Refrigerant-134a at 400 psia has a specific volume of 0.1384 ft3/lbm. Determine the temperature of the refrigerant based on (a) the ideal-gas equation, (b) the generalized compressibility chart, and (c) the refrigerant tables.

Respuesta :

Answer:

a

The temperature based on ideal gas is T = 526 R

b

The temperature  based on compressibility chart  is T = 694 R

c

The temperature based on refrigerant tables is T = 700 R

Explanation:

From the mathematical relation of an ideal gas we can define the temperature of the Refrigerant-134a as follows

                [tex]T = \frac{Pv}{R}[/tex]

Where  [tex]P[/tex] is the pressure of the refrigerant  and given as  = 400 psia

            v is the volume of the refrigerant and it is given as [tex]= 0.1384 ft^3/lbm[/tex]

           R is the gas constant and has a value of [tex]0.1052\ psia \ \cdot ft^3/lbm \ \cdot R[/tex] for Refrigerant-134a

            Substituting values

               [tex]T = \frac{(400psia)(0.1384\ ft^3/lbm)}{0.1052 pais \cdot ft^3/lbm \cdot R}[/tex]

                 [tex]= 526 R[/tex]

Considering the generalized compressibility chart

  looking at table of molar mass, gas constants and critical-point properties.The temperature of Refrigerant-134a denoted by [tex]T_{cr}[/tex] is 673.6 R and the critical pressure of Refrigerant-134a is 588.7 psia

    Mathematically  the reduced pressure is

                     [tex]P_R = \frac{P}{P_{cr}}[/tex]

    substituting given and value obtained from table

               [tex]P_R = \frac{400psia}{588.7psia} =0.679[/tex]

The pseudo-reduced specific volume  is Mathematically given as

                  [tex]V_R = \frac{v_{actual}}{RT_{cr}/P_{cr}}[/tex]

 [tex]Substituting \ 588.7\ psia \ for \ P_{cr} \ 673.6\ R \ for \ T_{cr} \ 0.1052\ psia \ \cdot \ ft^3 /lbm \cdot R\\\\ \ for \ R \ 0.1384ft^3/lbm \ for \ v_{actual}[/tex]

               [tex]V_R = \frac{0.1384}{(0.1052)(673.6)/588.7} = \frac{(0.1384)(588.7)}{(0.1052)(673.6)} =1.15[/tex]

Now the value of pseudo-reduced specific volume and reduced pressure would gives us a pointer to select the correct value of reduced temperature([tex]T_R[/tex]) from the generalized compressibility chart

and this is 1.03 for [tex]T_R[/tex]

   Hence the temperature of the Refrigerant-134a

                 [tex]T = T_R T_{cr}[/tex]

         Substituting values

           [tex]T = (1.03)(673.6 R)[/tex]

              [tex]= 694\ R[/tex]

Considering the refrigerant tables

           looking at the table of super-heated Refrigerant-134a the temperature for a pressure of 400 psia and

specific volume of [tex]0.1384ft^3/lbm[/tex] is 240°F

   Converting to Rankine scales we add 460

              [tex]T = 240 +460 = 700\ R[/tex]

Given,

P=400 psia

V=0.1384 [tex]ft^3/lbm[/tex]

Part(a):

As we know,

[tex]T=\frac{PV}{R} \\=\frac{400\times 0.1384}{0.1052}\\T=526 R[/tex]

Part(b):

By using generalized compressibility chart:

[tex]P_{cr}=673.6R[/tex]

Reduced Pressure [tex](P_R)[/tex] then,

[tex]P_R=\frac{P}{P_{cr}}\\=\frac{400}{673.6}\\P_{cr}=0.679[/tex]

Part(c):

To calculate Pseudo-reduced volume[tex](V_R)[/tex] .

[tex]V_R=\frac{0.1384\times 588.7}{0.1252\times 675.6}\\=1.15[/tex]

Now, calculaing the temprature,

[tex]T=T_RT_{cr}\\=1.03\times 673.6\\=694 R[/tex]

Part(c):

By using refrigerant tables.

[tex]T=240F\\=460+240\\T=700R[/tex]

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