Browsing by Author "Ikhlaq, Muhammad"

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Effect of actuator deflection on heat transfer for low and high frequency synthetic jets
(IEEE, 2014) Ikhlaq, Muhammad; Ghaffari, Omidreza; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Ikhlaq, Muhammad; Ghaffari, Omidreza
Synthetic jets are being investigated over the last four decades. Researchers have been interested in its unique applications for a wide range of flow control to thermal management of electronics applications. Synthetic jets are made up of actuators such as piezoelectric, magnetic, or linear piston technology etc. In this study, we performed an experimental and numerical investigation of a piezoelectric disk deflection over a range of frequencies in order to understand the performance for low and high frequency synthetic jets. First, we performed a numerical analysis of a piezoelectric based synthetic jet and, validated computational result with experimental findings. Numerical models are performed by using commercial finite element software. To understand the size effect on the operating frequency, three jets with different sizes are manufactured and examined. Two different low frequency synthetic jets manufactured in our laboratory and a commercially available high frequency jet are included in the present study. Heat transfer performance is given as an enhancement over natural convection heat transfer. The heat transfer enhancement factor of each of these jets with respect to natural convection is measured over a 25.4×25.4 (mm) vertical heater. Finally, power consumption of the low and high frequency synthetic jets were measured and compared. It is found that disk deflection and operating frequency are directly related to heat transfer enhancement factor, if the Helmholtz frequency of a cavity has no effect on the performance of a jet. The Helmholtz frequency of each jet was calculated to ensure that it has no effect on the synthetic jet, but we found that the commercial synthetic jet took partial advantage of Helmholtz phenomena to enhance the performances at high frequencies.
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An experimental study of impinging synthetic jets for heat transfer augmentation
(World Scientific Publishing Co, 2015-07) Ghaffari, Omidreza; Ikhlaq, Muhammad; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Ghaffari, Omidreza; Ikhlaq, Muhammad
According to recent trends in the field of miniature electronics, the need for compact cooling solutions compatible with very thin profiles and small footprint areas is inevitable. Impinging synthetic jets are recognized as a promising technique for cooling miniature surfaces like laptops, tablets, smart phones and slim TV systems. Effect of jet to cooled surface spacing is crucial in cooling performance as well as predicting Nusselt number for such spacing. An experimental study has been performed to investigate the cooling performance of two different synthetic jets actuated with piezoelectric actuators cooling over a vertical surface. Results showed that a major degradation of heat transfer when jets are close to the surface is occurred. Slot synthetic jets showed a better performance in terms of coefficient of performance (COP) than semi-confined circular jets for small jet to surface spacing. Later, a correlation is proposed for predicting Nu number for a semi-confined circular synthetic jet accounting the effects of Re number (500≤Rej≤1150500≤Rej≤1150), jet-to-surface spacing (H∕D=2H∕D=2 and H∕D=4H∕D=4) and the stroke length (1.75≤L0∕D≤4.751.75≤L0∕D≤4.75 and L0∕H<2.5L0∕H<2.5). It is found that correlation can provide predictions with an R2R2 value of over 98%.
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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.
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Predicting heat transfer for low- and high-frequency central-orifice synthetic jets
(IEEE, 2016-04) Ikhlaq, Muhammad; Ghaffari, Omidreza; Arık, Mehmet; Mechanical Engineering; ARIK, Mehmet; Ikhlaq, Muhammad; Ghaffari, Omidreza
As electronic devices are becoming more compact each day, the more effective and efficient active cooling technologies are needed. Microfluidic devices, such as synthetic jets, serve as a potential candidate to fulfill the thermal management needs of the next generation electronics. An experimental and computational study has been performed for circular central-orifice synthetic jets. First, a series of experiments was performed to quantify the actuator deflection, air velocity, heat transfer augmentation, and power consumption for central-orifice synthetic jets. Later, a computational study was performed utilizing the same boundary conditions in order to predict the deflection of the diaphragm. The experiments were conducted on three different types of synthetic jets, namely, low-, medium-, and high-frequency synthetic jets. Although a number of correlations were proposed for the prediction of Nu number for slot synthetic jets, no correlation was found to predict the average Nu number for a synthetic jet with a round orifice. Therefore, two correlations were developed, one for low- and medium-frequency synthetic jets and the other for high-frequency synthetic jets to predict the heat transfer coefficient as a function of the geometry, position, and operating condition for impinging flows. The proposed correlations are able to predict the impingement heat transfer of a synthetic jet with an accuracy of ±25% for a wide range of operating conditions and geometrical variables. Normalized frequency had the minimum impact on the average Nu number of a high-frequency synthetic jet compared with dimensionless distance, both have moderate impact on low- and medium-frequency jets.