How to Read Steam Tables - 5 Interpolation Example Problems

This Thermodynamics interpolation tutorial provides 5 Example Problems to show how to do Linear Interpolation. How to read steam tables (the vapor and liquid tables in textbook appendices) will help you find pressure, temperature, specific volume, internal energy, enthalpy, and entropy.
All problems show how to interpolate manually, and 1 example shows how to do double interpolation. The type of property table linear interpolation performed in this video will be used throughout your entire Thermodynamics course, as well as follow-up technical electives.
TIMECODES
0:00 Steam Table Introduction
0:58 Example 1 - Find Quality
3:06 Example 2 - Vertical Interpolation
5:40 Example 3 - Given v, Find h, without finding x
7:42 Example 4 - Double Interpolation
10:26 Example 5 - Superheated Vapor

[@mouten5532]

Doctor Bernard how do we find the enthalpy of a steam that has a temperature of 25°c and a pressure of 100 kpa

[@BrianBernardEngineering]

With both Temp and Pressure given - probably not saturated (only need 1 for saturated), but I go to saturated first to confirm whether it's Superheated Vapor or Subcooled Liquid. Since 100 kpa is 1 bar, I check the Pressure table, and see that Saturation Temp at 1 bar is 100C. 25

[@fatimazahraanouar8571]

@@BrianBernardEngineering thank you doctor we all apreciiate

[@BrianBernardEngineering]

@@fatimazahraanouar8571 Your welcome, and it really is my pleasure.

[@AJCook-on1in]

Great video thanks for the straight forward explanation. This 13 minute video helped more than an hour lecture.

[@BrianBernardEngineering]

I'm glad you liked it. You've perfectly described my goal in creating this and other videos on my channel - edit down lengthy lectures as short as they can be so that you still learn the concepts. I'm glad that it seems to be working.

[@JoshuaTsai-ru6bg]

Thank you, super useful especially at the interpolation part !

[@BrianBernardEngineering]

Ah yes, the interpolation part ... wait a sec ... that's the whole thing!

[@maloryknoxx666]

Doctor Bernard, great video, cleared up a few things. I'm taking thermo now and was wondering if there is a chart with all the info needed to find what state water is in with given values? My notes are all over the place. Like you said, if the question wants quality, you know it's liquid-vapor mix. The text book is ok but I'm trying to find something that has everything I need in one place. Btw, I'm posting this video for my classmates. Our professor did not address interpolation so a lot of people are very confused. Thank you!

[@BrianBernardEngineering]

Unfortunately, there's no single chart. Water has 3 charts (subcooled or compressed liquid, liquid-vapor mix, and superheated vapor). My recommendation is to just always check the liquid-vapor mix chart first. Suppose you know temperature - go to the temperature liquid-vapor chart. Then, to determine whether you are in the right place, or if you should go down to subcooled or up to superheated, use your next piece of data. If you have pressure - compare your given pressure to the saturation pressure at your given temperature. If your pressure is too high - it's compressed liquid because high pressure is compressing it so much. If your pressure is too low, superheated gas, low pressure expands like a gas. You can do similar if you have enthalpy or specific volume too. If your specific volume is off the chart high, even higher than the saturated gas - you'll move up to the gas table. If your enthalpy is off the chart too low, below the saturated liquid value, then you know you need to shift to the liquid table. To sum up: if you aren't sure of the phase - start in the liquid-vapor mixture table since that one is in the "middle". Check the numbers there, and if you are below the saturated liquid, move to the liquid tables. If you are above the saturated vapor values, move up to the gas tables.

[@KaranJadhavBEE]

Very helpful! Thanks you

[@BrianBernardEngineering]

You're welcome!

[@bedyyy3222]

Thank you! I do appreciate this video especially when my prof in school do not teach that much lol

[@BrianBernardEngineering]

It's useful to view college from your own perspective - you learning - and not from the prof's perspective - them teaching. Your education is about you, not the teacher. When you view it that way, your professor is just another tool for you to use, not that different from a textbook or youtube channel or any other resource you use to learn. If one resource (professor) isn't helping you as much as you need, then you need to learn using your other resources. I'm glad I was able to be a supplementary resource for you to use to help you teach yourself.

[@nanikorthurthi1188]

thank you sir

[@BrianBernardEngineering]

I'm glad to help.

[@DurianDragonStew]

Doctor Bernard I calculated specific volume of superheated R-134a @120kpa,353K to be 0.243535 by your method, but It wasn't right. It has to be 0.23669, I want to know how to get the answer.

[@BrianBernardEngineering]

I get the same answer as you. 120kpa is halfway in between .10mpa and .14mpa, so I take the average of the 80deg C v value on .10mpa and 80deg C value for v on the .14mpa table, and average them. Technically we should maybe interpolate since 353k is actually 79.85 C, not 80, but this will only change like the 3rd or 4th decimal probably, not nearly as big a difference as you are seeing. That .23669 is very close to the answer I get if the temperature were 70deg C - so I'd first double check that the problem doesn't actually ask for 343K not 353k. Otherwise, I think you are solving this problem correctly, and think that there may be a typo in the problem or solution that generated the .23 value.

[@alexandrealferan7144]

Nice

[@BrianBernardEngineering]

Thanks

[@peterwilliams8911]

Sir in the superheated steam tables, when the given pressure falls in between the smaller tables, can you use any number from each table at a given temperature and interpolate between them? For example you used the v's at 120 deg C but could you also have used the volumes at 280 deg C and get the same answer?

[@BrianBernardEngineering]

Yes, you can use whichever 2 pieces of information you have, and compare the corresponding values in each adjacent mini-table

[@nhaz652]

Hi, thanks for ur video! At timestamp @5:29 , may I check that you did cross multiplication? I got a different value for this. Please help. thanks!

[@BrianBernardEngineering]

Good catch, the .0198 in the denominator should have a negative sign in front of it. I described this in words as I was speaking, but must have forgot to write it down. The final answer is correct though.

[@adarshtiwari5355]

Hlw sir Is your channel for mechanical engineering

[@BrianBernardEngineering]

Yes, that's exactly right. If you check my channel page, you'll see content for Engineering Graphics, Statics, Mechanics of Materials, Thermodynamics, Fluid Mechanics, Design of Machinery - all part of the mechanical engineering degree.

[@cerquiglini6513]

PUT THE TABLE ONLINE PLEASE

[@BrianBernardEngineering]

If you only need metric units, then Claire Yan has a free online Thermodynamics book with tables included, pressbooks.bccampus.ca/thermo1/ . If a pdf is ok, I prefer Thermodynamics for Engineers by Robert Brown which you can find at github.com/robertbrown2/ThermodynamicsForEngineers . It also has steam tables in the back, and they are very well formatted. Only metric units though.