Lesson test: Flow work and the energy equation

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Flow work and the energy equation

1.[2p]
Why does enthalpy rather than internal energy appear in the energy balance for a stream crossing a port?

The fluid behind must do work $p v$ per kilogram to push it across, and $u + p v$ is enthalpy

Correct

Enthalpy is the only property tabulated for flowing fluids

The answer is: The fluid behind must do work $pv$ per kilogram to push it across, and $u + pv$ is enthalpy

Internal energy is not a state function for an open system

The answer is: The fluid behind must do work $pv$ per kilogram to push it across, and $u + pv$ is enthalpy

Flowing fluid has kinetic energy, and enthalpy includes it

The answer is: The fluid behind must do work $pv$ per kilogram to push it across, and $u + pv$ is enthalpy

2.[2p]
Steam at $3$ MPa has $v = 0.09056$ m³/kg. What is the flow work per kilogram at that port, in kJ/kg?

CorrectNot quite: 271.7

3.[2p]
At a turbine exhaust the steam has $h = 2263.5$ kJ/kg, $p = 10$ kPa and $v = 12.71$ m³/kg. What is its internal energy, in kJ/kg?

CorrectNot quite: 2136.4

4.[2p]
The work term $\dot{W}$ in the steady-flow energy equation includes the flow work at the ports.

True

The answer is: False

False

Correct

5.[3p]
Steam enters a turbine at $h_{1} = 3116.1$ kJ/kg and $45$ m/s and leaves at $h_{2} = 2263.5$ kJ/kg and $200$ m/s, adiabatically. What is the work per kilogram, in kJ/kg?

CorrectNot quite: 833.6

6.[3p]
Which terms may usually be deleted from the steady-flow energy equation for a well-lagged turbine at pipe velocities?

Select all that apply

The heat transfer term

Correct

The potential energy term

Correct

The enthalpy difference

The answer is: The heat transfer term, The potential energy term

The shaft work term

The answer is: The heat transfer term, The potential energy term

7.[3p]
A compressor takes $0.50$ kg/s of air and raises its enthalpy by $293.5$ kJ/kg, while losing $15$ kW from its casing. What shaft power does it need, in kW?

CorrectNot quite: 161.7

8.[2p]
Match each velocity to its kinetic energy per kilogram, in kJ/kg.

45 m/s
100 m/s
200 m/s
450 m/s

20
101
5.0
1.01

Show the answer

45 m/s: 1.01 100 m/s: 5.0 200 m/s: 20 450 m/s: 101

9.[2p]
What can the steady-flow energy equation not tell you about a turbine?

How much work it will actually produce, since the exit state is an input rather than an output

Correct

How much mass passes through it

The answer is: How much work it will actually produce, since the exit state is an input rather than an output

The heat lost through its casing

The answer is: How much work it will actually produce, since the exit state is an input rather than an output

The enthalpy of the steam entering it

The answer is: How much work it will actually produce, since the exit state is an input rather than an output

1.[2p] Why does enthalpy rather than internal energy appear in the energy balance for a stream crossing a port?

2.[2p] Steam at 3 MPa has v=0.09056 m³/kg. What is the flow work per kilogram at that port, in kJ/kg?

3.[2p] At a turbine exhaust the steam has h=2263.5 kJ/kg, p=10 kPa and v=12.71 m³/kg. What is its internal energy, in kJ/kg?

4.[2p] The work term W˙ in the steady-flow energy equation includes the flow work at the ports.

5.[3p] Steam enters a turbine at h1=3116.1 kJ/kg and 45 m/s and leaves at h2=2263.5 kJ/kg and 200 m/s, adiabatically. What is the work per kilogram, in kJ/kg?

6.[3p] Which terms may usually be deleted from the steady-flow energy equation for a well-lagged turbine at pipe velocities?

7.[3p] A compressor takes 0.50 kg/s of air and raises its enthalpy by 293.5 kJ/kg, while losing 15 kW from its casing. What shaft power does it need, in kW?

8.[2p] Match each velocity to its kinetic energy per kilogram, in kJ/kg.

9.[2p] What can the steady-flow energy equation not tell you about a turbine?

1.[2p]
Why does enthalpy rather than internal energy appear in the energy balance for a stream crossing a port?

2.[2p]
Steam at $3$ MPa has $v = 0.09056$ m³/kg. What is the flow work per kilogram at that port, in kJ/kg?

3.[2p]
At a turbine exhaust the steam has $h = 2263.5$ kJ/kg, $p = 10$ kPa and $v = 12.71$ m³/kg. What is its internal energy, in kJ/kg?

4.[2p]
The work term $\dot{W}$ in the steady-flow energy equation includes the flow work at the ports.

5.[3p]
Steam enters a turbine at $h_{1} = 3116.1$ kJ/kg and $45$ m/s and leaves at $h_{2} = 2263.5$ kJ/kg and $200$ m/s, adiabatically. What is the work per kilogram, in kJ/kg?

6.[3p]
Which terms may usually be deleted from the steady-flow energy equation for a well-lagged turbine at pipe velocities?

7.[3p]
A compressor takes $0.50$ kg/s of air and raises its enthalpy by $293.5$ kJ/kg, while losing $15$ kW from its casing. What shaft power does it need, in kW?

8.[2p]
Match each velocity to its kinetic energy per kilogram, in kJ/kg.

9.[2p]
What can the steady-flow energy equation not tell you about a turbine?