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U.S. Department of Energy Energy Efficiency and Renewable Energy
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Flash Tank Calculator watch tutorial view guide

Determines the mass flows and properties of any resulting outlet gas and/or liquid for given inlet conditions.


Inlet

Pressure* psig
* °C btu/lbm kJ/kg/K
Mass Flow * klb/hr
Tank Pressure * psig
* Required
Allowed Range / Limits
Minimum
Maximum
Examples: Mouse Over
Saturated Liquid Saturated Mixture

Calculation Details and Assumptions below


Calculation Details

Step 1: Determine Inlet Water Properties

Using the Steam Property Calculator, properties are determined using Inlet Pressure and the selected second parameter (Temperature, Specific Enthalpy, Specific Entropy, or Quality):

Step 2: Determine the Specific Enthalpy and other properties for Saturated Liquid and Gas at Flash Pressure


Step 3: Evaluate Flash Tank

>If Inlet Specific Enthalpy is less than the Saturated Liquid Specific Enthalpy, only liquid leaves the flash tank at inlet specific enthalpy and flash tank pressure.
>If Inlet Specific Enthalpy is greater than the Saturated Gas Specific Enthalpy, only Steam leaves the flash tank at inlet specific enthalpy and flash tank pressure.
>If Inlet Specific Enthalpy is in between, proceed to Step 4

Step 4: Determine Flash Properties

Using an mass and energy balance equations:
  1. Mass Flow = MF
  2. Specific Enthalpy = SE
  3. Energy Flow = MF * SE
  4. Inlet Water MF = Outlet Gas MF + Outlet Liquid MF
  5. [Inlet Water MF * Inlet Water SE] = [Outlet Gas MF * Outlet Gas SE] + [Outlet Liquid MF * Outlet Liquid SE]
  6. Outlet Gas MF = Inlet Water MF - Outlet Liquid MF
  7. [Inlet Water MF * Inlet Water SE] = [(Inlet Water MF - Outlet Liquid MF) * Outlet Gas SE] + [Outlet Liquid MF * Outlet Liquid SE]
  8. [Inlet Water MF * Inlet Water SE] = [Inlet Water MF * Outlet Gas SE] + [Outlet Liquid MF * Outlet Liquid SE] - [Outlet Liquid MF * Outlet Gas SE]
  9. [Outlet Liquid MF * Outlet Liquid SE] - [Outlet Liquid MF * Outlet Gas SE] = [Inlet Water MF * Inlet Water SE] - [Inlet Water MF * Outlet Gas SE]
  10. [Outlet Liquid MF * (Outlet Liquid SE - Outlet Gas SE)] = [Inlet Water MF * (Inlet Water SE - Outlet Gas SE)]
  11. Outlet Liquid MF = Inlet Water MF * (Inlet Water SE - Outlet Gas SE) / (Outlet Liquid SE - Outlet Gas SE)
  12. Outlet Gas MF = Inlet Water MF - Outlet Liquid MF

Assumptions

  • Total Inlet and Outlet Mass flows are equal. No mass is lost or gained.
  • Total Inlet and Outlet Energy flows are equal. No energy is lost or gained.