Design - Designing an Evaporator
Waste Water Evaporation Water Treatment Water Mister System
Designing an Evaporator
Engineering of our evaporator utilized some basic common sense facts and input from University sources:
1. It is generally accepted that evaporation is effected by humidity, temperature and wind conditions.
The greater the temperature, the less the humidity and the greater the wind conditions (which lengthen hang time), the greater the amount of evaporation. The only factor we could affect was the wind conditions, so we utilized our axle flow fan that we originally patented in 1968, and still use today in our agriculture production, to create a 100 mile per wind speed to generate sufficient volume to get the water droplets a lot and gain "hang time"
2. The smaller the droplet size the faster it will evaporate and the greater the potential is for drift. Combining small droplets with elevation is necessary.
"Spray droplet size is by far the most important factor affecting drift. Spray droplet diameters are measured in micrometers. A micrometer is 1/25,000 of an inch and is usually referred to as a micron. For reference, the thickness of a human hair or a sheet of paper is roughly 75 microns."
Read Ohio State University Bulliten 816 for more Information
In general the longer the droplets remain airborne, the greater the chances they are going to be carried by wind away from the application site. Small spray droplets are more susceptible to drift than the larger droplets because they tend to remain airborne much longer than the larger droplets.
Fig.5. Smaller droplets drift longer distances
Research shows there is a rapid decrease in the drift potential of droplets greater than about 150 or 200 microns. Droplet size where drift potential becomes insignificant depends on wind speeds, but lies in the range of 150 to 200 microns for wind speeds of 1 to 9 miles per hour (Bode, 1984). Small droplets can drift long distances because of their lightweight. For instance, as shown in Fig. 5, the theoretical distances that water droplets would be carried while falling 10 feet in air having a uniform horizontal velocity of 3 miles per hour would be only about 8 feet for 400-micron droplets,
but about 1,000 feet for 20-micron droplets.
Water particles under 50 microns in diameter remain suspended in the air indefinitely or until they evaporate
3. Based upon findings by Virginia Tech, we accept the following:
A water droplet size of 200 microns will drop at 2.4 ft/sec, and take 29 seconds to evaporate, therefore it must fall 69.6 ft to evaporate. Given this knowledge, our goal for loft of the water column was 75 feet and we achieved this with our wind tunnel.
A water droplet of 100 microns will fall 1.7 ft/sec and take 7 seconds to evaporate, which is a drop of 11.9 ft.
Following is a chart of finding from their Internet site
With this information we determined we wanted to minimize the average water droplet size, so positioning of our nozzles in the airstream became important based upon the following published information, again by Ohio State University
Read Ohio State University Bulliten 816 for more Information
Nozzle Orientation
Orientation of nozzles is not critical for ground applications, but plays an important role in reducing drift from aircraft applications. When a nozzle is pointed backward toward the tail of the aircraft, larger droplets are produced (Fig. 9). The same nozzle produces medium droplets when pointed downward and smaller droplets when pointed into the air stream.
We designed our nozzle ring to point the water droplets into the air stream produced by the wind tunnel, in the same way it occurs on an aircraft, thus obtaining the advantage of air sheer.
Fig.9. Nozzle orientation is critical with aircraft applicationsWe have assumed that since our application uses an axial flow fan to produce a wind speed of in excess of 100 mph exiting the top of our wind tunnel, the result is the same as an aircraft traveling at 100 mph, therefore by placing our nozzles at an angle, as we do, to the wind, we are shearing our water droplet size from a nozzle calibration using a 25 swirl with a DC6 nozzle, from a water droplet size of 280 microns (see chart below) down to 180 microns. Different size nozzles result in different size water droplets.