23-11-2012, 05:52 PM
Thrust Chamber Cooling
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COMBUSTION CHAMBER AND NOZZLE
• The combustion chamber is that part of a thrust chamber where the combustion or burning of the propellant takes place.
• The combustion temperature is much higher than the melting points of most chamber wall materials.
• So it is necessary either to cool the walls or to stop rocket operation before the critical wall areas becoming too hot.
HEAT TRANSFER DISTRIBUTION
• Heat is transmitted to all internal surface exposed to hot gases, namely the injector face, the chamber & nozzle walls.
• The heat transfer rate, that is, the local wall temperatures & heat transfer per unit area, varies within the rocket.
• The amount of heat transferred by conduction from the chamber gas to the walls in a rocket thrust chamber is negligible. By far the largest part of the heat is transferred by means of convection. A part (usually 5 to 35%) of the transferred heat is attributable to radiation.
Typical axial heat transfer rate distribution for liquid propellant thrust chambers and solid propellant rocket motors. The peak is always at the nozzle throat and the lowest value is usually near the nozzle exit
Steady state cooling
• The heat transfer rate and the temperatures of the chambers reach thermal equilibrium. This includes regenerative cooling and radiation cooling.
(i) Regenerative cooling is done by building a cooling jacket around the thrust chamber and circulating one of the liquid propellants (usually the fuel) through it before it is fed to the injector. This cooling technique is used primarily with bipropellant chambers of medium to large thrust. It has been effective in applications with high chamber pressure and high heat transfer rates. Also, most injectors use regenerative cooling.
Transient cooling
• The thrust chamber does not reach a thermal equilibrium, and temperatures continue to increase with operating duration. The heat absorbing capacity of the hardware determines its maximum duration. The rocket combustion operation has to be stopped just before any of the exposed walls reaches a critical temperature at which it could fail. This method has mostly been used with low chamber pressures and low heat transfer rates.