Mechanical Engineering Thermodynamics - Lec 23, pt 4 of 4: Example - Ideal Vapor-Compression

[@chrisperez7112]

Table A-12 is how you get h1, since in the problem it is stated that it is a Saturated Vapor, therefore you look at the table under 140 kPa and 800 kPa. By doing this you can find both Enthalpy and entropy. Correction, you do use the superheated tables but that is only for P2, where the line does show up outside of the saturated line. From there you interpolate to get h2 after assuming that S1=S2

[@ronhugo6225]

You use the superheated R-134a table at a pressure of 0.8 MPa. Knowing that the value of entropy at state 1 is equal to entropy at state 2 (3:25 in the video), this provides you with the value of entropy (s_2) at 0.8 MPa. You then interpolate for h_2 from the superheated table knowing s_2.

[@arnoldkazora9680]

Still unclear, kindly expound

[@mustafab83]

@@arnoldkazora9680 s1=s2 because isentropic device. we know that state 2 is in superheated region, therefore you lookup for s2 in 0.8MPa table and interpolate for h2.

[@shibaprasadb]

You are a legend sir!

[@adriprz_]

Haha how did you get H2 you don't have visual explanation.

[@Chess.Infinity]

why my h1 is differt form yours? how did you get that?

[@beef5030]

I think they're from the 410 table. For 134 at 140kpa x=1 I get 386 in my tables *nevermind, if your using Borgnakke and Sonntag Fundementals of Thermodynamics tables, they're different values on the lookup. Why I have no idea.

[@neetishneetishwaran4886]

hello sir ... i have trouble in finding h3 as the value in R-134a I used is way bigger than the value used in this video ... how to get 93.42 for h3... pls do help

[@hassannaser8863]

the problem with my superheated R-134a table is my pressure at .8mpa is not there. i got only pressure column for .6mpa and .10mpa

[@ronhugo6225]

You can still solve it, although it is a bit more work. You need to interpolate between the two states where you have information (0.6MPa and 1.0MPa) in order to determine values of entropy at 0.8MPa. With this you will be able to compute a value for T_2, from which you can determine h_2 - again by interpolating between the 0.6MPa and 1.0MPa data.

[@chandlerhaberlack4836]

for those having this same problem - google "how to interpolate table values thermodynamics" and you should get your answer. Pretty simple stuff once you do it a couple times.

[@axessoriiaxessorii7995]

Hey Ron, love your videos on thermodynamics, is there anyway I can message you for some help with some exam type cycle questions?

[@Arjun-ch2qb]

Really good video!

[@eslammohtady3045]

i cannot find h2 can you sir explain ?

[@tinytuny97]

Thank you so much

[@calm3337]

based on a P1 of 140 Kpa, and the fact that it is a sat. vapor why can you not find h1=approx 387 from the tables? All of your values for h and s are much lower than my tables even have?

[@beef5030]

I think he may have used R-410a instead of R134. I thought the same thing. *nevermind, if your using Borgnakke and Sonntag Fundementals of Thermodynamics tables, they're different values on the lookup. Why I have no idea.