13 replies to this topic

[manni]

sir,can you tell me the method to find steam temperature if its pressure is given?

[Art Montemayor]

Manni:

This is very basic knowledge you are asking. What level of education are you presently in? - secondary school or University? If in University, what courses have you taken up to now?

I want to answer your query; but I don't want to confuse you or to fail to give you sufficient details.

[manni]

[
sir,
i m currently doin B.E in chemical.i was bit confused about this.so jus thought of posting here.

[Art Montemayor]

Manni:

I don't know what a "B.E in chemical" is. You have not answered my questions; therefore, my reply is based on assumptions as to your preparation and training.

When dealing with steam, you must always identify if you are dealing with:

a) Saturated Steam; or,
b) Superheated Steam.

The majority of Steam heating applications have to do with the Saturated phase and in this case all you need to identify all the thermodynamic properties of the vapor is either the temperature or the pressure. The pressure is usually the measurement employed since it is faster, more accurate, and more convenient.

Superheated steam requires two known properties (at least) in order to identify its thermodynamic properties.

In either case, you should always identify WHAT phase of steam you are dealing with - something that you failed to do in your query.

[manni]

ok sir lets assume it is a saturated steam...

[Art Montemayor]

Manni:

By your own response that the steam phase you are alluding to is "saturated", you have definitely identified the temperature of the steam by merely knowing its pressure. The saturated state of steam is well defined by the "humped" curve shown in the Mollier Diagram for steam. Any point on this curve represents the saturated state. The left portion (left of the critical point) is the saturated liquid state. The right-hand part is the saturated vapor state.

You should be familiar with (& dominate) the Mollier diagram if you are to proceed on to an engineering degree. This is very basic knowledge that you should have been taught if you are studying engineering in a recognized university. If your instructors have not taught you the principles of a steam system and its phase equilibria, then I have to conclude you have received a deficient education - which I hope is not true. You have not answered my direct questions, so I can only presume at this point.

[Pronab]

Try this formula:

T = 100 * (P)^1/4

T= Deg. C
P= bar
saturated steam only.
regards.

[Adriaan]

Go to http://www.cheresour...iapwsif97.shtml .....

[pawan]

Either ur question is incomplete or u r confused.
Nobody can tell U the 'Steam' Temperature just by its pressure, It can be anything.

[djack77494]

Either ur question is incomplete or u r confused.
Nobody can tell U the 'Steam' Temperature just by its pressure, It can be anything.

pawan,
For a system consisting of a single chemical compound (water) and two phases (liquid and vapor) the degrees of freedom are

df = c - p + 2 = 1 + 2 - 2 = 1

Therefore, if you specify the temperature OR pressure OR any other thermodynamic property, all others are fixed. Likewise, if you stated that you had water at its triple point (p=3), all thermo properties would be fixed - you needn't state any other property because all would be known. If you had a single phase (p=1), for example with superheated steam, then you would need to specify two, such as temperature & pressure, to have a determinate system.

[pawan]

Yes DJack
U r right but here U have assumed two phases while there is no mention of two phases in the original question.

If U assume something U eliminated few possibilities already.
Thats why I wrote

Nobody can tell U the 'Steam' Temperature just by its pressure, It can be anything.

[djack77494]

ok sir lets assume it is a saturated steam...

If it is saturated, that is equivalent to saying there are two phases (i.e. you are at a point where two phases could exist in equilibrium).

[katmar]

The formula given by pronab is actually a very useful one because you can calculate P^(1/4) very quickly by hitting the square root button on your calculator twice.

Remember that the pressure must be in bar absolute and that it only works for saturated steam.