For a steady-flow control volume device, the following statement is valid. The v

Question

For a steady-flow control volume device, the following statement is valid. The volume of the control-volume remains constant although the mass and the total energy change with time. The properties such as temperature and pressure must be uniform (identical) throughout the space of the control volume The mass, the volume and the total energy of the control-volume remains constant during the steady-process. No mass transfer across the boundary of the control volume. For nozzles and diffusers, the following statement is valid For throttling salves, the following statement is valid Refrigerant-134a (Tows through a pipe at 800 kPa and 50 degree C. The specific flow work required to move this fluid through a cross-section of the pipe is: 22.84 kJ/kg 31.60 kJ/kg 37.21 kJ/kg 40.70 kJ/kg Helium gas is heated steadily by a 3 kW electric resistance heater as it flows through an insulated duct. If helium enters at 50 degree C at a rate of 0.08 kg/s and the specific heat of helium can be considered as constant, the exit temperature of helium will be: 50.6 degree C 57.2 degree C 62.0 degree C 71.9 degree C 112.0 degree C Oxygen can be considered as an ideal gas. The C, value is 1.035 kJ / kg K. Please find the values of the following properties

Explanation / Answer

1) for 1 option (c) is the correct answer as the rate at which mass,energy enters the control volume is = to the rate at which these properties leave the control volume.

Energy,mass remains constant.

2) for 2 option (c) is correct as for a nozzle and diffuse Q = W = P.E. = 0

but velocity changes.    K.E. 0

3) for qts 3 option (c) is correct as throttling is an isenthalpic ptocess

H = 0

4) here at P= 800 Kpa H_g = 263.86.3 KJ/Kg and at T = 50 C H = 286.7KJ/Kg

   work required = (H - Hg) = (286.7 - 263.86) = 22.84 KJ/Kg

option (a) is correct.

5) Q =m. Cp . (T2 -T1)

3000 = 0.08 x 5193 (T2 - 50)

T2 = 57 C

option (b) is correct

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