BUBBLE DYNAMICS IN FLUID PUMPING AND FORMATION OF SPRAYS AND JET

Ph.DDOCTOR OF PHILOSOPH

Statistical Processing of Subjective Test Data for Sound Quality Evaluation of Automotive Horn

Product sound quality has a significant role in buying decision and customer satisfaction. An often used method to assess the sound quality of any product or equipment is a subjective listening test where the sound is heard by a panel of subjects (jury) who then rate the sound quality. Subjects use a semantic differential rating wherein they evaluate the presented sounds based on a bipolar variable. The two extremes of the rating scale are labeled with an adjective and its antonym respectively. In the present study, a subjective listening test has been conducted to assess sound quality of automotive horns. The data obtained are then analyzed using statistics to gain insights. Twenty two horn sound samples were judged by thirty participants aged 20-40 years who had normal hearing. Binaural head set (BHS) instrument was used to record horn sound samples in open ground (neglecting wind noise effect). Sounds are recorded two meter from horn in front direction and used for subjective test. For the subjective test and subsequent statistical analysis, a four step procedure has been used. In the first step, the participants were asked to rate the sound quality for each horn based on seven bipolar variables. These bipolar variables are soft/loud, calm/frightening, slow/fast, relax/tense, safe/danger, vague/distinct and pleasant/unpleasant. For each bipolar variable, a seven verbal interval scale was used ranging from one extreme to another in degree, for example extremely pleasant to extremely unpleasant

Laser diagnostics for characterization of sprays formed by a collapsing non-equilibrium bubble

In this paper, we investigate the use of laser diagnostic tools for in-plane imaging of bubble induced spray using a laser sheet and Mie scattering technique. A perspex plate of thickness 10 mm with a hole of diameter 1 mm in the center is placed in the middle of a glass tank filled with water such that the top surface of the plate coincides with the water surface. A bubble is created just below the hole using a low-voltage spark circuit such that it expands against the hole. This leads to the formation of two jets which impact leading to a spray and break-up into droplets. The spray evolution is observed using a laser sheet directed in a plane through the center of the hole. The illuminated plane is imaged using a high-speed camera based on the Mie scattering from glass beads suspended in the liquid. Results show that Mie scattering technique has potential in studying bubble-induced sprays with applications such as in fuel sprays, drug-delivery etc, and also for validation of numerical codes. We present results from our ongoing experiments in this paper

Experimental Validation of Composite Solid Propellant Burning Rate Prediction Model (He-Qu-1D) using Ultrasonic Burning Rate (UBR)

A valid predictive tool of ballistic behaviour of composite solid propellant gives more advantage for a designer of solid propellant to freeze a composition for a particular application. Composite solid propellant in ISRO is composed of major fraction of ammonium perchlorate (AP) as oxidizer and hydroxyl terminated polybutadine (HTPB) as the fuel-cum-binder. In this work, attempt has been made to validate one of the latest burning rate prediction models: heterogeneous quasi one dimensional model (He-Qu-1D) developed at IIT, Madras utilizing ISRO compositions of solid propellant. Thus this model can be used for the new compositions development in ISRO, and invariably reducing the trails for the optimization of the composition. Composite solid propellant combustion is determined by the diffusion and premixing of decomposition products of AP and HTPB binder where the binder is surrounded around the AP particle. Hence, the particle size distribution of AP is very crucial information for solid propellant combustion modelling. In view of this, different techniques of particle size distribution viz., sieve analysis, laser scatter dry method, laser scatter wet method, image analysis has been explored and studied in detail to determine the best method for repeated measurement. Based on this standardized method of measurement, particle size distribution information of AP, is measured and is fed to the above said He-Qu-1D model and predictions were made for six compositions of propellants. The results thus obtained were compared with the ultrasonic burning rates (UBR) results measured experimentally. Details of these results are discussed in this report. It is observed that there is a good agreement between the prediction and experimental results of major compositions

Fish hook in classifier efficiency curves: An update

Fish hook in classifier efficiency curves has been receiving attention in the last three decades, more so with the advent of laser diffractometry. In the first part of this paper, we analyse two occurrences of fish hook reported recently in Separation and Purification Technology. It is shown that in both the cases, inaccuracies in measured particle size distributions could be the likely cause of the observed fish hook. In the second part, we re-examine the present state of knowledge on fish hook including the limitations of experimental observations reported so far and the drawbacks of theoretical explanations. Finally, we provide a basis on why it is to be considered nothing more than a scientifically insignificant placebo

Experimental studies on motion of falling flat thin disk inside liquid

This thesis is about experimental study on falling flat thin disks inside liquid and observing various possible paths of such disks. Based on few non dimensional numbers, i.e. Reynolds number (Re), dimensionless moment of inertia (I∗), and aspect ratio, this motion was classified into four types, which are steady falling, periodic, chaotic and tumbling motions. In this work, flat thin disks were made of three different types of materials, i.e. Aluminum, Steel, and Copper. Here Aluminum is a low density material and steel, copper are high density materials. To vary the viscosity of the surrounding medium, three different fluids were used, namely pure water, 50% water mixed with 50% glycerol liquid and 40% water mixed with 60% glycerol solution. Based on the results obtained, we constructed a phase diagram between Dimensionless moment of inertia and Reynolds number

Experimental Study of the Dynamics of Upward Propelled Droplets

This thesis involves the study of the dynamics of upward propelled droplets using the experimental method. An experimental setup was designed consisting of a pneumatic cylinder, an acrylic glass plate, a compressor, control valves, and tubing. A droplet is placed on an acrylic plate which is actuated to move up and down using a pressurized pneumatic cylinder. When the pressure is applied, the plate undergoes a sudden linear upward motion and launches the droplet into air whose behaviour is then recorded using a high-speed camera. We developed a MATLAB® code for image processing and using the code, we try to understand the behaviour of the droplet in terms of shape oscillation, aspect ratio, etc. by varying the size of the droplet and propulsive force. The results of this experimental setup agree well with earlier simulation results within our research group

Letter: Entrapment and interaction of an air bubble with an oscillating cavitation bubble

The mechanism of the formation of an air bubble due to an oscillating cavitation bubble in its vicinity is reported from an experimental study using high-speed imaging. The cavitation bubble is created close to the free surface of water using a low-voltage spark circuit comprising two copper electrodes in contact with each other. Before the bubble is created, a third copper wire is positioned in contact with the free surface of water close to the two crossing electrodes. Due to the surface tension at the triple point (wire-water-air) interface, a small dip is observed in the free surface at the point where the wire is immersed. When the cavitation bubble is created, the bubble pushes at the dip while expanding and pulls at it while collapsing. The collapse phase leads to the entrapment of an air bubble at the wire immersion point. During this phase, the air bubble undergoes a "catapult" effect, i.e., it expands to a maximum size and then collapses with a microjet at the free surface. To the best of our knowledge, this mechanism has not been reported so far. A parametric study is also conducted to understand the effects of wire orientation and bubble distance from the free surface. Published by AIP Publishing