Browsing by Author "Dogruoz, M. B."

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Acoustic analysis of an axial fan
(IEEE, 2017) Hashım, Hafız Muhammad; Dogruoz, M. B.; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Hashım, Hafız Muhammad
Axial fans are often used in cooling electronic enclosures where low noise levels are highly demanded. Therefore, methods for predicting the noise emitted by an application including single or multiple fans are desirable to improve, stimulate and reduce the cost of low-noise design. The prediction of sound generated from fluid flow has been difficult due to the non-linear form of the governing equations, however, recent developments in computational fluid dynamics (CFD) and computational acoustics allow us to determine sound pressure levels (SPL) in a fluid flow. In this study, time dependent flow field produced by an axial fan is computed via Large Eddy Simulations (LES), and the consequent sound pressure map is determined using the Ffowcs Williams-Hawkings (FW-H) model. Since an axial fan is a complex source of sound, for engineering design purposes, simplifications are needed when modelling its acoustic characteristics, therefore, the sound radiation of an axial fan in free space is examined by expanding the generated sound pressure field into spherical harmonics. In addition, acoustic measurements are carried out in a semi-anechoic chamber to validate the aforementioned computational models and make necessary comparisons. Comparison of the numerical results against the experimental data shows that, despite some discrepancies, the former is able to capture the trends observed in the measurements.
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An experimental and computational investigation of a thin piezofan cooler
(IEEE, 2017) Dogruoz, M. B.; Arık, Mehmet; Parsa, Shadi; Mechanical Engineering; ARIK, Mehmet; Parsa, Shadi
Recent trends in electronic cooling systems are targeted towards a reduction in size, therefore small form factor/miniature cooling devices are of interest to various applications. Among these devices are piezoelectric fans which are simply made of vibrating plates and shed vortices from their leading edge and enhance heat transfer from nearby target surfaces. This paper investigates the flow and temperature fields produced by a piezoelectric fan. An experimental study is performed to determine the temperature distribution of a vertically heated surface under various fan tip-to-target surface distances and driving conditions of the piezoelectric device (frequency). 2-D numerical simulations are carried out to predict the momentum and temperature fields in the domain of interest under the same boundary conditions of the experimental effort. The numerical results are in reasonably good agreement with the measured experimental data. The relevant dimensionless parameters such as Nusselt, Strouhal, and Keulegan-Carpenter numbers are determined. With a maximum Nusselt number of 20 and 57 for mylar and metallic piezo fans, respectively, the corresponding Strouhal, and Keulegan-Carpenter numbers suggest that a vortex formation occurs at the blade tip, however these vortices are weak such that they are neither able to approach the target surface as high strength structures nor improve heat removal significantly for the range of measurements.
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Investigation of power distribution on an axial fan
(IEEE, 2016) Hashim, Hafiz Muhammad; Yasa, Y.; Dogruoz, M. B.; Arık, Mehmet; Mese, E.; Mechanical Engineering; ARIK, Mehmet; Hashim, Hafiz Muhammad
Forced convection cooling systems utilize fans which can be axial or radial, small or large in many different configurations. Efficiency of a fan depends on its electrical and mechanical designs as well as the environmental conditions that the fan is exposed to. Typically, the overall efficiency of an axial fan varies between 15 to 40 percent. Power losses may be due to electrical, aerodynamic or mechanical design components. Losses occurring in an axial fan motor have become a critical issue in which high inertial effects, low power, low cost and high efficiency are desired. In order to design an efficient motor, it is important to accurately predict the power losses which are normally dissipated in the form of heat. The present study starts with an investigation of the power losses of an axial fan experimentally and computationally. Moreover, it deals with modeling of mechanical, electrical, thermal and electromagnetic losses which focus especially on an outer rotor brushless DC motor. Reduction of these losses leads to a decrease in the motor temperature and, therefore, has a positive effect on the fan reliability. Expressions for calculating the inverter losses, motor losses and mechanical losses are derived. The power losses obtained are then used as heat sources when evaluating the thermal performance of the motor. By using a two-dimensional model, computational fluid dynamics (CFD) simulations are performed to determine the iron losses across the motor. These results are utilized to determine evaluate the overall efficiency of the system.