Ahmet Koca

Estimation of solar radiation using artificial neural networks with different input parameters for Mediterranean region of Anatolia in Turkey

An artificial neural network (ANN) model was used to estimate the solar radiation parameters for seven cities from Mediterranean region of Anatolia in Turkey. As well known that Turkey is a bridge between Asia and Europe and it lies in a sunny belt, between 36^o and 42^oN latitudes. Indeed, the country has sufficient solar radiation intensities for solar applications. In order to make estimation of solar radiation, the data from the Turkish State and Meteorological Service were used. Data of 2006 were used for testing and data of 2005, 2007, and 2008 were estimated. Effects of number of input parameters were tested on solar radiation that was output layer. With this aim, number of input layer parameters changed from 2 to 6. The obtained results indicated that the method could be used by researchers or scientists to design high efficiency solar devices. It was also found that number of input parameters was the most effective parameter on estimation of future data on solar radiation.

Analysis of adaptive-network-based fuzzy inference system (ANFIS) to estimate buoyancy-induced flow field in partially heated triangular enclosures

Adaptive-network-based Fuzzy Inference System (ANFIS) was used to predict temperature and flow field due to buoyancy-induced heat transfer in a partially heated right-angle triangular enclosure. Results are obtained for two-dimensional, steady and laminar flow. Data were generated from earlier studies which were obtained from a CFD-based computer code writing in Fortran. Equations were analyzed using finite difference method. Effective parameters on flow and temperature fields are Rayleigh number, location of partial heater and height-to-base ratio of triangular enclosures. Both instability and accuracy related results will be discarded by using ANFIS. Thanks to using of ANFIS, computation time, memory space and effort were reduced.

Forecasting of entropy production due to buoyant convection using support vector machines (SVM) in a partially cooled square cross-sectional room

Forecasting of entropy generation of laminar natural convection in a partially cooled square cross-sectional room has been performed using support vector machines (SVM). The two-dimensional room was modeled as floor heating story with a window. Values of temperature and velocities were obtained by solving governing equations of natural convection with finite difference technique and using these values entropy generation was calculated with its definition. Forecasting of entropy generation due to fluid friction irreversibility (FFI) and heat transfer irreversibility (HTI) were made with known values for unknown parameters using SVM. Thus, calculation time was extremely reduced and values were obtained even for non-convergence cases. It was observed that the SVM was a strong method to predict the entropy generation without computational fluid dynamic analysis for all cases.

Using of Bejan's Heatline Technique for Analysis of Natural Convection in a Divided Cavity with Differentially Changing Conductive Partition

The issue of laminar natural convection and conduction in enclosures divided by a partition with different thicknesses is investigated numerically. The partition is accepted as conductive at different thermal conductivity ratio. The cavity is filled with air, and it is heated differentially from vertical walls while horizontal walls are adiabatic. The problem is solved for different values of Rayleigh number (103 ≤ Ra ≤ 106), thickness ratio of the partition, and thermal conductivity ratio (0.1 ≤ k ≤ 10.0). It is found that both heat transfer and flow strength strongly depend on the thermal conductivity ratio of the solid material of partition and Rayleigh numbers.

Numerical analysis of natural convection in shed roofs with eave of buildings for cold climates

A numerical study has been carried out on partially heated triangular enclosures with eave. The eave and inclined wall has a cold temperature. The laminar, two-dimensional, steady governing equations of natural convection are solved in the streamfunction-vorticity form using a finite difference technique. Streamline, isotherm and Nusselt number are presented for different parameters such as aspect ratio AR=H/L from 0.25 to 1, ratio of eave length E=L/n where n changes from 3 to 7 and Rayleigh number from 10^3 to 10^6. It is observed that the heat transfer decreases with increasing aspect ratio for small Rayleigh number but increases for higher Rayleigh number. Heat transfer also increases with decreasing eave length.

Effects of Inclination Angle on Natural Convection in Composite Walled Enclosures

Natural convection in square-cross-sectional inclined enclosures bounded by two attached solid walls (composite wall) was simulated by a numerical technique in this study. Conduction heat transfer through each part of a composite wall was examined for different solid wall thicknesses and thermal conductivities. The opposite wall was accepted as thin and it was isothermal at a lower temperature than that of the outside of the composite wall, while the remaining walls were adiabatic. The governing equations were solved by finite-difference technique for the governing parameters for different Rayleigh numbers, ranging from 103 to 106, with the thickness ratio of solid walls greater than 0.05 (for left vertical wall) and less than 0.2 (for right vertical wall), and thermal conductivity ratios for first and second materials to the fluid ranging from 1 to 5 and inclination angle ranging from 0° to 180°. The written code was tested with similar numerical and experimental studies in earlier literature and a good agreement was found. It was proved that lower heat transfer occurred when the wall with lower thermal conductivity ratio was located at the outside of the composite wall and it affected the flow strength in the enclosure. Inclination angle and other governing parameters were also used as control parameters for heat and fluid flow.

Energy and exergy analysis of a heat storage tank with a novel eutectic phase change material layer of a solar heater system

ABSTRACT Solar energy is one of the most important renewable energy sources, but it is not available every time and every season. Thus, storing of solar energy is important. One of the popular methods of heat storage is use of phase change materials (PCMs) which have large thermal energy storage capacity. In this study, the heat storage tank in a domestic solar water heating system was chosen as control volume. The experiments were performed in the province of Elazıg, Turkey, in November when solar radiation was weak due to cloudy sky. The heat storage tank of the system was modified to fill PCM between insulation and hot water part. A few PCMs which are Potassium Fluoride, Lithium Metaborate Dihydrate, Strontium Hydroxide Octahydrate, Barium Hydroxide Octahydrate, Aluminum Ammonium Sulfate, and Sodium Hydrogen Phosphate were analyzed to proper operating conditions using a Differential Scanning Calorimeter (DSC) and the best PCM was obtained with the Aluminum Ammonium Sulfate and Sodium Hydrogen Phosphate mixture. Thus, eutectic PCM was obtained and used in a heat storage tank of the solar water heating system. Energy and exergy analysis of heat storage tank was performed with and without the PCM. Energy and exergy analysis has shown that the heat storage tank with the PCM is more efficient than without the PCM and the maximum exergy efficiency was obtained as 22% with the heat storage tank with the PCM.

Numerical analysis of wave energy converting systems in case of using piezoelectric materials for energy harvesting

The aim of the study is to model and investigate the wave energy converting system with piezoelectric materials numerically. In this study, computational fluid dynamics software Fluent is used for ...

Performance Analysis of Wave Energy Harvesting System with Piezoelectric Element

Wave energy harvesting systems capture power from the sea or ocean waves. Piezoelectric elements are materials that can create electricity when subjected to a mechanical stress. In this study, wave energy harvesting system with piezoelectric element is used to generate power. For this aim, a wave tank with wavemaker was built in laboratory condition. Wavemaker generates sinusoidal twin waves with 4 cm height per second. An obstacle with piezoelectric element is placed in the tank. The parameters of the experimental study are obstacle position and piezoelectric element angle with water level. It is found that the position and angle of the piezoelectric element is very important to generate power for the wave harvesting systems.

Numerical Wave Tank Analysis for Energy Harvesting with Oscillating Water Column

In this study, analysis of Oscillating Water Column which is one of the Wave Energy Converters is made in Numerical Wave Tank base on Fluent consist of Finite volume Method. NWT is simulated based on Reynolds-averaged Navier–Stokes equations. Volume of Fluid method, k-epsilon turbulence model, Pressure Implicit with Splitting of Operator algorithm Dynamic Mesh Technique are employed in transient numerical analysis. User Defined Function is introduced for movement of Piston Type wave maker. The hydrodynamic energy absorbed from the waves by the OWC device during a wave period is calculated for two cases have different shore slopes at the same volume of water in tank. The comparison of two cases shows that the increase in the shore slope angle means decrease in the output power in air chamber of OWC device at the same volume of water.