Heat transfer characteristics of impinging steady and synthetic jets over vertical flat surface

Abstract

Due to copyright restrictions, the access to the full text of this article is only available via subscription.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

Cooling performance improvement of impingement hybrid synthetic jets in a confined space with the aid of a fluid diode

“…The integration of fluid diodes is designed to rectify oscillating air flow to suppress the backflow of hot (heated) air through the nozzle exit in the suction stroke. The volumetric efficiency is thus introduced to evaluate the rectifying effect of the proposed hybrid synthetic jet actuators on the air flow, which can be defined as [30]  = − + (10) where represents the air volume ejected out through the nozzle exit in one cycle by the actuators and denotes the air volume sucked back through the nozzle exit in one cycle.…”

“…Ingenious cooling schemes are absolutely essential to achieving effective thermal management of electronic devices to keep their temperatures within a suitable range. A promising cooling technology, called an impingement synthetic air jet, has gradually attracted widespread attention [4][5][6][7], due to its obvious advantages as follows compared with conventional cooling methods, such as natural convection, fan, steady jet: (1) a synthetic jet exhibits higher heat transfer capacity, which can be 4.5-10 times [8], 1.2-1.4 times [9] and 1.4 times [10] higher than those of natural convection, fan and steady jet, respectively; (2) it has no rotating parts, which are conducive to noise reduction, low energy consumption, stability, safety and reliability; (3) it does not need fluid pipe and complex pumping, offering a compact structure and ease of integration. Based on the above advantages, an impingement synthetic air jet is considered to be a more efficient manner for cooling of electronic devices, especially in limited space.…”

Measurements versus Numerical Simulations for Slotted Synthetic Jet Actuator

“…This feature has made this technology interesting among the main active flow control techniques [3] for applications where low weights and reduced sizes are required. Indeed, SJ actuators have been largely employed in several industrial applications as impinging jets (due to their enhanced mixing [4] and heat transfer [5] coefficients with respect to continuous jets); to control jets [6,7] and sprays [8]; to suppress separated flows [9] and optimize drag and lift on airfoils [10,11]. A huge bulk of literature papers can be found in cross-references of the mentioned articles.…”

An experimental investigation on comparison of synthetic and continuous jets impingement heat transfer

“…Four free synthetic jet flow morphology regimes were identified. He et al [24] experimentally compared heat transfer characteristics of single-slot impinging steady and synthetic jets on a 25.4 mm  25.4 mm vertical surface. For the steady jet study, the parameters varied in the testing were nozzle length (4 mm, 8 mm, 12 mm, 15 mm) with a fixed nozzle width of 1 mm and Reynolds number (100-2500).…”