The purpose of this book is to go through the main topics of interest and address a number of experimental and theoretical studies which focused on the nanofluids performance of tubes and carried out to cover the enhancement in heat transfer by using nanofluids in all applications and the effect of concentration, Reynolds number, Rayleigh number, type of nanofluid, angle of the tube and diameter of nanoparticle, these are the importance subject of growing in many applications, nanofluids are a new class of heat fluids consisting of nanometer - sized particles (less than 100 nm) dispersed in convectional fluids.