Does the length of the tube affect efficiency?
It depends; the most heat comes out of the tube where the temperature difference between the inside and the outside is the greatest. That exists in the first couple inches of the tube. The last inch of the tube, wherein the charge temperature is rapidly approaching the cooling media temperature, will transfer very little heat. It really depends upon the velocity of the air through the tube. In some cases significant heat transfer can still be occurring in the last few inches.
