I make my own beer at home. The end result of a brew day is a giant pot of boiling “wort,” or unfermented sugar-water. This fluid needs to be cooled to 70 degrees Fahrenheit so that yeast can be added & fermentation can be begin. It’s absolutely amazing how long 5 gallons of boiled wort will stay hot, even with the pot submersed in ice water. It takes as long as 10 hours to accomplish via ice bath. Ideally, you don’t want the wort sitting around long before adding yeast because bacteria from the air can start eating the sugars, causing bad off-flavors in the finished product. So to demonstrate aspects of heat exchangers, show how simple they are to build, and cool my wort quickly, I built a counter-flow heat exchanger. The one I build consists of a garden hose and inner copper tube. The inner copper tube caries the boiling wort, and the garden hose carries tap water in the opposite direction. On the ends are some copper fittings that seal everything up and allow connection to hoses. Here’s a pictorial of its construction and the device in action:
Though my first test of the heat exchanger (aka “counterflow wort chiller”) was brewing a batch of stout (it worked great! It cooled 5 gallons from boiling to 70 degrees in about 15 minutes, note however I had the cooling water coming from the faucet at near full blast), I did some actual tests to find epsilon, or the effectiveness of the chiller. I measured each volumetric flow rate by measuring how long it took to fill a 2 quart pitcher:
With this data, we can now approximate NTU, and approximate the overall heat transfer coefficient via E-NTU relationships:
I can’t find any data to compare this “wort chiller” to. But I think the effectiveness seems reasonable, and the the overall heat transfer coefficient seems wildly large compared to architectural materials (which are obviously designed to have low heat transfer coefficients).