Date of Graduation

1994

Document Type

Dissertation/Thesis

Abstract

The purpose of this investigation was to experimentally examine the enhanced heat transfer and emission reduction characteristics of periodically perturbed annular natural gas flames issuing into a cylindrical cavity. Perturbation modes for the fluidic nozzles included the use of steady, axially oscillating, and radially oscillating annular flames. The testing process involved two phases. Phase one quantified the instantaneous and time averaged heat fluxes and the amount of NOx production from the natural gas flames. For the three nozzle diameters (19 mm, 25.4 mm, and 38.1 mm) tested, the equivalence ratios ranged from 0.6 to 1.0, the pulsation frequencies from steady to 35 Hz, and the thermal throughputs from 9.6 kW to 16 kW. Tested Reynolds numbers ranged from 1,475 to 3,900 and were based on the diameter and flow rates of the heat transfer test article. Strouhal numbers ranged from 0.003 to 0.093 and were based on the nozzle diameters and flow rates. In general, the instantaneous heat transfer was found to be at a maximum at a radial pulsation frequency of 5 Hz, at an equivalence ratio of 0.6, and at an axial location of 30.48 cm. Using the radially pulsing flames, enhancements in the time averaged heat transfer of up to 20% and corresponding NOx reductions of up to 31% were found as compared to the steady flames. The time averaged heat flux distributions were found to have two peaks for the 19 and 25.4 mm nozzles, with the local maxima occurring at axial locations of 30.48 cm and 76.2 cm. The axial pulsations resulted in heat transfer rates less than a steady flame for all tested configurations. Phase two of this research involved the design and construction of an optimum geometry double pipe heat exchanger fitted with fins spanning the annulus. The heat exchanger was designed using the knowledge of the heat fluxes in conjunction with a finite difference computer code developed as part of the present work. Experimental tests of the heat exchanger to heat 8.5 m{dollar}\\sp3{dollar}/min of ambient air flowing through the annulus revealed the heat exchanger to be 41% efficient, while the computer code predicted the heat exchanger to be 63% efficient as based on the thermal throughput.

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