The discussion revolves around calculating pressures in a system containing liquid water and air, particularly focusing on the effects of temperature changes on vapor pressure and total pressure in a closed jar. The subject area includes thermodynamics and gas laws.
The discussion is active with various approaches being considered, including the use of polytropic processes and the impact of temperature on pressures. Participants are questioning assumptions about the system and exploring the relevance of liquid water density in their calculations.
There are assumptions regarding the negligible change in the volume of liquid water, and participants note the limitations of the precision of their inputs, suggesting that the density of liquid water may not significantly affect the results.
Why do you need to use a polytropic process? This is an equilibrium problem.dbag123 said:what about using the polytropic process to figure out the partial pressure of the dry air at 1 atm?, the increase would be 0.3375 bar and that is the right answer, initial temperature is 90C
You need to assume that the change in the volume of liquid water is negligible.dbag123 said:in a jar that has an airtight lid there is water. Temperature is raised to 120C, from 90C, where the pressure of water vapor is 0,7 bar and the air 1 atm and as a result the pressure of the water vapor is 1,99bar. Calculate the partial pressure of dry air and the total pressure.
One could account for the density of the liquid water. However, since liquid water is approximately 1000 times as dense as steam at 2.0 bars, one might expect such an accounting to affect the result only in the third significant digit. The inputs here look to be good to only two digits at best.Chestermiller said:You need to assume that the change in the volume of liquid water is negligible.