Faculty Publications
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Item Optimized radial basis function neural network model for wind power prediction(Institute of Electrical and Electronics Engineers Inc., 2016) Shetty, R.P.; Sathyabhama, A.; Srinivasa Pai, P.P.; Rai, A.In this paper an effort has been done in developing a fast and efficient Radial Basis Function (RBF) neural network model to predict the power output of a wind turbine. The performance of the RBF neural network has been improved by making use of a hybrid Particle Swarm Optimization based Fuzzy C Means (PSO-FCM) clustering algorithm. Extreme Learning Machine (ELM) algorithm has been used to improve the speed of learning. Particle Swarm Optimization (PSO) has also been used to optimize the number of centers and width of the RBF units of the developed neural network model. The simulation results show that the model developed has a compact network structure and good generalization ability with 100% accuracies on training, test and validation data sets. The novelty of the present work is the use of PSO in optimizing the RBF neural network model and use of ELM in training the same. © 2016 IEEE.Item Influence of surface roughness on pool boiling heat transfer(Institute of Physics Publishing helen.craven@iop.org, 2018) Walunj, A.; Sathyabhama, A.Experimental study of pool boiling heat transfer from the rough surface at pressure 1 bar, 5 bar and 10 bar is presented. Experiments are carried on 20 mm diameter copper sample at saturated condition of distilled water. Unidirectional scratches are made by different grit sandpaper. The surface roughness value Ra is varied from 0.106 μm to 4.03 μm. The effect of Ra on heat transfer at different pressure is reported. The variation in heat transfer coefficient with the heat flux for samples of different Ra is also examined. The predicted critical heat flux (CHF) by Kim's model is found to in good agreement with present experimental values with mean absolute error of 12.06%. © Published under licence by IOP Publishing Ltd.Item Bubble dynamics in pool boiling on rough surface under exponential heat supply(Begell House Inc. orders@begellhouse.com, 2018) Walunj, A.; Sathyabhama, A.In this paper, bubble dynamics in the pool boiling of distilled water on the horizontal copper test sample of 20 mm diameter at atmospheric pressure is studied. The experiments are carried under steady and exponential heat supply of γ=1 to rough copper sample with Ra ranging from 0.106 μm to 4.03 μm. The high speed camera of 1000 fps is used to observe the bubble morphology. The effect of surface roughness on boiling heat transfer during transient heat supply is reported. The effect of surface roughness on bubble departure diameter and bubble frequency is studied. The waiting time and growth time of the bubble for different samples is also compared. The effect of steady and exponential heat supply on bubble departure diameter and bubble frequency is also reported. © 2018 Begell House Inc.. All rights reserved.Item Wind Power Optimization: A Comparison of Meta-Heuristic Algorithms(Institute of Physics Publishing helen.craven@iop.org, 2018) Shetty, R.P.; Sathyabhama, A.; Srinivasa Pai, P.The wind being a most promising renewable energy, has become a strong contender for fossil fuels. Optimizing the blade pitch angle of a wind turbine is important to obtain the maximum power output, as the other variables are considered to be uncontrollable. In this paper an effort has been made to compare performances of three different optimization algorithms namely Particle swarm optimization (PSO), Artificial bee colony (ABC) and cuckoo search (CS) for optimizing the blade pitch angle and hence optimize the power output of a 1.5 MW capacity, pitch regulated, three-bladed horizontal axis wind turbine operating at a large wind farm in central dry zone of Karnataka. The objective function development is done using Artificial Neural Network. The CS algorithm is found to be faster and more efficient as compared to ABC and PSO for the problem under consideration. © Published under licence by IOP Publishing Ltd.Item Semi-Analytical Model for Bubble Departure Diameter Prediction for Triangular Grooved Surface(Toronto Metropolitan University, 2019) Sathyabhama, A.This paper presents experimental studies of pool boiling heat transfer from plain and triangular grooved surfaces to water at atmospheric pressure. Visualization technique is used to investigate the boiling phenomenon using high speed digital camera with image acquisition speed of 1000 fps at resolution of 320 x 240 pixels. It is observed that surface modification with grooves improves the boiling heat transfer. Various aspects of bubble behaviour on plain and grooved surfaces were investigated. The bubble generation frequency was higher for grooved surfaces. The average error in bubble departure diameter prediction of the semi-analytical model developed is 29.22%. © 2019, Toronto Metropolitan University. All rights reserved.Item Effect of Surface Roughness on Pool Boiling Characteristics under Variable Heat Supply(Toronto Metropolitan University, 2019) Walunj, A.; Sathyabhama, A.An experimental investigation of critical heat flux (CHF) for boiling heat transfer from the rough copper sample under steady and quasi-steady exponentially varying heat supply is presented in this paper. The unidirectional scratches are made on the 20 mm diameter copper sample to obtain a wide range of surface roughness, ranging from Ra=0.106 μm to Ra=4.03 μm. The boiling characteristics for steady and transient-state conditions are compared by considering the onset of boiling (ONB) and CHF. The effect of surface roughness on the surface wettability and CHF are also studied. The enhancement in the transient CHF for the roughest sample (Ra=4.03 μm) is found to be 98.88%. The Rohsenow correlation for heat transfer coefficient (HTC) is modified, which predicts the present experimental data of HTC with mean absolute error (MAE) of 10.36%. The hydrodynamic model with capillary wicking force predicts the CHF for a wide range of Ra with a mean absolute error of 4.14%. © 2019, Toronto Metropolitan University. All rights reserved.Item Comparative study on the aerodynamic performance of airfoil with boundary layer trip of various geometrical shapes(IOP Publishing Ltd, 2021) Sreejith, B.K.; Sathyabhama, A.; Sandeep Kumar, S.Performance of small scale wind turbine (SSWT) and miniature aerial vehicles (MAV) is always effected with Laminar separation bubble. The problem of a laminar separation bubble on the upper surface of an E216 airfoil operated at low Reynolds number (Re=100000) is investigated numerically. Incompressible steady two-dimensional simulation is carried out with Transition γ - Reθ turbulence model on the airfoil with a boundary layer trip (BLT). The performance of two different types of trips, namely, isosceles triangular (IT) and right-angled triangular (RA) is compared with that of the airfoil with a rectangular (RT) trip. The trip locations used are, 17% of the chord for location-1 and 10% of the chord for location-2 from the leading edge of the airfoil, while the trip heights selected are 0.3 mm, 0.5 mm, 0.7 mm, and 1 mm. Results showed that the boundary layer trip significantly affected the laminar separation and improved the aerodynamic performance of the airfoil. Maximum improvement in drag by 17.41% and corresponding lift to drag ratio by 10.86% are obtained for the isosceles trip at location-2 for the angle of attack of 6°. There is no observable advantage for isosceles and right-angled triangular trips over rectangular trips. Considering the geometrical complexity in fabrication, the rectangular trip is recommended. © Published under licence by IOP Publishing Ltd.Item Performance analysis of ammonia-based vapour absorption refrigeration system(Elsevier Ltd, 2022) Waghare, P.; Sathyabhama, A.In the past few years, absorption refrigeration systems (ARS) have captivated increasing research interests as it is a promising alternative and tenable solution to replace vapour compression refrigeration systems (CRS). Also, the refrigerants used in this system are environmentally friendly. NH3/H2O and H2O/LiBr are the most commonly used working fluids in ARS. However, the NH3/H2O ARS has a limitation in that it requires additional components such as a rectifier and analyzer. The proposed work focuses on improving the performance of the ARS by using other ammonia-based working fluids, namely NH3/LiNO3 and NH3/NaSCN. Various correlations are used to determine the thermodynamic properties of these working fluids and are later used in the thermodynamic simulation. NH3/H2O, NH3/LiNO3 and NH3/NaSCN ARS performance analyses are carried out using a computer program written in Python 3.0. The coefficient of performance of these systems is compared at different operating parameters, i.e., evaporator, condenser, generator, and absorber temperature. The results indicate that the working fluids, NH3/LiNO3 and NH3/NaSCN, perform better than the NH3/H2O ARS. Thus, NH3/LiNO3, NH3/NaSCN ARS provide better performance in more significant value of COP and do not require additional components such as a rectifier and analyzer. Hence, NH3/LiNO3 and NH3/NaSCN can be considered suitable alternatives to NH3/H2O in a vapour ARS. © 2022 Elsevier Ltd.Item Modelling of Subcooled Boiling in Corrugated Pipes(Springer Science and Business Media Deutschland GmbH, 2023) Madan, K.; Singh, K.; Sathyabhama, A.This paper presents a numerical investigation of subcooled flow boiling heat transfer in sinusoidal-corrugated vertical pipes using RPI wall boiling with Eulerian–Eulerian two-phase flow model. Numerical studies are performed for different values of corrugation length and wall heat flux at a constant mass flux, operating pressure and temperature which are representative of steam generation in nuclear reactors. The numerical results are also compared with the smooth/flat pipe in terms of wall temperature, heat transfer, pressure drop and volume fraction (vf) of vapour. The results showed that onset of nucleate boiling is delayed in the case of corrugated pipes as compared to the flat pipe. It is also observed that the vf of vapour at the outlet of flat pipe is higher as compared to corrugated pipes. Overall heat transfer is increased in corrugated pipes due to enhanced mixing which eventually improved convective heat transfer. However, improvement in the heat transfer is at the cost of pressure drop. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Numerical Analysis of Dynamic Stall of a Tubercled Airfoil(Springer Science and Business Media Deutschland GmbH, 2023) Sathyabhama, A.; Bala Krishna, L.The intention of the present work is to analyse numerically the effect of tubercles on the aerodynamic performance of an airfoil section in dynamic conditions at a low Reynolds number. The performance analysis is done for the airfoil section, E216 and the lift trends for its pitching motion are studied. Numerical simulation is carried in ANSYS FLUENT. The transition SST (4 equation) viscous model is considered for the study. The results show that the lift coefficient increases while pitching up motion of the airfoil up to an angle of attack of 15°. A hysteresis loop is formed while plotting the lift coefficient against the angle of attack, indicating that the lift coefficient during pitching up is higher than that during pitching back for the same angle of attack. The tubercles reduce the lift coefficient but considerably reduce the hysteresis loop in the lift. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.