed how you hope to reject the heat you extract. You talk about hundreds of watts of heat, a low IC case temperature - say 50 C, and
eexpect to reject this into the 20 C atmosphere.
[Edited on 22-7-2009 by not_important] |
this called for
