The rate of evaporation at high temperatures

In summary, the conversation discusses the evaporation of 2 litres of water in a venting system to cool down the airflow. The equation for Langmuir evaporation rate is mentioned, but the individual is struggling to make sense of it. According to their calculations, it would take roughly 108 seconds for the water to evaporate, but they express doubt in this result. They wonder if anyone can advise on their approach and express surprise at the short amount of time it would take for the water to evaporate.
  • #1
UOP Student
2
0
To whom it may concern
I'm a University of Portsmouth student in the UK and have a conundrum for one of my projects. I'm trying to evaporate a reservoir of water at the bottom of a venting system to cool down the airflow in a gap between two membranes for a period of time. The reservoir is at the bottom of the void and the temperature of the air above the water is 360 degrees C. How long would it be for 2 litres of water to evaporate?
I have looked for a simple solution for this and have come across Langmuir evaporation rate but I'm struggling to make sense of it. If this the correct way forward?
According to my findings I need to use the equation
(mass loss rate)/(unit area)= (vapour pressure- ambient partial pressure)* sqrt((molecular weight)/(2*pi*Gas constant*temperature in Kelvin))
The Surface area (unit Area) of the water will be 0.1m²
the vapour pressure of water at 360 degrees C is 18666
the pressure at ambient (20degrees) is 2.3392
Molecular weight of water is 0.014kg/mole
Gas Constant (R) = 461.5 for water vapour
Temperature in kelvin = 360+273=633

Therefore this would mean through calculus that the rate of evaporation is 0.185 kg/m²/sec(3 d.p.). Meaning 2 litres of water with a surface area of 0.1m² and an air temperature above of 360C will evaporate dry in roughly 108 seconds.
This surely can not be right.
Can anyone advise on the errors of my ways?
Thank you in advance if you can.
 
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  • #2
UOP Student said:
Meaning 2 litres of water with a surface area of 0.1m² and an air temperature above of 360C will evaporate dry in roughly 108 seconds.
This surely can not be right.
"Surely" because of an observation, or "surely" because it just doesn't sound right? I would be surprised if water could hang around for too long so high above its boiling point. Unfortunately, my oven doesn't get that hot, so I can't test it. But perhaps I will see how long it takes for 2 L of water at 561 K (288 C) to boil away.
 
  • #3
Surely in the sense that this time seems far too short a time for 2 litres of water to last. Air entering the vent system is 20 degrees and the air 250mm up is 360. That figure seems just too quick to me.
 

FAQ: The rate of evaporation at high temperatures

1. What factors affect the rate of evaporation at high temperatures?

The rate of evaporation at high temperatures is affected by several factors, including the surface area of the liquid, the humidity of the surrounding air, and the strength of the air currents. Higher surface area allows for more molecules to escape, while higher humidity slows down the process. Strong air currents also help to remove water molecules from the surface, increasing the rate of evaporation.

2. How does temperature impact the rate of evaporation?

Temperature plays a crucial role in the rate of evaporation. As temperature increases, the average kinetic energy of the liquid molecules also increases, causing them to move more quickly and escape into the air as gas. This results in a higher rate of evaporation. Additionally, higher temperatures also lower the relative humidity of the surrounding air, creating a larger gradient for water molecules to escape.

3. Can the rate of evaporation continue to increase with higher temperatures?

No, the rate of evaporation will eventually reach a maximum value even with increasing temperatures. This is because the liquid will eventually reach its boiling point, where the vapor pressure equals the atmospheric pressure. At this point, the rate of evaporation will not increase any further, regardless of the temperature.

4. How does pressure affect the rate of evaporation at high temperatures?

High pressure can inhibit the rate of evaporation at high temperatures because it increases the boiling point of the liquid. This means that the vapor pressure must be higher to match the atmospheric pressure, making it more difficult for molecules to escape into the air. This results in a lower rate of evaporation compared to when the liquid is under lower pressure.

5. What is the significance of understanding the rate of evaporation at high temperatures?

Understanding the rate of evaporation at high temperatures is important in various applications, such as in industrial processes, weather forecasting, and the study of climate change. It can also help in the development of materials and technologies that can withstand high temperatures and promote efficient evaporation processes.

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