Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
14 results
Search Results
Item Residual Stress and Distortion during Quench Hardening of Steels: A Review(Springer, 2022) Samuel, A.; Prabhu, K.N.Quench hardening is a widely used heat treatment process for achieving better mechanical properties in carbon steels. However, when high quench-sensitivity steel components having thin sections are quenched, they may get distorted due to thermal and phase transformation stresses. Appropriate steps have to be taken to minimize residual stresses and distortion during quenching operation in the heat-treating industry. Many factors such as quenchant type, quench severity, quenching process variables, the geometry of the component, and material properties significantly affect the evolution of residual stresses. The heat transfer from the metal surface to the quench medium is the critical physical phenomenon that drives the microstructure evolution and residual stresses during quenching. The nonuniformity in heat transfer between the heated metal and the quench medium is the key source of residual stress development in the quenched material. Modeling and simulation of the quenching process can predict the residual stress distribution in the quenched sample and the evolution of quench cracks and component failure. Optimizing quenching process conditions and selecting appropriate quenchants minimize residual stresses and distortion. One of the requirements for improving the accuracy of simulation models is the use of reliable spatiotemporal heat transfer boundary conditions. The present review addresses the evolution of residual stresses during quenching, factors affecting residual stresses such as geometry and section thickness of the quenched part, cooling uniformity, quenchant selection, and the interrelation between heat transfer and residual stresses. The methods to minimize residual stress and distortion in quenched parts are discussed. © 2022, ASM International.Item Characterization of heat transfer of large orbitally shaken cylindrical bioreactors(Elsevier, 2014) Raval, K.; Kato, Y.; Büchs, J.Disposable shaking bioreactors are a promising alternative to other disposable bioreactors owing to their ease of operation, flexibility, defined hydrodynamics and characterization. Shaken bioreactors of sizes 20. L and 50. L are characterized in terms of heat transfer characteristics in this research work. Water and an 80% glycerol-water system were used as fluid. Results indicated large heat generation due to shake mixing which was observed by temperature difference between the fluid inside the vessel and the surrounding air outside the vessel. Maximum temperature difference of ca. 30. K was encountered for a 50. L vessel, at 300. rpm and 20. L filling volume. Outside heat transfer rate was governing the overall heat transfer process. Lateral air flow did increase heat transfer rates to large extent. An empirical correlation of overall heat transfer coefficient was obtained in terms of filling volume, rotational speed and lateral air flow rate. However, as the vessel thickness increased, the overall heat transfer process was limited by vessel wall resistance. © 2014 Elsevier B.V.Item Influence of ambient air relative humidity and temperature on thermal properties and unsteady thermal response characteristics of laterite wall houses(Elsevier Ltd, 2016) Saboor, S.; Ashok Babu, A.B.P.S.This paper presents the experimental investigation of the effect of ambient air humidity and temperature on thermal properties of the laterite rocks used in South-West coastal India. The experimental technique employed was transient plane source method in the saturated salt solution humidity controlled chamber. Experimental results showed an increase of thermal conductivity by 14.7% and specific heat by 9.15% with an increase in the relative humidity of ambient air in the hygroscopic range. A porous and ferruginous matrix of laterite was studied using a scanning electron microscope. The effects of relative humidity of the ambient air and temperature on the unsteady state thermal heat transfer characteristics such as transmittance, admittance, decrement factor, time lag, surface factor, surface factor time lag and heat capacity for different thicknesses of the laterite rock walls were investigated analytically. One dimensional heat flow equation under periodic convective boundary conditions was solved using matrix algebra and a computer simulation program which employs a cyclic admittance method was developed using MATLAB to compute unsteady state thermal characteristics. Results indicate that the decrement factor reduces by 8.35% and time lag increases by 2.88% with an increase in the relative humidity of ambient air compared to the dry state for the Indian standard laterite rock thickness. © 2016 Elsevier Ltd.Item Optimizing the position of insulating materials in flat roofs exposed to sunshine to gain minimum heat into buildings under periodic heat transfer conditions(Springer Verlag service@springer.de, 2016) Saboor, S.; Ashok Babu, A.B.P.S.Building roofs are responsible for the huge heat gain in buildings. In the present work, an analysis of the influence of insulation location inside a flat roof exposed directly to the sun’s radiation was performed to reduce heat gain in buildings. The unsteady thermal response parameters of the building roof such as admittance, transmittance, decrement factor, and time lags have been investigated by solving a one-dimensional diffusion equation under convective periodic boundary conditions. Theoretical results of four types of walls were compared with the experimental results available in literature. The results reveal that the roof with insulation placed at the outer side and at the center plane of the roof is the most energy efficient from the lower decrement factor point of view and the roof with insulation placed at the center plane and the inner side of the roof is the best from the highest time lag point of view among the seven studied configurations. The composite roof with expanded polystyrene insulation located at the outer side and at the center plane of the roof is found to be the best roof from the lowest decrement factor (0.130) point of view, and the composite roof with resin-bonded mineral wool insulation located at the center plane and at the inner side of the roof is found to be energy efficient from the highest time lag point (9.33 h) of view among the seven configurations with five different insulation materials studied. The optimum fabric energy storage thicknesses of reinforced cement concrete, expanded polystyrene, foam glass, rock wool, rice husk, resin-bonded mineral wool, and cement plaster were computed. From the results, it is concluded that rock wool has the least optimum fabric energy storage thickness (0.114 m) among the seven studied building roof materials. © 2015, Springer-Verlag Berlin Heidelberg.Item Scaling and Integral Solutions to Mixed Convection Over an Exponential Stretching Sheet(International Information and Engineering Technology Association, 2020) Veerabhadrappa, R.M.B.; Ademane, V.; Gumtapure, V.; Hindasageri, V.The reported studies on mixed convection flow problems have been solved purely by method of similarity studies. Scaling analysis is an alternate method that can give better engineering insight of the problem being investigated. Integral solutions are mathematically simpler to handle as the engineering requirement is that of accurate solutions only close to the wall. In the present work, scaling and integral solutions are discussed for a typical mixed convection flow problem already discussed in literature by similarity technique. Scaling method has been demonstrated and is found in good agreement with the results obtained from similarity method. The integral solution is obtained by deriving the integral form of governing equation and solution is discussed for specific case of Prandtl number = 1. The solution obtained by Integral formulations is in good agreement with that of similarity method.Item Performance evaluation of novel tapered shell and tube cascaded latent heat thermal energy storage(Elsevier Ltd, 2021) B.V., B.V.; Nidhul, K.; Gumtapure, V.Geometric design of the storage system plays a vital role in the enhancement of heat transfer rate and thereby in the advancement of latent heat thermal energy storage (LHTES) technology. The present study numerically compares the heat transfer performance of tapered type shell and tube cascaded latent heat storage (CLHS) model with that of the conventional cylindrical CLHS model with special emphasis on melting rate at the slowest melting portions (bottom) of the shell and tube unit. Thermal properties like transition temperature, latent, and specific heat of the three organic PCMs OM 42, OM 46, and OM 48 have been obtained using differential scanning calorimetry (DSC), and the same is employed in the 2-D numerical simulation carried out using enthalpy-porosity method. Tapered CLHS unit exhibited superior performance owing to stronger natural convective currents demonstrated via streamlines, velocity, temperature and mass fraction contours. In tapered unit, 17.6% higher mean power is obtained for same volume of PCMs in cylindrical unit. In contrast, the mean power of the discharging process for a tapered type is 2.4% lesser than cylindrical type CLHS. The outcomes highlight that the tapered type CLHS model utilizes convective heat transfer, effectively enhancing the melting rate of PCM without any additional structural configurations such as fins. Hence is also economically justifiable for higher energy storage for the same volume compared to conventional cylindrical CLHS units. © 2020 International Solar Energy SocietyItem Estimation of tumor parameters using neural networks for inverse bioheat problem(Elsevier Ireland Ltd, 2021) Majdoubi, J.; Iyer, A.S.; Ashique, A.M.; Arumuga Perumal, D.A.; Mahrous, Y.M.; Rahimi-Gorji, M.; Issakhov, A.Background and objective: Some types of cancer cause rapid cell growth, while others cause cells to grow and divide at a slower rate. Certain forms of cancer result in visible growths called tumors. This work proposes an inverse estimation of the size and location of the tumor using a feedforward Neural Network (FFNN) model. Methods: The forward model is a 3D model of the breast induced with a tumor of various sizes at different locations within the breast, and it is solved using the Pennes equation. The data obtained from the simulation of the bioheat transfer is used for training the neural network. In order to optimize the neural network architecture, the work proposes varying the number of neurons in the hidden layer and thus finding the best fit to create a relationship between the temperature profile and tumor parameters which can be used to estimate the tumor parameters given the temperature profile. Results: These simulations resulted in a temperature distribution profile that could thus be used to locate and determine the parameters of the cancerous tumor within the breast. The prediction accuracy showed the capacity of the trained Feed Forward Neural Network to estimate the unknown parameters within an acceptable range of error. The model validations use the Root Mean Square Error method to quantify and minimize the prediction error. Conclusions: In this work, a non-intrusive method for the diagnosis of breast cancer was modelled, which yields conclusive results for the estimation of the tumor parameters. © 2021Item Experimental investigation of shellac wax as potential bio-phase change material for medium temperature solar thermal energy storage applications(Elsevier Ltd, 2022) B.V., B.V.; Thanaiah, K.; Gumtapure, V.Thermal performance of shellac wax as a novel bio-phase change material (BPCM) and Therminol®-55 as heat transfer fluid (HTF) in a vertical shell and tube latent heat thermal energy storage (LHTES) unit is analyzed experimentally. Operational parameters considered, namely HTF flow rate and inlet temperature in the range of 2–5 LPM and 100–120 °C, respectively. The comprehensive study of contours and plots reveals the impact of natural convection and the progress of the melting and solidification front in the charging and discharging process. As the HTF flow rate increases, the charging rate improves considerably, and a maximum reduction in melting time is obtained as 43.6% for 4 LPM. The maximum reduction in melting time and storage efficiency are 42.2% and 73.4%, respectively, at 120 °C and 4 LPM. However, the discharging process's increased flow rate has no significant effect on solidification and discharge efficiency, which attributes the dominant mode of heat transfer is conduction during the solidification. Shellac wax storage efficiency is comparable to existing paraffin wax, stearic acid and palmitic acid-based LHTES unit. In this regard, shellac wax can be a potential Bio-PCM for medium temperature range (60–80 °C) solar thermal applications such as domestic water heating and food drying. © 2021 International Solar Energy SocietyItem CFD and exergy analysis of subcritical/supercritical CO2 based naturally circulated solar thermal collector(Elsevier Ltd, 2022) Biradar, M.K.; Parmar, D.N.; Yadav, A.K.Solar water heating system is inefficient during winter due to the chances of water freezing and higher viscosity at low temperatures. Several investigations are being done to increase the efficiency of the solar water heater using various secondary fluids for different climatic conditions. This paper emphasises on the study of heat transfer and fluid flow behavior of CO2 based naturally circulated indirect solar water heating system. Subcritical (liquid and vapour) and supercritical CO2 are considered as loop fluid, and the results are compared with water based system. Three-dimensional computational fluid dynamics simulations are carried out for two different weather conditions i.e., winter (278 K) and summer (305 K). Results are obtained for 33° collector inclination angle from horizontal at various operating pressures 50–70 bar for subcritical and 80–100 bar for supercritical CO2. The CO2 based system yields very high Reynolds number (subcritical liquid: ∼160 times; subcritical vapour: ∼204 times; supercritical vapour: ∼260 times) and very high Nusselt number (subcritical liquid: ∼14 times; subcritical vapour: ∼19.5 times; supercritical vapour: ∼48 times) compared to water based system. Supercritical CO2 based system exhibits 12% higher energy efficiency compared to water. Whereas, subcritical vapour based system exhibits 140% higher exergy efficiency relative to water based system. © 2022 Elsevier LtdItem Analysis of functionally graded metal foams for the accomplishment of heat transfer enhancement under partially filled condition in a heat exchanger(Elsevier Ltd, 2023) Jadhav, P.H.; Gnanasekaran, N.; Mobedi, M.The use of partially filled high porosity graded aluminum and copper foams is explored to satisfy both heat transfer and pressure drop in a heat exchanger. Both positive and negative orientations are accomplished for the enhancement of heat transfer with reduction in the pressure drop. The present research includes three different configurations M1, M2 and M3 (porous layer inner diameter = 0.06 m, 0.04 m, and 0.02 m, respectively, while outer diameter = 0.10 m) partially filled with positive (i.e., increasing, 20/45 PPI) negative (i.e., decreasing, 45/20 PPI) and compound (i.e., 45 Cu/20 Al PPI) graded porous layer thickness. Each configuration involves three different graded porous layer to present the optimum graded porous layer thickness. The thermo-hydrodynamic characteristics are apprehended by using Darcy Extended Forchheimer (DEF) flow and local thermal non-equilibrium (LTNE) models for the partially filled graded porous structure and k-ω turbulence model is accomplished in open passage flow of the conduit. The decreasing graded foam located inside the models M1 and M2 performed 1.68%–12.85% and 13.42%–23.32% higher heat transfer rate compared to without graded metal foam of models M2 and M3, respectively accompanied with 55.43%–84.02% and 35.69%–50.31% lesser pumping power. © 2022 Elsevier Ltd