The main purpose of this paper is to study the effects of nanoparticles and Reynolds number on heat transfer coefficient, especially local heat transfer coefficient in laminar flow regime. The nanofluid heat transfer coefficient enhancement with respect to the base fluid was reported for most cases. In some cases, the nanofluid heat transfer coefficient enhancement increased with nanoparticle volume fraction consistently and in some cases, it was conditional. Indeed, the nanofluid heat transfer coefficient enhancement depends on effective parameters such as base liquid, flow regime, channel characteristics, concentration and characteristics of nanoparticles. The mechanisms of nanofluid heat transfer coefficient were studied and it was reported that the substantial heat transfer coefficient enhancement is not attributed purely to the nanofluid thermal conductivity enhancement, although, the nanofluid thermal conductivity enhancement has a significant impact on nanofluid convective heat transfer coefficient. However, the responsible mechanisms of the heat transfer coefficient enhancement have not been determined clearly, yet. Still, there are so many discrepancies among existing investigations and further investigation is necessary to find out the mechanisms of nanoparticles enhancement and how to maximize the nanofluid heat transfer coefficient.