It is very important to fully realize that the show the properties of what is
usually known as “Dry Saturated Steam”. This is steam which has been completely
evaporated, so that it contains no droplets of liquid water which contain no latent heat
BTUs. Latent heat is what does the heat transfer work!
In standard practice, steam often will carry tiny droplets of water with it and should
never be described as dry saturated steam. This is particularly true in district heating
systems where steam is piped great distances to the end user or where poorly insulated
or trapped systems are used. Nevertheless, we find that it is very important that the
steam used for process of heating is as dry as possible. We will in later documents
show how this is achieved, by the proper use of steam conditioning Thermaflo HSS
“Separators” and Thermaflo Steam “Traps”.
is described by its – the proportion of completely dry
steam present in the steam being used. The steam becomes ”wet” if water droplets in
suspension are present in the steam space, carrying no latent heat. Lets remember
that the latent heat does the work in all heat transfer systems. For example, the specific
enthalpy of steam at 125 psi with a dryness fraction of 0.95 can be calculated as
follows:
Each lb of the wet steam will contain the full amount of sensible heat, but as only 0.95 lb
of dry steam is present with 0.05 lb of water, there will only be 0.95 of the latent heat.
Thus, the specific enthalpy of the steam will be:
Hg = hf + (0.95 + hfg)
= 324 + (0.95 X 869.3)
= 1149.83 BTU/lb
HG = Total Heat BTU/lb (Example:1,194.0)
HF= Sensible Heat BTU/lb (Example: 352.8)
