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Optimum spacing between grooved tubes: An experimental study
Asif Afzal,Mohammed Samee A. D,Abdul Razak R. K,Sher Afghan Khan,Hurmathulla Khan 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.1
An experimental study on optimum spacing between grooved tubes is reported in this paper. Two grooved tubes having pitch of 10 mm and 15 mm and a plain tube were considered for the heat transfer analysis. The spacing between two tubes with same pitch was varied from 10 mm to 35 mm with a step size of 5 mm. Velocity of air flowing over the tube surfaces was changed from 0.4 m/s to 1 m/s using a blower fan. Based on Nusselt number (Nu) the optimum spacing between the tubes was decided. The optimum spacing between grooved tubes of pitch 10 mm and 15 mm was compared with that of plain tubes. From the experimental analysis it was noticed that with increase in air velocity (increase in Reynolds number) the tube surface temperature reduced irrespective of any tube considered. Nu increased with increase in air velocity for all the tubes. The important conclusion drawn from the present study was that, there exists a limiting spacing (optimum) between the tubes above which no change in Nu was observed. Spacing of 30 mm was found to be the optimum spacing between the tubes irrespective of its surface geometry modifications.
Jeonghyeon Kim,Asif Afzal,김현구,Cong-Truong Dinh,Sung Goon Park 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.12
Given that wind farms have high initial investment costs and are not easy to move after installation, the amount of energy that can be produced in the desired installation area needs to be predicted as accurately as possible before installation. Four machine learning algorithms are adopted to predict power production based on the daily wind speed average and standard deviation. The actual power output is calculated from the wind data generated by the numerical weather prediction, and its temporal resolution is 1 hour. The R-square (R 2 ) values of the models range from 0.97 to 0.98 while adopting the average value of daily wind speed as the input data, and it increases by -1 % with the additional input data of the standard deviation of wind speed. The power production is predicted based on the wind data at a relatively lower height of 10 m than the hub height, where the R 2 value ranges from 0.95 to 0.98. The results could provide the possibility of replacing the wind data measurement process at the hub height by that at a relatively lower height, reducing the cost of wind data measurement.
Ground state opto-electronic and thermoelectric response of cubic XSnO3 (X = Ba, Sr) compounds
M. Bilal Saddique,Muhammad Rashid,Adnan Afzal,Shahid M. Ramay,Farooq Aziz,Asif Mahmood 한국물리학회 2017 Current Applied Physics Vol.17 No.8
The density functional has been implemented to deliberate the cubic perovskite XSnO3 (X ¼ Ba, Sr) for their elastic, electronic, optical as well as thermoelectric characteristic. The XSnO3 (X ¼ Ba, Sr) illustrates good pact of lattice parameter for these iso-structural compounds having cubic perovskite structure. The generalized gradient approximation based on the exchange-correlation functional is applied for computing structural and mechanical characteristic, whereas the electronic, optical and thermoelectric properties have been studied by the functional suggested by Tran and Blaha that is termed as of modified Becke-Johnson (mBJ) functional. The thermodynamics stability is recognized through the expression of enthalpies of formation, which is further verified from the calculated structural properties of cubic perovskite XSnO3 (X ¼ Ba, Sr). Moreover, various elastic parameters such has bulk modules B, Cij, shear modulus G, Young's modulus Y, anisotropy factor, B/G ratio and Poisson's ratio n have also been reported. It has been observed by band structure computation that the studied compounds exhibit an indirect band gap between the unoccupied Ba/Sr 6s/5s and the occupied O 2p orbitals. Detailed study of optical properties is presented under the incident photon energy upto 28 eV. Our computed static dielectric constant ε2(0) and refractive index n(0) are comparable with other theoretical and experimental values. Thermoelectric properties are presented in terms of computed Seebeck coefficient, electrical and thermal conductivities and their variation with the rise in temperature suggest that the studied compounds may find applications in the construction of various thermo-electric devices.