A minimum volume (10% ~ 20%) is considered in expansion tank at start-up in cold conditions. As heating is started volume expands and tank sizing should be such that expanded volume fills (70% ~ 80%) of tank volume.

Expansion tank is provided in hot oil system to accommodate for the increased thermic fluid volume due to thermal expansion. It also helps in removal of moisture and non-condensables during start-up. This article will show how to do sizing of an expansion tank.

Size an horizontal expansion tank for hot oil system using Therminol VP-1 as thermic fluid. Fluid is heated from 30 °C to 350 °C. System hot oil volume is 7.87 m³. L/D to be used as 2.5. Thermic fluid density is 1056 Kg/m³ at 30 °C and 761 Kg/m³ at 350 °C.