Govindaraju Avinash

Bio: Govindaraju Avinash is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Diffusion flame & Flame spread. The author has an hindex of 1, co-authored 1 publications receiving 16 citations.

Experimental analysis of diffusion flame spread along thin parallel solid fuel surfaces in a natural convective environment

Abstract: An experimental investigation of diffusion flames spreading along thin solid fuels in concurrent and opposed configurations in a gravity induced flow is presented in this study. Flame spreading over one side as well as on both sides of the fuel is studied. MATLAB is used to post process high definition flame videos to obtain flame spread rate as a function of inclination angle of the fuel surface, number of fuel sheets and separation distance. For one side burning, present results are compared with those from literature. For double side burning, the inclination angle is varied from 90° (upward spread) to −90° (downward spread), measured with respect to the horizontal (0°). The spread rates in double side burning are higher and the maximum spread rate is observed for 90° case, as opposed to 120° in single side burning. The upward flame spread displays a non-uniform temporal variation, especially when the orientation angle is greater than 20°. Fuel cracking was noted to be most severe at 90°. However, the downward flame spread rate is almost steady. The multiple fuel sheets (2 and 3 sheets) are kept parallel to each other with the separation distance between them varied from 0.5 to 3 cm. In upward flame spread, for a small separation distance of 0.5 cm, multiple sheets produce spread rates lower than the single fuel case due to insufficient oxygen supply. At 1.5 cm separation, maximum flame spread rate is observed for multiple sheet cases, due to increased availability of oxygen and enhanced heat transfer from neighboring flames. At 3 cm, the spread rate is almost the same in all cases indicating that the interference effects have become weaker. The variation of flame-spread rate in multiple fuel sheets with respect to inclination angle is almost similar to that of single sheet cases.

Experimental and theoretical study on downward flame spread over uninhibited PMMA slabs under different pressure environments

Abstract: This paper presents an experimental and theoretical study of side-edge effects on downward flame spread over two parallel polymethyl methacrylate (PMMA) slabs under different pressure environments. Identical experiments of downward flame spread over thin PMMA slabs with side-edges unrestrained were conducted at different altitudes in Hefei (102 kPa), Geermu (73.2 kPa) and Lhasa (66.3 kPa). Experimental results show that the flame spread rate is controlled by ignition along the side-edge, rather than at the center of the samples, for experiments with both single and two parallel slabs. Based on these results, a thermal model is developed which describes flame spread along the edge and quantitatively agrees with experimental results. In the parallel-slab case, convective heating appears to influence the spread rate only when the separation distance is very small, with radiative heating playing a more important role as separation distance increases. The angle of the pyrolysis front, formed between the faster side-edge spread and slower center-region spread, hardly changes with pressure, but changes significantly with separation distance, due to differing modes of heat transfer between the side-edge and center region. In addition, variations of flame height with pressure and separation distance are reasonably interpreted from diffusion flame theory.

Combustion and fire safety of energy conservation materials in building vertical channel: Effects of structure factor and coverage rate

Abstract: Experimental study on combustion and fire safety of energy conservation materials (extruded polystyrene, i.e., XPS) in vertical channel with front openings of building facade is conducted, and effects of channel structure factor (α) and curtain wall coverage rate (β) are revealed. The XPS flame in the vertical channel is turbulent. There is a correlation between the flame height and pyrolysis length: x f = m x p n , where m and n vary with the change in structure factor and coverage rate. Upward flame spread rate decreases first and then increases as β rises. When 0 ≤ β 0.2 , the restraining effect of vertical channel on air entrainment dominates, while for 0.2 ≤ β ≤ 0.8 , the heat feedback from curtain wall dominates. When β = 0, the influence of α on flame spread rate is not significant. The flame spread rate increases with increasing α when 0.2 ≤ β ≤ 0.8 . A model is established to predict the flame spread rate under different coverage rates and structure factors. Compared with experimental results, the prediction error is smaller than 10%. Larger values of flame height and flame spread rate correspond to higher fire hazard. This work is beneficial for fire safety assessment of building thermal insulation materials and optimal design of energy-saving curtain wall.

Measurement of instantaneous flame spread rate over solid fuels using image analysis

Abstract: Spread rate is an overall property of flame propagation that characterizes the condition of a flame better than any other property. As a result, prediction and measurement of spread rate is central to flame spread studies over solid fuels. Significant amount of data have been collected over last four decades of research on flame spread over various fuels under different conditions. In most of these studies, however, only average spread rate is reported which is adequate for steady phenomena. Given that a flame may not face the same conditions during the spread, it is possible for the spread rate to change during the duration of the spread continually. In this work a methodology for image analysis is presented with the goal of evaluating instantaneous spread rate to study time-dependent phenomena. The parameters that control the error and time resolution of the flame spread history are identified, and a sensitivity study is carried out to validate the results of a scale analysis. A MATLAB-based Flame Image Analyzer (FIA) package is developed and applied to flame spread videos recorded in several experiments in different regimes of opposed-flow flame spread. An expression for the error in spread rate for a given time resolution is expressed in terms of the imaging parameters. The two parameters that are found most important are the pixel resolution and the frame rate. A non-dimensional imaging parameter is identified that is shown to govern the quality of imaging for spread rate measurement. Theoretical prediction from the error analysis is confirmed by doing various case studies using the Analyzer.

Experimental Analysis of Critical Acceleration Condition for Two-Sided Upward Flame Spread Over Inclined Thin Fuel Surfaces

Abstract: Most of previous work focused on the one-sided upward flame spread over inclined surfaces. However, few investigations have systematically addressed the dependence of spread rate on the inclination angle for two-sided upward flame spreading. The present paper investigates the two-sided upward flame behaviors over inclined surfaces by performing experiments using 0.255 mm thick, 100 cm tall and 5 cm wide cotton sample sheets with various inclination angles varying 0° to 90° from the horizontal. The pyrolysis spread rate, pyrolysis length, preheating length, ignition time, flame tilt angle and standoff distance are obtained and analyzed. The corresponding results are as follows: As the inclination angle increases, the pyrolysis spread rate, pyrolysis length and preheating length increase, but the ignition time decreases. One transition zone is observed around 10° to 15° for flame spread rate, pyrolysis length and preheating length, which is an external manifestation of the change of flame spread from steady state to acceleration. Two parameters of tilt angle and standoff distance are used to qualitatively modify the heat flux profiles ahead of the flame front, which control the flame spread rate. Generally, the tilt angle and standoff distance of upper flame decrease as a function of inclination angle. On the contrary, the standoff distance shows an opposite trend with inclination angle. The combined effects of radiation and convection of upper and lower flames result in a sharp increase in net heat flux, and correspondingly a transition zone occurs around 10° to 15°. The results of this study have implications concerning designs for fire safety and may help advance understanding of two-sided flame spread over inclined surfaces.

Upward Flame Spread Over an Array of Discrete Thermally-Thin PMMA Plates

Abstract: Experiments and theoretical analysis were conducted to investigate the upward flame spread over a homogenous PMMA plate and an array of discrete thermally thin PMMA elements. In the experiment, a digital video camera was used to record the flame spread process. An electronic balance and thermocouples were adopted to monitor the mass loss and pyrolysis front position, respectively, as a function of time. In the theoretical analysis, the mass loss rate of PMMA was correlated to the heat transfer during flame spread. The experimental results show that the flame spread rate peaks in the case of discrete PMMA elements with a fuel coverage around 80% rather than 100% (the homogenous case) because the gap with an appropriate spacing between neighboring elements accelerates the flame spread. However, the flame cannot spread over an array of discrete fuels at a coverage of 50% or smaller where the gap is too large to allow effective heat transfer required for flame spread. A smaller coverage of PMMA results in a larger mass loss rate per area since the gaps between elements can entrain more air to promote the burning. A logarithmic relation, that can well describe the mass loss rate as a function of PMMA coverage, was proposed based on the theoretical analysis and the fitting of experimental measurements.