... .high cold resistence 4.environmental friendly heat pipe vacuum tube Heat Pipe Vacuum TubeFeatures:Much more anti-frozen protection, especially suitable ... water heated to 55°CHigh absorption rate: αs≥902, low emission rate: εh≤8%, daily average thermal efficiency: ηd≥50Advantage ... flow of small, unstable defects. Overcome the issues of vacuum tube broken, seal and sealing between metal heat pipe glass ...