- #1
davehnc
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What equations should I use for an energy audit of an electromechanical system?
- Thread starter davehnc
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Discussion Overview
The discussion centers on selecting appropriate equations for conducting an energy audit of an electromechanical system. Participants are exploring various equations relevant to different stages of the audit process, including power calculations, potential energy, mass flow rates, and efficiency metrics.
Discussion Character
- Homework-related
- Technical explanation
- Exploratory
Main Points Raised
- One participant expresses difficulty in selecting the proper equations for each stage of the energy audit and requests specific equations for each part of the problem.
- Another participant provides equations used for various questions, including power calculations using real power and RMS values, potential energy calculations, and mass flow rates.
- For Q1, a participant suggests using RMS values of voltage and current for power calculations, noting that the provided diagram gives peak values.
- In Q2, a participant interprets the question as asking for the gain in gravitational potential energy, which aligns with the calculations presented.
- For Q4, there is a suggestion that the question may be looking for the rate of mechanical work done in lifting water, but there is uncertainty about the specific energy components involved.
- Another participant acknowledges the vagueness of the questions and expresses intent to continue with their current approach despite the lack of clarity.
Areas of Agreement / Disagreement
Participants do not reach a consensus on the appropriateness of the equations used, and there are differing interpretations of the questions and the required calculations. The discussion remains unresolved regarding the best approach to the energy audit.
Contextual Notes
There are limitations in the clarity of the questions posed, particularly regarding the definitions of terms like "specific energy" and the assumptions made in the calculations. The dependence on prior answers for subsequent questions adds complexity to the problem-solving process.
- #2
berkeman
Admin
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davehnc said:
Welcome to the PF.
Can you show the equations and your solutions for the parts that you have done so far?
- #3
davehnc
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Equations used so far
Q1: I USED EQUATION P/real=V*I*Cos ∅
P/real=340*4.24*Cos 45
P/real=1019.37 (W)
Q2:I USED EQUATION PE=MGH (mass of water =1000)
PE= 1500*9.81*10 (gravitity =9.81)
PE= 147150 (Joules)
Q3:I USED EQUATION Mass Flow= Mass/time
= 1500/480 ( 8mins =480 seconds)
= 3.125Kg/s
??Q4:1 USED EQUATION P=I*V
=4.24*340 OR should i of used Pout=Work done /time
= 1441.6 =147150/480
=306.56(watts)
??Q5 I WILL USE EQUATION Power out/Power in *100 to establish my efficency
Im not 100% that I've used the correct EQUATIONS , as each question draws on your previous answer , Any help would be appreciated. Thanks.
berkeman said:
Q1: I USED EQUATION P/real=V*I*Cos ∅
P/real=340*4.24*Cos 45
P/real=1019.37 (W)
Q2:I USED EQUATION PE=MGH (mass of water =1000)
PE= 1500*9.81*10 (gravitity =9.81)
PE= 147150 (Joules)
Q3:I USED EQUATION Mass Flow= Mass/time
= 1500/480 ( 8mins =480 seconds)
= 3.125Kg/s
??Q4:1 USED EQUATION P=I*V
=4.24*340 OR should i of used Pout=Work done /time
= 1441.6 =147150/480
=306.56(watts)
??Q5 I WILL USE EQUATION Power out/Power in *100 to establish my efficency
Im not 100% that I've used the correct EQUATIONS , as each question draws on your previous answer , Any help would be appreciated. Thanks.
Last edited by a moderator:
- #4
gneill
Mentor
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For Q1 I think you'll want to use RMS values of voltage and current if you're looking for power. The supplied diagram gives them as Peak values.
Q2 is a bit vague, asking for "The energy of liquid". presumably they mean the gain in gravitational potential energy as you've done it.
For Q4, I guess they're looking for the rate of mechanical work being done, since lifting the water is the 'output' of the system.
For the rest of the questions, I'm afraid that I'm not very familiar with the jargon or conventions involved in fluid/electromechanical system audits...
So, for example, I'm not sure what would be included in the 'specific energy' of the water leaving the pump; Does it include per unit volume kinetic energy and pressure? Gravitational potential energy too?
Q2 is a bit vague, asking for "The energy of liquid". presumably they mean the gain in gravitational potential energy as you've done it.
For Q4, I guess they're looking for the rate of mechanical work being done, since lifting the water is the 'output' of the system.
For the rest of the questions, I'm afraid that I'm not very familiar with the jargon or conventions involved in fluid/electromechanical system audits...
So, for example, I'm not sure what would be included in the 'specific energy' of the water leaving the pump; Does it include per unit volume kinetic energy and pressure? Gravitational potential energy too?- #5
davehnc
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Yeah, it is rather vague, but I'll motor on with what I've got... The questions seem to reflect on the answers to the previous ones... Thanks anyway D 
Last edited by a moderator:
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