An experimental method of determining the mean heat transfer coefficient for the nozzle of a solid propellant rocket engine, by means of constant flow calorimetry

An investigation has been made into the feasibility of predicting mean convective heat transfer coefficients for the nozzles of solid propellant rocket engines. The principle of the method used was constant flow calorimetry; the surface of a copper nozzle was heated with a flow of hot water, and cooled by air flow through the nozzle. Heat transfer coefficients were then derived from measurements of water flow, water temperature drop and nozzle surface temperatures. For a range of Reynolds numbers, the mean convective heat transfer for a star-shaped conduit could be expressed by the following equation: - Nu = 0.1976 Re 0.631 Pr 0.333 For a cigarette-burning charge the mean convective heat transfer could be expressed by the following equation : - = 0.7013 Re 0.491 Pr 0.333 The flow pattern into the nozzle was studied using a water flow visualisation rig involving both photographic and direct viewing techniques. In addition, investigations into the temperature and pressure distributions along the nozzle surface at ambient conditions were carried out using a perspex nozzle fitted with surface thermocouples and pressure tappings.