MECH4429: School of Mechanical and Chemical Engineering-Applied Engineering Thermodynamics Assignment

Internal Code: MAS344

Applied Engineering Thermodynamics Assignment:

Question: SCUBA divers breathe air from a pressurised tank through a pressure regulator. The regulator ensures that the air supplied to the diver is at the same pressure that the diver is experiencing underwater. Divers sometimes use a mixture of gases other than air, in order to limit the effects of nitrogen narcosis and the risk of developing decompression sickness (“the bends”). Commonly used gas mixtures are Nitrox I and Nitrox II, which consist of air enriched with additional oxygen, usually to give a molar fraction of 32% oxygen (Nitrox I) or 36% oxygen (Nitrox II). However, oxygen itself can become toxic if breathed at a partial pressure greater than 1.6 bar. (i) Calculate the depth a diver should not exceed if breathing Nitrox II to avoid oxygen toxicity. Show your working clearly, and state any assumptions that you make. (ii) Commercial divers working at extreme depths often use mixtures of helium and oxygen. If a diver working at 100m below sea level uses a mixture of 12% oxygen by volume, would this be a breathable mixture on the surface? Explain your answer.