A Thermodynamics Study for a Mixture of Natural Gas & Water Flowing Through a Supersonic Nozzle

In order to meet the specifications of transportation of natural gas in pipelines, there
is a need for efficient separation of water from natural gas mixture. To date,
supersonic separation has proven to be efficient in such a physical separation, yet
there is limited study on the thermodynamic of the system. Lack of suitable equation
of state in fluid flow simulation software ANSYS FLUENT 12.0 to model the non
negligible density changes in the compressible flow also calls for a source code that
can introduce real gas equations, that's also appropriate for hydrocarbon systems.
With that, the objective of this Final Year Project will focus on understanding the
thermodynamics of natural gas dehydration and producing a solution scheme based
on Soave-Redlich-Kwong equation of state using user defined functions in
computational fluid dynamics (CFD) software ANSYS FLUENT 12.0 to predict flow
behaviour and changes in other thermodynamic properties. Therefore, scope of study
for this project includes thermodynamics, real gas equation of state to accurately
study the compressible, turbulent, high velocity, single phase water vapour flow
behaviour and solution by means of computational fluid dynamics (CFD) software
ANSYS® FLUENT 12.0 in two-dimension. This will be done through extensive
literature review, identification of validation literature, writing of solution
mechanism, performing CFD simulation and finally post-processing for analysis.
Here, validation of simulation was done against Yang et al's (2009) paper on
numerical simulation of non equilibrium spontaneous condensation in supersonic
steam flow. Main findings showed that density change in compressible, high velocity
flow does significantly influence the thermodynamic properties of the fluid flow
system and super cooling resulting from isentropic expansion was also observed.
This further verified that the source code written for using Soave-Redlich-Kwong
equation of state to model density changes is successful. It was also proven that
Soave-Redlich-Kwong equation of state is more accurate and reliable when it comes
to modelling a system with high pressure variation, compared to ideal gas law.
This dissertation thus presents the results from literature review, solution
methodology, findings of this project and analysis. It is believed that such a study
will aid in understanding the system in order to achieve efficient separation of
impurities from natural gas in the future.