Browsing by Author "Solovitz, S. A."

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An investigation into flow and heat transfer for a slot impinging synthetic jet
(Elsevier, 2016-09) Ghaffari, Omidreza; Solovitz, S. A.; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Ghaffari, Omidreza
According to the latest trends in miniature consumer and military electronics, there is a need for compact cooling solutions to meet performance requirements at compact volumes. Successful technology must feature a thin profile and a small footprint area, while still removing a significant amount of heat dissipation. Impinging synthetic jets driven by a piezoelectric membrane are a promising method for cooling small-scale electronics. In this paper, we explore the thermal response of a miniature synthetic jet impinging upon a vertical heater. In addition, we study the local flow field using the particle image velocimetry (PIV) technique to couple heat transfer with fluid dynamics. Heat transfer results show that the maximum cooling performance occurs with a jet-to-surface spacing of 5 ⩽ H/Dh ⩽ 10, which is associated with the flow consisting of coherent vortex structures. There is a degradation of heat transfer for closer jet-to-surface spacings, such as H/Dh = 2. This was due to the incomplete growth of the vortices, along with re-entrainment of warm air from the impinging plate back into the jet flow. There was also some warm air sucked back into the jet during the suction phase of the synthetic jet. For a fixed value of Reynolds number, cooling was improved at high Stokes numbers, but with a reduced coefficient of performance.
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An investigation into flow and heat transfer of an ultrasonic micro-blower device for electronics cooling applications
(Elsevier, 2016-05-08) Ghaffari, Omidreza; Solovitz, S. A.; Ikhlaq, Muhammad; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Ghaffari, Omidreza; Ikhlaq, Muhammad
As compact electronics increase in functionality, new electronics cooling approaches must be more effective, and they must be lower in form factor. In this paper, we investigated the cooling performance of a miniature ultrasonic micro-blower impinging upon a vertical heater. We studied the temperature response at different operating conditions, determining the optimal thermal conditions. We further examined the local flow field using the particle image velocimetry (PIV) technique at the same operating conditions, providing explanations for the heat transfer response in terms of the fluid dynamics. Heat transfer measurements show that the maximum cooling performance occurs at a jet-to-surface spacing ratio of 15 < H/D < 30, and the performance slowly decays when the jet is located further away. The preferred operating frequency of the piezoelectric cooling device occurs at an ultrasonic frequency of over 20 kHz, meaning that this device can function outside the human hearing range. The PIV results demonstrate that the jet profile in the near field deviates significantly from a traditional turbulent free jet. In the far field, it nearly matches the self-similar, fully-developed jet profile. The jet cooling performance is sensitive to the frequency, with the thermal performance dropping by a factor of six when varying by less than 1 kHz from the peak. At the optimal heat transfer condition, the coefficient of performance is measured at approximately three, which is lower than that of some synthetic jets.