Mahesh V Panchagnula

Inter-subject variability in lung morphometry could influence the transport of any disease causing microorganism to the deep lung regions and the delivery of drug to such a targeted site. This study aims in establishing the relation between aerosol deposition and parameters determining the lung morphometry. The human respiratory system is idealized as a one-dimensional trumpet, whose cross section increases as the distance from the trachea increases. The transport of the aerosol is facilitated by the alveolar expansion, resulting in inhalation. The mass balance equation along with the complicated mechanisms of deposition including deposition by impaction, sedimentation and diffusion has been solved. The model has been validated using experimental data on total particle deposition and alveolar deposition over a range of particle sizes. The sensitivity deposition in the alveoli has been studied by performing a sensitivity analysis on the parameters determining the lung morphometry. From the sensitivity analysis it is concluded that the people with constricted distal airways are more susceptible to infection as well as can be targeted for efficient drug delivery. Thus the occurrence of secondary infection in patients with constricted lung dimensions could be explained. The sensitivity analysis also gives an important conclusion that the particles sizes which deposit in alveolar region of the lung in more concentration are the ones which are least sensitive to inter subject variability. Thus the drug which can be engineered in such particle sizes could result in maximum deposition at the targeted site. Based on the sensitivity co-efficient of deposition concentration of a particular particle size, the deviation of the given individual’s morphometry with respect to the base Weibel parameters is determined. Thus the deviation of the Weibel parameters can be used as a morphometric marker for treatment of the specific individual.

In the present study, we investigate the phenomenon of transition of a thermoacoustic system involving two-phase flow, from aperiodic oscillations to limit cycle oscillations. Experiments were performed in a laboratory scale model of a spray combustor. A needle spray injector is used to generate a droplet spray having one dimensional velocity field. This simplified design of the injector helps in keeping away the geometric complexities involved in the real spray atomizers. We investigate the stability of the spray combustor in response to the variation of the flame location inside the combustor. Equivalence ratio is maintained constant throughout the experiment. The dynamics of the system is captured by measuring the unsteady pressure fluctuations present in the system. As the flame location is gradually varied, self-excited high amplitude acoustic oscillations are observed in the combustor. We observe the transition of the system behaviour from low amplitude aperiodic oscillations to large amplitude limit cycle oscillations occurring through intermittency. This intermittent state mainly consists of a sequence of highamplitude periodic bursts separated by low amplitude aperiodic regions. Moreover, the experimental results highlight that during intermittency, the maximum amplitude of bursts oscillations, near to the onset of intermittency, is as much as three times higher than the maximum amplitude of the limit cycle oscillations. These high amplitude intermittent loads can have stronger adverse effects on the structural properties of the engine than the low amplitude cyclic loading caused by the sustained limit cycle oscillations. Evolution of the three different dynamical states of the spray combustion system (viz. stable, intermittency and limit cycle) are studied in three dimensional phase space by using a phase space reconstruction tool from the dynamical system theory. We report the first experimental observation of type-II intermittency in a spray combustion system. The statistical distributions of the length of aperiodic (turbulent) phase with respect to the control parameter, first return map and recurrence plot techniques are employed to confirm the type of intermittency.

The dispersion of polydisperse droplets in a pulsating air stream has been analyzed. The grouping and segregation of droplets in both steady and oscillating flow field has been studied. The effect of evaporation on the grouping process has also been investigated. Eulerian-Eulerian multiphase framework has been used to model the polydisperse drop phase. The model is employed to study the dynamics in a 1D plug flow evaporator. The variation in dispersion process of the droplets along the channels has been observed both without and with presence of evaporation of the droplets. It has been found that the larger size droplets responses weekly with the oscillating flow field whereas, the smaller size droplets clustered differently at different locations depending upon the phase angles of the oscillating flow field.

We report an experimental study on the near injector structure of spray exiting a Gas Centered Swirl Co-axial (GCSC) injector, where the effect of ambient pressure has been investigated. Cold flow tests were conducted with a conventional GCSC injector in an optically accessible high pressure chamber. Water and gaseous Nitrogen were the fluids used. The parameters varied during the study were the gas Reynolds number (0 − 46908) and ambient pressure (1 − 9bar). The liquid Reynolds number was kept constant at 2275. Spray characteristics have been analyzed at different operating conditions with the aid of high speed visualization. Qualitative analysis shows that ambient pressure exerts a strong influence on the morphology of the annular sheet. Mean spray cone angle increases and intact sheet length decreases with increase in ambient pressure at a particular gas Reynolds number. A higher flapping of the annular sheet is observed at elevated ambient pressures. The non-intrusive method of Feature Correlation Velocimetry (FCV) has been used for quantitatively characterizing the liquid sheet at a particular spatial location. This method relies on the advection of naturally formed features/corrugations on the surface of the annular sheet for retrieving the sheet velocity. The axial and swirl velocities remain relatively unchanged at high ambient pressures. In conclusion, the sheet thickness based on axial velocity values obtained from FCV analysis remains unaltered at elevated ambient conditions.

Intersecting sprays are important to several practical applications from rocket combustion to spray painting. The characteristics of these sprays are examined using water as the working fluid. Three types of atomizer configurations are used for this study: (i) Single spray (ii) Double spray- two pressure swirl atomizers of same type, separated by a distance in the exit orifice plane and (iii) Triple spray- three pressure swirl atomizers of same type, placed on the corners of an equilateral triangle. The Sauter mean diameter, joint velocity and diameter distributions as well as the radial and circumferential liquid distribution are experimentally measured using phase doppler interferometry (PDI) technique. From these results, it is observed that at low injection pressures the liquid sheets emerge from exit orifices interacts. As the injection pressure is increased, the breakup length tends to decrease and a regime is identified where the liquid sheets and droplet clouds interfere. In this regime, the drop clouds formed from the different sheets collide with each other resulting in further increases in velocity and drop size remain unaltered. As a result, the hollow cone nature of the overall spray is transformed into solid cone spray of almost an even mean drop size distribution downstream of the spray intersection region. The study demonstrates that the dynamics of wave propagation on the liquid sheets in intersecting sprays is markedly different from the non-intersecting spray. The superimposition of diameter and velocity distribution of two or more single spray is different from the mutual intersection of multiple sprays.

In the present work a 1D plug flow evaporator has been considered to study the evaporation, atomization and transport of polydisperse droplets in a pulsating air stream. The pulsation in the air flow is very common in the real combustor due to the thermo acoustic instabilities. Population balance modeling approach is used to study the continuous evaporation and atomization process. An Eulerian-Eulerian multiphase framework is used to capture the polydispersity of the system. For the evaporation the fixed drop size methodology of the D2 law has been used whereas, for the atomization the conservation of mass has been considered during the breakage. The objective of this work is to study the pulsation frequency on the dispersion of droplets without and with presence of the evaporation and atomization rate. From the results, clustering of particles in different locations has been identified. The variation of Sauter Mean Diameter (SMD) is presented and the non-linear behaviour has been identified in the process.

Miniature spray nozzles are interesting to several applications from micro-thrusters to lithographic patterning. We investigate geometric scaling effects of pressure swirl atomizers, both theoretically and experimentally. The objective of the study is to determine the range of length scales when performance - both in terms of drop size and flow rates - deviate from accepted correlations. The experimental study considers atomizers spanning an order of magnitude in dimensional scale (1x, 3x, 5x and 10x). These atomizers were all kinematically similar and are fabricated by using micro electro mechanical systems (MEMS) technology as well as rapid prototyping technology (RPT). The geometrical parameters such as ratio of exit orifice length to diameter, ratio of swirl chamber diameter to exit orifice diameter, ratio of inlet slot width to height are maintained same for all the trails. Each atomizer is operated at varying flow conditions with water as the working fluid. Spray characteristic parameters such as sheet thickness, breakup length, and spray cone angle are captured by high speed imaging. Sauter mean diameter (SMD) as well as joint drop size and velocity distributions are two of the key characteristics measured experimentally using Phase Doppler Interferometry (PDI) technique. The performance of a small scale atomizer to a large scale atomizer is compared over a wide range of operating condition of the atomizer. This study unravels the following three conclusions. (i) A length scale at which conventional correlations governing spray performance fail, is identified. (ii) An optimum range of scale factors are identified to yield good atomization, with miniaturized spray nozzles. (iii) It is observed that the air core structure of microsprays is markedly different for microsprays from that in macrosprays.