Hi,
I'm trying to make a dynamic (time dependent) model in excel of The pressure and temperature (liquid phase) in a tank during a constant volume gas outtake and a constant heat flow into the tank.
At t0 the tank contains both liquid CO2 and gaseous CO2. Temp=10 deg C and pressure 51 Bar
(1) At any time t the relation of CO2 in gasous form and liquid form are given by a function stating that the total density of CO2 in the tank must equal a mass fraction (x) of the density of liquid and (1-x) of gas.
Further
I’ve relation between pressure and temp (assume that they are in eq)
I’ve a function for densities (gas and liquid) as a function of pressure
At each time t a certain mass of CO2 leaves the tank (m’ out). (1) gives me the change of mass CO2 in liquid form from t-1 to t. (m’_vap) this is the amount that has boiled of during t to t-1
I assume the temperature decrease in the liquid phase comes from the vaporization of liquid only.
Hence the delta temperature change from t-1 to t would be
The energy loss due to evaporation of a m’_vap plus the energy added to the system divided by Cp (liquid CO2) and the total mass of liquid CO2
Excel must be put in “integration mode” in order for this to work of course but the collation freaks out after a couple of time steps.
I assume that my approach is wrong somehow since there seem to be many solutions for the set of equations used. I also have a CO2 add in for excel with most thermodynamic data and with these I’ve tried to solve this problem in a similar way but I get the same problem.
I’m looking forward to your ideas of how to solve such problem in excel.
I’ve attached a spreadsheet with my calculation. It’s the change in temperature that make to model freak out with change some parameters.
I'm trying to make a dynamic (time dependent) model in excel of The pressure and temperature (liquid phase) in a tank during a constant volume gas outtake and a constant heat flow into the tank.
At t0 the tank contains both liquid CO2 and gaseous CO2. Temp=10 deg C and pressure 51 Bar
(1) At any time t the relation of CO2 in gasous form and liquid form are given by a function stating that the total density of CO2 in the tank must equal a mass fraction (x) of the density of liquid and (1-x) of gas.
Further
I’ve relation between pressure and temp (assume that they are in eq)
I’ve a function for densities (gas and liquid) as a function of pressure
At each time t a certain mass of CO2 leaves the tank (m’ out). (1) gives me the change of mass CO2 in liquid form from t-1 to t. (m’_vap) this is the amount that has boiled of during t to t-1
I assume the temperature decrease in the liquid phase comes from the vaporization of liquid only.
Hence the delta temperature change from t-1 to t would be
The energy loss due to evaporation of a m’_vap plus the energy added to the system divided by Cp (liquid CO2) and the total mass of liquid CO2
Excel must be put in “integration mode” in order for this to work of course but the collation freaks out after a couple of time steps.
I assume that my approach is wrong somehow since there seem to be many solutions for the set of equations used. I also have a CO2 add in for excel with most thermodynamic data and with these I’ve tried to solve this problem in a similar way but I get the same problem.
I’m looking forward to your ideas of how to solve such problem in excel.
I’ve attached a spreadsheet with my calculation. It’s the change in temperature that make to model freak out with change some parameters.
