While the food industry might be more likely to select PGW over EGW for heat transfer, the power electronics, laser, and semiconductor industries might be more likely to choose dielectric fluids over water. A dielectric fluid is non-conductive and therefore preferred over water when working with sensitive electronics. Perfluorinated carbons, such as 3M’s dielectric fluid Fluorinert™, are non-flammable, non-explosive, and thermally stable over a wide range of operating temperatures. Although deionized water is also non-conductive, Fluorinert™ is less corrosive than deionized water and therefore may be a better choice for some applications. However, water has a thermal conductivity of approximately 0.59 W/m°C (0.341 BTU/hr ft °F), while Fluorinert™ FC-77 has a thermal conductivity of only about 0.063 W/m°C (0.036 BTU/hr ft °F).5 Fluorinert™ is also much more expensive than deionized water.
PAO is a synthetic hydrocarbon used frequently in military and aerospace applications for its dielectric properties and wide range of operating temperatures. For example, the fire control radars on today’s jet fighters are liquid cooled using PAO. For testing cold plates and heat exchangers that will use PAO as the heat transfer fluid, PAO compatible recirculating chillers are also available. PAO has a thermal conductivity of 0.14 W/m°C (0.081 BTU/hr ft °F). So although dielectric fluids provide low risk liquid cooling for electronics, they generally have a much lower thermal conductivity than water and most water-based solutions.
Water, deionized water, glycol/water solutions, and dielectric fluids such as fluorocarbons and PAO are the heat transfer fluids most commonly used in high performance liquid cooling applications. It’s important to select a heat transfer fluid that is compatible with your fluid path, 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. For more information on liquid cooling technologies and the proper working fluid to use in your system, contact Aavid, Thermal Division of Boyd Corporation.
1 Mohapatra, Satish C., “An Overview of Liquid Coolants for Electronics Cooling,” ElectronicsCooling, May 2006, p. 22.
2 The Dow Chemical Company, “The Importance of Using Good-Quality Water in Heat Transfer Fluid Solutions,” www.Dow.com , Form No.180-01396-1099QRP, October 1999.
3 The Dow Chemical Company, “How to Choose the Right Heat Transfer Fluid”, Process Heating, January 2008, Troy, MI, p. 52.
4 The Dow Chemical Company, “Engineering and Operating Guide for DOWTHERM SR-1 AND DOWTHERM 4000 Inhibited Ethylene Glycol-based Heat Transfer Fluids”, www.Dow.com , Form No. 180-1190-0901 AMS, September 2001, p. 6.
5 3M, “3M Fluorinert™ Electronic Liquid FC-77”, www.3M.com , 98-0212-2309-8 (HB), May 2000, p. 1.