NON-EQUILIBRIUM MOLECULAR DYNAMICS USED TO OBTAIN SORET COEFFICIENTS OF BINARY HYDROCARBON MIXTURES

Furtado, F. A.; Silveira, A. J.; Abreu, C. R. A.; Tavares, F. W.

doi:10.1590/0104-6632.20150323s00003445

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Selected papers from the VII Brazilian Congress of Applied Thermodynamics (CBTermo) • Braz. J. Chem. Eng. 32 (3) • Sept 2015 • https://doi.org/10.1590/0104-6632.20150323s00003445 copy

NON-EQUILIBRIUM MOLECULAR DYNAMICS USED TO OBTAIN SORET COEFFICIENTS OF BINARY HYDROCARBON MIXTURES

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The Boundary Driven Non-Equilibrium Molecular Dynamics (BD-NEMD) method is employed to evaluate Soret coefficients of binary mixtures. Using a n-decane/n-pentane mixture at 298 K, we study several parameters and conditions of the simulation procedure such as system size, time step size, frequency of perturbation, and the undesired warming up of the system during the simulation. The Soret coefficients obtained here deviated around 20% when comparing with experimental data and with simulated results from the literature. We showed that fluctuations in composition gradients and the consequent deviations of the Soret coefficient may be due to characteristic fluctuations of the composition gradient. Best results were obtained with the smallest time steps and without using a thermostat, which shows that there is room for improvement and/or development of new BD-NEMD algorithms.

Keywords:
Irreversible thermodynamics; Transport properties

Interaction Type	Group	Parameters
Bond stretching		k_r /k_b (K/Å²)		r_eq (Å)
Bond stretching	C - C	96500		1.54
Bond angle bending	C - C - C	k_θ / k_b (K/ rad²) 62500		θ_eq(º) 114.0
Dihedral torsional angle		c₀/ k_b (K)	c₁ / k_b (K)	c₂ / k_b (K)	c₃/ k_b (K)
Dihedral torsional angle	C - C - C - C	0	355.03	-68.19	791.32
Lennard-Jones		ε/ k_b (K)		σ(Å)	r_c(Å)
	CH₂	46.0		3.950	14.0
	CH₃	98.0		3.750	14.0

Components	ρ (kg/m³)		D (10^-9 m²/s)
Components	this work	exp.	this work	sim. (AUA1)	sim. (AUA2)	exp.
n-C5	621.5±0.1	621^a a - Dreisbach (1959);	7.59±0.17	612^b b - Mutoru et al. (2013);	618^b b - Mutoru et al. (2013);	5.62^c c - Douglas and McCall (1958);
n-C10	734.1±0.1	730^a a - Dreisbach (1959);	2.21±0.03	1.49^b b - Mutoru et al. (2013);	1.66^b b - Mutoru et al. (2013);	1.31^c c - Douglas and McCall (1958); ,1.38^d d - Ertl and Dullien (1973).
n-C5 + n-C10	694.2±0.1

Thermostat	Number of	Time step	N_exch	S_T,upper	S_T,lower	\|ΔS^T\|
	molecules	(fs)	(fs)	(10. K^-1)	(10^-3. K^-1)	(10^-3. K^-1)
None	1200	1	300	2.655±0.364	2.775±0.379	0.120
		1	400	2.317±0.561	2.576±0.508	0.259
		2	300	1.921±0.360	2.336±0.364	0.415
		2	400	2.291±0.406	1.801±0.413	0.490
	1800	1	300	2.631±0.324	2.820±0.362	0.189
	1800	1	400	2.662±0.363	2.077±0.454	0.585
	2400	1	300	2.677±0.383	2.335±0.309	0.342
	2400	1	400	3.365±0.456	3.034±0.389	0.331
Berendsen	1200	2	300 400	2.454±0.341 2.100±0.417	2.620±0.373 2.283±0.391	0.166 0.183

Thermostat	time-step	N_exch	β'_E	ΔT
	(fs)	(fs)	(%)	(K)
None	1	300	1.79	1.6
	1	400	1.06	0.6
	2	300	7.47	7.3
	2	400	4.68	4.6
Berendsen	2	300 400	-0.44 -0.06	-0.1 0.0

Thermostat	t-step/N_exch (fs)	S_T(10^-3. K^-1)
		This work^a a - R-NEMD, ST ± 2·υ<Y>;	BD-NEMD (HeX)	S-NEMD	exp.
None	1/300	2.70±0.24
	1/400	2.42±0.38	2.91±0.45^b b - Perronace et al. (2002), 300 K;	3.59±0.83^b b - Perronace et al. (2002), 300 K;	3.27±0.23^c c - Perronace et al. (2002), 300 K;
	2/300	2.18±0.26	2.91±0.45^b b - Perronace et al. (2002), 300 K;	3.59±0.83^b b - Perronace et al. (2002), 300 K;	3.27±0.23^c c - Perronace et al. (2002), 300 K;
	2/400	2.07±0.28
Berendsen	2/300	2.58±0.26			3.07^d d - Mezquia et al. (2014), 298 K.
Berendsen	2/400	2.16±0.28			3.07^d d - Mezquia et al. (2014), 298 K.

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[1] *To whom correspondence should be addressed, This is an extended version of the manuscript presented at the, VII Brazilian Congress of Applied Thermodynamics - CBTermo 2013, Uberlândia, Brazil.