Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
How to measure Sat steam quality
- Thread starter Cherdchai
- Start date
- Thread starter
- #4
I think these three links are fair enough to give you an idea about the throttling calorimetry. (just got from the keyword throttling calorimeter)
Generally the superheat maintained is 50C. When the quality of steam is bad initially, it may be difficult to reduce the pressure after throttling to get a superheat of 50C. In this case a separating and throttling calorimeter is used instead. some of the condensate is removed in a separator and then remaining steam is throttled to superheated condition. From the quantity of condensate separated and from the initial and final conditins, the dryness fraction can be calculated.
Electrical calorimeters superheat the steam by an electric resistor and in this case the final enthalpy will be the sum of initial enthalpy and the electric energy given to the unit quantity of steam.
Regards,
Generally the superheat maintained is 50C. When the quality of steam is bad initially, it may be difficult to reduce the pressure after throttling to get a superheat of 50C. In this case a separating and throttling calorimeter is used instead. some of the condensate is removed in a separator and then remaining steam is throttled to superheated condition. From the quantity of condensate separated and from the initial and final conditins, the dryness fraction can be calculated.
Electrical calorimeters superheat the steam by an electric resistor and in this case the final enthalpy will be the sum of initial enthalpy and the electric energy given to the unit quantity of steam.
Regards,
Peter E. Liley (a mechanical engineering professor at Purdue University) published, in Chemical Engineering/August 1994, a formula to determine qualities of wet steam between 95 and 100%, based on the temperature of the steam after expansion (in the calorimeter) to 1 bar that goes:
where t is the exhaust temperature (oC) for an exhaust pressure of 1 bar, for various line pressures (bars), the coefficients A and B are tabulated.
The author claims quite precise values are obtained by using his formula. He gives A and B values for 1 bar increases between 2 and 20 bar. As an example:
Line pressure, bars A(%) B(%/oC)
5 86.98 0.09547
10 85.00 0.09930
15 83.72 0.10312
20 82.78 0.10695
If a 10 bar steam when expanded to 1 bar shows a temperature of 115oC, its quality would be:
![[pipe]](/data/assets/smilies/pipe.gif "[pipe] [pipe]")
Quality(%)=A+Bt
where t is the exhaust temperature (oC) for an exhaust pressure of 1 bar, for various line pressures (bars), the coefficients A and B are tabulated.
The author claims quite precise values are obtained by using his formula. He gives A and B values for 1 bar increases between 2 and 20 bar. As an example:
Line pressure, bars A(%) B(%/oC)
5 86.98 0.09547
10 85.00 0.09930
15 83.72 0.10312
20 82.78 0.10695
If a 10 bar steam when expanded to 1 bar shows a temperature of 115oC, its quality would be:
85+0.0993*115=96.4%
Throttling calorimeters are more at home in the laboratory than the average steam plant - they're fiddly to use and not that accurate. Your best bet is to fit a proprietory steam separator in the steam line before the process control equipment. That way, even though you don't know the quality of your steam before the separator, you can be assured it's in pretty good shape after it's passed through. Plenty of 'steam' companies make these - suggest you contact a few of the big ones and make your mind up on the quality of their technical literature.
Moisture content in saturated steam is notoriously hard to measure reliabily in the power plant. To give you an idea of the extremes needed to measure it accurately, nuclear steam supplies (most of which are saturated) are sometimes tested by injecting radioactive tracers in the feedwater before the steam generator. It is assumed that the tracers are carried over only in the water droplets so the percentage residual radioactivity is assumed to be equal to the percent moisture in the steam supply out of the steam generator. Believe me, this type of test is an example of a test you DON'T want to do. You cannot imagine the bureaucratical mess needed to do this test. Even in nuclear plants, this measurement is done once or twice in it’s life time.
The Steam Quality is now required by the EN 285 and HTM 2010 for most medical devices and parenteral products. A kit is now provided by Keith Shuttleworth & Associates Ltd to measure the following properties in clean steam utilities:
a) non-condensable gases,
b) dryness value, and
c) superheat
Since you are looking for dryness test this information could definetilvely help you for your application.
For details see the following site:
a) non-condensable gases,
b) dryness value, and
c) superheat
Since you are looking for dryness test this information could definetilvely help you for your application.
For details see the following site:
- Status
Similar threads
- Locked
- Question
- Locked
- Question