Faculty Publications
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Item Assessment of heat transfer during solidification of Al-22% Si alloy by inverse analysis and surface roughness based predictive model(Springer India sanjiv.goswami@springer.co.in, 2012) Jayananda; Prabhu, K.N.Heat flux transients were estimated during unidirectional downward solidification of Al-22% Si alloy against copper, die steel and stainless steel chills. The chill instrumented with thermocouples was brought into contact with the liquid metal so as to avoid the effect of convection associated with the pouring of liquid metal. Heat flux transients were estimated by solving the inverse heat conduction problem. Higher thermal conductivity of chill material resulted in increased peak heat flux at the metal/ chill interface. Peak heat flux decreased when 100 lm thick alumina coating was applied on the chill surface. The lower thermal conductivity of alumina based coating and the presence of additional thermal resistance decreases the interfacial heat transfer. For uncoated chills, the ratio of the surface roughness (R a) of the casting to chill decreased from 6.5 to 0.5 with decrease in the thermal conductivity of the chill material. However when coating was applied on the chill, the surface roughness ratio was nearly constant at about 0.2 for all chill materials. The measured roughness data was used in a sum surface roughness model to estimate the heat transfer coefficient. The results of the model are in reasonable agreement with experimentally determined heat-transfer coefficients for coated chills.Item The effect of strontium modification on casting/chill interfacial heat flux and casting surface profile during solidification of Al-7Si alloy(Institution of Engineering and Technology jbristow@theiet.org, 2013) Vijayan, V.; Prabhu, K.N.The effect of Sr modification of Al-7%Si alloy on casting/chill interfacial heat flux transients was investigated. The alloy was solidified against polished surfaces of copper, brass and cast iron chills. The heat flux across the casting/chill interface was estimated using inverse modeling technique. On modification melt treatment, the peak heat flux increased by about 70%, 24% and 22% for copper, brass and cast iron chills respectively. The effect of Sr modification on casting surface texture was analyzed using a surface profilometer. The surface profile of the casting and the chill surfaces clearly indicated the formation of anair gap at the periphery of the casting. The arithmetic average value of the profile departure from the mean line, within a sampling length(Ra) and arithmetical mean of the absolute departures of the waviness profile from the centre line within a sampling length(W a) were reduced by 50% on modification. The enhancement in heat transfer achieved due to modification was attributed to the decrease in gap width formed at the interface. The width of the gap formed for the unmodified and modified casting surfaces at the periphery were found to be about 35μm and 19μm respectively. The gap width was used to determine the variation of heat transfer coefficient (HTC) acrossthe chill surface after the formation of stable solid shell.It was found that the HTC decreased along the radial direction.Item Conjugate heat transfer in a Hexagonal micro channel using hybrid nano fluids(American Society of Mechanical Engineers, 2016) Hegde, S.S.; Narendran, N.; Gnanasekaran, N.Research is being focused on the use of micro channels with nano fluids as the heat sinks. This requires fundamental understanding of the heat transfer phenomenon in micro channels. The objective of this paper is to present results from a numerical study on laminar forced convection in a Hexagonal Micro Channel (HMC) heat sink. In particular, the numerical study is carried out using a single phase model. The fluid considered is Alumina-Copper hybrid Nano fluid. The performance of Al2O3+Cu+water is compared with Al2O3+water nano fluid and pure water with different volume fractions. The solid region of the channel is assumed as aluminum with a hydraulic diameter of 175μm. The solid and fluid regions of the micro channel are discretized using finite volume method by combining Navier Stokes equation and energy equation for conjugate heat transfer. The thermo physical properties for alumina nanoparticles are calculated by considering it as a spherical particle of 45nm diameter. The effect of surface roughness on convective heat transfer coefficient and pressure drop for the case of nano fluids is also considered. The analysis is further extended by adding pulsating input and by varying the velocity sinusoidally. The Brownian motion of nano particles is increased to study the efficiency of the heat sink. This ensures all the nano particles are in suspension and the randomness increases the micro convection in the fluid. Incorporating the pulsating flow increases the dispersion of the heat in the nano fluid at a faster rate and also decreases particle settlement in laminar flow. The combined effect of surface roughness and pulsating flow accounts for the change in the velocity profile and thermal boundary layer of the channel. Also the effect of surface roughness ranging from 0.2-0.6 is attempted and the variations in pressure drop, Nusselt number, and heat transfer coefficient are studied. The influence of hexagonal geometry and its interaction with alumina nano fluids is intensively studied by evaluating a three dimensional conjugate heat transfer model. The effect of side wall angle of 45°, 50° and 55° are computed to relate the velocity function with pressure drop, surface roughness and local heat transfer coefficient. The variation of Nusselt number with very low volume fraction of nano particles with a minimal amount of pressure drop is also presented. © 2016 ASME.Item Effect of wire electrode materials on die-corner accuracy for Wire Electrical Discharge Machining (WEDM) of Inconel 718(Elsevier Ltd, 2018) Kumar, A.; Abhishek, K.; Vivekananda, K.; MAITY, K.In present investigation to analyzed the effects of tool electrode on machinability of Inconel 718 using wire electrical discharge machining. An L16 orthogonal array has been used for experimentation by considering machine controllable factors (i.e. pulse on time, wire speed, flushing pressure and discharge current). The influence of the process parameters on the responses, such as, surface Roughness and corner error were studied. From the results, it has been observed that tool material has the significant nature on determining performance variables. It has been also observed that zinc coated brass wire have better performance on surface roughness and corner error than the uncoated brass wire. © 2017 Elsevier Ltd. All rights reserved.Item Effect of machining process parameters on productivity rate and surface roughness of machined TiNiCo alloy(Elsevier Ltd, 2018) Soni, H.; Narendranath, S.; Ramesh, M.R.TiNiCo based shape memory alloy is an important alloy for biomedical applications such as bone staple due to their excellent biocompatibility, corrosion resistance, shape memory effect (SME) and pseudoelasticity (PE). Traditional machining of such kind of alloys is difficult due to their outstanding properties. Wire electro discharge machining (WEDM) is most suitable non-traditional machining process for machining of these alloys. Present study focuses on effect of WEDM process parameters on productivity rate and surface roughness. Pulse on time, servo voltage and wire speed were considered as WEDM process parameters with their five levels in the current study. Our observation exhibit that productivity rate and surface roughness increases with increasing pulse on time and both outputs decrease with increasing servo voltage while wire speed does not show much effect on productivity rate as well as surface roughness. © 2018 Elsevier Ltd. All rights reserved.Item Comparative study of turning process on EN47 spring steel with different nose radii using statistical technique(Elsevier Ltd, 2018) Mallesha, V.; Shivananda Nayaka, H.S.Spring steel (EN47) samples are machined (turning) using Sandvik make coated tungsten carbide tool insert with different nose radii (0.4 and 0.8mm) in dry condition and the results are compared with each other. Spring steel is widely used in the manufacturing of vehicle components such as crankshaft, knuckle and leaf spring. EN47 spring steel material is relatively low cost compare to other alloy steels. Experiments are conducted based on taguchi L9 technique. Input parameters are cutting speed, feed rate and depth of cut. The corresponding output parameters are cutting force, surface roughness and tool tip temperature have been analyzed. Experimental result reveals that better surface roughness obtained with higher nose radius. ANOVA results confirm that cutting force is influenced by depth of cut (ap), surface roughness is influenced by feed rate (f) and tooltip temperature is influenced by cutting speed (Vc). Chip morphology and machined surface samples are analyzed using scanning electron microscope (SEM). © 2018 Elsevier Ltd.Item Influence of surface roughness on pool boiling heat transfer(Institute of Physics Publishing helen.craven@iop.org, 2018) Walunj, A.; Sathyabhama, A.Experimental study of pool boiling heat transfer from the rough surface at pressure 1 bar, 5 bar and 10 bar is presented. Experiments are carried on 20 mm diameter copper sample at saturated condition of distilled water. Unidirectional scratches are made by different grit sandpaper. The surface roughness value Ra is varied from 0.106 μm to 4.03 μm. The effect of Ra on heat transfer at different pressure is reported. The variation in heat transfer coefficient with the heat flux for samples of different Ra is also examined. The predicted critical heat flux (CHF) by Kim's model is found to in good agreement with present experimental values with mean absolute error of 12.06%. © Published under licence by IOP Publishing Ltd.Item Bubble dynamics in pool boiling on rough surface under exponential heat supply(Begell House Inc. orders@begellhouse.com, 2018) Walunj, A.; Sathyabhama, A.In this paper, bubble dynamics in the pool boiling of distilled water on the horizontal copper test sample of 20 mm diameter at atmospheric pressure is studied. The experiments are carried under steady and exponential heat supply of γ=1 to rough copper sample with Ra ranging from 0.106 μm to 4.03 μm. The high speed camera of 1000 fps is used to observe the bubble morphology. The effect of surface roughness on boiling heat transfer during transient heat supply is reported. The effect of surface roughness on bubble departure diameter and bubble frequency is studied. The waiting time and growth time of the bubble for different samples is also compared. The effect of steady and exponential heat supply on bubble departure diameter and bubble frequency is also reported. © 2018 Begell House Inc.. All rights reserved.Item Comparative study of coated and uncoated tool inserts with dry machining of EN47 steel using Taguchi L9 optimization technique(American Institute of Physics Inc. subs@aip.org, 2018) Mallesha, M.; Shivananda, N.H.EN47 steel samples are machined on a self-centered lathe using Chemical Vapor Deposition of coated TiCN/Al2O3/TiN and uncoated tungsten carbide tool inserts, with nose radius 0.8mm. Results are compared with each other and optimized using statistical tool. Input (cutting) parameters that are considered in this work are feed rate (f), cutting speed (Vc), and depth of cut (ap), the optimization criteria are based on the Taguchi (L9) orthogonal array. ANOVA method is adopted to evaluate the statistical significance and also percentage contribution for each model. Multiple response characteristics namely cutting force (Fz), tool tip temperature (T) and surface roughness (Ra) are evaluated. The results discovered that coated tool insert (TiCN/Al2O3/TiN) exhibits 1.27 and 1.29 times better than the uncoated tool insert for tool tip temperature and surface roughness respectively. A slight increase in cutting force was observed for coated tools. © 2018 Author(s).Item Effect of surface treatment on wetting behavior of copper(Elsevier Ltd, 2019) Kalgudi, S.; Pavithra, G.P.; Prabhu, N.K.; Koppad, P.G.; Venkate Gowda, C.; Satyanarayan, S.Super-hydrophobic surfaces are very useful in cleaning activities. Surfaces with water contact angles above 150° are regarded as superhydrophobic surfaces. In the present study an attempt has been made to achieve superhydrophobicity on copper substrate by electrochemical etching and electro-deposition of Co-Ni alloy and Co-Ni-Graphene composite. A contact angle of about 105° was obtained on Cu surface with electro-deposited Co-Ni alloy and on electro-deposited Co-Ni-G alloy contact angle was found to be 106°. The contact angle was significantly higher at about 142° with electro etched surface. Corrosion test was carried out with electrochemically etched Cu. Electrochemical etching time was varied from 30 to 240 min. The electro-etched Cu substrate etched for 60 min. showed better corrosion resistance with a corrosion rate of 0.197 mm/year. The surface topography of both etched and electrodeposited samples was studied by atomic force microscopy (AFM) and the results were correlated with the wettability data. © 2019 Elsevier Ltd.