Faculty Publications
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Publications by NITK Faculty
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Item Effect of thermal conductivity and viscosity on cooling performance of liquid quench media(Maney Publishing Suite 1C, Joseph's Well, Hanover Walk Leeds LS3 1AB, 2014) Ramesh, G.; Prabhu, K.In this present work, the effect of the thermophysical properties of quenchants on its cooling performance was investigated. Water, brine solutions, polymer solutions and mineral oils were chosen to have quench media with varying thermophysical properties. Cooling curve analyses were carried out by using standard ISO/DIS 9950 quench probe. Grossmann H quench severity of the quench media was determined from the relation of H and cooling rate. Cooling curve analysis results showed that the change in thermophysical properties of the quench media had significant effect on the cooling history of the quench probe. The viscosity of the quenchant used for immersion quenching is the most important factor that controls the cooling performance of the quenchant compared to thermal conductivity of the quench medium. © 2014 IHTSE Partnership.Item Wetting kinetics, kinematics and heat transfer characteristics of pongamia pinnata vegetable oil for industrial heat treatment(Elsevier Ltd, 2014) Ramesh, G.; Prabhu, K.The suitability of pongamia pinnata vegetable oil as cooling medium for quench heat treatment was investigated. Wetting kinetics, kinematics and heat transfer characteristics of pongamia oil during immersion quenching of hot Inconel probe were determined and compared with palm and mineral oils. A comparison of the relaxation of contact angle indicated early attainment of equilibrium contact angle for pongamia oil droplet on Inconel substrate. The equilibrium contact angle value of pongamia oil was in between mineral and palm oils. However, the spreading kinetics was faster with pongamia oil. Pongamia oil showed the formation of a stable vapour film on the probe surface during quenching. This phenomenon was not observed in palm oil and other vegetable oils reported in literature. Pongamia pinnata oil exhibits uniform nature of wetting front, intermediate rewetting temperature and less variations in rewetting temperatures during quenching. The hardening power of pongamia oil was higher than palm and mineral oils and the cooling of the probe was more uniform during quenching in pongamia oil. The heat transfer characteristics of pongamia oil were found to be superior to palm and mineral oils after film/transition boiling. Pongamia oil showed lower heat transfer but more uniform cooling during film boiling. © 2014 Elsevier B.V.Item Wetting and cooling performance of mineral oils for quench heat treatment of steels(Iron and Steel Institute of Japan, 2014) Ramesh, G.; Prabhu, K.In the present work, wetting kinetics, kinematics and heat transfer characteristics of mineral oils having varying thermo-physical properties sourced from different suppliers were investigated using contact angle, online video imaging and cooling curve analysis techniques. The relaxation behavior of mineral oils of low viscosity and surface tension on Inconel substrate indicated improved wettability and fast spreading kinetics while mineral oils of high viscosity and surface tension showed reduced wettability and slower spreading kinetics. Further, the spreading behavior of mineral oils of lower viscosity and density showed the absence of viscous regime. During rewetting, formation of double wetting fronts and more uniform nature of wetting front were observed with mineral oils of high viscosity and flash point whereas no additional wetting front was observed for mineral oils of low viscosity and flash point. Among the convectional/fast/hot mineral oils, higher wetting front velocity and cooling rate were obtained for low viscosity mineral oil. The heat extracting capability of high viscosity mineral oils was higher during vapour and nucleate boiling and lower during liquid cooling stage. Further, highly viscous mineral oils showed uniform heat transfer compared to mineral oils having low viscosity. © 2014 ISIJ.Item Spatial dependence of heat flux transients and wetting behavior during immersion quenching of inconel 600 probe in brine and polymer media(Springer Boston, 2014) Ramesh, G.; Prabhu, K.Cooling curve analysis of Inconel 600 probe during immersion quenching in brine and polymer quench media was carried out. Thermal histories at various axial and radial locations were recorded using a high-speed data acquisition system and were input to an inverse heat-conduction model for estimating the metal/quenchant heat flux transients. A high performance smart camera was used for online video imaging of the immersion quenching process. Solution to two-dimensional inverse heat-conduction problem clearly brings out the spatial dependence of boundary heat flux transients for a Inconel 600 probe with a simple cylindrical geometry. The estimated heat flux transients show large variation on axial as well as radial directions of quench probe surface for brine quenching. Polymer quenching showed less variation in metal/quenchant heat flux transients. Shorter durations of vapor film, higher rewetting temperatures, and faster movement of wetting front on quench probe surface were observed with brine quenching. Measurement of dynamic contact angle showed better spreading and good wettability for polymer medium as compared to brine quenchant. The solid-liquid interfacial tension between polymer medium and Inconel substrate was lower compared with that of solution. Rewetting and boiling processes were nonuniform and faster on quench probe surface during immersion quenching in brine solution. For the polymer quench medium, slow rewetting, uniform boiling and repeated wetting were observed. © 2014 The Minerals, Metals & Materials Society and ASM International.Item A dimensional parameter for prediction of cooling performance of quenchants(ASTM International, 2014) Prabhu, K.; Ramesh, G.Computer aided cooling curve analysis was carried out during immersion quenching of ISO/DIS 9950 quench probe. Water, brine solutions, polymer solutions, mineral oils, and vegetable oils were used as quench media. The results showed that the quench medium used had a significant effect on the quench probe cooling curve parameters. An empirical correlation was proposed to predict the average cooling rate from surface tension, wetting angle, thermal conductivity, and kinematic viscosity of the quench medium. © 2014 by ASTM International.Item Cooling performance of select mineral oil and polymer quenchants(ASTM International, 2014) Tiwary, V.; Prabhu, K.In the present investigation, quench severity was determined for industrial oil quenchants and varying concentrations of PAG polymer. Viscosity, thermal conductivity, density, flash point, and fire point were measured for all quenchants. Cooling curve parameters were determined based on cooling curve analysis ISO/DIS 9950 technique. An Inconel 600 probe was used for this purpose. Severity of quenching was determined based on the Grossmann technique. Viscosity and thermal conductivity had a significant effect on quench severity. Heat flux and HTC at the metal/quenchant interface were computed by both lumped capacitance and Inverse modeling techniques. The effect of ultrasonic and Tensi agitation on cooling curve parameters was assessed. Polymer quenchants of lower concentrations showed marginally higher heat transfer rates compared to water particularly during unagitated condition. © © 2014 by ASTM International.Item Experimental and numerical heat transfer studies on quenching of Inconel 600 probe(Springer Verlag, 2015) Ramesh, G.; Prabhu, K.The effect of heat transfer coefficient and quench start temperature on cooling behaviour of Inconel 600 quench probe was assessed by numerical experiments. A quantitative model that relates the mean cooling rate and quench start temperature of the probe with the boundary heat transfer coefficient was proposed. Computed aided cooling curve analysis was carried out by heating Inconel 600 probe to temperatures varying from 100 to 850 °C followed by quenching in water. The results of quenching experiments and the data available in the literature were used to validate the proposed model. A good agreement between the measured and estimated value was observed. The results showed that the film and transition boiling of cooling stages were significantly influenced by quench start temperature of the material while nucleate boiling and convective cooling stages were strongly dependent on the boundary heat transfer coefficient. © 2014, Springer-Verlag Berlin Heidelberg.Item Effect of chilling and cerium addition on microstructure and cooling curve parameters of Al-14%Si alloy(Maney Publishing maney@maney.co.uk, 2015) Vijayan, V.; Prabhu, K.Al-14%Si alloys, with and without cerium, were cast at varying cooling rates by solidifying them in a crucible and against chills. The effect of melt treatment and chilling on microstructure and cooling curve parameters of the alloy was assessed. Ce treated alloys solidified in clay graphite crucible at a slow cooling rate showed refinement of primary silicon and the formation of Al-Si-Ce ternary intermetallic compound. The addition of Ce to the alloy solidified against chills resulted in simultaneous refinement and modification of primary and eutectic silicon. Nucleation temperatures of both primary and eutectic silicon decreased on addition of cerium. The formation of the intermetallic compound decreased with increase in cooling rate, leading to the modification of the eutectic silicon. The increase in the degree of modification of the eutectic Si was associated with the decrease in the volume fraction of the intermetallic compound formed. © 2015 Canadian Institute of Mining, Metallurgy and Petroleum Published by Maney on behalf of the Institute.Item Comparative study of wetting and cooling performance of polymer-salt hybrid quench medium with conventional quench media(Taylor and Francis Ltd., 2015) Ramesh, G.; Prabhu, K.Wetting kinetics, kinematics, and cooling performance of a polymer-salt hybrid quenchant were investigated. The rewetting phenomenon for brine, water, polymer, and polymer-salt hybrid solutions was characterized as rapid uniform, fast non-uniform, slow uniform, and fast uniform processes, respectively. A dimensionless rewetting time was proposed to assess the nature of the wetting front. The hybrid quenchant showed higher heat transfer during vapor and transition boiling and lower heat transfer during nucleate boiling and convective cooling. The presence of salt in the hybrid solution resulted in early destabilization of the vapor film and an increase in wetting front velocity and rewetting temperature. The polymer constituent delayed the rewetting phenomenon. © 2015 Taylor & Francis Group, LLC.Item Heat transfer and quench performance of aqueous CuO nanofluids during immersion quenching(Inderscience Publishers, 2016) Nayak, U.; Prabhu, K.The present work involves the assessment of quench performance of aqueous-copper oxide nanofluids. Distilled water-based copper oxide nanofluids of concentrations 0.01, 0.05, 0.1 and 1.0 vol.% were prepared by a two-step process. Cooling curves analysis was carried out using an inconel probe that was instrumented with thermocouples. The recorded temperature data during experiments was used to estimate spatiotemporal heat flux transients by solving inverse heat conduction problem. Quenching of probe in nanofluids resulted in longer vapour phase stage duration compared to distilled water. The addition of nanoparticles altered the peak flux and the time of its occurrence. Rewetting temperatures were found to be lower for nanofluids. The measured thermal conductivities and viscosities showed similar values for all quench media. © 2016 Inderscience Enterprises Ltd.