Numerical analysis of droplets subcritical evaporation and transcritical mixing using a tabulated real-fluid thermodynamics method coupled to a homogeneous equilibrium model
Ping Yi  2, 1@  , Sajad Jafari  2, 1@  , Songzhi Yang  1, 2@  , Chaouki Habchi  2, 1, *@  
2 : Institut Carnot IFPEN Transports Energies
IFP Energies Nouvelles
1 et 4 avenue de Bois-Préau, 92852 Rueil-Malmaison -  France
1 : IFP Energies nouvelles
IFP Energies Nouvelles
1 et 4 avenue de Bois-Préau, 92852 Rueil-Malmaison, France -  France
* : Corresponding author

In this paper, a fully compressible real-fluid and homogeneous equilibrium model (HEM) has been developed, in which the two-phase characteristics are obtained using a tabulated multicomponent vapor-liquid equilibrium approach. This classical HEM model consists of four balance equations posed in terms of mass density, partial species density, momentum, and internal energy (e). The thermodynamic properties of the mixture are calculated as a function of temperature, pressure and species composition ( ) based on the Peng-Robinson equation of state. Most importantly, a bijective look-up table linking ( , e ) and (T, P) is constructed using a computationally efficient isothermal isobaric (TPn) flash. This look-up table also includes various thermodynamic derivatives such as sound speed, heat capacity as well as the transport properties. During the simulation, all thermal and transport properties are linearly interpolated using (T, P, ). This tabulation approach has been successfully applied to the investigation of subcritical evaporation and transcritical mixing characteristics of spherical n-dodecane droplets in a nitrogen ambient. Primarily, an isolated droplet with uniform initial temperature is put into a moderate ambient condition ( K), in which it undergoes a classical evaporation process with the continuous diameter reduction. Then, the droplet is injected into a high temperature and pressure condition ( K), in which the droplet firstly remains spherical for a while, and then deforms to an olive shape. The predicted results are shown to be in good agreement with the recent experimental findings. The thermodynamic analysis also demonstrates that the droplet has entered the two-phase regime with a diffused interface in which vapor and liquid coexist. This proves that the experimentally observed clouds around the droplet at ( K) is still mainly generated by evaporation, and not due to diffusive mixing, even though the initial ambient gas is significantly above the n-dodecane critical point ( ). The transition from the subcritical classical evaporation to the supercritical mixing regimes is also discussed in this work based on thermodynamic arguments.

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