Rate of evaporation and steam tables

In summary, the conversation discusses the amount of heat needed to bring water to its boiling point and turn it into steam in an open boiler. The rate of steam generation remains constant as long as the heat supply is constant. The amount of heat required also depends on the starting temperature of the water.
  • #1
jankod
2
0
Looking at the steam table below, if I understand things correctly, it will take 419kJ to bring a kg of water to the boil at 100°C and a further 2257kJ to turn all of that boiling water into steam.

I assume that would have to be in an open boiler, as the pressure inside of a closed vessel would increase, in turn increasing the boiling point of the water.

But in the simple case of an open boiler, does the rate of steam generation (as in kg/s or m3/s) remain constant during the time it takes to boil away that water?

From the table, I would deduce that 210kJ would bring 0.5kg of water to the boil and a further 1128kJ would evaporate all of it, but does that mean 1128kJ would evaporate half of 1kg of boiling water?

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  • #2
The amount of heat required to raise water to its boiling point depends on the starting temperature. The value you gave is for water starting out at 0 C. Once you reach the boiling point, the rate of steam generation is constant if the rate at which you are supplying heat to the boiler is held constant. Otherwise, it will vary in proportion to the rate of heat supplied.
 
  • #3
Yes, that does make sense the more I think about it. Thanks.
 

1. What is the rate of evaporation?

The rate of evaporation refers to the speed at which a liquid changes into a gas. It is affected by factors such as temperature, humidity, and air flow.

2. How is the rate of evaporation measured?

The rate of evaporation can be measured by calculating the amount of liquid that has changed into a gas over a specific period of time. This is typically done by weighing the liquid before and after evaporation and calculating the difference.

3. What are steam tables and how are they used?

Steam tables are a set of data tables that provide information on the properties of water and steam at various temperatures and pressures. They are used to determine the characteristics of steam, such as temperature, pressure, and enthalpy, which are important in many industrial and scientific applications.

4. How do steam tables help in understanding the rate of evaporation?

Steam tables provide information on the properties of steam at different temperatures and pressures, which are important factors in the rate of evaporation. By using steam tables, scientists can calculate the rate of evaporation of water based on its temperature and pressure.

5. How does altitude affect the rate of evaporation?

Altitude can affect the rate of evaporation due to changes in atmospheric pressure and temperature. As altitude increases, the atmospheric pressure decreases, which can lead to a higher rate of evaporation. Additionally, lower temperatures at higher altitudes can also affect the rate of evaporation by slowing down the movement of water molecules.

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