Research On Thermal Properties Of Graphene Oxide Nanofluids And Application In Heat Pipes

Nanofluids are a kind of multiphase system formed by adding nano-size additives to the traditional heat transfer medium and the properties of nano additives are very important to the performance of nanofluids.Graphene Oxide(GO)is a kind of unique material with excellent thermal and good hydrophilicity properties,and it is an ideal additive for nanofluids.As a new type of heat transfer medium with high heat transfer efficiency,nanofluids have been widely used in the field of heat transfer.Heat pipes are commonly element used in the field of heat transfer,so it is great significant to improve the heat transfer efficiency and the heat transfer efficiency.The thermal properties of Graphene oxide nanofluids and its application in heat pipes are be studied in the paper.GO was prepared firstly,and then dispersed in the base fluid to form nanofluids.The thermal properties of GO nanofluids were investigated experimentally,and the factors affecting the thermal properties of GO nanofluids were also discussed.In addition,effects on the heat transfer capacity of heat pipe filled with GO nanofluids were further explored.The research can not only enriches the application of GO nanofluids but also promotes the design and optimization of heat pipes with nanofluids.The main contents of this paper are as follows:(1)Preparation of GO nanofluids.The graphite oxide was firstly prepared by Hummers method and the GO was obtained by ultrasonic stripping method.Three kinds of GO(5μm、10μm、20μm)were obtained by adjusting the stripping time.Then the GO nanofluids with mass fraction of 0.05%,0.1%,0.15%,0.2% and 0.25% were prepared by dispersing GO into water and ethylene glycol without adding any surfactant.The results of absorbance measurement showed that the prepared graphene nanofluids have good suspension stability.(2)Research on thermal properties of GO nanofluids.KD2-Pro thermal conductivity tester,Brookfield viscometer and JK99 B automatic interface tension meter were used to investigate the thermal properties of GO nanofluids under different conditions,including thermal conductivity,viscosity,surface tension,contact angle and other parameters.The results showed that the thermal conductivity and the viscosity of the base fuid increased,and the surface tension and contact angle decreased when the Graphene oxide was added to the base fluid.In addition,the experiment results also showed that the liquid temperature,the mass fraction and the size of GO had different effects on the thermal properties of nanofluids.Thermal conductivity of GO nanofluids improved with an increase of temperature while viscosity and surface tension of nanofluids decreased.Thermal conductivity,viscosity,surface tension of nanofluids increased with an increase of the concentration of GO nanofluids.The thermal conductivity and surface tension of GO nanofluidS decreased and the viscosity of nanofluids increased with the decrease of the size of GO.The experimental results of the thermal conductivity and viscosity of the graphene oxide nanofluids were compared with the theoretical results.(3)Investigation on the performance of heat pipes with GO nanofluids.The testing device was assembled to study the effect of GO nanofluids on the thermal performance of heat pipes,mainly on the start-up process,wall temperature distribution,thermal resistance,heat transfer coefficient and effective thermal conductivity of heat pipes.The results showed that the heat transfer performance of heat pipe with GO nanofluids was significantly higher than that of the base fluid.And thermal resistance of heat pipes with GO nanofluids was most reduced by 50%.The maximum effective thermal conductivity of heat pipes with GO nanofluids was 2.59 times of heat pipes with base fluid.The results of the lumped parameter method showed that the start-up process of heat pipes with Graphene oxide nanofluids can be well predicted.Finally,it was found that the main reason for the enhancement of the heat transfer performance of heat pipes with GO nanofluids was mainly related to the graphene oxide coating on the surface of the wick.