Fluid dynamics question

[prrriiide]

I have a HERMs running through 3/8" tubing. I am re-plumbing the rig with 1/2". My HEX is 3/8 od, 1/4 id copper. If I don't change that out, but up-size everything else to 1/2, will I keep volume, just increase pressure? Or am I going to wind up causing problems with the mis-matched sizes?

 

[motobrewer]

I have a HERMs running through 3/8" tubing. I am re-plumbing the rig with 1/2". My HEX is 3/8 od, 1/4 id copper. If I don't change that out, but up-size everything else to 1/2, will I keep volume, just increase pressure? Or am I going to wind up causing problems with the mis-matched sizes?

i've run into problems with this before. dip tube is 3/8" and my plumbing between kettles is 1/2". if you get everything primed really well before brewday it works fine but if you happen to get some air in the lines it's a pain to purge.

 

[prrriiide]

i've run into problems with this before. dip tube is 3/8" and my plumbing between kettles is 1/2". if you get everything primed really well before brewday it works fine but if you happen to get some air in the lines it's a pain to purge.

I have a priming valve on the pump, so purging shouldn't be a problem. I'm thinking that as the wort flows from the 1/2" out of the pump and through the line, it will accelerate (develop higher pressure) as it flows through the 1/4" ID copper of the HEX. I can offset this in the return manifold by opening up the holes to lower the pressure, as long as the volume doesn't decease substantially.

My concern is that I'll be pulling it out of the MLT through the 1/2" valve faster than it can be replaced via the 1/4" copper line.

 

[stevehaun]

Your flow will be limited by the resistance of the coil. If you have a typical mash pump, it will be happy because they like good return and resistance on the outflow. This is why they recommend the valve on the outflow. You will be fine as long as you are not doing very big batches.

 

[acidrain]

My concern is that I'll be pulling it out of the MLT through the 1/2" valve faster than it can be replaced via the 1/4" copper line.

That makes no sense. Do you think the wort will be stored somewhere in the system?
No, the pump will draw exactly as much as is pumped through the system.
The fact is, a bigger inlet is better that a bigger outlet. The smaller diameter HEX is acting as a control valve, which is fine.

 

[prrriiide]

You will be fine as long as you are not doing very big batches.

20-25 gallons

 

[stevehaun]

I wonder if you will get enough flow thru your herms to control the temp of your mash. I make 30 gallon batches. With a 25 foot, 1/2" OD herms coil, I could barely maintain mash temps. I ultimately went with a 25 foot, 5/8" OD herms coil and can maintain mash temps and slowly raise them.
Ability to raise temp is a function of thermal mass of the mash and flow of wort thru the mash (assuming that wort reaches desired temp at herms coil outlet).