Experimental Mapping of Local Heat Transfer Coefficients Under Multiple Piezoelectric Fans

2006 ◽  
Author(s):  
Mark Kimber ◽  
Suresh Garimella ◽  
Arvind Raman
Keyword(s):  
Heat Transfer ◽  
Fluid Motion ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Coefficient ◽  
Transfer Coefficients ◽  
Coverage Area ◽  
Heat Transfer Coefficients ◽  
Piezoelectric Fans

Piezoelectric fans have been shown to provide large enhancements in heat transfer over natural convection while consuming very little power. These fans consist of a piezoelectric material attached to a flexible cantilever. When driven at resonance, large oscillations at the cantilever tip cause fluid motion, which in turn, results in improved heat transfer rates. In this study, the local heat transfer coefficients are determined experimentally for piezoelectric fans vibrating close to an electrically heated stainless steel foil, and the entire temperature field is observed by means of an infrared camera. Various vibration amplitudes, distances from heater to fan tip (or gap), and fan pitches are considered for both single-fan and two-fan configurations in impinging orientations. Of particular interest is the increase in heat transfer performance with an additional fan present and the dependence of this increase on the variable parameters. Results show nearly uniform cooling within the envelope of vibration for single-fan experiments with small gaps, and the existence of an optimal gap distance which is dependent on vibration amplitude. The benefits of an additional fan include greater coverage area, but the resulting increase in peak convection coefficient is highly dependent on the fan pitch. Conditions exist where constructive interference is observed which causes a roughly 10% increase in peak convection coefficient while significantly increasing the coverage area. Understanding the local performance of piezoelectric fans provides an important tool to help implement these devices in practical cooling systems.

scholarly journals Local Heat Transfer Coefficients Induced by Piezoelectrically Actuated Vibrating Cantilevers

2007 ◽  
Vol 129 (9) ◽  
pp. 1168-1176 ◽  
Author(s):  
Mark Kimber ◽  
Suresh V. Garimella ◽  
Arvind Raman
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Fluid Motion ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Piezoelectric Fans

Piezoelectric fans have been shown to provide substantial enhancements in heat transfer over natural convection while consuming very little power. These devices consist of a piezoelectric material attached to a flexible cantilever beam. When driven at resonance, large oscillations at the cantilever tip cause fluid motion, which in turn results in improved heat transfer rates. In this study, the local heat transfer coefficients induced by piezoelectric fans are determined experimentally for a fan vibrating close to an electrically heated stainless steel foil, and the entire temperature field is observed by means of an infrared camera. Four vibration amplitudes ranging from 6.35to10mm are considered, with the distance from the heat source to the fan tip chosen to vary from 0.01 to 2.0 times the amplitude. The two-dimensional contours of the local heat transfer coefficient transition from a lobed shape at small gaps to an almost circular shape at intermediate gaps. At larger gaps, the heat transfer coefficient distribution becomes elliptical in shape. Correlations developed with appropriate Reynolds and Nusselt number definitions describe the area-averaged thermal performance with a maximum error of less than 12%.

Theoretical and Experimental Study of Electrohydrodynamic Heat Transfer Enhancement Through Wire-Plate Corona Discharge

1997 ◽  
Vol 119 (3) ◽  
pp. 604-610 ◽  
Author(s):  
B. L. Owsenek ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Fluid Motion ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Numerical Code ◽  
Transfer Coefficients ◽  
Camera System ◽  
Heat Transfer Coefficients ◽  
Fine Wire

Heat and mass transfer between a surface and the surrounding gas can be enhanced by the application of electric body forces that induce jet or plume-like fluid motion. Such enhancement causes no noise or vibration, can be applied in complex, isolated geometries, and allows simple control of surface temperatures. This paper examines the potentially useful case of multiple fine-wire electrodes suspended in the open air above a grounded and heated horizontal surface. An infrared camera system was used to obtain a complete and accurate distribution of local heat transfer coefficients on the impingement surface. A numerical code was developed and verified by comparison with experimental data. This code was then used to investigate and compare the heat transfer generated by novel electrode geometries.

Local Heat Transfer Characteristics of Flows Induced by Multiple Piezoelectrically Actuated Vibrating Cantilevers

2007 ◽  
Author(s):  
Mark L. Kimber ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Vibration Amplitude ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Constructive Interference ◽  
Heat Transfer Coefficients ◽  
Close Proximity ◽  
Piezoelectric Fans

Piezoelectric fans have been shown to provide substantial enhancements in heat transfer over natural convection while consuming very little power. The local heat transfer coefficients induced by multiple piezoelectric fans operating simultaneously in close proximity are determined experimentally. The fans vibrate close to an electrically heated stainless steel foil, and the entire temperature field is observed by means of an infrared camera. A vibration amplitude of 10 mm is considered, with the distance from the heat source to the fan tip chosen to vary from 0.01 to 2.0 times the amplitude, and the distance between the fans, or pitch, varying from 0.5 to 4.0 times the amplitude. The two-dimensional contours of the local heat transfer coefficient are compared to those observed for a single fan under similar conditions. Results show that the benefit of adding a second fan is highest at an intermediate pitch that is equal to the vibration amplitude. Constructive interference is observed under these conditions yielding a local performance increase over isolated fan operation. For a large fan pitch, separate contours surrounding each fan are similar to those of a single fan, but their performance is lower than that of the corresponding single fan. For a small fan pitch the cooling obtained with the fan pair is similar to that with just one fan, suggesting minimal benefit from adding the second fan in this case.

Experimental Investigation of Corona Wind Heat Transfer Enhancement With a Heated Horizontal Flat Plate

1995 ◽  
Vol 117 (2) ◽  
pp. 309-315 ◽  
Author(s):  
B. L. Owsenek ◽  
J. Seyed-Yagoobi ◽  
R. H. Page
Keyword(s):  
Heat Transfer ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Threshold Value ◽  
Local Heat ◽  
Heated Plate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Efficiency ◽  
Corona Wind

Corona wind enhancement of free convection was investigated with the needle-plate geometry in air. High voltage was applied to a needle suspended above a heated plate, and heat transfer coefficients were computed by measuring the plate surface temperature distribution with an infrared camera. Local heat transfer coefficients greater than 65 W/m2 K were measured, an enhancement of more than 25:1 over natural convection. The enhancement extended over a significant area, often reaching beyond the 30 cm measurement radius. At high power levels, Joule heating significantly reduced the effective impingement point heat transfer coefficient. The corona wind was found to be more efficient with positive potential than with negative. The heat transfer efficiency was optimized with respect to electrode height and applied voltage. The needle-plate heat transfer effectiveness improved rapidly with increasing height, and became relatively insensitive to height above a threshold value of about 5 cm.

Heat Transfer Enhancement in Duct With Rectangular Fin Arrays

2019 ◽  
Author(s):  
Md. Islam ◽  
I. Barsoum
Keyword(s):  
Heat Transfer ◽  
Flow Behavior ◽  
Heating Surface ◽  
Infrared Camera ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Longitudinal Vortices ◽  
Heat Transfer Coefficients

Abstract The need for efficient cooling techniques has motivated researchers to focus into heat transfer and flow behavior of various configurations of finned surfaces. Inclined rectangular fin is found to be an effective vortex generator for heat transfer augmentation, wherein longitudinal vortices is generated and keeps intensity at far downstream. It is expected that the heat transfer from the endwall and the fin surface can be improved and hence we have identified this configuration as very promising. Rectangular fins of different height were constructed and experimental investigation of heat transfer and flow with arrays of rectangular fins was conducted. Effect of velocity, attack angle, fin height and pitch ratio on local heat transfer coefficients is studied. In order to accomplish the experiment, 7 × 7 arrays of rectangular fins were attached on the heating surface and then placed in rectangular duct with different angle of attack to the free stream flow. Stream wise heat transfer coefficients were measured both at centerline and of 10 mm off line of heating surface by means of the thermocouples. T-type thermocouples and an infrared camera (TVS 8000) with a 160 × 120 point In-Sb sensor were used to measure the temperature and the detailed heat transfer from the endwall along with fin base.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

scholarly journals Heat Transfer Coefficient Determination in a Gravity Die Casting Process with Local Air Gap Formation and Contact Pressure Using Experimental Evaluation and Numerical Simulation

2021 ◽  
Author(s):  
T. Vossel ◽  
N. Wolff ◽  
B. Pustal ◽  
A. Bührig-Polaczek ◽  
M. Ahmadein
Keyword(s):  
Heat Transfer ◽  
Contact Pressure ◽  
Local Heat Transfer ◽  
Casting Process ◽  
Local Heat ◽  
Air Gap ◽  
Gap Formation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Die Casting Process

AbstractAnticipating the processes and parameters involved for accomplishing a sound metal casting requires an in-depth understanding of the underlying behaviors characterizing a liquid melt solidifying inside its mold. Heat balance represents a major factor in describing the thermal conditions in a casting process and one of its main influences is the heat transfer between the casting and its surroundings. Local heat transfer coefficients describe how well heat can be transferred from one body or material to another. This paper will discuss the estimation of these coefficients in a gravity die casting process with local air gap formation and heat shrinkage induced contact pressure. Both an experimental evaluation and a numerical modeling for a solidification simulation will be performed as two means of investigating the local heat transfer coefficients and their local differences for regions with air gap formation or contact pressure when casting A356 (AlSi7Mg0.3).

scholarly journals Condensation inside smooth horizontal tubes: Part 1. Survey of the methods of heat-exchange prediction

2015 ◽  
Vol 19 (5) ◽  
pp. 1769-1789 ◽  
Author(s):  
Volodymyr Rifert ◽  
Volodymyr Sereda
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Film Condensation ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

Survey of the works on condensation inside smooth horizontal tubes published from 1955 to 2013 has been performed. Theoretical and experimental investigations, as well as more than 25 methods and correlations for heat transfer prediction are considered. It is shown that accuracy of this prediction depends on the accuracy of volumetric vapor content and pressure drop at the interphase. The necessity of new studies concerning both local heat transfer coefficients and film condensation along tube perimeter and length under annular, stratified and intermediate regimes of phase flow was substantiated. These characteristics being defined will allow determining more precisely the boundaries of the flow regimes and the methods of heat transfer prediction.

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+), p/e, and e/D.

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