Partial 2-phase properties from separate liquid vapor properties

[takiyasamsama]

I need to find the properties of a stream which is in two-phase. I'm only given separate properties i.e. liquid and vapor properties. I need to find the enthalpy for the two-phase mixture from the liquid and vapor enthalpy. See the table below:

I would really like to know how do I find mixture properties i.e. density, thermal conductivity, specific heat, viscosity & enthalpy

 

[PaoloPemi]

for H (enthalpy) you can start from H(mixture) = H(vapor)+H(liquid)
with a similar expression for derivatives, cp = (dH/dT)p

the same for density, Density(mixture) = 1.0 / (Volume(vapor)+Volume(liquid))...

while for thermal conductivity, viscosity etc. you need mere elaborate expressions, see The Properties of Gases and Liquids or similar for details...

 

[takiyasamsama]

Hello PaoloPemi,

The H(mixture) = H(Vapor) + H(Liquid) as you mentioned; I got the calculated duty closed to the required duty.
I also tried another method which H(mixture) = [wt. fraction (vapor) x H(vapor)] + [wt. fraction (liquid) x H(liquid)] and I get really close duty to the required duty.

At first I also tried adding up the enthalpy but for different case sometimes I got duty which is way off from the required duty.

I needed to find the enthalpy mixture so that I could find the LMTD for a two-phase for a partial two-phase heat exchanger where one side is sensible heat (single phase) and the other side is latent heat (partial phase) then plotted T-h diagram for the process

 

[PaoloPemi]

it depends from the way you solve the flash operations, if you calculate specific enthalpies (for vapor and liquid phases) Ok for H(mixture) = [wt. fraction (vapor) x H(vapor)] + [wt. fraction (liquid) x H(liquid)],
I attach a (very basic) Excel page which calculates temperatures in diferent zones, but there are many similar examples...

 

[takiyasamsama]

PaoloPemi, you sir are very helpful. Thank you, I'll try your excel sheet and see the result.

Yes, basically (I think) I'm had to look for specific enthalpy because after I find the H(mixture) at specific temperature points, I had to make a cumulative enthalpy and from there multiply each cumulative enthalpy with mass flow to obtain required duty. Afterwards the program plot the T-h diagram with both streams and find its effective LMTD.