Methodical selection of thermal conductivity models for porous silica-based media with variation of gas type and pressure. (15th May 2022)

• Record Type: Journal Article
• Authors: Sonnick, Sebastian; Erlbeck, Lars; Meier, Manuel; Nirschl, Hermann; Rädle, Matthias
• Is Part Of: International journal of heat and mass transfer. Volume 187(2022)
• Publication Date: 2022-05-15
• Subjects: Effective thermal conductivity -- Vacuum insulation panels -- Silica -- Knudsen effect -- Smoluchowski effect -- Particle size; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2022.122519
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Pressure-dependent thermal conductivity of 15 silica materials with 7 gases. Pore size distribution, primary particle size, aggregate size and agglomerate size. Presentation and comparison of models for e_ective and gas thermal conductivity. Model recommendation for precipitated silica, fumed silica, silica gel & glass spheres. Graphical abstract: Abstract: If the effective thermal conductivity of a silica powder in any gas atmosphere is to be calculated analytically, one is faced with a whole series of decisions. There are a lot of different models for the gas thermal conductivity in the pores, the thermal accommodation coefficient or the effective thermal conductivity itself in the literature. Furthermore, it has to be decided which input parameters should be used. This paper gives an overview and recommendations as to which calculation methods are best suited for the material classes of precipitated silica, fumed silica, silica gel and glass spheres. All combinations of the described methods result in a total of 2800 calculation models which are compared with pressure-dependent thermal conductivity measurements of 15 powdery materials with 7 different gases using Matlab computations. The results show that with a model based on a spherical unit cell, which considers local Knudsen numbers, the measuring points of all powder-gas combinations can be determined best with an average variance of about 18.5%. If the material class is known beforehand, the result can be predicted with an average accuracy of about 10% with the correspondingly determined methods.