Engineering

Jet Impingement IntroductionImpinging jets of various configurations are used in numerous industrial processes because of their highly favorable heat and mass transfer characteristics. Impinging jets provide much higher convective heat and mass transfer rates than those with the same amount of gas flowing parallel to the target surface. 

 

 

The heat transfer coefficient for the typical application of impinging jets including many heating, cooling and drying processes is a few times higher than that of a cross circulation dryer. Moreover, impinging jets provide the potential of fine and fast control of local transfer rates by varying operating parameters such as the jet velocity and size of the nozzle opening. Depending upon the application, either slot or round jets, single or multiple jets and single phase or gas-particle two phases can be selected in impinging jets. The major applications of impinging jets include photographic films and paper, annealing of nonferrous metal sheet and glass, internal cooling of the leading edge of turbine blades, etc. Figure 1 shows the flow regions of a single semi-confined impinging jet. In the potential core region, the axial velocity remains almost the same as the nozzle exit velocity. In the impingement region, the static pressure increases as a result of the sharp decrease in mean axial velocity.

Flow regions of semi confined impinging slot jet

Although the basic heat and mass transfer in impinging slot jets can be shaped by the flow field, the effects of numerous parameters, such as nozzle geometry and size, nozzle configuration, location of exhaust ports, nozzle-to-target spacing, surface motion, and operating variables such as cross flow and jet axis velocity, complicate the analysis.

Geometry Creation: 

Geometry is created in Design Modeler. The jet inlet diameter D was 0.05 m, and the distance between the jet inlet and the wall H was 0.10m, resulting in an H/D ratio of 2.

Impingement Jet Configuration

Meshing:

Meshing is created in ANSYS according to the following parameters.

No. of Division = 1200 × 90 cells,  Mesh Type: Quadrilateral.

Thereafter the name selection for the configuration has been done as: inlet, outlet, plate, adiabatic.

meshing

                                                                                Figure 3: Cut Section View Of Meshing

 

name creation

                                                                      Figure 4: Name Creation

Boundary Conditions:

The Boundary Conditions used are as follows:

Inlet Velocity = 10 m/s, Temperature = 2273 K

Bottom Temperature = 673 K

Outlet Pressure = 180 x 105 Bar

Turbulence Model =  K- epsilon

 

Results:

Temperature Contour:

Temperature Contour

 

Velocity Contour:

Velocity Contour

 

Velocity Vector:

Velocity Vector

 

Nusselt Number:

Results for the heat flux distribution along the wall are presented in terms of the Nusselt number (Nu) distribution. The Nusselt number is calculated as Nu=hD/K. where the heat transfer coefficient h is determined as qw = (TJ-Tw). With qw being the wall heat flux. K is evaluated at the jet temperature at the inlet (Tj) consistent with the reference temperature used in the evaluation of the jet Reynolds number.

Graph

 

Future Work: 

The main aim of this research has been to assess the ability of computational fluid dynamics to accurately and economically predict the heat transfer rate in an impinging jet situation strongly relevant to industrial applications e.g. in electronic cooling.

The influence of parameters of interest such as nozzle to plate distance Reynolds number geometry of the impingement surface or confinement has been shown to be well captured. In comparison the widely used k - ɛ model does not properly represent the flow features highly over predicts the rate of heat transfer and yields physically unrealistic behavior.

It is planned to perform additional computations to cover a wider range of parameters (e.g. 3D configurations and a range of Prandtl numbers). In particular for electronic cooling applications, dielectric liquids in confined jet geometry and multiple jets configurations need to be explored.