Question about gas leak engineering units

In summary, the engineering units used in gas leak specifications are Pressure (P) x Volume (V) / Time (t). Pressure x Volume reduces to Energy (see, for example, the Ideal Gas Law, which is an energy balance equation: PV = nRT) and Energy / Time is Work or Power.
  • #1
MichaelY
1
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I have a somewhat mundane question that I hope somebody can help me with. I am working with several standards for performing leak testing on hermetically sealed electronics packages using helium bombing. The question I have is about the engineering units used in the leak test specifications. Both the NASA Leakage Testing Handbook (NASA CR-952) and the Nondestructive Testing Handbook - Leak Testing, 3rd Edition, published by the American Society for Nondestructive Testing indicate that the units to be used for specifying a gas leak are Pressure (P) x Volume (V) / Time (t). Pressure x Volume reduces to Energy (see, for example, the Ideal Gas Law, which is an energy balance equation: PV = nRT) and Energy / Time is Work or Power. This being the case, I would expect the units for a gas leak specification to be in terms of Power (Watts or other Power units). Instead, in every standard I have seen, the units are left in their unreduced form such as Atmosphere-Cubic Centimeters per Second, Pascal-Cubic Meters per Second, or Millibar-Liters per Second. To add to the confusion, some standards employ the abbreviation STD to indicate a leak rate at some "standard", sometimes unstated, conditions. An example of this would be STD cm^3 / sec. In this case they seem to have dropped the units of Pressure since, I am assuming, the Pressure is defined as part of the standard conditions (STD). Anyway, bottom line, I am looking for an explanation as to why unreduced engineering units are universally used in gas leak standards.
 
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  • #2
the reason might be that most measurements relate to the rate of flow of gas, such as the increase in concentration over time measured by a concentration-based sensor , or calculated from the ultrasonic sound signature of a leak, so an unreduced expression is more directly 'usable' without any calculations needed... the pressure should have already been known inside the pressurized chamber, and it is unlikely that a gas leak investigator will need to know the power output as a result of the gas leak, unless the gas is being mechanically used i.e. pneumatic system leaking leading to power loss, etc
 
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  • #3
Torr-liters per second is equivalent to mass flow per second. For example, since 22.41 liters of helium at 760 mm is 4 grams, 1 torr-liter per second of helium is 2.3 x 10-4 grams per second.
 
  • #4
Just saw this post and no nothing about this topic...but, I just wanted to say that sometimes units for certain quantities are given a set of units different from their reduced form just to be able to tell them apart. Or, like carmatic says, just to have them ready for their use in a rather practical manner...easy mental operation, easy look up tables, etc.

For example...what do you get when you multiply volts and amps?

Well, I am an electrical engineer and when it comes to generators, there are 3 popular quantities that have the same fundamental units, yet, they are given 3 different units just so that we know what we talking about...

Apparent Power
Real Power
Reactive Power

they are all powers and bascially volt-amperes or (mega volt-amperes), yet, we talked about them in units of

MVA mega volt-amperes
MW mega watts
MVAR reactive MVAs

so, sometimes it is just a convenience thing and that's it.
 
  • #5


Thank you for your question about gas leak engineering units. As you have correctly pointed out, the units used in leak testing specifications are often left in their unreduced form, such as Atmosphere-Cubic Centimeters per Second or Pascal-Cubic Meters per Second. This can be confusing, especially when considering the ideal gas law and its relationship between pressure, volume, and energy.

The reason for this is that leak testing is typically performed under a specific set of conditions, known as "standard conditions." These conditions include a defined pressure, temperature, and humidity, among others. In order to accurately measure and compare leak rates, it is important to keep all of these conditions constant. By leaving the units in their unreduced form, we are able to account for any changes in these conditions and still accurately measure the leak rate.

Additionally, using unreduced units allows for easier comparison between different leak testing methods and equipment. Different methods may have different sensitivities and may be used under different standard conditions. By keeping the units in their unreduced form, we are able to compare and evaluate these methods more easily.

The use of the abbreviation "STD" to indicate standard conditions is also common in leak testing standards. As you mentioned, this is often left unstated, but it is important to clarify these conditions when reporting leak rates.

In summary, the use of unreduced engineering units in gas leak standards allows for accurate and consistent measurement of leak rates under standard conditions, and allows for easier comparison and evaluation of different leak testing methods. I hope this explanation helps to clarify any confusion about the units used in leak testing specifications.
 

1. What units are used to measure gas leaks in engineering?

The most commonly used units for measuring gas leaks in engineering are parts per million (PPM), liters per hour (LPH), and cubic feet per minute (CFM). PPM is the most sensitive unit and is typically used for small leaks, while LPH and CFM are used for larger leaks.

2. How are gas leaks typically detected in engineering?

Gas leaks in engineering are typically detected through the use of gas detection instruments such as gas detectors, gas sensors, and gas analyzers. These instruments measure the concentration of gas in the air and can alert engineers to the presence of a leak.

3. What is the acceptable level of gas leaks in engineering?

The acceptable level of gas leaks in engineering varies depending on the specific industry and type of gas. However, in general, any gas leak should be taken seriously and addressed as quickly as possible to prevent potential hazards and damage.

4. How do engineers determine the severity of a gas leak?

Engineers use a variety of methods to determine the severity of a gas leak, including measuring the concentration of gas in the air, calculating the potential impact on human health and safety, and assessing the potential damage to equipment and the environment.

5. Can gas leaks be prevented in engineering?

While it is impossible to completely eliminate the risk of gas leaks in engineering, there are several measures that can be taken to prevent them. This includes regular maintenance and inspections of equipment, proper training for employees, and implementing safety protocols and procedures.

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