The gas expanding in the combustion space of a reciprocating engine has an initial pressure of 5 MPa and an initial temperature of 1623°C. The initial volume is 0.05 m^3 and the gas expands through a volume ratio of 20 according to the law PV^1.25 = constant. Calculate: a) Work transfer b) Heat transfer

Respuesta :

Answer:

a). Work transfer = 527.2 kJ

b). Heat Transfer = 197.7 kJ

Explanation:

Given:

[tex]P_{1}[/tex] = 5 Mpa

[tex]T_{1}[/tex] = 1623°C

                       = 1896 K

[tex]V_{1}[/tex] = 0.05 [tex]m^{3}[/tex]

Also given [tex]\frac{V_{2}}{V_{1}} = 20[/tex]

Therefore, [tex]V_{2}[/tex] = 1  [tex]m^{3}[/tex]

R = 0.27 kJ / kg-K

[tex]C_{V}[/tex] = 0.8 kJ / kg-K

Also given : [tex]P_{1}V_{1}^{1.25}=C[/tex]

   Therefore, [tex]P_{1}V_{1}^{1.25}[/tex] = [tex]P_{2}V_{2}^{1.25}[/tex]

                     [tex]5\times 0.05^{1.25}=P_{2}\times 1^{1.25}[/tex]

                     [tex]P_{2}[/tex] = 0.1182 MPa

a). Work transfer, δW = [tex]\frac{P_{1}V_{1}-P_{2}V_{2}}{n-1}[/tex]

                                  [tex]\left [\frac{5\times 0.05-0.1182\times 1}{1.25-1}  \right ]\times 10^{6}[/tex]

                              = 527200 J

                             = 527.200 kJ

b). From 1st law of thermodynamics,

Heat transfer, δQ = ΔU+δW

   = [tex]\frac{mR(T_{2}-T_{1})}{\gamma -1}+ \frac{P_{1}V_{1}-P_{2}V_{2}}{n-1}[/tex]

  =[tex]\left [ \frac{\gamma -n}{\gamma -1} \right ]\times \delta W[/tex]

  =[tex]\left [ \frac{1.4 -1.25}{1.4 -1} \right ]\times 527.200[/tex]

  = 197.7 kJ