Energy and first law thermodynamics help

civilengoo

Hey guys,
Have a thermodynamics exam coming in the next few days up based on the following topics. Energy and first law, Thermodynamic properties, First law: closed systems, First law: open systems/specific heat. When I have taken a look at the past exams it has been all calculations and therefore I won't need to worry about learning specific definitions. However, I'm having a really hard time getting my head around all of these questions and I literally have no clue where to start. Since the exam will be primarily calculation based (like the questions shown below) is there any process too going about these problems that will literally work for any question? I'll literally do anything if someone can fully teach me how to learn this stuff.
Thanks

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Chestermiller

Mentor
You need to do practice problems (after understanding the fundamentals outlined in your text). Are you saying that you don't know how to solve the two sample problems you showed?

jim hardy

Gold Member
2018 Award
is there any process too going about these problems that will literally work for any question?
Sure there is.

Draw a picture , or annotate the one they gave you.
"What parameters did they give me a number for?"
"What equation do i know that uses those parameters?"
Write those equations out with the numbers they gave you
and you'll see that whoever wrote the test question wants you to use the equations.

Both questions look easily solvable to me
first question gives volume and pressure of fluid and fraction of it that's vapor so you know masses of liquid and vapor, and from steam table their respective energy contents

second one gives a mass flow rate and temperatures hence rate of energy transfer, and you know energy is conserved,

so where's the problem?

old jim

civilengoo

You need to do practice problems (after understanding the fundamentals outlined in your text). Are you saying that you don't know how to solve the two sample problems you showed?
Yes, I have no clue the process of going about either of these problems.

civilengoo

Sure there is.

Draw a picture , or annotate the one they gave you.
"What parameters did they give me a number for?"
"What equation do i know that uses those parameters?"
Write those equations out with the numbers they gave you
and you'll see that whoever wrote the test question wants you to use the equations.

Both questions look easily solvable to me
first question gives volume and pressure of fluid and fraction of it that's vapor so you know masses of liquid and vapor, and from steam table their respective energy contents

second one gives a mass flow rate and temperatures hence rate of energy transfer, and you know energy is conserved,

so where's the problem?

old jim
I just have a hard time thinking of the respective equations I should be using, and what exactly the question is asking

berkeman

Mentor

At the PF, you are requred to post homework-type questions (including study questions) in the Homework Help forums, and not in the technical forums.

You are also required to post your best efforts at solving the problems. Just saying "I have no idea, teach me" is not allowed here.

Please repost one question at a time in the HH forums, and show the Relevant Equations and your best efforts at the solution. That is how you will do the best and learn the best as a student. Thank you.

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