Exploring the ultralow effective thermal conductivity of hollow glass microsphere at various pressures and temperatures

Abstract

Hollow glass microsphere (HGM) have been mainly used as an insulation system for containers storing cryogenic liquids like as LH2 and LO2 due to their very low effective thermal conductivity and high economic efficiency. However, a comprehensive understanding of its temperature and pressure-dependent thermal conductivity, as well as the underlying heat transport mechanism within HGM, remains elusive. This paper addresses these gaps by presenting a thorough investigation of the wide-ranging thermal conductivity of HGM, spanning from 0.0032 torr to 760 torr and temperatures ranging from 80 K to 300 K. Notably, we observe that HGM exhibits significantly lower thermal conductivity compared to typical silica aerogel at pressures below 0.1 torr. At 300 K and 0.0032 torr, the effective thermal conductivity of HGM reaches 0.0018 W & sdot;m- 1 & sdot;K- 1, whereas at 80 K and 0.0032 torr, it measures at 0.0009 W & sdot;m- 1 & sdot;K- 1. Fourier transform infrared spectroscopy (FTIR) measurements underscore that the radiative heat transfer of HGM is markedly lower than that of typical silica aerogel, contributing to its exceptionally low thermal conductivity. Our comprehensive measurements and thermal transport analysis for HGM offer valuable insights for the optimization of next-generation thermal insulation materials.