Pressure drop and coefficients of internal heat transfer necessary for transpiration cooling

The pressure drop and the coefficients of internal heat transfer necessary for transpiration cooling of high-temperature turbine nozzles and blades with the use of porous materials are calculated semi-empirically. Equating the empirical hydraulic drag coefficient in pores zeta = 420/Re sub d (Re sub d - Reynolds number for air in pores) to the theoretical hydraulic drag coefficient in pores zeta - d delta P/1/2 rho bar (V sup 2) delta yields the pressure drop delta P=1/2 rho bar (V sup 2) delta zeta/d = 210 G mu delta/rho (d sup 2)2 (rho, mu-density and dynamic viscosity of air at mean temperature and mean pressure, bar V - velocity of air in pores, delta - thickness of porous layer, d - diameter of pores, G - flow rate of air per unit surface area, 2 - porosity factor).