Dimensionless numbers used to characterize stratification in water tanks for discharging at low flow rates

Abstract

The efficiency of thermal energy storage and solar collector systems is improved if thewater tank is stratified. There are many parameters to characterize stratification but no work compares their suitability. This paper identifies the most used dimensionless numbers to characterize stratification inwater tanks and studies their suitability. Experiments with different flow rates were done and the dimensionless numbers were determined. Richardson is the best number to define stratification in a water tank, while Mix number presents some problems and a bad behaviour. The other numbers do not clearly characterize stratification but can be useful combined with Richardson.

The work was partially funded by the Spanish Government (project: ENE2005-08256-C02-01/ALT) and by the Catalan Government (project: 2005SGR 00324). The authors would like to thank the company LAPESA for its collaboration. Dr. Marc Medrano would like to thank the Spanish Ministry of Education and Science for his Ramon y Cajal research appointment.