The immersion probe surface temperature quickly reaches a very low temperature, as low as -100°C. Water reaches its latent heat of fusion at 0°C. As water molecules along the probe surface change state from liquid to solid, they attach themselves to the probe surface. This ice formation becomes an insulator between the remaining water molecules and the refrigerant within the probe. Therefore, no heat is being removed from the remaining water and the bath temperature does not change.
This same principle applies to other fluids as well. For example, aqueous solutions of 60% ethylene glycol or propylene glycol can have a freezing point as low as -70°C. If the immersion cooler probe temperature is above -70°C, then the unit will be able to cool the solution. If the probe temperature is lower than -70°C, the solution will freeze around the probe and will negate the cooling effect of the probe. Therefore, selecting a fluid with a freezing point that is lower than the coldest achievable temperature of the immersion probe cooler is key. Also, immersion probe coolers are very effective for dry applications, such as cooling differential scanning calorimeters.
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