| dc.description.abstract | This study applies heat-recirculation technology to develop a low NOx burner. A commercial numerical program (CFD-RC) is used as a design tool to model chemical reacting flow using propane/air mixtures in a Swiss-roll burner (SRB). Measurements of the temperature distributions, heat-recirculation rate, and concentrations of exhaust gas in the SRB are carried. We employ 2 K-type and 9 R-type thermocouples to measure temperature distributions of the SRB and estimate the heat-recirculation rate (HR=Qr×100%/(Qi +Qr)),
where Qr is the recirculation heat per unit time and Qi is the chemical heat of the fuel per
unit time. The experimental result shows, φ =0.5 and the Reynolds number (Re) ranging
from 60 to 880, values of the temperature distribution in SRB increase as Re increases. The
maximum temperature occurs in the center of combustor, proving that C3H8 /air premixed
flames can be stabilized in the combustion zone. We analyze the effect of Re on HR, for
which HR increases as Re increases. As Re increases from 60 to 880, the percentage of HR
increases from 11% to 25%. As Re increases, the wall temperature increases and more
reactants with ambient temperature enter into the SRB. Therefore, the temperature gradient
between the mixture and the walls is enhanced with increasing Re. This promotes the
convective heat transfer and thus increasing HR. Measurements of emissions show that NOx
concentrations are less 10 ppm at φ =0.5 for Re = 60~880. On the other hand, the
concentrations of CO increase as Re increases. This is probably because CO has insufficient
time to react to CO2 due to large Re, or the backward reaction step for CO2 to CO occurs
during high temperature in the combustion zone. For numerical simulations, only 2-D
simulations are carried out to compare with experimental result for Re = 630 at φ =0.5. The
comparison shows that the temperature distribution between numerical and experimental
results has similar trend, but there are quantitative differences due to 2-D numerical
simulation, the unstructured grid model, and the overly simplified chemical reaction steps.
Finally, as the goal of the present work, we combine a series of Bismuth Telluride
thermoelectric (TE) materials with the aforementioned SRB to successfully establish a
small TE power generator. The result indicates that only two TE chips, each with 3×3 cm2,
can easily produce more than 1.6 watts for lighting several small bulbs constantly. | en_US |