Wired-propellant burning

The heat flux transferred by metal wires is also dependent on the size of the wires. The rate of heat gain from the high temperature gas to the protruding wire from the burning surface is determined by the size of the wire. When the wire size is small, the rate of heat gain is fast because the heat capacity of the wire is small. However, the rate of heat loss from the heated wire to the propellant beneath the 

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Fig. 13.28 Combustion photographs of a wired propellant a cone-shaped burning surface is formed around the silver wire (0.8 mm in diameter) (a) 0.8 s after ignition and (b) 1.2 s after ignition.

In an attempt to understand the combustion mechanism of catalyzed double-base propellants, several investigators have conducted experiments to measure the burning rates of strands of liquid nitrate esters. The various measurement techniques were very similar to that employed in a conventional solid propellant strand burner. The liquid esters were placed in a tubular container, and the liquid surface regression speeds were measured by optical methods or by the fuse-wire method used in solid-propeUant strand burners. The only important difference between the solid and the liquid strand burning-rate measurements is that the liquid strand burning speed is very much dependent on the diameter of the container. 

Fig. 13.29 Effect of various metal wires on the burning rate of a propellant along the wires.

Fig. 13.31 Burning rate augmentation of an NC-NG double-base propellant and an AP-CMDB propellant along silver wires.

Higher burning rates are also obtained by incorporating chopped fine wires or chopped fine metal sheets into propellant grains during casting processes. Though... 

Fig. 13.32 Effect of silver wire diameter on burning rate augmentation of an AP-CMDB propellant.

Tq, of gas-generating pyrolants such as fuel-rich AP-HTPB and fuel-rich nitropoly-mer pyrolants are lower than those of rocket propellants such as AP-HTPB and nitropolymer propellants. The gas-phase temperature is low and hence the heat flux feedback through the wires is low for the gas-generating pyrolants as compared with propellants. However, r /ro appears to be approximately the same for both pyrolants and propellants. The obtained burning-rate augmentations are of the order of 2-5. 

Squib. 1) (General). Any of various small size pyrotechnic or explosive devices 2) (Specific). A small explosive device similar in appearance to a detonator, but loaded with low explosive, so that its output is primarily heat (flash). Usually electrically initiated, and provided to initiate action of burning type munitions, pyrotechnic devices and rocket propellants. An electrical squib consists essentially of a tube containing a flammable material, and a small charge of powder compressed around a fine resistance wire connected to electrical leads or terminals (Ref 40a, p 135)... 

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