Temperature-variation effect of piston-driven synthetic jet and its influence on definition of heat transfer coefficient

2020 ◽  
Vol 152 ◽  
pp. 119347
Author(s):  
Yuan-wei Lyu ◽  
Jing-zhou Zhang ◽  
Chan Tang ◽  
Xiao-ming Tan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Temperature Variation ◽  
Synthetic Jet ◽  
Definition Of

Thermo-mechanical analysis of a FGM plate subjected to thermal shock – A new numerical approach considering real time temperature dependent material properties

2021 ◽  
Vol 63 (4) ◽  
pp. 341-349
Author(s):  
Mete Onur Kaman ◽  
Nevin Celik ◽  
Resul Das
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Shock ◽  
Temperature Variation ◽  
Material Properties ◽  
Ambient Air ◽  
Transient Temperature ◽  
Heated Plate ◽  
The Heat Transfer Coefficient

Abstract In present the study, sudden cooling, in other words thermal shock, is applied to a plate that is originally a functionally graded material (FGM). The flat plate is assumed to have an edge crack on it. Hence a numerical couple-field analysis is performed on the plate. The FGM is a combination of Ni and Al2O3. The thermal and mechanical properties of the FGM are assumed to depend on temperature variation. The mixing percentages of the Ni and Al2O3 throughout the plate are considered to vary (i) linearly, (ii) quadratically and (iii) in half-order. In order to solve the problem, a new subroutine depending on temperature is written using APDL (ANSYS Parametric Design Language) codes. Three values of the heat transfer coefficient are applied to the initially heated plate. As a result, the transient temperature variation and stress intensity factor are presented to show the thermo-mechanical relation of the plate. The material properties changing with temperature results in more reliable temperature values. Increasing the heat transfer coefficient results in better cooling and in a lesser amount of time to reach ambient air temperature.

Predicting Heat Transfer From Unsteady Synthetic Jets

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Mehmet Arik ◽  
Tunc Icoz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Small Scale ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Synthetic jets are piezo-driven, small-scale, pulsating devices capable of producing highly turbulent jets formed by periodic entrainment and expulsion of the fluid in which they are embedded. The compactness of these devices accompanied by high air velocities provides an exciting opportunity to significantly reduce the size of thermal management systems in electronic packages. A number of researchers have shown the implementations of synthetic jets on heat transfer applications; however, there exists no correlation to analytically predict the heat transfer coefficient for such applications. A closed form correlation was developed to predict the heat transfer coefficient as a function of jet geometry, position, and operating conditions for impinging flow based on experimental data. The proposed correlation was shown to predict the synthetic jet impingement heat transfer within 25% accuracy for a wide range of operating conditions and geometrical variables.

Spot-Cooling by Confined, Impinging Synthetic Jet

2003 ◽  
Author(s):  
Jelena Vukasinovic ◽  
Ari Glezer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Ambient Air ◽  
Synthetic Jet ◽  
Strong Mixing ◽  
Parallel Plates ◽  
Flow Measurements ◽  
Heated Air ◽  
Spot Cooling

Spot-cooling of discrete electronic packages mounted on a printed wiring board (PWB) is achieved by the impingement of an axisymmetric synthetic jet when the jet actuator is attached to one board and cools target integrated circuit (IC) on the opposite board. Present work demonstrates that even when the jet outflow is confined between two closely-spaced boards, the jet entrains ample volume flow rate of cooler ambient air, induces effective cooling by strong mixing near the heated surface, and ultimately dispenses the heated air to ambient. The cooling performance of the jet module is investigated experimentally in a scaled up model that enables high-resolution thermal and flow measurements. The test setup comprises of two circular parallel plates (D = 158.8mm) where one plate contains an integrated jet actuator and the opposite plate includes a target heater (dh = 86mm). The spacing between the plates is variable between D/12 and D/3. The flow within the gap is mapped using particle image velocimetry (PIV). It is found that confined jet impingement induces a countercurrent radial flow within the gap that includes a layer of cool ambient air entrained along the actuator plane and a layer of heated air that is dispensed along the target surface. Particle pathlines demonstrate significant mixing between the countercurrent streams and strong entrainment into the vortex rings that synthesize the jet. Heat transfer coefficient attains a local maximum away from the stagnation point that can be attributed to strong vorticity diffusion into the thermal boundary layer and enhanced mixing that accompanies the vortex ring impingement. Although the jet Reynolds number does not exceed 3300, the stagnation heat transfer coefficient is about 90 W/m2K for H/D = 0.32.

Experimental Investigation of the Effect of Synthetic Jets on Local Heat Transfer Coefficients in Minichannels During Laminar and Turbulent Flow Conditions

2013 ◽  
Author(s):  
David M. Sykes ◽  
Andrew L. Carpenter ◽  
Gregory S. Cole
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Microchannels and minichannels have been shown to have many potential applications for cooling high-heat-flux electronics over the past 3 decades. Synthetic jets can enhance minichannel performance by adding net momentum flux into a stream without adding mass flux. These jets are produced because of different flow patterns that emerge during the induction and expulsion stroke of a diaphragm, and when incorporated into minichannels can disrupt boundary layers and impinge on the far wall, leading to high heat transfer coefficients. Many researchers have examined the effects of synthetic jets in microchannels and minichannels with single-phase flows. The use of synthetic jets has been shown to augment local heat transfer coefficients by 2–3 times the value of steady flow conditions. In this investigation, local heat transfer coefficients and pressure loss in various operating regimes were experimentally measured. Experiments were conducted with a minichannel array containing embedded thermocouples to directly measure local wall temperatures. Flow regimes ranged from laminar to turbulent. Local wall temperature measurements taken directly beneath the synthetic jet in a laminar flow regime indicated that when a synthetic jet was used, the heat transfer coefficient was increased as much as 2.8 times the value as when synthetic jets were not used. Significant heat transfer coefficient augmentation also propagated to the upstream location, where heat transfer was increased to 2.2 times the value as when the synthetic jets were not used. Additional measurements show that synthetic jets significantly altered the pressure loss coefficient of the minichannels and that this effect was more pronounced in laminar flow than in turbulent flow. The effect of operating frequency on heat transfer and pressure loss is also presented. It was shown that the optimal operating point for the synthetic jet within a minichannel was in transitional to weakly turbulent flow (2600<Re<4500) to maximize the increase in heat transfer coefficient and minimize the increase in pressure loss.

Experimental and Numerical Investigation of Thermal Performance of Synthetic Jet Impingement

2020 ◽  
Author(s):  
Pushpanjay K. Singh ◽  
Rohit Kothari ◽  
Santosh K. Sahu ◽  
Prabhat K. Upadhyay ◽  
Shashwat Singh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Specimen ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Geometrical Parameters ◽  
The Heat Transfer Coefficient ◽  
Plate Distance

Abstract Synthetic jet potentially useful in electronics cooling is investigated both numerically and experimentally. In the present study, a confined three dimensional synthetic jet with sinusoidal moving wall is considered. Computations are carried out using the FLUENT software with the coupled user defined function describing the diaphragm movement. In this study the effect of various geometrical parameters influencing the flow field and heat transfer are investigated. The effects of change in orifice geometry (circular, square and rectangular), orifice aspect ratio, and jet-to-plate distance are studied for a given hydraulic diameter. The heat transfer results obtained from the synthetic jet is compared with the continuous jet. An electromagnetic actuator is used as an oscillating diaphragm for the generation of synthetic jet. A stainless steel foil with 0.05 mm thickness is used as the test specimen. The surface temperature of the test specimen is measured by using a thermal imaging technique during synthetic jet impingement and a constant temperature anemometer has been employed for velocity measurement. Tests are carried out for Reynolds number of 5448, varied range of jet-to-plate distance (1–18). The maximum value of the heat transfer coefficient is found to be 16 times more than the heat transfer coefficient for natural convection.

Heat Exchanger Analysis Modified to Account for a Heat Source

2007 ◽  
Author(s):  
Vinod Narayanan ◽  
Murty Kanury ◽  
Jeromy Jenks
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Heat Source ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Source Term ◽  
Fluid Stream ◽  
Overall Heat Transfer Coefficient ◽  
Definition Of

The practice of determining the overall heat transfer coefficient using the classical definition of log-mean-temperature-difference in heat exchangers with a heat source term in the hot fluid stream is questioned. The motivation for this work arises from the heat exchanger analysis of an ammonia-water absorber heat exchanger where a heat-of-absorption source term arises in the solution side. A modified heat exchanger analysis is developed here with account for such a heat source. Results of the analysis are discussed and its utility in deducing the overall heat transfer coefficient from experimental measurements is demonstrated.

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