Steam Basics - FAQ

Following are answers to many frequently asked questions about the basics of steam.

1. How do I calculate gauge pressure from absolute pressure?
Simply subtract the atmospheric pressure.

2. When I get into my car on a clear, cold winter day, the inside is pleasantly warm. What causes this?
A heat transfer method called radiation.

3. At atmospheric pressure, what is the relationship of the volume of steam to water?
The volume of steam is 1,600 times greater than an equal mass of water.

4. What does hot condensate form when released to a lower pressure?
When released to a lower pressure, hot condensate becomes flash steam.

5. Water at 10 psig (0.68 bar) boils at what temperature?
240 degrees F (116 degrees C).

6. Steam temperature is a direct function of what?
Steam temperature is a direct function of pressure in a system.

7. What causes steam to flow from the boiler to the connected piping?

8. As steam pressure increases, what happens to the heat of the saturated liquid?
The heat increases, as well.

9. What does increasing temperature indicate?
Increased molecular motion.

10. On a finned-tube heater, how does heat get from the tube to the fins?
By conduction.

11. We put insulation on steam pipes to reduce heat loss. What is the primary reason for the heat loss?

12. What is latent heat?
Latent heat is the amount of energy that must be added to change water at the boiling point to steam.

13. Is vapor rising off open water in winter an example of steam?

14. At a given pressure, does flash steam have less latent heat than boiler steam?

15. Does sensible heat increase the temperature of water?

16. What is the temperature of steam at 15 psig (1 bar)?
250 degrees F (121 degrees C).

17. As pressure rises, what happens to the density of saturated steam?
The density increases.

18. What is the latent heat of steam at atmospheric pressure?
970 Btu/lb.

19. What color is live steam?
Live steam is clear and colorless.

20. Condensate is discharged from 100 psig (6.9 bar) down to 50 psig (3.45 bar). What would be the latent heat of the flash steam?
911 Btu/lb (2119 kJ/kg).

21. What is the temperature of steam in degrees Fahrenheit and the latent heat of steam in Btu at sea level and atmosphereric pressure?
212 degrees F (100 degrees C) and 970 Btu (2256 kJ/kg), respectively.

22. Is steam pressure usually measured in absolute pressure?

23. In a 15 psi (1 bar) steam supply, how many Btu of latent heat do we have to do work?
945 Btu/lb (2198 kJ/kg).

24. If one pound (0.454 kg) of water rises in temperature 1 degree F (0.56 degrees C) , how much heat has been added?
1.0 Btu (1.055 kJ).

25. Expansion. Conduction. Convection. Radiation. Which of the four does not transfer heat?

26. Is it true that condensing is the change of state of matter from a gas to a solid, resulting from a loss of latent heat?

27. Does a thermometer indicate sensible heat, latent heat or total heat?
Sensible heat.

28. Can latent heat be measured with a thermometer?

29. Why is low-pressure steam preferred for many heating applications?
Low-pressure steam is often preferred because it has a higher latent heat.

30. As pressure rises, what happens to the specific volume of saturated condensate?
It increases because of rising temperature.

31. What is the advantage of providing steam at high pressure in the main lines?
High-pressure steam has a higher density, so pipes can be smaller.

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