Effects of graphene oxide nanofluids on heat pipe performance and capillary limits

• Effects of GO/water nanofluids on thermal performances of heat pipes were studied.
• Enhanced boiling heat transfer coefficients were observed in GO nanofluid-filled heat pipes.
• Enhanced capillary limits were observed in GO nanofluid-filled heat pipes.

In the present study, thermal performances of water-filled and 0.01 and 0.03 vol% graphene oxide (GO)/water nanofluids-filled heat pipes with a screen mesh wick were studied in order to investigate the effects of nanofluids on the heat pipe operation. The wall temperatures of the GO/water nanofluids-filled heat pipes were found to be lower than those of the water heat pipe. Also, the heat pipes charged with GO/water nanofluids showed lower evaporator thermal resistances by about 25% compared with the water-filled heat pipe, although the condenser thermal resistances were similar in both cases. The 0.01 vol% GO/water nanofluid-filled heat pipe showed better boiling heat transfer than 0.03 vol% GO/water nanofluid because of the different structures of the deposited nanoparticle layers on the wicks. The capillary limit of the heat pipes containing GO/water nanofluids was higher than for the water heat pipe, because the nanoparticles-coated layer modified the effective capillary radius and meniscus, resulting in an increase of the maximum liquid flow rate through the wick structure. The SEM images and wetting properties for wicks of the heat pipes with nanoparticles-coated layers support the thermal performance characteristics of the heat pipes obtained in the study.