Radiant heat with the 14in clay base


 
S

Scott Piccolo

TVWBB Member
For those using a clay pot inside the standard WSM water pan, or thinking about it, I wanted to let you know the results of a test I am doing to see if radiant heat is an issue for the bottom rack. I have 2 racks of baby backs on the top rack with one probe and the bottom rack is empty with another probe. I am now almost 3 hours into the cook. For the first 1.5 hours, the lower rack was around 5 or 6 degrees lower than the top. After about 2 hours, the lower rack started climbing and is now about 5 degrees hotter. It has been steady now for an hour at 249 on the bottom and 244 on the top. It is around 75 to 80 degrees outside and slightly breezy. In my opinion, the WSM with a clay pot base is damn close to perfect. I also noted that on my prior two smokes with the clay pot, I used almost no fuel (minion method). I am going to try and cut back on the amount I use on the next smoke and hopefully I can get steady temps in the 220's.
 
I hate to say it, but your logic is flawed.

Radiant heat, by definition, heats only "stuff," not air. With nothing on the bottom rack, you aren't measuring the radiant effect you think you are, especially considering the rack itself and metal probe both are fairly reflective surfaces.

An experiment to judge the radiant effect would require either some hardcore materials science study of the absorptivity and emissivity of the pot bottom versus the water pan or a prolonged statistical study of results of the 2 cooking styles. Based on the fact that so many people are successfully cooking with the mod, my mind would conclude that the radiant properties are not significantly different enough to produce undesirable results.
 
I picked up a 16-inch terracotta plant pot base from Wal Mart for $ 8.50. It fits perfectly on the waterpan mounts without the waterpan. I going to try it out this weekend.

Rusty
 
Yeah.... Thanks Kevin. Anyway, the radiant heat effect that I was talking about was the radiant heat of the clay pot "stuff" causing high temps on the lower grate. It is a question that has been asked here a few times, so I wanted to test the effect of the clay pot versus a water pan full of hot water. The point I was making is that the clay pot does not seem to cause higher temps on the lower grate that would make it unusable for cooking.
 
Kevin,

I think you might want to reconsider that. What do radiators in houses do? What do they heat...we have them and we keep 'stuff" away from them. Maybe you're not old enough to remember radiators (thank your stars if you're not). In any case, air is "stuff," least that's what they were teaching when I went to school.
 
Rusty,

I think the 14in inside the standard water pan might work better for you. The reason being, it will act kind of like the piedmont double pan with an air space between the water pan and the clay pot base. Good luck and let us know how it works out if you use the 16in pot base without a water pan. Also, I didnt mention, I am using the clay pot without a stoker or guru.
 
I think you guys are dismissing Kevin's comments a little too quickly. While air is "stuff," it will not show the effects of radiant heating as measured with a thermometer probe. Heating the air occurs to some extent from radiant energy but it's mostly convection. That's the way your radiator in your home heats the room. Since it is hotter than its surroundings, there is a bit of radiant heating that occurs but the surface of the radiator itself does not get hot enough to contribute significant heating through radiation. The name "radiator" is somewhat of a misnomer in this case.
To illustrate the effect of radiant heat transfer as opposed to convection alone, think about the temperature difference between air and anything that's been lying out in the sun on a bright afternoon like an asphalt surface or your car. The asphalt surface can easily be 40 or 50 degrees hotter than the ambient temperature due to the way it absorbs radiant heat energy.
In the case of the WSM and clay pot base, the base becomes a source of radiant energy only after it's been heated by the fire. At that point, a piece of meat on the bottom rack is definately going to recieve more energy than one on the top rack. This is due to the fact that radiant energy's intensity lessens with distance from the source (and by the fact that the meat on the bottom rack is blocking that energy's path to the top grate). Think about how warm you get standing next to a fire. Does the air get as hot as your face? No. As you back away from the fire, this effect decreases dramatically because the radiant energy is becoming more diffuse.
The reason that radiant heat is not an issue with a pan full of water is because the temperature of that water never gets above 212 degrees. Once it rises beyond 212, it becomes a gas and it, along with it's heat energy, is distributed by convective means throughout the cooker.
In conclusion, it is very possible that due to convective currents within the cooker, that temperatures measured by a thermometer probe could be equal thoughout the cooking chamber, but the meat closest to a source of radiant heat is still going to cook faster. This has already been proven by those of us that have used sand in the pan.
Now, the important question that is raised is whether or not the base is a source of radiant and if so, does it radiate enough heat to alter cooking times? If the surface of the base gets as hot as the surface of a pan full of sand, then the answer is yes.
More food for thought: how would wrapping the base in foil affect it as a radiant heat source? If you wrap the bottom of the pan, radiant energy from the fire is reflected away from the pan back toward the bottom of the cooker. The base will not radiate as much heat from its surface if you do this. So what if you foil the top of the base? Well, the radiant heat from the surface of the base will travel across the air gaps between the base and the foil and it will stop right there. Some may be reintroduced into the cooking chamber by radiating off the surface of the foil but it's intensity will be diminished.
So where does this leave us? The easiest way to determine what's going on would be to cook similar pieces of meat, one on the top rack and one on the bottom, without flipping and look at the results. I have yet to do this but I would suspect that the surface of the meat on the bottom rack facing the base would be significantly more cooked and possibly drier than them top suface of the meat on the top rack. It would then be useful to try it foiled to see how much that helps diffuse the radiant heat and negate the effects we've been discussing.
 
Kirk is exactly correct. I can design you a radiant heating system for a building where the surface temperature never exceeds 80-85 degrees. Radiant heat requires an absorbent surface to absorb the heat. Like the sun on asphalt. You can fry an egg on the sidewalk when it's 90 degrees outside. If that energy were absorbed by air, the air would be able to fry eggs in the shell.

On the note about radiators in homes, the word radiator is really a misnomer. Old time steam radiators that got so hot you couldn't touch them produced a significant portion of their heat transfer from natural convection, ie hot air rising off them. There is a strong radiant component, but the human senses really don't appreciate radiant heating. This is primarily why radiant heating is so popular in buildings. You can keep the air temperature cooler because the heat is directly incident on the body (and chairs and walls and stuff) so you feel warm even will lower air temperatures.

Another prime example is those gas-fired patio heaters. Obviously the heat isn't transferred to the body by conduction because you're not touching it. There's no fan blowing air on you, so it's not convection. The heat is transferred to your body by radiation. If you were to measure the air temperature, it wouldn't be much different around the heater as not, but you sure feel warmer.

Sorry for the wordiness. Engineering gets the best of me sometimes.
 
Kirk,

I should have mentioned that I do in fact cover the clay base with foil. I don't press it into the base, but rather create a bowl shape to catch the drippings while leaving a slight air space between the foil and base. I also noticed that the drippings in the foil did not burn during the cook, which leads me to believe that what you said about the radiant heat being diminished by the foil is true. One question I do have about your post is that since the probe is a solid object just like the meat, and it is positioned exactly the same distance from the base, then why would it not be affected by the radiant heat in a similar manner? If I place a temp probe near a fire, it will heat up just like my hand or face would if I placed them the same distance from the fire. The air around the probe might be cooler, but the probe would heat up and register as such. I guess the next test should be as you said to try cooking similar pieces of meat on both levels and look at the results. I just did not want to try this at first because I did not know what to expect with regards to temps and didn't want to mess up a good piece of meat to test it. I will try it out on my next cook and let you know how it turns out.
 
Good discussion guys. I am definately interested to hear some test results. I have not cooked on the bottom rack yet. I currently use sand, but was thinking of trying the clay pot base on top the water pan.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Scott Piccolo:
One question I do have about your post is that since the probe is a solid object just like the meat, and it is positioned exactly the same distance from the base, then why would it not be affected by the radiant heat in a similar manner? </div></BLOCKQUOTE>
It will to a certain extent but it will also reflect radiant heat more than a similar sized area of the piece of meat that you're cooking due to its shape and, if it's clean, its color. Realize that my explaination of the whole radiant heat thing is not an all-encompasing scenario. There's a lot of factors at work here - too many to practically quantify for our purposes. The point I was trying to make is that you can't ignore the contribution of the radiant heat to the cooking/drying of the meat in close proximity to the source and your thermometer can't tell you the whole story. Unfortunately, I'm not going to have time to check this out for myself for about the next 3 weeks. Hopefully someone can do a test like I mentioned and give us the real skinny.
 
I just read another post regarding this issue (I think it was actually the one that got me thinking about testing the lower rack) and sure enough, someone cooked a butt on the top and bottom racks and there was no difference. Not really surprising to me as I mentioned in the original post, the temps don't seem any higher on the lower rack. The only difference between the probe (dark from smoke and certainly not reflective) and a piece of meat is the surface area being exposed to radiant heat. Both will show the effects (register temps) although I would suspect a large piece of meet to absorb more radiant heat and cook faster. This did not happen because there was not enough radiant heat to cause an issue, which is exactly what I was trying to determine. Another give away was the fact that, as I mentioned, the drippings did not burn in the base. I am still going to try a cook soon using both racks to further confirm this, but I feel much more confident about it now.
 
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