they're both heat deflectors! The clay tray isn't terribly effective as a heat sink because there's not much of it and the specific heat (amount of energy required to change the temperature) of the clay tray isn't that high.
But it doesn't matter because that's not why its better than water. Its better than water because if you don't fanny about with the smoker it doesn't need the extra thermal intertia to stay steady, and its more effecient because it doesn't evaporate like water, taking the energy out of the cooker and cooling it down. Plus its 10x easier to use, clean and you don't wake up to find it all evaporated and your temperatures all over the place.
Yes I though as much about the water method. I'm just wondering why the saucer in the empty water pan works better than the water pan alone. Seeing as how the saucer is in the pan, how is it doing any deflection?
It just spreads and evens the direct heat of the fire, like a thick bottomed saucepan, or at least thats the theory. but the jury is out on whether thats really required. Harry Soo doesnt use anything in the pan.
As has been pointed out, harry doesnt use a saucer and he uses a force draft system (stoker) AND he adds additional insulation by adding a blanket. This helps him keep a steady temp. On another note, I dont believe having water pan filled with water increases the moisture of the meat. Just like you dont add a bowl of water to your oven to get succulent roasts (as the meat pores close at around 140F). If anything moisture is being taken away from the meat via evaporation as the temperature rise, not absorbed.
yeah, dno't think anyone is suggesting the "steam makes it moist" thing.
As an experiment, I've been running my WSM 18 since 2pm today with no water pan at ALL. Its behaved exactly as it does with the pan and clay tray (i.e. rock steady, but over shoots when you take the lid off for a while) all day except its 25F higher than it normally is at the dome. Been cooking chicken, coming out great too!
Not trying to be controversial by the way, just discussing...