Control of Convective Heat Transfer in a Confined Laminar Impinging Jet by Low Amplitude Forcing

2002 ◽  
Author(s):  
Victor Adrian Chiriac ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Control Volume ◽  
Vortex Formation ◽  
Low Frequency ◽  
Separated Flow ◽  
High Amplitude ◽  
Asymmetric Vortex ◽  
Plate Spacing ◽  
Air Jet ◽  
Velocity Spectra

A numerical finite-difference model, derived using a control-volume approach, was used to compute the flow and heat transfer characteristics in a two-dimensional confined laminar air jet impinging on an isothermal surface. Several cases were considered with Re=650, 750, and nozzle to plate spacing, H/W=5. The behavior of the jet and the attendant heat transfer from the target wall were investigated when the jet was forced by fluidic excitation at the nozzle exit. At Re between 585 and 610, the unforced jet exhibits a transition to an unsteady regime leading to asymmetric vortex shedding and jet flapping [1, 2]. Investigation of the velocity spectra indicate three distinct dominant modes; the lowest frequency is associated with the jet flapping while the highest frequency is associated with the asymmetric vortex formation which causes buckling of the jet column. As a result of the two combined modes, the peak heat transfer is enhanced and the lateral cooling extent is broadened. The jet was subjected to forcing by introduction of numerical excitation at each side of the jet that modeled fluidic excitation. The jet was forced on both opposing sides at its exit, both with in-phase and out-of-phase modes. Under some conditions, out of phase forcing at Re=650 at the highest frequency leads to stabilization of the normally separated flow on one side only. This unusual asymmetric flow field is unsteady but repeatable, and results in an enhancement of the heat transfer. At Reynolds number of 750, forcing with an out of phase mode at the highest frequency leads to a complete stabilization of the jet. The forcing suppresses the high-amplitude low frequency flapping mode leaving only a high frequency vortex formation mode. The suppression of the jet flapping leads to a decrease in the peak heat transfer, but because separation is suppressed, the average wall heat transfer is enhanced.

Natural Convection in Vertically Vented Enclosures

1991 ◽  
Vol 113 (4) ◽  
pp. 912-918 ◽  
Author(s):  
D. M. Sefcik ◽  
B. W. Webb ◽  
H. S. Heaton
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Visualization ◽  
Flow Structure ◽  
Control Volume ◽  
Local Maximum ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heated Wall

Steady, laminar natural convection in vertically vented two-dimensional enclosures has been investigated both experimentally and analytically. A vertically vented enclosure is one in which the buoyancy-driven flow and heat transfer are restricted by vents in the top and bottom bounding walls of the enclosure. The local heat transfer along the heated wall was determined using Mach-Zehnder interferometry, and the flow structure was determined using a smoke generation flow visualization technique. Analytically, the governing conservation equations were solved numerically using a control volume-based finite difference technique. The results reveal strongly nonuniform local heat transfer along the isothermal wall as a result of the blockage at the inlet. A local maximum and minimum occur in the lower half of the enclosure. The flow visualization and analytical predictions for the flow field reveal that these heat transfer extrema are attributed to separated flow effects near the inlet gap with the associated primary inlet flow impingement and bifurcation at the heated wall. The analysis predicts well the flow structure and local and average heat transfer data. The results show asymptotic behavior to the classical vertical parallel plate result in the limit as the vent gap approaches the enclosure width.

A Study on Resonance Impinging and Wall Jets

2003 ◽  
Author(s):  
Toshihiko Shakouchi ◽  
Takumi Maruyama ◽  
Toshitake Ando ◽  
Koichi Tsujimoto ◽  
Atsushi Watanabe
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Impinging Jets ◽  
Heated Plate ◽  
Wall Jets ◽  
Maximum Heat ◽  
Plate Spacing ◽  
Air Jet ◽  
Nozzle Plate

Various kinds of impinging jets are used widely in many industry fields, such as the cooling of a heated plate or electronic components, drying of textiles, film, and paper because of their high heat and mass transfer rates at and near the stagnation point. Many studies on impinging jets from circular and orifice nozzles have been made [1]–[6]. It is well known that as nozzle-plate spacing decreases considerably the heat transfer rate becomes much larger, for example the maximum heat transfer rate of a circular impinging air jet with a low nozzle-plate spacing h/d = 0.1 (d: nozzle exit diameter) and Reynolds number Re = umd/ν = 2.3 × 104 is about 2.17 times of that for h/d = 0.2, but at the same time the flow resistance or operating power of the nozzle-plate system increases considerably. In order to improve or enhance the heat transfer rate, it is needed to increase the impinging mean and fluctuating velocities without increasing the operating power. To achieve this object it is considered to use a resonance jet. In this paper, the flow, acoustic and heat transfer characteristics of resonance free, impinging and wall jets are made clear experimentally. Moreover, flow visualization of the water jet flow by a tracer method is also made to examine the vortex structure at the shear layer and inside the resonance room. As a result, the heat transfer rate of the impinging jet by a resonance nozzle can be improved and enhanced considerably.

scholarly journals Vortex formation and heat transfer in the system of building models at turbulent separated flow

2018 ◽  
Vol 1105 ◽  
pp. 012019
Author(s):  
S Korobkov ◽  
A Gnyria ◽  
A Dyogin ◽  
M Sokol ◽  
V Terekhov
Keyword(s):  
Heat Transfer ◽  
Vortex Formation ◽  
Separated Flow ◽  
Building Models ◽  
Turbulent Separated Flow

Experimental Investigation on Staggered Impingement Heat Transfer on a Rib Roughened Plate With Different Crossflow Schemes

2010 ◽  
Author(s):  
Yunfei Xing ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Plate Spacing ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Rib Turbulators ◽  
Rib Roughened

A nine-by-nine staggered jet array impinging on a flat or rib roughened plate at Reynolds numbers from 15,000 to 35,000 has been studied by the transient liquid crystal method. The jet-to-plate spacings are adjusted to be 3, 4 and 5 jet diameters. Three jet-induced crossflow schemes, referred as minimum, medium and maximum crossflow correspondingly, have been measured. The local air jet temperature is measured at several positions on the impingement plate to account for an appropriate reference temperature of the heat transfer coefficient. The heat transfer results of the rib roughened plate are compared with those of the flat plate. The best heat transfer performance is obtained with the minimum crossflow and narrow jet-to-plate spacing no matter on a flat or roughened plate. The presence of rib turbulators on the target plate produce higher heat transfer coefficients than the flat plate for narrow jet-to-plate spacing by 7.5%. Note that this value is within the measurement uncertainty of 9%.

scholarly journals Optimum Jet-to-Plate Spacing of Inline Impingement Heat Transfer for Different Crossflow Schemes

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Yunfei Xing ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Plate Spacing ◽  
Impingement Plate ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Sudden Decrease ◽  
The Heat Transfer Coefficient ◽  
Minimum Medium ◽  
Better Than

A nine-by-nine jet array impinging on a flat plate at Reynolds numbers from 15,000 to 35,000 has been studied by the transient liquid crystal method. The spacing between the impingement plate and target plate is adjusted to be 1, 2, 3, 4, and 5 jet diameters. The effect of jet-to-plate spacing has been investigated for three jet-induced crossflow schemes, referred as minimum, medium, and maximum crossflow, correspondingly. The local air jet temperature is measured at several positions on the impingement plate to account for an appropriate reference temperature of the heat transfer coefficient. The jet-to-plate spacing, H/d = 3, is found to be better than the others for all the crossflow schemes. Jet-to-plate spacings H/d = 1 and H/d = 2 result in a sudden decrease in the stagnation zone. The large jet-to-plate spacings H/d = 4 and H/d = 5 could not provide higher heat transfer performance with higher crossflow.

Air Jet Impingement Heat Transfer at Low Nozzle-to-Plate Spacings Under a Fixed Pumping Power Condition

2009 ◽  
Author(s):  
Kyo Sung Choo ◽  
Sung Jin Kim
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flow Rate ◽  
Jet Impingement ◽  
Pumping Power ◽  
Heat Transfer Characteristics ◽  
Nusselt Numbers ◽  
Plate Spacing ◽  
Air Jet ◽  
Impingement Heat Transfer

Heat transfer characteristics of an impinging air jet are experimentally investigated under a fixed pumping power condition. The effects of dimensionless pumping power on the Nusselt number are considered. The focus is on cases where the nozzle-to-plate spacing is equal to or less than one nozzle diameter. The results show that the Nusselt number is independent of the nozzle-to-plate spacing under fixed pumping power conditions, while the Nusselt number increases with decreasing the nozzle-to-plate spacing under fixed flow rate conditions. Based on the experimental results, new correlations for the stagnation and average Nusselt numbers of the impinging jet are developed as a function of the pumping power alone.

Convective Heat Transfer From a Heated Plate to the Orthogonally Impinging Air Jet

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Abhishek B. Bhagwat ◽  
Arunkumar Sridharan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Jet Impingement ◽  
Secondary Peak ◽  
Plate Spacing ◽  
Air Jet ◽  
Plate Distance

The convective heat transfer process between the orthogonal air jet impingement on a uniformly heated flat plate is studied numerically. In this numerical study, three-dimensional (3D) simulations are carried out in Fluent 14.0 to investigate the effect of Reynolds number, distance between nozzle exit and the plate on the heat transfer characteristics. V2F turbulence model has been used to model turbulence. Standard κ–ε, Realizable κ–ε, κ–ε RNG, SST κ–ω, Standard κ–ω, V2F turbulence models have been studied for orthogonal jet impingement in this work. It is observed that for jet exit to plate distance (Z/d) of 0.5 ≤ Z/d ≤ 6, V2F model is best suited. For Z/d ≤ 0.5 and Z/d ≥ 6, numerical results vary significantly from the experimental results. Reynolds number of 12,000, 20,000, and 28,000 has been studied. In this paper, results for various jet exit to the plate distance (Z/d) from 0.5 to 10 are presented. At low jet plate spacing Z/d < 4, secondary peak in Nusselt number distribution over the plate is visible in experimental results. V2F model correctly predicts the secondary peak in Nusselt number variation over the plate. Other models fail to predict the secondary peak which is of significant importance in air jet impingement at low jet-plate spacing (Z/d < 4).

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