Faculty Publications
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Item Estimation of heat transfer coefficient and reference temperature in jet impingement using solution to inverse heat conduction problem(Pleiades journals, 2019) Kadam, A.R.; Hindasageri, V.; Kumar, G.N.The heat transfer estimation in case of impinging jets has been considered by mainly steady-state techniques. The present study reveals the transient technique to characterize the impinging jets. A solution to three-dimensional inverse heat conduction problem (IHCP) is used to estimate the unknown transient surface temperature distribution at the jet impinging side (front side) from known non-impingement side (backside) transient temperature distribution. Further to estimate front side heat flux distribution, the temperature gradient close to the front surface is computed by finite difference method, and then linearity between surface heat flux and corresponding surface temperature is utilized to find out heat transfer coefficient (HTC) and the reference temperature simultaneously. To validate and establish the present technique, numerical simulations are carried out in fluent. The numerically estimated back surface temperature data is used as input to the solution to IHCP. Hot as well as cold impinging jets are characterized with the help of this solution. Along with laminar jets, turbulent jets with varying Reynolds number are considered. The inversely estimated results are compared with numerically simulated data and match is within 1%. © Springer Nature Singapore Pte Ltd. 2019.Item A numerical study on heat transfer characteristics of two-dimensional film cooling(Pleiades journals, 2019) Ademane, V.G.; Hindasageri, V.; Kadoli, R.Determination of reference temperature and heat transfer coefficient in case of three temperature problems such as film cooling is one of the fundamental tasks in the design of gas turbines. In the present work, a two-dimensional numerical simulation is carried out for flat surface with 35° angle of injection from slot in case of film cooling problem. The reference temperature, which is represented as film cooling effectiveness, and heat transfer coefficient on the flat surface for different blowing ratio are studied. Heat transfer coefficient obtained from the present simulation is compared with the experimental results from the literature and found to be matching at lower blowing ratios. Turbulence intensity is found to a major contributor in enhancing the heat transfer coefficient. There is an increase in heat transfer with the blowing ratio due to increased turbulence intensity is observed. © Springer Nature Singapore Pte Ltd. 2019.Item 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.Item 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.Item Effect of quench probe material and section size on cooling severity(2012) Ramesh, G.; Prabhu, K.N.In the present work simulation of heat transfer during quenching was carried out using finite difference heat transfer based SolidCast software. Simulation experiments were aimed to assess the effect of boundary heat transfer coefficient, quench probe material and its size on the cooling curve of the quench probe at geometric centre. Simulation results show that all these parameters had a significant effect on the simulated cooling curve of the probe. For a material, there is a critical diameter above which increase in cooling rate at the centre of the probe is negligible and this critical diameter depends on the thermal conductivity of the material used for quenching. A quenching system with a D/h ratio value of greater 0.000075m3K/W has no significant effect on the cooling rate at the centre of the probe. A simple quantitative model which correlates average cooling rate, probe material, section size and cooling severity of quench media was proposed. The results of the model is independent of characteristics of quench probe used in assessment of cooling severity and could be used effectively for selection of quenchants during heat treatment. Copyright © 2012 ASM International® All rights reserved.Item Synergestic approach for the simultaneous estimation of heat transfer coefficient and heat flux using fin from steady state heat transfer experiments(Begell House Inc., 2015) Kumar, H.; Kumar, S.; Srinivasa Sagar, K.; Gnanasekaran, N.This paper reports simultaneous estimation of heat transfer coefficient and heat flux from natural convection fin heat transfer. The experimental setup contains rectangular mild steel fin of dimensions (250×154×6 mm) and an aluminium base plate of dimensions (250×150×8 mm). A slot of 4mm depth is created at the center of aluminium plate along its length (250mm) and mild steel fin is press fitted into this slot. Eighteen calibrated K-type thermocouples are used to record the temperature of the base plate and the fin. Beneath the base plate, a heater is placed with the dimensions of the base plate. To restrict the heat loss, bottom and sides of the heater are insulated with glass wool. Steady state experiments are carried out for different heat input. The problem considered is an inverse problem where in heat transfer coefficient and heat flux can be estimated simultaneously for the given temperature data from experiments/surrogate data. The forward model uses Asymptotic Computational Fluid Dynamics (ACFD) to obtain temperature distribution for the assumed inputs (heat transfer coefficient and heat flux). A powerful Markov Chain Monte Carlo method along with Metropolis-Hastings algorithm is used to minimize the objective function. Finally, the estimated values of heat transfer coefficient and heat flux are reported in terms of mean. © 2021, Begell House Inc. All rights reserved.Item Casting/mould interfacial heat transfer during solidification in graphite, steel and graphite lined steel moulds(Maney Publishing maney@maney.co.uk, 2003) Prabhu, K.; Mounesh, H.; Suresh, K.M.; Ashish, A.A.Heat flow between the casting and the mould during solidification of three commercially pure metals, in graphite, steel and graphite lined steel moulds, was assessed using an inverse modelling technique. The analysis yielded the interfacial heat flux (q), heat transfer coefficient (h) and the surface temperatures of the casting and the mould during solidification of the casting. The peak heat flux was incorporated as a dimensionless number and modeled as a function of the thermal diffusivities of the casting and the mould materials. Heat flux transients were normalised with respect to the peak heat flux and modeled as a function of time. The heat flux model proposed was used to estimate the heat flux transients during solidification in graphite lined copper composite moulds.Item Heat transfer during quenching and assessment of quench severity-A review(2009) 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.Item Nanoquenchants for industrial heat treatment(2008) Prabhu, K.N.; Fernades, P.The present work outlines the possibility of using nanofluids for industrial heat treatment. Development of nanoquenchants having (i) high quench severity for enhancement of heat transfer for thick sections with low quench sensitivity and (ii) low cooling severity for thin sections with high quench sensitivity would be extremely useful to the heat treating community. The temperature dependent heat transfer coefficient and the wettability of the medium are the two important parameters that can be used to characterize a nanoquenchant to assess its suitability for industrial heat treatment. © 2007 ASM International.