Attention physics fans...

[yap]

I've got a bit of a thermodynamics dilemma...

My knockout on a 7 BBL batch is taking 3 hours and I can't figure out why...

My HX is a 50 plate vicarb which should be more than enough cooling area. Originally it only had 30 plates and when I KO (using city water) I couldn't flow very fast or the output temperature would shoot up quick (over 100 F). When I get the thing "balanced" at 74 degrees output, the drain water out of the HX is barely above room temp. This led me to believe I didn't have enough surface area thus the addition of 20 more plates. The improvement - none.

Next I thought water flow was an issue. I removed a few restrictions from the supply side and increased the water flow through the HX from about 4 gpm to 5.5 gpm. The improvement - none. Output water is still barely above incoming water temp and i can only flow very slowly. so slow that if i turn on the inline O2 it stops the flow completely.

The only thing I can think to do is run the city water through a glycol pre-chill before the HX, but before I spend 7K on a bigger glycol system just to chill wort (my current one wont handle it - i tried) I feel like I'm "missing something". Is the water flow still too low? what else??

Thanks as always for the sage wisdom...

[RiverCityBrew]

slow knock out

Simple things first. It is set up in a counter flow direction (water is flowing opposite direction of work).

[yap]

Simple things first. It is set up in a counter flow direction (water is flowing opposite direction of work).

yes. flow direction is correct...

[fa50driver]

Are you sure you have the plates set up correctly? Even if you didn't have enough cold water flow, the water should still come out hot I would think.

[yap]

Are you sure you have the plates set up correctly? Even if you didn't have enough cold water flow, the water should still come out hot I would think.

I had the whole thing rebuilt by a company that specializes in re-building HX's. I assume its been put together correctly but ???

The output water will get hot if i increase the wort flow, but as soon as i do that the output wort temp shoots up too...

[ChesterBrew]

You could always try throttling back the water flow so it has more contact time with the wort. That should transfer more heat from the wort to the water. I do this with my plate chiller and it seems to do the trick for me.

[Scott M]

I do just the opposite. Water flow is maximized while I throttle the wort flow to allow more contact time with the cooling water to reach my desired temperature. Flow is controlled at the outlet side of the HX.

[yap]

You could always try throttling back the water flow so it has more contact time with the wort. That should transfer more heat from the wort to the water. I do this with my plate chiller and it seems to do the trick for me.

i would think that the opposite should then also work.

i.e. increase the wort flow to get the outlet water temp to increase. while this does work, it seems there is a fine line. if the outlet water temp is 110 F then you up the wort flow just a bit and the water temp rises to 150-160 but the wort temp also rises from 76 F up to 90 F or more.....

if i am flowing slow and the water outlet is not scalding hot then it would seem that i am running the wort too slow, but as soon as i increase the wort speed its temp goes up...

i am throttling the output wort side of the HX to maintain flow and controlling it there..

[ChesterBrew]

I do just the opposite. Water flow is maximized while I throttle the wort flow to allow more contact time with the cooling water to reach my desired temperature. Flow is controlled at the outlet side of the HX.

Yes, that definitely works the same as well, but I'm now consciously trying to minimize my water usage however I can.

[yap]

i see what you mean but that doesn't help me decrease my cooling time...

right now the water usage is of little concern. dms formation, hop overutilization and potential contamination are my biggest worries...

[ChesterBrew]

i would think that the opposite should then also work.

i.e. increase the wort flow to get the outlet water temp to increase.

No, as Scott says, you'd want to restrict the wort flow for more heat transfer. It sounds like something might be wrong with the rebuild if you don't see that result.

[fa50driver]

Before I took the HX apart I would increase the H2O flow by using a pump and reservoir. Then increase the wort flow to hit temp. Keep in mind that butterfly valves aren't the best for controlling flow, instead you could try using a variable controller for your kettle pump to fine tune flow control.

[jherrington]

So, is it better for the water output to running out of the HX colder or warmer? I have a lot of water pressure so I can run it fast or slow and have the output spit out hot or cold water. I can't really figure out which is more optimal and why?

[yap]

i'm controlling the flow using a variable speed pump on the inlet side of the HX to push the wort through. i cant get the flow rate low enough just using the pump so i have a ball valve restricting the flow on the outlet side of the HX.

I thought about the reservoir/pump method for the water, but I don't have the equipment for that...

i am thinking that glycol assisting the city water will help, but I'm not sure if it will fully solve my problem...

I just reconfigured things (again) and was able to get the time down to 2.5 hours but thats still 1.5 hours longer than it should be...

so. any thoughts on how much i might be able to increase flow if i can drop the city water from 74 F down to say 50 F (or less)...?

[ChesterBrew]

You could always try a rudimentary ice bath as a test (with an immersion coil of your water into the ice bath) to see if cooling your municipal water as a pre-chiller would be effective. It'd be a lot cheaper than dropping the cash on a glycol-based pre-chiller.