Micro thermal systems are convenient cooling devices for high heat flux applications. Besides, the nanofluids are used to improve the cooling capabilities. The suspended nanoparticles in the base fluid increase the thermal conductivity, fluid viscosity and fluid density but decrease the effective heat capacity. To analyze the suitability of using the nanofluids for cooling applications, the numerical simulations are made for nanofluid heat transfer and fluid flow in micro-heat sink with straight microtubes and multiple tangential inlet jets. The configurations with five inlet jets is considered and numerical simulations are based on a finite volume method. The Al2O3 water based nanofluid was used in simulations. The heat flux spread through the bottom surface of the heat sink was q = 50 W/cm(2). Re from 15 to 100 was considered to simulate the laminar fluid flow. The analysis is based on thermal and hydrodynamic results obtained for nanofluid and compared with results obtained for water. The results are analyzed on a fixed pumping power, Re or mass flow rate basis. It is observed that the conclusions are strongly dependent on the analysis constraint. Moreover the surface temperature difference is not very much improved by using the nanofluid. (C) 2013 Elsevier Ltd. All rights reserved.