ENTC 370: Announcements

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ENTC 370 Announcements

• Homework assignments No. 2
• Assigned Problems
• 2.4, 2.12, 2.20, 2.26, 2.38, 2.44, 2.61, 2.98.
• Due next Tuesday, September 16th before 1050 am
• For more information, go to
• http//etidweb.tamu.edu/classes/entc370

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Heating Process of Water at Constant Pressure
SHV
CL
SV
SL
MX
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States for Water and Refrigerants
P is independent of T T is independent of P
Compressed Liquid (CL)
Saturated (SL or f)
Saturated States Only one Psat for the
corresponding Tsat only one Tsat for the
corresponding Psat (Tsat ? Psat)
Mixture (MX or between f and g)
Saturated Vapor (SV or g)
P is independent of T T is independent of P
Superheated Vapor (SHV)
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Example

• A rigid tank contains 50 kg of saturated liquid
  water at 90 C. Determine the pressure in the
  tank and the volume.

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Example

• A piston-cylinder device contains 2 ft3 of
  saturated water vapor at 50 psia. Determine the
  temperature and the mass of the vapor inside the
  cylinder.

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What should I do if I do not find the exact
values in the Tables?

• Example
• Psat 115 kPa, what is Tsat?
• Interpolation is required
• Property 1 Property 2
• A X
• B Y?Unknown value
• C Z

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Interpolation
Then, solve for Y
You will use interpolation many times in this
course!
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Example

• A mass of 200 g of saturated liquid water is
  completely vaporized at a constant pressure of
  100 kPa. Determine (a) the volume change and (b)
  the amount of energy added to the water.

hfg is called the enthalpy of vaporization (or
latent heat of vaporization). Represent the
amount of energy per unit of mass at constant
pressure.
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The two-phase region for water
MX
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Saturated Liquid-Vapor Mixture (MX)

• During vaporization part liquid-part vapor
• Quality of Steam

x 0.0 (saturated liquid) 0.0 lt x lt 1.0
(mixture) x 1.0 (saturated vapor)
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Quality defined
P and T remain constant during phase change
process
Quality, x, allows location of states inside the
vapor-liquid region.
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Example

• A rigid tank contains 10 kg of water at 90 C.
  If 8 kg of the water is in liquid form and the
  rest in the vapor form, determine (a) the
  pressure in the tank and (b) the volume in the
  tank.

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Example

• An 80 L vessel contains 4 kg of R 134-a at a
  pressure of 160 kPa. Determine the temperature,
  quality (x), enthalpy and volume occupied by
  vapor phase.

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Superheated Vapor

• Single phase Pressure and Temperature are no
  longer dependent properties

SHV
SHV
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Superheated Vapor

• Superheated vapor (SHV) is characterized by
• P lt Psat at a given T
• T gt Tsat at a given P
• v gt vg at a given T or P
• u gt ug at a given T or P
• h gt hg at a given T or P

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Table A-6
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Example

• Determine the internal energy of water at 20 psia
  and 400 F (Hint Use table A-6E)
• Determine the temperature of water at a state of
  P 0.5 MPa and h 2890 kJ/kg

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Compressed Liquid (CL)

• Variation of properties with pressure is very
  mild (Table A-7)
• Approximation
• Compressed Liquids Saturated Liquids
• Good approximation for specific volume (v) and
  internal energy (u). For enthalpy (h)
• h hf_at_T vf_at_T(P Psat_at_T)

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Compressed Liquid (CL)

• Compressed liquid is characterized by
• P gt Psat at a given T
• T lt Tsat at a given P
• v lt vf at a given T or P
• u lt uf at a given T or P
• h lt hf at a given T or P

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Example

• Compressed liquid water at 80 C and 5 MPa.
  Determine the internal energy using compressed
  liquid table, and saturated liquid data. What is
  the error involved by using saturated liquid
  data? Hint Table A-7 and A-4.

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Determine Properties by Using H2O Tables
Legend CL Compressed Liquid SL Saturated
Liquid MX Mixture SV Saturated Vapor SHV
Super Heated Vapor