DOWTHERM SR-1 and DOWFROST HD Heat Transfer Fluids In ...

Automatic make-up water
systems
Automatic make-up water systems
should be avoided in order to
prevent undetected dilution or
loss of glycol and consequent loss
of freeze and corrosion protection.
A preferred system would be a low
level alarm on the expansion tank
to alert maintenance personnel in
case of a low fluid level condition
and prompt corrective action.
Expansion factor
Like any fluids, solutions of
DOWTHERM and DOWFROST
fluids expand as temperature
increases. Therefore, expansion
tanks must be sized appropriately.
To determine the volume of
expansion, use the following
formula:
ρ(T LOW )-ρ(T HIGH ) Expansion
_______________ x Volume =Volume
4
ρ(T HIGH )
Where,
ρ(T LOW ) = the density at the
lowest anticipated
temperature.
ρ(T HIGH ) = the density at the
highest anticipated
temperature.
Density data for DOWTHERM
SR-1 and DOWFROST HD fluids
are given in Tables 4 and 6
respectively.
One method for sizing an expansion
tank is to use the determined
expansion volume to calculate the
total size of the tank. A typical
tank size would allow the fluid to
fluctuate between the levels
associated with 15% and 80% full.
The tank size is calculated from:
Expansion Volume/0.65 = Tank Size
When using this method, ensure
that the minimum amount of fluid
in the tank will provide the NPSH
(net positive suction head) of the
pump if the tank is a portion of
the source of head.
It should also be noted that in
some ice storage systems, such as
the ice encapsulated systems,
when ice is made, the plastic
containers expand. This expansion
will cause the level of the
glycol water solution to rise and
should also be considered when
sizing the expansion tank for this
type of system. Manufacturers of
this type of ice storage system can
assist you with this calculation.
System cleaning
When preparing a system for the
addition of DOWTHERM SR-1
or DOWFROST HD heat transfer
fluid, certain procedures should be
followed. The procedure will vary
depending on whether you are
retrofitting an existing system or
filling a new system for the first
time.
New systems
New systems are typically coated
with oil, grease or a protective film
during fabrication, storage or
construction. Dirt, solder flux, and
welding and pipe scale can also
cause problems. Therefore, thorough
cleaning of new systems is
recommended. A solution of 1-2
percent trisodium phosphate can
be used with water for flushing the
system. System volume can be
calculated during this stage by
metering-in the initial fill of the
system or by chemical analysis of
cleaning chemical after known
quantities are introduced into the
system.
Existing systems
In existing systems, all lines and
materials should be cleaned and
flushed thoroughly before charging
the system with DOWTHERM
SR-1 or DOWFROST HD fluid.
This is especially important if fluid
previously in the system is
incompatible with the new
inhibited glycol fluid. A Dow
technical service representative
can help you determine the
compatibility of other fluids with
DOWTHERM and DOWFROST
fluids.
If fluid containing silicates (such
as automotive antifreeze) was
previously used, it may be necessary
to clean silicate residues from
the system.
It is also important to remove all
rust, scale and sediment in the
system. Traces of chloride should
be removed – whether from old
fluid or residue from acid cleaner –
because chlorides can contribute
to corrosion. For large systems or
systems where corrosion is already
evident, consult a professional
cleaning organization.
For heavily fouled or corroded
systems, an optimum cleaning
procedure includes the use of an
inhibited acid followed by neutralization
and phosphatization. This
procedure is quite involved and
should be done by a company
experienced in industrial cleaning.
If chemical cleaning is used, it is
important that all traces of the
cleaning agent be removed and
the system thoroughly flushed
with water.