Thermodynamic question: first law

In summary, to estimate the kilowatt pump needed to pump 450 L/min of liquid water at 20c through a rise in elevation of 100m, you can use the open system steady flow version of the first law. This equation takes into account the mass flow rate, change in specific enthalpy, and the work done by the pump. By inputting the given values, the answer should be -7.35kw.
  • #1
Superhawkkodaka
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Estimate the kilowatt pump you would need to pump 450 L/min of liquid water at 20c through a rise in elevation of 100m. Assume the water is pumped adiabatically and with negligible changes changes in temperature and kinetic energy.

answer given to us is -7.35kw..

Question.. what formula should i use?.. I am lost in this one.. please be specific guys.. I've used all i know and still can't get the answer..
 
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  • #2
Hints:

How much energy would it take to raise 1L (=1kg) up by 100m?
What is the equation that relates power, energy and time?
 
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  • #3
Superhawkkodaka said:
Estimate the kilowatt pump you would need to pump 450 L/min of liquid water at 20c through a rise in elevation of 100m. Assume the water is pumped adiabatically and with negligible changes changes in temperature and kinetic energy.

answer given to us is -7.35kw..

Question.. what formula should i use?.. I am lost in this one.. please be specific guys.. I've used all i know and still can't get the answer..
You are supposed to use the open system steady flow version of the first law:

##mΔh+mgΔz=Q-W_s##

where Ws is the rate of doing shaft work, m is the mass flow rate, and h is the specific enthalpy.

Chet
 
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  • #4
Chestermiller said:
You are supposed to use the open system steady flow version of the first law:

##mΔh+mgΔz=Q-W_s##

where Ws is the rate of doing shaft work, m is the mass flow rate, and h is the specific enthalpy.

Chet
weew thanks!
 

Related to Thermodynamic question: first law

1. What is the first law of thermodynamics?

The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only transferred or transformed from one form to another.

2. How does the first law of thermodynamics apply to heat and work?

The first law of thermodynamics states that the total energy of a closed system remains constant. This means that any heat added to a system must either be used to do work or increase the internal energy of the system.

3. What is an example of the first law of thermodynamics in action?

An example of the first law of thermodynamics is a car engine. The chemical energy in the gasoline is converted into heat energy, which is then used to do work by moving the pistons and powering the car.

4. Can the first law of thermodynamics be violated?

No, the first law of thermodynamics is a fundamental law of nature and cannot be violated. It has been proven to hold true in all physical processes.

5. How is the first law of thermodynamics related to the conservation of mass?

The first law of thermodynamics is closely related to the law of conservation of mass, which states that matter cannot be created or destroyed, only rearranged. The first law of thermodynamics includes the conversion of mass into energy, as seen in nuclear reactions, but the total amount of matter and energy in a closed system remains constant.

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