Fluid models iconFluid Models

Flownex Simulation Environment has various fluid types available to the user; these fluid types include gasses (compressible), liquids (incompressible), gas mixtures, homogeneous two-phase and non-condensable (Incondensable) mixtures.

Liquids (Incompressible)

Liquids are generally used for simulation of water reticulation, oil, and other liquid distribution systems, fuel systems, fire protection, liquid cooling, heating systems, etc.

Gasses (Compressible)

Gasses are commonly used for ventilation systems, pneumatic systems, control air systems, gas distribution and supply systems, gas turbine cycles, combined cycle power stations and more.

Gas Mixtures

Gas mixtures allow users to mix multiple streams of gas, and calculate the new gas mixture fractions; user can optimize mixtures and ensure correct delivery to components, systems and subsystems.

Gas mixtures are commonly found in fuel distribution systems, combustion chambers, pipelines, gas turbine cycles and gas supply systems.


The two-phase flow model assumes the two phases of the same fluid travels at the same speed and has the same temperature. The two phase models are simplistic enough to be used by any engineer and also accurate enough to model most of the general flow encountered in everyday engineering plants. These applications include anything from something as simple as boiler blow off studies or flow balancing in evaporative heat exchanger tubes to complex systems including complete Rankine cycles linked to the auxiliary systems and control. Flownex has been used to model steam primary and auxiliary systems like primary cycles of power stations, auxiliaries like soot blower systems, steam generators, combined cycle power stations, heat exchangers, super heaters, flow balancing of boiler water walls and many more. It is also used in refrigeration systems and any other systems where fluids change phase.

Non-Condensable (Incondensable) Mixtures

Non-condensables are a mixture of a homogeneous two phase fluid and a compressible gas that does not easily condense during cooling. Non-condensables are found in systems where condensation or evaporation occurs (air conditioning systems), two-phase systems with air leakage; heating and ventilating systems.

A typical example is the situation found in condensers/evaporators with air entrainment [1].

In this case, the air would be the incondensable gas with the saturated steam present in liquid and vapor phases.


Flownex models Non-Newtonian fluids such as slow/non-settling slurries and settling slurries. Slow/non-settling slurries are usually well described by non-Newtonian fluid models. However, settling slurries require additional calculation methods which are accounted for in Flownex.

Trace Elements

Trace elements in Flownex are elements suspended in a fluid that have an average concentration of less than 100 parts per million measured in atomic count or less than 100 micro-grams per gram. Users can define and track trace element concentrations throughout the system, identify concentration build-up and determine where elements are required to be added.


Why Simultaneous Simulation of Various Fluids?

Flownex allows the user to simultaneously integrate these fluids in a single simulation. This creates endless possibilities in predicting and managing a plant or design using the virtual plant modeled in Flownex; pressing the boundaries in simulation to approach reality.

Simultaneous Simulation of Liquids and Gasses

Flownex allows users to simulate any component with liquid and gas present, and ensure the fluid behavior is integrated.  Take, for example, a typical finned tube heat exchanger; within a finned tube heat exchanger air flows over the fins and water flows in the tubes. It is not possible to simulate the interaction (e.g. heat transfer) of the fluids especially at off-design conditions without the ability to simulate both liquids and gasses simultaneously.  

Simultaneous Simulation of Homogeneous Two-Phase Flow and Gas Mixtures

Boilers require the combustion of gasses to convert water to steam, therefore, to simulate accurate boiler behavior, accident and off-design scenarios, start up and shut down behavior and root cause analyses, the simultaneous simulation of the flue gas side and the water to steam on the primary Rankine cycle is essential to get a complete picture.

Simultaneous Simulation of Homogeneous Two-Phase Flow and Liquids

All primary Rankine cycles have essential auxiliary systems, for example safety auxiliary systems; fire protection lines; cooling and heating auxiliary systems to ensure the plant remains in acceptable operating conditions.  All these systems have an influence on plant operation and with the ability to integrate them in a single simulation we provide valuable insight into plant operation and the effect different systems have on each other through simulation. Auxiliary cooling water systems are typically not always upgraded if the power station is rated up to a higher heat load. This causes the Auxiliary cooling water system to be under pressure and operate at off-design conditions. To be able to predict how the mass flow distribution needs to change and how the control of the system needs to change to still be able to provide the desired heat removal requires an integrated approach.

Simultaneous Simulation of all Fluid Types in a Single Simulation

With simultaneous simulation of various fluids and intern multiple systems, Flownex allows users to integrate system behavior within a single simulation, ensuring interaction between various systems is taken into account. 

This implies the ability to model heat transfer between various fluid types, Auxiliary cooling systems, Primary Systems, Multi Fluid Sub-Systems, Heating and Ventilating Systems all simultaneously in a single simulation model.  

[1] Air entrainment is the intentional creation of tiny air bubbles and can also be intentional creation of tiny water droplets.