(Dr. Ben Zinn, advisor)

"Acoustic Enhancement of Water Evaporation in a Pulsating Combustion"

Abstract

Increased waste throughput demands and requirements for smaller, less intrusive waste management facilities are driving research aimed at improving the operation of liquid waste incinerators.  Since the main function of liquid waste incinerators is to evaporate water, improving this highly energy intensive process stands to improve the efficiency of current incinerators.  The purpose of this study was to determine whether the strongly oscillating flow in a pulse combustor could be utilized to improve the evaporation efficiency of a water spray.

Experiments were conducted while exciting quarter wave and three-quarter wave acoustic oscillations within the developed pulse combustor.  Heat input rates ranged between 150 and 250 MBTU/hr.  Water was injected downstream of the acoustic pressure antinode while operating with quarter wave pulsations.  When the developed combustor was operated with three-quarter wave oscillations, water was injected at a location corresponding to an acoustic velocity antinode.  Tests involved determining the maximum rates at which water could be injected prior to the detection of water accumulation for operation with and without maximum amplitude acoustic pulsations.  Additional testing compared the evaporation rates evaluated from a developed calculation procedure while operating the combustor with and without acoustics.  Results of experiments conducted while operating the developed combustor with quarter wave oscillations indicated that the evaporation of the injected water was not improved.  Water evaporation rates were found to increase by up to 29 percent, however, while operating the combustor with maximum amplitude three-quarter wave oscillations.  The acoustic enhancement of water evaporation was found to increase with heat input rate and the amplitude of pulsations. Comparison of the results obtained from the two testing methods were determined to offer good agreement.  Composition analysis of the exhaust gases indicated slightly increased combustion efficiency with acoustics.