What characteristic should oils intended for heat transfer fluid have?

Oils intended for use as heat transfer fluids should have a low vapor pressure at the operating temperature. This characteristic is important because a low vapor pressure indicates that the fluid is less likely to vaporize under heat, which helps to maintain effective heat transfer. If the fluid were to vaporize, it could lead to the formation of steam pockets or vapor bubbles within the system, disrupting the heat transfer process and potentially causing thermal inefficiencies or even damage to the system.

In heat transfer applications, the fluid needs to remain in its liquid state to efficiently transport heat from one location to another. A low vapor pressure ensures that the boiling point of the fluid is significantly higher than the operational temperatures, providing stability and reliability in heat transfer operations.

Other characteristics, such as viscosity and thermal density, play a role in fluid performance, but they are not the defining factors for effective heat transfer like vapor pressure is, especially at the operating temperature. High viscosity can hinder fluid movement, while high vapor pressure can lead to operational challenges. Low thermal density may affect energy transfer capability, but it’s the vapor pressure that is crucial for maintaining liquid state and effective heat transfer under thermal stresses.