Faculty Publications
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Publications by NITK Faculty
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Item 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.Item Carbonated aqueous media for quench heat treatment of steels(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Nayak, U.V.; Pranesh Rao, K.M.P.; Pai, M.A.; Prabhu, K.N.Distilled water and polyalkylene glycol (PAG)-based aqueous quenchants of 5 and 10 vol.% with and without carbonation were prepared and used as heat transfer media during immersion quenching. Cooling curves were recorded during quenching of an inconel 600 cylindrical probe instrumented with multiple thermocouples. It was observed that the vapor stage duration was prolonged and the wetting front ascended uniformly for quenching with carbonated media. The cooling data were analyzed by determining the critical cooling parameters and by estimating the spatially dependent probe/quenchant interfacial heat flux transients. The study showed significantly reduced values of heat transfer rate for carbonated quenchants compared to quenchants without carbonation. Further, the reduction was more pronounced in the case of PAG-based carbonated quenchants than carbonated distilled water. The results also showed the dependence of heat transfer characteristics of the carbonated media on polymer concentration. The effect of quench uniformity on the microstructure of the material was assessed. © 2016, ASM International.Item Effect of section thickness on heat transfer during quenching in vegetable oils(ASTM International, 2018) Nayak, U.V.; Prabhu, K.N.In the present work, mineral, sunflower, karanja, and neem oil were used as quench media. 304 stainless steel probes with diameters of 25 mm and 50 mm were quenched in these oils to assess the effect of section diameter on heat transfer during quenching. Cooling curve analysis was carried out by instrumenting the probes at various locations with thermocouples. The heat extraction ability of oil quench media was quantified using an inverse heat conduction method. Thermal data and the predicted hardness values showed the suitability of nonedible vegetable oils as potential quenchants to heat treat steels. The predicted hardness was higher during quenching in karanja oil compared to other oil media. © © 2018 by ASTM International.Item Heat transfer during quenching of inconel probe in non-edible vegetable oils; Wärmeübertragung während des Abschreckens der Inconel-Sonde in nicht essbaren Pflanzenölen(Carl Hanser Verlag Kolbergerstrasse 22 Munchen D-81679, 2018) Nayak, U.V.; Prabhu, K.N.Non-edible vegetable oils of Karanja and neem were used as quench media in the present investigation. The cooling characteristics of quenchants were obtained using Inconel 600 alloy probe and were compared with that of a fast-quenching mineral oil quench medium. Spatiotemporal heat flux was estimated using inverse heat conduction method. Heat removed from the probe during quenching showed higher and faster heat extraction by karanja oil quench medium compared to the mineral oil. Heat transfer characteristics of neem oil were comparable with the mineral oil. Rewetting time and temperature of vegetable oils were found to be higher than that of the mineral oil. © Carl Hanser Verlag GmbH & Co. KGItem Quench cooling performance-hardness correlation for AISI 1045 and 1090 steels(ASTM International, 2019) Nayak, U.V.; Prabhu, N.Heat transfer and microstructure evolution during quenching of AISI 1045 and 1090 steels in vegetable oils was investigated. To simulate the industrial quench heat treatment, reference probes made of medium and high carbon steels were quenched, and heat flux transients were estimated by taking into account the phase transformation. The cooling curves obtained with reference probes made from AISI 1045 and AISI 1090 steels showed kinks indicating enthalpy change accompanied with phase transformations during continuous cooling. This was reflected in the estimated heat flux curves. The section thickness effect on heat flux transients was examined by using probes of diameters 25 mm and 50 mm. The cooling rates measured at various locations across the section diameter of reference probes were related to the hardness using the quench factor technique. The heat transfer characteristics of the quench media, the evolved microstructure, and the resulting hardness were in complete agreement. © 2019 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.