Faculty Publications

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Inverse Estimation of Interfacial Heat Transfer Coefficient During the Solidification of Sn-5wt%Pb Alloy Using Evolutionary Algorithm
(Pleiades journals, 2019) Vishweshwara, P.S.; Gnanasekaran, N.; Mahalingam, M.
The study of the interfacial heat transfer coefficient (IHTC) is one of the major concerns during solidification of casting. In order to find out the IHTC at the metal–mold interface, a one dimensional transient heat conduction model is numerically investigated during horizontal directional solidification of Sn–5wt%Pb alloy. The forward model is solved using explicit finite difference method to obtain the exact temperatures for the known boundary conditions. The estimation of the unknown IHTC is attempted using Particle Swarm Optimization (PSO) as an inverse approach along with Bayesian framework. In order to prove the robustness of the proposed methodology, the estimation is accomplished for the simulated measurements. The simulated measurements are then added with noise to replicate the experimental data. The present approach not only minimizes the difference between simulated and measured temperatures but also takes in to account “a priori” information about the unknown parameters. © 2019, Springer Nature Singapore Pte Ltd.
Inverse modeling of heat transfer with application to solidification and quenching
(2002) Prabhu, K.N.; Ashish, A.A.
The inverse modeling of heat transfer involves the estimation of boundary conditions from the knowledge of thermal history inside a heat conducting body. Inverse analysis is extremely useful in modeling of contact heat transfer at interfaces of engineering surface during materials processing. In the present work, the one-dimensional transient heat conduction equation was inversely modeled in both cartesian as well as cylindrical coordinates. The model is capable of estimating heat flux transients, chill surface temperature, and total heat flow from the source to the sink for an input of thermal history inside the sink. The methodology was adopted to solve boundary heat transfer problems inversely during solidification and quenching. The response of the inverse solution to measured sensor data was studied by carrying out numerical experiments involving the use of varying grid size and time steps, future temperatures, and regularization techniques.
Experimental models for assessment of interfacial heat transfer in dip soldering
(2010) Nyamannavar, S.; Prabhu, K.N.
The success of a numerical simulation for solder solidification during soldering processes depends on an accurate knowledge of heat transfer phenomenon at the solder/substrate interface. Two experimental setups were designed to study the interfacial heat transfer at solder/substrate interface. In the first method, a cylindrical probe of substrate material was dipped in liquid solder and solder was allowed to solidify around the metal probe. In the second method the test probe was dipped in the bulk solder liquid of sufficiently large quantity and allowed to attain the surrounding solder liquid temperature. Temperature at the center of the probe was measured using thermocouple. Heat flux transients at the surface of the probe were estimated by lumped heat capacitance method. SEM study at the solder/substrate interfacial region for experiments of solidifying solder around the test probe revealed the existence of a clear gap with aluminum substrate. A conforming contact was obtained with copper substrate. The nature of heat flux transients was found to be different in two experiments. Â© (2010) Trans Tech Publications.
Assessment of heat transfer during solidification of Al-22% Si alloy by inverse analysis and surface roughness based predictive model
(Springer India sanjiv.goswami@springer.co.in, 2012) Jayananda; Prabhu, K.N.
Heat flux transients were estimated during unidirectional downward solidification of Al-22% Si alloy against copper, die steel and stainless steel chills. The chill instrumented with thermocouples was brought into contact with the liquid metal so as to avoid the effect of convection associated with the pouring of liquid metal. Heat flux transients were estimated by solving the inverse heat conduction problem. Higher thermal conductivity of chill material resulted in increased peak heat flux at the metal/ chill interface. Peak heat flux decreased when 100 lm thick alumina coating was applied on the chill surface. The lower thermal conductivity of alumina based coating and the presence of additional thermal resistance decreases the interfacial heat transfer. For uncoated chills, the ratio of the surface roughness (R a) of the casting to chill decreased from 6.5 to 0.5 with decrease in the thermal conductivity of the chill material. However when coating was applied on the chill, the surface roughness ratio was nearly constant at about 0.2 for all chill materials. The measured roughness data was used in a sum surface roughness model to estimate the heat transfer coefficient. The results of the model are in reasonable agreement with experimentally determined heat-transfer coefficients for coated chills.
Estimation of interfacial heat transfer coefficient for horizontal directional solidification of Sn-5wt%pb alloy using genetic algorithm as inverse method
(Springer Verlag, 2019) Vishweshwara, P.S.; Gnanasekaran, N.; Arun, M.
In the present work, a one-dimensional transient solidification heat transfer problem is solved to determine the unknown interfacial heat transfer coefficient (IHTC) at the moldâ€“metal interface using genetic algorithm (GA), an evolutionary and widely known algorithm, as an inverse method. The forward model is numerically solved to obtain the exact temperatures by incorporating the appropriate correlation for the IHTC that varies with time. In order to mimic experiments, the exact temperatures are then perturbed with the standard deviations of 0.01, 0.02, and 0.03. In the inverse estimation, genetic algorithm is used to minimize the objective function, thereby reducing the error between the measured and the simulated temperatures. The study on the performance parameters of the algorithm is also discussed in detail. Â© Springer Nature Singapore Pte Ltd. 2019.
A novel framework for the estimation of interfacial heat transfer coefficient using Bat algorithm during solidification of metal casting
(Toronto Metropolitan University, 2019) Vishweshwara, P.S.; Gnanasekaran, N.; Arun, M.
In the present work, the interfacial heat transfer coefficient (IHTC) at the mold metal interface is estimated during solidification of Al-4.5wt%Cu alloy using ANN-Bat-Bayesian framework. The forward model comprises of a one dimensional transient governing equation for the solidification of metal casting and is solved using explicit finite difference scheme with the available IHTC correlation from the literature. Within the range of values of constants of IHTC correlation, a set of numerical simulation is performed and corresponding temperature output is trained using Artificial Neural Network (ANN). The network created acts a fast forward model replacing the FDM scheme during IHTC estimation thus reducing computational time. Bat algorithm is used as inverse method along with the Bayesian framework, that drives towards the accurate retrieval of unknown parameters. Â© 2019, Toronto Metropolitan University. All rights reserved.
Heat transfer at the casting/chill interface during solidification of Al-11 % Si eutectic alloy (LM 6) was investigated. Experiments were carried out for various combinations of chill thickness, casting height and chill material. The thermal history at nodal locations in the chill was used to estimate the interfacial heat flux by inverse modelling. A new parameter called the heat flux penetration time was proposed to model the transformation of the interfacial condition from a perfect contact to a nonconforming contact. The heat transfer coefficient was modelled as a function of the chill thickness, casting height and the thermal diffusivity of the chill material. Real time x-ray imaging technique was adopted to observe the casting/chill interface during solidification of the alloy. The video pictures indicate that a gas gap forms in the case of thin chills. The formation of the gap in thick chills could not be detected. The widths of the gap formed at the interface were measured by an image analyser which revealed that the width of the gap not only varies with time but also with position along the chill surface.
(Maney Publishing michael.wagreich@univie.ac.at, Investigation of casting/chill interfacial heat transfer during solidification of Al-11% Si alloy by inverse modelling and real-time x-ray imaging) Prabhu, K.; Campbell, J.
1999
Heat transfer at the metal-sand interface was investigated for the case of solidification of cast iron in (1) cylindrical sand moulds and (2) ceramic cylindrical moulds with sand blocks at the bottom. An inverse method of solving the one-dimensional heat conduction equation was used to determine the metal-sand interfacial heat flux transients and heat transfer coefficients with the heat conduction equation modified to take into account the packed bed nature of the sand mould, the effect of convection of the mould gases and the evolution and absorption of heat due to mould reactions. However, temperature measurements in the moulds during the experiments revealed that the heat transfer in the cylindrical sand moulds was not truly radial and could therefore not be used to obtain accurate interfacial heat transfer results. In the case of solidification of cast iron against sand blocks, mean values of the heat flux of about 50 kWm-2 were measured for green and dry clay-bonded silica sands, with and without additions of seacoal. The corresponding heat transfer coefficients were about 625 Wm-2K-1. Within the scatter of results obtained there was no discernible difference in the heat flux or the heat transfer coefficients with the different sand formulations. The heat transfer mechanisms through the sand-casting interface were interpreted from an examination of the nature of the sand and casting surfaces. Heat transfer through the interface is proposed to occur by conduction through the gas forming the atmosphere of the interface and by radiation, in approximately equal amounts.
(Maney Publishing michael.wagreich@univie.ac.at, Metal/mould interfacial heat transfer during solidification of cast iron in sand moulds) Prabhu, K.; Griffiths, W.D.
2001
Heat transfer analysis during the solidification of lead, tin, and two lead-base solder alloys against two different chill materials (steel and copper) was carried out with and without flux coating on the chill surface. Temperatures at two known locations inside the chill and casting were recorded as the casting started solidifying, and the acquired chill temperature data were used for solving a one-dimensional heat conduction equation inversely to yield the metal/chill interfacial heat flux and chill surface temperature as a function of time. The initial heat flux was high due to good contact at the metal/chill interface. As the casting started solidifying, there was a reduction in the heat flux due to the nonconforming contact at the interface. Chills with flux coating resulted in finer microstructures near the solder/substrate interface compared to those obtained with uncoated chills. The fineness of the microstructure also increased when copper was used as the chill material. The estimated total heat flow was found to be higher with flux-coated and copper chills. This was in good agreement with the finer microstructures obtained near the solder/chill interfacial region for solidification against copper chills and chills withflux coating on their surface.
(Heat transfer at the metal/substrate interface during solidification of Pb-Sn solder alloys) Prabhu, K.; Kumar, S.T.; Venkataraman, N.
2002
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.
2003

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