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    Experimental and numerical investigation of heat transfer in a channel with multiple phase change materials (PCMs)
    (Elsevier, 2022) Akyol, Erhan; Hacihafizoglu, Oktay; Susantez, Cigdem; Kahveci, Kamil; Akyol, Ugur
    In this study, the thermal performance of an air-phase change material (PCM) unit used in free cooling applications was examined experimentally and numerically by Comsol finite element simulation software. Effects of the air inlet temperature, velocity and also PCM configuration on the efficiency of the air-PCM unit were investigated. Experiments were performed on PCM unit, which is a channel including PCM plates inside and exposed to medium air entrance from one side. The air in contact with the plates inside this unit is cooled and contributes the room temperature to decrease. The experimental work was carried out at two different ambient temperatures in a well-insulated room. Three different configurations of paraffin-based pure RT22HC and RT25HC were studied. Effects of air inlet temperature and velocity on the heat transfer, channel outlet temperature, performance of the air-PCM heat exchanger, cooling power of the system and also total amount of heat absorbed by the PCM were investigated. The initial temperature of the PCMs is 16 degrees C and experiments were carried out for two different average inlet temperature values (27 and 29 degrees C) and two different average velocities (1.3 and 1.8 m/s) of the air at the channel entrance. According to the results, it was concluded that the air inlet temperature and air inlet velocity have a substantial effect on the thermal performance of the air-PCM unit. It was observed that the melting time decreased and the channel outlet temperature increased with the increase of air inlet temperature and velocity. 2 degrees C increase of in the inlet temperature increased the total amount of heat absorbed by PCMs by 31%, while an increase of the inlet velocity by 0.5 m/s increased it by 16%. The results revealed that the increase of the inlet velocity and with the inlet temperature increased the thermal energy absorbed by 44%. In addition, it was observed that the average efficiency increased by 37% with 2 degrees C increase of inlet temperature and 0.5 m/s decrease in the inlet velocity.
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    Genetic Algorithm Optimisation of a TNT Solidification Model
    (Defence Scientific Information Documentation Centre, 2019) Susantez, Cigdem; Caldeira, Aldelio Bueno
    The control of the solidification process of energetic materials is important to prevent manufacturing defects in high explosive ammunitions. The present work aims to propose an optimisation procedure to determine the value of the model parameter, avoiding the traditional trial and error approach. In this work, the solidification of TNT has been numerically modelled employing apparent heat capacity method and the model parameter was optimised using genetic algorithm. One dimensional numerical model has been solved in Comsol Multiphysics Modeling Software and the genetic algorithm code was written in Matlab. The Neumann's analytical solution of the solidification front was used as a reference to build the fitness function, following the inverse problems concepts. The optimum model parameter has been predicted after 20 generations and among 30 candidate solutions for each generation. The numerical solution performed with the optimised model parameter has agreed with the analytical solution, indicating the feasibility of the proposed procedure. The discrepancy was 3.8 per cent when maximum difference between analytical and numerical solutions was observed.
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    Heat Transfer Modelling and Simulation of a 120 mm Smoothbore Gun Barrel During Interior Ballistics
    (Defence Scientific Information Documentation Centre, 2022) Susantez, Cigdem; Caldeira, Aldelio Bueno
    Understanding the heat transfer phenomenon during interior ballistics and consequently presenting a realistic model is very important to predict the temperature distribution inside the cannon barrel, which influences the gun wear and the cook-off. The objective of this work is to present a new detailed numerical model for the prediction of thermal behaviour of a cannon barrel by combining PRODAS interior ballistics simulation with COMSOL simulation. In this study, a numerical model has been proposed for the heating behaviour of a 120 mm smoothbore cannon barrel, taking into account the combustion equation of the JA-2 propellant. Temperature dependent thermophysical properties of product gases were used for the calculation of the convective heat transfer coefficient inside the barrel. Projectile position, velocity of the projectile, gas temperature inside the barrel, volume behind the projectile and mass fraction during interior ballistics have been obtained by PRODAS software and used in the numerical model performed by COMSOL multiphysics finite element modelling and simulation software. Temperature simulations show that maximum wall temperature inside the cannon barrel is observed after 3 ms from fire, when maximum value of the convective heat transfer coefficient inside the barrel is observed. The results reveal that the convective heat transfer coefficient of burned gases inside the gun has major effect than the burned gas temperature on the heat transfer phenomenon.
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    Investigation of models of the yarn-bobbin drying process by determination of their parameters using genetic algorithm
    (Sage Publications Ltd, 2017) Susantez, Cigdem; Hacihafizoglu, Oktay; Kahveci, Kamil
    In the first part of this study, the drying behavior of wool-acrylic yarn bobbins was investigated by a theoretical model and genetic algorithm method. Each candidate solution for D-o, D-1 and D-2 was presented on a single chromosome. The values of D-o, D-1 and D-2 yielding the best fit between the experimental and predicted moisture contents were obtained using the genetic algorithm. In the second part of this study, the suitability of various empirical and semiempirical models in the modeling of the drying process was investigated by the genetic algorithm. The population number was taken as 30 and the tournament selection method was used. The calculations were performed until the 20th generation for the theoretical model and 100th generation for the empirical and semiempirical models. The results show that the genetic algorithm can be successfully used in the modeling of the drying process of yarn bobbins. The results also show that the Verma etal. and Diffusion Approach models yield the best fit with experimental data.
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    INVESTIGATION OF THE TIME DEPENDENT THERMAL BEHAVIOR OF A CONTAINER WITH PCM WALLS DURING A HOT SUMMER DAY
    (Turkish Soc Thermal Sciences Technology, 2020) Susantez, Cigdem; Caldeira, Aldelio Bueno
    In this paper, the thermal comfort of a container with PCM walls has been investigated numerically for a hot summer day in Rio de Janeiro. Four different cases have been investigated. These cases are: (i) container made by Polyurethane plates, which is the reference solution, (ii) RT 22 HC plates, (iii) RT 25 HC plates and (iv) RT 28 HC plates. Analyses have been performed for 10 hours from 08:00 to 18:00 h, and dimensionless numerical results for all investigated cases have been presented. Nondimensional governing equations have been solved by COMSOL Multiphysics finite element modeling and simulation software. Results show that although thermal conductivity of polyurethane is one-eighth of that of PCM, the container with PCM walls present considerably better performance. It has been observed that the average value of the dimensionless temperature inside the container is equal to its initial value at the end of the investigation time for the cases of RT 22 HC and RT 25 HC are used. On the other hand, this value shows increments of 0.1235 (2.35 degrees C) and 0.7710 (14.65 degrees C) respect to initial temperature, respectively for the cases of RT 28 HC and polyurethane are used at the end of that time.
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    Natural convection effects on TNT solidification inside a shaped charge mold
    (Keai Publishing Ltd, 2022) Susantez, Cigdem; Caldeira, Aldelio B.; Loiola, Bruna R.
    High Explosive Anti-Tank (HEAT) warheads and ammunitions are frequently produced by explosive casting inside an axis-symmetric mold with an inverted conical geometry in the basis. In order to prevent manufacturing defects, the solidification process must be controlled. In this study, a dimensionless solidification model has been proposed to investigate the heat transfer considering the natural convection inside the liquid explosive and the numerical simulations were performed by using COMSOL Multiphysics and Modeling Software, employing trinitrotoluene (TNT) thermophysical properties. The effect of three different boundary conditions on the top of the mold have been evaluated: convection, adiabatic and isothermal. It has been observed that solidification process was faster for convection case and slower for isothermal case, while an intermediary total solidification time value was found for adiabatic case. Moreover, liquid explosive was completely surrounded by solid explosive during the solidification process for convection case and also for adiabatic case through the end of the process. Otherwise, it was not observed for isothermal case. The natural convection effects promoted a vortex inside the liquid explosive, accelerating the heat transfer process. It has been concluded that isothermal mold top boundary condition should be preferred to prevent manufacturing defects, avoiding high thermal stress.(c) 2021 China Ordnance Society. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
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    NUMERICAL INVESTIGATION OF BUOYANCY DRIVEN HEAT TRANSFER OF WATER-BASED CuO NANOFLUIDS IN A RECTANGULAR ENCLOSURE WITH AN OFFCENTER SOLID CONDUCTING BODY
    (Turkish Soc Thermal Sciences Technology, 2017) Susantez, Cigdem; Kahveci, Kamil
    In this study, buoyancy driven heat transfer of water-based CuO nanofluid in a rectangular enclosure with a solid cylinder was investigated numerically for different values of aspect ratio, location and diameter of solid cylinder, solid volume fraction and Rayleigh number. While bottom and upper walls of enclosure are adiabatic, sidewalls are isothermal. Thermal conductivity of solid cylinder was assumed to be equal to that of the base fluid. Governing equations were solved numerically by Comsol Multiphysics finite element modeling and simulation software. Results show that heat transfer rate increases considerably with an increase in the Rayleigh number and solid volume fraction and with a decrease in the solid cylinder diameter. Results also show that heat transfer rate shows an increase with an increase of aspect ratio for low values of Rayleigh number. Finally, results show that heat transfer rate gets its highest value for square enclosure case for high values of Rayleigh number.
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    NUMERICAL INVESTIGATION OF INTERMITTENT DRYING OF A CORN FOR DIFFERENT DRYING CONDITIONS
    (Vinca Inst Nuclear Sci, 2019) Hacihafizoglu, Oktay; Susantez, Cigdem; Kahveci, Kamil; Yilmaz, Sercan
    In this study, intermittent drying process of corn was studied numerically for various intermittent periods and drying air temperatures. An Arrhenius type dffusi-coefficient D = e((-b.T)). 10(-9) m(2)/s was proposed for the moisture diffusion inside the corn. Numerical simulations were performed by choosing the suitable value for drying constant, b, that yields the best agreement with experimental drying rates. The experimental results were obtained via an experimental setup for intermittent periods of 30 minute and 60 minute, and drying air temperatures of 40 degrees C, 50 degrees C, 60 degrees C, and 70 degrees C. The results show that overall agreement between the experimental and theoretical prediction is good. On the other hand, the theoretical results overestimate the moisture ratio at the initial stage and underestimate it at the later stage of drying.
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    Numerical investigation of latent heat thermal energy storage unit with different configurations and phase change materials
    (Elsevier, 2022) Susantez, Cigdem
    In this work melting behavior of PCMs inside the LHTES (latent heat thermal energy storage) unit for six different cases has been numerically investigated by Comsol Multiphysics and Simulation Software. Two different PCMs (phase change materials), namely lauric acid and n-octadecane, have been used in the analysis for two different configurations. When configuration-1 has only one region for PCM, configuration-2 contains two regions. Simulations show that melting is completed at the upper side of the LHTES unit first due to the natural convection effects. On the other hand, it has been shown that LHTES unit in the form of configuration-1 with n-octadecane completes phase change earliest and absorbs most heat at the end of the process. This also demonstrates that not only latent heats of the PCMs, but also parameters affecting natural convection have an important effect on the heat transfer. Because when PCM with a lower melting temperature is used, buoyancy force, consequently absorbed heat increases. Inside boundaries also inversely affect absorbed heat by PCMs due to the non-slip boundary condition on these boundaries. The maximum efficiency of the LHTES unit is obtained for the configuration-1 with lauric acid due to not only high value of absorbed heat as a result of fewer obstacles of the geometry, but also the smaller values of latent heat and specific heat of lauric acid affecting E-max.
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    A simplified numerical approach to hydrogen and hydrocarbon combustion in single and double-layer porous burners
    (Pergamon-Elsevier Science Ltd, 2020) Caldeira, Aldelio Bueno; Susantez, Cigdem
    Motivated by the fuel hydrogen applications in porous combustors, as well as hydrogen production in syngas porous devices, this work shows a simplified one-dimensional, steady state heat and mass transfer model for stabilized premixed flames in porous inert media. Single-layer and double-layer porous burner are studied. The model has three conservation equations, describing the heat transfer in the solid and fluid phases and the mass transfer in the reacting flow. The model considers a plug flow and is solved numerically by using the finite volume method. The results are compared with benchmark data, depicting the superadiabatic flames and the heat recirculation process. A parametric analysis of the model reveals the effects of the porous media properties and the Lewis and Peclet numbers on the heat and mass transfer processes. Furthermore, the effects of the flame stand-off parameter in double layer porous burner are also analyzed. The results have considered the values of the dimensionless parameters based on reference data for hydrogen/air and methane/air combustion in porous burners built with SiC and Al2O3. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.