Gas Turbine Handbook : Principles and Practices

100 Gas Turbine Handbook: Principles and Practices
and a temperature control valve can be installed. Air/oil coolers may
also include top louvers to protect the cooling coils from hail. These
louvers are not effective for temperature control. Appendix C-5 includes
a checklist that summarizes the requirements of an air/oil
cooler.
Tube And Shell Coolers
Tube and shell coolers usually use a water glycol mix as the cooling
media when it is available in the area. It would not be economical
to use water/glycol to cool the lube oil and then cool the water/glycol
with an air cooler. To prevent contamination of the oil, in case of
cooler failure, the oil side operating pressure should be higher than
the water side operating pressure and water/glycol should be on the
tube side of the cooler. Also, it is important that vent and drain connections
are provided on both the water and oil sides of the cooler. Oil
temperature control is best accomplished with a cooler bypass control
loop and a temperature control valve. Schematically this is similar to
the control loop around the air/oil cooler in Figure 6-6.
CHARACTERISTICS OF LUBE OILS
Physical and chemical properties of lube oils are determined by
a number of standard laboratory tests. The more common physical
and chemical tests are discussed in this section. 4
Specific Gravity
Specific gravity, ρ, is defined as follows:
ρ = Mo
Mw
where,
Mo is the mass of a given volume of oil
Mw is the mass of the same volume of water
both measured at the same temperature, usually 60°F.
Specific gravity is not a significant indicator of oil quality and,
therefore, is not used in the selection of lube oils. Specific gravity is
an important “first indicator” of oil contamination.