Faculty Publications
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Item Effect of addition of aluminum nanoparticles on cooling performance and quench severity of water during immersion quenching(2012) Ramesh, G.; Prabhu, K.N.In the present work, the effect of the addition of aluminum nanoparticles in concentrations varying from 0.001 to 0.5 vol. % on the cooling performance and quench severity of water during immersion quenching is investigated. The results of cooling curve analyses show that an increase in nanoparticle concentration increased the cooling rates at critical temperatures up to 0.05 vol. % and decreased them thereafter. The transition from the vapor blanket stage to the nucleate boiling stage was also altered by quenching in nanofluids. A finite difference heat transfer program was employed to generate cooling curves at different values of heat transfer coefficient from thermo-physical properties of the quench probe material. A Grossmann H quench severity versus cooling rate curve was established, and from this curve, the H factors of prepared nanofluids were estimated. An increase in nanoparticle concentration up to 0.05 vol. %resulted in an increase of the H value of water from 63 m 1 to 93 m 1, and any further increase in the concentration of nanoparticles resulted in a decrease in H. The results suggest both the enhancement and the deterioration of the cooling performance of water by the addition of aluminum nanoparticles. Copyright © 2012 by ASTM International.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 Effect of Polymer Concentration on Wetting and Cooling Performance During Immersion Quenching(Springer Boston, 2016) Ramesh, G.; Prabhu, K.N.The effect of varying concentrations (0 to 100 vol pct) of glycol polymer solution on wetting kinetics, kinematics, and cooling performance during immersion quenching was studied by using goniometry, online video imaging, and cooling curve analysis techniques. An increase in concentration of the polymer solution resulted in improved wettability and accelerated spreading kinetics of the quench medium. The quench medium showed medium-fast-nonuniform, fast-uniform, slow-uniform, explosive/rapid, repeated, and slow-nonuniform rewetting phenomena depending on the concentration of the polymer solution. The collapse of the vapor film was by an instantaneous rupture process in the quench medium containing more water and by nucleation of bubbles caused by the selective rupture process in the quench medium enriched with polymer. The quench medium consisting of an equal amount of water and polymer showed an explosive collapse of the vapor film on the quench probe surface. The nature of the wetting front was uniform with polymer quench media except at 100 vol pct concentration of polymer quenchant. There was enhancement in the cooling performance of the quench medium, which was enhanced for a lower volume concentration of the polymer solution. However, an increase in the concentration of the polymer resulted in a decreased cooling performance. The cooling of the probe was more uniform with polymer quenchants (5 to 25 vol pct), which exhibited fast and uniform rewetting. Polymer quenchants (75 to 100 vol pct) that exhibited repeated and slow-nonuniform rewetting showed large variation in heat transfer over the quench probe surface. © 2015, The Minerals, Metals & Materials Society and ASM International.Item Wetting and Cooling Performance of Vegetable Oils during Quench Hardening(John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2016) Ramesh, G.; Prabhu, K.N.Wetting kinetics, kinematics, and cooling performance of vegetable oils (sunflower, gingelly, palm, and coconut oils) during quenching of Inconel 600 probe were studied using goniometry, online video imaging, and cooling curve analysis. The results were compared with a conventional mineral oil quench medium. Improved wettability was obtained for vegetable oils with lower viscosity. Cooling curve analyses showed three stages of cooling for both mineral and vegetable oils. Video imaging of the quenching process and differential scanning calorimetry analysis confirmed that the first stage of cooling was caused by the formation of vapor film in mineral oil and due to the occurrence of a heated liquid layer around the quench probe surface in vegetable oils. Vegetable oils showed continuous boiling phenomenon during the convective cooling stage of quenching. The cooling performance of vegetable oils was found to depend on the concentration of mono-unsaturated fatty acid. The heat extracting capability of vegetable oils with lower mono-unsaturated fatty acid oils was found to be higher. However, no correlation was observed between fatty acid composition and uniformity of heat transfer. When compared to mineral oil quenching, vegetable oil quenching produced faster wetting kinematics and better cooling performance. © 2016 Wiley Periodicals, Inc.Item Effect of Bath Temperature on Cooling Performance of Molten Eutectic NaNO3-KNO3 Quench Medium for Martempering of Steels(Springer Boston, 2017) Pranesh Rao, K.M.; Prabhu, K.N.Martempering is an industrial heat treatment process that requires a quench bath that can operate without undergoing degradation in the temperature range of 423 K to 873 K (150 °C to 600 °C). The quench bath is expected to cool the steel part from the austenizing temperature to quench bath temperature rapidly and uniformly. Molten eutectic NaNO3-KNO3 mixture has been widely used in industry to martemper steel parts. In the present work, the effect of quench bath temperature on the cooling performance of a molten eutectic NaNO3-KNO3 mixture has been studied. An Inconel ASTM D-6200 probe was heated to 1133 K (860 °C) and subsequently quenched in the quench bath maintained at different temperatures. Spatially dependent transient heat flux at the metal–quenchant interface for each bath temperature was calculated using inverse heat conduction technique. Heat transfer occurred only in two stages, namely, nucleate boiling and convective cooling. The mean peak heat flux (qmax) decreased with increase in quench bath temperature, whereas the mean surface temperature corresponding to qmax and mean surface temperature at the start of convective cooling stage increased with increase in quench bath temperature. The variation in normalized cooling parameter t85 along the length of the probe increased with increase in quench bath temperature. © 2017, The Minerals, Metals & Materials Society and ASM International.Item A Comparative Study on Cooling Performance of Hot Oil and Molten Salt Quench Media for Industrial Heat Treatment(Springer, 2020) Pranesh Rao, K.M.; Prabhu, K.N.The present work presents a comprehensive comparative study on the cooling performance of hot oil and molten 54%KNO3-7%NaNO3-39%NaNO2 eutectic mixture quench media. The study was conducted using a cylindrical Inconel probe of 12.5 mm diameter and 60 mm length. Cooling curves at different locations in the probe were acquired and were subsequently used to calculate spatially dependent transient heat flux at the metal/quenchant interface. The heat extraction mechanism in hot oil and NaNO2 eutectic mixture was found to be different. Heat transfer occurred in two stages, namely boiling stage and convective cooling stage during quenching in molten NaNO2 eutectic mixture. In the case of hot oil, apart from these two stages, third stage of cooling, namely vapor blanket stage, was observed. A detailed study was conducted to compare the magnitude and uniformity of heat extraction during each stage of quenching. Molten salt offered a higher cooling rate and more spatial uniform cooling as compared to that obtained in hot oil quench medium. The non-uniformity in surface temperature during boiling stage in Inconel probe was ten times lower in molten salt medium as compared to that observed in the hot oil medium. However, the non-uniformity in surface temperature during convective cooling stage in both the media were comparable. Based on the distribution of characteristic cooling time (t85) calculated in quenched Inconel probe, higher and uniform hardness distribution is predicted in steel parts quenched in molten NaNO2 eutectic mixture media as compared to that in hot oil. © 2020, ASM International.Item Assessment of Cooling Performance of Neem Oil for Distortion Control in Heat Treatment of Steel(Springer, 2020) Pranesh Rao, K.M.; Prabhu, K.N.Growing concerns over the hazardous impact of mineral oil-based industrial quench media on human health and the environment have forced researchers to seek renewable and non-hazardous alternatives. Non-edible vegetable oil-based quench media are perceived to be a potential replacement for mineral-based industrial quench media. The present work focuses on assessing the cooling performance of neem oil as compared to commercial hot oil quench media. Inconel and steel probes were used to characterize the cooling performance of these quench media maintained at bath temperatures 100 °C, 150 °C and 200 °C. The heat extraction rates and uniformity of heat extraction in Inconel probes quenched in neem oil were observed to be substantially higher at all bath temperatures. The hardness of AISI 52100 steel probe quenched in neem oil at all bath temperatures was observed to be higher. The pearlitic microstructure was observed in the steel probe quenched in hot oil maintained at 200 °C bath temperature. In contrast to this, a mixture of bainite, martensite and carbide was observed in case of steel probes quenched in neem oil maintained at 200 °C. Oxidation experiments revealed that neem oil is susceptible to an increase in viscosity due to oxidation. An increase in the viscosity by about 15% was observed in the case of neem oil as compared to only 4% increase in viscosity of hot oil. However, after an initial increase, the viscosity of neem oil stabilized and further no significant change in viscosity due to oxidation were observed. Oxidation had no significant effect on the cooling performance hot neem oil quench medium, and thus, it can be considered as an effective replacement for hot oil. © 2020, ASM International.Item Reprocessed waste sunflower cooking oil as quenchant for heat treatment(Elsevier Ltd, 2020) Prathviraj, M.P.; Samuel, A.; Prabhu, K.N.The growing concern to minimize the use of petroleum derived mineral oil in heat treatment industries has led to the search for alternative eco-friendly quenchants. Although vegetable oils seem to be a viable option, the higher cost and inferior thermal and oxidation stability have limited their application in the heat treatment industry. The reuse of waste cooking oils for industrial heat treatment would not only make quenchants cost-efficient but also environment friendly. In this study, the cooling performance of waste sunflower cooking oil was assessed and compared with that of unused sunflower cooking and mineral oils. The waste sunflower oil was made suitable for quenching by cleaning and chemical treatment. The experiment to assess the suitability of reprocessed oil for quenching was conducted using an Inconel 600 standard probe according to ISO 9950 and ASTM D 6200 standards. The thermal history acquired while quenching of the probe was used to estimate the surface heat flux transients. The results indicated that the chemically treated waste sunflower cooking oil had a higher cooling performance than that of unused sunflower and the mineral oils. A good agreement was found between the heat flux transients and hardness data obtained with the quenched AISI 4140 steel probe. The simulation of temperature and hardness distribution indicated more uniformity along the length of the probe indicating more uniform cooling with chemically treated waste sunflower cooking oil. © 2020 Elsevier LtdItem The Effect of Thermal Quench Cycling on the Stability and Heat Transfer Characteristics of Transesterified-Epoxidized Used Cooking Oil Blended Quench Medium(Springer, 2024) Samuel, A.; Prabhu, K.N.Mineral oil is a widely used quench media in the heat treatment industries. They are derived from petroleum crude oil, and are toxic, and non-biodegradable. Therefore, in order to minimize the use of mineral oil, the fatty acid methyl esters (FAME) derived from the used cooking oil through the transesterification process can be blended with mineral oil. However, due to the high amount of unsaturation, blending of FAME in mineral oil would decrease the thermal-oxidative stability of the oil. Therefore, in the present work, to improve the stability of the mineral/FAME blend quenchant, the unsaturation in the FAME is decreased through epoxidation. The stability of epoxidized FAME/mineral blended oil is assessed by thermogravimetric analysis and thermal quench cycling. The quench cycles were performed using an ISO 9950 Inconel 600 standard probe. The viscosity and cooling performance of the oil were assessed periodically after the 1st, 10th, 50th, and 100th quench cycle. Investigation of cooling performance was performed by carrying out cooling curve analysis and estimating metal/quenchant interfacial heat flux tranisents. The results indicated that the thermal stability of the blend quenchant was improved with the epoxidation of FAME. The relative increase in viscosity was lower for blend quenchants than that for the mineral oil. The epoxidized FAME/mineral oil blend showed comparable cooling performance as that of mineral oil as the number of quench cycles were increased. © ASM International 2023.