Research Papers

Thermocline Bed Properties for Deformation Analysis

[+] Author and Article Information
Brian D. Iverson

Department of Mechanical Engineering,
Brigham Young University,
Provo, UT 84602
Sandia National Laboratories,
Albuquerque, NM 87185
e-mail: bdiverson@byu.edu

Stephen J. Bauer

Sandia National Laboratories,
Albuquerque, NM 87185

Scott M. Flueckiger

School of Mechanical Engineering,
Purdue University,
West Lafayette, IN 47907

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received August 13, 2013; final manuscript received March 10, 2014; published online May 13, 2014. Assoc. Editor: Nathan Siegel. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Sol. Energy Eng 136(4), 041002 (May 13, 2014) (9 pages) Paper No: SOL-13-1226; doi: 10.1115/1.4027287 History: Received August 13, 2013; Revised March 10, 2014

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.

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Grahic Jump Location
Fig. 1

(a) Instrumented test sample mounted on the base of the pressure vessel and (b) schematic of the triaxial test setup

Grahic Jump Location
Fig. 2

Unload/reload cycles performed during ramp up to the set confining pressure and used to determine elastic properties

Grahic Jump Location
Fig. 3

(a) Mohr–Coulomb failure theory enabling calculation of cohesion and internal angle of friction through triaxial measurements that yield multiple Mohr circles. (b) Idealized relation for dilation angle from slope of plastic region of volumetric strain.

Grahic Jump Location
Fig. 4

Stress/strain data for quartzite/silica mixture and water obtained during triaxial testing at various confining pressures

Grahic Jump Location
Fig. 5

(a) Bulk modulus as determined from unload-reload cycles during ramp up to confining pressures of 0.276, 0.345, and 0.414 MPa. (b) Young's modulus and (c) Poisson's ratio as a function of mean stress at indicated confining pressure values.

Grahic Jump Location
Fig. 6

Points of tangency to Mohr's circle at various confining pressure and used to determine the slope and intercept to the failure criterion

Grahic Jump Location
Fig. 7

Mohr's circle based on (a) peak and (b) yield as the principle stress. Also shown are the obtained linear tangents (Mohr–Coulomb failure criteria) based on regression of the data.

Grahic Jump Location
Fig. 8

Sample data for a confining pressure of 0.276 MPa illustrating volumetric strain versus axial strain. The trendline indicates the range over which the dilatancy angle was determined.




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