Influence of Boundary Conditions on Sub-Millimeter Combustion

Abstract

Growing interest in small-scale, portable energy systems such as fuel cells has necessitated the development of small-scale fuel processing or reforming systems. Many fuel reforming systems require reliable heat sources as in some cases temperatures in excess of 600°C maybe required. Sub-millimeter combustors can provide such a heat source; however, a broader set of design rules are needed for constructing systematically engineered heat sources. In this article, experimental observations and computational fluid dynamics modeling results are presented for stable and steady confined flame structures within an alumina sub-millimeter combustor. Influence of inlet flow and thermal boundary conditions are evaluated through a parametric study. The inlet flow rates and relative gas composition, the thermal boundary conditions that include thermal conductivity of the walls, convection of heat to and from the walls, and radiation of heat energy through the walls all determine the position, structure, and temperature of the reacting fluid and combustor walls. The model shows the importance of radiative heat transfer in the formation of the steady-state flame structures within the microcombustor.

Competing Fluid Forces Control Endothelial Sprouting in a 3-D Microfluidic Vessel Bifurcation Model

“…A previous in vivo study in the context of embryonic development showed that angiogenic sprouts form from points with local minimum shear stress except when the minimum shear occurs at the convergence of two blood vessels [30]. Interestingly, the fluid mechanical conditions at vessel convergences are comparable to flow characteristics at point of flow stagnation (locally stagnated flow with average negligible shear stress), which is based on the included angle of the incoming streams and the relative fluid shear of the converging fluid streams [31]. Furthermore, it was recently demonstrated that 38 dyn/cm 2 BFF at the BP for 6 h induced a significant decrease in endothelial permeability, thus causing stabilization of the endothelium [14].…”

Competing Fluid Forces Control Endothelial Sprouting in a 3-D Microfluidic Vessel Bifurcation Model

“…A previous in vivo study in the context of embryonic development showed that angiogenic sprouts form from points with local minimum shear stress except when the minimum shear occurs at the convergence of two blood vessels (Ghaffari et al, 2015). Interestingly, the fluid mechanical conditions at vessel convergences also show similar flow characteristics of possible flow stagnation based on the included angle of the incoming streams and the relative fluid shear of the converging fluid streams (Prakash et al, 2009). Furthermore, it was recently demonstrated that 38 dyn/cm 2 BFF at the BP for 6 hours induced a significant decrease in endothelial permeability, thus causing stabilization of the endothelium (Akbari et al, 2018).…”

Energy and Environmental Applications

“…Flame studies by Prakash et al [1] in alumina-based sub-millimeter combustors have led to establishing the fundamentals of microcombustion on sustaining homogeneous flames in confined spaces by managing a variety of parameters as discussed next. Flame studies by Prakash et al [1] in alumina-based sub-millimeter combustors have led to establishing the fundamentals of microcombustion on sustaining homogeneous flames in confined spaces by managing a variety of parameters as discussed next.…”

“…The idea has undergone several iterations in the past 10À15 years and recently a silicon combustor with Reproduced with permission from [1]. The idea has undergone several iterations in the past 10À15 years and recently a silicon combustor with Reproduced with permission from [1].…”