Water or oil: how to choose the thermal fluid
The fluid determines what temperature it can work up to and how heat is transferred. Here we compare water and oil—their properties and ranges—and link to each SMART Series technology for a deeper dive.
He agua work until 90 °C in open tank and, pressurized, up to a maximum of 180 °C. Below 90 °C, either of the two technologies - tank or pressurized - can be used, depending on the installation. He oil covers up to 150 °C in open deposit and up to 300 °C in closed circuit.
The fluid conditions precision, cost and safety
The thermal fluid determines what temperature it can work up to and how heat is transferred to the process.
It influences the precision (transfer capacity and stability), in the cost (energy and size of the equipment) and in the maintenance (fluid quality, cleaning and conservation). That is why the range is organized into families according to fluid and technology.
Each fluid, its technologies
Each technology, its temperature
Why does water reach 180 °C and no more?
For water to remain liquid above 100°C, the pressure in the circuit must be maintained above its saturation pressure (the vapor pressure at that temperature). This pressure rises sharply: the real working pressure of the circuit can be around 16 bar a 180 °C.
Working with water above 180 °C adds inconveniences: the necessary pressure increases very quickly (on the order of 40 bar towards 250 °C, plus the pressure provided by the pump), with the safety requirements that entails (adequate hoses and connections, periodic review of the circuit); and at high temperatures, water treatment becomes more critical (limescale, scale and corrosion), requiring desalination and inhibitors. That's why 180°C is the maximum of the pressurized water family: above, the high range is covered with oil, which does not boil at these temperatures and does not require pressurizing the circuit.
A nuance: below 90 °C the water can be worked both in open and pressurized tank —there the choice depends on the installation and the process. On the pressurized water page we develop the closed circuit, the expansion vessel and how the working pressure is calculated.
The transfer of each fluent
The specific heat of water is 4,18 kJ/kg·K and the oil 2,0 kJ/kg·K: water transports approximately double of energy per kilogram, and its heat transfer coefficient is also on the order of double, so it transfers heat more efficiently.
Water adds other advantages: low and almost constant viscosity throughout its range, less expansion and does not crack (does not form coke), which allows more compact equipment and simple maintenance focused on fluid quality. The oil, on the other hand, reaches temperatures that water cannot achieve without high pressure, in exchange for monitoring its oxidation and degradation over time. Each fluid covers its range with its own technology.
water and oil, property to property
| Property | Water | Thermal oil |
|---|---|---|
| Temperature range | ≤ 90 °C open · 90–180 °C pressurized | ≤ 150 °C open · ≤ 300 °C closed circuit |
| Specific heat | 4,18 kJ/kg·K | 2,0 kJ/kg·K |
| heat transfer | Alta | Minor |
| Goo | Low and stable | Elderly; varies with temperature |
| thermal expansion | Minor | Larger (requires larger expansion vessel) |
| Coking | No | Possible at high temperature |
| Working pressure | Atmospheric (open) or pressurized | Atmospheric (deposit) closed circuit |
| Fluid maintenance | Water quality (limescale/corrosion) | Oxidation/thermal degradation |
| Cleaning and handling | Simple | Requires more care |
The team tailored to your process
Tell us your temperature, power and flow and the configurator sizes the equipment for the corresponding family.
A platform, five families
We manufacture the five families on the same SMART platform, with the same control system: Open tank water (≤90 °C), Direct pressurized water (WDC) and indirect (WIC) (90–180 °C), Open tank oil (≤150 °C) and Closed circuit oil (≤300 °C).
Common questions
What temperature does each fluid reach?
Water: 90 °C in open tank and up to 180 °C pressurized. Oil: 150 °C in open tank and up to 300 °C in closed circuit.
Why does water need pressure above 90°C?
Because at atmospheric pressure water boils at 100 °C. By pressurizing the circuit it remains liquid up to 180 °C in the pressurized family.
What is the difference between WDC and WIC?
There are two families of pressurized water according to the cooling method: WDC (direct) and WIC (indirect).
Why does water transfer more heat?
Due to its higher specific heat (4.18 compared to 2.0 kJ/kg·K) and higher transmission coefficient.