Natural convection in a partially divided enclosure has been examined numerically using a differe... more Natural convection in a partially divided enclosure has been examined numerically using a differential quadrature method. Governing equations for the flow and heat transfer have been constructed by the vorticity-stream function formulation and computational results have been obtained for the Rayleigh numbers, 10, 10, 10, the locations of the partition, 0.2, 0.4, 0.6, 0.8, and the partition ratios, 0.25, 0.50,
Drying is one of the mostly used food preservation techniques, which reduces moisture content suf... more Drying is one of the mostly used food preservation techniques, which reduces moisture content sufficiently to prevent bacterial growth. One of the drying methods that gained popularity in recent years is microwave drying. Accordingly, in this study, microwave drying behavior of mushroom slices in various thicknesses was studied experimentally for various microwave power levels. In the study, 90W and 360W were selected as microwave power level, and 2mm, 4mm and 6mm were selected as slice thickness. During the experiment, the amount of moisture removed from the product was determined by weight measurements with a scale mounted to microwave oven. Experimental results show that microwave power has a significant effect on the drying rate of product and decreases the drying time considerably. The results also show that the effect of slice thickness is relatively small as compared with the microwave power level. The results also indicate that the Midilli et al. model is an appropriate model to describe the moisture content during microwave drying of mushroom slices. A color analysis was also conducted in this study in order to examine the effect of microwave drying on product quality in terms of color. The results show that there is a decrease in the color quality of the product due to the microwave drying.
In this study, drying characteristics of
brick have been investigated experimen+
tally. Evaluatin... more In this study, drying characteristics of brick have been investigated experimen+ tally. Evaluating experimental results under these circumstances diffusion coefficients and drying diagrams were determined.
The effect of high-Prandtl number on steady fully developed microscale flow and heat transfer bet... more The effect of high-Prandtl number on steady fully developed microscale flow and heat transfer between two parallel plates exposed to a constant heat flux is investigated analytically in this study. The Prandtl number over several orders of magnitude (5 < Pr <10 3) as well as different Knudsen number (0 < Kn <0.1) and different modified Brinkman number (-0.1 < Br <0.1) are considered. The momentum and energy equations are solved for first order boundaries of slip velocity and temperature jump. The influences of the Prandtl number, Knudsen number and Brinkman number on the temperature distribution and heat transfer characteristics are discussed.
In this paper, flow and heat transfer around a compact coil condenser of a built-in refrigerator ... more In this paper, flow and heat transfer around a compact coil condenser of a built-in refrigerator was studied numerically for various pitch values between the coils. Condenser in a housing was assumed to be cooled by an exhaust fan. This configuration is in accordance with a number of practical applications. Flow inside the housing was assumed turbulent. The fluid was assumed to be incompressible and Newtonian. The governing equations were solved by a computational fluid mechanics simulation software. The results show that when the pitch between the coils is increased, the heat transfer performance increases significantly. An increase of 27% in heat transfer rate is seen when the pitch value is increased from 6mm to 10mm. Further increase in the pitch value from 10mm to 12mm provides an extra 9% increase in heat transfer rate. As the increase in pitch value also increases condenser length, the pitch value of 10mm can be considered an optimum value when there is a strong restriction on space in chassis region.
In this paper, natural convection in a square enclosure cooled by Peltier effect is investigated ... more In this paper, natural convection in a square enclosure cooled by Peltier effect is investigated numerically. The thermoelectric cooler is assumed to be mounted on the left sidewall of the enclosure. The right sidewall of the enclosure is at constant temperature and horizontal walls are adiabatic. Flow is assumed to be two dimensional, Newtonian, and incompressible. Governing equations are derived using Boussinesq approximation. Computational results are obtained for values of electric current ranging from 2 to 8A. The results show that a thermal plume develops at the bottom left part of the enclosure in the early stage of the flow. Flow field consists of a counter clockwise cell. As the electric current and hence the heat flux on the left wall of the enclosure increases, a secondary circulation cell develops at the bottom part of the enclosure as a result of the thermal plume. With the thermoelectric cooler, very low temperatures can be reached within a relatively short time.
Natural convection heat transfer of silicone oil-based Al 2 O 3 nanofluid in a cylindrical enclos... more Natural convection heat transfer of silicone oil-based Al 2 O 3 nanofluid in a cylindrical enclosure used as a control unit in the subsea hydrocarbon and injection wells is investigated in this study. The governing equations obtained with the Boussinesq approximation are solved using Comsol Multiphysics finite element analysis and simulation software. Computational results are obtained for nanoparticle solid volume fraction in the range of 0%-8% and for Rayleigh number in the range of 10 5-10 7. The results show that temperature inside the enclosure decreases considerably when nanoparticles are used in the cylindrical electronic control. The results also show that temperature inside the enclosure decreases substantially with an increase in the Rayleigh number.
In this study, a software has been developed to predict the optimum drying conditions of viscose ... more In this study, a software has been developed to predict the optimum drying conditions of viscose based yarn bobbins for drying in a pressurised hot air dryer. For this purpose, firstly, a suitable drying model has been found in defining the drying behaviour of bobbins using the experimental drying behaviour. After that, additional regression analyses have been made to take into account the effect of drying parameters on drying. Then, a software has been developed using Visual Basic programming language. With the aid of this software, optimum drying conditions for drying time and energy consumption can be obtained.
Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with... more Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with top wall at higher and bottom and side walls at lower uniform temperatures were considered and the governing equations were solved numerically. Flow field is consist of a single eddy with clockwise rotation for all cases considered. Center of the eddy shifts from a location near the side wall to a location near the top disc as the aspect ratio increases.
Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with... more Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with bottom wall at higher and top and side walls at lower uniform temperatures were considered and the governing equations were solved numerically. Flow field consists of a single eddy with clockwise rotation for low Rayleigh numbers. As the rotational Reynolds number and Rayleigh number increase a second eddy with counterclockwise rotation forms near the centerline.
Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder heat... more Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder heated with uniform heat flux from the bottom disc while the upper disc and the side wall are kept at a uniform temperature were considered and the governing equations were solved numerically. Flow field is consist of a single eddy with clockwise rotation for low Rayleigh numbers. As the rotational Reynolds number and Rayleigh number increase a second eddy with counterclockwise rotation forms near the centerline.
Dzet Ani olarak harekete gef{irilmi~, donen, eksenel simetrik, izotermal ve gef{irgen yuzeyli bir... more Dzet Ani olarak harekete gef{irilmi~, donen, eksenel simetrik, izotermal ve gef{irgen yuzeyli bir cisim uzerinden "aminer Slnlr tabaka akl~lnln geli~imi kan~lk ve dogal konveksiyon durumlan if{in incelendi. Aklm fonksiyonu, ~evresel hrz ve slcaklrk zaman cinsinden kuvvet serileri Be ifade edildi. Genel sonuf{lar, karr~lk konveksiyon durumunda yuzey gef{irgenligi ve kaldlrma kuvvetinin hlz ve slcakllk alanl Ozerine etkisini belirlemek; dogal konveksiyon durumunda slnlr tabaka akl~ rejimlerini ortaya f{lkarmak if{in d6nen bir kGreye uygulandl. Anahtar Kelirneler : D6nen cisimler, daimi olmayan rejim, Slnlr tabaka, laminer ve aynlml~ akl~ CHARACTERISTICS OF UNSTEADY SEPARATED LAMINAR BOUNDARY LAYER FLOWS OVER SPINNING BODIES Abstract Initial development of the laminar boundary-layer flow over an impulsively started spinning isothermal permeable body of revolution in mixed and free convection is investigated. Stream function, swirl velocity and temperature were expanded in series of time. The general results were applied to a spinning sphere to determine the effects of surface transpiration and buoyancy on the velocity and temperature fields in the case of forced convection and to investigate the type of boundary layer flow regimes in the case of free convection. Keywords: Spinning bodies, unsteady, boundary layer, laminar and separated flow 1. Introduction Boundary-layer flow over spinning bodies of revolution has important engineering applications involving projectile motion, reentry missile behaviour and rotary machine design. The flow field is greatly affected by the rotation of the body. In the case of a bluff body, the boundary layer separates and the flow field becomes more complex. The centrifugal force caused by the rotation of the body is known to facilitate and speed up the flow separation. Surface blowing and suction also influence the onset of separation providing a boundary-layer control mechanism. Furthermore when the temperature difference between the surface and the fluid is large and the velocity is small, the buoyancy force due to the density variation interacts with the centrifugal force altering the velocity field. In the case of free convection from a heated vertical body spinning in an otherwise quiescent fluid, interaction between the buoyancy and the centrifugal forces determines the boundary layer flow regimes. The number of solutions of the boundary-layer flows including the swirl velocity is very few. Flow about a spinning body of revolution has been investigated by Illingworth (1), Chu and Tifford (2). Schlichting (3) and Hoskin (4). These are all momentum-integral approximations and of uncertain accuracy. Measurements of Luthander and Rydberg (5) and the study of Hoskin (4) show that there is a marked influence of rotation on drag and separation on a spinning sphere in an axial stream. The problem of mixed convection about a rotating sphere in a stream has been investigated by Rajasekaran and Palekar (6). Tile results show that velocity profiles affected by buoyancy display an overshoot beyond a local free stream velocity for aiding flow. Le Palec and Daguenet (7) have used power series expansions for the stream function and temperature to study the laminar mixed convection about an isothermal rotating sphere in a stream of arbitrary direction with respect to the axis of rotation and solved the boundary layer equations numerically. Mixed convection over a spinning sphere with blowing and suction has been investigated numerically by Lien et al (8) and Wang and KleinstrelJer (9) to show that the wall suction and body rotation enhances heat transfer for aiding flow.
'TIle initial laminar thennal boundary-layer flow past an impulsively started translating and spi... more 'TIle initial laminar thennal boundary-layer flow past an impulsively started translating and spinning rotational symmetric, penneable isothennal body is investigated. Velocity components and temperature are expanded in series in powers of time. Leading, first and second order functions are obtained analytically and the thlrd, forth and fifth order functions are detennined numerically. Application of the general results to a sphere shows that the unsteady now field displays complex patterns. Slu-face blowing is observed to aid body spin in facilitating flow separation. SlU'face heat flux is t:nhanced near the front stagnation point and in the reversed flow region and reduced around the point of separation. SlU'face suction is fOllnd to increase the heat transfer while slU'face blowing decreases it. NOMENCLATURE F= gauge function for stream function G= gauge flmction for circumferential velocity I[= dimensionless temperature K= boundary layer nonnal scale
Drying is one of the mostly used food preservation techniques, which reduces moisture content suf... more Drying is one of the mostly used food preservation techniques, which reduces moisture content sufficiently to prevent bacterial growth. One of the drying methods that gained popularity in recent years is microwave drying. Accordingly, in this study, microwave drying behavior of mushroom slices in various thicknesses was studied experimentally for various microwave power levels. In the study, 90W and 360W were selected as microwave power level, and 2mm, 4mm and 6mm were selected as slice thickness. During the experiment, the amount of moisture removed from the product was determined by weight measurements with a scale mounted to microwave oven. Experimental results show that microwave power has a significant effect on the drying rate of product and decreases the drying time considerably. The results also show that the effect of slice thickness is relatively small as compared with the microwave power level. The results also indicate that the Midilli et al. model is an appropriate model to describe the moisture content during microwave drying of mushroom slices. A color analysis was also conducted in this study in order to examine the effect of microwave drying on product quality in terms of color. The results show that there is a decrease in the color quality of the product due to the microwave drying.
Abstroct The WlBteady laminar boundary-layer flow over e.n impulsively started translating e.nd s... more Abstroct The WlBteady laminar boundary-layer flow over e.n impulsively started translating e.nd spinning rotational symmetric permeable body is investigated. Stream function and swirl velocity are expanded in series of functions in powers of time. The leading order functions are determined e.nalytically and the higher order functions are obtained numerically. The general results ere applied to a sphere and the surfBCe blowing is found to aid the centrifugal force created by the body apin in fBCilitating the fiow separation while the suction rete.rds it.
Rough rice has high moisture content at harvest, and if their moisture content is not reduced to ... more Rough rice has high moisture content at harvest, and if their moisture content is not reduced to about 12% on the dry basis they decay due to infestation and mold growth. Drying process is generally performed by heating ambient air and then sending it by forced convection over the rough rice to be dried. The aim in heating air to a certain temperature is to reduce the relative humidity of the air, which has a positive effect on the drying potential. In this study, drying behavior of single layer rough rice for different drying air temperature was simulated by means of a liquid diffusion model numerically by finite element modeling and simulation software. The results show that temperature is an effective factor on the drying rate. The results also show that as drying proceeds, a moisture gradient develops within the grain. This slows down the drying rate considerably. Therefore, it can be concluded that performing drying with an intermittent period instead of continuous drying will cause a considerable energy-saving.
Steady, laminar, eentrifugally driven eonveetive heat transfer in a spinning cireular eylinder wa... more Steady, laminar, eentrifugally driven eonveetive heat transfer in a spinning cireular eylinder was eonsidered. The governing equations were solved numerieally. Aspeet ratjo, Reynolds and Rayleigh numbers have a signifieant effeei on the veloeity and temperature fields. DISTRIBUTION CENTRIFUGE DE L'ECOULEMENT ET TRANSFERT DE CHALEUR DANS UN CYLlNDRE EN ROTATION CHAUFFE UNIFORMEMENT PAR LE FOND RESUME Stable, laminar, le transfert de ehaleur de eonveetive eentrifugation eonduit dans un eylindre eireulaire de rotation a ete examine. Les equations gouvernantes ant ete resolues numeriquement. La proportion d'aspect les nombres de Reynolds et Rayleigh ant un effet signifieatif sur de vitesse et les champs de temperature.
International Communications in Heat and Mass Transfer, 2015
Three dimensional blood flow in compliant, tapering vessels of a truncated vascular system model ... more Three dimensional blood flow in compliant, tapering vessels of a truncated vascular system model containing two levels of bifurcation was investigated numerically using a commercially available finite element analysis and simulation software. Although the branching pattern and the geometry of the human vascular system are complex, they can be specified for small arteries using Murray's hypothesis that the structure of the vascular system obeys the principle of minimum work. Accordingly, in the current vascular system model, the parent/ daughter diameter ratios and the angles of bifurcation were specified according to Murray's law. Another geometrical parameter, the ratio of blood vessel length to diameter, was determined according to data found in the literature. The vascular system model also includes a 5 mm thick layer of tissue surrounding the vessels. This tissue layer helps to resist artery deformation during the cardiac cycle. Experimentally measured time dependent blood velocity data, available in the literature, were used as the inlet boundary condition to represent the cardiac cycle. An outflow boundary model, consisting of an elastic tube followed by a contraction tube, was used at the four outlets to represent both the compliance and the pressure drop of the small arteries, arterioles, and capillaries that would follow the truncated vascular system. The results show that, at each bifurcation, the blood flow velocity decreases significantly in the transition from the parent vessel to the daughter vessels due to the higher total cross-sectional area of the daughter vessels as compared to the parent vessel. This decrease in velocity is partially recovered along the arteries due to the tapering of the blood vessels. It can also be observed from the results that the pressure distributions and pressure drops along the vascular system are in good agreement with the physiological data found in the literature. The results also show that the velocity profiles immediately following a bifurcation are not initially symmetric, with their maxima shifted toward the inner part of the bifurcation in the daughter vessels. Finally, the results show that the maximum deformation is about 2% of the average vessel radius, which is relatively small and typical for small arteries.
ABSTRACT Drying of multi-layer rough rice was investigated. Stacks of rough rice having different... more ABSTRACT Drying of multi-layer rough rice was investigated. Stacks of rough rice having different heights were dried with a forced convection of warm air and the time rate of change of the bulk moisture ratio was experimentally determined. A theoretical model developed for a single ...
Natural convection in a partially divided enclosure has been examined numerically using a differe... more Natural convection in a partially divided enclosure has been examined numerically using a differential quadrature method. Governing equations for the flow and heat transfer have been constructed by the vorticity-stream function formulation and computational results have been obtained for the Rayleigh numbers, 10, 10, 10, the locations of the partition, 0.2, 0.4, 0.6, 0.8, and the partition ratios, 0.25, 0.50,
Drying is one of the mostly used food preservation techniques, which reduces moisture content suf... more Drying is one of the mostly used food preservation techniques, which reduces moisture content sufficiently to prevent bacterial growth. One of the drying methods that gained popularity in recent years is microwave drying. Accordingly, in this study, microwave drying behavior of mushroom slices in various thicknesses was studied experimentally for various microwave power levels. In the study, 90W and 360W were selected as microwave power level, and 2mm, 4mm and 6mm were selected as slice thickness. During the experiment, the amount of moisture removed from the product was determined by weight measurements with a scale mounted to microwave oven. Experimental results show that microwave power has a significant effect on the drying rate of product and decreases the drying time considerably. The results also show that the effect of slice thickness is relatively small as compared with the microwave power level. The results also indicate that the Midilli et al. model is an appropriate model to describe the moisture content during microwave drying of mushroom slices. A color analysis was also conducted in this study in order to examine the effect of microwave drying on product quality in terms of color. The results show that there is a decrease in the color quality of the product due to the microwave drying.
In this study, drying characteristics of
brick have been investigated experimen+
tally. Evaluatin... more In this study, drying characteristics of brick have been investigated experimen+ tally. Evaluating experimental results under these circumstances diffusion coefficients and drying diagrams were determined.
The effect of high-Prandtl number on steady fully developed microscale flow and heat transfer bet... more The effect of high-Prandtl number on steady fully developed microscale flow and heat transfer between two parallel plates exposed to a constant heat flux is investigated analytically in this study. The Prandtl number over several orders of magnitude (5 < Pr <10 3) as well as different Knudsen number (0 < Kn <0.1) and different modified Brinkman number (-0.1 < Br <0.1) are considered. The momentum and energy equations are solved for first order boundaries of slip velocity and temperature jump. The influences of the Prandtl number, Knudsen number and Brinkman number on the temperature distribution and heat transfer characteristics are discussed.
In this paper, flow and heat transfer around a compact coil condenser of a built-in refrigerator ... more In this paper, flow and heat transfer around a compact coil condenser of a built-in refrigerator was studied numerically for various pitch values between the coils. Condenser in a housing was assumed to be cooled by an exhaust fan. This configuration is in accordance with a number of practical applications. Flow inside the housing was assumed turbulent. The fluid was assumed to be incompressible and Newtonian. The governing equations were solved by a computational fluid mechanics simulation software. The results show that when the pitch between the coils is increased, the heat transfer performance increases significantly. An increase of 27% in heat transfer rate is seen when the pitch value is increased from 6mm to 10mm. Further increase in the pitch value from 10mm to 12mm provides an extra 9% increase in heat transfer rate. As the increase in pitch value also increases condenser length, the pitch value of 10mm can be considered an optimum value when there is a strong restriction on space in chassis region.
In this paper, natural convection in a square enclosure cooled by Peltier effect is investigated ... more In this paper, natural convection in a square enclosure cooled by Peltier effect is investigated numerically. The thermoelectric cooler is assumed to be mounted on the left sidewall of the enclosure. The right sidewall of the enclosure is at constant temperature and horizontal walls are adiabatic. Flow is assumed to be two dimensional, Newtonian, and incompressible. Governing equations are derived using Boussinesq approximation. Computational results are obtained for values of electric current ranging from 2 to 8A. The results show that a thermal plume develops at the bottom left part of the enclosure in the early stage of the flow. Flow field consists of a counter clockwise cell. As the electric current and hence the heat flux on the left wall of the enclosure increases, a secondary circulation cell develops at the bottom part of the enclosure as a result of the thermal plume. With the thermoelectric cooler, very low temperatures can be reached within a relatively short time.
Natural convection heat transfer of silicone oil-based Al 2 O 3 nanofluid in a cylindrical enclos... more Natural convection heat transfer of silicone oil-based Al 2 O 3 nanofluid in a cylindrical enclosure used as a control unit in the subsea hydrocarbon and injection wells is investigated in this study. The governing equations obtained with the Boussinesq approximation are solved using Comsol Multiphysics finite element analysis and simulation software. Computational results are obtained for nanoparticle solid volume fraction in the range of 0%-8% and for Rayleigh number in the range of 10 5-10 7. The results show that temperature inside the enclosure decreases considerably when nanoparticles are used in the cylindrical electronic control. The results also show that temperature inside the enclosure decreases substantially with an increase in the Rayleigh number.
In this study, a software has been developed to predict the optimum drying conditions of viscose ... more In this study, a software has been developed to predict the optimum drying conditions of viscose based yarn bobbins for drying in a pressurised hot air dryer. For this purpose, firstly, a suitable drying model has been found in defining the drying behaviour of bobbins using the experimental drying behaviour. After that, additional regression analyses have been made to take into account the effect of drying parameters on drying. Then, a software has been developed using Visual Basic programming language. With the aid of this software, optimum drying conditions for drying time and energy consumption can be obtained.
Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with... more Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with top wall at higher and bottom and side walls at lower uniform temperatures were considered and the governing equations were solved numerically. Flow field is consist of a single eddy with clockwise rotation for all cases considered. Center of the eddy shifts from a location near the side wall to a location near the top disc as the aspect ratio increases.
Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with... more Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with bottom wall at higher and top and side walls at lower uniform temperatures were considered and the governing equations were solved numerically. Flow field consists of a single eddy with clockwise rotation for low Rayleigh numbers. As the rotational Reynolds number and Rayleigh number increase a second eddy with counterclockwise rotation forms near the centerline.
Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder heat... more Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder heated with uniform heat flux from the bottom disc while the upper disc and the side wall are kept at a uniform temperature were considered and the governing equations were solved numerically. Flow field is consist of a single eddy with clockwise rotation for low Rayleigh numbers. As the rotational Reynolds number and Rayleigh number increase a second eddy with counterclockwise rotation forms near the centerline.
Dzet Ani olarak harekete gef{irilmi~, donen, eksenel simetrik, izotermal ve gef{irgen yuzeyli bir... more Dzet Ani olarak harekete gef{irilmi~, donen, eksenel simetrik, izotermal ve gef{irgen yuzeyli bir cisim uzerinden "aminer Slnlr tabaka akl~lnln geli~imi kan~lk ve dogal konveksiyon durumlan if{in incelendi. Aklm fonksiyonu, ~evresel hrz ve slcaklrk zaman cinsinden kuvvet serileri Be ifade edildi. Genel sonuf{lar, karr~lk konveksiyon durumunda yuzey gef{irgenligi ve kaldlrma kuvvetinin hlz ve slcakllk alanl Ozerine etkisini belirlemek; dogal konveksiyon durumunda slnlr tabaka akl~ rejimlerini ortaya f{lkarmak if{in d6nen bir kGreye uygulandl. Anahtar Kelirneler : D6nen cisimler, daimi olmayan rejim, Slnlr tabaka, laminer ve aynlml~ akl~ CHARACTERISTICS OF UNSTEADY SEPARATED LAMINAR BOUNDARY LAYER FLOWS OVER SPINNING BODIES Abstract Initial development of the laminar boundary-layer flow over an impulsively started spinning isothermal permeable body of revolution in mixed and free convection is investigated. Stream function, swirl velocity and temperature were expanded in series of time. The general results were applied to a spinning sphere to determine the effects of surface transpiration and buoyancy on the velocity and temperature fields in the case of forced convection and to investigate the type of boundary layer flow regimes in the case of free convection. Keywords: Spinning bodies, unsteady, boundary layer, laminar and separated flow 1. Introduction Boundary-layer flow over spinning bodies of revolution has important engineering applications involving projectile motion, reentry missile behaviour and rotary machine design. The flow field is greatly affected by the rotation of the body. In the case of a bluff body, the boundary layer separates and the flow field becomes more complex. The centrifugal force caused by the rotation of the body is known to facilitate and speed up the flow separation. Surface blowing and suction also influence the onset of separation providing a boundary-layer control mechanism. Furthermore when the temperature difference between the surface and the fluid is large and the velocity is small, the buoyancy force due to the density variation interacts with the centrifugal force altering the velocity field. In the case of free convection from a heated vertical body spinning in an otherwise quiescent fluid, interaction between the buoyancy and the centrifugal forces determines the boundary layer flow regimes. The number of solutions of the boundary-layer flows including the swirl velocity is very few. Flow about a spinning body of revolution has been investigated by Illingworth (1), Chu and Tifford (2). Schlichting (3) and Hoskin (4). These are all momentum-integral approximations and of uncertain accuracy. Measurements of Luthander and Rydberg (5) and the study of Hoskin (4) show that there is a marked influence of rotation on drag and separation on a spinning sphere in an axial stream. The problem of mixed convection about a rotating sphere in a stream has been investigated by Rajasekaran and Palekar (6). Tile results show that velocity profiles affected by buoyancy display an overshoot beyond a local free stream velocity for aiding flow. Le Palec and Daguenet (7) have used power series expansions for the stream function and temperature to study the laminar mixed convection about an isothermal rotating sphere in a stream of arbitrary direction with respect to the axis of rotation and solved the boundary layer equations numerically. Mixed convection over a spinning sphere with blowing and suction has been investigated numerically by Lien et al (8) and Wang and KleinstrelJer (9) to show that the wall suction and body rotation enhances heat transfer for aiding flow.
'TIle initial laminar thennal boundary-layer flow past an impulsively started translating and spi... more 'TIle initial laminar thennal boundary-layer flow past an impulsively started translating and spinning rotational symmetric, penneable isothennal body is investigated. Velocity components and temperature are expanded in series in powers of time. Leading, first and second order functions are obtained analytically and the thlrd, forth and fifth order functions are detennined numerically. Application of the general results to a sphere shows that the unsteady now field displays complex patterns. Slu-face blowing is observed to aid body spin in facilitating flow separation. SlU'face heat flux is t:nhanced near the front stagnation point and in the reversed flow region and reduced around the point of separation. SlU'face suction is fOllnd to increase the heat transfer while slU'face blowing decreases it. NOMENCLATURE F= gauge function for stream function G= gauge flmction for circumferential velocity I[= dimensionless temperature K= boundary layer nonnal scale
Drying is one of the mostly used food preservation techniques, which reduces moisture content suf... more Drying is one of the mostly used food preservation techniques, which reduces moisture content sufficiently to prevent bacterial growth. One of the drying methods that gained popularity in recent years is microwave drying. Accordingly, in this study, microwave drying behavior of mushroom slices in various thicknesses was studied experimentally for various microwave power levels. In the study, 90W and 360W were selected as microwave power level, and 2mm, 4mm and 6mm were selected as slice thickness. During the experiment, the amount of moisture removed from the product was determined by weight measurements with a scale mounted to microwave oven. Experimental results show that microwave power has a significant effect on the drying rate of product and decreases the drying time considerably. The results also show that the effect of slice thickness is relatively small as compared with the microwave power level. The results also indicate that the Midilli et al. model is an appropriate model to describe the moisture content during microwave drying of mushroom slices. A color analysis was also conducted in this study in order to examine the effect of microwave drying on product quality in terms of color. The results show that there is a decrease in the color quality of the product due to the microwave drying.
Abstroct The WlBteady laminar boundary-layer flow over e.n impulsively started translating e.nd s... more Abstroct The WlBteady laminar boundary-layer flow over e.n impulsively started translating e.nd spinning rotational symmetric permeable body is investigated. Stream function and swirl velocity are expanded in series of functions in powers of time. The leading order functions are determined e.nalytically and the higher order functions are obtained numerically. The general results ere applied to a sphere and the surfBCe blowing is found to aid the centrifugal force created by the body apin in fBCilitating the fiow separation while the suction rete.rds it.
Rough rice has high moisture content at harvest, and if their moisture content is not reduced to ... more Rough rice has high moisture content at harvest, and if their moisture content is not reduced to about 12% on the dry basis they decay due to infestation and mold growth. Drying process is generally performed by heating ambient air and then sending it by forced convection over the rough rice to be dried. The aim in heating air to a certain temperature is to reduce the relative humidity of the air, which has a positive effect on the drying potential. In this study, drying behavior of single layer rough rice for different drying air temperature was simulated by means of a liquid diffusion model numerically by finite element modeling and simulation software. The results show that temperature is an effective factor on the drying rate. The results also show that as drying proceeds, a moisture gradient develops within the grain. This slows down the drying rate considerably. Therefore, it can be concluded that performing drying with an intermittent period instead of continuous drying will cause a considerable energy-saving.
Steady, laminar, eentrifugally driven eonveetive heat transfer in a spinning cireular eylinder wa... more Steady, laminar, eentrifugally driven eonveetive heat transfer in a spinning cireular eylinder was eonsidered. The governing equations were solved numerieally. Aspeet ratjo, Reynolds and Rayleigh numbers have a signifieant effeei on the veloeity and temperature fields. DISTRIBUTION CENTRIFUGE DE L'ECOULEMENT ET TRANSFERT DE CHALEUR DANS UN CYLlNDRE EN ROTATION CHAUFFE UNIFORMEMENT PAR LE FOND RESUME Stable, laminar, le transfert de ehaleur de eonveetive eentrifugation eonduit dans un eylindre eireulaire de rotation a ete examine. Les equations gouvernantes ant ete resolues numeriquement. La proportion d'aspect les nombres de Reynolds et Rayleigh ant un effet signifieatif sur de vitesse et les champs de temperature.
International Communications in Heat and Mass Transfer, 2015
Three dimensional blood flow in compliant, tapering vessels of a truncated vascular system model ... more Three dimensional blood flow in compliant, tapering vessels of a truncated vascular system model containing two levels of bifurcation was investigated numerically using a commercially available finite element analysis and simulation software. Although the branching pattern and the geometry of the human vascular system are complex, they can be specified for small arteries using Murray's hypothesis that the structure of the vascular system obeys the principle of minimum work. Accordingly, in the current vascular system model, the parent/ daughter diameter ratios and the angles of bifurcation were specified according to Murray's law. Another geometrical parameter, the ratio of blood vessel length to diameter, was determined according to data found in the literature. The vascular system model also includes a 5 mm thick layer of tissue surrounding the vessels. This tissue layer helps to resist artery deformation during the cardiac cycle. Experimentally measured time dependent blood velocity data, available in the literature, were used as the inlet boundary condition to represent the cardiac cycle. An outflow boundary model, consisting of an elastic tube followed by a contraction tube, was used at the four outlets to represent both the compliance and the pressure drop of the small arteries, arterioles, and capillaries that would follow the truncated vascular system. The results show that, at each bifurcation, the blood flow velocity decreases significantly in the transition from the parent vessel to the daughter vessels due to the higher total cross-sectional area of the daughter vessels as compared to the parent vessel. This decrease in velocity is partially recovered along the arteries due to the tapering of the blood vessels. It can also be observed from the results that the pressure distributions and pressure drops along the vascular system are in good agreement with the physiological data found in the literature. The results also show that the velocity profiles immediately following a bifurcation are not initially symmetric, with their maxima shifted toward the inner part of the bifurcation in the daughter vessels. Finally, the results show that the maximum deformation is about 2% of the average vessel radius, which is relatively small and typical for small arteries.
ABSTRACT Drying of multi-layer rough rice was investigated. Stacks of rough rice having different... more ABSTRACT Drying of multi-layer rough rice was investigated. Stacks of rough rice having different heights were dried with a forced convection of warm air and the time rate of change of the bulk moisture ratio was experimentally determined. A theoretical model developed for a single ...
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Papers by Kamil Kahveci
brick have been investigated experimen+
tally. Evaluating experimental results under
these circumstances diffusion coefficients
and drying diagrams were determined.
brick have been investigated experimen+
tally. Evaluating experimental results under
these circumstances diffusion coefficients
and drying diagrams were determined.