Element power for RIMs
Making the jump from 120V to 240V. My 120 element is 1650W but I'm wondering how big to go for my RIMs tube. 5500W seems like too much for mashing. I will be using PID control and thought about going big and limiting max power in the PID control or is it more efficient to just go with something like 3000W using max power? Just looking for input as I progress with my design.
Oh man this is one of my favorite topics... I can't respond right now but will within the next few hours! Keep an eye here.
OK... so I've done a fair amount of research on RIMs tubes as I implemented on the fly sparge water heating. That requires a lot of power for that purpose, but of course you need very little for mash temp control.
First thing to consider, and please understand there is a shameless plug coming, is the RIMs element and the resulting density. We want low density and the avoidance of dumping a lot of heat into a local area. That causes a lot of wort stress. The other thing needed in a RIMs application is to ensure movement and turbulence in the tube to ensure the same body of wort has minimal contact with the element. But, lots of turbulence is bad too, as it is rough on the wort.
The heaters we typically use for RIMs tubes are not built for the purpose. When we use a very long 5500W (or 4500W) foldback element and run it at 120V, we get a reasonable density, and this could probably suffice for mash temp and steps. Those elements are still thin, resulting in a lot of dead space in the tube (you ideally want minimal dead space and mostly contact surface area with the element), so I would suggest some type of baffling be added. I have successfully used stainless steel wire, wrapped in a criss-cross around the element. This helps cause some movement in the tube and distributes heat.
Now, in my application I ran the element at full 240VAC power for strike water heating and sparging, and 120VAC for mashing. I did this via a relay that switched one of the element feeds between Neutral and Line 2. But in your case you are asking about 240VAC. I *believe* and its with good confidence, that you can run your element at 25% maximum duty cycle and achieve the same result as 100% at 120VAC. So your range is 0-25%, and to keep the resolution right, you need to keep the cycle time fast. I would say 1 second, and know that your SSR will be cycling fast, which will add a bit more heat and stress on it. You could also opt for a proportional SSR... more $ but seemless control.
Now the plug... we built a purpose-made RIMs element for the purpose of low density, called the QuadZilla. It is the equivalent of a ripple foldback, using 4 cartridge heaters and really maximizes surface area in a normal 1.5" RIMs tube. It has two baffles inline too, to ensure the wort is mixing well.
Also, per above, you want as narrow a tube as you can fit the element in (bigger is not better here). You want a big element:tube ratio. Also, mount the RIMs tube vertically with the probe at the top pointed down toward the element - it will perform better this way, but will also ensure that in a zero flow situation, scorching will be minimized or eliminated.
I gotta say, that QuadZilla is pretty cool. My RIMs tube is 15 3/4" long from flange-to-flange which means my temp probe thermowell would protrude down between the 4 elements...any issue with that?
My other option is just design a 120VAC system keeping my existing 1650LWD SS element, I boil with propane and heat my HLT with propane. For heating the strike water I start the system up early enough to heat it in the MT using recirculation.
I've just about finished the Power side of the design.
The QZ is 15" flange to tips. Add the gasket and you have a hair over 3/4" clearance... You can have the probe in between the elements without too much concern I think. But more important is to ensure that the probe tip is in the stream of liquid which is exiting the tube. You don't want the probe to be far above the exit, then it will not be reading correctly.
@pbruno3 No problem there, the thermowell extends below the RIMs exit into the MT