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Refrigerant-134a enters an adiabatic compressor at 100 kPa and –24°C with a flow rate of 1.25 m3/min and leaves at 800 kPa and 60°C. Determine the mass flow rate of R-134a and the power input to the compressor. Use data from the steam tables. Heat transfer with the surroundings is negligible. Neglect kinetic and potential energy changes.

Respuesta :

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  • The mass flow rate is m = 0.107 kg / s.
  • The power input is W = 6.47 kW.

Explanation:

  • The mass flow rate is determined by the inlet volume flow rate and specific volume from given pressure and temperature using interpolation.

                                  [tex]m =[/tex]  [tex]\frac{V_{1} }{\alpha_{1} }[/tex]

                                       = ((1.25 / 60) / 0.19473)

                                  m = 0.107 kg / s

  • The power input to the compressor is determined from the energy balance where the enthalpy were obtained for given pressure and temperature.

                               [tex]m[/tex][tex]h_{1}[/tex] + W = [tex]mh_{2}[/tex]

                                         W = [tex]m(h_{2}- h_{1} )[/tex]

                                              = [tex]\frac{V_{1} }{\alpha_{1} } (h_{2}- h_{1} )[/tex]

                                              = ((1.25 / 60) / 0.19473) (296.82 - 236.34) kW

                                        W  = 6.47 kW.

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