Experimental investigation into the effect of heat transfer on compressible air stream in a duct

A converging nozzle-constant area parallel passage with an outer duct encasing the constant-area passage has been built for investigating the effect of heat transfer on subsonic flow of an air stream. It is concluded experimentally as can be predicted analytically that large quantities of heat are needed in order to accelerate very slow air stream (incompressible) to sonic conditions. It is observed experimentally as confirmed analytically, that the increase in Mach number with heat addition is associated with a decrease in the local static pressure along the axis of the duct. It could be concluded that any more heat added beyond thermal choking will be accompanied by a decrease in the mass flow rate of the compressible flowing air.Nomenclature A cross-sectional area of the duct - C _{P air} specific heat of air joules/kg. °K - C _d discharge coefficient - D duct diameter - d orifice diameter m - dA _d elemental lateral area of the duct - h overall heat transfer coefficient - h head across orifice, mm. - M Mach number - m _air mass flow rate of air - P local static pressure - P _b back pressure at duct outlet - P ₀₁ stagnation pressure at duct inlet - gas density - _u air density upstream of orifice - _q incremental heat flow - T local static temperature - T ₀₁ stagnation temperature at duct inlet - T _h hot water temperature - q heat added per kg of flowing air - V flow speed