The HEX started out with 6m of 12.7mm copper (formed into a coil around a short length of 100mm PVC pipe) which fitted neatly into a length of 150mm DWV pipe. DWV is heat tolerant up to around 80C before funny things happen.(Manufacturers maximum recommended continuous is 60C). Hottest I demand of it is 75C for mashout and sparge.
The element is a compact 2200W (from a cheapy Woolies jug), and is mounted at the bottom on the base cap, and protrudes upwards about 80mm or so.
To cover the coil completely used around 4.3 litres water, so the water/coil length ratio wasn't too bad, but the PID had it's work cut out maintaining the temp to close tolerances.
So - how to improve it? Enter the RHR* (rotating hollow rotor) assembly. Fabricated from some 65mm DWV, four thin gal sheet vanes screwed onto it to improve heat circulation and transfer, and a 12v geared DC motor to rotate it. In operation, power used is 2.5W.
Insulation is air-cell, but I'll find something better.
*RHR - my contribution to the ever-increasing list of TLAs to confuse the uninitiated.
