Chillers...Immersion and Counterflow

Oops, misunderstood.

 

If the ice water isn't moving, then it will most certainly be slower than counterflow, but perhaps faster than immersion if you are recirculating the wort back through the rig. One pass would for sure not be enough.

The situation you describe will create a layer of heated water around the copper coil. It'll take time for that heat to transfer to the rest of the ice water. In fact, I imagine with one pass through the rig you describe, the last gallon of wort would hardly cool down at all as it passed through the copper tubing.

This is the purpose of a counterflow chiller, to ensure a fresh supply of cooling water is in contact with the transfer tubing at all times.

Edit: Also just noticed you said "3 feet." Not a f'in chance that's long enough.

 

Some heat transfer basics.

Maximize the surface area. Three feet of copper is inadequate, but a little more might work in a counter flow set up.

Maximize the temperature difference. A counterflow does this. Stirred immersion chillers do this to a degree.

Maximize the flow rate in the cooling loop. This gives you turbulent flow, and more mass transfer to carry off the heat.

 

I just built a pre-chiller for my immersion chiller. I t's a coil of 25' of 3/8" copper tubing, with tubing going to the hose fitting, and more tubing going to the immersion chiller. I drop it into a cooler during brew day and toss in some ice. Before this gizmo, cooling took FOREVER. First time I used the pre-chiller, cooling took about 20 minutes. You can visibly see that a considerable portion of the ice melts, even though the water going into the ice bucket is around 75F. I wasn't sure how well it would work, but the first trial proved that it works quite well (better than I expected).

This is a guess, but I'm fairly sure it's a pretty good guess... Only three feet of copper coil would probably not work nearly as well. When the water is moving through the tubing, it needs time and surface area to lose its heat to the ice. I doubt 3' would allow enough time and contact to make a big difference. I would probably work a little, but not nearly as well as 25' does.

I haven't used plate chillers, so can't comment there.