mguerra Posted March 31, 2009 Report Posted March 31, 2009 If you do an overnight cook and the ambient air temperature is dropping, the colder air is more oxygen dense and your fire temp will rise for the same vent settings. Have y'all noticed this? I'm talking about after you have heat soaked your cooker and stabilized the temp. Something to keep in mind if you are going to sleep and not using a Guru or Stoker.
johnnyboy Posted March 31, 2009 Report Posted March 31, 2009 Excellent point! What do you think we are talking on an average, +/-10 F. swing?
jdbower Posted March 31, 2009 Report Posted March 31, 2009 And if you are using a Guru/Stoker I've noticed the reverse effect, in cold weather the blower has to work harder since it's blowing cold air into the chamber (I should try comparing the 10CFM with the 5CFM sometime to see if the 5CFM is actually more efficient). Of course this is pretty transparent to you since the temperature remains the same, but interesting nonetheless. I'm also not sure that what I call "cold" exists in Texas outside of superconductor research facilities.
linuxwrangler Posted March 31, 2009 Report Posted March 31, 2009 I think it would take some very careful controlled research to determine the effect of air temperature alone. Yes, cold air is denser and thus has more oxygen. But it is also "thicker" and thus more resistant to being pulled through the openings in the KK. And as things cool down, more energy will be required to heat the intake air and the whole cooker. You would also need to account for moisture in the food and the charcoal, condensation on the lid and all sorts of other effects. One effect that I've noticed is that charcoal absorbs water. I frequently see the cooker "stall out" at about 200F then start a rapid rise. I attribute this to the elimination of water in the charcoal. If you try to start out for a low-n-slow at in the vicinity of 200, it can take a long time for the water to leave and you can be surprised by an unwanted rise. My solution is to open the vents and always let the temp get past the 200 level, perhaps to 350 or so, then damp it back to the desired temp. As long as you're watching, you won't overheat things and the temp will drop right back to desired. Another effect is condensation but this causes an unwanted drop. If you are cooking a lot of food low-n-slow on a chilly day, the water driven from the food can start to condense around the cap and block off airflow - pretty easy to happen when the gap is 0.025"
Firemonkey Posted March 31, 2009 Report Posted March 31, 2009 .0025?? My POSK has cracks bigger than that
jdbower Posted March 31, 2009 Report Posted March 31, 2009 Anyone know where I can find a thermodynamics research grant? I've got access to an environmental chamber used for compliance testing and I'm sure I can load a KK up with a few hundred thermal probes to do some testing. KKEC would be great for this since it's much more uniform than standard lump
Firemonkey Posted March 31, 2009 Report Posted March 31, 2009 I hear the US gov is giving away all kinds of scratch right now. If you aligned your proposal to sound like you were going to promote a tax on BBQ emissions, you might have a shot at the fast track
johnnyboy Posted March 31, 2009 Report Posted March 31, 2009 The problem FM is; you have to be irresponsible to qualify for the scratch. I don't see JD falling in that arena!!! Ha!
mguerra Posted March 31, 2009 Author Report Posted March 31, 2009 blasted variables OK, Linuxwrangler, I knew somebody was going to pipe up with a comment about all the variables! Of which there are many, as you say. IF you controlled all the other variables, colder air holds more O2 than warmer air and produces a hotter fire. Just like it does in an internal combustion engine; ask any pilot! An aircraft engine running at full throttle on a cold day makes more power and results in a shorter take-off run than on a warmer day. That is in spite of the the increased aerodynamic drag caused by the denser air. During a full power takeoff, the throttle opening is the same size, regardless of ambient air temperature. It's fully open. Yet the colder, denser "thicker" air isn't impeded enough in its' passage thru the throttle bore to produce less power, the engine makes MORE power. This is an empirical fact, shown on a dynamometer. Lycoming and Continental have horsepower versus air temperature charts on their websites showing this very clearly. The inflow of cold air does not cool the combustion fire in the engine, the combustion fire is hotter the colder the air gets. How do we know? The measured power! The horespower the engine makes is derived from the thermal expansion of the gasses pushing down on the pistons, the hotter the combustion gasses, the more expansion and power. The absolute worst conditions for a pilot are the hottest days, when some aircraft cannot make enough power to get off the ground. That is in spite of the decreased aerodynamic drag from the thinner air. There just isn't enough O2 for the engine to make power. Every summer we have pilots misjudge the poor engine performance they are going to get in hot air conditions and the take-off accidents that occur are predictable. It happens every year here in Texas (and elsewhere). So, colder air does produce a hotter fire, that is an absolute fact, not an opinion. But there are many other variables that can affect the actual cooking temperature at the grate surface in our cookers, as you say.
DachsieSlave Posted March 31, 2009 Report Posted March 31, 2009 I agree with everything the doc said except (don't you just love the excepts ) the increased drag in cold air and decreased drag in hot air. While true it is a very small part of the equation. There is actually more lift in cold,more dense, air and less lift in hot, thinner, air which multiplies the problems of less horsepower on those hot days. I know this has nothing to do with the discussion at hand, but he started it, really he did.
mguerra Posted April 1, 2009 Author Report Posted April 1, 2009 lift I did not address lift. Thus, there is no "except" required. We are in absolute agreement! Actually, you swerved into reinforcing my point about colder air not having much increase in drag as it enters the vent of the KK. The increase in O2 of cold air far outweighs the tiny increase in drag.
DennisLinkletter Posted April 1, 2009 Report Posted April 1, 2009 I Love this Forum! Who wudda thunk there are so many variables involved just with the air that can affect our tasty Q and KK cookin'! I Love this Forum!
linuxwrangler Posted April 1, 2009 Report Posted April 1, 2009 Firemonkey: .025 not .0025. On my mexi-k the cap thread is 10-pitch (.1" gap per full turn) and I need 1/4 turn for 220F hence 0.025" gap. Having struggled out of Reno on a hot afternoon in a gross-weight Cessna 152 following the air races(those casinos ahead weren't shrinking nearly as fast as I wanted...) and departing desert airports when the temperature is pushing 110, I've got my own experience with density altitude. (What is it about these things that attract pilots, sailors and geeks?) Yes, aircraft can produce more lift at low density altitude. As you say, one effect is that the engine produces more power. Although the denser air is, in fact, more impeded in its flow that is far more than made up for by the greater number of oxygen molecules in the denser air that makes it into the engine. But additionally, the denser air gives the propeller more to bite into and the wings more to act on. But there is also more drag - your climb-rate and lift capability are greater in dense air but your miles-per-gallon improve the higher you go. Long-distance airline flights step to higher and higher altitudes as they burn off fuel often ending up cruising 10,000 feet higher toward the end of the flight than they cruised at the start. Fortunately I haven't, yet, had to concern myself with my cookers lifting capability It is a bit difficult to compare a cooker where the combustion air is the result of convection draft and an engine where air is drawn in by mechanical means and typically compressed anywhere from 6:1 to 10:1 in a normally aspirated engine. I don't actually know how much effect air density alone has on cooking. I have never personally observed a temperature rise that correlated with nighttime temperature drops but who knows - maybe I need to keep looking. Or, perhaps, when the air cools it leads to a greater temperature gradient hence more lifting force and greater airflow. Dunno. I'm just saying that there are so many variables (I keep thinking of more and more all the time - like size of the air opening changing with temperature and the effects of solar heating - my unlit cooker can exceed 150F on a warm day and back in the desert I'm sure it would be far higher still) that without sufficient controls on the myriad other variables it is difficult for me to see that air density alone will cause a significant change in my cooking. But the discussion is fun....
maherussell Posted April 1, 2009 Report Posted April 1, 2009 Please excuse my asking, but what is a POSK??? I have searched high and low and cannot find that acronym anywhere.
dub Posted April 1, 2009 Report Posted April 1, 2009 One effect that I've noticed is that charcoal absorbs water. I frequently see the cooker "stall out" at about 200F then start a rapid rise. I attribute this to the elimination of water in the charcoal. If you try to start out for a low-n-slow at in the vicinity of 200, it can take a long time for the water to leave and you can be surprised by an unwanted rise. My solution is to open the vents and always let the temp get past the 200 level, perhaps to 350 or so, then damp it back to the desired temp. As long as you're watching, you won't overheat things and the temp will drop right back to desired. Okie Dokie LW - you just put into words what had been perkin' in my own cranium for a while! I contend that my cooker runs at the temperature it "wants" to,on any given day, in spite of any consarned variables! Dub(where's my grant application boilerplate?)
Sanny Posted April 1, 2009 Report Posted April 1, 2009 Re: I Love this Forum! Who wudda thunk there are so many variables involved just with the air that can affect our tasty Q and KK cookin'! I Love this Forum! Shoot, all the same ones are involved in the gas mileage on my Prius! You should SEE what goes into the calculations!
Sanny Posted April 1, 2009 Report Posted April 1, 2009 Please excuse my asking' date=' but what is a POSK??? I have searched high and low and cannot find that acronym anywhere.[/quote'] POS has the standard derogatory meaning with which you are probably familiar. K (for Kamado) refers to a cooker produced by another manufacturer. Several people on this site have experienced the other manufacturer's cooker (alternatively known as Mexi-K, or Indo-K, depending on location of the factory, but all the same manufacturer). Not all have had positive experiences (let's leave that understatement alone, shall we?). Hence, "POSK."
mguerra Posted April 1, 2009 Author Report Posted April 1, 2009 background If you would like to know more about the other brand of cooker and the source of the acronym, see: http://www.kamadofraudforum.org/ Remember that what you are reading there has nothing to do with the Komodo Kamado brand product. However, there are a number of people here in these forums who love cooking on ceramic cookers and own that other brand. They just like this message board. As such they will occasionally refer to their POSK. Don't let that confuse you.
Firemonkey Posted April 1, 2009 Report Posted April 1, 2009 Very well stated by the previous posters, I am not sure I could have delivered that message as delicately I do have a KK which is what I do my cooking on. The "other brand" cooker is sitting off to the side right now, with a broken firebox so it gets no use.
Sanny Posted April 1, 2009 Report Posted April 1, 2009 Very well stated by the previous posters' date=' I am not sure I could have delivered that message as delicately [/quote'] Quoting the Wicked Witch in Wizard of Oz, "These things must be done de...licately..." ::::wiggle long green fingers::::
