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 Understanding the role of modeling and simulation in pyrolysis of biomass and waste plastics: A review(Elsevier Ltd, 2022) Ramesh, R.; Suriapparao, D.V.; Sankar Rao, C.S.; Kumar, T.H.The valorization of resources from biomass and plastic waste using thermochemical platforms is an innovative approach. Pyrolysis is thermochemical technology that is very effective in the production of fuels and chemical intermediates. It's conducted by conventional heating, solar heating, and microwave-controlled heating. Compared to conventional pyrolysis, microwave-assisted pyrolysis is more advantageous. The temperature distribution, mass transfer, and heat transfer rates depend on the operation mode through process parameters. The optimization of the pyrolysis process is crucial for scale-up. Computer-assisted modeling and simulation techniques help to develop suitable configurations and experimental methods for better efficiencies. Modeling allows the identification of optimum operating parameters and understanding of transportation mechanisms involved in pyrolysis. Modeling, simulation, and optimization are ideally suited to understanding and analyzing the complex stages of pyrolysis. This review provides insight into existing heat, mass, and momentum transfer models for pyrolysis. The effects of transport properties on pyrolysis are dealt with. © 2022 Elsevier LtdItem The evaporative drying of a two-dimensional rectangular brick is studied numerically as a conjugate problem. The conservation equations for the solid are obtained using the continuum approach. The Navier-Stokes equations have been employed for obtaining the flow field and the corresponding flow solutions are used for predicting the drying behavior of the brick. The predictions of temperature and moisture content show that the leading edge dries faster compared to other sides of the solid. The full two-dimensional solutions differ considerably from the solutions based on heat and mass transfer through the boundary layers over the top surface. Average heat and mass transfer coefficients appropriate to the conjugate problem have been defined, based on constant temperature and moisture differentials between the solid and the ambient. The corresponding Nusselt and Sherwood number values indicate that analogy does not exist between heat and mass transfer, until the entire brick reaches wet bulb conditions. Free convection effects on drying are also studied for some initial period for low Reynolds number. Due to the influence of buoyant forces imparted by gravity, the overall drying rate has improved. © 2001 Elsevier Science Ltd. All rights reserved.(Elsevier Ltd, A theoretical model of brick drying as a conjugate problem) Murugesan, K.; Suresh, H.N.; Seetharamu, K.N.; Aswatha Narayana, P.A.; Sundararajan, T.2001Item Item Heat transfer at the metal/chill interface during solidification of commercially pure aluminium square bar castings with cast iron chill at one end was investigated. Experiments were carried out for different chill thicknesses and superheats. The inner surface temperature of the chill initially was found to increase at a faster rate for higher superheats. The effect of chill thickness on the inner surface temperature of the chill was observed only after the heat from the solidifying casting had sufficient time to diffuse to the interior of the chill material. Inverse analysis of the non-linear one-dimensional Fourier heat conduction equation indicated the occurrence of peak heat flux at the end of filling of the mould. The effect of superheat on heat flux was minimal after filling. However, the effect of chill thickness had a significant effect on the heat flux after the occurrence of peak heat flux. Higher heat flux transients were estimated for castings poured at higher superheats. The corresponding heat transfer coefficients were also estimated and reported. The heat flux model presented in this work can be used for determination of casting/chill interfacial heat flux as a function of chill thickness and superheat. These heat flux transients could be used as boundary conditions during numerical simulation of solidification of the casting. © 2002 Elsevier Science B.V. All rights reserved.(Effect of chill thickness and superheat on casting/chill interfacial heat transfer during solidification of commercially pure aluminium) Gafur, M.A.; Haque, M.N.; Prabhu, K.2003Item For successful modelling of the solidification process, a reliable heat transfer boundary condition data is required. These boundary conditions are significantly influenced by the casting and mould parameters. In the present work, the effect of sodium modification melt treatment on casting/chill interfacial heat transfer during upward solidification of an Al-13% Si alloy against metallic chills is investigated using thermal analysis and inverse modelling techniques. In the presence of chills, 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 and electrical conductivities are also found to be higher. This is attributed to (i) improvement in the casting/chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal on addition of sodium and (ii) increase in the electronic heat conduction in the initial solidified shell due to change in the morphology of silicon from a acicular type to a fine fibrous structure and increase in the ratio of the modification rating to the secondary dendrite arm spacing. © 2003 Elsevier B.V. All rights reserved.(Elsevier BV, Effect of modification melt treatment on casting/chill interfacial heat transfer and electrical conductivity of Al-13% Si alloy) Prabhu, K.; Ravishankar, B.N.2003Item Heat transfer during the solidification of an Al-Cu-Si alloy (LM4) and commercial pure tin in single steel, graphite, and graphite-lined metallic (composite) molds was investigated. Experiments were carried out at three different superheats. In the case of composite molds, the effect of the thickness of the graphite lining and the outer wall on heat transfer was studied. Temperatures at known locations inside the mold and casting were used to solve the Fourier heat conduction equation inversely to yield the casting/mold interfacial heat flux transients. Increased melt superheats and higher thermal conductivity of the mold material led to an increase in the peak heat flux at the metal/mold interface. Factorial experiments indicated that the mold material had a significant effect on the peak heat flux at the 5% level of significance. The ratio of graphite lining to outer steel wall and superheat had a significant effect on the peak heat flux in significance range varying between 5 and 25%. A heat flux model was proposed to estimate the maximum heat flux transients at different superheat levels of 25 to 75°C for any metal/mold combinations having a thermal diffusivity ratio (?R) varying between 0.25 and 6.96. The heat flow models could be used to estimate interfacial heat flux transients from the thermophysical properties of the mold and cast materials and the melt superheat. Metallographic analysis indicated finer microstructures for castings poured at increased melt superheats and cast in high-thermal diffusivity molds.(Effect of superheat, mold, and casting materials on the metal/mold interfacial heat transfer during solidification in graphite-lined permanent molds) Prabhu, K.; Suresha, K.M.2004Item Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell, which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall thickness and increase in the casting thickness. © ASM International.(Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds) Prabhu, K.; Chowdary, B.; Venkataraman, N.2005Item Heat transfer during quenching of modified and unmodified gravity die-cast A357 cylindrical bars(2006) Prabhu, K.; Hemanna, P.Heat transfer during quenching of chill-cast modified and unmodified A357 Al-Si alloy was examined using a computer-aided cooling curve analysis. Water at 60°C and a vegetable oil (palm oil) were used as quench media. The measured temperatures inside cylindrical probes of the A357 alloy were used as inputs in an inverse heat-conduction model to estimate heat flux transients at the probe/quenchant interface and the surface temperature of the probe in contact with the quench medium. It was observed that modified alloy probes yielded higher cooling rates and heat flux transients. The investigation clearly showed that the heat transfer during quenching depends on the casting history. The increase in the cooling rate and peak heat flux was attributed to the increase in the thermal conductivity of the material on modification melt treatment owing to the change in silicon morphology. Fine and fibrous silicon particles in modified A357 probes increase the conductance of the probe resulting in higher heat transfer rates. This was confirmed by measuring the electrical conductivity of modified samples, which were found to be higher than those of unmodified samples. The ultrasound velocity in the probes decreased on modification. ©ASM International.Item Effect of section thickness and modification on thermal analysis parameters of A357 alloy(2006) Hegde, S.; Kumar, G.; Prabhu, K.Thermal analysis technique relies on the cooling curve obtained when the sample is cooled in a sampling cup. This may not represent the cooling behaviour of the real casting. The microstructure developed during solidification depends not only on the nucleation and modification potential of the melt but also on the thermal gradient imposed during solidification by the mould. The factors affecting the thermal gradient are the mould material and casting section thickness. In the present investigation the effect of modification melt treatment, cooling rate and casting section thickness on the thermal analysis parameters of A357 alloy was studied. It is found that the dimensionless heat flux parameter is high for small section thickness castings. The metal/mould interfacial heat flux is high in a copper mould. Thermal analysis parameters of A357 alloy are found to be affected significantly by the combined action of modification, chilling and section thickness. © 2006 W. S. Maney & Son Ltd.