Numerical investigation of local heat transfer distribution on surfaces with a non-uniform temperature under an array of impinging jets with various nozzle shapes

Numerical calculations of heat transfer characteristics of an impingement cooling system with
a non-uniform temperature on a cooled surface using ANSYS CFX have been performed. The
influence of a surface heat flux qw(x) and a nozzle shape on the Nusselt number distribution on the
cooled surface has been studied. The setup consisted of a cylindrical plenum with an inline array of
ten impingement jets. Cylindrical, convergent divergent shapes of nozzles and linear temperature
distribution on the cooled surface have been considered for various heat fluxes qw(x). Results
indicate that geometry of the cylindrical nozzles resulted in the highest Nusselt numbers along the
cooled surface. The line of the averaged Nusselt number has a trend to increase in the direction of
the flow for the cooling system with increasing values of the surface heat flux q(x). This tendency
can be observed for all presented shapes of jets. On the other hand, for decreasing functions of the
heat flux qw(x), the Nusselt number distribution is more uniform. It can be observed for all types
of nozzles. Very similar values of the Nusselt number occur especially for the non-uniform heat flux
5000-2500W/m2. For constant values of the heat flux q(x) = 5000W/m2, the line of the average
Nusselt number has a trend to increase slightly in the direction of the flow. Numerical analysis
of different mesh density results in good convergence of the GCI index, what excludes mesh size
dependency. The presented study is an extension of the paper (Marzec and Kucaba-Piętal, 2016)
and aims at answering the question how the Nusselt number distribution on the cooled surface is
affected by various geometries of nozzles for a non-uniform surface heat flux qw(x).