Turbulent heat transfer for impinging jet flowing inside a cylindrical hot cavity (original) (raw)
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Turbulent jet impinging a cylindrical hot cavity
Heat and Mass Transfer, 2014
The possibility of improving the heat transfer is investigated numerically using finite volume method. The Reynolds number increase has a minor effect on flow structure but generates a systematic rise of Nusselt Number. The maximum heat exchange occurs when the cavity bottom is located at the potential core end. The main heat exchange occurs on the cavity bottom for every case. The stagnation Nusselt number is correlated according some problem parameters.
Steady interaction of a turbulent plane jet with a rectangular heated cavity
Thermal Science, 2014
Turbulent heat transfer between a confined jet flowing in a hot rectangular cavity is studied numerically by finite volume method using the k-w SST one point closure turbulence model. The location of the jet inside the cavity is chosen so that the flow is in the non-oscillation regime. The flow structure is described for different jet-to-bottom-wall distances. A parametrical study was conducted to identify the influence of the jet exit location and the Reynolds number on the heat transfer coefficient. The parameters of this study are: the jet exit Reynolds number (Re, 1560< Re <33333), the temperature difference between the cavity heated wall and the jet exit (DT=60?C) and the jet location inside the cavity (Lf, 2? Lf? 10 and Lh 2.5
Heat Transfer Prediction of a Jet Impinging a Cylindrical Deadlock Area
Journal of Heat Transfer, 2014
The turbulent heat transfer by a confined jet flowing inside a hot cylindrical cavity is investigated numerically in this paper. This configuration is found in several engineering applications such as air conditioning and the ventilation of mines, deadlock, or corridors. The parameters investigated in this work are the Reynolds number (Re, 20,000 ≤ Re ≤ 50,000) and the normalized distance Lf between jet exit and the cavity bottom (Lf, 2 ≤ Lf ≤ 12). The numerical predictions are performed by finite volume method using the second order one-point closure turbulence model (RSM). The Nusselt number increases and attains maximum values at stagnation points, after it decreases. For an experimental test case available in the literature Lf = 8, the numerical predictions are in good agreement. Processes of heat transfer are analyzed from the flow behavior and the underlying mechanisms. The maximum local heat transfer between the cavity walls and the flow occurs at Lf = 6 corresponding to the...
In this paper the three dimensional round jet impinging on a circular pedestal is simulated. The predictions are carried out through numerical procedure based on finite volume method. The effects of the nozzle to target spacing (H/D=2, 4 and 6) and Reynolds numbers (23000 and 50000) are investigated. The flow field is considered to be incompressible and the buoyancy and radiation heat transfer effects are neglected. Turbulent fluctuations in the velocity field are modeled using the Reynolds Averaged Navier-Stokes (RANS) methodology and various turbulence models such as SST k , RNG k , Realizable k and 2 f are also used. The results of convective heat transfer obtained on the pedestal and the flat plate, using 2 f turbulence model have good agreement with the experimental data compared to the other models and also heat transfer increases with increasing Reynolds number and the maximum heat transfer coefficients occur for H/d equals to six.
Heat transfer prediction in a shallow cavity effect of incoming flow characteristics
Thermal Science, 2016
This study deals numerically with a heat transfer in a turbulent flow over a shallow cavity. Two different configurations of the incoming flow are considered: a boundary layer flow and a plane wall jet flow, in order to examine the wall jet outer layer effect on the heat transfer. This layer is an important additional turbulence source in the wall jet flow. Reynolds number and turbulence intensity effects were investigated in the boundary layer incoming flow case. The cavity depth to nozzle height ratio effect was examined in the wall jet incoming flow case. The numerical approach is based on k-? standard turbulence model. This study reveals that the heat transfer is very sensitive to the incoming flow characteristics. The turbulence intensity increase accelerates the reattachment of the shear layer at the cavity floor and enhances the heat transfer. The reattachment phenomenon seems to be less affected by the Reynolds number. However, an increase in this parameter ameliorates the h...
International Journal of Thermal Sciences, 2008
The flow field of confined circular and elliptic jets was studied experimentally with a Laser Doppler Anemometry (LDA) system. In addition, heat transfer characteristics were numerically investigated. Experiments were conducted with a circular jet and an elliptic jet of aspect ratio four, jet to target spacings of 2 and 6 jet diameters, and Reynolds number 10 000. The toroidal recirculation pattern was observed in the outflow region for both geometries at dimensionless jet to plate distance 2. Higher spreading rates in the minor axis direction of the elliptic jet have also been mapped. Along the target plate, different boundary layer profiles were obtained for circular and elliptic jets at H/d = 2, but profiles became similar when dimensionless jet to plate distance was increased to 6. Positions of maximum radial and axial velocities and turbulence intensities have been determined for both geometries. For the confined circular and elliptic jet geometries, analysis of flow field measurements and numerical heat transfer results showed that inner peaks in local heat transfer closely relate to turbulence intensities in the jet and radial flow acceleration along the wall. Differences between the circular and elliptic jet, in terms of flow field and heat transfer characteristics, reduced with increase in the jet to plate distance.
Aerodynamic and heat transfer analysis of a impinging jet on a concave surface
International Journal of Thermal Sciences, 2017
Impinging jets are often used in applications requiring important localized cooling. For example, this technique is commonly used to reduce blade temperatures inside gas turbines. When the jet impacts the inner surface of the leading edge of a gas turbine blade, this geometrical configuration is similar to a jet impinging a concave surface inside a cavity. Previous studies have shown that for a certain range of geometrical and dynamic parameters, a jet injected in a cavity may sometime become unstable which is characterized by an oscillatory or flapping movement of the flow within the cavity. The objectives of this study are to investigate some features of this behaviour from velocity fields inside the cavity, pressure coefficients and Nusselt number distributions on the concave surface. This was accomplished using unsteady numerical simulations of a laminar flow at different Reynolds numbers for six different cavity configurations. Furthermore, PIV measurements were realized for some of the configurations in order to validate the numerical results. The results show that for four geometrical configurations, the flow entered in an oscillatory movement inside the cavity. This behaviour can be related to the difference in pressure between the output channels and the main vortex structure present inside the cavity. However, no clear link has been established between the frequency of the oscillatory flow and the geometrical parameters used.
Journal of Mechanical Engineering and Technology
Impinging jets have been used effectively in several applications including films and foods, rapid cooling and heating processes, tempering of glass and metal, drying of papers, coating, and freezing of tissue. In this work, a numerical simulation of steady and unsteady flow and heat transfer due to a confined 2-D slot jet impinging on constant heat flux plate is presented. Two cases of problem were considered. In the first case, jet-to-plate spacing was varied from 2 to 5 at a fixed jet Reynolds number of 500. In the second case, jet Reynolds number was varied from 200 to 750 at fixed jet-to-plate spacing of 5. In the steady regime, the stagnation Nusselt number was found to increase linearly with increasing Reynolds number, and the distribution of heat transfer in the wall jet region was found to be highly influenced by flow characteristics of the jet. A strong correlation between pressure distribution and Nusselt number was noticed. The critical Reynolds number at which the symmetry of the flow in the formation of vortex sheets is highly disrupted was determined. It was observed that, at the critical Reynolds number, the area-averaged heat transfer coefficient is high and influence the drastic changes of the Nusselt number in the unsteady regime.
International Journal of Thermal Sciences, 2018
In this paper, details of experimental and numerical investigations carried out on slot jet impingement over a heated circular cylinder with and without a flow confinement have been presented. In this study, to enhance heat transfer rate in the rear side of the cylinder, circular, quadrilateral and hexagonal flow confinements with openings at the top and bottom of the confinements are used around the target cylinder. The Reynolds number, Re D , defined based on the average velocity at the nozzle exit and the cylinder diameter, is varied from 6000 to 20000. The non-dimensional distance between the nozzle exit and the heated cylinder, H/S is varied in range of 2 ≤ H/S ≤ 12. The ratio of the cylinder diameter to the slot width, D/S = 8.5 is fixed in all the cases considered in the present study. The results of present study shows that the bottom surface of the cylinder is substantially cooled when flow confinement walls are used compared to the case of unconfined flow. The overall enhancement in the average Nusselt number over the heated cylinder due the quadrilateral and the hexagonal confinements is in the range of 20-42%.