Pulse combustion pressurized-chamber dryers

An alternative mode of pulse combustion drying was suggested by Zinn et al. (1990), where pulse combustion is mainly applied to generate a large-amplitude pulsation in the drying chamber and, in this condition, provides small portion of heat for moisture evaporation. This kind of pulse combustion dryer consists of a combustor and a dying chamber where the hydro-dynamic action of pressure and velocity waves enhances drying rates. Under certain conditions, these pressure waves can be favorably amplified by an acoustic resonance. To excite... 

The term pulse combustion originates from intermittent (pulse) combustion of solid, liquid, or gaseous fuel in contrast to continuous combustion in conventional burners. Such periodic combustion generates intensive pressure, velocity, and to a certain extent, temperature waves propagated from the combustion chamber via a tailpipe (a diffuser) to the process volume (an applicator) such as a dryer, calciner, or incinerator. Because of the oscillatory nature of the momentum transfer, pulse combustion intensifies the rates of heat and mass transfer. 

Recent studies on pulse combustion indicate that design of the combustion chamber and the geometry of a combustor-dryer system may affect the level of noxious emission. Noticeably lower concentrations of CO, NO, and NOx were obtained for those combinations of the combustor volume and lengths of the tailpipe that provide smoother and sinusoidal pressure fluctuations (Zbicinski et al., 1999). 

One possible design of a frequency-tunable pulse combustor takes advantage of the natural non-longitudinal acoustic modes of the process chamber, such as a dryer or incinerator (Zinn and Daniel, 1988). In order to obtain maximum benefit from the pressure/velocity osdllations in the process chamber, the pulse combustor can be tuned to one (or more) of these acoustic modes by modulating the flow of fuel to the combustion chamber. Such modulation may be accomplished by exciting the acoustic resonance within the fuel line, or via periodic interruptions of the fuel flow, using a rotary valve. 

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