Seyfettin Bayraktar

Computational Fluid Dynamics and Heat Transfer Analysis for a Novel Heat Exchanger

Computational fluid dynamics (CFD) and heat transfer simulations are conducted for anovel heat exchanger. The heat exchanger consists of semi-circle cross-sectioned tubesthat create narrow slots oriented in the streamwise direction. Numerical simulations areconducted for Reynolds numbers (Re) ranging from 700 to 30,000. Three-dimensionalturbulent flows and heat transfer characteristics in the tube bank region are modeled bythe k-e Reynolds-averaged Navier–Stokes (RANS) method. The flow structure predictedby the two-dimensional and three-dimensional simulations is compared against thatobserved by the particle image velocimetry (PIV) for Re of 1500 and 4000. The adequateagreement between the predicted and observed flow characteristics validates the numeri-cal method and the turbulent model employed here. The three-dimensional and the two-dimensional steady flow simulations are compared to determine the effects of the wall onthe flow structure. The wall influences the spatial structure of the vortices formed in thewake of the tubes and near the exit of the slots. The heat transfer coefficient of the slottedtubes improved by more than 40% compare to the traditional nonslotted tubes.[DOI: 10.1115/1.4029764]Keywords: heat transfer, slotted tube, computational fluid dynamics, turbulence, Reyn-olds-averaged Navier–Stokes

Numerical investigation of a water flow in a rib-roughened channel by using Reynolds stress model

In this paper, water flow in a rib-roughened channel is investigated numerically by using Reynolds stress turbulence models (RSM) on a three-dimensional (3-D) domain. Computational results for mean streamwise velocity component and turbulent kinetic energy show good agreements with available experimental data. Five rib pitch-to-height ratios (p/h) of 1, 5, 10, 15 and 20 are analysed for six different Reynolds numbers (Re) of 3000, 7000, 12,000, 20,000, 40,000 and 65,000. Velocity vectors, streamlines and Reynolds stresses are showed for these ratios and Re numbers. Streamlines revealed that Reynolds numbers do not affect flowfield but play an important role in the Reynolds stresses.

Efficiency optimisation of gas turbine based cogeneration cycle

AbstractThis paper presents an optimisation of a cogeneration system based on alternative performance criteria. The system includes a gas turbine which is operated in a Brayton cycle and a heat recovery steam generator (HRSG). In the analysis, total produced exergy, energy utilisation factor (EUF), artificial thermal efficiency and exergy efficiency have been defined as function of the design parameters of the gas turbine and the HRSG. The optimum values of the design parameters of the cogeneration cycle were determined for different criteria. In this context, the effects of design parameters on the exergetic performance are investigated and the results are discussed. The obtained results may guide towards a more realistic criterion for actual cogeneration plants.

Cfd and Analytical Analysis of Exhaust System of a Gas Turbine Used in a Ship

In this study, exhaust system of the gas turbine of a ship with CODOG (Combined Diesel Or Gas‐turbine) system is analyzed both analytically and numerically. The results obtained from these two different methods are then compared. The flow and heat transfer analysis of the exhaust system is done using a full scale two‐dimensional (2‐D) model and in the simulation velocity vectors, pressure and temperature fields are obtained. The gas turbine exhaust system velocity is 40 m/s, especially just after the inlet. For the mathematical model, time‐averaged, steady‐state, mean flow equations of continuity, momentum and energy equations can be written in Cartesian tensor notation. In commercially available computational fluid dynamics (CFD) code FLUENT 6.2, the governing equations are discretized using second order upwind interpolation scheme, and the discretized equations are solved using SIMPLEC algorithm. The Standard k‐e turbulence model is used for the turbulence closure. The boundary layer meshes are applied ...

Heat and Fluid Flow Analyses of an Impinging Jet on a Cubic Body

In the present study, the problem of impinging jet on a cubic body is taken into account by means of computational fluid dynamics (CFD). Effects of density changes of the working fluid on the flow and heat transfer have been investigated for various Reynolds numbers. For this purpose three different approaches have been adopted where the density of the fluid is kept constant, density changes according to Boussinesq approximation, and finally density changes linearly with temperature. Since the flow is taken to be fully turbulent, standard k-e (SKE) turbulence model has been adopted. The successful validation process implies that the used mesh structure and mesh number are appropriate and SKE turbulence model can be used for impinging jet on a cubic body in the stagnation region. The correlation between Nusselt number and Reynolds number has been proposed. In addition, a similarity between two different approaches is detected.