Thermocline Bed Properties for Deformation Analysis

Thermocline tanks have been considered as an alternative to traditional two-tank molten salt thermal storage in concentrating solar power systems due to their potential for cost reduction. One concern for thermocline usage is thermal ratcheting caused by the internal rock bed deformation during cyclic operation and significant temperature fluctuations. Thermal ratcheting studies have been performed in the literature to identify the possibility of tank rupture. However, these studies numerically modeled the ratcheting behavior utilizing bed properties that have never been measured for the materials used in thermocline storage systems. This work presents triaxial test data quartzite and silica thermocline filler materials to better inform future investigations of thermal ratcheting. Molten salt is replaced with water as the interstitial fluid due to similarity in dimensionless numbers and to accommodate room temperature measurement. Material property data for cohesion, dilatancy angle, internal angle of friction, Young's modulus, Poisson's ratio, and bulk modulus are presented for 0.138–0.414 MPa confining pressure. The material properties are then compared to those assumed in the literature to comment on the potential impact of this property data relative to thermal ratcheting.