Browsing by Author "Sharma, R."

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Characteristics of low reynolds number steady air jet impingement heat transfer over vertical flat surfaces
(IEEE, 2012) He, X.; Lustbader, J. A.; Arık, Mehmet; Sharma, R.; Mechanical Engineering; ARIK, Mehmet
In this paper, heat transfer characteristics of single-slot steady-impinging air jets on a 25.4 mm × 25.4 mm vertical surface were experimentally investigated. The experiments were conducted with four different nozzles (length × width: 4 mm × 1 mm, 8 mm × 1 mm, 12 mm × 1 mm, and 15 mm × 1 mm). The parameters varied in the testing were Reynolds number (Re) (100 - 2,000) and dimensionless nozzle-to-plate spacing (H/Dh = 5, 10, 15, and 20). Correlations for average Nusselt numbers (Nu) were developed that accurately predict experimental data. The heat transfer coefficient over a vertical surface increases with increasing Re. For a small nozzle-to-plate spacing (H/Dh = 5), the average Nu correlation is not only a function of Re but also a function of nozzle length. For large nozzle-to-plate spacing (H/Dh ≥ 10) and nozzle length larger than 8 mm, the heat transfer coefficient is insensitive to H/Dh and nozzle length. A subset of this data was then compared to synthetic jet data in a separate study.
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Comparison of synthetic and steady air jets for impingement heat transfer over vertical surfaces
(IEEE, 2012) Arık, Mehmet; Sharma, R.; Lustbader, J.; He, X.; Mechanical Engineering; ARIK, Mehmet
Natural convection air cooling is the method of choice for many low-power electronics applications due to cost, availability, and reliability considerations. This method is not only limited to low-power applications, but is also constrained by the buoyancy dependence of the flow. Therefore, further enhancement of natural convection is needed. Enhanced natural convection allows higher heat dissipation while maintaining the simplicity of passive cooling. Synthetic jet devices operating on the microfluidics principle provide unique cooling advantages for local cooling with high coefficients of performance. Synthetic jets used in the current study are piezoelectrically driven, small-scale, pulsating devices capable of producing highly turbulent jets formed by periodic entrainment and expulsion of the fluid through an orifice. The compactness of the jet actuator coupled with the high exit air velocities can significantly reduce the size of thermal management systems. In this paper, we present experimental results for impingement heat transfer for both steady and unsteady jets over a Reynolds number range of 100 to 3,000. A range of nozzle-to-plate surface distances is discussed. To mimic a comparable electronics component, we used a 25.4-mm square heated surface.
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Heat transfer characteristics of impinging steady and synthetic jets over vertical flat surface
(Elsevier, 2015-01) Hea, X.; Lustbader, J. A.; Arık, Mehmet; Sharma, R.; Mechanical Engineering; ARIK, Mehmet
In this paper, heat transfer characteristics of single-slot impinging steady and synthetic jets on a 25.4-mm × 25.4-mm vertical surface were experimentally investigated. The experiments were conducted with a fixed nozzle width of 1 mm. For the steady jet study, the parameters varied in the testing were nozzle length (4 mm, 8 mm, 12 mm, 15 mm), Reynolds (Re) number (100–2500), and dimensionless nozzle-to-plate spacing (H/Dh = 5, 10, 15, 20). Correlations for average Nusselt (Nu) number were developed to accurately describe experimental data. The heat transfer coefficient over a vertical surface increases with increasing Re number. For a small nozzle-to-plate spacing (H/Dh = 5), the average Nu number is not only a function of the Re number, but also a function of nozzle length. For large nozzle-to-plate spacing (H/Dh ⩾ 10) and a nozzle length larger than 8 mm, the heat transfer coefficient is insensitive to H/Dh and nozzle length. An 8-mm × 1-mm synthetic jet was studied by varying the applied voltage (20–100 V), frequency (200–600 Hz), and dimensionless nozzle-to-plate spacing (H/Dh = 5, 10, 15, 20). Compared to the steady jet, the synthetic jet exhibited up to a 40% increase in the heat transfer coefficient. The dynamic Re number was introduced to correlate heat transfer characteristics between synthetic jets and steady jets. Using the dynamic Re number collapses the synthetic and steady jet data into a single Nu number curve.
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Steady and unsteady air impingement heat transfer for electronics cooling applications
(ASME, 2013) Arık, Mehmet; Sharma, R.; Lustbader, J.; He, X.; Mechanical Engineering; ARIK, Mehmet
This paper focuses on two forced convection methods—steady jet flow and pulsating flow by synthetic jets—that can be used in applications requiring significant amounts of heat removal from electronics components. Given the dearth of available data, we have experimentally investigated steady jets and piezoelectrically driven synthetic jets that provide pulsating flow of air at a high coefficient of performance. To mimic a typical electronics component, a 25.4-mm × 25.4-mm vertical heated surface was used for heat removal. The impingement heat transfer, in the form of Nusselt number, is reported for both steady and unsteady jets over Reynolds numbers from 100 to 3000. The effect of jet-to-plate surface distance on the impingement heat transfer is also investigated. Our results show that synthetic jets can provide significantly higher cooling than steady jets in the Reynolds number range of 100 to 3000. We attribute the superior performance of synthetic jets to vortex shedding associated with the unsteady flow.