Journal Articles
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/19884
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Item Use of a CFD code in the investigation of cross corrugated heat transfer surfaces(2010) Ashok Babu, T.P.A.; Shekoor, T.M.The variation of main geometric details of cross corrugated surfaces (i.e. aspect ratio and angle of corrugation) makes it increasingly difficult to have a general design method. In the absence of adequate 'database' covering all possible configurations, it is nearly impossible to predict the highly effective configuration. Thus CFD simulation is effective, as it allows computation for various geometries, and study of the effect of various design configurations on heat transfer and flow characteristics. The present paper discusses the use of a CFD code to select the cross corrugated heat transfer surface (CC surface) with minimum core volume of a recuperator matrix. Due to difficulties Induced by geometry and computational time, simple model is used as a first step. The SS T turbulence model was preferred over other flow models for simulations. This simple model, comprised of three corrugated plates having their crest nearly in contact, with hot and cold fluids flow alternately through passage created between the plates. Some selected cross corrugated heat transfer surfaces are used for the analysis. The results for the simplified model, presented in terms of outlet temperatures, heat transfer coefficients and skin friction coefficients, is encouraging to undertake extensive work in CFD simulation and create more 'database' on various configurations. Design calculations of a recuperator matrix for a 10 kW micro turbine have been carried out for the selected surfaces. The relation between the minimum core volume of the matrix from design calculation and average skin friction coefficient from CFD analysis is established to use CFD analysis for selection of heat transfer surfaces with minimum recuperator matrix core volume. The analysis is carried out with air and nitrogen as heat transfer fluids.Item Transient analysis of subcritical/supercritical carbon dioxide based natural circulation loops with end heat exchangers: Numerical studies(Elsevier Ltd, 2014) Yadav, A.K.; Ram Gopal, M.; Bhattacharyya, S.Transient analysis of carbon dioxide based natural circulation loop (NCL) with end heat exchangers has been carried out. Subcritical and supercritical phases of CO2 are considered with operating pressures in the range of 50-100 bar for an operating temperature range of 323 K to 363 K. Studies are carried out for various loop tilt angles, different initial conditions, and different water mass flow rates. Results: are obtained for various inlet temperatures of water in the hot heat exchanger while keeping the inlet temperature of cooling water in the cold heat exchanger fixed. Effect of tilting the loop in XY and YZ planes on transient as well as steady state behaviour of loop are also studied. Validation of simulation results against experimental and numerical results reported in the literature in terms of modified Grashof number (Grm) and Reynolds number (Re) show good agreement. © 2014 Elsevier Ltd. All rights reserved.Item Effect of preheated mixture on heat transfer characteristics of impinging methane-air premixed flame jet(Elsevier Ltd, 2015) Tajik, A.R.; Kuntikana, P.; Prabhu, S.V.; Hindasageri, V.Energy from spent flame or other low grade energy can be used to increase the temperature of the air before mixing with fuel. This would improve the heat transfer characteristics of the impinging flame jet. The studies on impinging flame jets reported in the literature are based on the fuel-air mixture at ambient temperature. In the present work, the inlet air for mixture is heated by an electrical heater. The heat flux distribution is estimated using an inverse heat conduction (IHCP) technique. The Nusselt number (Nu) and effectiveness (?) distributions are obtained by estimating the adiabatic wall temperature (Taw) by the analytical-numerical method. A circular burner of 13.5 mm is used for impingement on quartz plate of 3 mm thickness. Reynolds number (Re) varying from 500 to 2000 for the non-dimensional burner tip to impingement plate spacing (Z/d) of 2-6 and stoichiometric condition (Ø = 1.0) is considered for varying preheated condition. The effect of equivalence ratio is studied for Ø = 0.75 to 1.5 for Re = 1000 and Z/d = 4. By increase in preheat temperature, the stagnation point heat flux increases from 20% to 50% unless the inner premixed zone touches the impingement plate. CFD simulations are carried out in FLUENT software to explain the distribution of heat flux. © 2015 Elsevier Ltd. All rights reserved.Item Coupled computational fluid dynamics-discrete element method simulations of a pilot-scale batch crystallizer(American Chemical Society service@acs.org, 2015) Ali, B.; Börner, M.; Peglow, M.; Janiga, G.; Seidel-Morgenstern, A.; Thévenin, D.Computational fluid dynamics (CFD) coupled with the discrete element method (DEM) has been used to investigate numerically crystal dynamics in an existing pilot-scale batch crystallizer. The CFD-DEM combination provides a detailed description of crystal dynamics considering a four-way coupling. In a previous analysis,1 CFD had been coupled with a discrete phase model (DPM) using a simple one-way coupling. The corresponding predictions are then compared with those obtained through four-way coupling considering KH2PO4 crystals in water. From the CFD-DEM simulation, it is possible to investigate quantitatively the driving force controlling crystal growth and the interaction of crystals with reactor walls, baffles, and impellers. This delivers essential data for process improvement. Different seeding procedures were also compared. The seed crystals have been injected either within the complete liquid volume or, as in the experiments, through a funnel. By varying the most important crystallization process parameters, we found optimal conditions for a liquid phase volume in the crystallizer of 24 L, for injection through a funnel above the baffle, and for an initial seed crystal size of 0.5 mm. © 2014 American Chemical Society.Item The effect of cordierite/Pt catalyst on the NOx reduction in a diesel and Jatropha bio-diesel operated single cylinder engine(Elsevier Ltd, 2015) Kumar, A.P.M.; Sreekumar, J.S.; Mohanan, P.Bio-diesel is an alternative energy resource, which can be successfully used in diesel engines. One major disadvantage of using bio-diesel is the higher emission of NOx. Hence some after treatment devices have to be adopted to reduce NOx in order to meet the stringent limits on emission standards. In the current research work honeycomb structured circular Cordierite/Pt SCR catalyst is used as an aftertreatment device. Studies revealed that SCR (Selective catalytic reduction) catalyst exhibits better performance at a higher temperature range (>500 °C), which can be successfully used in Trucks and Buses. But many catalysts failed to exhibit better performance at a lower temperature range varies from 180 to 400 °C, which makes these catalysts unsuitable to use with light and medium duty vehicles. The main objective of this study is to assess the suitability of Cordierite/Pt catalyst for light and medium duty vehicles and study the effect of SCR catalyst on bio-diesel blends in order to reduce NOx in a single cylinder diesel engine. The experimental work has been carried out using diesel and bio-diesel as a fuel and the NOx reduction is tabulated. The results are validated with CFD code AVL FIRE. The ammonia flow rate has been varied from 0.2 to 0.8 kg/h. It has been found that among all the blends B15 has shown maximum NOx conversion of 60% and NH3 conversion of 34%. © 2015 Elsevier Ltd. All rights reserved.Item A numerical investigation on heat transfer and emissions characteristics of impinging radial jet reattachment combustion (RJRC) flame(Elsevier Ltd, 2015) Tajik, A.R.; Hindasageri, V.Radial Jet Reattachment combustion (RJRC) flame jet is used in applications where the impingement surface is delicate and demands low impingement pressure. In the present study, a two dimensional axisymmetric computational fluid dynamics (CFD) simulation is carried out. The turbulence-combustion interaction in the flame field is modeled in a k-?/EDM framework. The distribution of heat flux, pressure coefficient and emissions is presented for varying Reynolds number (Re = 1000 to 30,000) and different non-dimensional nozzle tip to plate spacing (X/R = 0.5 to 3). It is found that the peak heat flux increases and pressure coefficient reduces significantly with the increase in Reynolds number. However, with the increase in the nozzle tip to plate spacing the peak heat flux and the pressure coefficient decrease. Furthermore, the concentrations of NOx and CO emissions increase with the increase in Reynolds number and the distance of the location of the nozzle tip from the impingement plate. © 2015 Elsevier Ltd. All rights reserved.Item A neural network based method for estimation of heat generation from a teflon cylinder(Global Digital Central, 2016) Kumar, S.; Kumar, H.; Gnanasekaran, N.The paper reports the estimation of volumetric heat generation (qv) from a Teflon cylinder. An aluminum heater, which acts as a heat source, is placed at the center of the Teflon cylinder. The problem under consideration is modeled as a three dimensional steady state conjugate heat transfer from the Teflon cylinder. The model is created and simulations are performed using ANSYS FLUENT to obtain temperature data for the known heat generation qv. The numerical model developed using ANSYS acts as a forward model. The inverse model used in this work is Artificial Neural Network (ANN). Estimation of heat generation is carried out by minimizing the error between the simulated temperature and the experimental/surrogated temperature. The efficacy of the ANN method is explored for the estimation of unknown heat generation as both forward model and inverse model. The concept of Asymptotic Computational Fluid Dynamics (ACFD) is introduced as a fast forward model which is obtained by performing CFD simulations. The unknown heat generation is estimated for the surrogated data using ANN. In order to mimic experiments, noise is added to the surrogated data and estimation of heat generation is also carried out for the perturbed/noise added temperature data. © 2016, Global Digital Central. All rights reserved.Item Computational fluid dynamic approach to understand the effect of increasing blockage on wall shear stress and region of rupture in arteries blocked by arthesclerotic plaque(UK Simulation Society Clifton Lane Nottingham NG11 8NS, 2016) Hegde, S.S.; Deb, A.; Nagesh, S.Computational bio-mechanics is developing rapidly as a non-invasive tool to assist the medical fraternity to help in both diagnosis and prognosis of human body related issues such as injuries, cardio-vascular dysfunction, atherosclerotic plaque etc. Any system that would help either properly diagnose such problems or assist prognosis would be a boon to the doctors and medical society in general. This project is an attempt to use numerical analysis techniques; in particular, computational fluid dynamics (CFD) to solve hemodynamics related problems. The mathematical modeling of the blood flow in arteries in the presence of successive blockages has been analyzed using CFD technique. Different cases of blockages in terms of percentages have been modeled to study the effect of blockage on wall shear stress values and also the effect of increase in Reynolds number on wall shear stress values. The concept of fluid structure interaction (FSI) has been used to study the effect of increasing von Mises stress on arteries and to determine the region of rupture in arteries. The simulation results are validated using in vivo measurement data from existing literature. © 2016, UK Simulation Society. All rights reserved.Item Heat transfer distribution of impinging flame and air jets - A comparative study(Elsevier Ltd, 2016) Kadam, A.R.; Tajik, A.R.; Hindasageri, V.Heat transfer distribution of impinging flame jet is compared with that of the impinging air jet based on the experimental data reported in literature for methane-air flame jet and air jet impingement for Reynolds number, R=600-1400 and the non-dimensional nozzle tip to impingement plate distance, Z/d=2-6. The comparative data based on mapping experimental data reported in literature suggest that there is a good agreement between the Nusselt numbers for higher Z/d near stagnation region. However, away from the stagnation region, the Nusselt number for flame jet is higher than that of air jet for similar operating conditions of Re and Z/d. A CFD simulation for impinging air jet and impinging flame jet is carried out to explain the physics and reason for the deviations observed in experimental data. A scale analysis is carried out to identify the dominant forces and their influence on the heat transfer distribution on the impingement plate. © 2015 Elsevier Ltd. All rights reserved.Item Effect of tilt angle on subcritical/supercritical carbon dioxide-based natural circulation loop with isothermal source and sink\(American Society of Mechanical Engineers (ASME) infocentral@asme.org, 2016) Yadav, A.K.; Ram Gopal, M.R.; Bhattacharyya, S.In recent years, a growing popularity of carbon dioxide (CO2) as a secondary fluid has been witnessed in both forced as well as in natural circulation loops (NCLs). This may be attributed to the favorable thermophysical properties of CO2 in addition to the environmental benignity of the fluid. However, an extensive literature review shows that studies on CO2-based NCLs are very limited. Also, most of the studies on NCLs do not consider the three-dimensional variation of the field variables. In the present work, threedimensional computational fluid dynamics (CFD) models of a NCL with isothermal source and sink have been developed to study the effect of tilt angle in different planes. Studies have been carried out employing subcritical (liquid and vapor) as well as supercritical phase of CO2 as loop fluid at different operating pressures and temperatures. Results are obtained for a range of tilt angles of the loop, and a significant effect is observed on heat transfer, mass flow rate, and stability of the loop. It was also found that changing the orientation of the loop could be an elegant and effective solution to the flow instability problem of NCLs.