Experimental determination of heat and mass transfer in an oscillatory flow

Oscillating flows occur in many engineering applications. Engineering systems that exhibit undesirable flow oscillation include solid propellant rocket motors that may exhibit acoustic oscillations affecting the burning rate of the propellant. Acoustic erosion occurs when the scrubbing action of the acoustic wave increases the mean burning rate of the propellant. It has been postulated that this increased burning rate is due to the transition to turbulence and the resulting increased heat transfer to the propellant surface. The use of naphthalene made it possible to study the heat and mass transfer rates at different axial locations in a duct containing an oscillatory flow. Mass transfer from a solid surface to a periodic (sinusoidal) oscillating flow is considered. The heat transfer coefficients is deduced (via the analogy between heat and mass transfer) from mass transfer coefficients measured by the use of the naphthalene sublimation technique. The research utilized this technique to investigate the acoustically introduced oscillatory erosion in solid rocket motor which contributes to the velocity coupling phenomenon. The work involved the design, and construction of the simulation facility and measurement of mass transfer rate along the length of the chamber using the naphthalene sublimation technique.; Acoustic pressure and mass transfer rate measurements indicate the existence of a coupling mechanism, strongly dependent on velocity amplitude, between the acoustic disturbance and naphthalene sublimation process. Because of the standing wave nature of the oscillatory behavior, it was possible to correlate the change in mass transfer rate at each location in the duct with the nature of the acoustic environment. The mass transfer rate was higher in locations where the amplitude of velocity oscillations was large (velocity antinode). Acoustically induced turbulent forced convection may be partly responsible for the increase in the sublimation rate of the naphthalene. Hot film anemometry indicates the occurrence of turbulence in the case of strong acoustic excitation and turbulence has been proposed to be one of the principal mechanisms in the velocity coupling phenomenon. A developed empirical correlation showed that the mass transfer and heat convection rates were dependent on the acoustic Reynolds number to the 0.8 power at any location in the chamber. This result was found to apply into the range of acoustic Reynolds number where turbulence is believed to occur. At the center of the chamber (velocity antinode at resonance) the developed empirical correlation showed the dependence of turbulent mass transfer or heat convection rates on the acoustic Reynolds number to the 0.8 power and Schmidt or Prandtl number to the 1/3 power with a constant coefficient of 0.145. Comparison with previous experiments conducted with real solid propellants shows a striking similarity in the energy transfer mechanism.