Conference Papers
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Item 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.Item 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. © (2010) Trans Tech Publications.Item 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.Item Replacement of heat sink fan by nanocoolants for enhancement of CPU efficiency(Institution of Engineering and Technology journals@theiet.org, 2013) Siddique, A.B.; Prabhu, K.N.The highest temperature under which a CPU can operate without interruption is 90°C. Heat sink fans generally provided for removal of heat produced by the processor are proved to be inadequate when CPU usage is 100%. The objective of this work is to exploit the enhanced thermal properties of nanofluid for dissipation of heat from the Intel (R) Core (TM) i5- 2310 CPU @ 2.9GHz quad-core processor for cooling it to a suitable operating temperature. Nanocoolants were prepared with two types of nanoparticles, titania and copper. The volume percentage of nanoparticles in nanocoolants were 0.01 and 0.1. It was observed that nanofluids are more efficient coolants than the base fluid and found to be significantly better than the traditional heat sink fan, as indicated by the CPU temperature, under the same loading condition. The average CPU temperatures were 90°C, 58°C, 56.6°C and 54.5°C with heat sink fan, deionized water, 0.1 vol% TiO2 and 0.1 vol% Cu nanofluids respectively at the flow rate of 700ml/min and CPU usage of 100%. The lowest CPU operating temperature (54.5°C) was obtained with 0.1 vol% Cu at the flow rate of 700ml/min. The cooling of CPU was also affected by the flow rate and the volume fraction of nanoparticles in the nanocoolant.Item Prediction of heat transfer with discrete heat sources in a vertical channel filled  ith high porosity metal foam(Dalian University of Technology, 2018) Kotresha, B.; Gnanasekaran, N.This paper discusses about the numerical prediction of isothermal condition with discrete heat sources in a vertical channel filled with high porosity metal foams. The problem considered consists of a vertical channel in which discrete heat source assembly is placed at the centre and high porosity metal foams are placed on either side of the aluminium plates to enhance the heat transfer. The flow through the metal foam porous medium is predicted by using Darcy Extended Forchheimer model and Local thermal non-equilibrium model as well as local thermal equilibrium model is used for heat transfer prediction. The results are presented in terms of temperature excess over the ambient for both empty and metal foam filled channel. Finally, the heat input through the discrete heat sources is varied to obtain an isothermal condition on all the heat sources at a constant inlet velocity. © 2018 by the authors of the abstracts.Item Numerical analysis of mixed convection in a lid-driven cavity with Cu-water nanofluid using artificial compressibility method(Dalian University of Technology, 2018) Katti, A.S.; Maniyeri, R.In this paper, we present a computational model based on an artificial compressibility method to study mixed convection in a lid-driven square cavity containing Cu-water nanofluid for two cases: i) adiabatic vertical walls and horizontal walls kept at constant temperature, and ii) adiabatic horizontal walls and sinusoidal temperature heating along vertical walls. The artificial compressibility method is used to couple pressure and velocity, and solve the momentum and continuity equations. This method is used because of its simplicity in solving steady state incompressible flow problems. The streamlines, isotherms, variation of local Nusselt number at hot walls, and variation of average Nusselt number with change in Cu-nanoparticle concentration are presented. Also, the variation of local Nusselt number with change in Richardson number (0.1 < Ri < 10), keeping Grashof number constant (Gr = 100), is obtained. For both cases, it is found that heat transfer increases with increase in Cu-nanoparticle concentration, keeping Richardson number constant, and also with a decrease in Richardson number, keeping Grashof number constant. © 2018 by the authors of the abstracts.Item Effect of sliding speed and rise in temperature at the contact interface on coefficient of friction during full sliding of SS304(Elsevier Ltd, 2019) Palanikumar, P.; Gnanasekaran, N.; Subrahmanya, K.; Kaliveeran, V.The present study focuses on the effect of sliding speed and rise in temperature on the coefficient of friction at the contact interface of SS304 alloys subjected to full sliding. Dry sliding experiments were conducted on Rotatory Type Pin on Disk Tribometer. Pins of 3 mm radius and 165 mm diameter circular disk having flat surface were fabricated to simulate Hertzian contact configuration. Experiments were conducted at three different sliding speeds of 1 m/s, 2 m/s and 3 m/s under constant normal load of 1 kg. All the experiments were conducted up to sliding distance of 100 m. From the full sliding experiments, the coefficient of friction decreased with increase in sliding speed and the stabilized coefficient of friction for SS304 alloy was in the range of 0.15-0.28. The temperatures due to friction were measured using K-type thermocouples and they were located to the pins at 4 mm and 7 mm distance from the contact surface. The temperature at the contact surface during dry sliding experiment was obtained from the acquired data using inverse heat transfer method. Temperature measured at different locations along the longitudinal axis of the pin increased with increase in sliding speed and sliding distance. The increase in temperature at the contact interface was observed due to increase in friction at the contact interface during sliding. The temperature had shown stabilized trend, when the coefficient of friction curve got stabilized during sliding process. © 2019 Elsevier Ltd.Item Effect of CO2 based natural circulation loop for low temperature applications: CFD analysis(Toronto Metropolitan University, 2019) Wahidi, T.; Nagrani, P.P.; Yadav, A.K.Natural circulation loop (NCL) is a simple and economical heat transfer device in which flow occurs due to the buoyancy effect caused by thermally generated density gradient. In the present study, computational fluid dynamics (CFD) analyses are carried out to emphasize on the fluid ow and heat transfer characteristics of carbon dioxide (CO2 ) based NCL at low temperature (-38°C to 12°C). Studies are conducted in a three-dimensional (3-D) CFD model of NCL at different heat inputs i.e., 100W, 250W, 350W and 500W by keeping the loop fluid at pressure of 50 bar. Methanol is used as coolant in the heat exchanger at a fixed mass flow rate. Effect of loop operating pressure 50 bar on system performance is also investigated. Result are presented in the form of heat transfer rate, pressure drop, Reynolds number (Re) and temperature. Obtained results are validated with available correlations in the form of non-dimensional numbers, and found in good agreement. © 2019, Toronto Metropolitan University. All rights reserved.Item Flow and Heat Transfer Phenomena Through Porous Media Under Turbulent Regime(Springer Science and Business Media Deutschland GmbH, 2024) Begum, S.D.; Trilok, G.; Gnanasekaran, N.Porous media are known to improve heat transfer and fluid flow properties at the expense of pressure drop. Numerical modelling techniques open up a broad scope of research avoiding colossal cost and time. The flow of fluid in an upright symmetrical passage is dealt through this numerical research. The numerical model consists of a heater plate assembly next to a partially filled porous metallic foam. Metal foams with 4 distinct PPIs of 10, 20, 30, and 45 and porosity spanning from 0.90 to 0.95 are the subject of numerical calculations. Various structural arrangements of the aforementioned porous media (combinations of various porosity and pore density) are considered. Heat is dispersed through forced convection with air as working fluid. This study's comparison focuses solely on the differences between laminar and turbulent flows when there is a porous media in terms of fluid flow characteristics and heat transfer qualities. The Darcy–Forchheimer equation, coupled with the local non-thermal equilibrium model, is incorporated in the partially filled metal foam region. Numerical outcomes of the laminar scenario are validated against the findings of earlier research. Reaffirming the solution process, the turbulent case's outcomes are compared. © 2024, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.