The Al_2O_3-water nanofluid was prepared by using the two-step method

and the optimal ultrasonic dispersion time was determined to be 2hours.Then

the heat transfer characteristics of the flat heat pipe with micro-grooves using the Al_2O_3-water nanofluid as the working fluid were experimentally investigated.The results show that

as the working fluid

the nanofluid can dramatically enhance the heat transfer ability of the flat heat pipe with micro-grooves.The optimal volume concentration of the Al_2O_3 nanoparticles is about 1.5%

with which the heat transfer ability of the flat heat pipe reached the highest.Compared with the deionized water

using nanofluid as the working fluid can increase the equivalent thermal conductivity of the heat pipe by 15.6%.The nanofluid is a novel heat transfer working fluid which can be applied to the flat heat pipes with micro-grooves

it has good prospect and development potential for improving the thermal performance of flat heat pipes with micro-grooves.