23 September 2011
A vapor refrigerant injection heat pump cycle with a flash tank has proven to be
effective in significantly improving system performance at low ambient temperatures.
However, ensuring effective liquid and vapor separation in the flash tank becomes one of the
major challenges with regards to the reliable operation of this type of system. This paper
investigates the liquid-vapor two-phase separation behavior in a flash tank by utilizing the
Computation Fluid Dynamics (CFD) and flow visualization. A 3-dimensional flash tank model
was built and utilized to simulate the two-phase separation under different liquid levels and a
wide range of operating conditions. The modeling results were compared with the actual twophase flow visualization results obtained through experiments. Good agreement between the
modeling and experimental results was reached. The flash tank liquid level, inlet velocity, and
flash tank size have been studied and found to be critical parameters for reliable two-phase
separation. Results of this work could establish design guidelines for the design of a flash
tank for a vapor injection heat pump cycle.