... , Φ=58±0.7mm &=1.6mm, Φ=70±0.7mm &=2.0mm Internal pipe diameter and thickness Φ=37±0.7mm &=1.6mm, Φ=47±0 ... .7mm &=1.6mm, Φ=58±0.7mm &=1.6mm Pipe length 800mm, 1200mm, 1500mm, 1600mm, 1800mm, 1900mm, 2000mm, 2100mm Absorbing ... flows into solar vacuum tube for another heating process. heat pipe vaccum tube evacuated