Journal Articles
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Item Thermal Resistance at the Polymer/Mold Interface in Injection Molding(Springer, 2022) Kamala Nathan, D.K.; Prabhu, K.N.In injection molding, the thermomechanical condition of the solidifying part inside the cavity determines the morphology developed during cooling and thus the final properties of the component. This condition is significantly affected by the thermal contact resistance (TCR) at the polymer/mold interface. TCR is one of the most significant heat transfer characteristics that affect the quality of injection-molded components. TCR values significantly influence the simulated temperature distribution of the solidifying part inside the cavity. Using incorrect TCR values affect the accuracy of the simulated results leading to defects in the molded components. Further, the overall heat transfer during injection molding is influenced by the coolant characteristics and the thermophysical properties of the mold material. This paper gives an insight into the role of thermal transport phenomenon in the injection molding process, and particularly the importance of TCR during simulation of injection molding. © 2021, The Indian Institute of Metals - IIM.Item Heat transfer and solidification behaviour of modified A357 alloy(2007) Kumar, G.; Hegde, S.; Prabhu, K.N.Al-Si alloys are subjected to melt treatment like modification to improve their mechanical properties. Non-destructive technique like thermal analysis is generally used to assess the effectiveness of melt treatment. In the present study, the behaviour of the melt treated Al-7Si-Mg alloy (A357) during solidification with or without chilling was investigated using thermal analysis. Thermal analysis and heat transfer parameters were determined. Thermal analysis parameters were affected significantly by modification and chilling. Modification treatment resulted in the increase of cooling rate, heat evolved, casting/mould interfacial heat flux and eutectic growth velocity. A theoretical model based on undercooling from the equilibrium temperature during eutectic solidification was used to predict growth velocities and eutectic grain size. The eutectic grain sizes estimated using the model and those measured from casting microstructures were found to be in good agreement. © 2006 Elsevier B.V. All rights reserved.Item Effect of section size and agitation on heat transfer during quenching of AISI 1040 steel(2007) Fernandes, P.; Prabhu, K.N.In the present work an attempt has been made to determine the heat flux transients during quenching of Ø28 mm × 56 mm height and Ø44 mm × 88 mm height AISI 1040 steel specimens during lateral quenching in brine, water, palm oil and mineral oil. The heat flux transients were estimated by inverse modeling of heat conduction. The variation of heat flux transients with surface temperature for different quenching media is investigated. Higher peak heat flux transients are obtained for 28 mm diameter specimen than 44 mm diameter specimen during quenching in aqueous media. However quenching with oil media shows opposite results. Agitation of quenching medium increases the peak heat flux during the quenching of steel specimen in all the quenching media. Peak hardness is obtained at the surface and with smaller diameter specimens during agitation. © 2006 Elsevier B.V. All rights reserved.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.Item Comparative study of heat transfer and wetting behaviour of conventional and bioquenchants for industrial heat treatment(2008) Fernandes, P.; Prabhu, K.N.An investigation was conducted to study the suitability of vegetable oils as bioquenchants for industrial heat treatment. The study involved the assessment of the severity of quenching and wetting behaviour of conventional and vegetable oil quench media. Quench severities of sunflower, coconut and palm oils were found to be greater than mineral oil. The quench severity of aqueous media is greater than oil media although their wettability is poor as indicated by their higher contact angles. A dimensionless contact angle parameter defined in this work is found to be a better parameter to compare the wetting behaviour with heat transfer. © 2007 Elsevier Ltd. All rights reserved.Item Thermal contact at solder/substrate interfaces during solidification(2009) Nyamannavar, S.; Prabhu, K.N.Heat flux transients at the solder/substrate interface during the solidification of Sn-37Pb and Sn-3.5Ag solder alloys against metallic substrates were estimated by the lumped heat capacitance model and the contact condition was assessed by scanning electronic microscopy (SEM). Copper substrates yielded maximum contact heat flux followed by brass and aluminium substrates. The SEM study in the solder/substrate interfacial region revealed the existence of a clear gap with the aluminium substrate. A conforming contact was obtained with copper and brass substrates. © 2009 Institute of Materials, Minerals and Mining.Item Heat flux transients and casting surface macro-profile during downward solidification of Al-12% Si alloy against chills(American Foundry Society, 2011) Prabhu, K.N.; Sharath, K.; Ramesh, G.Heat flux transients were estimated during downward solidificationofAl- 12%Sialloy(A413)againstaluminumand graphite chills. The thermal plot of graphite chill indicated one-dimensional heat flow in the initial stages which then changes to two-dimensional heat transfer. The heat transfer becomes one-dimensional again during the final stages of solidification. In aluminum chill, heat flow was nearly one- dimensional. Experiments were designed to verify whether the peak heat flux is an artifact of the experiment. The results clearly showed that the occurrence of the peak in the heat flux transients is not an artifact of the inverse model or the experimental technique. The macro-profile of the casting surface in contact with the chill revealed the occurrence of crests and troughs. A mechanism based on the convection within the liquid metal below the solid shell was proposed to account for the formation of wavy casting surface. Copyright © 2011 American Foundry Society.Item Effect of chemical modification of Al-Si alloys on thermal diffusivity and contact heat transfer at the casting-chill interface(2012) Prabhu, K.N.; Jayananda; Hegde, S.The heat flow during the unidirectional downward solidification of Al-7Si and Al-12Si alloys was analyzed using thermal analysis technique and inverse modeling. Chills instrumented with thermocouples were brought into contact with a small pool of liquid metal so as to minimize the effect of convection caused by pouring and temperature gradients. Modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting-chill interfacial region. The corresponding interfacial heat flux transients were also found to be higher. The thermal diffusivities of alloys were measured using a laser pulse technique and were found to be higher for modified alloys. However, the increase in the heat flux transients was attributed mainly to the improvement in the casting-chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal upon the addition of sodium. Copyright © 2012 by ASTM International.Item Heat transfer at the casting/chill interface during solidification of commercially pure Zn and Zn base alloy (ZA8)(2012) Ramesh, G.; Prabhu, K.N.Casting/chill interfacial heat transfer during solidification of commercially pure zinc and ZA8 alloy against copper, hot die steel, stainless steel and aluminiuminstrumented chills was investigated. The peak heat flux strongly depends on the thermophysical properties of chill, chill surface condition and superheat of the castingmaterial. Contact angles of alumina coatingmeasured on various substrates suggested that the adhesion of the coating material on copper chill was significantly better as compared to other chill materials. The heat flux curve in the case of coated chills is characterised by a double peak indicating remelting of the solidified casting shell. The second peak in the HTC curve is lower for high conductivity and higher for low conductivity chills as compared to the first peak. It is possible that solid shell formation and remelting occurred in the case of high thermal conductivity chills, whereas shell remelting did not happen in lower thermal conductivity chills. © 2012 W. S. Maney & Son Ltd.Item Effect of boundary heat transfer coefficient and probe section size on cooling curves during quenching(ASTM International, 2012) Ramesh, G.; Prabhu, K.N.In the present work the effect of boundary heat transfer coefficient and section size of quench probe material on cooling curves was investigated by using finite difference heat transfer based SolidCast software. Simulations were carried out at different combinations of heat transfer coefficient and quench probe diameter and thermal history at the geometric center of the probe was estimated to generate cooling curves. Simulation results show that both boundary heat transfer coefficient and quench probe diameter had a significant effect on the average cooling rate. A relationship between Grossmann quench severity (H), thermal conductivity of material, size of the probe, and average cooling rate was established. By using this model, for a known quench medium, probe size, and material it is possible to predict the average cooling rate of the probe. On the other-hand, for a given material and required cooling rate, cooling severity required from the quench media could be predicted and accordingly an appropriate quench medium can be selected. © 2012 by ASTM International.