The solar simulator is an important device for simulating solar irradiation in cold black and vacuum environments and has a wide range of application prospects. In this work, a method of thermal conductivity measurement by a double specimen protection thermal plate method under vacuum conditions was proposed, and the thermal conductivity of a new thermal insulation material under a cryogenic vacuum environment was studied. By designing a vacuum adjustment device and a multi-layer insulation structure with a low outgassing rate, it is possible to adjust the vacuum pressure from 10⁻⁴ Pa to atmospheric. A temperature control and thermal conductivity test can be realized from −160 °C to 280 °C by the joint temperature control of liquid nitrogen cooling and electric heating. Then, the measurement accuracy of the device was checked by the national standard sample, the thermal conductivity of the sample was measured under different vacuum and temperature conditions, the uncertainty analysis of the device was given, and, finally, the thermal conductivity of the new material was tested.

Solar–thermal conversion and migration characteristics of nanofluids have attracted intensive attention recently. Due to the strong absorption of solar energy, solar collectors with nanofluids have wide applications in many areas including desalination and power generation. Researchers have mainly focused on the macroscopic performance of nanofluids in solar collectors, but the nanoparticles’ migration characteristics with vapor during phase transformation have not been further investigated. Therefore, an experimental investigation on solar–thermal conversion characteristics of nanofluids and migration characteristics with vapor during phase transformation was conducted in this work, in order to verify the enhancement effect of nanoparticles on solar energy absorption and explore the nanoparticles’ migration behavior with vapor. It was found that part of Ag nanoparticles migrate out of the nanofluids with generated vapor by boiling nanofluids, and most of the nanoparticles remained in the nanofluids. In addition, more Ag nanoparticles migrated with vapor with the increased heating power. The concentration of migrated nanofluids was 20.58 ppm with a power of 16.2 W and 31.39 ppm with a power of 20 W. The investigation pointed out the potential danger of nanofluids in the process of utility and provided a reference for the standardized application of nanofluids.