Share
Explore BrainMass

Suraj Joshi - clarification required - wet steam properties

Suraj,

Firstly, thanks for your initial answer, and apologies for not rating it. I didn't realise I needed to rate it upon receipt, rather than when convenient.

If you could just clarify a couple of points relating to your answer though, we'll have another go at the rating bit.

(1) "At critical point of water, T= 647.1K, P = 22.064 MPa, v = 2.84 cc3/g"

T & P are fine, but where/how did you derive the value of V? If from steam tables, would it be possible to include a scan/link to the table in question?

(2) Dryness Fraction.

In the answer you provided, "v" was seemingly taken from values relating to water at Tc, whereas the other values (Vf & Vg) were taken from the values of water at 151 degrees.

Could you explain why you did this?

Also, is the dryness fraction a constant at both 374 degrees celcius and 151 degrees celcius? If so, why?

(3) "The internal energy is then given as: u = 2029 kJ/kg (approx.)"

Again, if using tables to derive the value of "u", could you enclose a scan/link? Alternatively, could you explain how to arrive at that value using the equation H = V + PV, (where H=Enthalpy, V=Volume & P=Pressure), that would actually be better.

(4) "Hence the total change in internal energy = mu = 2029*1 kJ = 2029kJ"

This one totally lost me! How does the change in internal energy = the value of "u"? Would there not be respective values for the two points cited in the question (Tc & 151 degrees celcius), the change being the difference between the value of "u" at both points?

Since I'm new to thermodynamics, the logic behind the answer is far more important than the answer itself.

Many thanks in anticipation of your response.

Attachments

Solution Preview

Please see attached file

Dear Student:
Thanks for your posting. Please read my responses in between the lines:

Firstly, thanks for your initial answer, and apologies for not rating it. I didn't realise I needed to rate it upon receipt, rather than when convenient.

If you could just clarify a couple of points relating to your answer though, we'll have another go at the rating bit.

(1) "At critical point of water, T= 647.1K, P = 22.064 MPa, v = 2.84 cc3/g"

T & P are fine, but where/how did you derive the value of V? If from steam tables, would it be possible to include a scan/link to the table in question?
I used the water properties available at the following URL:
http://www.connel.com/freeware/steam.shtml.
If you enter pressure as 220.64 bar in Situation 2 section and check appropriate radio buttons for units, you get all the properties. It shows specific volume of saturated liquid as: 2.838336 cubic centimeters per gram, which is the desired v (because ...

Solution Summary

The clarification required for wet steam properties are examined. The points and critical points are given.

$2.19