Gamze Gediz Ilis

Bio: Gamze Gediz Ilis is an academic researcher from Gebze Institute of Technology. The author has contributed to research in topics: Adsorption & Heat transfer. The author has an hindex of 8, co-authored 21 publications receiving 353 citations. Previous affiliations of Gamze Gediz Ilis include İzmir Institute of Technology & Indesit Company.

Effect of aspect ratio on entropy generation in a rectangular cavity with differentially heated vertical walls

Abstract: In the present study, entropy generation in rectangular cavities with the same area but different aspect ratios is numerically investigated. The vertical walls of the cavities are at different constant temperatures while the horizontal walls are adiabatic. Heat transfer between vertical walls occurs by laminar natural convection. Based on the obtained dimensionless velocity and temperature values, the distributions of local entropy generation due to heat transfer and fluid friction, the local Bejan number and local entropy generation number are determined and related maps are plotted. The variation of the total entropy generation and average Bejan number for the whole cavity volume at different aspect ratios for different values of the Rayleigh number and irreversibility distribution ratio are also evaluated. It is found that for a cavity with high value of Rayleigh number (i.e., Ra = 10(5)), the total entropy generation due to fluid friction and total entropy generation number increase with increasing aspect ratio, attain a maximum and then decrease. The present results are compared with reported solutions and excellent agreement is observed. The study is performed for 10(2) < Ra < 10(5), 10(-4) < 0 < 10(-2), and Pr = 0.7. (Less)

A new adsorbent bed design: Optimization of geometric parameters and metal additive for the performance improvement

Abstract: A numerical simulation is performed for an innovative star fin type adsorbent bed with metal additive in order to determine the optimum geometrical parameters. Also, the effect of the addition of metal additives to the adsorbent bed on performance of an adsorption chiller is analyzed. The Fuji RD-type silica gel/water is used as the adsorbent/adsorbate pair. The material, shape and the location of the heating/cooling fluid pipe, as well as the adsorbent particle radius, are predicted, and their influence on the specific cooling performance (SCP) of the adsorption chiller is analyzed. The average temperature, concentration and the duration of the whole process in the two-dimensional star finned bed are analyzed by Taguchi method for different geometrical configurations to find the best configuration for the highest SCP. Besides, the aluminum metal particles are added to the best adsorbent bed configuration, and the effect of the metal additive on SCP is also investigated. The obtained results showed that the adsorbent particle radius change and the distance between the fins have important roles in SCP. The effect of aluminum particle additive on SCP of the adsorption heat pump is observed as 300% of increment.

A dimensionless analysis of heat and mass transport in an adsorber with thin fins; uniform pressure approach

Abstract: A 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, Λ = 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.

Pumping power and heat transfer rate of converging microchannel heat sinks: errors associated with the temperature dependency of nanofluids

Abstract: To find the sensitivity and dependence degree of the numerical simulation predictions on the property variations arising from the temperature gradients, a 3D conjugate heat transfer of Al2O3–water nanofluid convecting through rectangular microchannel heat sinks (MCHS) is considered in the present study. The Koo–Kleinstreuer–Li model is adopted to capture the temperature-dependent nature of thermophysical properties of the working nanofluid compared to the pure fluid (i.e., water). Both straight and width-tapered flow passages are studied using finite volume method within the laminar flow regime to see how sensitive are the predictions to the temperature dependency of the thermophysical properties for both the pure base fluid and nanofluid. Results show that the constant property assumption obtains unrealistic results up to 140% for the Reynolds number, which may mislead in predicting the flow regime (laminar/turbulent). The constant property approach predicts the convection heat transfer coefficient and the pumping power, respectively, 31% lower and 33% higher than those of the temperature-dependent property approach. In addition, the present study concludes that the MCHS should be simulated based on the temperature-dependent thermophysical property approach to be more realistic, especially for converging flow passages due to high-temperature gradients and for nanofluids for their induced temperature-dependent properties. The last two issues induced each other and increase the deviation of the predictions based on the constant property assumption. Finally, because of underestimating the heat transfer rate and overestimating the pumping power, the MCHS would be over-designed if one adopts the constant property assumption for conceptual design and the MCHS would perform under inefficient and off-design conditions.

Heat Transfer Reduction due to a Ceiling-Mounted Barrier in an Enclosure with Natural Convection

Abstract: Effects of a ceiling-mounted barrier on natural convection heat transfer in a square cavity with differentially heated wall are numerically investigated. A limit case, in which the partition has small thickness and low thermal conductivity, is studied. The study is performed for nine different locations of barrier on the ceiling, two different lengths of barrier as 15 and 50% of the side wall, and Rayleigh numbers from 103 to 106. The vorticity and streamfunction approach is used to obtain velocity distribution, and the energy equation is solved to determine temperature field in the cavity. The variations of the local Nusselt number on the hot and cold walls and the change of mean Nusselt number with the location of barrier in the cavities with different Rayleigh numbers are presented. The obtained results show that a wall-mounted barrier can be used to reduce heat transfer rate through the cavity; however, its effectiveness depends on length and location of barrier and Rayleigh number.

Convection Heat Transfer

Abstract: Geometry: shape, size, aspect ratio and orientation Flow Type: forced, natural, laminar, turbulent, internal, external Boundary: isothermal (Tw = constant) or isoflux (q̇w = constant) Fluid Type: viscous oil, water, gases or liquid metals Properties: all properties determined at film temperature Tf = (Tw + T∞)/2 Note: ρ and ν ∝ 1/Patm ⇒ see Q12-40 density: ρ ((kg/m) specific heat: Cp (J/kg ·K) dynamic viscosity: μ, (N · s/m) kinematic viscosity: ν ≡ μ/ρ (m/s) thermal conductivity: k, (W/m ·K) thermal diffusivity: α, ≡ k/(ρ · Cp) (m/s) Prandtl number: Pr, ≡ ν/α (−−) volumetric compressibility: β, (1/K)

A review on entropy generation in natural and mixed convection heat transfer for energy systems

Abstract: This paper reviews the second law analysis of thermodynamics in enclosures due to buoyancy-induced flow for energy systems It defines entropy generation minimization or thermodynamic optimization In addition, the article summarizes the recent works on entropy generation in buoyancy-induced flows in cavity and channels Studies on mixed convection were also included in the study Presentation was performed for flow in porous media and viscous fluid filled media at different shaped enclosures and duct under buoyancy-induced force

Studies on natural convection within enclosures of various (non-square) shapes – A review

Abstract: Natural convection in an enclosure (internal convection) is an important problem due to its significant practical applications. In energy related applications, natural convection plays a dominant role in transport of energy for the proper design of enclosures in order to achieve higher heat transfer rates. This review summarizes the studies on natural convection heat transfer in triangular, trapezoidal, parallelogrammic enclosures and enclosures with curved and wavy walls filled with fluid or porous media. In addition, this review also summarizes the natural convection studies in the nanofluid filled enclosures. Studies have been performed for the enclosures subjected to different thermal boundary conditions. A number of the studies demonstrated that the variation of the aspect ratio and base angle of the triangular and rhombic/parallelogrammic enclosures had a wide influence on the flow distribution pattern. In the trapezoidal enclosure, the aspect ratio of the cavity as well as the presence of the baffles along the walls played a significant role in the temperature and flow distribution. The flow patterns within the complex enclosures were found to be largely dependent on the amplitude-wavelength ratio and number of undulations of the wavy walls. In addition, the researchers have also studied the effect of the various parameters such as the Rayleigh numbers, Prandtl numbers, Darcy numbers, Darcy–Rayleigh number, irreversibility distribution ratios, volume fraction of the nanoparticles, etc. Overall, the current review paper presents an useful insight into the potential strategies for enhancing the convection heat transfer performance.

Review on sorption materials and technologies for heat pumps and thermal energy storage

Abstract: Sorption is used for absorption/adsorption heat pumps (sorption refrigeration) and sorption for thermal energy storage (TES). This paper is the first review where the research on both applications is shown together. Sorption has advanced very much due to the immense amount of research carried out around heat pumping and solar refrigeration. Moreover, sorption and thermochemical heat storage attracted considerable attention recently since this technology offers various opportunities in the design of renewable and sustainable energy systems. The paper presents the operation principle of the technology and the materials used or in research are listed and compared. Absorption heat pumping and refrigeration research is today more focussed in the decrease of unit costs and increase of energy efficiency, adsorption is focussed in finding more efficient working pairs, and storage is testing the first prototypes and designing new ones with different or enhanced storage materials and new reactor concepts to optimize energy output.

Simulation of heat transfer and entropy generation of MHD natural convection of non-Newtonian nanofluid in an enclosure

Abstract: In this paper, heat transfer and entropy generation on laminar natural convection of non-Newtonian nanofluids in the presence of an external horizontal magnetic field in a square cavity has been analyzed by Finite Difference Lattice Boltzmann Method (FDLBM). The cavity is filled with water and nanoparticles of copper (Cu) while the mixture shows shear-thinning behavior. This study has been conducted for the certain pertinent parameters of Rayleigh number (Ra = 104–105), power-law index (n = 0.6–1), Hartmann number (Ha = 0–90) and the volume fraction has been studied from φ = 0 to 0.04. Results indicate that the augmentation of the power-law index causes heat transfer to drop in the absence of the magnetic field, by contrast, the heat transfer increases with the rise of power-law index in the presence of the magnetic field. The addition of nanoparticle augments heat transfer for multifarious studied parameters. The heat transfer drops with the increase in Hartmann number generally and also affects the power-law index and nanoparticles influences on heat transfer. Augmentation of the volume fraction and Rayleigh number enhance all kinds of entropy generations of heat transfer, fluid friction, and the magnetic field in different studied parameters. The increase in the Hartmann number causes the total entropy generation to drop and affects the influences of the power-law index and the volume fraction on the entropy generations.