Love the design, and wondering if anyone followed Luke A’s design change of using a 1/4″ inner tube? If it’s sufficient, it should be a lot easier to get through the garden hose!

The rate of heat transfer from the wort to the coolant is proportional to the temperature difference between them. If the there is no temperature difference between coolant and wort, then there will be no heat transfer.

Suppose that the wort and coolant are flowing in the same direction. There will be a great deal of heat transfer at first because the wort would be very hot and the coolant very cool. But after traveling along together for a short while, they would reach an equilibrium, wort and coolant at the same temperature… the average temperature. No matter how long the chiller was, you’d never get the wort any cooler, or the coolant any hotter. They would emerge together at the far end both luke-warm.

Conversely, suppose they’re flowing in opposite directions. In that case, the coolant near the end of its travel is encountering incoming wort at very high temperature. And the wort at the end of its travel is encountering incoming coolant at very low temperature. So, even at the ends of the chiller, there is still going to be some heat transfer going on. As the length of the chiller approaches infinity, the heat exchange asymptotically approaches 100%. At infinity, the wort temperature out exactly equals the coolant temperature in, and vice versa.

In practice, you can get very close to 100% heat exchange with a practical chiller length. I get wort coming out that is cold, and coolant coming out steaming hot. I get one hell of a cold-break too. My chiller is, I think, rather longer than it needs to be, which costs me in flow-rate. It takes a fairly long time to drain my kettle into the fermenter.

But it does need to be counterflow, or the whole thing is shot.

Now for the tech talk. Despite the comments above, I will admit to being a mechanical engineer (witha masters degree and professional egineering license) and a government worker. Scientists always complain about engineer’s assumptions, but without them no practical device gets built. I went through the counter flow heat exchanger calculations using the NTU method (number of transfer units) and found the calculation is quite sensitive to the assumptions (a factor of four or more). The flow inside and outside the tube is borderline turbulent (no wire, smooth concentric tubes assumed), depending on the assumed flowrates. I used 1 gpm on the hot side and 2.5 on the cold. Additionally, the Reynolds number is also considerably effected by the temperature which changes significantly along the tubes and fully turbulent can’t be assumed unless Re > 4000. I can’t calculate the effect of the wire, but in all areas (turbulence, fin, keeping tubes centered) it is in the direction of goodness, though I do think it makes inserting it into the hose more difficult.

I suspect 1 gpm is too high for a gravity system (I have a pump); kettle-to-carboy is not more than a few feet of hieght drop and 20+ feet of 1/4″ ID tubing has a significant frictional effect that cannot be ignored. A decent thumbrule (for cold water) would be about 0.2-0.7 psi pressure loss per foot when flowing at 1 gpm in 1/4 ID line (depending on material and smoothness). Using the low end of the range and 20 ft of tubing would require 4 psi, which would require over 9 feet to get 1 gpm.

Anyway, engineering calculations regarding fluid flow and heat transfer are usually crude and must be validated with empirical data.

Also, regarding Mike’s question above: Yes it will work, however. . .

You will hve to melt almost a pound of ice for each pound of wort (about 8 lbs per gallon) to keep the ice bath at 32F. You might be able to use a little less if you let the water bath (melted ice) increase in temperature at the end. Tube length could be almost any length you want depending on how fast the flow is (faster flow, longer tube) and how much you stir the ice bath. A CFC will use 2-3 times more water, but no electricity is wasted freezing the ice.

I’d considered putting a small “immersion” chiller (in a bucket full of ice) in line with my CFC water inlet to drop the temperature to improve cooling. However, that adds complexity to my setp and the same cooling effect could be achieved by reducing the flowrate of the wort (my inlet water never gets above 60F).

As a side note, I had been using an immersion chiller which worked pretty well, but decided to go with a CFC to save the 25-45 minutes of chill time (10-12 gal) since chilling and racking will now be simultanious. With the IC, I found a great improvement by doing a few things: 1) make sure the coils are at the top of the wort level, 2) mist/spray water on the outside of the kettle, and 3) stir the wort occasionally using the immersion coils. I intend to continue to spray down the kettle when I use my CFC.

Scott

But in your case, unless you take steps, the coolant will be motionless. The coolant in close proximity to the copper tubing will quickly warm up to the hot wort temperature, and then heat transfer will stop. The rate of heat transfer is proportional to the temperature difference. As the coolant temperature outside the tubing approaches the wort temperature inside the tubing, the rate of heat transfer approaches zero.

If the coolant is motionless, then the copper windings will not help induce turbulence. I would suggest that you should get the coolant moving yourself. You could use a pump to circulate the coolant, drawing from the bottom of the bucket, and returning to the top. Since it’s only coolant, not beer, the pump can be any cheapo Home Depot pump, it doesn’t have to be food-grade or magnetically-coupled or anything fancy.

Alternatively, you could put some kind of impeller in the bucket to keep things moving.