Study On Thermal Conductivity And Application Of Carbon-coated Iron Nanofluids With Core-shell Structure

Enhanced heat transfer technology has been widely used in the automotive, energy, chemicals, electronics and other field, among them, the thermal media occupies a very important position. With the continuous development of science and technology, the common thermal media such as water, oil, glycol and other inorganic or organic solvents has been unable to meet the heat transfer needs, nanofluids have higher thermal conductivity than conventional thermal media, the small size of nanoparticles decreases the friction coefficient of heat transfer interface, nanofluids has lots of advantages of making the transfer interfacial thermal resistance to further lower, it shows a great prospect in the field of heat transfer enhancement.There is an innovative way to study the carbon-coated iron (CCIN) with core-shell structure, and nanofluids which was prepared by saline and CCIN in this thesis. A uniform particle size of CCIN nanoparticles is prepared by Vacuum Graphite Arc Method, and the core-shell structure of CCIN was characterized by TEM & XRD, and the core-shell structure was also discussed. CCIN was added into saline-based fluid, and the nanofluids with high thermal conductivity property were prepared by two-step method.|Different mass fraction of CCIN nanoparticles and three types of surfactants (SDBS, GA, PVP) was added into saline, after an appropriate sonication time, and finally the pH value of fluid was adjusted by HCl & NaOH, the CCIN nanofluids was prepared. The main factors affecting the dispersion and stability of nanofluids was investigated, and the thermal conductivity of nanofluids with different mass fractions of CCIN nanoparticles was studied. The results show that, precipitation effect of carbon and iron atom in different solubility and different crystal growth mechanism were the main reasons for the formation of core-shell structure of CCIN nanoparticles. Sonication time, pH value of nanofluids and surfactant type were the main factors affecting the dispersion and stability of nanofluids. The thermal conductivity of nanofluids changed while the mass fraction of nanoparticles changed, and they were not a linear relationship. The highest thermal conductivity is 0.94 W/(m-K), when the mass fraction of CCIN in nanofluids is 0.11% with PVP surfactant.The applications of nanofluids research concentrate on the efficient heat conduction performance at present, mainly on enhanced heat transfer to industrial. In this thesis, the nanofluids was applied to Radiofrequency ablation (RFA), which was a rapid developing treatment of primary liver cancer in recent years.Primary liver cancer is one of the malignant diseases of a serious threat to the health of people. Radiofrequency ablation (RFA), as the representative of the local treatment with advantages such as broad indications, light trauma and quick recovery and so on, is one of the important means of treatment of hepatocellular carcinoma. The clinical data showed that:in case that the scope of hepatocelleular is less than or equal to 3.0cm, efficacy of RFA on small hepatocellular was similar to efficacy of surgical resection. For hepatocellular carcinoma with large scope, repeated treatments were required and the efficacy was poor. Expanding the scope of ablation is the key to improve efficacy of RFA. There is an innovative way to conduct the RFA experiments with pork liver using CCIN nanofluids, and the results show that CCIN nanofluids had better heat transfer effect and greater ablation range than saline in RFA experiments, the effect enhancement of RFA is corresponded with the mass fraction and thermal conductivity of nanofluids; Compared with saline, the ablation cross-sectional area of nanofluids expanded up by 56%. For toxicity studies on the biological nanomaterials is still a lack of status quo, acute toxicity experiments of CCIN in SD rats were also conducted in this research. The result of studying the acute toxicity of CCIN nanofluids in SD rats showed, with low doses nanofluids injected into rat liver, the liver function and bloody system of SD rats weren’t affected and suffered significantly.