Thermal conductivity

[Alphonse]

Regarding pit/grill selection, I am guessing we are all interesting in cooking functionality, aesthetics, durability, and thermal efficiency. All these are influenced by the material of construction of the pit. Some materials we see in pit construction are ceramic, brick, steel, enameled steel, stainless steel, cast iron, and aluminum.

Here are some thermal conductivity values for these various materials.
For a rough reference, thermal conductivity (W/mK) of:

Aluminum - 205

Cast Iron - 80

Steel - 50

Stainless - 16
Fire Brick - 0.15

So yes, fire brick is a lot better insulator than aluminum! Of course wall thickness does affect heat loss and retention. (Thick is better and does impede heat flow/loss.)

For metal, stainless looks really good but its expense usually results in a sheet metal product. However, it turns out that a sheet metal stainless pit may perform as well as my PK from a thermal perspective.

Not trying to stir the pot, but I am not too keen on an aluminum kamado. For a kamado I am personally going to stick with ceramic.

I am also not believing my PK is a superior insulator because it is aluminum, it is not. However, my beloved PK360 is rugged and my go to for a searing machine! But its heat retention isn't enhanced because it is aluminum. It is durable and will likely last a lifetime.

These numbers also support my observation that my cast iron skillet performs better for me than my stainless steel pan in terms of response time and efficiency. Given the choice, I am always going to throw my big cast iron skillet on the outdoor burner if the size of the cook accommodates it vs. my bigger stainless steel grill/Wok.

So, just some food for thought . . . .

[tbob4]

That is good info!

[ScottyC13]

I think you we need to know the grade of steel or stainless steel to get an exact number. You also need to factor in any coatings and color for radiant heat loss. There is more to heat flux than just conductivity. FWIW, I use a welding blanket on my Weber Performer. Works great.

https://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html

[Mark V]

Interesting, are you a mechanical engineer? I rarely see such data outside of that profession. Physics major?

[Alphonse]

Yes, mechanical engineer.

[RobertC]

Here are some thermal conductivity values for these various materials.
For a rough reference, thermal conductivity (W/mK) of:

Aluminum - 205

Cast Iron - 80

Steel - 50

Stainless - 16

Fire Brick - 0.15

I'm not sure thermal conductivity is the key design characteristic to focus on for a pit. Air has a thermal conductivity around 0.03 but an open air fire probably isn't that great as a pit. Which isn't to say that material isn't important -- just that thermal conductivity should probably take a backseat to other design criteria.

[Alphonse]

I'm not sure thermal conductivity is the key design characteristic to focus on for a pit. Air has a thermal conductivity around 0.03 but an open air fire probably isn't that great as a pit. Which isn't to say that material isn't important -- just that thermal conductivity should probably take a backseat to other design criteria.

Sorry if I wasn't clear enough. I didn't mean to say it was the only criteria. Yes, there are lots of factors influencing a good pit's intended function but for my money, material of construction is a big piece of the puzzle. Just trying to give folks some food for thought.

BTW, if you find a pit whose containment shell is made out of air and affordable, please let us know!

[RobertC]

This isn't meant as a value judgement, just an observation: it seems like a lot of people here want big pits even if they usually cook only one pork butt because they want the option to cook four of them. Normal advice is to load the burn chamber with a consistent amount of fuel no matter how much you're cooking. So, observationally, fuel efficiency appears secondary to capacity, durability, portability, cost, controlability, and country of manufacture.

[Alphonse]

Robert, OK, thanks.

I think you are spot on with pit size! I see what appears to be some folks buying pits that are far too large for their needs. I notice this particularly on a FaceBook Group I watch from time to time. Unfortunately it seems to be driven by "my pit is bigger than you pit" rationale. I often wonder if it doesn't drive some good deals on used pits that look like new when they discover a huge pit is not real effective at cooking one chicken and a pork tenderloin!

[JakeT]

In some cases, could increased thermal conductivity help to eliminate temperature variances in a closed environment? From one side of the grill to the other I mean. Similar to the use of copper pans for even heating across the cooking surface. (Copper is 385 according to google)

[RobertC]

In a pan, we care about thermal conductivity because it means heat gets transferred to what's in the pan quickly. But we're not cooking on the outside surface of the pit, we're cooking inside of it. Mostly, we cook with hot air (though in grilling, radiant heating too). Thermal conductivity of the "shell" and its design influences how much fuel you use to maintain a particular temp, and maybe fluctuations in it.

[Alphonse]

In some cases, could increased thermal conductivity help to eliminate temperature variances in a closed environment? From one side of the grill to the other I mean. Similar to the use of copper pans for even heating across the cooking surface. (Copper is 385 according to google)

Yes.

An example is one of the claims to fame by PK. If you look at their website they claim the effect you are describing. (snippet attached) The downside of course is there is a higher heat release through the shell and in cold and windy weather, you may take note of it.

[RobertC]

That's pretty amusing.