Water can be used as a heat transfer fluid, meeting the
needs of most liquid-cooling applications. Tap or facility water is cheaply and
readily available, non-toxic and has a high thermal capacity. Due to the low
viscosity of water, it is easy to pump. Using good quality water is recommended
to minimise the potential for corrosion and to optimise thermal performance.
The qualities of ‘good water’ can be seen in the table below:
| Mineral | Recommended Limit |
| Calcium | <50ppm |
| Magnesium | <50ppm |
| Total Hardness | <100ppm |
| Chlorine | <25ppm |
| Sulphate | <25ppm |
If tap or facility water contains high levels of minerals,
salts, or other impurities, it is important to either filter the water prior to
use, or purchase filtered or deionised water. More sensitive applications may
require deionised water.
Deionised water is made by running source water through one
or more separate electrically charged resins, removing all, or most, of the
ions. Ions removed include sodium, calcium, iron, copper, chlorine, and
bromide. Removal of harmful minerals, salts, and other impurities can protect
the system from corrosion or scale formation, damaging machine health. ATC
supply the option to install in-line deionising cartridges, polishing the
recirculating water to better than 1 microsiemens/cm² or 10 megaohm/cm².
Deionised water has a higher resistivity than tap water.
Resistivity provides a measure of waters ionic content. It is worth noting that
as resistivity rises, as does corrosivity. Stainless steel or ABS piping is
required when using deionised water as a heat transfer fluid to ensure that
particles from plumbing materials are not leeched into the water circuit,
potentially causing fouling and blockages.
Conductivity provides a measurement of a fluid’s ability to
conduct electrical current. If resistivity is high, conductivity will be low.
As it is an excellent insulator, with very low conductivity, deionised water is
often used in the manufacturing of electrical components where parts must be
electrically isolated.
The relationship between conductivity and resistivity can be
seen in below.
| Conductivity (microsiemens/cm²) |
Resistivity (megaohm/cm²) |
| 0.056 | 18 |
| 0.063 | 16 |
| 0.071 | 14 |
| 0.083 | 12 |
| 0.100 | 10 |
| 0.133 | 7.5 |
| 0.200 | 5 |
| 0.500 | 2 |
| 1.000 | 1 |
| 1.333 | 0.75 |
| 2.00 | 0.5 |
| 4.00 | 0.25 |
| 10.00 | 0.1 |
| 20.00 | 0.05 |
| 40.00 | 0.025 |
| 80.00 | 0.013 |
| 100.00 | 0.01 |
| 200.00 | 0.005 |
| 500.00 | 0.002 |
| 1000.00 | 0.001 |
| 2000.00 | 0.0005 |
| 5000.00 | 0.0002 |
| 10000.00 | 0.0001 |
There are three grades of deionised water.
Grade 1 water, or ultrapure water, is the purest form of
water available. This type of water should be used for advanced analytical
procedures and critical applications. It can also be used in applications that
require grade 2 water. Applications using grade 1 water include liquid
chromatography, gas chromatography, inductively coupled plasma mass
spectrometry (ICP-MS) and molecular biology.
Grade 2 water does not have the same level of pureness as grade
1 water, but still maintains high levels of purity. Although grade 2 water
cannot be used for applications requiring type 1 water, it can be used as a
feed water in the production of grade 1 water. Applications using grade 2 water
include general lab practices, electrochemistry, and general spectrophotometry.
Grade 3 water, or RO water, is water produced through
reverse osmosis. It has the lowest level of purity and is used for many basic
lab applications such as heating baths and media preparation. RO water can also
be used as feed water in the production of grade 1 water.
Please see the table below for the International
Organisation for Standardisation (ISO) requirements for the grading of
deionised water under ISO 3639:1987.
| Parameter | Grade 1 Water | Grade 2 Water | Grade 3 (RO) Water |
| pH value at
25°C
| - | - | 5.0 - 7.0 |
| Conductivity
(µS/cm) at 25°C
| 0.1 | 1.0 | 5.0 |
| Oxidisable
matter Oxygen content (mg/l), max
| - | 0.08 | 0.4 |
| Absorbance at
254nm and 1cm optical path length, absorbance units, max.
| 0.001 | 0.01 | - |
| Residue after
evaporation on heating at 110°C (mg/kg), max
| - | 1 | 2 |
| Silica
(SiO₂), content (mg/l), max
| 0.01 | 0.02 | - |
As water, and deionised water, alone have no antimicrobial
properties, they are vulnerable to contamination. Microbial contamination can
be a difficult problem to remedy once it enters a system, as it causes growth,
leading to internal fouling and blockages. To minimise this risk, in-line UV
decontamination packs allow any growth to be prevented by passing the water
through a steel tube which contains a UV lamp.
When water passes under the ultraviolet light, the genetic code of
microorganisms is attacked, rearranging the DNA/RNA, meaning that the
microorganism is unable to reproduce or function.
However, water has a low boiling point and freezes easy, which
makes it unstable and difficult to manage under extreme temperature conditions.
ATC offer frost protection to protect chillers using water
as a heat transfer fluid, allowing the chiller to function in freezing
temperatures by altering the wiring and thermostat to prompt the pump to run
should the machine drop below +6°C.
To support chillers located in lower temperatures, Applied
Thermal Control offer a low temperature pack, allowing the chiller to operate
below 4°C. Addition of a low
temperature pack will allow chillers to be operated down to -15°C, although
heat transfer fluids containing glycol are recommended at temperatures.
ATC also
offer a heater pack, making it possible to raise the operating temperature of
the chiller above 35°C.