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Subject: search.filters.subject.Heat flux transients

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Now showing 1 - 10 of 21
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    Development of clay based nanofluids for quenching
    (2012) Ramesh, G.; Prabhu, K.N.
    In the present work the effect of addition of nanoclay particles having concentrations of 0.001, 0.01 and 0.1 vol% on cooling performance of water during immersion quenching was investigated. Cooling curve analyses were carried out by using standard ISO/DIS 9950 quench probe. Wetting behavior of nanoquenchant was studied using dynamic contact angle analyzer. The spreading behavior of droplets of quench media on INCONEL 600 substrate indicates improved wetting behavior of nanofluids. The peak cooling rate and cooling rate at 700°C for water decreased by addition of nanoparticles. Further, quenching in nanofluid shows longer vapour blanket stage as compared to water. The estimated flux transients and Grossmann H factor clearly show that decreased cooling performance of water by addition of nanoparticles. Copyright © 2012 ASM International® All rights reserved.
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    The determination of quench severity and the quantification of the boundary conditions at the metal/quenchant interface would be of considerable utility to the heat treating community. In the present work, an attempt has been made to determine the quench severity of various quench media including three vegetable oils, by the Grossmann Hardenability Factor method and by estimation of heat flux transients by inverse modeling of heat conduction in 304 stainless steel quench probes. The heat flux transient technique was found to be more accurate than the Grossmann technique in assessing the severity of quenching. This finding was supported by the hardness data and microstructure @@@ with the quenched steel specimens. New heat flux parameters are proposed to assess the severity of quenching. The boundary heat flux transients during end quenching of AISI 1040 steel specimens were also estimated. The estimated heat flux transients could be used for modeling of heat transfer during quenching. An attempt has also been made in the present work to assess the feasibility of three vegetable oils, namely coconut, sunflower, and groundnut oils, as quenching media. Further investigation is required in this direction to explore the suitability of these oils for industrial heat treating applications. This application would have immense environmental and economical benefits.
    (Metal/quenchant interfacial heat flux transients during quenching in conventional quench media and vegetable oils) Prabhu, K.; Prasad, A.
    2003
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    Effect of section size and agitation on heat transfer during quenching of AISI 1040 steel
    (2007) Fernandes, P.; Prabhu, K.N.
    In the present work an attempt has been made to determine the heat flux transients during quenching of Ø28 mm × 56 mm height and Ø44 mm × 88 mm height AISI 1040 steel specimens during lateral quenching in brine, water, palm oil and mineral oil. The heat flux transients were estimated by inverse modeling of heat conduction. The variation of heat flux transients with surface temperature for different quenching media is investigated. Higher peak heat flux transients are obtained for 28 mm diameter specimen than 44 mm diameter specimen during quenching in aqueous media. However quenching with oil media shows opposite results. Agitation of quenching medium increases the peak heat flux during the quenching of steel specimen in all the quenching media. Peak hardness is obtained at the surface and with smaller diameter specimens during agitation. © 2006 Elsevier B.V. All rights reserved.
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    Heat flux transients and casting surface macro-profile during downward solidification of Al-12% Si alloy against chills
    (American Foundry Society, 2011) Prabhu, K.N.; Sharath, K.; Ramesh, G.
    Heat flux transients were estimated during downward solidificationofAl- 12%Sialloy(A413)againstaluminumand graphite chills. The thermal plot of graphite chill indicated one-dimensional heat flow in the initial stages which then changes to two-dimensional heat transfer. The heat transfer becomes one-dimensional again during the final stages of solidification. In aluminum chill, heat flow was nearly one- dimensional. Experiments were designed to verify whether the peak heat flux is an artifact of the experiment. The results clearly showed that the occurrence of the peak in the heat flux transients is not an artifact of the inverse model or the experimental technique. The macro-profile of the casting surface in contact with the chill revealed the occurrence of crests and troughs. A mechanism based on the convection within the liquid metal below the solid shell was proposed to account for the formation of wavy casting surface. Copyright © 2011 American Foundry Society.
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    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.
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    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.
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    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.
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    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.
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    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.
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    Wetting Behavior and Heat Transfer of Aqueous Graphene Nanofluids
    (Springer New York LLC barbara.b.bertram@gsk.com, 2016) Nayak, U.V.; Prabhu, K.N.
    Aqueous graphene nanofluids having concentrations 0.01, 0.1, and 0.3 vol.% were used as heat transfer media during quenching of ISO 9950 inconel alloy probe. Contact angle measurements were carried out to assess the wettability of graphene nanofluids. Nanofluids showed better wettability compared to base water with over 16% reduction in their contact angles. The cooling performance of the quench media was assessed by cooling curve analysis during quenching of an instrumented inconel probe from 860 °C into the quench medium. Recorded temperature readings showed longer vapor phase stage during quenching with nanofluids. The severity of nanofluids was found to be lower relative to water. During quenching with nanofluids, the estimated spatiotemporal heat flux transients at the metal/quenchant interface showed that more heat was removed during the vapor phase stage of cooling. The present study brings out the possibility of using stable water-graphene nanoplatelet suspensions for quench heat treatment of steel components requiring cooling severity between water and oil/polymer quenchants. © 2016, ASM International.