Chemical & Biomolecular Engineering

Permanent URI for this communityhttp://hdl.handle.net/1903/2219

Formerly known as the Department of Chemical Engineering.

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    ASSESSING THE IMPACT OF ELECTROCHEMICAL-MECHANICAL COUPLING ON CURRENT DISTRIBUTION AND DENDRITE PREVENTION IN SOLID-STATE ALKALI METAL BATTERIES
    (2023) Carmona, Eric Alvaro; Albertus, Paul; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The relationship between mechanical stress states and interfacial electrochemical thermodynamics of Li metal/Li6.5La3Zr1.5Ta0.5O12 and Na metal/Na-β”-Al2O3 systems are examined in two experimental configurations with an applied uniaxial load; the solid electrolytes were pellets and the metal electrodes high-aspect-ratio electrodes. Our experimental results demonstrate that (1) the change in equilibrium potential at the metal/electrolyte interface, when stress is applied to the metal electrode, is linearly proportional to the molar volume of the metal electrode, and (2) the mechanical stress in the electrolyte has negligible effect on the equilibrium potential for an experimental setup in which the electrolyte is stressed and the electrode is left unstressed. Solid mechanics modeling of a metal electrode on a solid electrolyte pellet indicates that pressure and normal stress are within ~0.5 MPa of each other for the high aspect ratio (~1:100 thickness:diameter in our study) Li metal electrodes under loads that exceed yield conditions. To assess the effect of electrochemical-mechanical coupling on current distributions at Li/single-ion conducting solid ceramic electrolyte interfaces containing a parameterized interfacial geometric asperity, we develop a coupled electrochemical-mechanical model and carefully distinguish between the thermodynamic and kinetic effects of interfacial mechanics on the current distribution. We find that with an elastic-perfectly plastic model for Li metal, and experimentally relevant mechanical initial and boundary conditions, the stress variations along the interface for experimentally relevant stack pressures and interfacial geometries are small (e.g., <1 MPa), resulting in a small or negligible influence of the interfacial mechanical state on the interfacial current distribution for both plating and stripping. However, we find that the current distribution is sensitive to interface geometry, with sharper (i.e., smaller tip radius of curvature) asperities experiencing greater current focusing. In addition, the effect on the current distribution of an identically sized lithium peak vs. valley geometry is not the same. These interfacial geometry effects may lead to void formation on both stripping and plating and at both Li peaks and valleys. This work advances the quantitative understanding of alkali metal dendrite formation within incipient cracks and their subsequent growth, and pore formation upon stripping, both situations where properly accounting for the impact of mechanical state on the equilibrium potential can be of critical importance for calculating the current distribution. The presence of high-curvature interface geometry asperities provides an additional perspective on the superior cycling performance of flat, film-based separators (e.g., sputtered LiPON) versus particle-based separators (e.g., polycrystalline LLZO) in some conditions.
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    DETERMINING ELONGATION AT BREAK OF CABLE INSULATIONS USING CONDITION MONITORING PARAMETERS
    (2022) Gharazi, Salimeh; Al-Sheikhly, Mohamad; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Many United States nuclear power plants are seeking to renew life licenses to extend the operational life of the plant to an additional 20 or 40 years. Degradation of insulation and jacket of cables, which are originally designed for 40 years in the second round of operation, is a critical issue which can impair the safe and reliable function of cables and ultimately the plant. The main criterion for assessing the end of life of these insulations is defined when the elongation at break reaches 50% of its original value. However, measuring the elongation at break is done by tensile tests, which are destructive and need large samples; the feasibility of these tests is significantly limited on installed cables at nuclear power plants. A new model was developed to relate the changes in the activation energy corresponding to EAB in terms of the changes in the activation energies corresponding to non-destructive condition monitoring, NDE-CM, parameters. The coefficients of the model are obtained by normalizing the calculated activation energy of each CM parameter’s changes with the activation energy of EAB changes. Therefore, it is possible to estimate EAB values, in the present developed equations, from the substitution of activation energy corresponding to EAB changes with the correlated activation energy of the non-destructive condition monitoring parameters. Cable Polymer Aging database, C-PAD, which is provided by Electric Power Research Institute, and supported by the U.S. Department of Energy, along with experimental results done in the University of Maryland, UMD, laboratory was used as the database. While taking advantage of C-PAD database which contains condition monitoring parameters of insulation cables such as Elongation at break, Modulus and Density provided by many U.S. and international research institutes, extensive aging experimental results on two cables, each with two grades provided us with not only a database but also a better understanding of the aging mechanism. The published experimental results of cable insulations are used to validate the model. A good fit between the experimental and modeled results confirms the validity of the model.
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    Modeling and Optimization of a Photoelectrochemical Solar Hydrogen Cell with TiO2 as a Photo-anode
    (2014) Alobaid, Aisha A.; Adomaitis, Raymond; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A photoelectrochemical (PEC) cell model for solar hydrogen production with titanium dioxide (TiO2) as a photo anode and platinum (Pt) as a cathode is developed. Despite the wide bandgap of TiO2 resulting in limited photon absorption from the sun, it is still a good candidate due to its stability in liquid electrolytes and reasonable cost. In this model, Beer-Lambert law is used in conjunction with the empirical diode equation to calculate the electron/hole pair generation rate in the photo-anode, and the external current reaching the cathode to estimate and optimize the hydrogen generation rate evolving at the cathode with TiO2 and ITO thicknesses as optimization variables. The model revealed an optimal solution of TiO2 thickness of 3230 nm at 400 nm ITO thickness, with optimal external current value of 26.9 A/m2, hydrogen generation rate of 1.394x10-4 mol/(m2s), and an overall cell efficiency of 3.4 %.
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    Biomethanol Conversion from Sugar Beet Pulp with Pectin Methyl Esterase
    (2006-08-09) Wang, Quanzeng; Wang, Nam Sun; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Conversion of renewable biomethanol was studied from sugar beet pulp with pectin methyl esterases (PMEs). An analytical method for methanol and PME activity was developed based on potassium permanganate assay. Results showed that this method was sensitive, accurate and stable. Two PMEs, natural and mutated, were then produced and characterized. The kinetics parameters of Michaelis-Menten model and thermal deactivation model were determined. Based on the characterization results of PMEs, the methanol conversion from beet pulp was further studied and the effects of organisms, pH values, pulp size, and temperature were evaluated. After this, methods for separation and concentration of methanol from water, including striping, distillation and pervaporation, were studied and a model for the recovery of methanol from beet pulp after reaction was developed. Finally, the whole methanol conversion process was designed. The economic cost based on this design was estimated.
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    FLUID AND PARTICLE DYNAMICS IN AN AEROSOL VIRTUAL IMPACTOR
    (2004-05-03) Charrouf, Marwan; Calabrese, Richard V; Chemical Engineering
    The collection and characterization of chemical and biological aerosols is essential to many areas of particle research such as toxicological studies, pollutant sampling, and biohazard assessment. This work presents the simulation of a low cutpoint, high volume aerosol sampling device known as the "virtual impactor". A steady state, three dimensional RANS type calculation is done using the FLUENT(TM) computational fluid dynamics code to predict the turbulent flow field inside the device. Particle collection efficiency and wall losses are then obtained by solving the particle equation of motion governed by drag for mono-dispersed samples of spherical particles in the 0.1-0.4 micro-meter diameter range. Predictions of the mean fluid velocity field with the incompressible Reynolds stress model and the compressible k-epsilon turbulence model are relied upon for conducting particle tracking calculations. FORTRAN 90 computer code is developed to solve the particle equation of motion using an implicit second order accurate time integration scheme. In addition, a multi-variate, scattered point interpolation method is implemented to obtain the fluid velocity at a position away from an Eulerian mesh point. It is found that "adaptive" drag law models are necessary to correctly account for slip and compressibility. The results indicate the trends observed in the experiments, and a 50% cutpoint diameter between 0.250 and 0.275 micro-meter. Recommendations for improved modeling in future work are made.