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    Analysis of natural convection in a square cavity in the presence of a rotating cylinder with a specific number of roughness components
    (Pergamon-Elsevier Science Ltd, 2020) Hassanzadeh, Rahim; Rahimi, Reza; Khosravipour, Aysan; Mostafavi, Sajad; Pekel, Hakan
    This work investigates the effects of a rotating rough cylinder within a square cavity on the natural convective heat transfer process. Six different cases consist of case 1 (cavity without a cylinder), case 2 (cavity with a rotating smooth cylinder), case 3 (cavity with a rotating rough cylinder having one roughness component), case 4 (cavity with a rotating rough cylinder having two roughness components), case 5 (cavity with a rotating rough cylinder having three roughness components), and case 6 (cavity with a rotating rough cylinder having four roughness components) are computed under various parameters such as the Rayleigh numbers (Ra) in the range from 10(3) to 10(6), radius ratios (R) of 0.1, 0.2, and 0.3, and non-dimensional rotating speeds (RS) between -1000 and 1000. It is found that the difference between the cases is more evident at lower Rayleigh numbers and higher rotating speeds. In addition, under effective Rayleigh numbers (Ra= 10(3) and 10(4)), the rate of the heat transfer is maximum in case 2 regardless of the rotating speed and radius ratio. Beyond case 2, case 5 presents the highest heat transfer rate. The maximum heat transfer enhancement occurs in case 2 with 252% under Ra = 10(3), R = 0.3, and RS = -1000.
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    Effects of Shell Aspect Ratio and Combustion Chamber Location on Thermal-Hydraulic Performance of Hot-Water Steel Boilers Under Steady-State Operation
    (Springer Heidelberg, 2021) Hassanzadeh, Rahim; Rahimi, Reza; Pekel, Hakan
    In the present research, a simplified two-dimensional hot-water steel boiler was studied numerically by means of the finite volume approach. Effects of various non-dimensional combustion chamber locations and shell aspect ratios were investigated for different Richardson numbers under steady-state operation. The obtained results were validated against the available data and found in good agreement. It is illustrated that both chamber location and shell aspect ratio have considerable effects on overall heat transfer and pressure drop within a hot-water steel boiler. In addition, considering the goodness factor as the thermal-hydraulic performance of boiler, it was concluded that by moving the chamber location toward the upper side of the boiler and by increasing the shell aspect ratio, the boiler performance reduces dramatically under all Richardson numbers. Therefore, the chamber location of S = -0.5 and shell aspect ratio of AR = 1.0 are realized as the best parameters providing the maximum thermal-hydraulic performance for a steel boiler. It is hoped that the reported results provide interesting information among the hot-water steel boiler designers.
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    The Effect of Strain-Rate Sensitivity on Formability of AA 5754-O at Cold and Warm Temperatures
    (SPRINGER, 2011) Ozturk, Fahrettin; Pekel, Hakan; Halkaci, Huseyin S.
    Aluminum-magnesium (Al-Mg) alloys have been widely used in diverse applications ranging from automotive bodies to food processing industries because of their excellent high-strength-to-weight ratio, corrosion resistance, and recyclability potential. The formability of these alloys is decreased at room temperature (RT) and is related with the strain-rate sensitivity. This study presents the effect of strain-rate sensitivity on formability of AA 5754-O alloy sheet at a test temperature range of -60 to 250 A degrees C by duplicate tensile test at different strain rates. The test results indicated that the formability change with positive or negative strain-rate sensitivity values. It was observed that the strain-rate sensitivity values increased at negative temperatures with respect to RT. The best formability condition for this alloy in the test ranges was observed at 250 A degrees C and 0.0016 s(-1).