Prediction of the Effective Thermal Conductivity of Powder Insulation

Abstract

The powder insulation method is widely used in structural and cryogenic systems such as transportation and storage tanks of cryogenic fluids. The powder insulation layer is constructed by small particle powder with light weight and some residual gas with high porosity. So far, many experiments have been carried out to test the thermal performance of various kinds of powder, including expanded perlite, glass microspheres, expanded polystyrene (EPS). However, it is still difficult to predict the thermal performance of powder insulation by calculation due to the complicated geometries, including various particle shapes, wide powder diameter distribution, and various pore sizes. In this paper, the effective thermal conductivity of powder insulation has been predicted based on an effective thermal conductivity calculation model of porous packed beds. The calculation methodology was applied to the insulation system with expanded perlite, glass microspheres and EPS beads at cryogenic temperature and various vacuum pressures. The calculation results were compared with previous experimental data. Moreover, additional tests were carried out at cryogenic temperature in this research. The fitting equations of the deformation factor of the area-contact model are presented for various powders. The calculation results show a good agreement with the experimental results.

Thermal Conductivity Measurement of Bulk Solids

“…These calculations are an integral part of many manufacturing and engineering processes. Thermal conductivity is an effective feature which has previously been the subject of intense theoretical and experimental research [1][2][3][4][5][6][7][8][9]. The literature offers tabular values for the commonly available materials used, e.g., in construction or in mechanical engineering.…”

“…The overall summary of the theoretical models used to determine the thermal conductivity of soil, which is essentially equivalent to consolidated bulk materials, is analyzed in an article by Alrtimi et al [11]. (1) Conduction in the particles, (2) conduction in air, (3) radiation in air, (4) convection in pore air, (5) convection in liquid, (6) vapor diffusion, (7) conduction in liquid.…”

“…This paper presents the realized device together with the results of experiments measuring the thermal conductivity of selected samples at different temperatures and operating conditions. Experimental measurement and the validation of numerical models is important because it is still difficult to predict the thermal properties of powders by using empirical equations, due to the wide distribution of particle sizes and shapes and different pore sizes .…”

Towards Cryogel Z and glass spheres insulated cryostats for superconducting detector solenoids : R&D in the frame of the 2014 - 2020 Future Circular Collider study at CERN

“…The thermal performance and life-cycle-cost advantage of glass microspheres have been tested by several authors [55,[77][78][79][80][81]. In this section these reports are summarized.…”

“…der to investigate the effects of these parameters, yet reported results are often scattered [55,[77][78][79][80][81]. The most common glass spheres commercially available at reasonable cost come as a batch comprising microspheres of different diameter and wall thickness.…”