COMBUSTION IN DOUBLE SPIRAL BURNERS

Double spiral devices have been employed as combustors for exceedingly lean mixtures (for example, for methane, mixtures of fuel content cor responding to less than 1/5 of the lower limit of flammability have be en successfully burned), and the leanest mixture combustible is determ ined by losses. For any given burner an optimum flow exists as at low flows, losses are critical, and at high flows there is inadequate area for heat transfer (also at high flows, large pressure losses occur). Mathematical modeling of the spiral device demonstrates that radiation is significant even at modest elevations in temperature and that spir als of many turns help control these losses. With metal burners, condu ction losses can be critical. Several parameters are presented to iden tify design limits for spirals including wall emissivity, conductivity , and thickness.