Engineering task and calculation objective
The Sodium module provides the thermophysical properties of sodium for thermal calculations: density, specific heat capacity, enthalpy, entropy, heat of evaporation, thermal conductivity, dynamic viscosity, surface tension, coefficient of thermal expansion, thermal diffusivity and Prandtl number – from the region near the melting point at about 98 °C across the entire technically used temperature range of the liquid phase.
Liquid sodium is the classic heat transfer medium for high-temperature applications: in sodium-cooled fast reactors, in solar-thermal receivers, in high-temperature heat storage systems and in sodium heat pipes. Its outstanding thermal conductivity leads to Prandtl numbers far below 1 – behaviour fundamentally different from water or thermal oil, requiring dedicated liquid-metal heat transfer correlations. Consistent property data over temperature are the indispensable basis for this.
Anyone who wants to calculate the properties of sodium or retrieve them for design work obtains, with this module, the temperature-dependent data as direct inputs for heat exchanger, pressure drop and balance calculations in sodium circuits.
Calculation workflow
- Specify the state point: The temperature – together with the pressure where required – defines the evaluation point; the relevant range is the liquid phase between the melting point (approx. 98 °C) and an application-dependent upper limit well below the boiling point of around 883 °C at atmospheric pressure.
- Calculate the properties from the stored correlations: Density, heat capacity, thermal conductivity, viscosity, surface tension and caloric quantities such as enthalpy, entropy and heat of evaporation are determined from temperature-dependent correlations of the liquid-metal property compilations.
- Form the derived characteristic numbers: From the basic quantities, the thermal diffusivity, the coefficient of thermal expansion and the Prandtl number are formed – the latter is characteristically small for sodium, with values of the order of 0.01 or below.
- Pass the values to the application modules: The property data are available to the downstream calculations – for example heat transfer with liquid-metal correlations, pressure drop or circuit balances – consistently for the selected state point.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Temperatur | Temperatur | °C |
| Pressure | p | bar |
| Berechnungstemperatur | ps | bar |
| Density | Rho | kg/m³ |
| ges | ges | kg/m³ |
| Density | Rho | kg/m³ |
| ges | ges | kg/m³ |
| Specific Volume | v | m³/kg |
| ges | ges | m³/kg |
| Specific Volume | v | m³/kg |
| ges | ges | m³/kg |
| Specific enthalpy | h | kJ/kg |
| ges | ges | kJ/kg |
| Specific enthalpy | h | kJ/kg |
| ges | ges | kJ/kg |
| Specific entropy | s | kJ/(kg·K) |
| ges | ges | kJ/(kg·K) |
| Specific entropy | s | kJ/(kg·K) |
| ges | ges | kJ/(kg·K) |
| Specific heat capacity | Cp | kJ/(kg·K) |
| ges | ges | kJ/(kg·K) |
| Specific heat capacity | Cp | kJ/(kg·K) |
| ges | ges | kJ/(kg·K) |
| Dynamic viscosity | Eta | Pa·s |
Frequently asked questions
Why does sodium need its own heat transfer correlations?
Because of the extremely small Prandtl number: in liquid metals, molecular heat conduction is the dominant transport mechanism even in turbulent flow, and the thermal boundary layer is much thicker than the velocity boundary layer. Common correlations such as Dittus-Boelter or Gnielinski, developed for Pr around 1 and above, fail here; liquid-metal approaches based on the Peclet number are used instead.
In which temperature range is sodium used as a heat transfer medium?
Typically between about 150 °C and 550 to 600 °C: limited at the lower end by the melting point of around 98 °C plus a safety margin against freezing, at the upper end by corrosion and strength limits of the structural materials. Since the boiling point lies at about 883 °C, sodium circuits operate almost unpressurised – a substantial safety and cost advantage over water-steam systems at the same temperature.
Which safety-related aspects must be considered in the design?
Sodium reacts violently with water and burns in air; circuits are therefore operated under cover gas (argon), and sodium-water heat exchangers receive dedicated leak monitoring and pressure relief. In addition, all components must be trace-heated to manage freezing during start-up and shutdown. These boundary conditions influence the equipment design more strongly than the heat transfer calculation itself.