In the last few decades, research on nanofluids has increased rapidly. Traditional heat transfer fluids with
order of nanometer sized particles (1–100 nm) suspended in them are termed as nanofluids. Nanofluids
have been proved as better heat transfer fluids despite of various contradictions in results by different
research groups. The aim of this article is to review and summarize the recent experimental and theoretical
studies on convective heat transfer in heat exchangers using constant heat flux boundary condition.
The use of different types of nanoparticles with different base fluids by different research groups has been
presented and compared. Further an overview of experimental results about heat transfer abilities of
hybrid nanofluids from available literature sources is also presented. Finally, the challenges and future
directions in which research can be further progress are discussed