Refrigerant-134a enters a diffuser operating at steady state as saturated vapor

Question

Refrigerant-134a enters a diffuser operating at steady state as saturated vapor at 800 kPa with a velocity of 120 m/s, and it leaves at 900 kPa and 40 degree C with a velocity of 60 m/s. The refrigerant is gaining heat at a rate of 2.5 kW as it passes through the diffuser. Determine the mass flowrate, in kg/s. How much larger than the inlet is the exit? 1.47 kg/s, 82.4% An insulated, vertical piston-cylinder device initially contains 10 kg of water, 6 kg of which is in the vapor phase. The mass of the piston is such that it maintains a constant pressure of 200 kPa inside the cylinder. Now steam at 0.5 MPa and 360 degree C is allowed to enter the cylinder from a supply line until all the liquid in the cylinder has vaporized. Determine the mass, in kg, of the steam that has entered. 19.45

Explanation / Answer

at 800 Kpa, enthalpy = 415.78 KJ/Kg

cpecific volume = 0.02513 m^3/Kg

c1 = 120 m/s

at 900 Kpa and 40 C, enthalpy = h2 = 422.3 KJ/Kg

C2 = 60 m/s

and specific volume = 1.76 m^3/Kg

so, m.h1 + c1^2/2 = m.h2 + c2^2/2 + Q

so, m x 415.78 + 120^2/2000 = m x 422.3 + 60^2/2000 + 2.5

so, mass flow rate = m = 1.48 kg/s

b) inlet area = m/(120 x 0.02513)

and outlet area = m/(60 x 1.76)

so % more = ( m/(120 x 0.02513) - m/(60 x 1.76) ) / m/(120 x 0.02513)

= 82.41 %

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