Thermodynamics Tables: Pressure Conversion Explained

[bigu01]

Hello,

I've got a question about thermodynamics tables, in some tables pressure is given in bars and vf= a number times 10^3 , but in some tables the pressure is given in kPa and vf= a number times 10^-3 , how can this be explained, I do not get it.

Kind regards,

Astrit Imeri

ME student

 

[sanka]

It seems that you are just getting confused with your units. Pressure can be expressed in many different units but traditionally when dealing with steam, pressure is epressed in bar which is 10^5 pascals (or 10^5 N/m^2). So if you have a pressure of 60 bar in a given thermodynamics table, this is equivalent to 6000kPa. As for Vf (specific volume), this is simply the inverse of density so its units will be consistent with the density for the liquid phase or vapour phase. As a guess, I would say you are confusing your Vf with Vg. They usually differ by a few order of magnitudes.

 

[assaad]

to put it simply, since vf is the specific volume of the saturated liquid. On earth, no liquid has a vf in the order of 10^3 (m^3/kg). Check the units of vf and if they are in m3/kg. its just an error. I mean, give me a liquid on Earth which has a kilogram of mass and occupies 1000m^3 of volume.

 

[bigu01]

to put it simply, since vf is the specific volume of the saturated liquid. On earth, no liquid has a vf in the order of 10^3 (m^3/kg). Check the units of vf and if they are in m3/kg. its just an error. I mean, give me a liquid on Earth which has a kilogram of mass and occupies 1000m^3 of volume.

Well, where the pressure is in bars the vf is given on 10^3 m^3/kg , but when the pressure is given in kPa, the volume is given in 10^-3.However,in my university we are using the kPa, and when I am reading the tables I am taking vf= as 10^-3.I agree with the logic, I just was confused how could that be.

 

[Boldhawk]

Tables? Or Calculators...

I have had nothing but grief with Thermodynamic table...

Maybe someone can suggest a table that exists already. Or create one where many parameters can be changed by a user of the table...

I want to watch the progression of 10ml of water in a sealed container move from room temperature, to, say 300 C degrees, and want to see cumulative BTU's have had to be used as temperature/pressure increased, and see the cumulative expansion of the liquid. I think asking that in a table or calculator may already be too much. But I also would like to see how fast (in seconds?) a given amount of added water will go from room temperature into the container, already at say 300 C degrees, to reach the 300 C degrees.

Another quick question. Assuming 1ml of water upon becoming steam at 100 C, expands about 1600 times, what's the expansion progression as the temperature increases? I have the intuitive sense that at higher temperature the expansion is greater... and it is NOT linear.

 

[SteamKing]

It would help you case, Boldhawk, by posting your question in its own thread, and not hijacking another thread.