Abstract: As the pressure increases, air behaves very differently from a perfect gas. Such real gas behavior can have major effects on a supersonic turbulent boundary layer and on the corresponding heat transfer process near the wall. A 206.9Mpa (30,000psi) blow-down facility was designed and used to conduct a series of experiments at various stagnation pressures and temperatures where real gas effects are substantial. The Mach number, displacement thickness, Stanton number and recovery factor of the supersonic, turbulent boundary layer were measured with initial stagnation pressures from 69Mpa (10,000psi) to 206.9Mpa (30,000psi) and initial stagnation temperatures from 300K to 360K. Strong real gas effects were found. The data became comprehensible when the usual transport of heat for a perfect gas ρc _pν'T' was recast in terms of the enthalpy flux ρν'h' and the Stanton number and recovery factor were defined not in terms of temperatures but in terms of enthalpies. Self consistent sets of Stanton numbers and recovery factors have been obtained, notwithstanding the complexity of the equation of state and the substantial real gas effects, the quasi-steady nature of the experiments and the variation in one experiment from positive to negative heat transfer. The data now forms a basis for evaluating various compressible boundary layer turbulence models and parameters including the choice of turbulent Prandtl number and its dependence on Mach number etc. Considerations of the energy equation, independent of the equation of state, lead to an expectation that the wall recovery temperature can be much higher than the plenum temperature as a result of strong real gas effects at high pressure. Nozzle wall survivability becomes a substantial issue for a very high pressure, high Mach number wind tunnel such as the RDHWT proposed by Brown and Miles. A coaxial flow experiment with a co-flowing, cooler, outer layer of nitrogen has been designed by extending the single vessel blow-down facility to include a second pressure vessel, which provides this cool outer coaxial flow. The mixing between the heated core flow and the cool outer flow was investigated and the cooling efficiency of a particular design was measured.