The onset of turbulence in a gas flowing within a circular tube occurs at Re_D,c ≈ 2300, while a transition from incompressible to compressible flow occurs at a critical Mach number of Ma_c ≈ 0.3. Determine the critical tube diameter D_c, below which incompressible turbulent flow and heat transfer cannot exist for 

(i) Air,
(ii) CO₂, 

(iii) He. Evaluate properties at atmospheric pressure and a temperature of T = 300 K.