While numerical modelling of different types of nanofluids in various microchannel heat sink geometry under different flow conditions are many, few involved utilizations of experimental data. Reports so far have indicated the potential cooling capability of nanofluids in general, yet none have investigated the effects of the surfactant alone on the fluid flow, in particular the thermofluid flow pattern. This paper reports the results of a numerical simulation with CFD on the fluid flow of Triton TX-100 surfactant with boron nitride nanotubes (BNN) in distilled water (base fluid) at 30 and 50 °C. The nanofluid (BNNT) operated at high temperature provided a lower thermal resistance. A higher pumping power was found for BNNTs and TX-100 at 30 ℃ compared to distilled water at both temperatures. The outcomes of the present study provide a better understanding of flow characteristic and flow visualization along a microchannel heat sink so that better design decision can be made for improvement of this application for different needs.