The Borexino Thermal Monitoring & Management System and simulations of
the fluid-dynamics of the Borexino detector under asymmetrical, changing
boundary conditions
A comprehensive monitoring system for the thermal environment inside the
Borexino neutrino detector was developed and installed in order to reduce
uncertainties in determining temperatures throughout the detector. A
complementary thermal management system limits undesirable thermal couplings
between the environment and Borexino's active sections. This strategy is
bringing improved radioactive background conditions to the region of interest
for the physics signal thanks to reduced fluid mixing induced in the liquid
scintillator. Although fluid-dynamical equilibrium has not yet been fully
reached, and thermal fine-tuning is possible, the system has proven extremely
effective at stabilizing the detector's thermal conditions while offering
precise insights into its mechanisms of internal thermal transport.
Furthermore, a Computational Fluid-Dynamics analysis has been performed, based
on the empirical measurements provided by the thermal monitoring system, and
providing information into present and future thermal trends. A two-dimensional
modeling approach was implemented in order to achieve a proper understanding of
the thermal and fluid-dynamics in Borexino. It was optimized for different
regions and periods of interest, focusing on the most critical effects that
were identified as influencing background concentrations. Literature
experimental case studies were reproduced to benchmark the method and settings,
and a Borexino-specific benchmark was implemented in order to validate the
modeling approach for thermal transport. Finally, fully-convective models were
applied to understand general and specific fluid motions impacting the
detector's Active Volume.Comment: arXiv admin note: substantial text overlap with arXiv:1705.09078,
arXiv:1705.0965
