Abstract: A panel 1, 1A, adapted for the flow of coolant, therethrough, comprising coolant flow tubing having a coolant inlet aperture 11C at an inlet end of the coolant flow tubing and a coolant outlet aperture 12A at an outlet end of the coolant flow tubing, characterized in that the coolant flow tubing comprising a plurality of elongate tube lengths 2, 2A, 2B formed from hollow rectangular section material, the tube lengths 2, 2A, 2B being disposed in parallel relationship, either stacked one on top of the other or side-by-side, with adjacent external faces of adjacent top and bottom walls 3, 4 of adjacent tube lengths 2, 2A, 2B abutting one another, with the end of each tube length 2, 2A, 2B closed off, and with coolant flow apertures 11, 11A, 11B, 12, 12A, 12B communicating between adjacent tube lengths 2, 2A, 2B adjacent the ends thereof such that, in use, coolant flows in at one end of each tube length, along the tube length, and out at the other end of each tube length, to and through successive tube lengths of