If the temperature of power electronics with liquid cooling falls below +2 ° C, an anti-freezing agent must be added to the cooling water. Usually,a water/glycol mixture is used as heat transfer medium in the cooler. The thermal resistance Rth of the liquid cooling with water/glycol mixture isdue to the viscosity of the glycol dependent on the coolant temperature and the mixing ratio.Transient temperature profile of an IGBT, measured at Pv = 1000W, comparison: distilled water / water/glycol mixture
The picture shows the cooling curve with destilled water and with water/glycol mixture (frost protection -25°C).
Cooling: open water cooler, coolant flow temperature=20°C, flow=10l/min, heating/cooling time: 100s each.
The two cooling curves were created from the extracted R/C elements of the measurement curve.
Rth values of one IGBT (Pv=500W), measured at different flows and flow temperatures