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Atomization and Sprays

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ISSN Print: 1044-5110
ISSN Online: 1936-2684

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Atomization and Sprays

DOI: 10.1615/AtomizSpr.v20.i7.20
pages 581-593

n-HEPTANE DROPLET VAPORIZATION USING MOLECULAR DYNAMICS

Brad A. Petrilla
Applied Research Laboratory, Pennsylvania State University, University Park, Pensilvania 16801, USA
Mario F Trujillo
Department of Mechanical Engineering, University of Wisconsin, Madison, Wisconsin 53706, USA
Michael Micci
Aerospace Engineering

ABSTRACT

The vaporization of a n-heptane (C7H16) droplet is investigated using molecular dynamics (MD). This constitutes one of the first studies of droplet vaporization employing a polyatomic molecule. A torsion potential is employed for intramolecular interactions and a truncated Lennard-Jones (2.5σ) for all intermolecular and a select number of intramolecular interactions. During each integration step the structure of the molecule is maintained by constraining bond lengths and bond angles iteratively, using the RATTLE algorithm. Initial equilibration of the liquid- and gas-phase systems is done separately using an NVT simulation; velocity rescaling is applied for both the internal and translational temperatures. Four simulations are performed on systems composed of a total of 1526, 1529, 3031, and 3041 molecules under pressures of 1 and 2 atm, respectively. This corresponds to a single-species droplet vaporization process occurring in a superheated gaseous environment. Results in terms of molecular-time-averaged forces show noticeable departures from spherical symmetry in the droplet shape. This is attributed in part to the lack of symmetry of the C7H16 molecule, which translates to manifestations at the droplet scale. The Amsterdan method is employed to investigate droplet size histories. Relatively close agreement with D2-law behavior is reported, even though the Knudsen numbers are in an intermediate regime between the kinetic theory and continuum limits.