1,106 research outputs found
Novel Fuel Injection Systems for High-Speed Combustors
No full textA spray nozzle which can produce extremely small droplet size (≤10 μm) finds relevance in drying, liquid-fueled engines, etc. In addition to the droplet size, its momentum too has equal importance in high-speed combustion systems like scramjets, pulse detonation engines for rapid mixing. Many of the nozzles which adopt standalone techniques (pressure, air-assist) fail to produce finer size droplets. Efforts have been made to hybridize two or more techniques to achieve the finer atomization. For instance, standard air-assist atomizer can be combined with effervescent/ultrasonic means to achieve further reduction in droplet size. This chapter presents the comprehensive aspects of such type of hybrid atomizers. Features such as mode of operation, benefits, shortcomings, areas of application are discussed in greater details
On Primary Atomization in Propulsive Device Fuel Injectors—A Short Review
No full textThis chapter provides a brief review of primary atomization mechanisms in spray nozzle relevant to the propulsive devices. Attention which focused on experimental efforts has been made in understanding the primary atomization. Primary atomization involved in two widely used class of nozzles namely, pressure jet and twin-fluid (air-assist) atomizer is explicitly considered
Tweets informing about resource needs and availabilities in post-disaster situation
No full text<p>This is the dataset for the paper:</p>
<p>Moumita Basu, Anurag Shandilya, Prannay Khosla, Kripabandhu Ghosh, Saptarshi Ghosh. Extracting Resource Needs and Availabilities from Microblogs for Aiding Post-Disaster Relief Operations. IEEE Transactions on Computational Social Systems, 2019.</p>
<p>The data contains tweetids of tweets (from Twitter) posted during (1) the 2015 Nepal earthquake, and (2) 2016 Italy earthquake. The tweets that inform about need and availability of various types of resources are identified.</p>
<p>The dataset can be used for developing algorithms for microblog retrieval / classification, and for understanding social media activity in the aftermath of a disaster event.</p>
Video: Dancing liquid sheet - the evolution of liquid sheet in swirl flow
No full textThis video describes the dynamics of liquid sheet injected to highly turbulent swirl flow. High fidelity laser diagnostic tools like time -resolved PIV and high speed shadowgraphy has been employed to understand the governing fluid dynamic phenomenon. The more details on theoretical description of the work can be found in "RAJAMANICKAM, K. & BASU, S. 2017 Insights into the dynamics of spray–swirl interactions. J. Fluid Mech. 810, 82–126
Bahumukhī mana, bahurupī prema
No full textThe document contains a novel written by the Bengali author Nirpendra Kumar Basu (1898-1979). The monograph is from the private collection of Sharmadip Basu
Outer Length Scales in Nocturnal Stable Boundary Layers
No full textRecently, Basu and Holstlag (2021) proposed a unified framework for describing outer length scales (OLS). By utilizing this framework, we document various characteristics of OLS in nocturnal boundary layers over the US Great Plains.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Atmospheric Remote Sensin
Insights of Evaporation Dynamics of an Interacting Linear Array of Droplet System
No full textManipulation of an array of sessile droplets organized in an ordered structure turns out to be of immense consequence in a wide variety of applications ranging from photonics, near field imaging and inkjet printing on one hand to bio-molecular analysis and DNA sequencing on the other. While evaporation of a single isolated sessile droplet has been well studied, the collective evaporative dynamics of an ordered array of droplets on a solid substrate remains elusive. Physically, the closed region between the centre and side droplets in the ordered array reduces the mobility of the diffusing vapour, resulting in its accumulation along with enhanced local concentration and a consequent increment in the lifetime of the center droplet.
Here, we present a theoretical model to account for evaporation lifetime scaling in closely placed ordered linear droplet arrays. In addition, the present theory predicts the limiting cases of droplet interaction; namely, critical droplet separation for which interfacial interaction cease to exist and minimum possible droplet separation (droplets on the verge of coalescence) for which droplet system achieves maximum lifetime scaling. Further experimental evidences demonstrate the applicability of the present scaling theory to extended dimensions of the droplet array, generalizing our physical conjecture. It is also worth noting that the theoretical timescale is applicable across a wide variety of drop-substrate combinations and initial droplet volumes. We also highlight that the scaling law proposed here can be extended seamlessly to other forms of confinement like an evaporating droplet inside a mini channel as encountered in countless applications ranging from biomedical engineering to surface patterning.
Having established the framework of collective dynamics of droplet evaporation, we turn our attention to the case of self-agglomeration deposits, which are observed in evaporating sessile linear array of droplets. When a spilled drop of coffee dries on a solid surface, it leaves a dense, ring-like deposit along the perimeter, i.e., forming “coffee ring” on the surface. Ring-like stains are not particular to coffee and are commonly seen in the droplets containing dispersed solutes. Many of the industrial application requires uniform deposition like in inkjet printing, genotyping and complex assembly. In this section, we have presented the mixing of colloidal particles suppresses the coffee ring stains and forms uniform deposition.
One of the promising areas where the self-aggregation of colloids is highly useful is photonic crystals. Photonic crystals have emerged as a potentially powerful platform that were previously impossible. Photonic crystals have emerged as a powerful tool to achieve light manipulation. Central concept for the photonic behavior is the formation of a photonic ‘band gap’ - a range of frequencies for which light is forbidden to exist within the bulk of the photonic crystal. The presence of a band gap depends on a particular periodic structure within the crystal. Self-agglomeration of colloidal particles can also form periodic arrays, which may serve as a template of photonic crystal. To find out the arrangement of the colloidal particles, packing fraction of colloidal particles have been calculated from centre to the edge of the agglomerate. Optical reflectance shows the variation in the reflectivity along the diametrical line which have been correlated to the peak reflectance of light beam incident on the colloidal crystal. We show that by controlling the evaporative behavior of the droplet in a linear array, it is possible to effect changes in the photonic behavior of the final precipitate
Study of Droplet Dynamics in Heated Environment
No full textDroplets as precursor are extensively applied in diverse fields of science and engineering. Various contributions are provided previously towards analysis of single phase and multi-phase droplets of single and multiple components.
This thesis describes modelling of multi-phase (nano fluid) droplet vaporization. The
evaporation of liquid phase along with migration of dispersed particles in two-dimensional plane within droplet is detailed using the governing transport equations
along with the appropriate boundary and interface conditions.
The evaporation model is incorporated with aggregate kinetics to study agglomeration
among nano silica particles in base water. Agglomeration model based on population
balance approach is used to track down the aggregation kinetics of nano particles in
the droplet. With the simulated model it is able to predict different types of final
structure of the aggregates formed as observed in experimental results available in
literature. High spatial resolution in terms of agglomeration dynamics is achieved
using current model. Comparison based study of aggregation dynamics is done by
heating droplet in convective environment as well as with radiations and using
different combination of heating and physical parameters. The effect of internal flow
field is also analysed with comparative study using levitation and without levitation
individually. For levitation, droplet is stabilized in an acoustic standing wave.
It is also attempted to study the transformation of cerium nitrate to ceria in droplets when heated under different environmental conditions. Reaction kinetics based on modified rate equation is modelled along with vaporization in aqueous cerium nitrate droplet. The thermo physical changes within the droplet along with dissociation
reaction is analysed under different modes of heating. The chemical conversion of
cerium nitrate to ceria during the process is predicted using Kramers' reaction velocity
equation in a modified form. The model is able to explain the kinetics behind
formation of ceria within droplet at low temperatures. Transformation of chemical
species is observed to be influenced by temperature and configuration of the system.
Reaction based model along with CFD (computational fluid dynamics) simulation
within the droplet is able to determine the rate of chemical dissociation of species and
predict formation of ceria within the droplet. The prediction shows good agreement
with experimental data which are obtained from literature
Dynamics of Hollow Cone Spray in an Unconfined, Isothermal, Co-Annular Swirling Jet Environment
No full textThe complex multiphase flow physics of spray-swirl interaction in both reacting and non-reacting environment is of fundamental and applied significance for a wide variety of applications ranging from gas turbine combustors to pharmaceutical drug nebulizers. Understanding the intricate dynamics between this two phase flow field is pivotal for enhancing mixing characteristics, reducing pollutant emissions and increasing the combustion efficiency in next generation combustors. The present work experimentally investigates the near and far-field break-up, dispersion and coalescence characteristics of a hollow cone spray in an unconfined, co¬annular isothermal swirling air jet environment. The experiments were conducted using an axial-flow hollow cone spray nozzle having a 0.5 mm orifice. Nozzle injection pressure (PN = 1 bar) corresponding to a Reynolds number at nozzle exit ReN = 7900 used as the test setting. At this setting, the operating Reynolds number of the co-annular swirling air stream number (Res) was varied in four distinct steps, i.e. Res = 1600, 3200, 4800 and 5600. Swirl was imparted to the co¬axial flow using a guided vane swirler with blade angle of Ф=45° (corresponding geometric swirl number SG = 0.8). Two types of laser diagnostic techniques were utilized: Particle / Droplet imaging analysis (PDIA) and shadowgraph to study the underlying physical mechanisms involved in the primary breakup, dispersion and coalescence dynamics of the spray. Measurements were made in the spray in both axial and radial directions and they indicate that Sauter Mean Diameter (SMD) in radial direction is highly reliant on the intensity of swirl imparted to the spray. The spray is subdivided into two zones as function of swirl in axial and radial direction: (1) near field of the nozzle (ligament regime) where variation in SMD arises predominantly due to primary breakup of liquid films (2) far-field of the nozzle where dispersion and collision induced coalescence of droplets is dominant. Each regime has been analyzed meticulously, by computing probability of primary break-up, probability of coalescence and spatio-temporal distribution of droplets which gives probabilistic estimate of aforementioned governing phenomena. In addition to this, spray global length scale parameters such as spray cone angle, break-up length, wavelength of liquid film has been characterized by varying Res while maintaining constant ReN
Density Stratified Thermal Energy Storage System and Associated Fluid Dynamic Perturbations
No full textThe hunger of humankind for energy has reached unprecedented levels with the ever-rising industrialization and global population surge. We are witnessing a global economic evolution towards a clean, affordable, sustainable and reliable sources of energy which could transform our lives and the planet itself. The mismatch between the supply of solar energy which is one among the most promising renewable energy and the demand for its utilization, compel us to incorporate a solar energy storage. Such storage systems are essential in various fields including power generation sectors like power plants based on solar thermal, thermal (non-renewable) and nuclear.
The study is primarily an experimental investigation of single tank sensible stratified thermal energy storage which sheds light on the experimental procedure to establish a stable and sustainable thermocline thermal energy storage. Moreover, in order to have an understanding of the causes of capacity loss in such stratified storage tanks, various studies are conducted, both numerically as well as experimentally. The performance of the TES depends on the integrity of the temperature gradient region (thermocline thickness). Mixing and spatio-temporal perturbations at the thermocline region is the foremost cause of capacity loss and the most important mechanism which destroys the stratification is vortex/plume entrainment in a thermocline-based storage tank. In a stably stratified TES, vortex entrainment occurs when a relatively cold mass of fluid is injected into the tank. Vortex-thermocline interaction creates vortices by baroclinicity, leading to entrainment and mixing. Hence any vortex entrainment in the thermocline region is critical and determines the efficiency of such thermal storage.
Density stratification formed in terms of salinity as an analogy to that due to temperature as well as the effect of disturbances are studied. As a corollary, various distributors are compared numerically and tested the advantage of a novel distributor design. The work provides quality experimental data in order to meet with its inadequacy in the related literature as well as deeper understanding into the establishment of a stable and sustainable thermocline thermal energy storageThis thesis is based upon work supported in part by the India– US partnership to Advance Clean Energy-Research (PACE-R) for the Solar Energy Research Institute for India and the United States (SERIIUS), funded jointly by the U.S. Department of Energy (Office of Science, Office of Basic Energy Sciences, and Energy Efficiency and Renewable Energy, Solar Energy Technology Program, under Subcontract DE-AC36-08GO28308 to the National Renewable Energy Laboratory, Golden, Colorado) and the Government of India, through the Department of Science and Technology under Subcontract IUSSTF/JCERDC-SERIIUS/2012 dated 22nd November 2012 and DST-SERI-Project No: DST/TMC/SERI/FR/136
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