On Numerical Investigation of Non-dimensional Constant Representing the Occurrence of Secondary Peaks in the Nusselt Distribution Curves

The cooling of the heat sinks in electronic packaging system is generally achieved through theimpingement of air jet. Here, the characteristic study of heat dissipation rate is done with bynumerically evaluating the radial distribution of Nusselt magnitudes. These profiles are reported forvarious injection and geometric parameters in the present research. A very contagious look towardsthese profiles shows the occurrence of secondary and localized rise. However these local rises areobserved provided the Nusselt profiles are accurately predicted. To achieve this, the present researchtakes an effort in numerically simulating a computational domain, analogous to actual experimentalconditions. For this, an appropriate turbulence model is selected with its validation with presentexperimental result, in order to accurately predict the development of flow regime and necessary heatinteractions. The computational simulations at lower nozzle-target spacing and higher impingingvelocity revels the occurrence of secondary rise in Nusselt profiles. No doubt, the occurrence of suchsecondary peaks increases the magnitude of area average heat transfer rate. Hence this is of greatconcerned. A very less light is observed in determining the exact cause and the intervening range forthe occurrence of such peaks in the profiles. Looking into which, the current research focuses on thedetermination of the critical constant and its magnitude within which these peaks exists in the profile.The non dimensional constant representing the critical magnitude is defined as a ratio of diameterbased Reynolds number with nozzle - target spacing (Z/d). While the corresponding critical magnitudewas approximately investigated to be 6000. However, the mapping of velocity contours at differentvalues of this non-dimensional constant enables the physical understanding of the transition regionoccurring in the flow profile. A very judicious look towards these contours conveys the occurrence ofturbulence flow in near wall region to be responsible for the secondary rise in heat transfer rate.