slow temperature fall on fermenters, flow??? clean out jackets?

[ScottD50]

Ok I've searched the posts and still looking for answers. We have a call into our chiller supplier out of the northwest for their 7x7 model but would like anyones opinion. So we have 4x10 bbl batches in our 4x15 bbl 18 yr old DME fermenters that came with our used system. The chiller has 35% glycol mix per manufacturer, 2 inch trunk line to 1 inch drops to 3/4 inch adapters on tanks. The chiller is set at 25 degrees right now. Attempting to crash from 68 but the fermenters are crashing at 5 degrees a day. The 15 bbl CLT doesn't seem to have a problem. Our new 30 bbl tank is crashing very well. I'm thinking it could be a flow problem into the old fermenters? Is there a way to drain the glycol then clean out the jackets of anything that accumulated over 18 years of use then in storage for 3 years?

thanks,
Scott

[ScottD50]

Just got off phone with manufacturer. It seems the flow rate was too high and there was not enough heat exchange, forming ice inside jacket/fermenter slowing crash time. One way to check they said was if Ice was forming on the outlet/return of the jackets then this could be the case due to no heat exchange and the glycol is coming out as cold as going in. Increased set point of chiller to 35 degrees until ice melts and have throttled back the supply side of fermenters at ball valve. Will see if this works.

Scott

[Johnson_Thermal]

For what it's worth there is no such thing as "too much flow so I am not getting heat transfer."

"Too much flow" only means you are using too much pumping energy or could be causing erosion to your heat transfer surface.

An increase in flow rate on the cold side would mean a decrease in your leaving fluid temp, which makes it seem like less heat transfer. But the heat transfer only the product of the flow times the DT, so if you decrease one the other goes up.

Mostly you are going to be limited by the heat transfer coefficient on the inside of the vessel. You could increase the flow of the glycol to 300 GPM and it wouldn't make a difference (or not one that is worth it). As everything seems to work on on your newer tanks, I would guess it has something to do with crap in the jackets like you suggested or those older tanks had a different design that has less heat transfer capacity for the given surface area.

If ice has built up shutting of the glycol or raising its temp thaw out the insulating ice layer and improve the overall heat transfer.

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[ScottD50]

right now only the cone jacket is cooling the tanks as we have not filled them fully yet. So it could be an old design issue as they are pretty small jackets and they still arent crashing well at this point using mostly the bottom cone jacket. Is there a way to clean out the jackets of anything that could have accumulated over time? Or just have to fill the tanks and utilize both jackets as much as possible.

thanks,
Scott