Molecular Simulation of NH /Ionic Liquid Mixtures for ... · Molecular Simulation of NH 3/Ionic...
Transcript of Molecular Simulation of NH /Ionic Liquid Mixtures for ... · Molecular Simulation of NH 3/Ionic...
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Molecular Simulation of NH3/Ionic Liquid Mixtures for Absorption Heat
Pump CyclesAbhishek KABRA, Tim M. BECKER, Meng WANG*, Carlos A. INFANTE FERREIRA, Thijs J.H. VLUGT
Process and Energy Department, TU Delft
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Content
● Introduction● The Absorption Heat Pump Cycle● Property predictions● Results and discussions● Conclusions
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Content
● Introduction● The Absorption Heat Pump Cycle● Property predictions● Results and discussions● Conclusions
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Industry Heating Buildings HeatingOther Heat ElectricityTransport Non-Energy Use ● highly efficient space heating & cooling
● utilization of low-grade energy: waste heat, concentrated solar heat
BackgroundWorld Total Final Energy Consumption (IEA)
Absorption heat pump (AHP)
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Low temp. heat from surroundings
Air Earth Water
High temp. driving heat
AHP
1 J
1 J 2 J
Mid temp. heat application
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Motivation
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Working pairs
Crystallization (H2O/Libr)
Additional process and equipment (NH3/H2O)
Ionic liquid (IL)
• High boiling point• high chemical and thermal stability• Good affinity with refrigerants• Adjustable design of anion and
cationStre
ngth
s
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Roles of Molecular Simulation
● To screen the optimum ionic liquid for absorption cycles?
● To determine the performance of the cycle..
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Content
● Introduction● The Absorption Heat Pump (AHP) Cycle● Property predictions● Results and discussions● Conclusions
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AHP with IL
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Single-effect AHP
• In steady state.• The solution is at equilibrium leaving GEN, 5 K subcooling leaving ABS,• The refrigerant in outlets of CON or EVA is saturated.• 5 K for the pinch temp. difference in SHX.• Heat losses, pressure losses and pumping work are neglected.A
ssum
ptio
ns
𝐶𝑂𝑃 =𝑄&'(𝑄)*+
𝑓 =𝑚.̇𝑚0̇
=1 − 𝑤4𝑤5 − 𝑤4
CON
EVA2
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4 7
Heating Water
Hot Water (Driving Heat)
ABS
SHX
GEN
1
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Heating Water
Chilled Water
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Content
● Introduction● The Absorption Heat Pump (AHP) Cycle● Property predictions● Results and discussions● Conclusions
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Necessary properties
● Solubility (VLE) --à● Heat capacity● Heat of absorption
• Coefficient of performance• Circulation ratio
• Test cases: [emim][TF2N] & [emim][SCN] with NH3
P-T-x
enthalpies
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Solubility (VLE)
● Solubility (VLE) à● Monte Carlo(MC) simulations in the osmotic ensemble are
performed to compute the solubility of NH3 in IL
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Heat capacities of ILs
Cp (ILs) = Cpig + Cpres
↑ ↑• QM calculations • MC in NPT ensemble
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Enthalpy of absorption
↑ ↑ ↑• MC in osmotic ensemble • NIST • MC in NPT ensemble
])1([ ILNHNHNHsolabs 333 hxhxhh -+-=D
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resres res
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Content
● Introduction● The Absorption Heat Pump (AHP) Cycle● Property predictions● Results and discussions● Conclusions
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Solubilities
(a) (b)
Computed NH3 solubilities (blue/green/cyan/magenta) in (a) [emim][TF2N] and(b) [emim][SCN], compared to solubilities calculated with the experimentaldata (open) and correlated (black), and simulation results of Shi and Maginn(2009) (red) at 308.15 K, 347.15 K, 373.15 K, and 393.15 K.
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Heat capacities
Comparison between computed total heat capacities (blue), computational results ofMaginn et al. (2014), and experimental measurements of Ge et al. (2008) (green),Paulechka et al. (2007) (cyan), Ferreira et al. (2012) (magenta), Navarro et al. (2013)(purple), and Ficke et al. (2010) (orange) for (a) [emim][TF2N] and (b) [emim][SCN].
(a) [emim][TF2N] (b) [emim][SCN]
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Enthalpies of Absorption
● Enthalpies of absorption at different cycle conditions
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Performance prediction
• Prediction is in principle possible, but not precise
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Content
● Introduction● The Absorption Heat Pump Cycle● Property predictions● Results and discussions● Conclusions
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Conclusion & Outlook
● It is possible to use MS to screen and assess NH3/IL in AHP, but better force fields are required!
● Might be still useful in the complete absence of experimental data.
● Has potential to extend the experimental range and to predict mixture properties.
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Question?Meng WANG*, Carlos A. INFANTE FERREIRA
[email protected] and Energy Department,
Delft University of Technology
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Backup slides
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● Simulation details» TraPPe force field for NH3
» ILs force fields are taken from Liu et al. (Ind. Eng. Chem. Res., 51, 7242-7254, 2012.) The anion
and the alkyl part of the cation are considered flexible while the ring of the cation is considered rigid.
» Lennard-Jones interactions are truncated and shifted at 12Å.
» Electrostatic interactions are considered via the Ewald summation technique with a relative precision
of 1074.
» MC simulations are performed using RASPA.
» The solubility is computed by conducting MC simulations in the osmotic ensemble.
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Backup slides
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● Simulation details» Pure component enthalpies are calculated in the NPT ensemble.
» The fluctuation formula in the NPT ensemble is applied to compute the residual part of the heat
capacity.
» The ideal part of the heat capacity is calculated via QM.
» QM calculations of the isolated ions are performed using Gaussian.
» The B3LYP functional with a 6-31+G(2df,p) basis set is used.
» A scaling factor of 0.965 is applied to the vibrational frequencies.
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Backup slides
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● Enthalpies of solutions» Saturated solution (T, P, wNH3)
– for IL
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( ) ( ) ( ) ( )3 3 3 3, , = , ,NH NH NH IL IL mix NHh T P w w h T w h T h T P w+ +D( ) ( )
00 0
T ILIL pTh T h T C dT= + ò
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