sled_mack said:
First of all I am not an expert but my thinking on one fan being more efficient versus two is the amount of air supplied will not be traveling at the same velocity and pressure because the volume will be less. With your blower settings currently cut so far back you are not only reducing volume you are also reducing pressure if there are no obstructions in the path of the air. Obstructions would be wood/coals over the nozzle and reduced settings for primary and secondary air. Air entering the primary chamber is by design going to exit the nozzle at a lower velocity than it entered the chamber because the nozzle is a larger opening than the combined openings for the primary air inlet at least until coals/wood begin to cover the nozzle. If all things are equal the air entering the primary chamber will exit at the same speed. If there is a 50% reduction in the area that the gasses exit the primary chamber in comparison to the area the air enters the primary chamber the primary chamber will pressurize (back up until the source of the pressure stops or the restriction is removed or burned out). The pressurization of the primary chamber increases pressure on the secondary air supply because the fan is still producing the same amount of air that now has fewer places to go, and forces greater velocity through the secondary air exit (flow equalization) if the secondary air channel is the path of least resistance (adjustment is the factor here). Once the velocity of either the primary air or the secondary air gets too high the mix for the best burn will suffer as pockets of air or gas will shoot through the mix and either cool the gasses or leave the gasses in too thin of a mix to burn (secondary supply) or slip through the gaps in the secondary ports and be too rich to burn (primary gasses) until the gasses can mix as they spread (generally a cooler orange flame) out on their way to the heat tube and chimney. Two blowers have a greater potential for over pressurization. In your set up by reducing the available air for the burn you have demonstrated that two blowers are not currently needed for your mix setting (a change in settings could require two fans). One 20 cfm blower cannot supply the volume of two 20 cfm blowers. (arbitrary number) So in theory the mix is more apt to be more equally disbursed at the critical time and place for greatest heat generation because the air flow is gentler. One blower will not create pressurization spikes as quickly as two and should give a more regulated overall flow of air. The gasification burn process is always in a state of flux so exact equalization is not going to exist for 100% of the burn, it's too volatile, but the closer we get to balance and not spike the closer we get to regulated controlled burns. Sorry to be windy...it's late.
