Iso-paraffins as low temperature secondary fluids.

Abstract

Ethylene and propylene glycol water based secondary solutions are very popular due to their low corrosivity character, low freezing point, high boiling point and low fire hazards. The main drawback of ethylene glycol solutions is its potential toxicity both to the environment, animals and food products. Therefore, propylene glycol is the most common substitute for ethylene glycol. The biggest disadvantage of propylene glycol solutions is its very high viscosity at low temperatures, which results in higher pumping power and lower system performance. For very low temperatures, it is common to use non-aqueous synthetic fluids, which have lower viscosities at these temperatures. Thus, the aim of this paper is to propose a new generation of synthetic iso-paraffins having better thermophysical properties compared to existing synthetic products used for very low temperature applications. The first results showed that the new generation of iso-paraffins having the freezing temperature of – 50 °C or lower had significantly lower viscosity (between 75 % and 98 %) at very low temperatures compared to 60 wt-% propylene glycol (PG 60 %) and 60 wt-% ethylene glycol solution (EG 60 %). Iso-paraffin 1 showed better performance than iso-paraffin 2 by giving the lowest freezing point, the lowest dynamic viscosity and kinematic viscosity as well as the highest thermal conductivity. Instead, iso-paraffin 2 had higher specific heat capacity. As seen, the different composition of iso-paraffin mixture can result in different properties and operating temperature ranges. Thus, iso-paraffins could become an interesting alternative for very low temperature cooling applications.