... axial structure Glass material High borosilicate 3.3 glass External pipe diam eter and thickness Φ=47±0.7mm &=1. ... 47±0.7mm &=1.6mm, Φ=58±0.7mm &=1.6mm Pipe length 800mm, 1200mm, 1500mm, 1600mm, 1800mm, 1900mm, 2000mm, ... efficiently by the coating with little loss of heat because of the vacuum between the inner and ... solar vacuum tube for another heating process. heat pipe vaccum tube evacuated