4 replies to this topic

[ktrone]

What does the entropy indicate in steam Table?

I mean to say
Example:
At temperature 15 degree centigrade the absolute pressure is 0.01704 and specific entropy for water is 0.224 kJ/kg K.

then at temp 20 degree centigrade the absolute pressure is 0.02337 and specific entropy for water is 0.296 kJ/kg K.

I want to understand the practical meaning of sp. entropy, when studied at different temperature and pressure.

[Art Montemayor]

Ktrone:

We always have the same difficulties with students. But that’s OK. That’s why you are a student and why I know that you are mixed up and having difficulties writing what you are thinking.

Let’s start with the basics. What is your present academic background? This is important – especially if you want to discuss entropy and thermodynamics.

You are making basic, first-year engineering mistakes by not even telling us the units of your pressure data – so I must assume you have just entered your first thermodynamics class. Am I correct?

Why do you use the term “specific entropy”? Has this been taught to you or have you originated it?

I am attaching an Excel workbook with thermodynamic data on water at two temperatures: 15 oC and 20 oC. Both tables have a range of pressures which I had to assume since you didn’t tell us exactly and correctly the pressure that you mean. Note that I have identified the entropy value of the condition of the water that I think you mean.

Please respond with all of your relative background that will help us understand your level of knowledge and also tell us all the specifics about what is troubling you and what it is that you want to know. Be specific, concise, and accurate - especially about your thermodynamics knowldege. We can't teach you thermo; we can only assist you in understanding it. Therefore, if you don't do your homework and learn your lectures and textbooks, there is little hope you will understand what entropy is and what role it plays in engineering.

Await your reply.
 Thermo_Properties_of_Water.xls   898KB   43 downloads

[riven]

Higher temperature has the higher entropy: why?

Very simple entropy is a measure of disorder. At higher temperaure a molecule vibrates more than it would at lower temperatures. It exhibits more disorder and therefore a higher entropy.

[ktrone]

Respected Sir,

I'm very happy that you have understood my basic problem, I'm first year chemical engineering student, I did big mistake by not mentioning the units.
I always approach any subject by practical way, I try to take the basic understanding even when it is in more complexed form, that gives me the insight of concept.

For example:What do we mean by Joules?
For me the answer would be when 100 gram of apple is lifted by one meter up,we would spend energy of one joule.This is the way I understand the concepts.

Now my question is what does the term entropy mean when it comes to steam?
Since the entropy deals with randomness or disorder in the system , then how to correlate with the steam.If enthalpy deals with the energy of the steam at specified temperature and pressure,then what about entropy.

I hope you could understand this question with the vast experience you have.

Thank you for time and assistance.

[Patrician]

For example:What do we mean by Joules?
For me the answer would be when 100 gram of apple is lifted by one meter up,we would spend energy of one joule.This is the way I understand the concepts.

Are you sure its "100g of apple lifted by one meter up"?

Things to do:
Learn the book and then ask you question precisly.
Do not memorize it, understand it.