Browsing by Author "Ranganayakulu, Chennu"

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Aerodynamic and Thermal Optimization of Plate Heat Exchanger Fin Arrangements
(Springer, 2024-02) Ranganayakulu, Chennu
Plate-fin heat exchanger systems today are exceedingly prevalent but greatly unoptimized because of the use of off-the-shelf heat exchangers, which considerably affect system efficiency. This study aims to provide a methodology for a plate-fin heat exchanger’s aerodynamic and thermal optimization to create a bespoke cooling solution based on given constraints and operating conditions. The authors studied a radiator to cool the EMRAX 208 electric motor to develop the requisite analytical and numerical models. A literature review was undertaken to compare and shortlist the best configurations, optimized through a MATLAB algorithm, and analysed and iterated in Ansys Fluent on a case-by-case basis. The results of the study point towards the superiority of serpentine fins over the other kinds, with approximately 40% higher heat transfer coefficients (at 80kmph) compared to the triangular finned models, which results in an indirect reduction in the frontal area and, subsequently, lower drag and pressure losses. The study concluded with the serpentine finned cylindrical tube heat exchanger as the best cooling solution. The exact dimensions and layout of the heat exchanger, along with the optimal fin distribution, can be obtained with the combination of the created algorithm and CFD analysis.
Analysis of Energy saving between Bleed Air and Bleed less Environmental Control Systems in a typical Aircraft
(IEEE, 2022) Ranganayakulu, Chennu
Normally, the required quantity of hot air is drawn from an engine compressor for an Aircraft Environmental Control System (ECS). The present work aims to illustrate the energy saving that can be realized by using a bleed-less aircraft environment control system (ECS) that is powered by an auxiliary ram air compressor: This paper presents a direct comparison between the energy consumption of a conventional bleed air system and a bleed-less ECS. A conventional bleed air ECS system is first modeled using MATLAB and validated with results in the open literature. The system is modeled to match the temperature profile with that of an Airbus 320 during cruise conditions. Then, a bleed less system is modeled by modifying the bleed air system to use a ram-air compressor for the air intake as a bleed less ECS. Finally, the fuel mass penalties associated with each environment control system are calculated. The bleed air system incurs fuel penalties due to bleed air extraction, and additional drag due to the ram air intakes for the large heat exchanger ram-air scoops. Whereas the bleed-less system incurs penalties due to drag from the small ram-air intakes for the heat exchanger and the ram air compressor scoop and a dedicated electrical power system for the ram air compressor. It was found that the total fuel mass penalties calculated for the bleed less system are about 80% lesser compared to a conventional bleed air ECS without a dedicated electrical power system.
Boiling of R134a in a Plate-Fin Heat Exchanger Having Offset Fins
(ASME, 2015-12) Ranganayakulu, Chennu
This paper presents experimental results on boiling heat transfer of R134a in a compact plate fin heat exchanger. The exchanger is made of aluminum and has high density offset fins (30 fins/in.). Such heat exchangers are widely used in air separation industry and aerospace applications because of their high compactness and low weight. The test heat exchanger is attached to a vapor cycle refrigeration basic module to study the effects of boiling phenomena and its influence on performance as there is limited information available for this type of fins. This in turn allows for discussion on boiling mechanism of R134a inside the fins using the water circuit on the other side of the test heat exchanger. The water side single phase heat transfer coefficient (Colburn j factor) is calculated using the cfd tool fluent and validated with available open literature. The results are presented for heat fluxes up to 5500 W/m2 and mass fluxes up to 20 kg/(m2s) with water side flow rate varying from 0.033 to 0.17 kg/s for water temperatures of 10, 15, 20, 25, and 30 °C.
Bubble formation with pool boiling on tubes with or without basic surface modifications for enhancement
(Elsevier, 2004-04) Ranganayakulu, Chennu
Bubble formation is investigated on a single, horizontal copper tube (D=25.4 mm) before and after applying surface modifications in the form of macrocavities with comparatively simple shapes (size: 200 × 100 μm on the tube surface and 50 μm in depth) in order to link bubble formation and heat transfer to the geometric features of the cavities. Two kinds of cavities exist in parallel, one with reduced mouth width (so-called “main structure”) and one without this reduction (“secondary structure”). Pool boiling experiments with different organic liquids have been performed with variation of heat flux and saturation pressure. The resulting bubble formation on the tubes with and without surface modifications is discussed in terms of characteristic parameters such as local distribution and temporal activation behavior of the nucleation sites for bubble formation at active nucleation sites (“primary bubbles”) or for bubbles released from the macrocavities (“secondary bubbles”).
Colburn ‘j’ Factor and Fanning Friction Factor ‘f’ Correlations of Triangular Plain Fin Surface of a Compact Heat Exchanger Using CFD
(Scientific net, 2015) Ranganayakulu, Chennu
This paper presents the heat transfer and friction coefficient correlations for triangular plain fin surfaces of plate fin compact heat exchanger. It will be prohibitively expensive and time consuming to fabricate heat exchanger cores and conduct experiments over reasonable ranges of all the geometric variables. In contrast, it is relatively easy and cost effective to carry out a parametric study through numerical simulation and derive acceptable correlations for use in industry. A numerical model has been developed for the triangular plain fin of plate fin heat exchanger. The CFD analysis is carried out using FLUENT 12.1, Colburn factor j and fanning friction factor f are calculated for different Reynolds numbers. These values are compared with the available literature data of j and f factors. The correlations have been expressed in terms of two separate equations over the low and high Re regions along with dimensionless geometric parameters.
The combined effects of inlet fluid flow and temperature nonuniformity in cross flow plate-fin compact heat exchanger using finite element method
(Springer, 1997-06) Ranganayakulu, Chennu
An analysis of a crossflow plate-fin heat exchanger accouning for the combined effects of inlet fluid flow nonuniformity and temperature nonuniformity on both hot and cold fluid sides is carried out using a Finite Element Model. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in inlet fluid flow. Using these fluid flow maldistribution models, the exchanger effectiveness and its deteriorations due to flow/temperature nonuniformity are calculated for entire range of design and operating conditions. It was found that the performance deteriorations are quite significant in some typical applications due to inlet fluid flow/temperature nonuniformity.
The combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity in crossflow plate-fin heat exchangers
(Elsevier, 1999-07) Ranganayakulu, Chennu
An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effects of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distribution is carried out using a finite element method. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in fluid flow. Using these models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance variations are quite significant in some typical applications.
The combined effects of wall longitudinal heat conduction and inlet fluid flow maldistribution in crossflow plate-fin heat exchangers
(Springer, 2000-05) Ranganayakulu, Chennu
An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effect of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow distribution on both hot and cold fluid sides is carried out using a finite element method. Using the fluid flow maldistribution models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction and flow nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance deteriorations are quite significant in some typical applications due to the combined effects of wall longitudinal heat conduction and inlet fluid flow nonuniformity on crossflow plate-fin heat exchanger.
The combined effects of wall longitudinal heat conduction, inlet fluid flow nonuniformity and temperature nonuniformity in compact tube–fin heat exchangers: a finite element method
(Elsevier, 1999-01) Ranganayakulu, Chennu
A finite element analysis of a crossflow tube–fin compact heat exchanger is presented. The analysis takes into account the combined effects of one-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distributions on both hot and cold fluid sides. A mathematical equation is developed to generate different types of fluid flow⧹temperature maldistribution models considering the possible deviations in fluid flow. Using these fluid flow⧹temperature maldistribution models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction and flow⧹temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance deteriorations are quite significant in some typical applications due to the combined effects of longitudinal heat conduction, temperature nonuniformity and fluid flow nonuniformity on crossflow tube–fin heat exchanger.
The combined effects of wall longitudinal heat conduction, inlet fluid flow nonuniformity and temperature nonuniformity in compact tube–fin heat exchangers: a finite element method
(Elsevier, 1999-01) Ranganayakulu, Chennu
A finite element analysis of a crossflow tube–fin compact heat exchanger is presented. The analysis takes into account the combined effects of one-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distributions on both hot and cold fluid sides. A mathematical equation is developed to generate different types of fluid flow⧹temperature maldistribution models considering the possible deviations in fluid flow. Using these fluid flow⧹temperature maldistribution models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction and flow⧹temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance deteriorations are quite significant in some typical applications due to the combined effects of longitudinal heat conduction, temperature nonuniformity and fluid flow nonuniformity on crossflow tube–fin heat exchanger.
Compact Heat Exchangers – Analysis, Design and Optimization using FEM and CFD Approach cover image Compact Heat Exchangers – Analysis, Design and Optimization using FEM and CFD Approach
(Wiley, 2018-02) Ranganayakulu, Chennu
A comprehensive source of generalized design data for most widely used fin surfaces in CHEs Compact Heat Exchanger Analysis, Design and Optimization: FEM and CFD Approach brings new concepts of design data generation numerically (which is more cost effective than generic design data) and can be used by design and practicing engineers more effectively. The numerical methods/techniques are introduced for estimation of performance deteriorations like flow non-uniformity, temperature non-uniformity, and longitudinal heat conduction effects using FEM in CHE unit level and Colburn j factors and Fanning friction f factors data generation method for various types of CHE fins using CFD. In addition, worked examples for single and two-phase flow CHEs are provided and the complete qualification tests are given for CHEs use in aerospace applications. Chapters cover: Basic Heat Transfer; Compact Heat Exchangers; Fundamentals of Finite Element and Finite Volume Methods; Finite Element Analysis of Compact Heat Exchangers; Generation of Design Data by CFD Analysis; Thermal and Mechanical Design of Compact Heat Exchanger; and Manufacturing and Qualification Testing of Compact Heat Exchanger. Provides complete information about basic design of Compact Heat Exchangers Design and data generation is based on numerical techniques such as FEM and CFD methods rather than experimental or analytical ones Intricate design aspects included, covering complete cycle of design, manufacturing, and qualification of a Compact Heat Exchanger Appendices on basic essential fluid properties, metal characteristics,
Comparative Study of Straight and Venturi Channel Cross Sections of Microchannel Heat Exchangers
(ASME, 2024-09) Ranganayakulu, Chennu
This study provides extensive research on fluid flow and heat transfer for four-layered ceramic-compact counterflow microchannel heat exchangers (CFMCHE) using CFD-ACE®, a computational fluid dynamics (CFD) package. The goal is to build and expand upon previous studies in this area to identify a more efficient channel shape or cross section for better performance of the microchannel through numerical analysis under the same operating conditions. To develop the methodology for numerical analysis, a three-dimensional (3D) computational model of the CFMCHE was developed and validated with published and experimentally tested results with a percentage difference in outlet temperatures of 3–5% for hot fluids and 6–12% for cold fluids across the entire design of experiments (DoEs). Microchannel heat exchangers (MCHEs) exhibit high heat-transfer rates and area-to-volume ratios, making them suitable for industrial applications. In this study, various design options for channel cross sections in a venturi shape were assessed numerically using a validated methodology in a segmented venturi CFMCHE to enhance performance. The steady-state performance of the Venturi CFMCHE was compared to that of the straight CFMCHE baseline design under the same bucket volume, area, and operating conditions. It was found that the venturi CFMCHE showed a ∼4–9% improvement as compared to the straight CFMCHE, but same time the pumping power was also 15–40% under the same operating conditions. Making the right choice regarding feasibility often involves weighing the pros and cons. The high-power requirements are manageable in terms of the cost of high thermal performance for ground applications, such as power plants, industrial refrigeration, and air-conditioning. However, for aviation, space, and automobiles, weight/power requirements are given more weight than thermal performance. Therefore, the Venturi CFMCHE can be used for ground applications, whereas the straight CFMCHE can be used for aviation, space, and automobile applications. When the Goodness factor is plotted for all configurations for all operating conditions, it is also concluded that an improvement of ∼7.5% is observed in the two design configurations with the Venturi channel (20pc_TOP_BTM_Step and 40pc_BTM_Step) with respect to the straight channel. This implies that these two best designs can be used for all applications over the straight-channel CFMCHE.
Condensation heat transfer and pressure drop of R-134a saturated vapour inside a brazed compact plate fin heat exchanger with serrated fin
(Springer, 2016-05) Ranganayakulu, Chennu
This paper presents the experimental heat transfer coefficient and pressure drop measured during R-134a saturated vapour condensation inside a small brazed compact plate fin heat exchanger with serrated fin surface. The effects of saturation temperature (pressure), refrigerant mass flux, refrigerant heat flux, effect of fin surface characteristics and fluid properties are investigated. The average condensation heat transfer coefficients and frictional pressure drops were determined experimentally for refrigerant R-134a at five different saturated temperatures (34, 38, 40, 42 and 44 °C). A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 22 kg/m2s. In the forced convection condensation region, the heat transfer coefficients show a three times increase and 1.5 times increase in frictional pressure drop for a doubling of the refrigerant mass flux. The heat transfer coefficients show weak sensitivity to saturation temperature (Pressure) and great sensitivity to refrigerant mass flux and fluid properties. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. Correlations are provided for the measured heat transfer coefficients and frictional pressure drops.
Configuration Studies of Aircraft Environmental Control System Using Exergy Analysis of Compact Heat Exchangers for Multi-disciplinary Optimization
(Springer, 2023-03) Ranganayakulu, Chennu
Traditionally 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.
Development of colburn ‘j’ factor and fanning friction factor ‘f’ correlations for compact heat exchanger plain fins by using CFD
(Springer, 2013-03) Ranganayakulu, Chennu
A numerical model has been developed for plain fin of plate fin heat exchanger. Plain fin performance has been analyzed with the help of CFD by changing the various parameters of the fin, Colburn ‘j’ and fanning friction ‘f’ factors are calculated. These values compared with the standard values. The correlations have been developed between Reynolds number Re, fin height h, fin thickness t, fin spacing s, Colburn factor ‘j’ and friction factor ‘f’.
Development of Colburn j Factor and Fanning Friction Factor Correlations for Compact Surfaces of the Triangular Perforated Fins Using CFD
(Taylor & Francis, 2015-07) Ranganayakulu, Chennu
The necessity of increased heat transfer surface area has resulted in the development of compact heat exchangers, which are widely used in the aerospace and automobile industries. Hence perforations are made on triangular plain fins to study the effects on the heat transfer coefficient. A numerical model has been developed for the perforated fin of a triangular plate fin heat exchanger. Perforated fin performance has been analyzed with the help of computational fluid dynamics (CFD) by changing the various parameters of the fin. The Colburn j factor and the Fanning friction factor are calculated for different Reynolds numbers. The values of the Colburn j factor and the Fanning friction factor are validated for known geometric fins with available data in the literature and extended to triangular perforated fins. The correlations have been developed between Reynolds number, Colburn j factor, and Fanning friction factor by taking into account fin height, fin thickness, and fin spacing. The present numerical analysis is carried out for air media.
Development of heat transfer coefficient and friction factor correlations for offset fins using CFD
(Emerald, 2011-11) Ranganayakulu, Chennu
In 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.
Development of Heat Transfer Coefficient and Friction Factor Correlations for Serrated Fins in Water Medium using CFD
(David Publishing Company, 2015) Ranganayakulu, Chennu
The 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.
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, Chennu
Two 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.
The effects of inlet fluid flow nonuniformity on thermal performance and pressure drops in crossflow plate-fin compact heat exchangers
(Elsevier, 1996-10) Ranganayakulu, Chennu
An analysis of a crossflow plate-fin compact heat exchanger, accounting for the effects of two-dimensional nonuniform inlet fluid flow distribution on both hot and cold fluid sides, is carried out using a finite element model. A mathematical equation is developed to generate different types of fluid flow maldistribution models considering the possible deviations in fluid flow. Using these fluid flow maldistribution models, the exchanger effectiveness and its deterioration due to flow nonuniformity are calculated for an entire range of design and operating conditions. In addition to thermal analysis, the pressure drops and their variations are also calculated for these models. It was found that the performance deteriorations and variation in pressure drops are quite significant in some typical applications due to fluid flow nonuniformity