Faculty Publications

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Author: search.filters.author.Prabhu, K.N.Subject: search.filters.subject.Heat transfer characteristics

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    Comparison of Grossmann and lumped heat capacitance methods for assessment of heat transfer characteristics of quench media
    (2011) Prabhu, K.N.; Ali, I.
    The suitability of Grossmann and lumped heat capacitance (LHC) methods for estimation of quench severity of nanofluids, brine solutions and a laboratory detergent based medium was investigated. The study involved the assessment of the effect of section thickness of the probe on heat transfer coefficients for different quench media. Computer aided cooling curve analysis during quenching of type 304 stainless steel probes was carried out. The measured thermal history data were used to estimate heat transfer coefficients by Grossmann and LHC methods. The LHC method based on a 10 mm diameter stainless steel probe was found to be applicable for characterising media having quench severity less than 20 m-1. Although Grossmann method is based on the concept of average heat transfer coefficient, it can be used for quench media having varying severity of quenching. Grossmann method is found to be more sensitive to the effect of section thickness on heat transfer. © 2011 IHTSE Partnership.
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    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.
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    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. KG
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    Assessment of PCM-container interfacial heat transfer using a hot/cold probe technique
    (John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2019) Sudheer, R.; Prabhu, K.N.
    A novel technique for assessing heat transfer characteristics of salt-based phase change materials (PCM) was proposed here. The method is based on solution to inverse heat conduction problem. Nanoparticles (Graphite, Graphene, and multi wall carbon nanotube [MWCNT]) were dispersed in the PCM (KNO3) to assess their respective influence on heat transfer in the PCM. Graphite added PCM offered highest heat flow values and heating rates, while the pure salt-PCM offered the least. The probe material had a significant influence on the heat transfer rates at the PCM-probe interface. © 2018 Wiley Periodicals, Inc.
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    The effect of nanocoatings on critical heat flux (CHF) under pool boiling conditions
    (ASTM International, 2021) Reddy, S.; Prabhu, K.N.; Nayak, U.V.
    The effect of nanomaterial coating on heat transfer characteristics of a copper substrate during pool boiling with distilled water (>99.9 %) was studied. The peak on the pool boiling curve between nucleate and transition boiling is termed the critical heat flux. Multi-walled carbon nanotubes and graphene were used to obtain coatings on the copper substrate. Experiments were carried out at atmospheric pressure. The results showed enhanced critical heat flux for the coated substrates. Graphene-coated copper showed the highest critical heat transfer characteristics compared with that on bare and multi-walled carbon nanotube-coated substrates. The study has significant implications for the enhancement of heat transfer during quench heat treatment. © © 2021 by ASTM International.