Calculate pressure inside closed container

[Bartbol]

A small container is filled with water (30ml). Next it is heated at 140°C. I need to determine the internal pressure caused by the heating process.

The containers dimensions:
height : 100mm
Diameter: 39 mm
Volume= circa 0,0203 m³

First thing I did was to look it up at steamtables. For saturated steam at 140°C it corresponds to 0,3616 kPa.

Now I was wondering how to bring the volume of the container in consideration. Intuitive I thaught, that an increase of volume of the container results in a decrease of pressure inside the container. So I was wondering how I could take the volume of the container in account with the data from the steamtables (I'm stuck at this point).

I hope someone can help me on the way!

kind regards

 

[Chestermiller]

A small container is filled with water (30ml). Next it is heated at 140°C. I need to determine the internal pressure caused by the heating process.

The containers dimensions:
height : 100mm
Diameter: 39 mm
Volume= circa 0,0203 m³

First thing I did was to look it up at steamtables. For saturated steam at 140°C it corresponds to 0,3616 kPa.

Now I was wondering how to bring the volume of the container in consideration. Intuitive I thaught, that an increase of volume of the container results in a decrease of pressure inside the container. So I was wondering how I could take the volume of the container in account with the data from the steamtables (I'm stuck at this point).


I hope someone can help me on the way!

kind regards

The pressure would have to be higher than the equilibrium vapor pressure so that it could stay a liquid. The liquid would tend to thermally expand, so the pressure would have to be high enough to compressively offset the thermal expansion (and maintain the volume constant). If there were initially head space in the container, however, this would change everything.

 

[Bartbol]

Well, there is a head space in the container. The container is filled approximately 1/3 with water, before the heating process starts. Is it correct to say that the absolute pressure is 3,6154 bar at 140°C, just reading the steam table (see attachment) ? Or am I wrong here ?

 

[Chestermiller]

Well, there is a head space in the container. The container is filled approximately 1/3 with water, before the heating process starts. Is it correct to say that the absolute pressure is 3,6154 bar at 140°C, just reading the steam table (see attachment) ? Or am I wrong here ?

You're absolutely correct. Just a small fraction of the liquid would have to evaporate to achieve this pressure in the vapor phase.
Chet

 

[rezeew]

Hello,

Calculating the pressure inside a closed container is an important step in understanding the behavior of gases and liquids under different conditions. In this case, we can use the ideal gas law to determine the internal pressure caused by the heating process.

The ideal gas law states that the pressure of a gas is directly proportional to its temperature and the number of moles of gas present, and inversely proportional to its volume. In this case, we know the temperature of the water inside the container (140°C) and the volume of the container (0.0203 m³). We also know the number of moles of water in the container, which can be calculated using the molecular weight of water (18.01528 g/mol) and the mass of water in the container (30 ml).

Using the ideal gas law equation (PV = nRT), we can rearrange it to solve for pressure (P). This gives us the equation P = (nRT)/V, where P is the pressure, n is the number of moles, R is the universal gas constant (8.314 J/mol·K), T is the temperature in Kelvin, and V is the volume.

Plugging in the values we have, we get P = (0.001667 mol)(8.314 J/mol·K)(413.15 K)/(0.0203 m³) = 346.5 kPa. This is the pressure inside the container at 140°C.

It is important to note that this calculation assumes that the container is completely sealed and there is no change in the number of moles of water or the volume of the container during the heating process. If there is any leakage or evaporation of water, the pressure inside the container may be different.

I hope this helps you understand how to calculate the pressure inside a closed container. If you have any further questions, please let me know. Best of luck with your research!