Knowing when to go by pressure and when to go by temp

[alberto23]

I'm taking a 300 level introductory course to thermodynamics (i am a mechanical engineering major). I am having trouble using the tables, such as knowing when to go by pressure and when to go by temp, etc. i know a lot of this just comes with experience. but i was wondering if there was a flowchart or something on the internet that laid out the process. our exams are open-notes so it would really help. Thanks!

 

[mathmike]

where are u going to school

 

[asdf1]

i have the same problem too! :P

 

[HeartbreakidX]

Yeah dude it is tricky
But remmember you at least need two properties to locate your self in the tables, you must use the preassure tables if they give you preassure and temperature.
If they give you temperature then you use temp tables, but they need to tell you where are you located (mixture region, sat liq, sat vap, compress liq, or superheated liq)

 

[alberto23]

yes

that is exactly the kind of info i need!

most of the other students in my class have the solutions manual, but i chose to do all my homework myself. i usually look up the final answer in the back of the book before i start each problem. so i know when i have the right answer. i just don't seem to be able to remember the process very well when it comes test time.

 

[Astronuc]

Sounds like the good old steam tables.

In general,

If P > P_sat or T < T_sat, then one has compressed liquid.

If P < P_sat or T > T_sat, then one has superheated steam or vapor.

There is off-course when T is above the critical point - supercritical steam.

Under saturated conditions, one needs to determine the quality.

See if this helps - http://www.engineersedge.com/thermodynamics/table_contents.htm

Become familiar with P-T, P-v and P-v-T diagrams, and perhaps the Mollier diagrams.

 

[morry]

Can you give us some examples of questions you are unsure of?

The tables I use are pretty straightforward. The only tricky bit is interpolation, which is a bit of a hassle. If you keep having a go, youll get it pretty quickly.