Thermodynamics calculation: Flashing water at 75C

[Keeskwaak]

Homework Statement

need to figure this out and why

Relevant Equations

m = Q / (h_vap - h_liq)

Hello all,
For a project I really need to know some number i can't seem to produce myself.

we are flashing water @75 degrees Celsius, the water after flash-cooling is 67 degrees constant pressure is 0.27 bar (absolute) flow rate is 15000 KG/per hour.

how much water is vaporized?

Help is much appreciated

 

[berkeman]

Do you mean in a vacuum flash cooling system like this one?

https://www.dekkervacuum.com/flash-cooling/

 

[Keeskwaak]

Yes, though its i think somewhat bigger, it features a vacuum pump and a condenser to maintain a low pressure, Basic goal is oe eliminate dissolved oxygen and air bubbles, i need to figure out how much volume is lost

 

[Chestermiller]

What is the pressure before the flash, atmospheric?

 

[Keeskwaak]

What is the pressure before the flash, atmospheric?

Yes its almost atmospheric

 

[Chestermiller]

Applying the open system (control volume) version of the 1st law of thermodynamics and assuming an adiabatic flash, we have $$\Delta h=0$$
State 1: 1 kg liquid water at 75 C

State 2:
x kg saturate water vapor at 0.27 bar and 67 C
(1-x) kg saturated liquid water at 0.27 bar and 67 C

From the steam tables, what is the enthalpy of liquid water at 75 C and 67C?
What is the enthalpy of saturated water vapor at 67 C?

 

[Keeskwaak]

enthalpy for Liquid water @75C is 313.97, @67C is 280.45
the enthalpy of saturated water vapor at 67C is 2620.96

 

[Chestermiller]

enthalpy for Liquid water @75C is 313.97, @67C is 280.45
the enthalpy of saturated water vapor at 67C is 2620.96

So what is the parameter x equal to ?

 

[Keeskwaak]

I'm so sorry but I don't get it

 

[Chestermiller]

$$\Delta h=280.45(1-x)+2620.96x-313.97=0$$

 

[Keeskwaak]

but how does that work and how to translate it to 15000kg/h?

 

[Chestermiller]

but how does that work and how to translate it to 15000kg/h?

This tells you the fraction of water that is lost to vapor.

 

[Keeskwaak]

This tells you the fraction of water that is lost to vapor.

As much as i appreciate your help and answers, I still can't make the equation

 

[Chestermiller]

As much as i appreciate your help and answers, I still can't make the equation

x=0.014, so 1.4% of the liquid vaporizes.

 

[Keeskwaak]

x=0.014, so 1.4% of the liquid vaporizes.

I still cant make the equation but I see what you are doing, you make a energy balance.
Next question to make it more interesting: what if the water was milk? I don't know the Enthalpy numers for milk. but I do know the water in milk is 87%, and because the condensate is clear (mostly) is it safe to asume the water vapor will also be 87% of 1.4%?
The water inlet is 87% of 15000kg? or am i making a to short cut?

 

[Chestermiller]

I still cant make the equation but I see what you are doing, you make a energy balance.
Next question to make it more interesting: what if the water was milk? I don't know the Enthalpy numers for milk. but I do know the water in milk is 87%, and because the condensate is clear (mostly) is it safe to asume the water vapor will also be 87% of 1.4%?
The water inlet is 87% of 15000kg? or am i making a to short cut?

To be conservative, I would just use the 1.4%.

 

[Keeskwaak]

To be conservative, I would just use the 1.4%.

yes to be on the safe side, but that is no science

 

[Chestermiller]

yes to be on the safe side, but that is no science

Then go out and spend some money to do some VLE experiments on milk to get a 13% more accurate answer. Have you considered the effect off Jupiter's gravity on the system since "science" tells us that that might have some (tiny) effect too.

 

[Keeskwaak]

Then go out and spend some money to do some VLE experiments on milk to get a 13% more accurate answer. Have you considered the effect off Jupiter's gravity on the system since "science" tells us that that might have some (tiny) effect too.

Hi,
No pun and no disrespect intended, as I mentioned before: "Next question to make it more interesting", its just that.
i was not asking for a accurate answer, maybe just how someone else looks at this.