Super Heat Test in Steam Quality

I would like to bring you a query that for super heat test in steam quality .boiling point of water we are considering is 100 degree, so after calculation we are getting the value in negative sign (e.g. -1.7 i.e. 98.6-100=-1.4) is it acceptable to record in negative value?
98.6 is the measure of temperature in expansion tube of steam. kindly suggest me whether I could consider the boiling point of water based on the local condition .or any other solution as suggested.

also that can we use the boiling point of water at sea level of that particular place
because it change based on altitude if yes kindly suggest any document reference.

thanks and regard

Water will boil at a lower temperature at higher elevation, but can also change slightly if it is a low pressure day (with change in barametric pressure). Here is a calculator.

Also, water boiling point will change if the water has some salt or other chemical dissolved in it - so make sure you have deionized/purified water as your test water to get an extremely accurate reading (if you are being that precise).


thanks Jared for the suggestion .we will consider this points…

can we use the boiling point of water other than 100 degree based on particular sea level of that area (altitude) for calculating superheat test if yes provide some reference?

You can calculate boiling point from steam tables if you know the local atmospheric pressure.
Please see FAQ
Q. Why does the result of my Superheat test produce negative values?
This is the same answer as the previous FAQ for Dryness Test because both tests are linked.
The Dryness Value and Superheat tests are both methods of measuring
‘Dryness’. The Dryness Value test only works well for minimum values and
the Superheat test only works well for maximum values. Providing the
results of both tests fall within the limits of EN 285, the results will
be acceptable.
A negative Superheat value is not uncommon (there is no minimum).
A dryness value of greater than 1 is possible (there is no maximum).
It should be noted that this a test for dryness value and should not be
considered as a true dryness fraction test.

1 Like