Refrigerant R134a flows steadily at a mass flow rate of 2 kg/s through a well-in

Question

Refrigerant R134a flows steadily at a mass flow rate of 2 kg/s through a well-insulated nozzle with a circular cross-section. The refrigerant enters the nozzle at 500 kPa, 30 C, 25 m/s and exits at 100 kPa. a) Determine the largest possible outlet velocity and the corresponding outlet temperature. b) If the outlet velocity is 250 m/s, determine the outlet temperature, isentropic nozzle efficiency, rate of entropy production in the nozzle, and the inlet and outlet diameters. Neglect changes in potential energy.

Explanation / Answer

the pressure are P1 = 500 kPa and P2 = 100 kPa

let A1 and A2 be the entering and leaving areas

let the velocities be v1 = 25 m/s and v2

the force on the fluid is

F = (dm/dt) x v1

we know that

(P1 - P2) = F/A2

or A2 = (F/P1 - P2)

Also,

A1 x v1 = A2 x v2

or v2 = (A1 x v1/A2)

let the temperatures be T1 = 30 oC and T2

we know that

(P1/T1) = (P2/T2)

or T2 = P2 x (T1/P1)

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