Prashant Khare

Decomposition and Ignition of HAN-Based Monopropellants by Electrolysis

In this paper, electrolytically-induced HAN ignition has been studied. The purpose of the present study is to identify the various parameters and mechanisms dictating the electrolytic ignition of HAN-based monopropellants. Electrochemical mechanisms are established and incorporated into an existing chemical kinetics scheme developed by Lee and Litzinger. The ignition of HAN-water solution by electrolysis has been treated numerically using a constant pressure, homogeneous reactor model. A stiff ODE solver was used in the analysis to handle the highly stiff species conservation and the energy equations. The analysis focuses on the temporal evolution of temperature and condensed and gas phase species. Parametric studies were conducted to investigate the effect of electric current, voltage, volume, initial temperature, and HAN concentration on the ignition time delay. The ignition time delay is found to decrease with increase in current, temperature, and HAN concentration and increase with volume.

Atomization patterns and breakup characteristics of liquid sheets formed by two impinging jets

ligament, are studied. The circumferentially space drops were shed from the periphery of the sheet, as well as the ligaments were fragmented from the leading edge of the sheet and then broke into droplets following the Rayleigh mechanism. The periodic waves from the point of impingement were apparent on the surface of the sheet. The impact waves caused early breakdown of the sheet downstream of the impingement point, whereas waves amplied by aerodynamic stresses controlled the breakdown of the rest of the sheet and the ligaments. The impinging jets for non-Newtonian uid are also investigated, two dierent ow patterns are observed.

Energy and Mass Transfer during Binary Droplet Collision

The present study focuses on binary droplet interactions over a wide range of Weber numbers and impact parameters. The formulation is based on the complete set of conservation equations for both the liquid and surrounding gas phases. An improved volume-of-fluid (VOF) technique, augmented by an adaptive mesh refinement (AMR) algorithm, is used to track the liquid/gas interfaces. Detailed information about the droplet dynamics, including collision, deformation, coalescence, separation, and mass and energy transfer, is obtained systematically. Various underlying processes of droplet dynamics are investigated by analyzing the overall energy budget. In addition, an advanced visualization technique using the Ray-tracing methodology is implemented to gain direct insight into the detailed physics of droplet interaction. Theories are also established to predict the droplet behavior after collision. Good agreement is achieved with simulation and experimental results.

Phenomenology of Secondary Breakup of Newtonian Liquid Droplets

In this paper, deformation and breakup of Newtonian liquid droplets at elevated pressures have been studied. Detailed physics pertaining to four different breakup regimes, oscillatory, bag, multimode and shear breakup modes , has been investigated using an incompressible interface tracking methodology. The accuracy and efficiency of the code was enhanced by incorporating an adaptive mesh refinement (AMR) techni que. In general, the aerodynamic drag force exerted by the ambient fluid causes the droplet to deform. The deformation is resisted by viscous and surface tension forces. The breakup mechanism becomes progressively violent as the We number increases, and moves from oscillatory to shear breakup regime. Quantitatively, the droplet lifetime decreases as the inertial force is increased in comparison to the deformation resisting, surface tension force. A criterion to mark the beginning of breakup has been quantified in terms of surface and kinetic energy associated with the droplet. Critical We numbers for the three regimes have also been identified for 100 atm pressure conditions. A generalized regime diagram, for Oh < 0.1, was developed to predict the various breakup modes, taking into account the pressure effect on critical We number, using data from previous experimental investigations , and simulations conducted during the current study.

Breakup of non-Newtonian Liquid Droplets

Deformation and fragmentation of non-Newtonian liquid droplets is investigated using an Eulerian-Eulerian, volume-of-fluid (VOF) interface capturing technique. It is found that the breakup behavior of shear thinning, non-Newtonian liquid droplets is drastically different as compared to their Newtonian counterparts. Several flow features commonly exhibited by non-Newtonian fluids are observed during the breakup process. The breakup initiates with the formation of beads-in-a-string. This is followed by rapid rotation of the droplet with the appearance of helical instability and liquid budges, which forms the sites for primary and satellite droplet shedding. Child droplet size distributions are also examined and it is found that a Gaussian function universally characterizes the droplet sizes produced during the breakup of a single non-Newtonian droplet.