Engineering task and calculation objective
The T-OIL module provides thermophysical properties of heat transfer oils (thermal fluids) for the thermal design of plants. More than 100 organic heat transfer media are stored — mineral oils, synthetic aromatics, and silicone oils — with their temperature-dependent property data: density, specific heat capacity, thermal conductivity, dynamic and kinematic viscosity, and vapor pressure. The data are based on the manufacturers' product information.
Anyone who wants to calculate a thermal oil circuit, a heater, or a heat exchanger with an organic heat transfer fluid needs these property values at every temperature point — for example to determine Reynolds, Prandtl, and Nusselt numbers, pressure drop and pump power, or to check the vapor pressure against the system pressure. The module delivers the values at freely selectable temperatures and additionally reports the fluid structure, the manufacturer, former product names, and the permissible operating range.
A suitable thermal oil is selected by criteria such as maximum service temperature, maximum film temperature, or manufacturer name. The module thus supports both the design of new thermal fluid systems (e.g. to DIN 4754) and the replacement of discontinued products with current equivalents.
Standard and calculation basis: Produktinformationen der Hersteller
Calculation workflow
- Select the heat transfer oil: The oil is chosen from the database by name; filter criteria such as maximum service temperature, manufacturer, or fluid structure (mineral, synthetic aromatic, silicone oil) narrow down the selection. Former product names help locate renamed oils.
- Check the operating range: The module displays the applicability of the selected oil — in particular the permissible temperature range. The operating temperature of the plant must lie within this range, and the maximum film temperature at the heating surface must not be exceeded.
- Specify temperature points: The property values are output in parallel for up to two temperatures, so that, for example, the inlet and outlet states of a heat exchanger can be compared directly.
- Output the property values: The output comprises density, specific heat capacity, thermal conductivity, dynamic and kinematic viscosity, and the vapor pressure at the selected temperatures — the complete basis for heat transfer and pressure drop calculations in the thermal oil circuit.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Name of the oil | _Name | – |
| Material structure | Teilbez.) | – |
| Manufacturer | Teilbez.) | – |
| Former product / Comment | _Bemerkung | – |
| Range of application | _Einsatzmöglichkeit | – |
| Pour point | _Fließgrenze | °C |
| Initial boiling point | _Siedebeginn | °C |
| Minimum operating temperature | Verwendungsbereich | °C |
| Maximum operating temperature | Verwendungsbereich | °C |
| Minimum temperature filling | Füllen | °C |
| Maximum film temperature | Filmtemperatur | °C |
| Flash point | _Flammpunkt | °C |
| Ignition temperature | _Zündtemperatur | °C |
| Neutralization number | _Neutralisationszahl | mgKOH/g |
| Coke residue | _Koksrückstand | % |
| Explosion limit | _Explosionsgrenze | Vol-% |
| Molar mass | _Molmasse | kg/kmol |
| Density | ρ | kg/m³ |
| Specific heat capacity | cp | J/(kg·K) |
| Dynamic viscosity | η | mPa·s |
| Kinematic viscosity | ν | m²/s |
| Thermal conductivity | λ | W/(m·K) |
| Vapour pressure | pD | Pa |
| Density | ρ | kg/m³ |
Frequently asked questions
Why is the maximum film temperature more important than the maximum service temperature?
The film temperature is the temperature in the boundary layer directly at the heating surface and lies well above the bulk temperature of the oil. If it is exceeded, the oil cracks thermally: low boilers form (flash point drop, vapor pressure rise) along with coke on the heating surface, which further degrades heat transfer and raises the film temperature even more. The heater design must therefore verify the film temperature, not just the supply temperature.
How strongly does the viscosity of thermal oils change with temperature?
Very strongly and nonlinearly: between a cold start at 20 °C and operation at 300 °C, the kinematic viscosity can fall by two to three orders of magnitude. For the design this means that pressure drop and pump power in the cold state, as well as the laminar/turbulent transition, must be checked as functions of temperature — an oil that flows turbulently at the operating point may be laminar during start-up and deliver considerably lower heat transfer coefficients.
What is the vapor pressure of the heat transfer oil needed for?
The vapor pressure determines the temperature above which an open or unpressurized system can no longer be operated, and which blanketing pressure (e.g. nitrogen) is required in the expansion vessel to prevent vaporization and cavitation at the pump suction side. Synthetic heat transfer fluids can have substantial vapor pressures at high temperatures, whereas mineral oils usually stay below 1 bar.
How reliable are property values taken from manufacturer data?
The data come from the manufacturers' product data sheets and are sufficiently accurate for process design. However, they are typical values, not guaranteed analytical values; in service, ageing (cracking, oxidation) changes the properties. For aged oils, the characteristic values should be verified regularly by oil analyses.