Absolute Pressure vs. Gauge Pressure in Steam Turbine Condensers

Absolute pressure - gauge pressure = constant = 14.7 psi = 101.3 kPa

OK PWSlack,

How very astute of you (that's me rolling my eyes).

Please allow me to amend:

Absolute pressure - Gauge pressure at standard atmospheric pressure = constant = 14.7 psi = 101.3 kPa.

Happy now?

Mike

This discussion, and your reply got me thinking again about seeing advertising for handheld elevation meters:

http://www.holidaytechnologies.com/pdf/Ramsey%202008%20catalog.pdf

With a swing of 32.0inHg to 25.7inHg in atmospheric pressure (lowest and highest barometric pressures recorded, respectively), this corresponds to, at standard atmospheric pressure, -600m to 1250m. How can elevations be calculated with any certainty, seeing the amount of atmospheric pressure swing? For aircraft, I'm thinking they get barometric telemetry from ground stations nearby and can compensate with the pressure readings of the aircraft.

In this case, how can they compensate for the weather effects to get an accurate elevation?

This question is not just for PWSlack, but for anyone who has info about this.

Mike

I have no information specific to the use of a hand held altimeter but I can tell you that as part of flight prep I would dial-in (or key-in) a barometric reading provided by the national weather service and would update this setting based on information from tower communication in route. I would assume the same method would work for a hand held altimeter (national weather info you can obtain on the cell phone). Two other comments. Newer flight instruments may receive telemetric data to automatically adjust in flight. Second, a hand held GPS unit would accomplish the same thing by actually triangulating your position on the globe including your distance above sea level.

Sorry, but there's no question mentioned above...

The question is implied in the subject. I'm getting better myself at recognizing that some who post here use English as a second language and some times the subject is as good a question as you will get from them. Of course they are to be commended for their effort as some like me (English is all I know) have not mastered a second language and I am impressed with their effort.

An ABSOLUTE pressure gauge reads from zero pressure below atmospheric pressure, and will have a vacuum scale included before the zero on the gauge scale. The zero on the scale being the start of gauge pressure, that is, pressure above atmospheric pressure.

Regards JD

Thermodynamic calculations get really weird when some of the pressures are negative, as will be the case if you use gauge pressure.

In some cases gage pressure is best for calculations to eliminating atmospheric variability as an error term. Chromatography is the perfect example. Back pressure on the vent port is easily accommodated in this way. See my patent #7,506,533