MCBÜ Açıkerişim Sistemi :: Browsing by Author "Yurddas, A"

Browsing by Author "Yurddas, A"

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Applicability of cogeneration system in gas turbines used in natural gas storage facilities
Türkoglu, S; Yurddas, A; Bektas, A
Underground natural gas storage facilities are of critical importance on energy supply security. Storage activity in facilities performing underground storage is mostly carried out in spent natural reservoirs. In this study, the applicability of cogeneration system was investigated in order to generate electricity from flue gas at an average temperature of 500 degrees C and 144.4 t/h flow rate obtained from three gas turbines in storage facilities and to recover the waste heat we lost. This designed system would have three HRSGs and one steam turbine, 16.23 MW energy would be generated from each HRSG in this system. After a total of 48.70 MW energy, obtained from two HGRSs, enters into the steam turbine operating in 24% efficiency, 12.20 MW mechanic energy and 11.84 MW electric energy is generated. Therefore, a total of 97.05 MW energy entering into combined cycle power plant was transformed into a total of 42.25 MW useful energy, including 30.41 MW mechanical and 11.84 MW electricity, and the efficiency of system was calculated as 43.5%. It was aimed that the electric energy to be generated from this cogeneration system would contribute to the related facility and the electricity supply of the public against its price. [Received: October 17, 2020; Accepted: May 03, 2021]
NUMERICAL ANALYSIS OF PULSATING FORCED CONVECTION IN A BACKWARD-FACING STEP FLOW SUBJECTED TO NANOFLUIDS
Çavdar, PS; Solmaz, B; Selimefendigil, F; Yurddas, A
The numerical investigation of pulsating forced convection in a backward-facing step flow using water-based nanofluids has been presented. This study is performed for different Reynolds numbers (based on the step height) in the range of 10 and 200, different inlet velocity and different Strouhal number. The effects of water-based nanofluids, which contain Al2O3 (Aluminium oxide) and Cu (Copper) nanoparticles with volume fractions ranging from 1% to 5%, on the heat transfer were determined. All numerical solutions were evaluated by using the Finite Volume Method of Computational Fluid Dynamics. The effects of related parameters as Reynolds number and pulsating frequency on the fluid flow and heat transfer characteristics have been numerically analyzed. Increasing the Cu nanoparticle volume ratio gets the heat transfer better than of all.
Prediction of heat and fluid flow in microchannel condensation
Basaran, A; Benim, AC; Yurddas, A
The condensing flow inside the microchannel has gained importance as the microchannel heat exchangers are widely used in the industry. In this study, a number of numerical simulations on condensing flow inside the microchannel were conducted to investigate heat transfer characteristic. Circular microchannel geometries with the various diameters were considered. The Volume of Fluid model was used to model two-phase flow. The phase change at the saturation temperature was modeled by the Lee model. In the considered geometries, different from the conventional channels, surface tension forces can be important compared to other forces. Therefore, surface tension was considered in the simulations. Constant wall heat flux and constant saturation temperature were applied as simulation conditions, similar to actual operating conditions. The predictions were validated by comparisons with the experimental results that exist in the literature. A satisfactory agreement of the present predictions with the experimental data was observed.
EFFECTS OF ENVIRONMENTALLY FRIENDLY FLUIDIZED BED DRYING ON THE QUALITY OF Viburnum opulus
Bölek, S; Mercan, M; Vursavas, M; Arslan, D; Yurddas, A
Owing to their high antioxidant activity, fiber, vitamin and mineral content, dried fruits are healthy and nutritious snacks. However, some quality characteristics of fruits are adversely affected by drying. Therefore, drying temperature is very important to obtain healthy and nutritious dried products. Recently, fluidized bed drying technology has been spread all over the world as it is an efficient and environmentally friendly technique. This study investigated the effects of fluidized bed drying, which is a thermodynamic equilibrium drying technique, on quality characteristics of Viburnum opulus. For this aim, the V. opulus fruits were dried at 60 degrees C, 70 degrees C and 80 degrees C with an air flow rate of around 60 m(3)/h for 5 h, 4 h and 3 h respectively. The moisture contents of V. opulus fruits were reduced by half (for medium-high temperature cases) after 90 min of drying process. Thanks to environmentally friendly fluidized bed drying system, V. opulus fruits moved on the bed during drying. As the fruits did not stay in the same place, heat and mass transfer increased and uniform drying was achieved. Color, rehydration capacity, shrinking ratio, antioxidant activity, pH and sensory analysis were conducted to compare the sensory, chemical and physical properties of dried V. opulus fruits. The drying temperature affected the quality characteristics of V. opulus fruits significantly (p<0.05). The V. opulus fruits dried at 60 degrees C has the highest rehydration capacity and they were the most appreciated samples with regards of appearance, flavor and overall impression among the dried fruits (p<0.05).
Numerical Simulation of the Condensation Flow of the Isobutane (R600a) inside Microchannel
Basaran, A; Benim, AC; Yurddas, A
A numerical investigation of the condensing flow of isobutane inside microchannel has been performed. Impact of mass flux, hydraulic diameter, and vapor quality on the heat transfer rate and pressure drop is determined. To this purpose, steady-state numerical simulations of condensation flow of isobutane have been performed at mass fluxes ranging from 200 to 600 kg/m(2)s inside a single circular microchannel with varying diameter. Similar to the usual operation conditions, the simulations have been conducted for constant saturation temperature and constant wall heat flux as the thermal boundary condition. The proposed model has been based on the volume of fluid approach, which is an interface tracking method. The Lee model has been used to model the phase change mass transfer at the interface. A verification study has been performed by comparing the proposed model results with the experimental and visual data available in the literature. The currently available correlations are assessed by comparisons with the simulation results. Based on the presently validated simulations, a new correlation has been proposed for the heat transfer coefficient and pressure drop of isobutane condensing flow inside small-scale channels. This is a novel aspect of the present paper, since such a correlation does not yet exist.
Thermal modeling and designing of microchannel condenser for refrigeration applications operating with isobutane (R600a)
Basaran, A; Yurddas, A
The present study has focused on thermally performance modeling and designing of microchannel condenser (MC-C). It is aimed at contributing to new MC-C designs for refrigeration applications working with isobutane (refrigerant R600a). To this purpose, a novel thermal simulation model has been developed as a design tool to predict the heat capacity, outlet temperature and pressure of the MC-C. The existing correlations in the literature about heat transfer and pressure drop of refrigerant flow inside the microchannel have been evaluated to improve the accuracy of the thermal simulation model. A new heat transfer coefficient correlation has been employed in the model with the purpose of further improvement of the accuracy. An experimental study has been performed to validate thermal simulation model results. It is found that the model predicted isobutane temperature at the outlet of the MC-C and heat transfer capacity with deviations in the range of +/- 2% and +/- 1%, respectively. The model has an average of 6.8% MAE for the prediction of the isobutane pressure at the outlet of the MC-C The theoretical air-cooled MC-C designs have been performed to investigate the effect of hydraulic diameter microchannels and pass arrangement on heat transfer performance. The theoretical air-cooled MC-C designs have been modeled and discussed with the experimentally validated thermal simulation model for refrigeration applications. According to the model results, although the heat transfer coefficient inside microchannels increases as the hydraulic diameter decreases, heat transfer capacity decreases. When the pass arrangement is modeled, it is concluded that the designs with high tube numbers in the passes at which vapor quality is still high exhibit higher heat transfer capacity in the MC-C.
Assessments of thermal performance of hybrid and mono nanofluid U-tube solar collector system
Yildirim, E; Yurddas, A
Solar energy systems are of great importance for water heating, where we spend most of the energy. U -tube solar collectors have a very important place in water heating among solar energy systems. Compensation of the intense energy used for water heating by this type of environmentally friendly solar energy system, will reduce CO2 and SO2 emissions for a cleaner nature. Therefore; the thermal perfor-mance of a U-tube complete system from evacuated tube solar collector (ETSC) systems was assessed. The heat transfer capability of the system, which contains 10 U-tubes, has been examined by considering the fact that it has different work fluids and different heat fluxes and flow rates. The finite volume method is used for this analysis. The model has been verified by many experimental and numerical studies. In the system under consideration has been used 10 vacuum U-tubes inclined at 30 degrees, and water and nanofluid (SiO2-Cu) which were used as working fluid in the manifolds connected to these tubes. Nanoparticles modeled in the work fluid are considered as hybrid and mono at different volume frac-tions. The thermal and hydrodynamic behaviors of the system have been examined by taking into ac-count the Boussinesq approach, and the system outlet temperatures have been calculated. As a result of analyzes and comparisons made, it has been seen that the use of nanofluid improves the thermal capability of the system under consideration. It has been determined that this improvement reaches up to 15% compared to water. The thermal effects of using SiO2 nanoparticles, which are lighter than Cu nanoparticles, were observed in terms of the precipitation problem encountered in many systems when using hybrid nanofluids. Thus, instead of using more Cu nanoparticles in volume, using smaller amounts together with SiO2 nanoparticles as a hybrid both eliminates the problem of precipitation and improves the heat capability of the work fluid. (c) 2021 Elsevier Ltd. All rights reserved.
Nonlinear vibrations of axially moving multi-supported strings having non-ideal support conditions
Yurddas, A; Özkaya, E; Boyaci, H
In this study, nonlinear vibrations of an axially moving multi-supported string have been investigated. The main difference of this study from the others is in that there are non-ideal supports allowing minimal deflections between ideal supports at both ends of the string. Nonlinear equations of the motion and boundary conditions have been obtained using Hamilton's Principle. Dependence of the equations of motion and boundary conditions on geometry and material of the string have been eliminated by non-dimensionalizing. Method of multiple scales, a perturbation technique, has been employed for solving the equations of motion. Axial velocity has been assumed a harmonically varying function about a constant value. Axially moving string has been investigated in three regions. Vibrations have been examined for three different cases of the velocity variation frequency. Stability has been analyzed and stability boundaries have been established for the principal parametric resonance case. Effects of the non-ideal support conditions on stability boundaries and vibration amplitudes have been investigated.
Optimization and thermal performance of evacuated tube solar collector with various nanofluids
Yurddas, A
Evacuated tube solar collectors (ETSC) constitute an important place among water heating systems. The use of solar energy systems will reduce CO2 and SO2 emissions for green nature. In this context, geometric and technical values of the open-ended ETSC systems were optimized by considering different parameters. In the optimization study, the solar tube collector with vacuum tube which gives the most appropriate results was discussed and its effects on heat transfer according to the presence of different work fluids were investigated. For this study, a numerical study was carried out by applying the finite volume method, one of the computational fluid dynamics methods. We confirmed our numerical study with both experimental and numerical studies. In our study, water and water-based nano-fluids are used as heat transfer fluid in 24 heat tubes with 300 inclination and the related tank that connected to it. The water-based nano-fluids we used are water as the basic fluid and MWCNT, TiO2, SiO2 and Cu as the nanoparticles. We modeled nanofluids homogeneously by handling them for different volumetric ratios. The thermal and hydrodynamic conditions of the collector were investigated using the Boussinesq Approach and the tank exit temperatures were determined. As a result of this study, it was seen that the use of nano-fluids improved the heat transfer in the ETSCs and the best thermal recovery among the nano-fluids we used in our study was realized in Cu-Water nano-fluid. Improving the thermal performance of the ETSC is important for better energy conversion. For this reason, the effects of nano-fluid usage on thermal performance in solar energy systems of pollution-free energy are promising. (C) 2020 Elsevier Ltd. All rights reserved.
Numerical analysis of fin effect in heat exchangers used in split air conditioners
Balkanli, B; Yurddas, A; Aksoy, Y
In this study, heat exchangers in split air conditioners which are one of the most used air conditioning system applications in our daily life are chosen as a subject Most commonly used heat exchanger type is chosen. The mathematical model was validated. The effects of design parameters on thermal capacity and system efficiency have been examined numerically under real-like operating conditions. Although design parameters have a wide working area; variations on pipe diameter, horizontal and vertical distance between pipes, space between fins and fin thickness are examined in this study. The effects of the design variations on heat transfer, pressure decrease and flow velocity under laminar flow and certain boundary conditions were investigated using Finite Volume Methods software for this type of heat exchanger. Nusselt number and heat transfer amount depending on the convection coefficient are found after analyses. Considering these values new optimal design parameters are presented for revision of the heat exchangers.
Nonlinear vibrations and stability analysis of axially moving strings having nonideal mid-support conditions
Yurddas, A; Özkaya, E; Boyaci, H
In this study, nonlinear vibrations of an axially moving string are investigated. The main difference of this study from other studies is that there is a nonideal support between the opposite sides, which allows small displacements. Nonlinear equations of motion and boundary conditions are derived using Hamilton's principle. Equations of motion and boundary conditions are converted to nondimensional form. Thus, the equations become independent from geometry and material properties. The method of multiple scales, a perturbation technique, is used. A harmonically varying velocity function is chosen for modeling the axial movement. String as a continuous medium is investigated in two regions. Vibrations are investigated for three different cases of the excitation frequency . Stability analysis is carried out for these three cases, and stability boundaries are determined for the principle parametric resonance case. Thus, differences between ideal and nonideal boundary conditions are investigated.
Numerical analysis of evacuated tube solar collectors using nanofluids
Mercan, M; Yurddas, A
In this study, numerical analysis of water and water based nanofluids in ETSCs were made by using CFD. Validation of the study was made by comparing an experimental and two different numerical results. Thanks to the analyzes, the effects of water based Al2O3-H2O and CuO-H2O nanofluids compared to water on heat transfer for different volume fractions of nanoparticle, different collector angles, different mass flow rates and different numbers of evacuated tubes were examined. According to these parameters, the thermal and hydraulic statuses of the collector were examined by using the Boussinesq approximation and the tank outlet temperatures were determined. It has been determined that the use of nanofluid in ETSC systems has improved heat transfer and the best improvement was obtained with CuO-H2O nanofluid.
Design of single and two phase modeled nanofluid CPU cooler and their numerical analysis
Özdiler, EP; Yurddas, A
The heating problems in electronic devices have become even more significant with the development of technology and the rapid increase in areas of use. In cases where passive cooling and active cooling processes are not sufficient to improve overheating in electronic devices, high temperature generation is prevented by liquid cooling if convenient. The effect of nanofluid use on heat transfer to improve the thermal performance of liquid cooling systems was examined with computational fluid dynamics from numerical methods in this research. For different cooler designs, both single-phase and multiphase modeling methods were utilized in fluid modeling in the research involving forced convection and heat transfer in laminar and turbulent flow. The mathematical models utilized were validated on different experimental and numerical researches. The single-phase modeling was conducted for pure H2O, 1% Al2O3, 5% Al2O3 nanofluids at different Reynolds numbers. The analyzes were conducted at different Reynolds values and the increase in Reynolds value decreases the maximum temperature value at the output. In the multiphase modeling method, the nanofluid Al2O3 is defined and modelled as a separate phase suspended in different sizes into the base fluid H2O. The use of nanofluid increased the thermal conductivity in both methods compared to the use of pure H2O. At the same time, the use of nanofluids at 5% concentration gave better results than 1% concentration. As the temperature distributions are examined, the Mixture model, one of the single-phase and multiphase modeling methods, presents very similar distributions. The effect of nanofluids on thermal performance varies depending on many parameters. A significant one is the size of the suspended nanoparticle. Different particle sizes, 20, 30, and 40nm, were investigated in both Mixture and Eulerian modeling approaches in this research. Two different design coolers were utilized in the researches. In these designs, the flow is distributed in parallel and serpentine. The flow distribution and pressure drop also had an effect on thermal performance. The temperatures were read lower in the serpentine block, which provides a more regular flow distribution.
Numerical analysis of heat transfer of a nanofluid counter-flow heat exchanger
Özenbiner, Ö; Yurddas, A
One of the most significant facts for every economy is energy, regardless of big or small. The need for energy does not expire however it increases day by day, and this brings along the renovation activities. The energy sector is the most effective sector, especially in the climate change problem we have encountered during the recent years. Increasing the thermal capability of heat exchangers in almost every area where there is heating and cooling is very significant in terms of energy efficiency and savings. The numerical analysis of water and nanofluids with water as base fluid in a double-pipe, counter-flow heat exchanger with corrugated tube inside was performed using computational fluid dynamics in this research. The results of a different study were validated by the mathematical method to be utilized in the study. The analyzes we have performed for the heat exchanger we have discussed, the thermal performances of nanofluids obtained with Al2O3, CuO, TiO2 nanoparticles, whose base liquid is water, were analyzed according to different Reynolds numbers, different volumetric concentrations, each other and water. Optimum values were determined by making comparisons of many parameters with each other. It was determined that the use of nanofluid improves heat transfer compared to water, the heat transfer increases based on the increasing nanoparticle volume fraction, the increase in the Reynolds number of the workflow decreases the heat transfer, the increase in the Reynolds number of the refrigerant increases the heat transfer and the highest heat transfer is obtained in the CuO-H2O nanofluid and in heat transfer, and a 23.6% improvement was observed.
AN ANALYTICAL STUDY ON THE ENTROPY GENERATION IN FLOW OF A GENERALIZED NEWTONIAN FLUID
Aksoy, Y; Gurkan, N; Aksoy, AB; Durgun, DD; Yurddas, A
In this study, an analytical investigation on pressure driven flow of Powell-Eyring fluid is conducted to understand the irreversibilities due to heat transfer and viscous heating. The flow between infinitely long parallel plates is considered as fully developed and laminar with constant properties and subjected to symmetrical heat fluxes from solid boundaries. The internal heating due to viscous friction accompanies external heat transfer, that is, viscous dissipation term is to be involved in the energy equation. As a cross-check, accuracy of analytical solutions is confirmed by a predictor-corrector numerical scheme with variable step size.
NUMERICAL ANALYSIS OF MIXED CONVECTION HEAT TRANSFER IN PULSATING FLOW FOR A HORIZONTAL CHANNEL WITH A CAVITY HEATED FROM VERTICAL SIDE AND BELOW
Selimefendigil, F; Yurddas, A
In this study, a channel with a cavity heated from below and a left vertical side is numerically investigated for the mixed convection case in pulsating flow for a range of Richardson numbers (Ri = 0.1, 1, 10, 100) and Reynolds numbers of 300, 500, and 800 in the laminar flow regime. At the inlet of the channel, pulsating velocity is imposed for Strouhal numbers of 0.25, 0.5, 0.75 and 1 and velocity amplitude ratios of 0.7, 0.8, and 0.9. The effect of the pulsation frequency, amplitude, Reynolds number, and Richardson number on heat transfer enhancement is analyzed numerically. The results are presented in terms of streamlines, isotherm plots, and averaged Nusselt number plots. Transfer function plots for the Nusselt number response to single sinusoidal velocity forcing at the inlet and nonlinearity in the response is also provided.
The determination of the thermal characteristics of the microchannel heat exchangers for single-phase R600a flow
Basaran, A; Yurddas, A
In this study, the mathematical modeling of microchannel heat exchangers (MCHEs) has been experimentally examined for applications where there is a single-phase refrigerant flow such as pre-heating/cooling, superheating/subcooling. A mathematical simulation model has been developed for louvered fin MCHEs where the working fluid is R600a, which estimates the outlet temperature, total heat transfer capacity and entropy generation of the R600a. To imrpove the accuracy of the model, different mass velocities in the passes and uniform air velocities at the face of MCHE have been taken into consideration in the proposed model. Different from other models in the literature, a calculation system created by two discretization level has been applied to take into account these effects. Non-uniform air velocities have been taken into consideration via dividing the face of the MCHE into airflow regions in the model. Experimental study has been performed to validate the model results. It concluded that the model predicts the outlet temperature with an average absolute deviation within +/- 10% for all investigated test conditions. It is found that the taking into consideration non-uniform air velocity improves accuracy of the model. The entropy generation mechanisms in the MCHE have been investigated and it has been determined that the contribution of the fluid flow irreversibility to entropy generation is quite low compared to heat transfer irreversibility.
Energy and exergy analysis of the heating and cooling system of a public building
Sevim, S; Yurddas, A
Efficient use of energy spent in existing systems is of great importance in terms of energy saving. The aim of this study was to carry out the energy and exergy analyses of the existing heating and cooling systems of a public building and determine the system performances, and bring the system to a thermoeconomic structure by making necessary improvements. In the building, natural gas is used as energy source (fuel) in hot water boilers within the existing heating installation, and electricity is used as energy source in air-cooled water chillers within the cooling system. As a result of the calculations, it was determined that the biggest exergy destruction in the heating system was in the hot water boiler and the biggest exergy destruction in the cooling system was in the water chiller. Other point data obtained were evaluated and heating and cooling system efficiencies were determined.
The effects of the use of hybrid and mono nanofluids on thermal performance in flat-plate solar collectors
Yurddas, A; Cerçi, Y; Cavdar, PS; Bektas, A
Since considerable amount of energy is spent in water heating processes in the world, solar energy systems are of great importance while heating water. Amongst these systems, flat-plate solar collector systems have an extensive area of use in residences. Therefore, nanofluid system has been investigated in order to enhance the efficiency in water heating through flat plate solar collectors and to benefit from solar energy more effectively. A simplified model has been taken into consideration to design the model of this system and complete the analyzes more rapidly. To identify the accurateness of the model, comparisons have been made against an experimental and a numerical study; and, a decent convergence to the experimental data has been obtained. Nanofluids used in the system have been applied in hybrid structure. The analysis has been conducted for the case of that two different nanometer-sized metal nanoparticles (SiO2 and Cu) are mixed in water-based base fluid with different volume concentrations. Influences of nanofluids in different volume fractions on thermal performance have been investigated and compared against water and each other. In the system having 30 degrees angle, diversified flow rates and heat fluxes have also been evaluated. It is concluded that water-based nanofluids enhances thermal performance; and, amongst these, the nanofluid including Cu nanoparticles augments thermal performance much better. To avoid precipitation problems within the system, thermal performance has been increased by virtue of using nanofluids with lower volumetric concentrations in hybrid form by adding certain amount of Cu nanoparticle instead of using high volumetric concentrations of SiO2 nanoparticles. In comparison to water, these nanofluids we utilized have increased thermal performance in the rates of 2.03% (2%SiO2 + 1%Cu-H2O), 3.218% (1%SiO2 + 2%Cu-H2O), 0.943% (3%SiO2-H2O), 4.076% (3%Cu-H2O), 4.083% (3%SiO2 + 2%Cu-H2O), 4.935% (2%SiO2 + 3%Cu-H2O), 1.569% (5%SiO2-H2O), and 6.508% (5%Cu-H2O).
NUMERICAL ANALYSIS OF HEAT TRANSFER IN A FLAT-PLATE SOLAR COLLECTOR WITH NANOFLUIDS
Yurddas, A; Çerçi, Y
Heat transfer aspects of a typical flat-plate solar collector utilizing water-based nanofluids as the working fluid were analyzed numerically. Water-based nanofluids of various compositions containing metallic Al2O3 and Cu nanoparticles with volume fractions ranging from 1% to 5% were examined, and the effects of the nanofluids on the heat transfer were quantified. Relevant parameters such as the heat flux, Reynolds number, and the collector tilt angle were calculated and compared to each other at different boundary conditions. The flat-plate solar collector geometry was simplified, and only a fluid carrying pipe with an absorber surface was chosen as a numerical model with a particular attention to symmetry, instead of taking the entire collector geometry. The numerical model was controlled and confirmed by applying it to similar studies existing in the pertinent literature. All numerical solutions were carried out by using a commercial finite volume soft ware package called ANSYS Fluent. The results show that the nanofluids increase the heat transfer rate ranging from 1% to 8%, when compared to water as a working fluid.

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