Yam, I thought Henny Youngman said that (about the evils of reading).
Any who, new here but this caught my eye. Not a geek but just my gut on the thermodynamics involved. First, AJ et al seem right on about the air flow since there is an obvious and audible difference when the kettle is put in place. Is this the pot that you will likely be using there all of the time? You might want to consider that before you go cutting and drilling just in case the size or material changes.
If you look at commercial gas cooking stoves they all use some sort of very dense cast iron or thick steel burner grate to support the vessel over the burner and to allow adequate flame spread. The flame doesn't have to contend with the wind so what they use just makes it easier to slide big stock pots around while storing some of the flame's heat energy and imparting it through direct conduction.
Your tubular frame being in close proximity of blow back from the burner flame plus being in contact with the pot and the wind guard may actually be acting as a heat sink. In other words, if the pot was only in direct contact with a big chunk of solid iron that was also being heated by the flame then all or most of the heat absorbed by the grate would likely be conducted directly into the pot and consequently its contents. The effect of retarding the flame spread by choking the air flow would likely be that the flame is spreading laterally but not necessarily finding enough room to try and wrap around the base of your pot evenly. Meanwhile your tubing is wicking heat away from where you're trying to concentrate it.
You're basically trying to capture the exhaust heat of a jet engine with your pot. Without gettin' too tech'ed out maybe try observing your flame pattern after dark when you can see the full spectrum better. Then try different height spacers when you're able to observe just how they are affecting the flame spread before you go making any permanent adjustments.
It seems that there are limited possibilities, either inadequate oxygen for combustion, dissipation rather than concentration of the heat, or a combination of both.
I'm not certain exactly how it could be done but radiant heat can also be reflected very effectively using shiny metal, such as you see used under the resistance coils on an electric stove top. Maybe some way to incorporate that with the idea of the heat concentrating jacket that was mentioned, after you get the air flow straightened out.
I'm a newbie and usually just gopher when my friends brew, but we usually set up on a sunken patio in my back yard where we are screened from any wind by a 5' stone wall right behind us. Sometimes a wind break can actually worsen heat loss from wind by being positioned incorrectly relative to a lateral air flow. Was there any significant breeze blowing the day that you were doing this. If you were set up just inside the garage door and the prevailing breeze was blowing across the door opening it would create a low pressure just out side of the opening, thereby pulling your heat and oxygen out away from where you needed it. Maybe try some sort of floor standing screen that sits a foot or so to the windward side and use a shorter ring close to the burner? Just a thought. Interesting conundrum. Good luck.
I was also curious though about the reflectivity of the s/s and aluminum pots. The gas flame is just like the heat energy from the sun, so dark colors absorb it more readily and light colors reflect. Just wondering why a pot on a gas burner wouldn't heat more quickly if the bottom of the pot was coated with carbon. Another off the wall shot...if rapid heating is the ultimate, why not do the reverse of what your doing to cool for pitching yeast. Maybe a s/s immersion cooler placed in the pot while heating somehow and circulate H/W off of your water heater to help from the inside. Maybe an acoustical Sterling engine for a heat source coupled with Peltier effect heat exchangers. Just kiddin', I was just reading about them for a different project.
Isn't this one of those times when you're just supposed to relax and have a home brew?
