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    Experimental and Numerical Analysis of one Dimensional Heat Transfer on Open Cell Aluminum Foams
    (Gazi Univ, 2015) Sertkaya, Ahmet Ali; Ates, Ali; Altinisik, Kemal; Dincer, Kevser
    In this study, one dimensional heat transfer of open cell aluminum metal foams is investigated both experimentally and by using numerical methods as well. Open cell aluminum foams with pore densities of 10, 20 and 30 (Number of Pores Per Inch) PPI were shaped into heat exchangers. The foams having sizes of 200 x 100 x 20 mm were insulated on their three faces. Steady heat flux was maintained on the base section of the foam by heating a plate shaped coil electrically. Temperature distributions on the vertical sections and mostly on locations near heaters were measured with the thermocouples located on the aluminum foams. With the help of the recorded temperatures from the tests the graphs of open cell aluminum foams with pore densities of 10, 20 and 30 were plotted. First of all, one dimensional heat transfer equations were derived for the numerical solution of the system. The governing equations obtained were then discretized by using the Central Difference Method and finally solved with the Finite Difference Method. The results obtained were converted into graphs and compared with the empirical results obtained beforehand. The fastest drop in temperature close to the heater was observed at the foam with 10 PPI while the lowest falling rate took place at the foam with 30 PPI pore density. At an interval of three aluminum foams, the temperature difference was found to be higher near the heater and lower away from the heater. It was found that both experimental and numerical results are closely related.
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    EXPERIMENTAL INVESTIGATION AND NUMERICAL MODELING OF THERMAL PERFORMANCE OF FIN-TUBE EVAPORATOR UNDER FROSTING CONDITIONS
    (Turkish Soc Thermal Sciences Technology, 2014) Ozen, Dilek Nur; Altinisik, Kemal; Dincer, Kevser; Ates, Ali
    Formation of frost in a heat exchanger reduces air passage area and lowers the performance of the heat exchanger due to the insulation effects it possesses. In this study, the performance of finned tube evaporator at transient regime was investigated both experimentally and numerically. When the experimentally obtained values of the evaporator's the total conductivity (UA) are compared with those obtained from the numerical model, it is found that they are very close to one another. On the numerical model, the effects of inlet air temperature, relative humidity and air velocity on evaporator's total conductivity (UA), air side pressure drop (Delta P-a) and frost thickness (delta(fst)), were respectively, studied. The results obtained from the numerical model show that Delta P-a and delta(fst) values increase with increasing air temperature and relative humidity while decreasing UA values.
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    Rule-based Mamdani-type fuzzy modelling of thermal performance of fintube evaporator under frost conditions
    (E D P Sciences, 2016) Ozen, Dilek Nur; Altinisik, Kemal; Dincer, Kevser; Ates, Ali; Sertkaya, Ahmet Ali; Tolu, Muhammed Emin
    Frost formation brings about insulating effects over the surface of a heat exchanger and thereby deteriorating total heat transfer of the heat exchanger. In this study, a fin-tube evaporator is modeled by making use of Rule-based Mamdani-Type Fuzzy (RBMTF) logic where total heat transfer, air inlet temperature of 2 degrees C to 7 degrees C and four different fluid speed groups (ual=1; 1.44; 1.88 m s-1, ua2=2.32; 2.76 m s-1, ua3=3.2; 3.64 m s-1, ua4=4.08; 4.52; 4.96 m s-1) for the evaporator were taken into consideration. In the developed RBMTF system, outlet parameter UA was determined using inlet parameters Ta and ua. The RBMTF was trained and tested by using MATLAB (R) fuzzy logic toolbox. R-2 (%) for the training data and test data were found to be 99.91%. With this study, it has been shown that RBMTF model can be reliably used in determination of a total heat transfer of a fm-tube evaporator.
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    Transient conjugated heat transfer in thermally developing laminar flow in thick walled pipes and minipipes with time periodically varying wall temperature boundary condition
    (Pergamon-Elsevier Science Ltd, 2016) Altun, Aziz H.; Bilir, Sefik; Ates, Ali
    Transient conjugated heat transfer for thermally developing laminar flow in thick walled pipes is analyzed involving two-dimensional wall and axial fluid conduction. A two-regional, initially isothermal pipe is considered and the problem is handled for hydrodynamically developed flow with periodically timevarying outer wall temperature in the downstream region. The problem is solved numerically by a finite-difference method and a parametric study is done to analyse the effects of four defining parameters namely, wall thickness ratio, wall-to-fluid conductivity ratio, wall-to-fluid thermal diffusivity ratio, the Peclet number and also the effect of angular frequency. Considerable amount of heat is transferred through the upstream region due to both wall and fluid axial conduction. Heat transfer characteristics change periodically in time similar to the periodic change in the outer wall temperature. The results are found to be affected by the parameter values and by the angular frequency. (C) 2015 Elsevier Ltd. All rights reserved.