Browsing by Author "N., Gnanasekaran"

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A Comprehensive Investigation of Thermal and Flow-Resistance Behaviour of Metal Based Porous Media
(National Institute of Technology Karnataka, Surathkal., 2024) G., Trilok; N., Gnanasekaran
This thesis work presents numerical investigation of metal based porous media such as metal foams and stacked wire mesh porous structures, focusing on addressing the issue of incurred flow resistance that is always accompanied with the enhanced heat transfer associated with such media. Key features of porous medium such as their twin structural properties (porosity and pore density), thickness and method of formation (stacking types in terms wire mesh porous structures) are identified as potential influencing parameters that play a key role in the thermo-hydraulic phenomenon. In the first part, influence of porosity and pore density of porous media is demonstrated for their combined effect on flow resistance and heat transfer enhancement behavior. Significance of considering both of these twin structural properties in analyzing the characteristics of porous medium particularly in forced convection regime is further emphasized through Nusselt number correlations. In the second part, thickness of porous medium is considered as another parameter along with the structural properties, and various trade-off scenarios between enhanced heat transfer and incurred flow resistance is comprehensively analyzed. TOPSIS A multi-objective, multi-attribute decision making technique is utilized in this regard, and unique potentials of a porous medium corresponding to its various combination of structural and thickness conditions are evaluated in terms of their ability to minimize flow resistance and maximize heat transfer. In the last part, potentials of stacked wire mesh porous structures are investigated for their various trade-off scenarios between enhanced heat transfer and incurred flow resistance. Expressions pertaining to key morphological features such as porosity, pore density and specific surface area of wire mesh porous structures of various stacking types are derived and used in the porous media modeling to comprehensively analyze the phenomenon of increased pressure drop with increase in heat transfer corresponding to variations in structural properties (porosity and pore density), stacking types and thickness scenarios.
Detection of Breast Cancer Using Thermal Patterns and Artificial Intelligence
(National Institute of Technology Karnataka, Surathkal., 2024) Venkatapathy, Gonuguntla; N., Gnanasekaran
Breast cancer remains one of the leading causes of cancer-related deaths among women worldwide, emphasizing the crucial need for early detection to enhance treatment outcomes and survival rates. While advanced screening technologies have significantly benefited developed countries, underdeveloped and developing nations face significant challenges due to limited access and high costs. Traditional screening methods, though effective, are often invasive, uncomfortable, costly, and expose patients to harmful radiation. Present study explores the potential of thermography as a non-invasive, cost-effective adjunct tool for breast cancer screening. By utilizing advanced computational techniques and artificial intelligence, the study aims to improve the accuracy and reliability of breast cancer detection through thermal patterns on the surface of the breast. The initial phase of the research investigates the feasibility of using breast skin surface temperature variations, caused by underlying tumors, to estimate tumor size and location. A simplified two-dimensional numerical model is developed using COMSOL Multiphysics software to simulate breast thermal patterns resulting from underlying tumors. A dataset comprising of surface temperatures is generated that are correlated with tumor diameters and locations. This dataset is then used to train an artificial neural network, which demonstrates that thermography can serve as an effective adjunct screening tool alongside the more invasive gold standard technique, mammography. The study further develops a comprehensive numerical thermal image dataset through successive numerical simulations, addressing the absence of actual labelled thermal images. A three-dimensional breast model, representing a spherical tumor within a hemispherical breast, is created to simulate numerical thermal images for different sizes and locations of the tumor. Various machine learning regression models including linear regression, support vector regression, K-nearest neighbor regression, and decision tree regression, are evaluated. Among these, the decision tree regression model shows superior predictive performance, effectively distinguishing minor temperature variations that correspond to tumor characteristics. In the following phase, instead of numerical thermal image data a limited set of temperature data on the surface of the breast used to train a random forest machine learning algorithm. Random forest, which is an ensemble of decision trees, accurately estimates the tumor size and location, demonstrating the effectiveness of using temperature patterns data in breast cancer detection. The final phase of the research integrates real thermal imaging with deep learning to propose a novel, non-invasive breast cancer diagnosis framework. Using the database for Mastology Research with Infrared Image (DMR-IR) dataset, a specialized segmentation algorithm is developed to identify regions of interest within thermal images. These segmented images are then used to train a convolutional neural network based on the AlexNet architecture, which achieves exceptional classification accuracy. This integrated approach, combining segmentation, classification, and thermal analysis provides a reliable and cost-effective system for early breast cancer detection. Present study demonstrates that thermography, supported by computational models and artificial intelligence offers a promising supplementary tool for breast cancer screening. It bridges the gap between non-invasive imaging and precise tumor localization, contributing to the early detection and treatment of breast cancer.
Enhancement of Heat Transfer in Solar Air Heater Using Porous Media
(National Institute of Technology Karnataka, Surathkal., 2024) Rawal, Diganjit Shashikant; N., Gnanasekaran
The solar air heater (SAH) is very much useful to dry the vegetables, fruits etc. It works on the basis of solar radiation available at the respective location. So, it saves the electricity i.e. reduces the dependency on the fossil fuel. SAH is easy to operate, simple in design. It has less maintenance. The limitations of the SAH are low thermal efficiency due to handling of large volume of air. Also, the air has low thermal capacity. Hence, this problem can be solved by using addition of different metal porous media of different porosities and pores per inch (PPI) inside the empty channel SAH. Initially the empty channel rectangular domain single pass solar air heater (SPSAH) is designed analytically for 0.03 to 0.05 kg/s mass flow rates. The same has been validated with 2D geometry numerical study in ANSYS fluent software to observe the accuracy and performed the comparative study of thermal performance of SPSAH. Then, the discrete arrangement at equal distance of copper metal foam having thickness of 22, 44 and 88 mm of thicknesses with 10 (Φ=0.8769), 20 (Φ=0.8567), and 30 (Φ=0.92) PPI has used to test the thermohydraulic performance parameter in order to enhance the heat transfer in SPSAH. The numerical study shows that the 22 mm thick metal foam is 5.02 % and 16.61 % higher THPP than 44 and 88 mm thick metal foam. The 3D geometry further developed by Rosseland radiation model with solar ray tracing method has been used to account for solar radiation. Renormalization group (RNG) k-epsilon enhanced wall function with local thermal equilibrium (LTE) model has been considered to obtain the heat transfer characteristics in numerical study. Aluminium wire mesh samples with 3 (Φ=0.894), 9 (Φ=0.812), and 18 (Φ=0.917) PPI has been used for numerical and experimental study. The configurations has been combined together to form graded wire mesh (GWM) including 3-9-18, 9-18-3 and 18-3-9 of 5 mm thickness for each wire mesh. The THPP of 9 18-3 PPI wire mesh are 13.04 % and 11.92 % higher than the other two cases. Later, 25 % of 9-18-3 GWM has been considered at four different locations, i.e. 0, 0.5, 1 and 1.5 m away from the inlet and analysed best location for efficient heat transfer. 1.5 m away from the inlet is the best location among the different locations. The experiment results of GWM at 1.5 m away from the inlet demonstrated 20.91 % and 23.32 % increase in thermal efficiency compared to empty channel for the 0.027 and 0.058 kg/s mass flow rates respectively. Further investigations involve a comparative study of transverse arrangement of three layers of 9 (Φ=0.812), and 18 (Φ=0.917) PPI one over the another and same quantity of wire mesh of 50% is folded in the same direction. So, these combinations are (9-18, 18-9) T, (9-18, 18-9) L to obtain GWM in transverse and longitudinal direction, respectively. THPP of 9-18 L has an average of 2.45 % higher than all other combinations mentioned above. The thermal efficiency of 9-18 L has an average of 63.45 % higher than the empty channel for 0.05 and 0.08 mass flow rates. The GWM arrangement reduce the time of drying by 26.78 % and 55 % for tomato and onion respectively compared to empty channel SPSAH. The assessed simple payback period is 0.89 year which is shorter than lifespan of the SPSAH which is profitable. The present study was also focused on the solar panel battery operated fan and all the measuring instruments operated by battery which reduces the dependency on the external electric supply.
Heat and Fluid Flow In an Integrated Rectangular Microchannel: A Combined Numerical-Experimental Study
(National Institute of Technology Karnataka, Surathkal, 2022) G., Narendran; N., Gnanasekaran; D., Arumuga Perumal
This thesis work presents numerical and experimental investigations on flow maldistribution based conjugate axial conduction problems in parallel type channels for high density electronic cooling applications. Majorly, three issues relating to the practicality of the integrated parallel channel heat sinks are explored in the thesis: (a) The effect of integrated heat spreaders in mitigating the flow induced high temperature zones using parallel type heat sink, (b) The study of axial conduction and entrance effects of heterogeneous integrated heat sink and (c) the use of inertial channels to reduce flow maldistribution induced axial conduction in parallel flow type configuration heat sink. In the first part, heat transfer investigations are performed to reduce hotspots with heat spreader integrated microchannel using nanofluid. The results of Nusselt number are compared with the benchmark literatures. Numerical simulations on microchannel heat sink are performed to understand the temperature distribution in the spreader and an elaborate discussion is provided for the deviations observed between numerical and experimental data. Critical effects like response time and bulk diffusion are discussed by varying hotspot, aspect ratio and processor cores. Reduction in flow induced hotspot has been observed by providing graphene oxide nanofluid with very low volume fraction. In the second part, both the numerical and experimental analyses are performed to investigate axial conduction in heterogeneous integrated microchannel using TiO2 nanofluid. The inlet flow rate, volume fraction and power rating are varied to check the effects of axial conduction on heterogeneously integrated substrates. The thermo physical properties of the TiO2 nanofluid are measured and characterized. Significant effect of axial conduction is seen for nanofluid at higher concentration at reduced flow rates. On the other hand, it has been observed that the effect of conjugate heat transfer decreases at higher flow rates. The last part of the work presents the investigation on the special type of inertial channels to reduce the maldistribution induced axial conduction. The study is carried out on ribbed channels with three different geometrical configurations i.e. normal, inclined and lifted channels. The average temperature of the sink reduces for ribbed channels than normal straight channels. The effect of axial conduction is observed less for ribbed inclined channel due to the obstruction in flow, flow separation and increased fluid momentum in extreme channels.
Investigations of Phase Change Material (Pcm) Based Heat Sinks with Different Thermal Enhancers
(National Institute Of Technology Karnataka, Surathkal, 2023) Muthamil, Selvan N; N., Gnanasekaran
Effective thermal management is crucial for ensuring the maximum performance and reliability of electronic devices. As the internal heat generation within a device increases, the risk of failure rises, leading to a decrease in its overall lifespan. A passive cooling method involving the use of Phase Change Materials (PCMs) proves to be a suitable technique for electronic cooling. However, due to the inherently poor thermal conductivity of PCMs, various enhancers, such as fins, metal foams, and nano-particles are employed to mitigate the thermal resistance they pose. Furthermore, the heat sink design must be optimized to establish an efficient storage and retrieval system under the charging and discharging cycles. The current thesis work aims to present both numerical and experimental investigations of PCM-filled heat sinks using different thermal enhancers Numerical simulations are conducted using ANSYS Fluent, employing the enthalpy porosity formulation to model the melting/solidification of PCM. Subsequently, experiments are carried out to further explore the parametric aspects of the investigation. In the first work, both the melting and solidification of n-eicosane filled heat sink are studied numerically. In order to enhance the thermal conductivity, fins and foams are used in this study. Here, a PCM-filled hybrid system of two cases is considered. In case 1, no fin case is compared with rectangular fins and tapered fins. In case 2, different filling heights, such as 10 mm, 15 mm, and 20 mm, with horizontal tapered fins are investigated. Results show that tapered fins are good for the distribution of temperature and uniform melting within the system. During solidification, the fin shape does not influence the process due to the poor natural convection effects. Regarding the foam filling height, during the melting process, filling heights have less significant effect. But it is observed that the solidification rate is faster by increasing the filling heights. For solidification cases, 20 mm filling height foam performs better than all other cases. Following this study, a multi-objective optimization is carried out using a reliable multi-criteria decision making approach for a hybrid heat sink with fins and foams. Different weightage is distributed to the objective functions in this method depending on the choice of the user. The pore size of 0.8-0.95 and pore density of 5-25 pores per inch vary for various filling heights, and 60 cases are considered for both the cycles. When the weightage is biased towards solidification or equally shared between melting and solidification, the 25 PPI, which possesses a more solid structure, has a better performance score. However, when the weightage is biased towards melting, the 0.95 porosity has a higher performance score due to the larger PCM volume. From the results, guidelines for selecting a preferable pore structure are provided based on the filling height and applied weightage. In the next study, Phase change materials (PCM) RT-28HC, RT-35HC, and RT-44HC, with similar thermal properties, are considered, and a combination of PCM acts as an enhancer. The PCM is oriented in increasing order of melting temperature from the left to the right side of the heat sink. Additionally, the fins are attached to the heat sink longitudinally, and its orientation effects are studied. The effect of fins on the charging cycle is assessed by comparing a single and double PCM heat sink. Three initial conditions are investigated by altering the initial temperature to 300 K, 303 K, and 310 K. For high heat input, the negatively angled fins possess a higher melting rate. For different initial conditions, -60o provides higher enhancement, and +60o possesses prolonged melting for almost all cases and applied weightage. In the last study, a modified variable height fin heat sink is compared with the conventional constant height fin heat sink. Experiments are performed for constant loads and also different power surge conditions. The pulsed heat loads are applied for two scenarios: 1. Constant load 4 W - power surge and constant load 4 W - power surge - 1800 s no-load condition, and 2. Power surge (50 s, 100 s, and 150 s) - no-load conditions of 1800 s. During experiments, the proposed variable height fin heat sinks possess better thermal performance for all load scenarios. The variable height fin heat sink accelerates any load's melting rate. The time difference between the wall and the PCM is also less for the variable height fin heat sink. Similar to the melting, a faster discharging rate is noticed during solidification in the variable height fin heat sink.
Numerical Analysis of Conjugate Heat Transfer In the Presence of Porous Medium
(National Institute Of Technology Karnataka Surathkal, 2023) Jadhav, Prakash Heerasing; N., Gnanasekaran; D, Arumuga Perumal
The intent of the current research is to emphasize the computational modelling of forced convection heat dissipation in the presence of high porosity and high thermal conductivity metallic foam in a circular pipe for different regimes of fluid flow for a range of Reynolds number. For a constant heat flux condition, the goal is to find out the efficient metal foam and configurations when air is considered as a working fluid. Flow dynamics and heat transport phenomenon are captured using Darcy Extended Forchheimer (DEF) flow and local thermal non-equilibrium (LTNE) models within the porous filled region of the pipe. The numerical results are initially matched with experimental and analytical results for the purpose of validation. Initially, the effect of fully filled foam (i.e., L􀭤 = 0.6L (i.e., 60% L), 0.8L (i.e., 80% L) and L (i.e., 100% L), i.e., L􀭤 = length of the foam, L = length of test section), and discrete filled foam (i.e., L􀭤 = 0.6L (i.e., 60% L) and 0.8L (i.e., 80% L)), in a pipe is accomplished to decrease and increase the pressure drop and heat transfer rate, respectively. The average Nusselt number for fully filled foam (L􀭤 = L) is found to be higher compared to other filling rate of metallic foams and the clear pipe at the cost of pressure drop. Further, in the presence of discrete filled foam (L􀭤 = 0.8L), the heat transfer rate deteriorates significantly while increases considerably for fully filled foam (L􀭤 = 0.8L) accompanied with the same pressure drop. As an important finding, it has been observed that the laminar and transition flow gives higher heat transfer enhancement ratio and thermal performance factor compared to turbulent flow. This work resembles numerous industrial applications such as solar collectors, heat exchangers, electronic cooling, and microporous heat exchangers. The novelty of the work is the selection of suitable flow and thermal models in order to clearly assimilate the flow and heat transfer in metallic foam. The parametric study proposed in this work surrogates the complexity and cost involved in developing an expensive experimental setup. Further in this contemporary research, a parametric analysis of partially filled high porosity metallic foams in a horizontal pipe is performed to augment heat transfer with reasonable pressure drop. The investigation includes six different models filled partially with aluminium foam by varying internal diameter of foams from the wall side and external diameter of foam from the core of the pipe. The pore density of the foam ranges from 10 to 45 PPI (pores per inch) and their porosity varies from 0.90 to 0.95. The results showed that the thermal performance factor of 10 PPI aluminium foam performs close to the 10 PPI expensive copper foam. The performance factor is found to be higher for 30 PPI aluminium foam amongst the PPI’s of the foam considered. However, the performance factor is found to be 2.93, 2.22 and 1.73 for 30PPI, 45 PPI and 20PPI with their porosities of 0.92, 0.90 and 0.90, respectively for the model 1, model 2 and model 3 at lower Reynolds number of 4500 and then it decreases progressively with increasing flow rates of the fluid. Further, optimization study is proposed to optimize for various (six) filling rate of the metallic foam in a horizontal circular pipe. Optimization study in flow through metal foams for heat exchanging applications is very much essential as it involves variety of fluid flow and structural properties. Moreover, the identification of best combinations of structural parameters of metal foams for simultaneous improvement of heat transfer and pressure drop is a pressing situation. In this work, six different metal foam configurations are considered for the enhancement of heat transfer in a circular pipe. The foam is aluminium with PPI varying from 10 to 45 and almost the same porosity (0.90-0.95). The aluminium foams are chosen from the available literature and they are partially filled in the pipe to reduce the pressure drop. A special attention is paid to the preference between pressure drop and heat transfer enhancements. Hence, Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) optimization techniques with five different criteria (contains the combination of the weightage/priority of heat transfer and pressure drop) is used. Based on the numerical results of heat and fluid flow in pipe, it is found that when an equal importance is given to both heat transfer and friction effect, 30 PPI aluminium foam with 80% filling on the inner lateral of the pipe provides the best score as 0.8197.