Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications in the fields of automotive, aerospace, electronic and process industry. A possible solution to obtain efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the introduction of nanoparticles in the working fluids can be considered in order to improve the thermal performances of the base fluids. In this paper a numerical investigation on confined impinging slot jets working with water or water/Al2O3 nanofluid is described. The flow is turbulent and a constant temperature is applied on the impinging surface. A single-phase model approach has been adopted. Different geometric ratios and nanoparticle volume concentrations have been considered at Reynolds numbers ranging from 5000 to 20000. The aim consists into study the thermal and fluid-dynamic behaviour of the system. The stream function contours showed that the intensity and size of the vortex structures depend on the confining effects, Reynolds number and particle concentrations. The local Nusselt number profiles show the highest values at the stagnation point and the average Nusselt number increases for increasing particle concentrations and Reynolds numbers and the highest values are observed for H/W = 10 The required pumping power increases as particle concentration as well as Reynolds number grow and it is at most 4 times greater than the values calculated in the case of base fluid.

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