Oil at 300 °C: closed circuit
When the process exceeds what water and oil provide in an open tank, the high heat is transported with thermal oil in a closed circuit. Here we explain how this technology works: why oil, why closed and how it is safely heated and controlled.
For higher temperatures, heat is transported with thermal oil in closed circuit, isolated from the atmosphere. The oil does not boil in that range - it avoids the pressures that water would need; The closed circuit stops its oxidation, and a heating of forced circulation keeps the fluid protected. Marse covers this range up to 300°C.
Each fluid has its ceiling
Water, even pressurized, stops at around 180°C. Thermal oil remains liquid much higher without the need to pressurize the circuit by boiling, which allows working up to 300 °C.
In exchange, it transfers less heat per kilo than water—on the order of 2,0 in front of 4,18 kJ/kg·K—, a difference that is compensated by the flow and design of the equipment. It is the fluid of the upper section: die casting, technical materials and processes that require heat above what water provides.
Isolate the oil from the atmosphere
At these temperatures, the oil is worked in a closed circuit: does not come into contact with air. Keeping it isolated from the atmosphere has two key effects.
On the one hand, stops oxidation of the oil—which is what ages it and shortens its useful life—; on the other, prevents vapors from escaping. And expansion tank, outside the main loop, absorbs the expansion of the oil when it heats up and keeps the circuit full and stable.
warming up forced circulation
When heating with resistances, the oil does not rise in temperature equally: the very thin layer attached to the surface of the resistance—the film temperature— is always hotter than the rest of the fluid. It is the hottest point of the entire circuit and, therefore, the one that marks the design limit. If this layer exceeds the maximum temperature that the oil tolerates, the fluid decomposes (cracking) and leaves carbonaceous residues—coke—on the resistance; This deposit acts as an insulator, overheats the element even more and accelerates the aging of both the oil and the resistance itself.
To avoid this, heat is not applied over stagnant oil, but rather with forced circulation: the pump maintains a high and guided flow on the resistances, which continually renews that film and draws away the heat before the surface overheats. Thus the temperature of the film remains close to that of the rest of the oil. Combined with a power density contained in the resistors and the low thermal inertia of the system, this protects the fluid and allows regulation quickly and accurately.
Security designed for high temperature
The whole – defined flow rate, closed circuit and film temperature control – is what extends oil life and maintains stable performance at high temperature.
closed circuit oil, at a glance
| Parameter | SMART 5A 180 | SMART 6 plus A300 |
|---|---|---|
| Maximum temperature | 180 °C | 300 °C |
| Circuit | Closed (isolated from the atmosphere) | Closed (isolated from the atmosphere) |
| Heating | 9 / 16 kW | 9 – 72 kW (3 clases) |
| Refrigeration | 40 / 60 kW (placas, ≤200 °C) | 85 / 120 kW (coaxial) · 230 kW (tubular) |
| Heating cylinder | 5 L | 16 / 32 L |
| Expansion tank | 9 L | 30 / 60 L |
| Bomba | Centrifuge (6 bar) | Leak-free magnetic (6–8 bar) |
| Stable | TouchScreen TG111 | TouchScreen TG111 |
The A300 is offered in three power classes (9–18, 27–36 and 45–72 kW), with cylinder, expansion tank and pump sized for each class.
Thermal oil for your temperature
Tell us your temperature, power and flow and the configurator sizes the appropriate closed circuit oil equipment.
Closed circuit oil SMART Series
Marse covers this range with closed circuit oil, Up to 300 °C, within the SMART Series, with expansion tank, indirect cooling and stainless steel construction. In its higher temperature model, the magnetic drive pump – without mechanical seal – eliminates the typical high temperature leak point. Below 180°C, the open tank oil family covers up to 150°C.
Common questions
Why oil above 180°C?
Because oil does not boil in that range; Maintaining liquid water at those temperatures would require very high pressures. The oil prevents this and allows working up to 300 °C.
What is film temperature?
It is the temperature of the very thin layer of oil stuck to the surface of the resistors, always hotter than the rest of the fluid. It is the hottest point in the circuit: if it exceeds the oil limit, it decomposes and forms coke. Keeping it under control—with sufficient flow over the resistances—is what extends the life of the oil.
What is forced circulation heating?
A heater through which the oil passes with a defined flow rate and guided over the elements, so that the film temperature remains controlled. It has little thermal inertia, which improves regulation.
Why closed circuit?
To keep the oil isolated from the atmosphere: without contact with air, its oxidation is stopped and vapors are prevented from escaping. An expansion tank absorbs fluid expansion.
What temperature does it reach?
Marse covers this range with closed circuit oil up to 300°C. Below 180 °C, the oil is also processed in an open tank (up to 150 °C).