Experimental Study on the Influence of Gas-Solid Heat Transfer in a Mesoscale Counterflow Combustor

ABSTRACT

Combustion at small scales is inhibited by the large amount of external surface area leading to excessive heat losses and extinguishment. This limitation is diminished by transferring heat from the products to the reactants through solid surfaces leading to the development of heat recirculating reactors. A promising design is the counterflow configuration in which reactants in one channel are preheated by energy transferred through the wall from the products in the adjacent channel. In the lean equivalence ratio limit of the reactor, this arrangement encourages the stabilization of the flame. In the high equivalence ratio limit, the enhanced heat transfer may encourage blow-off. Therefore, it is important to understand the relationship between heat transfer and the operating range of the reactor. In this paper, the importance of the channel surface area-to-volume ratio is investigated analytically and experimentally in a mesoscale combustor. Reactors with different channel shapes were fabricated via additive manufacturing and studied. The change in heat transfer area affected the stable operating range, maximum temperature, and location of flame stabilization. The emission measurements showed low CO and NO_x emissions. For all reactors, the stable range was limited by flashback when the burning rate exceeded the flow velocity and by blow-off when the burning rate was insufficient. This work quantifies the importance of heat transfer surface area to the operation of the counterflow reactor and guides the optimization of reactor design.

KEYWORDS:

• Heat recirculating reactor
• excess enthalpy combustion
• mesoscale combustion
• superadiabatic
• counterflow

Acknowledgments

The authors would like to acknowledge the generous help of the Laboratory for Freeform Fabrication at the University of Texas at Austin. Special gratitude goes to Dr. David Bourell for sharing his extensive knowledge of material science and associated processing.

Disclosure statement

No potential conflict of interest was reported by the author(s).