What Types of Coolant Can Be Used for Circulator Pumps in Closed Liquid Cooling Systems?

Circulator pumps can be used for hydraulic heating system and cooling system. In heating system, the liquid for heat transfer is just tap water. It is common to see in our daily life.

However, today we are going to talk about the circulator pumps and coolant types in cooling system.

Using liquids for heat transfer is an important cooling method in many industries. Selection of the best heat transfer fluid for a cooling system involves consideration of performance, compatibility, and maintenance factors.

The most commonly used coolants for liquid cooling applications today are:

  • Water
  • Deionized Water
  • Inhibited Glycol and Water Solutions
  • Dielectric Fluids


Water has high heat capacity and thermal conductivity. It is compatible with copper, which is one of the best heat transfer materials to use for your fluid path. Facility water or tap water is likely to contain impurities that can cause corrosion in the liquid cooling loop and/or clog fluid channels. Therefore, using good quality water is recommended in order to minimize corrosion and optimize thermal performance.

If you determine that your facility water or tap water contains a large percent of minerals, salts, or other impurities, you can either filter the water or can opt to purchase filtered or deionized water.

Deionized Water

The deionization process removes harmful minerals, salts, and other impurities that can cause corrosion or scale formation. Compared to tap water and most fluids, deionized water has a high resistivity. As water’s resistivity increases, its corrosivity increases as well. When using deionized water in cooling system, it is recommended to use circulator pump with stainless steel body.

Inhibited Glycol and Water Solutions

Water as a coolant in a recirculating system is also susceptible to biological fouling. Algae, bacteria or fungi are likely to form depending on the system’s exposure to light and heat and the availability of nutrients in the wetted components. The resultant slime or biofilm can inhibit heat transfer between the fluid and wetted surfaces. Sufficient concentration of the water additive agent must be considered. Glycol as a water additive is commonly used as a control against biological growth.

The two types of glycol most commonly used for liquid cooling systems are ethylene glycol and water (EGW) and propylene glycol and water (PGW) solutions. Ethylene glycol has desirable thermal properties, including a high boiling point, low freezing point, stability over a wide range of temperatures, and high specific heat and thermal conductivity. It also has a low viscosity and, therefore, reduced pumping requirements. Although EGW has more desirable physical properties than PGW, PGW is used in applications where toxicity might be a concern. PGW is generally recognized as safe for use in food or food processing applications, and can also be used in enclosed spaces.

In most cases, a mixture of the glycol and water is used with a lower concentration of glycol due to the superior performance of water over either glycol type. EGW requires lower concentrations than PGW for equivalent freezing point depression, boiling point elevation, and burst temperature depression. However if concentrations less than 20%, the effectiveness of control against biological growth is limited; in fact, below 1%, propylene glycol and ethylene glycol act as a bacterial nutrient.

Dielectric Fluid

A dielectric fluid is non-conductive and therefore preferred over water when working with sensitive electronics. Direct immersion cooling of electronics, for performance or strict temperature control for testing purposes, obviously requires a low electrical conductivity. Dielectric fluids such as XG Galden or Fluorinert are employed for these purposes, with dielectric strengths in the tens of kilovolts per 1/10”. These organic fluids often have higher viscosities than water, so it is useful to get supplier data for a candidate circulator pump’s flow and pressure characteristics when operating at your desired fluid’s viscosity.

Cost Considerations

Tap water is obviously the cheapest option, and purified coolant water will be costlier depending on the purity type and level required.

Coolant solutions that require periodic flushing and recharging during their lifetime, as well as solutions that must be handled at the end of a system’s life, may have costs of disposal that exceed the initial cost of the coolant.

Over time, in an imperfectly closed system (leaks in the seams or seals), the fluid levels can be expected to decrease. Addition of a water/coolant mix to top off fluid levels should involve specifically controlled concentrations of coolant to match the existing system fluid. However, glycols can break down over time into organic acids – measurement of system fluid pH and checking for solid and biological contamination can be an indicator that changing the coolant solution is required.


Water, deionized water, glycol/water solutions, and dielectric fluids are the heat transfer fluids most commonly used in high performance liquid cooling applications.

It is important to select a heat transfer fluid that is compatible with your fluid path including circulator pumps, offers corrosion protection or minimal risk of corrosion, and meets your application’s specific requirements. With the right chemistry, your heat transfer fluid can provide very effective cooling for your liquid cooling loop.