Hello Stefan, Well, if really necessary one could cool the barrel from inside - not by filling it with water from the pipe of course; and carrying such an amount of distilled water to a portable site
Hi Wolfgang, Yes, i know about the optimum L/d ratio but i haven't such a Wasserfass ;-) Cooling the coil by water inside is rather a joke i assume? :-P The high epsilon r (81) would slightly decreas