Recently I made a counterflow wort chiller. I made it with 10m (30 ft) of soft copper pipe of 8mm (5/16") OD and 6 mm (1/4) ID inside a 15mm (1/2") garden hose. I used a pipe so narrow to get the temperature of my cooling water, 14º C (57º F), because I want to lager. It is gravity feed (no pump). I think the height difference betwen the kettle and the chiller is enought: 10 cm (4").
I am getting good cooling: the wort temperature equals the water one. But flow rate is a problem: less than 0.5 L per minute (<0.5qt/min). That means that I cool my whole brew pot of 50L (13.2 gal) in little less than 2 hours. This is boring and a high risk of infection.
I would like to know if the velocity would be higher if I reduce its leght (I was thinking to cut out 4 m of it). I think I can do this whithout problem because the cooling water comes out of the cooler only 4 º C (7.3º F) hotter than it comes in, and it was just half open the inlet valve. What do you think?
I hope you can understand me and forgive my bad english.
Before you do anything dramatic, you might try elevating the kettle. While 1/4" ID tubing is pretty darned skinny, and perhaps nothing is going to provide a significant increase in flow rate, 4" of head is quite small. If there's any way to get that to a couple of feet, I'd try that before cutting up your new chiller...
btw: Your english is better than that of a lot of folks here
Thank you very much for your tip, I will try that before cutting anything. I am sorry I haven't answered sooner. I am thinking to adapt an old washing machine pump to increase the velocity... we'll see.