ABSTRACT
While the temperature range covered by water and gases for heat transfer theoretically accounts for all high-temperature requirements, neither of these media is suitable for many industrial applications. The problems with water (or steam) are related to the high vapor pressures at elevated temperatures and to a lesser extent the associated corrosion which necessitates extensive water treatment facilities. Gases suffer the drawback of very poor heat transfer rates (particularly at moderate or low pressures); this rules out their use except in special circumstances such as the nuclear industry or as products of combustion. Specially formulated organic fluids with reasonable heat transfer characteristics and low vapor pressures, sometimes termed hot oils, satisfy a relatively small but very important demand in the range 150 to 400°C.
