Wyniki wyszukiwania - BazTech

1

Heat transfer enhancement from a heated plate with hemispherical convex dimples by forced convection along with a cross flow jet impingement

Patro P., Garnayak S.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 1

127--141

EN

In the present study, heat transfer from a small three dimensional rectangular channel due to turbulent jet impinging from a nozzle normal to the main flow at the inlet has been investigated. Hemispherical convex dimples are attached to the bottom plate from where heat transfer calculations are to be performed. Numerical simulations were performed using the finite volume method with […] turbulence model. The duct and nozzle Reynolds number are varied in the range of […], respectively. Different nozzle positions (X/D = 10.57, 12.88, 15.19) along the axial direction of the rectangular duct have been considered. It has been found that higher heat transfer is observed at X/D = 10.57 as compared to the other positions. The heat transfer enhancements with and without cross-flow effects have also been compared. It has been shown that the heat transfer rate with cross-flow is found to be much higher than that without crossflow. Also, the effect of dimples on the heated surface on heat transfer was investigated. The heat transfer is found to be greater in the presence of a dimpled surface than a plane surface.

2

Thermal and hydraulic phenomena in boundary layer of minijets impingement on curved surfaces

Kura T., Fornalik-Wajs E., Wajs J.

Archives of Thermodynamics

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2018

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Vol. 39, no 1

147--166

EN

Presented work considers flow and thermal phenomena occurring during the single minijet impingement on curved surfaces, heated with a constant heat flux, as well as the array of minijets. Numerical analyses, based on the mass, momentum and energy conservation laws, were conducted, regarding single phase and two-phase simulations. Focus was placed on the proper model construction, in which turbulence and boundary layer modeling was crucial. Calculations were done for various inlet parameters. Initial single minijet results served as the basis for the main calculations, which were conducted for two jet arrays, with flat and curved heated surfaces. Such complex geometries came from the cooling systems of electrical devices, and the geometry of cylindrical heat exchanger. The results, regarding Nusselt number, heated surface temperature, turbulence kinetic energy, production of entropy and vorticity, were presented and discussed. For assumed geometrical parameters similar results were obtained.

3

Cold Zone Exploration Using Position of Maximum Nusselt Number for Inclined Air Jet Cooling

Ingole S. B., Sundaram K. K.

Archive of Mechanical Engineering

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2017

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Vol. LXIV, nr 4

533--549

EN

Inclined jet air cooling can be effectively used for cooling of electronics or other such applications. The non-confined air jet is impinged and experimentally investigated on the hot target surface to be cooled, which is placed horizontally. Analysis and evaluations are made by introduction of a jet on the leading edge and investigated for downhill side cooling to identify cold spots. The jet Reynolds number in the range of 2000 ≤ Re ≤ 20 000 is examined with a circular jet for inclination (θ) of 15 less than θ less than 75 degree. Also, the consequence of a jet to target distance (H) is explored in the range 0.5 ≤ H/D ≤ 6.8. For 45 degree jet impingement, the maximum Nusselt number is widely spread. Location of maximum Nusselt number is studied, which indicates cold spots identification. At a higher angle ratio, the angle is the dominating parameter compared to the Reynolds Number. Whereas at a lower angle ratio, the inclined jet with a higher Reynolds number is giving the cooling point away from leading edge. It is observed that for a particular angle of incident location of maximum Nusselt Number, measured from leading edge of target, is ahead than that of stagnation point in stated conditions.

4

Experimental investigation of a liquid film formed by impingement of an axisymmetric jet on a flat heated surface

Bykuć S.

Turbulence : international journal

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2005

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Vol. 11

235-237

EN

The aim of the present work was to study experimentally hydrodynamic and heat transfer characteristics of the flow of a liquid film over a surface. A round jet of water impinging vertically on a horizontal plane forms a thin film flowing radially until the sudden increase of depth occurs (hydraulic jump). During the experiment, the temperature of the solid surface and liquid film thickness in the suhcritical region (downstream of the hydraulic jump) and supercritical region (upstream of the hydraulic jump) were measured. Radial film thickness and Nusselt number distributions were achieved. Experiments were performed for a range of flow rates between 0.3 and 0.8 I/min. The liquid film thickness upstream of the hydraulic jump was an order of magnitude smaller than that of the subcritical region. With the growth of the flow rate, the radius of the hydraulic jump and film thickness after the jump, increased. It was found that the local Nusselt number reached maximum near the stagnation region and decreases gradually with radius as the flow moves downstream with the biggest drop corresponding to the location of hydraulic jump. Downstream of the jump, Nu was approximately uniform. Higher Nusselt numbers were reached for higher flow rates. These differences for various flow rates were much bigger in the supercritical region than that in the subcritical one.