Conference Papers

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Author: search.filters.author.Prabhu, K.N.Subject: search.filters.subject.Wetting

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    Severity of quenching and kinetics of wetting of nanofluids and vegetable oils
    (ASTM International, 2010) Jagannath, V.; Prabhu, K.N.
    In the present work, the suitability of vegetable oil blends with mineral oil and alumina based nanofluids as quench media for industrial heat treatment was investigated. Sunflower oil, palm oil, and mineral oil were used for preparing the blends. Alumina based nanofluids of varying concentrations ranging from 0.01-4 % were used. The size of alumina particles was about 50 nm. The severity of quenching and heat transfer coefficients were estimated during quenching of copper probes. Heat transfer coefficients were estimated using a lumped heat capacitance model. The static contact angle was measured on copper substrates having a surface texture similar to the probes used for estimation of heat transfer coefficients. A dynamic contact angle analyzer was used for this purpose. The measured contact angles of nanofluids on copper were high compared to oils, indicating poor wetting by quench media that are polar in nature. Wetting characteristics had a significant effect on heat transfer coefficients estimated during quenching. Copyright © 2009 by ASTM International.
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    Heat transfer during quenching and assessment of quench severity - A review
    (ASTM International, 2010) Prabhu, K.N.; Fernandes, P.
    In the heat treatment of steel, quenching is done to prevent ferrite or pearlite formation and allows formation of bainite and martensite. For a particular grade of steel, the effectiveness of quenching depends on the cooling characteristics of the quenching medium. The cooling rate is not a constant throughout the quenching process; instead it varies depending upon the various stages that occur during the quenching process. Knowledge of heat transfer during various stages of quenching and kinetics of wetting of the quench medium is fundamental to the understanding of the relationship between material, quench medium, microstructure, and properties. In this paper the characteristics of various quench media, the effect of process parameters on quenching, mechanisms of thermal transport, methods of assessing severity of quenching, and techniques of estimation of heat transfer coefficients are reviewed. An attempt is also made to highlight the importance of wetting kinetics of liquid media on quenching. Copyright © 2009 by ASTM International.
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    Wetting characteristics of sn-0.7cu lead-free solder alloy on copper substrates
    (Trans Tech Publications Ltd ttp@transtec.ch, 2012) Satyanarayan, S.; Prabhu, K.N.
    In the present work, the effect of surface texture on wetting characteristics of lead-free solder Sn-0.7Cu on copper substrates have been investigated at 298°C. The wetting tests were carried out using FTA 200 (First Ten Angstrom) dynamic contact angle analyzer. The surface texture of copper substrate significantly affected the wetting properties of Sn-0.7Cu solder alloy. Contact angles of about 30° were obtained on Cu substrate having smooth surface texture (Ra = 0.0155μm). On other hand contact angles on rough copper surface texture (Ra = 1.1194μm) were reduced to 20°. The contact angles decreased with increasing surface texture of Cu substrate. For rough Cu substrate, it seems that the solder atoms dissolve into the substrate in the time period of 200-600s. © (2012) Trans Tech Publications.
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    Wetting behavior of lead-free solders on copper substrates
    (Institution of Engineering and Technology jbristow@theiet.org, 2013) Satyanarayan, S.; Prabhu, K.N.
    The effect of substrate surface roughness on the wetting behavior of Sn-0.7Cu and Sn-0.3Ag-0.7Cu solder alloys on copper (Cu) substrates was investigated. The contact angles of both solder alloys decreased with increase in substrate surface roughness. The exponential power law (EPL), φ = exp (-Kτn), was used to model the relaxation behaviour of solders. Solder spreading kinetics was successfully represented by the (EPL). EPL parameters (K and n) alloy decreased with an increase in surface roughness. Spreading of solder alloys on both substrates exhibited capillary, gravity and viscous regimes. High spreading rates in the capillary regime, moderate in gravity regime and almost constant rates in viscous regimes were observed.
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    Determination of multiple heat flux transients during quenching of inconel 600 probe
    (ASM International joanne.miller@asminternational.org, 2013) Ramesh, G.; Prabhu, K.N.
    The time temperature data at axial and radial locations were measured during immersion quenching oflnconel 600 probes in a mineral oil quench medium. The temperature data and thermo-physical properties were used as input to an inverse heat conduction model for estimating spatially dependent heat flux transients. The estimated temperature data agreed very well with measured temperature data for increasing number of unknown surface heat flux components. The peak heat flux value decreased to a minimum and then increased to a high value in the axial direction. The inverse analysis indicated non uniform nature of wetting front and boiling of mineral oil on the quench probe surface resulting in large temperature gradients within the quench probe. The present work clearly indicates spatial dependence of boundary heat flux transients even for a simple cylindrical probe and the need for their estimation during quenching.