Study Of Stability And Thermal Physical Property Of Graphene Oxide And TiO₂Nanofluids

Reducing degree of supercooling of cool storage material and shortening thefreezing time can improve the energy efficiency of refrigeration units and increase theamount of ice storage.Graphene oxide and TiO₂-H₂O nanofluids was prepared. Theirstability,surface tension, latent heat and degree of supercooling were studiedexperimentally, and their nucleation power and nucleation rate were calculated studiedtheoretically, specific as follows:①Graphene oxide nanofluids was prepared by ultrasonic vibrating. By contrast,TiO₂-H₂O nanofluids was also prepared. The dispersion and stability of nanofluids werecharacterized by standing observation, particle size and zeta potential measurement,STEM observation. The result shows that the stability of Graphene oxide nanofluidswas better than TiO₂-H₂O nanofluids.②The surface tension of nanofluids was measured by ring method. Comparedwith deionized water, the surface tension of Graphene oxide and TiO₂-H₂O nanofluids issmall increase. With the increase of temperature, the surface tension of nanofluidsdecreases.③The latent heat of nanofluids was measured by DSC. With the increase ofconcentration, the latent heat of nanofluids decreases. The latent heat of nanofluids oflow concentration is close to deionized water. It is large enough for cold storage.④Characteristics of Solid-liquid phase change of Graphene oxide nanofluids wasstudied experimentally. The result shows that degree of supercooling of Graphene oxidenanofluids is lower and freeze time of Graphene oxide nanofluids is shorter, comparedwith deionized water. Degree of supercooling of graphene oxide nanofluids of0.05%is2.1℃.The degree of supercooling is reduced by69.1%and the freeze time is reducedby66%compared with deionized water. By contrast, degree of supercooling ofTiO₂-H₂O nanofluids was also measured. The partical size and concentration of twokinds of nanofluids influences the degree of supercooling. With the increase ofconcentration, the degree of supercooling of nanofluids decreases first and thenincreases. With the decrease of the particle size, the degree of supercooling of Grapheneoxide nanofluids decreases first and then increases, and the degree of supercooling ofTiO₂-H₂O nanofluids increases. The influence on the degree of supercooling which iscreated due to change of partical size and concentration of nanofluids relates to variation range.⑤The nucleation force and nucleation rate of Graphene oxide and TiO₂-H₂Onanofluids were studied theoretically. The result shows that adding nanoparticles intothe water is able to reduce the critical nucleation power and increase the rate ofnucleation, so as to reduce the degree of supercooling, which is same as experimentalresult. Condition of nucleation on the surface of Graphene oxide nanoparticles wasconsidered.And expression of minimum size of Graphene oxide nanoparticles thatmeets nucleation on the surface was derived. The critical nucleation force of flat surfaceand spherical surface was calculated. The result shows that the critical nucleation forceof flat surface is less than spherical surface, so production of steady crystal nucleus onsurface of Graphene oxide nanoparticles is easy than surface of TiO₂nanoparticles.With the increase of nanoparticles size，the critical nucleation force of sphericalsurface decreases. On the basis of nucleation of nanofluids, formula of calculatingnucleation rate of fluid containing suspended particles was revised. And the nucleationrate of Graphene oxide nanofluids and TiO₂-H₂O nanofluids was calculated. Comparedwith TiO₂-H₂O nanofluids, specific surface area of nanoparticles that Graphene oxidenanofluids contains is greater, and the critical nucleation power of Graphene oxidenanofluids is less. With the same degree of supercooling, Graphene oxide nanofluids hasmore nucleation rate than TiO₂-H₂O nanofluids, so Graphene oxide nanofluids offersadvantages over TiO₂-H₂O nanofluids in decreasing degree of supercooling. Particlesize and concentration influences the nucleation rate of nanofluids. According theanalysis result, nucleation rate of nanofluids is also influenced by stability.