TODAYS LESSON IN PHYSICS: THE RELATIONSHIP BETWEEN STEAM PRESSURE AND TEMPERATURE

Source: Ware Inc.

When water molecules heat up, they attain kinetic energy. The more they are heated, molecules eventually reach velocities great enough to break the surface of the water and become steam.

Steam is the heart of industry. It’s powerful. It holds incredible amounts of energy; energy which has been harnessed by ancient civilizations and by the technologically advanced culture we live in today.

The relationship between steam pressure and steam temperature are critical in understanding the energy in the steam that a boiler produces. The relationship is quite simple in all reality, what is not simple is striking the perfect balance between pressure and temperature to provide the best steam solution for a customer. Don’t panic, I know a guy, who knows a guy, who knows a boiler company that can help you! *Cough, Cough, HSI, Cough*

The higher the pressure of a boiler the more heat must be applied to make steam. With the increased pressure, you in turn get steam at higher temperatures. Higher temperature steam contains more energy per pound, which is known as Enthalpy.  Enthalpy is defined as the thermodynamic potential made up of energy and pressure. In the US, its common unit of measurement is BTUs/Lb.  So, if the pressure on a boiler is greater, the BTU/Lb of steam will also be greater.

To sum all of that up: higher boiler pressure = hotter steam = more energy per pound of steam

Now what does all of this mean in the real world? How do these relationships effect dollars and cents? Very little is free in this world, and the same is true here. Typically if a boilers pressure is higher, more material is needed to help the boiler withstand the heat necessary to generate the steam. More material means more dollars. Don’t panic yet, there is some good news!

Let’s break down a few real world examples:

Boiler A 600 psig

  • At 600 psig the temperature of your steam would be 486.38 F
  • At 600 psig your enthalpy is 1203.68 btu/lb

Boiler B 300psig

  • At 300 psig the temperature of your steam would be 416.68 F
  • At 300 psig your enthalpy is 1202.85 btu/lb

The good news is that Boiler B, though it is half the pressure of Boiler A, still contains almost as much enthalpy or btu/lb. In a real world example, Boiler B would typically be less cost to the customer without sacrificing much in the way of energy contained within each pound of steam produced.

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If you are reading this, you probably have an interest in steam. You are also probably the kind of person who would be interested in the nH2O app. This app allows you to see firsthand, the relationship between steam pressure and steam temperature. Interested?Download it here.

Ware Inc. is a great resource for more information.  We highly suggest you subscribe to their newsletter.

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