Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

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VIT University

Mechanical

In this paper, numerical simulation is performed to investigate the turbulent thermal convection flow and heat transfer characteristics of nanofluids inside a cubical enclosure with partially mounted heat and cold source. A transient, three-dimensional, two-phase mixture model with LamBremhorst k−ϵ turbulence model is developed, validated and solved using finite difference method. The heat transfer performance of different water based nanofluids such as aluminum oxide (Al2O3), copper (Cu) and silver (Ag) are investigated for a wide range of Grashof numbers (Gr) varying between 106 ≤ Gr ≤ 1010. The nanoparticle diameter (dp) and volume fractions (ϕ) are varied between 20nm ≤ dp ≤ 80nm and 2% ≤ ϕ ≤ 4%. The results indicate that the random Brownian motion of nanoparticles increases the thermal convection and enhances the rate of energy exchange between the fluid and particle phase. The average heat transfer rate increases with increase in Grashof number and volume fraction. It is found that the effect of volume fraction on average heat transfer rate is more effective in transitional flows than fully turbulent flows. The average heat transfer rate increases with decrease in particle size and the influence of nanoparticle size on heat transfer enhancement are significant in turbulent flows than transitional flows. © 2020

School of Mechanical Engineering

Chennai Campus

World University root node

International Journal of Mechanical Sciences

Turbulent thermal convection of nanofluids in cubical enclosure using two-phase mixture model

Air flow is a major characteristic in the tunnel ventilation design, to avoid severe disasters like smoke suffocation problems in tunnel and fire accidents. Tunnels are best ways to reduce distance between two adjacent places. It may be underground or above ground, depending upon the usage of it. There are different types of tunnel ventilation, e.g. roof vents, side vents, mechanical ventilation, naturally ventilated etc. This paper majorly focuses on roof vents mass extraction with different sizes of the heat sources and it also records the horizontal and normal velocity for different sizes of heat sources. The Reynolds Number is low but still turbulence occurs when we deal with buoyant smoke keeping density as incompressible ideal gas. Ratio of height by width is taken into account and the transient air flow is simulated for 10 seconds, and mass flow is recorded at each time step of 0.1 seconds using Large Eddy turbulence Model to capture the flow physics. It is observed that with changing the heat source size, mass flow rate from each vent changes significantly and it drastically affects the air flow patterns and heat transfer characteristics inside the tunnel. © 2021 Institute of Physics Publishing. All rights reserved.

Fulltext

Journal of Physics: Conference Series

Turbulent thermal characteristics and air flow patterns in a naturally ventilated tunnel with roof openings

Polyurethane foam is a versatile material for many applications like acoustic, thermal insulation, as well as for energy absorption. The main aim of this paper is to improve acoustic properties by adding weight percentage of 2, 4, and 6 of magnesium hydroxide (Mg(OH)2) micro-particles in polyurethane (Pu) foam. To investigate the influence of micro-particles on acoustic properties, the samples are tested in an impedance tube to measure sound absorption coefficient. The experimental results are compared to finite element results predicted from Johnson–Champoux–Allard model. For thermal properties, the samples are experimented in thermal conductivity and fire retardant test. The results indicate that the significant improvement in the acoustic and thermal properties due to the addition of magnesium hydroxide. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Influence of Magnesium Hydroxide Fillers on Acoustic, Thermal, and Flame Retardant Properties of Pu Foam

Interaction of polydisperse droplets in a turbulent air flow features prominently in a wide range of phenomena, such as warm rain initiation as an example. In the current study, we present an experimental investigation on the effects of initial droplet field characteristics on the maximum droplet size growth. By performing experiments in a vertically oriented air flow facility, the air flow turbulence was able to be controlled through the mean flow velocity and an active turbulence generator. The initial droplet field characteristics (droplet diameter range of 0-120 m) were varied using spray nozzles of different flow numbers. Based on quantitative measurements of the droplet size distribution at various spatial locations using phase Doppler interferometry (PDI), we estimated the droplet size growth rate as a function of turbulence intensity, initial droplet number density and initial mean droplet size. For each (,), we observed the occurrence of an optimum turbulence intensity, with the corresponding maximum droplet size growth rate being. Two different trends were observed. When and were simultaneously increased and decreased, respectively, their competing influences resulted in small variations in. In contrast, when was held constant with a corresponding Stokes number smaller than unity, there existed a threshold above which increased rapidly with. These trends were then understood through long-distance microscopy (LDM) measurements. Beyond the aforementioned threshold, the fraction of uncorrelated small-sized <![CDATA[(St droplet pairs was found to rapidly increase with. Further detailed analysis of droplet tracking in the LDM images identified that the velocity fluctuations in the small-sized droplet pairs being induced by close encounters with inertial droplets was the underlying mechanism for the rapid increase of with. This mechanism potentially explains how droplet collisions can be enhanced in small droplets if the droplet field is sufficiently polydisperse. ©

Journal of Fluid Mechanics

Experimental study of the effects of droplet number density on turbulence-driven polydisperse droplet size growth

The effect of uniform temperature on dynamic characteristics of a sandwich plate with functionally graded (FG) core is analyzed by finite element methods. The top and bottom of the sandwich plate are considered as metal and ceramic, and the core is considered as functionally graded. Aluminum and alumina materials are used as top and bottom face sheets, and the same materials are graded through thickness for FGM core. The material properties of FG core vary throughout the thickness direction according to the power law index. The effective material properties are calculated using the Voigt technique. The Buckling temperature of sandwich plate is analyzed for different boundary conditions and used as criteria to study the effect of temperature on natural frequencies and mode shapes. © 2021, Springer Nature Singapore Pte Ltd.

Studies on Dynamic Characteristics of Sandwich Functionally Graded Plate Subjected to Uniform Temperature Field

Automatic speech recognition (ASR) has gained a lot of popularity in the mobile robotics, where the commands could be provided to the robot wirelessly to maneuver. A navigation system combined with ASR is a complex system to carry out, because the system has difficulty in recognizing the voice commands when the environment involved already has disturbances like road noise, air conditioner, music, and passengers. The objective of this research is to operate a mobile robot with a single-arm manipulator, where the robot can perceive the speech and it can react to the individual speech commands provided by the operator swiftly and precisely. In order to recognize the speech, mel-frequency cepstral coefficient (MFCC) speech recognition algorithm is chosen and implemented in MATLAB. Various training and testing have been done in MFCC algorithm where it has to carry out the real-time processing of speech data and respond to it. Based on both the training and testing the voice commands collected from the five test subjects both male and female, the speech recognition system achieved 89% efficiency for the test database. © 2021, Springer Nature Singapore Pte Ltd.

Speech Recognition Using Neural Network for Mobile Robot Navigation

Friction stir welding (FSW) technique was preliminary developed to join various low strength and high strength alloys by considering different inputs and known to surpass the flaws which occur in conventional welding processes. The present study is focused on the FSWed interlock lap joint of AA7475-T7 using three-level three factor (33) full factorial design methodology to study the correlation among process parameters with the lap shear strength and hardness. To compare the strength and hardness of interlock lap joint, a typical lap joint has been made with an optimized input parameter obtained from the FSW interlock lap joint. Microstructure analysis, hardness and tensile strength of FSWed interlock lap joints and typical lap joints were done to analyze the robustness of the welds made. Results proved that the strength of FSWed interlock lap joints is high compared to typical lap weld with a ultimate tensile strength of 172.88 N and hardness of 200 HV when the process parameter level is at tool rotation speed of 1400 r/min, welding speed 30 mm/s plunge speed rate 0.06 mm/s. At the tool rotation speed of 1400 r/min dynamic recrystallization of the material occurs which thereby leads to the formation of fine grains in the SZ of the weld metal. © IMechE 2021.

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Microstructure and mechanical properties of interlock friction stir weld lap joint AA7475-T7 using fractional factorial design

The objective of this study is to prepare a bio-based and light-weight electromagnetic interference (EMI) shielding material in the range of 8–12 GHz. Organic castor oil-based polyurethane (PU) foam was synthesized by the mechanical stirrer mixing process, whereas absorption and hydrothermal reduction processes have been used to reinforce the multi-walled carbon nanotube (MWCNT), cupric oxide (CuO) and bamboo charcoal (BC) nanoparticles in the organic PU foam. The EMI shielding properties of the PU foam composite were tested using a vector analyzer test setup. Identification of the structural property of the nanocomposite was analyzed using field-emission scanning electron microscopy images. The density of the organic PU foam composite reinforced with nanoparticles was calculated with the help of mass and volume. Response surface methodology has been used to systematically design and analyze the experiments of EMI shielding effectiveness (EMI SE) and the physical properties of the reinforced foam. Using the EMI SE experimental results, mathematical models were developed to forecast the results and validate them with error estimation. An optimization study has revealed that 0.75 wt.% of MWCNT, 1.5 wt.% of CuO, and 1.5 wt.% of BC are the optimum parameters with 0.063750 g/cm3 density for obtaining the maximum EMI SE. © 2021, The Minerals, Metals & Materials Society.

Journal of Electronic Materials

An Investigation of EMI Shielding Effectiveness of Organic Polyurethane Composite Reinforced with MWCNT-CuO-Bamboo Charcoal Nanoparticles

The concept of reuse and recycle plays a very important role in using waste materials effectively. Fabrication of green composites, which adopts the reinforcement of natural and biodegradable fibres in place of synthetic fibres, is a constructive way to achieve reusability and recyclability. Hence, the sugarcane fibre, fly ash, and carbon nano tube are selected as reinforcement/filler materials for fabricating epoxy polymer matrix composite. This work is intended to investigate the flexural behaviour of the fabricated epoxy polymer composite by varying the wt. % of CNT/sugarcane fibre/fly ash. Central composite design of response surface methodology, one of the concepts of design of experiments, is used to make the experimental specimens. Further, analysis of variance is used to accomplish the influence of CNT/sugarcane fibre/fly ash on the flexural behaviour of composite. Optimized parameters are obtained to achieve the improved flexural behaviour, and the same is confirmed by the confirmation experiment. Copyright © 2021, IGI Global.

International Journal of Surface Engineering and Interdisciplinary Materials Science

Flexural analysis of epoxy polymer composite reinforced with sugarcane fibre/fly ash/carbon-nanotube

This study presents the finite element analysis of the weld joints used in the off-highway vehicles. A coupled field thermal and static analysis is performed to find the residual stresses in weld and its effect on the fatigue life of the double plate full penetration weld joint. The Design of Experiments approach, via Response Surface Methodology (RSM), is used considering the influence of the parameters like Plate Thickness, Load and Prep angle on the fatigue life. The central composite design, a model in RSM is used to minimize the number of simulations. The Analysis of Variance (ANOVA) is carried out to find the influences of Plate Thickness, Load and Prep angle on the fatigue life. The Regression Equation, obtained through ANOVA, helps to understand the influences of parameters on fatigue life. Later the regression equation is validated with finite element results. The Optimization study is carried out to find optimized parameters for maximum fatigue life. Confirmation simulation using finite element analysis reveals the integrity of optimization study. © 2021, Politechnica University of Bucharest. All rights reserved.