Susan Krumdieck

Test Method and Equivalent Circuit Modeling of a PEM Fuel Cell in a Passive State

A novel test protocol is proposed for fuel cells that are in a nonfunctioning or passive state. Standard fuel-cell test methods are reviewed, along with the equivalent circuit models (ECMs) used to represent functioning or active fuel cells. Standard active tests focus on single cells, while the passive test is shown to be applicable to testing multiple cells. The passive test measures electrical characteristics of the fuel cell in the absence of electrochemical reactions. A simple ECM is developed to describe the cell behavior under the passive test conditions. Circuit model parameters of many series-connected cells can be acquired using the results of a single stack test. Proton exchange membrane fuel cells (PEMFCs) from three manufacturers were tested, ranging in system power from 12-500 W. Test results for each PEMFC exhibited similar behavior that is well predicted by the ECM. A strong similarity between a passive fuel cell and a double layer capacitor is discussed.

Delivering Sustainable Infrastructure that Supports the Urban Built Environment

Sustainable living will require megacity-level infrastructural support designs and paradigms.

Growth Rate and Morphology for Ceramic Films by Pulsed-MOCVD

Abstract Titania films were deposited on nickel substrates from a dilute solution of titanium isopropoxide (TTIP) in toluene in order to study the growth rate and degree of microstructure control attainable with a metalorganic chemical vapor deposition system called pulsed-MOCVD. This novel system employs pulsed liquid injection with ultrasonic atomization to deliver the precursor to the low-pressure reactor. The film growth rate was studied as a function of temperature and precursor injection rate. An Arrhenius behavior was evident for susceptor temperatures below 500°C. At higher temperatures, the growth rate was nearly equal to the injection rate. Films 45±0.1-μm thick were deposited at rates of up to 0.5±0.008 μm/min. Two methods were employed for measurement of film growth rate, direct in situ observation of color-fringe evolution and calculation from final film thickness measurements using an optical microscope. The influence of deposition parameters on morphology was studied. The microstructure was characterized using optical and scanning electron microscopy (SEM) and X-ray diffraction (XRD). At temperatures below 500°C the film was dense with small equiaxed crystals. At higher temperatures films were textured and columnar. With the combination of high injection rate and high temperature, fully dense oriented films were produced.

Kinetic model of low pressure film deposition from single precursor vapor in a well-mixed, cold-wall reactor

Abstract A phenomenological model was derived to describe the deposition kinetics of oxide film growth from thermally activated decomposition of vapor precursor on a heated surface at low pressure. A Langmuir derivation of mass balance on the growing film surface with surface saturation condition was used to model the deposition. Growth rate of solid oxide film was modeled as a function of molecular arrival rate, adsorption rate, and surface reaction rate. The model was applied to a novel metalorganic chemical vapor deposition process (Pulsed-MOCVD). The process features precisely controlled pulsed injection of precursor solution with ultrasonic atomization to deliver the precursor vapor to the reactor with no carrier gas. Growth behavior was predicted for an experimental investigation in which a dilute solution of Ti(OPr) 4 (isopropoxide) in toluene was used as the liquid precursor for TiO 2 rutile film on nickel substrate.

Experimental Characterization and Modeling of Pulsed MOCVD with Ultrasonic Atomization of Liquid Precursor

Layers of titania were deposited on nickel substrates by an innovative process called pulsed MOCVD. Variation in growth rate, conversion efficiency, crystallographic orientation, and microstructure were studied as functions of precursor injection rate and deposition temperature. Pulsed-MOCVD was found to provide a great deal of control of microstructure, optimization for high growth rates, and high conversion efficiency. A Langmuir derivation of mass balance on the growing film surface with a surface saturation condition was used to model the deposition.

Evaluating the Feasibility of Biomass Pyrolysis Oil for Spray Combustion Applications

Current fuel conversion technology is a result of decades of experience with fossil fuels. The liquid fuels derived from the pyrolysis of biomass are significantly different from fossil fuel oils. The chemical and physical properties of typical pyrolysis oils were investigated and compared to fossil fuels. Special fuel handling requirements for the bio-oil were incorporated into a fuel delivery system design and a laboratory scale spray combustor system was constructed. The implications of the viscosity and surface tension on the atomization were analyzed, leading to an experimental combustion chamber and air swirler design. Hot-gas filtered pyrolysis oil made from poplar wood at NREL was used in the combustion experiments. Emissions were monitored and CFR 40 part 60 methods were used to sample stack gas. These results were used to determine optimal operating conditions. It was concluded that, within specific constraints, an industrial size boiler or furnace could be constructed and operated to reliably b...

Researching Travel Behavior and Adaptability

This article describes a virtual reality role-playing game that was developed as a survey tool to collect travel behavior data and explore and monitor travel behavior adaptation. The Advanced Energy and Material Systems Laboratory has designed, developed a prototype, and tested such a game platform survey tool, called Travel Activity Constraint Adaptation Simulation (TACA SIM). A main objective is investigating adaptability under the simulated situation of rapid fuel price. The computer game survey approach has the potential to capture real behavior data through a well-controlled experiment, because the participant experiences the survey as a role-play exploration. Feedback from participants confirms that TACA SIM collects data efficiently in an acceptable time while the participants enjoyed the experience. The authors propose that this gamed-based survey approach provides the basis for collecting and evaluating travel behavior data and adaptation behavior.

Implementation of unsteady sampling procedures for the parallel direct simulation Monte Carlo method

An unsteady sampling routine for a general parallel direct simulation Monte Carlo method called PDSC is introduced, allowing the simulation of time-dependent flow problems in the near continuum range. A post-processing procedure called DSMC rapid ensemble averaging method (DREAM) is developed to improve the statistical scatter in the results while minimising both memory and simulation time. This method builds an ensemble average of repeated runs over small number of sampling intervals prior to the sampling point of interest by restarting the flow using either a Maxwellian distribution based on macroscopic properties for near equilibrium flows (DREAM-I) or output instantaneous particle data obtained by the original unsteady sampling of PDSC for strongly non-equilibrium flows (DREAM-II). The method is validated by simulating shock tube flow and the development of simple Couette flow. Unsteady PDSC is found to accurately predict the flow field in both cases with significantly reduced run-times over single processor code and DREAM greatly reduces the statistical scatter in the results while maintaining accurate particle velocity distributions. Simulations are then conducted of two applications involving the interaction of shocks over wedges. The results of these simulations are compared to experimental data and simulations from the literature where there these are available. In general, it was found that 10 ensembled runs of DREAM processing could reduce the statistical uncertainty in the raw PDSC data by 2.5-3.3 times, based on the limited number of cases in the present study.

THE SURVIVAL SPECTRUM: THE KEY TO TRANSITION ENGINEERING OF COMPLEX SYSTEMS

This paper puts forward a simple idea describing the time, space and relationship scales of survival. The proposed survival spectrum concept represents a new way to think about sustainability that has clear implications for influencing engineering projects in all fields. The argument for the survival spectrum is developed sequentially, building on theory, definition, examples and history. The key idea is that sustainability can be effectively addressed by emergence of a new field, Transition Engineering. This is a parallel of safety engineering but with longer time scale, broader space scale, and more complex relationship scale. The past 100-year development of safety engineering is examined as a model for development of sustainability risk management and mitigation. The conclusion is that the new field, Transition Engineering, will emerge as the way our society will realize reduction in fossil fuel use and reduction in the detrimental social and environmental impacts of industrialization.

Modelling of organic Rankine cycle system and heat exchanger components

Numerical models of a standard organic Rankine cycle (ORC) system and the heat exchangers comprising the system are developed as a design tool platform for a flexible design. The objective is design of an efficient, cost-effective ORC power plant that can effectively exploit low-grade industrial waste heat or low to medium-temperature geothermal fluid. Typical heat exchanger configurations were modelled, including the circular finned-tube evaporator, air-cooled condenser, and flat-plate preheater. A published ORC configuration and process conditions from experiments are used for the thermodynamic cycle analysis in order to validate of the system model. Heat transfer correlations and friction factors are described for the modelling of the heat exchangers. The simulation results of the ORC system provide the design requirements for the heat exchangers. Geometric specifications and performance of the heat exchangers are determined by iterative simulations.