Vapor Pressure in Condensing Steam System

In summary, the individual is asking for clarification on measuring vapor pressure and provides their scenario of conducting steam condensation measurements in a vacuum. They explain that they initially let in steam at atmospheric pressure, then trap it in a closed system and introduce air flow. As the temperature of the steam decreases, the pressure also reduces until reaching the ambient air temperature. The individual asks if at this point, there is a vapor-water interface in equilibrium and if recommencing the steam flow would increase the pressure.
  • #1
sanka
52
3
Hi all,

Just have a quick question regarding the measurement of vapor pressure.

Firstly, let me explain my scenario. I am carrying-out some measurements of steam condensation in a vacuum. The steam is being condensed in a air-cooled heat exchanger.
Initially, I let in a quantity of steam (at atmospheric pressure) into my heat exchager. I then close off the inlet & exit valves to trap a quantity of steam in the heat exchanger (creating a closed system) and commence the air flow. Thus there is a fixed mass of steam in my heat exchanger. The energy from this steam is transferred to the surrounding air flow and eventually, the temperature of the steam (vapor) decreases until it reaches the ambient air temperature. With no air leaks occurring, the pressure I measure also reduces to the saturation pressure for that given ambient temperature.

Firstly, am I right in assuming that at this point I have a vapor-water interface in my heat exchanger, which is in equliibrium (rate of evaporation=rate of condensation) at the given ambient temperature? Once the system has reached steady-state of course?

Secondly, if I recommence the steam flow into the system, I see that the pressure I am measuring increases...why is this? Should the steam entering the system not be under a vacuum and have a temperature and pressure determined by the ambient air temp?

Thanks for any help
 
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  • #2
Multiple posts with the same topic in different forums is discouraged.

Check the General Physics section for my reply.
 

1. What is vapor pressure?

Vapor pressure is the measure of the pressure exerted by a vapor in equilibrium with its liquid phase at a given temperature. It is the force exerted by the molecules that have escaped from the liquid and entered the gas phase.

2. How is vapor pressure calculated?

Vapor pressure can be calculated using the Antoine equation, which takes into account the temperature and properties of the substance. It is also determined experimentally by measuring the pressure of the vapor above the liquid at different temperatures.

3. What factors affect vapor pressure?

Temperature and intermolecular forces are the main factors that affect vapor pressure. As temperature increases, so does vapor pressure, since more molecules can escape into the gas phase. Stronger intermolecular forces result in lower vapor pressure, as more energy is needed to overcome these forces and escape into the gas phase.

4. How does vapor pressure relate to boiling point?

Vapor pressure and boiling point are inversely related. As vapor pressure increases, so does the likelihood of a substance boiling. When vapor pressure equals atmospheric pressure, the substance will reach its boiling point and begin to boil. Therefore, substances with higher vapor pressures tend to have lower boiling points.

5. What is the significance of vapor pressure in everyday life?

Vapor pressure is important in many industrial and household applications, such as in the production of fuels, pharmaceuticals, and food products. It also plays a role in weather patterns, as water vapor in the atmosphere exerts a significant vapor pressure and can lead to precipitation. Understanding vapor pressure can also help in the design and maintenance of storage containers to prevent leaks.

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