Reacting flows
Hydrogen generation by water splitting in thermochemical reactor using Solar Energy
Water splitting is the chemical reaction in which water is broken down to oxygen and hydrogen. In this fuel-hungry world, hydrogen can prove as an alternative, clean source of energy. The generation of hydrogen has been in research since 1960s, but the efficiency and feasibility have to be improved to reach a practically viable state. Production of Hydrogen using Solar concentrated power was found to be the most efficient.
Experimental study of flame characteristics and stability regimes of biogas – Air cross flow non-premixed flames
Biogas is an alternative fuel that typically contains around 45% carbon-dioxide by volume, besides methane. Due to the inherent content of carbon-dioxide, it is necessary to study the flame characteristics and stability limits in cross-flow non-premixed burners. In this study, cross-flow non-premixed flames, where biogas is injected through a horizontal porous plate and air is blown parallel to the fuel injector, are studied systematically. In order to increase the stable operating regime, devices such as backward facing steps and cylindrical bluff-bodies are commonly employed. Different step-heights and locations from leading edge of the fuel injector are considered for the cases with backward facing steps. A rectangular cylindrical bluff-body is also used as a flame stabilizing obstacle. Baseline cases are studied without any backward facing step or cylindrical bluff-body. Volume flow rate of biogas is varied from 36 liter per hour to 360 liter per hour. Air velocity is varied in the range of 0.2 m/s to 3.0 m/s. For a given fuel velocity, air velocity is gradually increased in order to record the transition of flame from one regime to another. Flame stabilization is carefully assessed by monitoring the high definition direct flame photographs captured from front and top views, for all the cases. The cases are repeated at least three times to ensure repeatability. Stability maps are plotted as a function of fuel velocity and air velocity for all the cases. For cases with backward facing steps, both step height and its location play an important role in delineating the boundaries of the flame regimes. Parametric variations show interesting features. Bluff-body flames become quite oscillatory and three dimensional at higher air velocities. For this case, stability maps of flames from biogas and pure methane are compared.
A. Harish et al., Fuel, 223 (2018) 334-343
Premixed combustion instabilities in confined channels
Premixed flames in confined channels give rise to some of the interesting physical phenomena. The evolution path of the flame kernel and flow field after ignition are very important in determining final flame and flow features. The problem of stability of the premixed flames in meso-channels is studied widely in the literature due to its widespread applications. The study concerns about this aspect of flame holding in meso-channels and associated flame and flow instabilities.
Experimental study of burning of methanol fed porous spheres in grid generated turbulent field
Experimental investigation of the effect of flow turbulence on the steady state burning of methanol is reported. A vertical air tunnel has been mounted with a grid at its exit plane in order to generate turbulence in the free jet stream. The flow field has been characterized using a hot-wire anemometer. Mean and fluctuating flow velocities and integral scale have been measured at an axial location of around 2 times its exit diameter (D). Three types of grids have been used. Classical porous sphere experiments have been carried out to analyze the steady-state burning rate of methanol over the surface of an inert sphere having constant diameter. Experiments have been done at atmospheric pressure under ambient temperature and normal gravity conditions. A porous sphere is positioned at an axial location of 2D, where the approaching flow has been characterized in detail. Results show that the burning rate as well as the flame stability are greatly influenced by the free stream turbulence. The ratio of turbulent time scales and the chemical time scales for grid mounted cases have been estimated from the integral scale, root mean square velocity fluctuation, flame stand-off distance and the vapor blowing velocity. Empirical expression relating the normalized burning rates to diffusion scale based Damköhlar number has been presented. A correlation for Sherwood number as a function of Reynolds number and turbulent intensity has also been proposed.
P. Senthil Kumar et al., International Journal of Heat and Mass Transfer, 114 (2017) 354-362
Investigation of structure and spread rate of flames over PMMA slabs
Experimental and numerical investigations of upward and downward flame spread over flat polymethyl methacrylate (PMMA) slabs are presented here. Experiments have been carried out using PMMA slabs of different thickness in the range of 1.6 mm–5.4 mm. Downward and upward flame spread processes have been recorded under atmospheric pressure and normal gravity conditions. Careful repeatable high resolution measurements of temperature and species fields have also been carried out, to fill the scarcity of such data in literature. A simple numerical model, used widely to simulate flame spread over condensed surfaces, called Fire Dynamics Simulator (FDS), has been employed to numerically simulate the experimental cases. Results from FDS have been validated against numerical and experimental data from literature, by comparing quantities such as mass loss rate, flame spread velocity and flame structure. FDS is seen to capture essential transport processes of a spreading diffusion flame. The overall comparison of the trends has been quite reasonable. Numerical model is capable of predicting the unsteady and steady features of downward spread as well as transient rapid upward flame spread, as observed in the experimental results.
H R Rakesh Ranga et al., Applied Thermal Engineering, 130, 2018, (477-491)
Steam Reforming of Ethanol in Meso and Micro-channel systems for Hydrogen production
With the need for sustainable energy, demand for clean and renewable energy is increasing. Hydrogen fuel cells is hence, gaining popularity for its application in the Automotive sector. However, there are safety concerns with regard to handling and storing of hydrogen. Therefore, the idea is to produce hydrogen on the spot and feed it directly to the Fuel cells. This can be done through a process called steam reforming, where hydrocarbons can be broken down in the presence of heat. Study of such a process is done using meso and micro-channel systems in view of space and process optimization. (Read More...
S. Roychowdhury et al., Int. J. of Micro-Nano scale Transport, 5 (2014)
An Experimental and Numerical Investigation of Non-Reacting and Reacting Vortex Rings.
A jet of fluid intermittently ejects from a nozzle causes the roll-up of boundary layers, there by it leads to the formation of vortex rings. A vortex ring consists of rotating core fluid at its top portion, followed by a tail at its bottom. During the upward motion of the vortex ring, the rotating vortex core drags the ambient fluid along with it through viscous action. This will improve the mixing between vortex fluid and the surrounding ambient fluid. In the current research work, mixing between the fuel and the oxidizer are studied for different vortex generating conditions. The fuel-air mixture inside the vortex rings is ignited and the resulting reacting (combusting) vortex rings are also studied for the different fuel-air mixture compositions of vortex fluid.
Prasad, M. Jogendra, and T. Sundararajan, Int. J. of Heat and Fluid Flow 62 (2016), 174-188.