BadWolfBrewing
Well-Known Member
slowing down the flow through the coil acts sort of non-intuitively.
While it would help the temperature inside the coil match the HLT, in the end you are adding less energy to the MLT. Essentially, the rate of heat transfer is proportional to the difference in temp between inside and outside. If the temp in the coil is equal to the temp outside the coil, you are not getting any more heat into the MLT from that section of the coil. By increasing the flow rate to the max that the false bottom can handle it, you are delivering as much energy to the MLT as the coil can provide. I'm still not certain what the max recirc rate is. I go 1 gpm, which is the max my pump can push through the coil.
I did find a solution, though. I spoke to a thermal expert at the research group I work with, and he questioned my derivation assumptions. I assumed that since I was recirculating the HLT at such a high rate (10 GPM, the center inlet pumps can really fly), that the outside surface of the coil would be a uniform temperature, which would be the same as the output of the HLT.
So, being a good little engineer, I went home with a spool of thermocouple wire, and probed the crap out of it. Turns out, the volume of water located inside the coil was significantly cooler (10 degs) than the volume outside the coil. So, the inside wall of the coil wasn't being productive, and was possibly hurting the heat transfer.
It is due to how I was recirculating. I used a 90 deg return barb hooked to the recirculation return port on the HLT, just like shown in Kal's website. However, the coil in the stout-tanks is a much smaller diameter, and the volume of water inside the coil wasn't being recirculated much, and was only affected by natural convection from the heating element below.
Finally, the fix: I had some extra tri-clamp stuff sitting around, so I made a tee on the inside of the recirculation port that split the return flow to outside the coil at an angle, like it was, and to shoot down the center of the coil as well.
The problem went away. The effluence of the coil (the output) was at the same temp as the HLT at my maximum recirculation rate. The MLT still lagged the HLT by 1.5 degs, but that isn't too bad, and I might add insulation to be able to step faster anyways.
While it would help the temperature inside the coil match the HLT, in the end you are adding less energy to the MLT. Essentially, the rate of heat transfer is proportional to the difference in temp between inside and outside. If the temp in the coil is equal to the temp outside the coil, you are not getting any more heat into the MLT from that section of the coil. By increasing the flow rate to the max that the false bottom can handle it, you are delivering as much energy to the MLT as the coil can provide. I'm still not certain what the max recirc rate is. I go 1 gpm, which is the max my pump can push through the coil.
I did find a solution, though. I spoke to a thermal expert at the research group I work with, and he questioned my derivation assumptions. I assumed that since I was recirculating the HLT at such a high rate (10 GPM, the center inlet pumps can really fly), that the outside surface of the coil would be a uniform temperature, which would be the same as the output of the HLT.
So, being a good little engineer, I went home with a spool of thermocouple wire, and probed the crap out of it. Turns out, the volume of water located inside the coil was significantly cooler (10 degs) than the volume outside the coil. So, the inside wall of the coil wasn't being productive, and was possibly hurting the heat transfer.
It is due to how I was recirculating. I used a 90 deg return barb hooked to the recirculation return port on the HLT, just like shown in Kal's website. However, the coil in the stout-tanks is a much smaller diameter, and the volume of water inside the coil wasn't being recirculated much, and was only affected by natural convection from the heating element below.
Finally, the fix: I had some extra tri-clamp stuff sitting around, so I made a tee on the inside of the recirculation port that split the return flow to outside the coil at an angle, like it was, and to shoot down the center of the coil as well.
The problem went away. The effluence of the coil (the output) was at the same temp as the HLT at my maximum recirculation rate. The MLT still lagged the HLT by 1.5 degs, but that isn't too bad, and I might add insulation to be able to step faster anyways.