Troubleshooting Units in Energy Balance Problem

  • Thread starter Xyius
  • Start date
  • Tags
    Units
In summary, the problem is dealing with energy balance and involves water flowing through a nozzle. The specific energy and kinetic energy equations are used, but the book uses a conversion factor of 25037 to convert from BTU/lbm to ft2/sec2. The reason for this conversion is not clear, but it could be due to the units being in English instead of metric.
  • #1
Xyius
508
4
I do not want to post the entire homework problem as I understand all of it except this one part.

The problem deals with energy balance and it states that water is flowing through a nozzle. (From a bigger cross sectional area to a smaller one.) I am trying to calculate the energy of the kinetic energy but my book does something weird to me.

The problem is in English units. (Very annoying!) The kinetic energy of a fluid would be..
[tex]\frac{1}{2}mv^2=[Btu][/tex]
So the specific energy should be..
[tex]\frac{1}{2}v^2=[\frac{Btu}{lbm}][/tex]

In the book they do the following..
[tex](\frac{1}{2}v^2)(\frac{1[Btu/lbm]}{25037 [ft^2/s^2]})[/tex]

That 25037 is throwing me for a loop. Why do I need this conversion? I thought KE was already in the correct units?

My assumption is that it is similar to metric units since KE is in Joules and normally you want it in KJ. Seems like I am just ignorant of English units. Can anyone shed some light on this?
 
Physics news on Phys.org
  • #2
It's just a conversion factor.

[tex] 1 \frac{BTU}{lbm} = 25037 \frac{ft^2}{s^2} [/tex]

So they're converting from BTU/lbm to ft2/sec2 for whatever reason (no doubt made clear by what then follows).
 

FAQ: Troubleshooting Units in Energy Balance Problem

What is the purpose of troubleshooting units in an energy balance problem?

The purpose of troubleshooting units in an energy balance problem is to ensure that all units of measurement used in the problem are consistent and accurate. This is important because using incorrect units can lead to incorrect calculations and ultimately, incorrect solutions.

Why is it important to convert units when troubleshooting an energy balance problem?

Converting units is important because different units of measurement may be used for the same quantity in different equations. In order to have a consistent and accurate solution, all units must be converted to a common unit.

What are some common units used in energy balance problems?

Some common units used in energy balance problems include joules (J) for energy, watts (W) for power, kilograms (kg) for mass, meters (m) for distance, and seconds (s) for time. Other units may also be used depending on the specific problem.

How can I check if my units are correct in an energy balance problem?

You can check if your units are correct by performing dimensional analysis, which involves checking that the units in your equations cancel out to give you the correct units for your final answer. You can also use unit conversion factors to ensure that all units are consistent.

What should I do if I encounter inconsistent units in an energy balance problem?

If you encounter inconsistent units, you should convert all units to a common unit and double check your calculations to ensure accuracy. If the problem still persists, you may need to review your understanding of unit conversions and seek assistance from a mentor or colleague.

Back
Top