So we've been talking about applying some actual science to our whirlpool speed, rather than "eh, looks about right." Considering our current practice is 1) get it spinning with the steel paddle, 2) turn on the VFD until the pump's just starting to make annoying noise, then 3) throttle the whirlpool valve until it stops making annoying noise...yeah it's probably time to take a closer look. Thus I've spent the morning trying to figure out from the pump curve on our Ampco AC+ 1 horse 1.5" pump what the flow rate is. And now it's two hours later and my head hurts.
The MBAA Practical Handbook #1 (totally pick these up BTW!) says whirlpool transfers should go in about 7-8 feet per second flow velocity. It gives the formula:
V = (0.408 x GPM)/D2
Where V is wort velocity, GPM is gallons per minute and D is inner pipe diameter.
This is for transfer to a separate whirlpool, and ours is combined, but I imagine the idea is to spin the kettle about as long as you would take to transfer to a separate whirlpool, 10-15 minutes. So:
If we want to transfer (i.e. spin) 11bbls in 10 minutes we need to go at:
GPM = (11bbl x 31gal/bbl)/10 min = 34.1
Our pipe diameter is 1.5" so D squared is 2.25
So V = (0.408 x 34.1 gpm)/2.25 or 6.18 ft/sec. So a bit slow actually. But it's 7.25 ft/sec at 40 gal/min. So let's set that as the target flow rate. Which makes sense. A little over a barrel a minute to transfer 11bbls in about 10 minutes.
Now to the pump curve. Ugh. So here's the curve for my pump. It's got a 1 horse powering it. Of course, I have no idea without unshipping it what the impeller diameter is, but I'm going to guess probably 3.5" since it's got a one horse on it.
Looking at the curve, if I want 40 gpm it should be somewhere between 3/4 and 1 horse. Which would be like 85% on the VFD, which is WAY faster than we've been running it. Is this right? How much should we throttle down the pump with the VFD? Or am I obviously not a fluid process engineer and reading the chart wrong?
The MBAA Practical Handbook #1 (totally pick these up BTW!) says whirlpool transfers should go in about 7-8 feet per second flow velocity. It gives the formula:
V = (0.408 x GPM)/D2
Where V is wort velocity, GPM is gallons per minute and D is inner pipe diameter.
This is for transfer to a separate whirlpool, and ours is combined, but I imagine the idea is to spin the kettle about as long as you would take to transfer to a separate whirlpool, 10-15 minutes. So:
If we want to transfer (i.e. spin) 11bbls in 10 minutes we need to go at:
GPM = (11bbl x 31gal/bbl)/10 min = 34.1
Our pipe diameter is 1.5" so D squared is 2.25
So V = (0.408 x 34.1 gpm)/2.25 or 6.18 ft/sec. So a bit slow actually. But it's 7.25 ft/sec at 40 gal/min. So let's set that as the target flow rate. Which makes sense. A little over a barrel a minute to transfer 11bbls in about 10 minutes.
Now to the pump curve. Ugh. So here's the curve for my pump. It's got a 1 horse powering it. Of course, I have no idea without unshipping it what the impeller diameter is, but I'm going to guess probably 3.5" since it's got a one horse on it.
Looking at the curve, if I want 40 gpm it should be somewhere between 3/4 and 1 horse. Which would be like 85% on the VFD, which is WAY faster than we've been running it. Is this right? How much should we throttle down the pump with the VFD? Or am I obviously not a fluid process engineer and reading the chart wrong?
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