This paper presents a computational study of mixed convection cooling of four in-line electronic chips by alumina-deionized (DI) water nanofluid. The chips are flush-mounted in the substrate of one wall of a vertical rectangular channel. The working fluid enters from the bottom with uniform velocity and temperature and exits from the top after becoming fully developed. The nanofluid properties are obtained from the past experimental studies. The nanofluid performance is estimated by computing the enhancement factor which is the ratio of chips averaged heat transfer coefficient in nanofluid to that in base fluid. An exhaustive parametric study is performed to evaluate the dependence of nanoparticle volume fraction, diameter of Al2O3 nanoparticles in the range of 13–87.5 nm, Reynolds number, inlet velocity, chip heat flux, and mass flowrate on enhancement in heat transfer coefficient. It is found that nanofluids with smaller particle diameters have higher enhancement factors. It is also observed that enhancement factors are higher when the nanofluid Reynolds number is kept equal to that of the base fluid as compared with the cases of equal inlet velocities and equal mass flowrates. The linear variation in mean pressure along the channel is observed and is higher for smaller nanoparticle diameters.