BITS Faculty Publications
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Item Neural Network Analogy over Numerical Analysis on Thermo-Hydraulic performance factors j & f correlations development for Compact Heat Exchangers(Begell House, 2023) Ranganayakulu, ChennuA Compact Heat Exchanger (CHE) is a device used to transfer energy from one fluid to another, vital role in the efficient energy transfer. The optimum design of these Compact heat exchangers is a challenging skill for making minimum pumping power in terms of minimum pressure drop and efficient heat transfer. The generation of thermo-hydraulic performance factors, Colburn factor ‘j’ and fanning friction factor ‘f’ correlations for CHE take a large number of simulations in numerical analysis and the same is very expensive in modelling the model for Experimental analysis. In the open literature, experimentally developed fins performance as a function of Reynolds number and geometric parameters, which is expensive. The Numerical model has been developed by simulating Reynolds number Re and geometric parameters, such as fin height h, fin spacing s and fin thickness t for generation of fanning friction factor f and Colburn factor j. The 144 fin geometric parameters are used in the numerical model to develop a correlation. The numerical model is analyzed using ANSYS Fluent®. This tremendous process of correlation development is faster by using Artificial Neural Networks (ANN). This Paper focused on developing design data requirements for rectangular plain fin compact heat exchangers using CFD and Neural Networks(NN). The Analogy of correlation developed by Neural Network Prediction and CFD Fluent are verified and validated using open literature. The correlations from Neural Networks using limited data are faster and has better agreement with open literature.Item Endurance Life Estimation of Aircraft Compact Heat Exchanger(Journal of Aerospace Sciences and Technologies, 2012) Ranganayakulu, ChennuHeat Exchangers are used in various engineering systems to transfer heat from a hot fluid to cold fluid across an impermeable wall. The necessity of increased heat transfer surface area has resulted in the development of Compact Heat Exchangers (CHE). Due to their compactness, high performances and less weight, CHE is used for aerospace applications. CHE used in combat aircrafts experience arduous and extreme working conditions during their operation. Before its integration with aircraft, CHEs are required to be tested for performance and qualified for airworthiness by evaluating its endurance life. This paper provides the details of the facility established to experimentally evaluate the endurance life. A computational analysis was carried out to estimate the endurance life with respect to fatigue effects using Finite Element Analysis to calculate stress distribution due to pressure and temperature in CHE during maximum and minimum operating conditions. This was then utilized to calculate fatigue life of CHE. The results were compared with experimental data and it is understood that fatigue alone does not determine the endurance life and there are other parameters that significantly influence the life of CHE.Item Development of vapour compression refigeration system test rig and eavaluation of test data for R134A condensation in compact heat exchangers with serrated Fin(International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, 2015) Ranganayakulu, ChennuTwo phase flow analysis for the condensation of refrigerants within the compact plate fin heat exchangers is an area of ongoing research. Compact plate fin heat exchangers are becoming very popular due to their high effectiveness and compactness. This paper presents the sizing of compact plate fin heat exchanger and development of test rig to generate the Refrigerant (R134a) condensation heat transfer coefficient and pressure drop in Brazed Compact Plate Fin Heat Exchangers (BCPHE) with Serrated (Lance&Offset) fins. Also the theoretical design, manufacturing and testing of BCPHE for generation of R134a condensation heat transfer coefficient has been presented. CFD methodolgy has been used to develop the Single phase water side heat transfer coefficient and friction factor correlations for Serrated fin using ANSYS Fluent 14.5. The heat balance analysis has been carried out for calibration of the test rig using measured test data on both circuits and recorded a maximum deviation of 8%. Heat transfer coefficient for condensation of refrigerant R134a in compact heat exchangers with serrated fin is estimated using measured experimental data.Item Configuration Studies of Aircraft Environmental Control System Using Exergy Analysis of Compact Heat Exchangers for Multi-disciplinary Optimization(Springer, 2023-03) Ranganayakulu, ChennuTraditionally the performance of an aircraft environmental control system (ECS) is evaluated through energy balance and the weight of the system components is optimised to meet the strength and performance requirements. The simulation models developed both with off-the-shelf software and inhouse developed codes are all of this category. It is necessary to optimise the ECS system configuration from the entropy generation point of view to identify precisely the components that contribute to the maximum destruction of the exergy. This paper details the procedure to perform the multi-disciplinary optimization through simulation at configuration studies stage during the design of the ECS system from fundamentals. This is not yet embedded in the commercial simulation software that are available for ECS system simulation and design. The procedure presented herein would be useful to all ECS designers to modify and develop the model that suits their requirements. It would also be useful to the ECS designers to evaluate the existing designs to see the scope for improvement.Item Numerical Analysis of Generation of Colburn-j Factor for the Plain Rectangular Fins of a Compact Heat Exchanger Using CFD Approach(Springer, 2023-04) Ranganayakulu, ChennuA Compact Heat Exchanger is characterized by a high heat transfer area per unit volume, which can be achieved by using very high-density fins. A plain fin is one of the most commonly used fins as it has advantages such as low-pressure drop and it is easy to fabricate several types of fins by changing its geometric parameters such as fin height (h), fin spacing (s), and fin thickness (t). In this study, a numerical investigation is carried out on a plain rectangular fin to establish a correlation for the Colburn-j factor. The analysis is done for a wide range of Reynolds (Re) numbers covering both the laminar region (400 ≤ Re ≤ 2500) and turbulent region (3500 ≤ Re ≤ 12000). A CFD-based numerical study is performed using ANSYS Fluent 21 with air at 300 K as the working fluid. In this numerical analysis, the Colburn-j factor data is obtained for different Reynolds numbers as well as for the different non-dimensional geometrical parameters such as the fin height, fin spacing, and fin thickness values. This data has been validated with experimental data available in the open literature. The correlations of the Colburn-j factor are established for a wide range of Reynolds numbers along with the geometric parameters of the plain fins covering the entire operational range of the Compact Heat Exchangers for Aerospace as well as for other applications.Item Experimental and CFD analysis of multi nozzle ejector system for aircraft compact heat exchanger applications(Taylor & Francis, 2021-10) Ranganayakulu, ChennuIn the present study, analysis of multi-nozzle ejector systems for aircraft compact heat exchanger applications is performed. CFD procedure is validated with experimental data of a single-nozzle ejector. Experimentation is carried out with a multi-nozzle ejector to evaluate the performance of the system at ambient temperature (307 K). Based on the pressure drop data obtained from the experiment, the computational domain for CFD studies is simplified. Further the analysis of air ejector systems at higher operating temperature (813 K) is performed. Primary air inlet temperatures and pressure are varied as parameters. Velocity contour, pressure contour and temperature contours are plotted for cold and hot fluid cases. High pressure zones are observed in the mixing regime of primary and secondary fluid. Improper mixing of primary and secondary fluid is observed. The mass ratio is reduced with increase in primary pressure. Based on the CFD results at high temperature, the performance of the compact heat exchanger is computed using the heat exchanger carpet curve for the different secondary (cold) air flows induced by the ejector.Item Heat Transfer and Flow Friction correlations for Compact Wavy Plate Fin Heat Exchanger(JNTU, 2008) Ranganayakulu, ChennuThe most popularly used fins in Compact Heat Exchangers (CHEs) are the plain fins, offset strip fins, louvered fins and wavy fins. Thermo hydraulic performance of the above mentioned fins are strongly depends upon the geometric parameters and flow parameters. The wavy fin performance is generally evaluated based on the fin thickness, wavelength, curvature radius, amplitude, fin spacing and fin height. The objective of the present study is focused on investigation of the influence of above mentioned fin parameters and establishing a correlation in terms of dimensionless parameters such as Colburn factor (j), Fanning friction factor (f), geometrical parameters and flow parameters. A CFD approach has been used for numerical analysis of different fin configurations to determine the thermo-hydraulic parameters. The investigations include the study of flow pattern for laminar and turbulent regimes and validated with available data.Item Development of Heat Transfer Coefficient and Friction Factor Correlations for Serrated Fins in Water Medium using CFD(David Publishing Company, 2015) Ranganayakulu, ChennuThe most popularly used fin types in compact heat exchangers are the serrated fins, wavy fins, louvered fins and plain fins. Amongst these fin types the serrated fins assume lot of importance due to its enhanced thermo-hydraulic performance. Thermo-hydraulic design of CHEs (Compact heat exchangers) is strongly dependent upon the predicted/measured dimensionless performance (Colburn j factor and Fanning friction vs. Reynolds number) of heat transfer surfaces. This paper describes the numerical analysis to study the heat transfer coefficient and friction factor of Serrated fins in water medium. CFD (Computational fluid dynamics) methodology has been used to develop the single phase water heat transfer coefficient and friction factor correlations for serrated fins using ANSYS Fluent 14.5. The results are compared with previous air-cooled models and experimental results of water. The water cooled CFD analysis results shows that the Prandtl number has a large effect on the Nusselt number of the serrated fin geometry. Finally, the generalized correlations are developed for serrated fins taking all geometrical parameters into account. This numerical estimation can reduce the number of tests/experiments to a minimum for similar applications.Item Measurement of heat transfer coefficient and pressure drops in a compact heat exchanger with lance and offset fins for water based Al2O3 nano-fluids(Springer, 2019-07) Ranganayakulu, ChennuCompact Heat Exchangers (CHEs) are widely used in various applications in thermal fluid-systems including aerospace due to their compactness and light weight coupled with high effectiveness. Among the different types of CHEs for Aircraft Environmental Control System (ECS) and Avionics cooling applications, a cross-flow CHE with Lance & Offset fin is of special interest because of their high heat rejection capability. In the present work, the heat transfer coefficient of water based Al2O3 nano-fluid (NF) flowing in a Compact Plate-fin Heat Exchanger having Lance & Offset fins is studied experimentally. As part of experimental investigation a test setup is designed and developed. Experiments are conducted in the range of mass flux from 50 to 350 kg/s m2 (100 ≤ Re ≤ 600) at room temperature as well as at higher temperatures up to 70 °C. In this study, Al2O3 volume concentration in water is varied from 0.255% to 0.51%. The variation of heat transfer coefficients and pressure drops of Al2O3 nano-fluid with respect to water are presented in graphical form for different mass fluxes. The heat transfer coefficient gets enhanced in low NF temperature regions (between 30 °C-45 °C) up to 25% for 1%NF and up to 35% for 2%NF, where as there is only a marginal improvement at higher operating temperatures (between 60 °C-75 °C). The uncertainty analysis is carried out for heat transfer coefficient based on sensors specification.Item Development of heat transfer coefficient and friction factor correlations for offset fins using CFD(Emerald, 2011-11) Ranganayakulu, ChennuIn aerospace applications, due to the severe limitations on the weight and space envelope, it is mandatory to use high performance compact heat exchangers (CHEs) for enhancing the heat transfer rate. The most popularly used ones in CHEs are the plain fins, offset strip fins (OSFs), louvered fins and wavy fins. Amongst these fin types, wavy and offset fins assume a lot of importance due to their enhanced thermo‐hydraulic performance. The purpose of this paper is to investigate the influence of geometrical fin parameters, in addition to Reynolds number, on the thermo‐hydraulic performance of OSFs.