TDI-Dynaload Division
WCL488 Series Water Cooled Electronic Loads
Operation & Programming Manual
402828, Rev. B1
Page 11
Special Information for Ethylene Glycol Users
The WCL and WCS series of water-cooled electronic loads are designed to operate using water as
the cooling fluid. The use of an antifreeze such as ethylene glycol in the coolant water will affect
the thermal efficiency of the system. Since ethylene glycol is not as efficient as water for cooling,
a higher flow rate and/or a lower coolant inlet temperature is needed. Otherwise, the maximum
power of the system must be de-rated. The following graph shows the recommended de-rating
requirements verses flow rate for different percentages of ethylene glycol (inlet temperature of
10ºC). Other types of glycols, such as propylene glycol, have approximately the same de-rating
requirements.
Figure 8. Recommended Power De-rating Versus Flow Rate
for Different Ethylene Glycol Levels
Working within the design limitations of 120 PSI it may not be practical to raise the input
pressure of the system in order to achieve the required flow rate. It is best to use pure water with
no additives to reach full power ratings.
If the use of a high percentage of glycol mix cannot be avoided, and acceptable flow rates can not
be achieved, we suggest the use of a fluid/fluid heat exchanger and pump to create a secondary
cooling loop so water can be used for the load requirements. Remember that the same transfer
inefficiencies will exist in the fluid/fluid heat exchanger as would exist in the load. Careful
calculations should be used when choosing the heat exchanger.
There are several other factors to take into account. Thermal transfer as a function of flow rate is
an inverse log graph and there are only minimal gains to be made above 6 GPM. The use of
glycol will also change the viscosity of the coolant, which will have an effect on the flow rate
verses pressure.
P
er
ce
nt
o
f R
at
ed
P
ow
er
100%
90%
80%
70%
60%
50%
40%
2
3
4
5
6
7
Flow R ate (G PM )
402828-02-06.C D R
100% Water
10% G lycol
20% G lycol
30% G lycol
40% G lycol
50% G lycol
