WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 3Validation on of Local Thermal Equilibrium and Uniform Pressure Assumptions for an Isobaric Adsorption Process in an Adsorbent Bed(Türk Isı Bilimi ve Tekniği Derneği, 2016) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraBu çalışmanın amacı, adsorbent yatakta ısı ve kütle transferini analiz etmek için kullanılan yerel ısıl denge ve sabit basınç yaklaşımı varsayımların geçerliliğini araştırmaktır. İçerisinde silika jel partikülleri içeren bir yatak ile su kabı olan bir deney düzeneği tasarlanmış ve adsorpsiyon sürecinde yatağın içinde farklı yerlerde yerel sıcaklık ve basınç ölçülmüştür. Ayrıca, sabit basınç yaklaşımı ve yerel ısıl denge varsayımlara dayalı ısı ve kütle transferi denklemleri çözülmüştür. Sayısal sonuçlar, ilgili deneysel sonuçlarla karşılaştırılmış ve aralarında oldukça iyi bir uyum tespit edilmiştir. Gerçekleştirilen karşılaştırmaya dayanarak, incelenen yatak için iki önemli sonuç şu şekildedir: a) katı madde ve su buharı arasında yerel ısıl denge bulunmaktadır, b) bir yatak içinde parçacıklar arası kütle transferi direnci ihmal edilebilir düzeyde olup konsantrasyonunun ve sıcaklığın belirlenmesi için sabit basınç yaklaşımı geçerlidir. Ayrıca, bu çalışmada sunulan deneysel sonuçlar diğer araştırmacıların sayısal çalışmalarının geçerliliğini doğtulamak için değerli veriler sağlayacaktır.Article Citation - WoS: 55Citation - Scopus: 60Effect of Regeneration Temperature on Adsorption Equilibria and Mass Diffusivity of Zeolite 13x-Water Pair(Elsevier Ltd., 2016) Sayılgan, Şefika Çağla; Mobedi, Moghtada; Ülkü, SemraThe adsorption equilibrium and mass diffusivity of zeolite 13X-water pair for different adsorption and regeneration temperatures were determined by a homemade volumetric system. The isotherms of the zeolite 13X-water pair were obtained by collecting pressure versus time data and applying ideal gas law. The effective diffusivity of the pair was calculated by using long term analytical solution of mass diffusivity based on Fick's law. The experimental study showed that the adsorption capacity of zeolite 13X-water pair was 23% (kg/kg), 21% (kg/kg) and 19% (kg/kg) when the adsorption temperature was 35, 45 and 60 °C respectively for the desorption temperature of 90 °C. Furthermore, the adsorption capacity increased from 22% (kg/kg) to 24% (kg/kg) when the desorption temperature was increased from 90 °C to 150 °C. It was observed that the present adsorption equilibrium results were compatible with the reported results in the literature. The mass diffusivity of the pair was found in the range of 4 × 10-9-6 × 10-8 m2/s for the long time period when the initial adsorptive pressure was 2000 Pa. The effective mass diffusivity depends on concentration and it was decreased with increasing adsorbate concentration.Article Citation - WoS: 11Citation - Scopus: 11Comparison of Uniform and Non-Uniform Pressure Approaches Used To Analyze an Adsorption Process in a Closed Type Adsorbent Bed(Springer Verlag, 2013) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraHeat and mass transfer in an annular adsorbent bed filled with silica gel particles is numerically analyzed by uniform and non-uniform pressure approaches. The study is performed for silica gel-water pair, particle radius from 0.025 to 1 mm and two bed radii of 10 and 40 mm. For uniform pressure approach, the energy equation for the bed and the mass transfer equation for the particle are solved. For non-uniform pressure approach, the continuity and Darcy equations due to the motion of water vapor in the bed are added, and four coupled partial differential equations are solved. The changes of the adsorbate concentration, pressure, and temperature in the bed throughout the adsorption process for both approaches are obtained and compared. The obtained results showed that the particle size plays an important role on the validity of uniform pressure approach. Due to the interparticle mass transfer resistance, there is a considerable difference between the results of the uniform pressure and non-uniform pressure approaches for the beds with small size of particles such as 0.025 mm.Article Citation - WoS: 23Citation - Scopus: 25Microcalorimetric Investigation of Water Vapor Adsorption on Silica Gel(Springer Verlag, 2011) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraWater vapor adsorption on silica gel was investigated using Tian-Calvet-type microcalorimetry. Differential heat of adsorption data was obtained. The setup of microcalorimetry was used volumetric system to determine adsorption isotherms of water vapor-silica gel. The Langmuir model was used in the interpretation of the adsorption data. The Clausius-Clapeyron diagram was also given. Effective mass diffusivity of water vapor in the silica gel particle as a function of temperature was also determined. The silica gel, which was degassed under vacuum at 10 -7 mbar and 120 °C for 18 h, was found to adsorb 0.6, 0.98, 1.1, 1.4, 2, 3.5, 11, 13, and 14 wt% water vapor at 120, 110, 100, 90, 75, 60, 40, 35, and 30 °C, respectively. The diffusivities of water vapor inside the silica gel for short- and long-range periods were described using kinetics data as a function of temperature in the Arrhenius form.Article Citation - WoS: 23Citation - Scopus: 25A Dimensionless Analysis of Heat and Mass Transport in an Adsorber With Thin Fins; Uniform Pressure Approach(Elsevier Ltd., 2011) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed assisted with radial fins for an isobaric adsorption process is performed. A uniform pressure approach is employed to determine the changes of temperature and adsorbate concentration profiles in the adsorbent bed. The governing equations which are heat transfer equation for the adsorbent bed, mass balance equation for the adsorbent particle, and conduction heat transfer equation for the thin fin are non-dimensionalized in order to reduce number of governing parameters. The number of governing parameters is reduced to four as Kutateladze number, thermal diffusivity ratio, dimensionless fin coefficient and dimensionless parameter of Γ which compares mass diffusion in the adsorbent particle to heat transfer through the adsorbent bed. Temperature and adsorbate concentration contours are plotted for different values of defined dimensionless parameters to discuss heat and mass transfer rate in the bed. The average dimensionless temperature and average adsorbate concentration throughout the adsorption process are also presented to compare heat and mass transfer rate of different cases. The values of dimensionless fin coefficient, Γ number and thermal diffusivity ratio are changed from 0.01 to 100, 1 to 10 -5 and 0.01 to 100, respectively; while the values of Kutateladze number are 1 and 100. The obtained results revealed that heat transfer rate in an adsorbent bed can be enhanced by the fin when the values of thermal diffusivity ratio and fin coefficient are low (i.e., α -=0.01, δ=0.01). Furthermore, the use of fin in an adsorbent bed with low values of γ number (i.e. γ=10 -5) does not increase heat transfer rate, significantly.Article Citation - WoS: 3Citation - Scopus: 3Heat and Mass Transfer in the Adsorbent Bed of an Adsorption Heat Pump(Taylor and Francis Ltd., 2011) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraThe heat and mass transfer equations governing an adsorbent bed in an adsorption heat p mp and the mass balance equation for the adsorbent particles in the adsorbent bed were solved numerically to simulate the cycle of a basic adsorption heat pump, which includes isobaric adsorption, isosteric heating, isobaric desorption, and isosteric cooling processes. The finite difference method was used to solve the set of governing equations, which are highly nonlinear and coupled. The pressures of the evaporator and condenser were 2 and 20 kPa, respectively, and the regeneration temperature of the bed was 403 K. Changes in the temperature, adsorptive pressure, and adsorbate concentration in the adsorbent bed at different steps of the cycle were determined. The basic simulated cycle is presented in a Clausius-Clapeyron diagram, which illustrates the changes in average pressure and temperature of the adsorbent bed throughout the cycle. The results of the simulation indicated that the most time-consuming processes in the adsorption heat pump cycle were isobaric adsorption and isobaric desorption. The high thermal resistance of the bed slows down heat transfer, prolonging adsorption and desorption processes.Article Citation - WoS: 12Citation - Scopus: 11A Parametric Study on Isobaric Adsorption Process in a Closed Adsorbent Bed(Elsevier Ltd., 2010) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed filled with adsorbent granules for an isobaric adsorption process is performed. In order to reduce the number of independent parameters that influences heat and mass transfer in the bed, the governing equations and related initial and boundary conditions for the problem are non-dimensionalized and this yields two dimensionless parameters as G and Γ. The G dimensionless parameter is the ratio of heat of adsorption to sensible heat stored by adsorbent particle and Γ parameter compares mass diffusion within the adsorbent particle and heat diffusion in the radial direction of the adsorbent bed. The obtained results show that the total dimensionless time for an adsorption process can be reduced by increasing of Γ value. The total dimensionless time is independent from G for low values of Γ (i.e. Γ=105). The results also show that the instantaneous equilibrium model can provide accurate results only for an adsorbent bed with a low value of Γ (i.e. Γ=105). The present study is performed for Γ values from 105 to 1 and G value from 1 to 100. © 2010 Elsevier Ltd.Article Citation - WoS: 61Citation - Scopus: 66The Use of Metal Piece Additives To Enhance Heat Transfer Rate Through an Unconsolidated Adsorbent Bed(Elsevier Ltd., 2010) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraThe effects of metal piece additives on effective thermal conductivity and diffusivity of an unconsolidated adsorbent bed in which adsorbent is silica gel were investigated. The metal piece additives were copper, brass, aluminum and stainless steel with two different sizes as 1.0-2.8 mm and 2.8-4.75 mm. The effective thermal conductivity and diffusivity of the mixed bed were predicted by comparison of the experimental results with the solution of dimensionless heat conduction equation for the bed. The performed experiments showed that the addition 15wt% of aluminum pieces with sizes between 1.0 and 2.8 mm enhances the effective thermal diffusivity and conductivity of a pure silica gel bed by 157% and 242%, respectively. © 2010 Elsevier Ltd and IIR.Article Citation - WoS: 62Citation - Scopus: 64Effects of Porosity on Heat and Mass Transfer in a Granular Adsorbent Bed(Elsevier Ltd., 2009) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraIn the present study, the mechanism of heat and mass transfer in an annulus adsorbent is handled. The heat and mass transfer equations for the adsorbent bed and the mass balance equation for the adsorbent granules are numerically solved to obtain the distributions of temperature, pressure, adsorptive density and adsorbate concentration in the adsorbent bed. The study is performed for the silica gel-water pair and for three different values of porosity as 0.1, 0.2 and 0.3. The distributions of temperature and adsorbate concentration are considerably influenced from the bed porosity. The adsorption period increases with the increase of the porosity value. The porosity affects the pressure and adsorptive density distributions at the beginning of the process and after a relatively short time, the averages of these dependent variables approach to the final equilibrium state.Article Citation - WoS: 325Citation - Scopus: 366A Review on Adsorption Heat Pump: Problems and Solutions(Elsevier, 2008) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraAdsorption heat pumps have considerably sparked attentions in recent years. The present paper covers the working principle of adsorption heat pumps, recent studies on advanced cycles, developments in adsorbent-adsorbate pairs and design of adsorbent beds. The adsorbent-adsorbate pair features for in order to be employed in the adsorption heat pumps are described. The adsorption heat pumps are compared with the vapor compression and absorption heat pumps. The problems and troubles of adsorption heat pumps are classified and researches to overcome the difficulties are discussed.