Contact Resistance Measurement and Its Effect on the Thermal Conductivity of Packed Sphere Systems

Abstract

There has been a growing interest in porous systems with a smaller length-scale modeling requirement on the order of each particle, where the existing tools tend to be inadequate. To address this, a Discrete Conduction Model was recently proposed to allow for the transient temperature calculation of 3D random packed-sphere systems for various microstructures. Since many of the motivating applications involve contacting spheres and since there has been a limited number of contact-resistance studies on spheres undergoing elastic deformation, the objective of this study is to obtain measurements of the contact resistances between metallic spheres in elastic contact, as well as to quantify their influence on the effective thermal conductivity. To accomplish this, an experiment was constructed utilizing air and interfacial resistance to replace the functions of the guard heater and vacuum chamber, and in so doing, enabled transient observations. The overall uncertainty was estimated to be ±6%, and the results were benchmarked against available data. A correlation was obtained relating the contact resistance with the contact radius, and results showed the contact resistance to have minimal transient behavior. The results also showed that the neglect of contact resistance could incur an error in the effective thermal conductivity calculation as large as 800%, and a guideline was presented under which the effect of the contact resistance may be ignored. A correlation accounting for the effect of contact resistance on the effective thermal conductivity was also presented.