Calculating Mass Flow Rate: Inlet & Outlet

The difference between them is the change in energy while the flow is in the system. In summary, the problem involves an inlet and outlet with specific data such as average velocity, pressure, elevation, tube diameter, and water density. The goal is to calculate the mass flow rate through the pump and determine the required rate of shaft work input with 85% efficiency at an outlet pressure of 300 kPa. The mass flow rate should be calculated based on the given data, and the conservation of energy should be applied to determine the change in energy while the flow is in the system.
  • #1
Sabacca6
1
0

Homework Statement



Inlet
Average Velocity at Inlet = 2.50 m/s
Pressure Abs. = 100 Kpa
Elev = 2.00 m
Inlet tube diameter 12.0 cm
Water density 997 kg/m^3

Outlet
Average velocity at outlet = 8.00 m/s
Elevation = 2.00m

a.) Calculate mass flow rate through the pump
b.) w/ an outlet pressure of 300 kPA what is required rate of shaft work input has 85% efficiency?

Homework Equations



m'=pVA

The Attempt at a Solution



My attempt was to just average the two Ave. velocities and plug into mass flow equation, not correct as I got no points on the HW. Part b.) I could not complete I would think it would involve calculating the change in mechanical, potential, and flow work and then multiplying kW by efficiency super frustrated. please help!
 
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  • #2
Sabacca6 said:
1.

The Attempt at a Solution



My attempt was to just average the two Ave. velocities and plug into mass flow equation, not correct as I got no points on the HW.


Not a good idea. Compute the mass flow based on input data. Mass flow out in unit time must be the same as mass flow in, must it not?
Part b.) I could not complete I would think it would involve calculating the change in mechanical, potential, and flow work and then multiplying kW by efficiency super frustrated. please help!

Conservation of energy! What is the energy of 1 sec. worth of flow at the input & at the output.
 

Related to Calculating Mass Flow Rate: Inlet & Outlet

1. What is mass flow rate?

Mass flow rate is the amount of mass that passes through a given point in a system per unit time. It is typically measured in kilograms per second (kg/s) or other units of mass per unit time.

2. How do you calculate mass flow rate?

Mass flow rate can be calculated by dividing the mass of a substance passing through a given point by the time it takes to pass through that point. The formula is: mass flow rate = mass / time. The units of mass flow rate will depend on the units used for mass and time.

3. What is the difference between inlet and outlet mass flow rate?

Inlet mass flow rate refers to the amount of mass entering a system through an inlet. Outlet mass flow rate refers to the amount of mass leaving a system through an outlet. Inlet and outlet mass flow rates may be equal if there is no accumulation of mass within the system, but they can also be different if there is a change in mass within the system.

4. How is mass flow rate affected by changes in pressure and temperature?

Mass flow rate is directly proportional to pressure and temperature. This means that an increase in pressure or temperature will result in an increase in mass flow rate, and a decrease in pressure or temperature will result in a decrease in mass flow rate. This relationship is described by the ideal gas law, which states that as pressure and temperature increase, the volume of a gas will also increase, resulting in a higher mass flow rate.

5. What are some applications of calculating mass flow rate?

Calculating mass flow rate is important in many different fields, including engineering, physics, and chemistry. Some specific applications include determining the amount of fuel needed for a rocket to reach a certain altitude, measuring the flow rate of liquids or gases in industrial processes, and monitoring the flow of blood in medical procedures.

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