Varannan månad ger SteamTeam Nordic tillsammans med vår samarbetspartner TLV ut ett kortare e-magazine där vi lyfter fram och diskuterar vanliga problem som våra kunder stöter på i sina ång -och kondensatsystem.
I den här utgåvan tar vi en närmare titt på den mycket användbara, men kanske svårtolkade, ångtabellen! Mer information finner ni nedan.
How to Read a Steam Table
Steam tables are indispensable tools for any engineer working with steam. Reading them, however, can be a challenge. This edition of the Steam Bulletin will explain some of the trickier aspects, and test your knowledge of steam tables with quizzes! You’ll find the answers to the quiz questions at the bottom of this email.
Before you start reading, you may want to get your saturated steam table ready!
What do ”f” and ”g” represent?
The data found in a saturated steam table always refers to steam at a particular saturation point, also known as the boiling point. This is the point where water (liquid) and steam (gas) can coexist at the same temperature and pressure. Because H2O can be either liquid or gas at its saturation point, two sets of data for specific volume are required: data for saturated water (liquid), which is typically marked with an ”f” in subscript, and data for saturated steam (gas), which is typically marked using a ”g” in subscript.
Latent, sensible, or total?
There are three categories of data for specific enthalpy: ”hf”, ”hg”, and ”hfg”.
”hfg” refers to ”latent heat”, the heat energy that is absorbed by steam when it changes from liquid into vapor at a constant temperature. It is the ”hidden” heat within steam that is imparted on the product in an indirect heating process.
”hf” is the ”sensible” heat; the heat that, when exchanged, changes the temperature of the body. Saturated water contains only sensible heat, and so will change temperature in a heat exchange.
”hg” is the ”total heat” contained within saturated steam. Steam contains both latent and sensible heat energy, so hg is the sum of saturated steam’s latent and sensible energy.
Absolute or gauge?
Care should be taken when reading a steam table regarding whether the pressure data displayed is ”absolute” or ”gauge” pressure.
Absolute pressure is zero-referenced against a perfect vacuum, while gauge pressure is zero-referenced against atmospheric pressure (101.3 kPa, or 14.7 psi).
If your steam table shows absolute pressures, be sure to add atmospheric pressure to any gauge values before using the table.
For more information…
… on how to read steam tables, read the Steam Theory article, ”How to Read a Steam Table”.
The TLV Toolbox® app for iOS and Android makes using steam tables on your mobile device easy! TLV Toolbox® also features over 50 useful calculations for steam systems. Download it free today!
Quiz Answers: 1. B), 2. C), 3. C)
We hope you enjoyed this edition of Steam Bulletin.
Previous editions of Steam Bulletin are available by accessing the Archive Page.
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