Study On Solar Salt Doped With One-dimensional Carbon Nanomaterial And Its Thermophysical Properties

The energy storage material about molten nitrate has the advantages of low melting point,wide temperature range,low vapor pressure,low corrosivity and low cost,it becomes the best heat storage medium in concentrated solar thermal power generation system?Concentrated Solar Power,CSP?.However,its low thermal conductivity limits its utilization efficiency for solar energy to a certain extent,and the one-dimensional carbon nanomaterial has excellent thermal conductivity and mature preparation process.Therefore four different carbon nanotubes were selected:single-walled long carbon nanotubes?CNTA?,single-walled short carbon nanotubes?CNTB?,multi-walled large-diameter carbon nanotubes?CNTC?,and multi-walled small-diameter carbon nanotubes?CNTD?,they were introduced into the salt salt?60wt%NaNO₃+40 wt%KNO₃?molten nitrate system to obtain energy storage materials with high thermal conductivity,providing theoretical guidance for the development of new heat storage fluids,promoting the development of solar thermal power generation industry.This paper used differential scanning calorimetry?DSC?,thermogravimetric analyzer?TGA?,thermal conductivity meter?TCA?,X-ray powder diffractometer?XRD?,X-ray photoelectron spectroscopy?XPS?,laser Raman spectroscopy?Raman?and other methods to study the thermal properties and characterization of Solar-salt/CNTA system?SSCNTA?,Solar-salt/CNTB system?SSCNTB?,Solar-salt/CNTC system?SSCNTC?and Solar-salt/CNTD system?SSCNTD?.The specific research contents and results are as follows:1.Preparation of composite materials.The SSCNTA system and the SSCNTB system were prepared by the method of multiple mixing and melting at450°C/6h+300°C/2h to obtain the composite molten salt doped with single-walled carbon nanotubes.The SSCNTC system and the SSCNTD system were prepared by the method of single mixing and melting at 400°C/4h to obtain the composite molten salt doped with multi-walled carbon nanotubes.2.Structural characterization of composite materials.The structure of the composite materials was characterized by XRD and XPS.It was found that the main structure of the composite materials was not destroyed,and there were still sodium nitrate and potassium nitrate.In the SSCNTA system and the SSCNTB system,the main structure of the single-walled carbon nanotubes remained unchanged,and the purity was high,the surface impurity groups contents were small.The original multi-walled carbon nanotubes in the SSCNTC system and SSCNTD system had more impurities,but after mixing and melting in high temperature,the impurity groups were purified,and the main structure of the carbon nanotubes was not destroyed.3.Study on the thermal properties of composite materials.When these four types of carbon nanotubes were introduced into the Solar salt,the melting point was lowered,the decomposition temperature was increased,and the temperature range of the molten salt was broadened.These four types of systems can also maintain good thermal weight loss by the thermal weight loss cycle experiments at different temperatures.Subsequently,the study of heat storage performance was carried out by the three-step DSC method.The four types of carbon nanotubes had little effects on the specific heat value of Solar salt,and no significant improvement was observed.The thermal conductivity in the molten state was measured by the transient plane source method,and the thermal conductivity was found to be significantly improved.The thermal conductivity of the SSCNTA system increased the most,increasing by25.18%to 0.5227 W/?m·K?,while the thermal conductivity of the SSCNTB system was increased by 13.68%to 0.4531 W/?m·K?.The thermal conductivity of the SSCNTC system was increased by 16.65%to 0.4692 W/?m·K?.However,the thermal conductivity of the SSCNTD system showed a peak point?SSCNTD3?with the increase of the doping amounts.For this special phenomenon,the Raman spectrum was further characterized.We speculated that the dispersion of carbon nanotubes in SSCNTD3 was the most uniform,resulting in the strength of the N-O bond in the nitrate was most reduced,and the Raman red shift phenomenon was occured.At this inflection point,the thermal conductivity increased the most,increasing by 10.69%to0.4379 W/?m·K?.After introducing these four types of carbon nanotubes into the molten salt,the thermal properties of the molten salt were improved to some extent,and the thermal conductivity was also significantly improved,which was conducive to reducing the cost of power generation,and was expected to improve the efficiency of molten salt working fluid in the solar thermal power generation.