Papers by Prof. Dr. Emrah Özahi
Lecture Notes in Mechanical Engineering, 2019
Biodegradable wastes are becoming a serious problem in terms of health and ecological balance in ... more Biodegradable wastes are becoming a serious problem in terms of health and ecological balance in parallel with the increasing of local and global populations in recent years. These wastes should be disposed in both efficient and eco-friendly ways. Considering biodegradable wastes as an energy source, it is necessary to be sure that those disposal methods should be focused on energy recovery. However, the existing waste disposal methods have not reached technologically targeted lines yet. It is very important that waste-to-energy recovery systems should have high energy conversion efficiency. Nowadays, there are many current studies based on the methods of wastes incineration. One of the most significant among these systems is fluidized or spout-fluidized bed incineration system. Unfortunately, the targeted points of the technological development of these systems in view of efficient energy recovery have not been reached yet. Existing incineration systems and current studies on this issue are generally concentrated on conventional fluidized bed systems. However, there are few studies of new generation spout-fluidized bed incineration systems which increase homogeneity and prevent waste from adhering to inner wall of a combustor. This study is focused on the conducted numerical studies in this research field. The latest developments and researches on both fluidized and spout-fluidized bed incineration systems will be investigated and discussed. The remarkable results will be pointed out by using the comparison in order to identify the gaps of the scientific literature.
Renewable Energy, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Acta Physica Polonica A, 2017
This paper presents the energy and exergy analyses of some different organic fluids which can be ... more This paper presents the energy and exergy analyses of some different organic fluids which can be used in an organic Rankine cycle adapted to a municipal solid waste power plant in the frame of energy recovery. The novelty of the study is to adapt a well-known organic Rankine cycle system theoretically to the existing municipal solid waste power plant where the exhaust gas with a temperature of almost 560 • C is sent to atmosphere causing both energy loss and air pollution, and also violating the related legislation. The efficient organic fluid that can be used in such a plant is estimated by means of the thermodynamic analyses. It is known that, in a typical municipal solid waste power plant, a considerable amount of energy is sent up from a plant chimney to the atmosphere. This waste energy can be utilized by using an adapted organic Rankine cycle system with a proper organic fluid. In this frame, some different organic fluids were examined and compared thermodynamically in this study. The optimal operation conditions of some organic fluids, R141b, isobutane, R245fa, n-pentane and n-hexane have been evaluated by means of ASPEN and EES software programs. The effects of the outlet temperature of heat source on the energetic and exergetic efficiencies and the net power output at a given pinch point temperature difference were investigated. It can be deduced from the analyses that n-hexane has the highest energetic and exergetic efficiencies at all outlet temperatures of the heat source such as 8.92% and 34.47% at 82.08 • C, respectively. It can also be stated that the maximum net power output is obtained by using the organic fluid n-hexane.
Acta Physica Polonica A, 2017
This paper presents a thermoeconomic analysis and assessment of a municipal solid waste power pla... more This paper presents a thermoeconomic analysis and assessment of a municipal solid waste power plant system in Gaziantep. The operation of an existing municipal solid waste power plant is described in detail and a thermoeconomical methodology based on exergoeconomic relations and specific exergy costing (SPECO) method is provided to allocate cost flows through subcomponents of the plant. SPECO method is based on a step by step procedure which begins from identification of energy and exergy values of all states defined in the present system through fuel (F) and product (P) approach and ends at the point of establishing related exergy based cost balance equations together with auxiliary equations. The actual exergy efficiency of the solid waste power plant is determined to be 47.84% which shows that 52.16% of the total exergy input to the plant is destroyed. The net electrical power output of the Gaziantep municipal solid waste power plant is 5.655 MW. The total cost rate of the power plant is evaluated as 18.44$/h as a result of thermoeconomic analyses.
Measurement, 2017
The interactive influences of oscillation frequency and velocity amplitude ratio on onset of tran... more The interactive influences of oscillation frequency and velocity amplitude ratio on onset of transition in pulsatile pipe flow are investigated experimentally in the ranges of time-averaged and oscillating Reynolds numbers of 1019±35≤ ta Re ≤4817±164 and 107±4≤ os Re ≤4261±145 with velocity amplitude ratio of 0.05±0.0017≤ 1 A ≤0.96±0.03 for 227 runs. Oscillation frequency is in the range of 0.1 Hz≤ f ≤14 Hz corresponding to Womersley number range of 2.72≤ ω ′ ≤32.21 covering quasi-steady, intermediate and beginning of inertia dominant regimes of pulsatile laminar flow. The onset of transition in laminar pulsatile pipe flow can be retarded up to crit ta, Re =4817 at ω ′ =3.85 in the covered experimental range. No more effect of 1 A on crit ta, Re is seen for ω ′ >8.61 although there is a considerable effect of 1 A on crit os, Re. The effect of ω ′ on crit ta, Re and crit os, Re is not observed for 1 A <0.30. The interactive influences of ω ′ and 1 A are also investigated on crit ta,
International Journal of Hydrogen Energy, 2017
In this study, five models are considered for the use of biogas-based electricity and sewage slud... more In this study, five models are considered for the use of biogas-based electricity and sewage sludge obtained from a municipal wastewater treatment plant for green hydrogen production. These models include alkaline, PEM, high temperature water electrolysis, alkaline hydrogen sulfide electrolysis and dark fermentation biohydrogen production processes. Energy and exergy analyses are performed on these models by applying thermodynamic procedures and the results are compared. The daily hydrogen production rates of the
Renewable and Sustainable Energy Reviews, 2016
Municipal solid waste (MSW) management has emerged as probably the most pressing issue many gover... more Municipal solid waste (MSW) management has emerged as probably the most pressing issue many governments nowadays are facing. Traditionally, Waste-to-Energy(WtE) is mostly associated with incineration, but now, with the emergence of the bioeconomy, it embraces a broader definition comprising any processing technique that can generate electricity/heat or produce a waste-derived fuel. Under the ambit of the circular economy many nations are looking for, additional effort must be made to be sure of acquiring the most updated information and paving a sustainable path for managing MSW in such a frame. In this regard, we have undertaken a critical review of various technologies, with their updated progress, involved in the exploitation of MSW as a renewable resource, along with the critical advantages and limitations on energy and material cycling for sustainable MSW management. Incineration, the most widely used method, is nowadays difficult to further apply due to its dubious reputation and social opposition. Meanwhile, to address the organic fraction of MSW which currently is mostly unrecycled and causes disposal issues, the biological approach presents an attractive option. The new emphasis of bioeconomy leads us to understand how environmental biotechnologies should be better connected/integrated for more sustainable MSW management. This article is concluded with advances of future prospects, which can serve as a timely reminder to encourage competent authorities/researchers to work towards further improvement of the present MSW management system.
Batch type fluidized bed drying is one of the most used and successful methods in food, pharmaceu... more Batch type fluidized bed drying is one of the most used and successful methods in food, pharmaceutical and chemical industries due to its higher efficiency. For this reason, many studies in lab- and industry-scales are continued on fluidized bed drying concept for improvements of their performance characteristics. This paper reports the recent significant experimental studies on batch type fluidized bed dryers giving their fundamental results. The signal acquisition and processing steps via daqboad, PC and program devised in LabView 2009SP1® for control and operation of the devices in a planned experimental study are introduced in the light of the literature survey. Moreover a case study is carried out in order to give the view point according to the conducted studies, in which the effects of particle types to be dried, drying medium velocities and heating methods on drying times are discussed at some constant drying temperatures.
Measurement, 2015
A batch type fluidized bed dryer is designed and constructed in order to investigate drying perfo... more A batch type fluidized bed dryer is designed and constructed in order to investigate drying performance of a batch type fluidized bed drying process of corn and unshelled pistachio nut regarding to energetic and exergetic efficiencies. A series of experiments is carried out for the purpose in the covered range of 100 g≤ p m ≤300 g, 50 °C≤ T ≤75 °C, 6.87 m/s≤ m U ≤10.86 m/s and 47632≤ Re ≤75296. An increase in particle mass is found to cause an increase of drying time. On the other hand, an increase in drying air temperature and drying air velocity result in a decrease of drying time. The experimental results in terms of energetic and exergetic efficiencies are compared with the available ones in the literature by means of the previously proposed model of the authors. There is a good conformity between the present data and available data in the literature with a mean deviation of ±14% for energetic efficiency during drying process of corn. However, the deviation is raised to ±37% for energetic efficiency during drying process of unshelled pistachio nut, diverging from Eq. (9) which was previously proposed for corn drying. It can be deduced that both energetic and exergetic efficiencies are strongly dependent on air mass flow rate, particle mass and moisture content of particle to be dried and also ambient temperature.
Powder Technology, 2008
An experimental study was conducted on the pressure drop characteristics of a variety of vertical... more An experimental study was conducted on the pressure drop characteristics of a variety of vertical packed beds in turbulent flow of air. The materials of different particle diameter, D p , with a range of sphericity Φ, 0.55 ≤ Φ ≤ 1.00 were used in random loose packing to produce beds of different lengths, L, with a range of porosity, ε, 0.36 ≤ ε ≤ 0.56. In the covered test cases the cross-sectional velocity distribution at the exit plane of the packed beds and the pressure drop ΔP Bed were measured in a particle Reynolds number range of Re p , 675 ≤ Re p ≤ 7772. The particular emphasis of the study was given to determine the influence of ε, Φ, D p , L, Re p on ΔP Bed. In this respect the measurements of ΔP Bed were compared with the well-known Ergun's Equation and the data were expressed in terms of correlations through introduced dimensionless parameters of pressure coefficient, ΔP ⁎ and exit Reynolds number Re exit. The proposed correlations of ΔP ⁎ = ΔP ⁎ (εRe p D p / L) and Re exit = Re exit (Re p D p / L) are found to be appropriate for the determination of ΔP Bed and mean exit velocity, U, respectively with an acceptable fit of experimental data in an error margin less than ± 20%. The methodology is presented in this paper as an alternative approach to the available literature on packed beds.
Measurement, 2014
This paper gives the hardware and software of a test rig with its experimental procedure, methodo... more This paper gives the hardware and software of a test rig with its experimental procedure, methodology and uncertainty analyses of measurements for batch type fluidized bed drying of corn and unshelled pistachio nut. The test rig is designed, constructed and operated for the analyses of drying performance of corn and unshelled pistachio nut in a batch type fluidized bed drying. The details of the test rig, the experimental procedure, the uncertainty analyses and the investigation of the effects of drying parameters on drying performance are the major scope of the paper. The accuracy of the experimental study herein is based on velocity, pressure, temperature and moisture measurements. Therefore it is vital and sensitive phenomenon for the determination of the uncertainties of the measurements before the current study as is the case with all other studies. The test rig is designed and constructed in accordance with literature review which is mentioned briefly in this paper. The basic terminology which is used in this study is also introduced herein. The overall uncertainties of velocity, pressure, temperature and moisture measurements are performed and found as 1.7%, 1.3%, 0.3% and 1.6%, respectively. Some pioneering studies related on conventional batch type fluidized bed dryers operated under atmospheric pressure are also tabulated as an original contribution to literature. Moreover, the effects of the particle mass, drying air temperature and drying air velocity on drying performance of the batch type fluidized bed dryer which is assisted with a conventional electrical heater unit are outlined without going into details in thermo-and fluid-dynamics of drying process.
Flow, Turbulence and Combustion, 2012
ABSTRACT Transition to turbulence in axially symmetrical laminar pipe flows with periodic time de... more ABSTRACT Transition to turbulence in axially symmetrical laminar pipe flows with periodic time dependence classified as pure oscillating and pulsatile (pulsating) ones is the concern of the paper. The current state of art on the transitional characteristics of pulsatile and oscillating pipe flows is introduced with a particular attention to the utilized terminology and methodology. Transition from laminar to turbulent regime is usually described by the presence of the disturbed flow with small amplitude perturbations followed by the growth of turbulent bursts. The visual treatment of velocity waveforms is therefore a preferred inspection method. The observation of turbulent bursts first in the decelerating phase and covering the whole cycle of oscillation are used to define the critical states of the start and end of transition, respectively. A correlation study referring to the available experimental data of the literature particularly at the start of transition are presented in terms of the governing periodic flow parameters. In this respect critical oscillating and time averaged Reynolds numbers at the start of transition; Reos,crit and Reta,crit are expressed as a major function of Womersley number, √ώ defined as dimensionless frequency of oscillation, f . The correlation study indicates that in oscillating flows, an increase in Reos,crit with increasing magnitudes of √ώ is observed in the covered range of 1 &lt; √ώ &lt; 72. The proposed equation (Eq. 7), Reos,crit = Reos,crit (√ώ), can be utilized to estimate the critical magnitude of √ώ at the start of transition with an accuracy of ±12 % in the range of √ώ &lt; 41. However in pulsatile flows, the influence of √ώ on Reta,crit seems to be different in the ranges of √ώ &lt; 8 and √ώ &gt; 8. Furthermore there is rather insufficient experimental data in pulsatile flows considering interactive influences of √ώ and velocity amplitude ratio, A1. For the purpose, the measurements conducted at the start of transition of a laminar sinusoidal pulsatile pipe flow test case covering the range of 0.21&lt; A1 &lt;0.95 with √ώ &lt; 8 are evaluated. In conformity with the literature, the start of transition corresponds to the observation of first turbulent bursts in the decelerating phase of oscillation. The measured data indicate that increase in v is associated with an increase in Reta,crit up to √ώ = 3.85 while a decrease in Reta,crit is observed with an increase in √ώ for √ώ &gt; 3.85. Eventually updated portrait is pointing out the need for further measurements on i) the end of transition both in oscillating and pulsatile flows with the ranges of √ώ &lt; 8 and √ώ &gt; 8, and ii) the interactive influences of √ώ and A1 on Reta,crit in pulsatile flows with the range of √ώ &gt; 8.
Flow Measurement and Instrumentation, 2013
ABSTRACT The hardware and software of an experimental test system which has been designed, constr... more ABSTRACT The hardware and software of an experimental test system which has been designed, constructed and operated for the analysis of transitional characteristics of a laminar time-dependent flow field into turbulence with comprehensive uncertainty analysis are the major contents of the paper. Therefore presentation herein aims to offer an application case in terms of time-dependent measurement and data acquisition technology using an electronic digital mass flow control (MFC) unit at laboratory site instead of previously used pressure driven mechanisms. The flow field is a sinusoidal pulsatile one in order to simulate the real practice and to utilize the simplicity in production, control and analysis of oscillation. The previous background and the updated portrait on the transitional pulsatile flow 1 and 2 are outlined to determine the relevant flow parameters and their critical ranges, the details of the measurement and data acquisition systems and the proposed methodologies. The production of the controlled pulsatile flow and the generated flow characteristics, the methodology for the analysis, accuracy and sensitivity of the measurement and data acquisition chains are given for the purpose. The overall uncertainties of the velocity and pressure measurement chains are found to be ±3.2% and ±1.3%, respectively. The range of the experimental research devised to investigate the interactive influences of oscillation frequency, f and velocity amplitude ratio, A1 in the intermediate and the inertia dominant regions of pulsatile flow field with an emphasis on transition to turbulence is presented via sample measurements of mean velocity and pressure waveforms as solid outputs without going into details on physical aspects of flow dynamics.
Flow Measurement and Instrumentation, 2011
Flow field measurements behind pipe entrance inserts called as flow conditioners in a mean flow R... more Flow field measurements behind pipe entrance inserts called as flow conditioners in a mean flow Reynolds number range 547≤Re≤9000 are presented herein. A tube bundle, a Laws’ perforated plate and an etoile were located at the entrance of a smooth circular pipe of inner diameter, D=26.6mm. The covered ranges of open area ratio, β and non-dimensional length, L/D were 0.49≤β≤0.74 and 0.123≤L/D≤2 respectively. The cross-sectional axial velocity u=u(r) profiles at the downstream stations of X/D=75,X/D=375,X/D=680 together with pressure losses ΔP are referred to determine the influence of utilized designs.The flow conditioners have a single performance characteristic expressed through a relationship of pressure loss coefficientK=K(Reβ) which provides a practical method for the calculation of time-averaged pressure loss, ΔP̄ in an average error margin of ±18%. The laminar flow inside the pipe without an insert in the range of Re2450 is not fully developed sensed with u=u(r) profiles having a ±20% deviation from the Blasius profile for the lengths X/D680. Meanwhile flow conditioners provide a fully developed laminar flow independent of Re and X observed in terms of downstream u=u(r) profiles with a better fit to the Blasius profile in a mean error margin of ±10%.The laminar flow control via flow conditioners is analyzed through a discussion in terms of the introduced local non-dimensional velocity parameters. The used methodology is based on the definition of entrance length Reynolds Number; ReX=(X/D)Re. The proposed equations “ReXβ=C” (where C is a constant) can be used for the estimation of settling distance of the flow conditioners and laminar entrance length. The experimental data are in conformity with the magnitudes of C=2.87×104 and C=3×105 with the corresponding error margins of ±4% and ±6% respectively.
Flow Measurement and Instrumentation, 2010
This paper presents two calibration methods for a CTA probe valid at low speeds covering a range ... more This paper presents two calibration methods for a CTA probe valid at low speeds covering a range of 0.029m/s≤U≤1.79m/s. The well-known in situ calibration method using a simple laminar pipe-flow set-up was used for a mean Re number range of 25≤Re≤1590. The rotating disc method is the proposed calibration method in the speed range of 0.05m/s≤U≤1.05m/s. Both calibration methods were
Energy, 2013
An original model for thermodynamic analysis of a batch type fluidized bed dryer is proposed here... more An original model for thermodynamic analysis of a batch type fluidized bed dryer is proposed herein considering two separate systems comprised of drying air medium as a control volume and particles to be dried as a control mass. By means of the proposed model, energetic and exergetic analyses of a drying column of a batch type fluidized bed dryer are carried out as an original contribution to literature since there is no such like model in which the analyses are performed considering two separate systems. The energetic efficiencies evaluated by means of the proposed model using the data in literature are compared with those in literature and a good conformity is satisfied with an acceptable error margin of AE9%. A new correlation is also developed with a mean deviation of AE10% in order to evaluate the energetic efficiency for not only corn drying process but also drying processes of other particles at inlet air temperature of 50 C. Effects of air mass flow rate, mass of particle and ambient temperature on energetic and exergetic efficiencies are analyzed and some concluding remarks are highlighted for further studies.
Advanced Powder Technology, 2008
An experimental study was conducted to determine the pressure drop characteristics of cylindrical... more An experimental study was conducted to determine the pressure drop characteristics of cylindrical packed beds through which turbulent pipe flow was passing. This study was planned to clarify the applicability of the well-known Ergun correlation proposed for beds composed with spherical particles on beds with nonspherical particles. The experimental packed beds were constructed by using two different irregular-shaped and one spherical-shaped packing materials for understanding the effects of particle shape or sphericity, particle size, bed porosity, and bed length to diameter ratio on the pressure drop. The beds were constructed by using zeolite, chickpea and glass bead materials to cover the particle sphericity range of 0.55 1.00. Systematic experiments and the data analysis procedure showed that the well-known Ergun correlation can be applied to all of the experimental beds composed with non-spherical and/or spherical particles with a maximum deviation of ±20%. This deviation can, however, be decreased to a negligible level of ±4% if some simple modifications, including the use of particle Reynolds number, Re p , a new form of particle friction factor, f * p , and some adopted empirical constants in the well-known Ergun correlation, are used.
Advanced Powder Technology, 2009
Despite the presence of a variety of studies dealing with the magnitude of particle Reynolds numb... more Despite the presence of a variety of studies dealing with the magnitude of particle Reynolds number, Re p defining transition from laminar to turbulent regime for flow through packed beds, the manner is still one of the unknowns. An approach based on the experimental data concerning upward airflow through fixed cylindrical packed beds is presented in this paper. The utilized packed beds had the following ranges of; sphericity, U, 0.55 6 U 6 1.00, packing material diameter to bed length ratio, D p /L, 0.04 6 D p /L 6 0.72, and bed porosity, e, 0.36 6 e 6 0.56. The test cases covered the ranges of particle Reynolds number, Re p 708 6 Re p 6 7772 and particle Froude number; Fr p 2.86 6 Fr p 6 10.39. The measurements of pressure drop through packed bed; DP Bed and superficial mean exit velocity; U are used to determine bed frictional effects in reference to the available literature on particle friction factors, f p. The magnitude of Re p defining transition is assumed to be 2000 with particular emphasis to the flow dynamics. The definitions of Bird et al. [R.B. Bird, W.E. Stewart, E.N. Lightfoot, Transport Phenomena, John Wiley and Sons, NY, 1960] are used to calculate f p. The calculated f p for the covered test cases are given as a function of pressure coefficient, DP* and Re p, Fr p , U, e, D p /L in the approximate ranges of laminar and turbulent flow for Re p < 2000 and Re p > 2000, respectively. The proposed separate equations of f p = f p (DP*, Re p , Fr p , U, e, D p /L) are satisfied for laminar and turbulent flows with corresponding average error margins of ±7.6% and ±18%. Furthermore ranges of transitional and fully rough flow through packed beds are estimated as 2000 6 Re p 6 4000 and Re p > 5000 with an analogy to the well-known Moody Chart in pipe flows.
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Papers by Prof. Dr. Emrah Özahi