41 documents found, page 1 of 5
Weekly self-scheduling, forward contracting, and pool involvement for an electr...
Lima, Ricardo M.; Novais, Augusto Q.; Conejo, Antonio J.his paper addresses the optimization under uncertainty of the self-scheduling, forward contracting, and pool involvement of an electricity producer operating a mixed power generation station, which combines thermal, hydro and wind sources, and uses a two stage adaptive robust optimization approach. In this problem the wind power production and the electricity pool price are considered to be uncertain, and are d...
Deterministic optimization of the thermal Unit Commitment problem: A Branch and...
Marcovecchio, Marian G.; Novais, Augusto Q.; Grossmann, Ignacio E.This paper proposes a novel deterministic optimization approach for the Unit Commitment (UC) problem, involving thermal generating units. A mathematical programming model is first presented, whichincludes all the basic constraints and a set of binary variables for the on/off status of each generator ateach time period, leading to a convex mixed-integer quadratic programming (MIQP) formulation. Then,an effective...
Multi-period design and planning of closed-loop supply chains withuncertain sup...
Zeballos, Luís J.; Mendez, Carlos A.; Barbosa-Póvoa, Ana Paula; Novais, Augusto Q.A design and planning approach is proposed for addressing general multi-period, multi-product closed-loop supply chains (CLSCs), structured as a 10-layer network (5 forward plus 5 reverse flows), with uncertain levels in the amount of raw material supplies and customer demands. The consideration ofa multi-period setting leads to a multi-stage stochastic programming problem, which is handled by amixed-integer li...
Kinetic modeling of self-hydrolysis of aqueous NaBH4 solutions by model-based i...
Retnamma, Rajasree; Novais, Augusto Q.; Rangel, C. M.; Yu, Lin; Matthews, Michael A.The present work reports the kinetic modeling of self-hydrolysis of non-buffered, nonstabilized NaBH4 solutions by model-based isoconversional method. The overall kinetics is described by a ‘reaction-order’ model in a practical operating window of 10-20 wt% NaBH4 solutions at 25-80 ºC and 0-50% conversions. The apparent activation energy and preexponential factor are interrelated through a kinetic compensation ...
Electrochemical impedance spectroscopy modeling using the dis-tribution of rela...
Lopes, Vitor V.; Rangel, C. M.; Novais, Augusto Q.This paper proposes a new approach to determine the distribution of relaxation times (DRT) directly from the electro-chemical impedance spectroscopy (EIS) data, i.e. without the use of an equivalent electrical circuit model. The method uses a generalized fractional-order Laguerre basis to represent EIS where both the parameters of the basis and their co-efficients are estimated by solving a nonconvex minimizati...
Kinetics of sodium borohydride hydrolysis in aqueous-basic solutions
Retnamma, Rajasree; Rangel, C. M.; Novais, Augusto Q.; Matthews, Michael A.Liquid-phase catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production necessitates long-term stability of base-stabilized NaBH4 solutions at higher temperatures. The present paper reports the kinetics of aqueous-basic solutions containing 20 wt% NaBH4 with 1-15 wt% sodium hydroxide (NaOH) at 80 0C. The established kinetic model employs a modified isoconversional method assuming single-step kin...
Modelling and identification of the dominant phenomena in hydrogen fuel-cells b...
Lopes, Vitor V.; Rangel, C. M.; Novais, Augusto Q.This paper proposes the use of the distribution of relaxation times (DRT) for the analysis of the dynamic behavior of hydrogen fuel-cells. With this aim it presents a new method to compute the DRT directly from electrochemical impedance spectroscopy (EIS) data. The method is formulated as a nonconvex complex domain optimization problem where each EIS spectra is approximated by a general fractional-order Legendr...
Assessing cell polarity reversal degradation phenomena in PEM fuel cells by ele...
Travassos, Maria Antónia; Lopes, Vitor V.; Silva, R. A.; Novais, Augusto Q.; Rangel, C. M.Electrochemical impedance spectroscopy (EIS) is identified as one of the most promising in-situ diagnostics tools available for assessing fuel cell ageing and degradation. In this work, the degradation phenomena caused by cell polarity reversal due to fuel starvation of an open cathode 16 membrane electrode assembly (MEA) – low power (PEM) fuel cell (15 W nominal power) – is reported using EIS as a base techniq...
Electrochemical impedance spectroscopy modeling using the dis-tribution of rela...
Lopes, Vitor V.; Rangel, C. M.; Novais, Augusto Q.This paper proposes a new approach to determine the distribution of relaxation times (DRT) directly from the electro-chemical impedance spectroscopy (EIS) data, i.e. without the use of an equivalent electrical circuit model. The method uses a generalized fractional-order Laguerre basis to represent EIS where both the parameters of the basis and their co-efficients are estimated by solving a nonconvex minimizati...
Kinetics of sodium borohydride hydrolysis in aqueous-basic solutions
Retnamma, Rajasree; Rangel, C. M.; Novais, Augusto Q.; Matthews, Michael A.Liquid-phase catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production necessitates long-term stability of base-stabilized NaBH4 solutions at higher temperatures. The present paper reports the kinetics of aqueous-basic solutions containing 20 wt% NaBH4 with 1-15 wt% sodium hydroxide (NaOH) at 80 0C. The established kinetic model employs a modified isoconversional method assuming single-step kin...