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Colin H. Miller

Bio: Colin H. Miller is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Flame spread & Boundary layer. The author has an hindex of 6, co-authored 9 publications receiving 202 citations.

Papers
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Journal ArticleDOI
01 Jan 2017
TL;DR: In this article, a detailed experimental investigation of turbulent diffusion flames under forced flow was conducted to study local heat fluxes to a nearly adiabatic surface downstream of a gaseous line burner.
Abstract: A detailed experimental investigation of turbulent diffusion flames under forced flow was conducted to study local heat fluxes to a nearly adiabatic surface downstream of a gaseous line burner. A variety of ambient wind velocities and fuel flow rates were employed to study different fire scenarios modeling the dynamics of wind-driven fire spread as found in wildland, mine or tunnel fires. The downstream heat flux distribution was correlated as a piecewise function with the Richardson number in two regimes, the first with higher heat fluxes, where the flame remained attached the downstream surface (attached region) and the second with a steeper decay of heat fluxes (plume region). Analysis of the heat flux distribution revealed that local heat fluxes roughly reach a maximum where the Richardson number equaled unity. This was thought to be a good marker of the regime where the flame detaches from the surface, e.g. where buoyancy from the flame overcomes inertial forces from the oncoming flow. This observation was further corroborated by analysis of side-view images of the flame, which showed the attachment location was linearly correlated with the location where the Richardson number equaled unity. The results from this study suggest that local heat flux values reach a maximum at the transition between a momentum-dominated (attached, wind-driven) to buoyancy-dominated (plume or fire) regime in forced flow scenarios. The results have interesting implications to the problem of flame attachment, which is known to accelerate fire spread in both inclined and wind-driven fire scenarios.

59 citations

Journal ArticleDOI
01 Jan 2017
TL;DR: In this paper, a detailed experimental study investigating sample width and thickness effects on steady horizontal flame spread, including detailed measurements of the components of radiation, convection, and conduction, is presented.
Abstract: In previous studies, it was found that there exists a minimum flame spread rate under a certain range of sample widths for steady burning horizontal flame spread. While this was hypothesized to occur due to a transition between convectively-dominated to radiation-dominated flame spread, no measurements were performed to quantify this process. This paper presents a detailed experimental study investigating sample width and thickness effects on steady horizontal flame spread, including detailed measurements of the components of radiation, convection, and conduction. Water-cooled heat flux gauges, R-type micro-thermocouples traversed through the gas phase, and K-type thermocouples embedded in the solid phase were all used to deduce these heat transfer components. Results show that convective heat transfer decreases with increasing sample width as the shape of the flame front is on average farther from the fuel surface, while radiation increases as the view factor from the fire to unignited fuel increases with larger sample size. Conduction measured within the fuel sample is, as expected, confirmed to be negligible. Comparing a combination of these components, the total heat flux first decreases as the competition between radiation and convection changes, followed by steadily increasing heat fluxes as the width of the sample increases. Heat feedback also influences the sample pyrolysis rate, so there was a coupled response following this trend. The apparent dip followed by an increase in total heat flux can now explain why a period of minimum flame spread rate exists. Modification of an existing theory also matches experimental results very closely. Finally, a dimensionless heat-release rate for different sample configurations is used to scale the dimensionless flame heights with a power-law correlation having exponents 0.39 for Q * > 1 and 0.6 for Q *

57 citations

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the upward flame spread over discrete fuels through experiments on vertical arrays of alternating lengths of PMMA and inert insulation board, and found that the fuel coverage was below unity, which indicates that a homogeneous fuel bed approximation is unsuitable for arrays with low fuel coverage.

54 citations

Journal ArticleDOI
TL;DR: In this paper, the problem of flame spread is revisited, with a particular emphasis on the effect of flow and geometry on concurrent flame spread over solid fuels, and areas for future research will be highlighted.

47 citations

Journal ArticleDOI
01 Jan 2019
TL;DR: In this article, a detailed experimental and theoretical study was performed to investigate the controlling mechanisms of flame spread through arrays of wooden dowels, with dowel spacings of 0.75, 0.875, and 1.5 cm.
Abstract: Fuel loads in real-world fire scenarios often feature discrete elements, discontinuities, or inhomogeneities; however, most models for flame spread only assume a continuous, homogeneous fuel. Because discrete fuels represent a realistic scenario not yet well-modeled, it is of interest to find simple methods to model fire growth first in simple, laboratory-scale configurations. A detailed experimental and theoretical study was therefore performed to investigate the controlling mechanisms of flame spread through arrays of wooden dowels, with dowel spacings of 0.75, 0.875, and 1.5 cm. Flames were found to spread vertically for all spacings; however, for the 1.5 cm spacing, the gap was too large for horizontal flame spread to occur. A radiation-controlled model for horizontal flame spread was developed that predicted the horizontal flame spread rate through various arrays of dowels. Combined with an existing convection-based model for vertical flame spread, both horizontal and vertical flame spread was modeled to predict the number of burning wooden dowels as a function of time. Using models for the burning rate of wooden dowels and boundary-layer theory, a global burning rate model was developed that provided reasonable agreement with experimental results.

37 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors reviewed the physics and correlations for the burning behavior of pool fires in wind, and discussed also challenges for future research on this topic, especially for wind-blown large scale pool fires.

182 citations

Journal ArticleDOI
TL;DR: The aim of this work was motivated by the research of sample width and thickness effects on upward flame spread behavior, including flame spread rate during acceleration propagation for different sample thickness and width, theoretical global mass loss prediction based on Emmons's hypothesis, and dimensionless flame height scaling with dimensionless heat release rate for steady stage burning.

87 citations

Journal ArticleDOI
TL;DR: In this article, the orientation effects during inclined downward flame spread processes were thoroughly investigated by experimental and theoretical methods, and the mechanism of orientation effect during the flame spread process was qualitatively analyzed in detail, and simplified expressions of flame spread rate of the two insulation materials with different orientations were deduced.

83 citations

Journal ArticleDOI
TL;DR: In this paper, a large-scale flame spread experiment was conducted inside an orbiting spacecraft to study the effects of microgravity and scale and to address the uncertainty regarding how flames spread when there is no gravity and if the sample size and the experimental duration are, respectively, large enough and long enough to allow for unrestricted growth.

59 citations

Journal ArticleDOI
15 May 2019-Energy
TL;DR: In this paper, a waste rigid polyurethane (RPU) was selected to conduct thermogravimetric analysis experiments with four different heating rates, and thermal degradation kinetics were analyzed by model free, model fitting, and distributed activation energy model (DAEM) fitting methods.

58 citations