Influence of asymmetric blockage at flow exit on flow and heat transfer for an impinging slot jet on semi-concave surface

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.Experimental studies of single slot jet impinging upon a concave surface are conducted by classical Particle Image Velocimetry (PIV) and infrared thermography, with nozzle exit Reynolds number (Re = 3200), dimensionless impinging height (H/b = 3 & 7) and relative curvature of the wall (Dc/b = 5). Results indicate that the oscillatory impinging jet generated a uniform and symmetric heat transfer area while the stabilized impinging jet caused an asymmetric heat transfer. This type of jet may be controlled by changing the outlet condition.vk201

Influence of Reynolds number synthetic jet dynamic in crossflow configuration on heat transfer enhancement

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Flow and heat transfer of a compressible impinging jet

International audienceThe influence of injection Mach number over the flow and heat transfer of an impinging air jet is investigated. For a given injection Reynolds number, jets with different injection diameters have been studied, decoupling the effects of injection Reynolds and Mach numbers. Three injection diameters were used, varying injection Mach number from 0.3 to 0.8. The effects of injection-to-plate distance were also studied. Flow was studied using Particle Image Velocimetry and infrared thermography was used to investigate both Nusselt number and adiabatic wall temperature (also called recuperation temperature) variations along the plate. The main effect of Mach number rise on the flow is a decrease in the number of Kelvin-Helmholtz vortices, reducing the amplitude of the secondary maximum of Nusselt number, particularly for low injection to plate spacing. Moreover, for Mach number low values, the adiabatic wall temperature is nearly constant whereas for higher values variations occur depending on injection-to-plate distance. For low distances, the mean radial velocity close to the wall, which presents relatively high values, reduces the temperature above the jet injection total temperature. For higher injection-to-plate distances, ambient air, with higher static temperature, is brought into the jet, increasing the static temperature of the jet and leading to adiabatic wall temperature superior to jet injection total temperature

Influence of multi-perforation synthetic jet configuration on heat transfer enhancement

International audienceThe multi-perforated wall of synthetic jets bas been analyzed to enhance heat transfer under laminar and turbulence cross-flow and for several dynamic configurations. To study the role of cross-flow and synthetic jet interactions, a dedicated experimental set-up was developed with convective heat transfer coefficients along the wall. Multi-perforated results were directly compared to single synthetic jet data. Sensitive parameters such as jet frequency, piston amplitude displacement and cross-flow velocity were determined. Heat transfer from the synthetic jet device can be amplified from 23 to as much as 175% depending on experimental conditions. The role of multi-perforating plate with regard to the single row configuration is clearly demonstrated. It is reinforced by continuous interaction between the main flow and synthetic jets

Convective heat transfer in the entry region of an annular channel with slotted rotating inner cylinder

This paper investigates the convective heat transfer of a complex annular channel with an inner rotating wall. This configuration corresponds to the air gap of an open four-pole synchronous motor. The channel is constituted of a smooth static outer cylinder and a rotating inner cylinder with four slots such that the channel’s diameter is 15.8 mm. Experiments were performed for axial Reynolds numbers from 2140 to 6425 and rotational Reynolds numbers from 1750 to 35,000 (corresponding to Taylor numbers from 104 to 4. 106). Local heat transfer on both cylinders (rotor and stator) was measured using an infrared thermography device. PIV measurements were carried out in rotor slots. Results show a clear difference of heat transfer between slots sides and poles. In both cases, Nusselt number variation is comparable to the variation encountered in the entry region of a stationary channel. Both variation and level of heat transfer nonetheless depend on axial speed as well as rotational speed