Engineering task and calculation objective
The HFO module provides the physical properties of heavy fuel oils and diesel as a function of temperature. Stored are the commercially common heavy fuel oil grades HFO 30, 60, 100, 180, 380, 420, 640 and 700 – the number denotes the kinematic viscosity in mm²/s at 50 °C – as well as lubricating oil (Lubeoil). The outputs are density, specific heat capacity, thermal conductivity, viscosity, Prandtl number, thermal diffusivity and coefficient of thermal expansion.
These properties are needed for the design of heavy fuel oil systems in power plants, on ships and in refineries: preheaters that bring the oil to injection viscosity, trace heating and tank heating coils, pump and piping design, and pressure drop calculations. Since the viscosity of heavy fuel oil drops by several orders of magnitude between storage and injection temperature, evaluating the properties at the correct temperature is decisive for every heat transfer and hydraulic calculation.
The module makes the values available consistently to the downstream calculations – for example shell-and-tube preheaters or pressure drop modules – so that the oil selection and operating temperature only have to be defined once.
Calculation workflow
- Select the oil grade: Via the oil selection, one of the stored grades is chosen (HFO 30 to HFO 700, diesel or Lubeoil); the selected oil is displayed for verification.
- Specify the operating temperature: The properties are evaluated at the temperature of the respective application – for example the storage temperature, the pumping or preheating temperature, or the mean temperature of a heat exchanger.
- Evaluate the viscosity as a function of temperature: The strongly nonlinear viscosity-temperature relationship is determined from the stored grade curves; from these follow the dynamic and kinematic viscosity at the operating point.
- Provide the remaining properties: Density (with the coefficient of thermal expansion), specific heat capacity and thermal conductivity are determined as functions of temperature; from these the module forms the Prandtl number and thermal diffusivity for the heat transfer calculation.
- Hand over to subsequent calculations: The values are available to the connected modules (preheater, pressure drop and tank heating calculations) as a consistent property data set.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Oil selection: | Öle | - |
| Selected oil: | Öl | - |
| Temperature | ϑ ϑ | °C |
| Temperature | ϑ ϑ | °C |
| Density | ρ ρ | kg/m³ |
| Density | ρ ρ | kg/m³ |
| Specific heat capacity | cp cp | J/(kg·K) |
| Specific heat capacity | cp cp | J/(kg·K) |
| Dynamic viscosity | η η | mPa·s |
| Dynamic viscosity | η η | mPa·s |
| Kinematic viscosity | ν ν | m²/s |
| Kinematic viscosity | ν ν | m²/s |
| Thermal conductivity | λ λ | W/(m·K) |
| Thermal conductivity | λ λ | W/(m·K) |
| Thermal diffusivity | a a | m²/s |
| Thermal diffusivity | a a | m²/s |
| Prandtl number | Pr Pr | - |
| Prandtl number | Pr Pr | - |
| Coefficient of thermal expansion | β β | 1/K |
| Coefficient of thermal expansion | β β | 1/K |
| Gasölen | Gasölen | - |
Calculation options
Oil selection:
1 · 3 · 4 · 5 · 6 · 7 · 8 · 9 · 11 · 12 · 13 · 14
Frequently asked questions
What does the number in the designations HFO 180 or HFO 380 mean?
It gives the maximum kinematic viscosity in mm²/s (cSt) at 50 °C, in line with the grade classification of ISO 8217 (there e.g. RMG 380). HFO 380 thus has up to 380 mm²/s at 50 °C – at ambient temperature it is practically no longer pumpable and must be stored and transferred heated.
Why is the viscosity-temperature curve so critical for the design?
Between 40 °C and 130 °C, the viscosity of heavy fuel oil drops by two to three orders of magnitude. Whether the flow in a preheater is laminar or turbulent, whether a pump delivers, and how large the pressure drop becomes therefore depend almost entirely on the correct temperature assignment. An error of just a few kelvin in the assumed operating temperature can change the viscosity by several tens of percent.
To what temperature must heavy fuel oil be preheated for engines and burners?
The governing value is the required injection or atomization viscosity, typically about 10 to 20 mm²/s. Depending on the grade, this means preheating temperatures from around 90 °C (lighter grades) up to about 150 °C for HFO 700. The module provides the corresponding viscosity curve, from which the required preheating temperature is read off or the preheater is designed.
How accurate are grade-based property data, given that heavy fuel oil is a natural mixture?
Heavy fuel oils are residual products with varying composition; the stored curves represent typical mean values for each grade. For density and viscosity at the grade limits, this is sufficiently accurate; for critical designs (e.g. borderline cases of pumpability), analysis values of the actual batch – density at 15 °C, viscosity at 50 °C – should be cross-checked.