Liquid CO2 Specific Heat Capacity vs Temperature
Liquid CO2 Specific Heat Capacity vs Temperature
(OP)
Can anybody explain why liquid CO2 has such a temperature dependant heat capacity, especially at lower pressure (~1,000 psi - see attached graph)?
From the PVT diagram I don't see any phase changes at the peak heat capacities.
I am planning a job where we will be injection liquid CO2 into an oil well, but because of wellhead limitations, the CO2 needs to be heated before entering the well.
From the PVT diagram I don't see any phase changes at the peak heat capacities.
I am planning a job where we will be injection liquid CO2 into an oil well, but because of wellhead limitations, the CO2 needs to be heated before entering the well.





RE: Liquid CO2 Specific Heat Capacity vs Temperature
RE: Liquid CO2 Specific Heat Capacity vs Temperature
http://www.union.dk/media/CO2-GB.pdf
Engineering is the art of creating things you need, from things you can get.
RE: Liquid CO2 Specific Heat Capacity vs Temperature
There's better thermophysical properties data on the net from NIST here: http://webbook.nist.gov/chemistry/fluid/
RE: Liquid CO2 Specific Heat Capacity vs Temperature
Why the increase in heat capacity even at 2,000 psi?
RE: Liquid CO2 Specific Heat Capacity vs Temperature
However, there isn't any other distinction one can easily make between gas and liquid. Above the critical pressure, the molecules still act like liquid molecules and the fluid is relatively incompressible if cold enough, and the molecules act like gas molecules if they are very warm. But there's still an 'overlap' between the two phases such that as temperature decreases, the compressibility factor (Z) decreases meaning it becomes more and more incompressible (like a liquid). The closer you are to the critical pressure, the more distinct that transition is. Conversely, the farther you are away, the less distinct that transition is. So as pressure increases, the 'bump' in the line you see, becomes less distinct.
*Note in 'real life' there is rarely such a distinct separation. Generally, the liquid is subcooled in some areas and boiling in others while the gas is superheated in some areas and condensing in others.
RE: Liquid CO2 Specific Heat Capacity vs Temperature
The top edge is 120 bar (1740 psi). The spacing of the isotherms is proportional to the amount of heat required per unit temperature change (Cp). You can see this spacing is large in the 313 to 333K range resulting in the high Cp value.
Engineering is the art of creating things you need, from things you can get.
RE: Liquid CO2 Specific Heat Capacity vs Temperature
Best regards
Morten
RE: Liquid CO2 Specific Heat Capacity vs Temperature
At critical point specific heat reaches its absolute maximum. There are anyway pseudocritical points, characterized by pressure above the critical pressure and temperature above the critical temperature, exhibiting relative maximum values of the specific heat at this particular pressure.