Technical Brief

Transient Turbulent Natural Convection in Isochoric Vertical Thermal Energy Storage Tubes: A Dimensionless Model

[+] Author and Article Information
Reza Baghaei Lakeh

California State Polytechnic University, Pomona, 3801 W Temple Ave., Pomona, CA 90066

Richard E. Wirz

University of California Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095

Pirouz Kavehpour

University of California Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095

Adrienne S. Lavine

University of California Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095

1Corresponding author.

ASME doi:10.1115/1.4038587 History: Received October 14, 2016; Revised October 19, 2017


In this study, turbulent natural convection heat transfer during the charge cycle of an isochoric Thermal Energy Storage system was studied computationally and analytically. The storage fluids considered in this study (supercritical CO2 and liquid toluene) cover a wide range of Rayleigh number. The storage fluids are stored in vertical and sealed storage tubes. The volume of the storage tube is constant and the thermal storage happens in an isochoric process. A computational model was developed and validated to study turbulent natural convection during the charge cycle. The results of this study show that the aspect ratio of the storage tube (L/D) has an important effect on the heat transfer characteristics. The computational results were further utilized to develop a conceptual and dimensionless model that views the thermal storage process as a hot boundary layer that rises along the tube wall and falls in the center to replace the cold fluid in the core. The dimensionless model predicts that dimensionless mean temperature of the storage fluid and average Nusselt number of natural convection are functions of L/D ratio, Rayleigh number, and Fourier number that are combined to form a Buoyancy-Fourier number.

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