2 replies to this topic

[krishnamurthy]

In PSV sizing for the fire case wetted wall we normally define the liquid outlet stream and we will put the heater and at the outlet of the heater we define the relieving pressure and the vapour fraction as 0.0001 (or)0.05 mole fractions.

 

I want to know why we define the vapour fraction as 0.0001 or 0.05 instead of putting 1.

 

Because i feel all the liquid quantity should become vapour so we should put 1 as vapour fraction at the heater outlet stream . But we are using 0.0001 as vapour fraction for the liquid tream after the heater for calculating the latent heat .

 

can u please explain why we need to use vapour fraction as 0.0001 to  calculate the latent heat instead of putting 1. Plz explain.

[oscarsender]

latent heat will be calculated using the enthalpy of vapor minus that of liquid. It means we need to simulate the enthalpy of both phase. If we specify vapour fraction as 1.0 (pure vapor) then obtaining the latent heat is impossible from simulation since it wont show the latent heat of liquid phase.

[Bobby Strain]

You must characterize the vapor rate and properties throughout the process until you are assured that you have defined the maximum orifice required.

 

Bobby