Heat pulse combustion

Convection heat transfer is dependent largely on the relative velocity between the warm gas and the drying surface. Interest in pulse combustion heat sources anticipates that high frequency reversals of gas flow direction relative to wet material in dispersed-particle dryers can maintain higher gas velocities around the particles for longer periods than possible ia simple cocurrent dryers. This technique is thus expected to enhance heat- and mass-transfer performance. This is apart from the concept that mechanical stresses iaduced ia material by rapid directional reversals of gas flow promote particle deagglomeration, dispersion, and Hquid stream breakup iato fine droplets. Commercial appHcations are needed to confirm the economic value of pulse combustion for drying. 

Pulsatile drug delivery systems, 9 57-61 Pulsating heat pipes (PHP), 13 235-236 Pulse combustion heat sources, 9 104-105 Pulse cycles, 9 778 Pulsed baffle reactors, 15 709-710 Pulsed discharge detector (PDD) gas chromatography, 4 614 Pulsed dye lasers, 23 144 Pulsed electrochemical machining (PECM), 9 604-605... 

SAFETY PROFILE Poison by ingestion. Moderately toxic by inhalation and skin contact. Corrosive to skin. A mild allergen. Symptoms of exposure are sweating, flushing, shormess of breath, and slow pulse. Combustible when exposed to heat or flame can react with oxidizing materials. To fight fire, use foam, CO2, dry chemical. When heated to decomposition it emits toxic fumes of NOj. See also AMINES. 

Eibeck, P A., Keller, J. O., Bramlette, T. T, and Sailor, D. J. "Pulse Combustion Impinging Jet Heat Transfer Enhancement." Combustion Science and Technology 94 (1993) 147-65. 

Corliss, J.M. and Putnam, A.A. (1986). Heat-transfer enhancement by pulse combustion in industrial... 

Use of superheated steam in direct dryers Increased use of indirect (conduction) heating Use of combined (or integrated) heat transfer modes Use of volumetric heating (microwave [MW]/radio-frequency [RF] fields) in specialized situations Use of two-stage (or multistage) dryers Use of intermittent heat transfer Use of novel combnstion technologies (e.g., pulse combustion for flash drying)... 

New or more efficient methods of heat generation and utilization (e.g., pulse combustion)... 

Whereas the idea of pulse combustion has been known since the turn of the century, interest in this technique to enhance energy-intensive processes has grown in recent years because of its potential to increase productivity, reduce poUutant emissions, and produce significant fuel savings. The term pulse combustion originates from the fact that the combustion and heat-release processes vary periodically in time. Such periodic combustion of a liquid or gaseous fuel creates... 

Industrial applications of pulse combustion were limited so far to space and water heating mainly becanse of the difficulty of resonating the process volume at a fixed frequency if its acoustic characteristics vary with operating conditions. However, the progress in tunable-freqnency pulse combustors... 

Kudra, T., Zbicinski, I., and Benali, M. 2003. Pulse combustion drying aerodynamics, heat transfer and drying kinetics. 

Pulse combustion is a specific form of combustion-driven oscillation. Combustion oscillations can be an inherent problem or a potential benefit in enclosed combustion systems, such as gas turbine combustors, afterburners, furnaces, and rocket engines. Oscillations can produce beneficial increases in heat transfer rates and reduce pollutant formation. In other situations, these instabilities are undesirable because they may reduce the thermodynamic efficiency of a combustor or become a source of system failure if their amplitude is not kept within an acceptable range. Oscillations in the pulse combustion drying systems are desired and useful. Combustion with oscillations may be treated as some regular form of unstable combustion. 

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... 

Pulse combustion drying combines high economic of direct fire heating system with high intensity of drying of disperse material. Typical power consumption is 3,000-3,500 kJ/kg H2O evaporated (4,500 to -11,500 for spray dryer and 3,200-6,500 for drum dryer) [53,54]. The main advantages of pulse combustion drying are as follows ... 

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. 

Figure 14.9 Unit heat consumption by a pulse combustion dryer (Fig. 14.8b). (From Buchkowski, 1999.)...

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