Mass Flow Controller Research Articles

Yanqing solar field: Dynamic optical model and operational safety analysis

A dynamic optical model was established for the Yanqing solar field at the parabolic trough solar thermal power plant and a simulation was conducted on four separate days of clear weather (March 3rd, June 2nd, September 25th, December 17th). The solar collector assembly (SCA) was comprised of a North-South and East-West layout. The model consisted of the following modules: DNI, SCA operational, and SCA optical. The tracking angle characteristics were analyzed and the results showed that the East-West layout of the tracking system was the most viable. The average energy flux was simulated for a given time period and different SCA layouts, yielding an average flux of 6kW/m2, which was then used as the design and operational standards of the Yanqing parabolic trough plant. The mass flow of North-South layout was relatively stable. The influences of the defocus angles on both the average energy flux and the circumferential flux distribution were also studied. The results provided a theoretical basis for the following components: solar field design, mass flow control of the heat transfer fluid, design and operation of the tracking system, operational safety of SCAs, and powerproduction prediction in the Yanqing 1MW parabolic trough plant.

Thermodynamic optimization of heat exchanger tanks by exergy analysis method

The paper introduces heat exchanger tanks, detailing their dominant thermodynamic relations to obtain the exergy analysis relations of heat exchanger tanks. Heat exchanger tank is examined under various laboratory conditions, including the power of heat element inside the tank, mass flow rate of cooling water of tank wall and the mixer speed inside the tank which were all variable. The needed data relating to the water temperature inside the tank as output water after cooling the tank wall based on these conditions. The exergy loss (irreversibility) and efficiency diagrams were then drawn and the optimization parameters of performance and their range were evaluated using exergy analysis. This was meant to increase the efficiency and decrease the energy consumption. The results indicate that under thr circumstances of controlling mass flow rate of input cold water and power of heat element as well as the mixer speed, respectively, in their possible minimum and maximum measures, the system performs in optimal conditions according to exergy analysis. Keywords: Thermodynamic optimization; heat exchanger tank; exergy analysis

PROTON EXCHANGE MEMBRANE FUEL CELL/SUPERCAPASITOR HYBRID POWER MANAGEMENT SYSTEM FOR A GOLF CART

This paper presented the transformation of a golf cart system powered lead acid battery into an environmental friendly hybrid vehicle. The design developed by using an advantage contributes by the uprising alternative power source candidate which is Proton Exchange Membrane Fuel Cell (PEMFC) and the maintenance free energy storage device, a supercapacitor (SC). The fuel cell (FC) stack was an in house manufactured with 450 W (36 V, 12.5 A) power, while the SC was from Maxwell Technologies (48 V, 165 F). This two power sources were controlled by the mechanical relay, meanwhile the reactant (hydrogen) are control by mass flow controller (MFC) both signaled by a National Instrument (NI) devices. The power management controller are programmed in the LabVIEW environment and then downloaded to the NI devices. The experimental result of the power trend was compared before and after the transformation with the same route to validate the effectiveness of the proposed power management strategy. The power management successfully controls the power sharing between power sources and satisfies the load transient. While the reactant control managed to vary the hydrogen mass flow rate feed according to the load demand in vehicular applications.

Tunisian European Cooperation Project: PEM Fuel Cells Technology

This paper presents one of the research goals of Empowering Tunisian Renewable Energy Research Activities (ETRERA). ETRERA is a cooperation project between the Research and Technologies Centre of Energy (CRTEn) from Tunisia and European partners. European partners are CNR-ITAE and Innovabic from Italy and polytechnic Nantes from France. This paper focuses on the design and realization of a fuel cell test station. The test station is used to advance CRTEn's activities in new and emerging alternative energy technologies. The fuel cell test station was developed and built in order to evaluate and qualify proton exchange membrane fuel cells (PEMFC). A circuit of gas was developed and a rack was designed and built taking in consideration several aspects such as pressure drop, condensation phenomena and security. Development of an interface in the LABVIEW environment was performed to enable mass flow controller and the solenoid valves control. It also allows PC-based data acquisition of fuel cell power, temperature, pressure and others. Preliminary tests have been conducted to confirm the proper functioning of the test bench.

Controlled Expansion of Supercritical Solution: A Robust Method to Produce Pure Drug Nanoparticles With Narrow Size-Distribution

We introduce a robust, stable, and reproducible method to produce nanoparticles based on expansion of supercritical solutions using carbon dioxide as a solvent. The method, controlled expansion of supercritical solution (CESS), uses controlled mass transfer, flow, pressure reduction, and particle collection in dry ice. CESS offers control over the crystallization process as the pressure in the system is reduced according to a specific profile. Particle formation takes place before the exit nozzle, and condensation is the main mechanism for postnucleation particle growth. A 2-step gradient pressure reduction is used to prevent Mach disk formation and particle growth by coagulation. Controlled particle growth keeps the production process stable. With CESS, we produced piroxicam nanoparticles, 60 mg/h, featuring narrow size distribution (176 ± 53 nm).

Coexistence of detonation with deflagration in rotating detonation engines

Rotating detonation engines of high thermal efficiency and specific impulse have been studied a lot. However, rotating detonation waves lead to uneven flow field, local high temperature and high pressure, tending to damage the combustor. An experimental way to keep both rotating detonation waves and deflagration in the combustor and to combine the advantages of rotating detonation engines and deflagration engines, is introduced here. Pressure sensors measure the pressure of rotating detonation waves and gas mass flow controllers control the mass flow rates of reactants. A standard speed camera captures the events of rotating detonation and deflagration. It is discovered that the rotating detonation is much more intense than deflagration. Both upstream rotating detonation waves and downstream deflagration respectively dependent on the trunk stream and the tributary can coexist in the combustor. The predetonator is the boundary between the detonation region and deflagration region in the combustor. The coexistence of detonation and deflagration weakens the combustion instability caused by rotating detonation, which may be helpful for rotating detonation to be applied.

The gas chromatographic analysis of the reaction products of the partial isobutane oxidation as a two phase process

The partial oxidation of isobutane to t-butyl hydroperoxide (TBHP) has been studied analytically for the first time as a two-phase process in a capillary micro reactor. In order to obtain detailed information on products, yields, selectivities and reaction pathways, the products have been investigated by GC/MS. An Rxi-5ms column and a PTV-injector have been used to analyze the liquid products. TBHP, di-t-butyl peroxide (DTBP), t-butanol (TBA), and propanone as main products as well as further by-products e.g. methanal, isopropanol, isobutanol and isobutanal in minor quantities have been identified by MS. The liquid products have been obtained by quenching the reaction and vaporizing the isobutane afterwards by pressure reduction using a mass flow controller allowing a constant mass flow. For all liquid reaction products calibrations, a validation of the method including limits of quantification and detection as well as calculation of uncertainties has been performed. The results have been applied successfully for the investigation of the selectivities of the main products (TBHP, DTBP, TBA, propanone) of the isobutane oxidation. In the frame of the analytical investigation of this reaction a correlation coefficient of r2>0.999 for TBHP and DTBP, which is necessary to perform a validation, has been obtained for the first time. The gaseous phase has been analyzed using a GASPRO column, a DEANS switch, a mole sieve column and a TCD detector. Apart from the gaseous reactants, isobutene has been found.

Numerical analysis of a high-temperature proton exchange membrane fuel cell under humidified operation with stepwise reactant supply

Dynamic response is a very important issue in a vehicle powered by a proton exchange membrane fuel cell (PEMFC) due to its frequent load change. In this study, three-dimensional transient simulation was conducted to investigate the dynamic response of a high temperature PEMFC. A stepwise change in the cell voltage was conducted to simulate the sudden load change during vehicle operation. After the load change, the oxygen concentration, ionic conductivity, and local current density were analyzed, and the water transport through the membrane electrode assembly (MEA) was also evaluated to determine the characteristics of overshoot and settling time. The result showed that the overshoot was mainly due to the pre-existing excessive oxygen. At the humidified condition, the overshoot increased with increasing relative humidity due to higher ionic conductivity and electrochemical reaction rate. In addition, a stepwise mass flow control strategy for the reactants decreased the overshoot and settling time by decreasing the amount of oversupplied oxygen immediately after the load change. The settling time for the stepwise mass flow control was approximately 30% lower than that for the constant mass flow rate control.

Design of a heated micro-cantilever optimized for thermo-capillary driven printing of molten polymer nanostructures

Here we present an atomic force microscope (AFM) cantilever design capable of patterning millions of polymer nanostructures with integrated mass flow sensing and control. The micro-cantilever has two embedded joule heaters connected via a microchannel, where thermo-capillary forces induced by the temperature gradient between heaters can deliver 40ng of polymer to the tip. We used multi-physics finite element analysis to optimize the thermo-mechanical and thermo-fluidic performance of the device. A modal analysis of the cantilever vibration during operation show the resonant frequencies of the first four cantilever modes are sensitive to the location of the advancing polymer meniscus within the channel, where the frequency shifts by 1.7%, 0.2%, 0.4%, and 1.8% for modes 1–4, respectively. The cantilever frequency shift thus provides a facile measure of mass flow rate within the channel. We further model the temperature rise in each heater, showing that the heaters can reach temperatures exceeding 400°C with a temperature gradient along the channel between the two heaters tunable from −2,000,000 to 2,000,000°C/m. Computational fluid dynamics simulations of molten polymer flowing in the microchannel shows the leading edge advances as t according to Washburn’s equation, and the velocity of the leading edge depends significantly on the imposed temperature gradient. Large temperature gradients in the direction of polymer imbibition serve to increase the leading edge velocity for faster channel filling, while large temperature gradients opposing capillary filling can decrease filling speeds, hold the leading edge still, and even reverse polymer flow. Thus, the cantilever tip can be inked, cleaned, and re-inked by controlling the temperature of the integrated heaters. The design presented here provides a platform for wafer scale polymer nanostructure fabrication with mass flow control required for nano-manufacturing complex polymer-based devices.

Recommended Practice for Flow Control and Measurement in Electric Propulsion Testing

Accurate control and measurement of propellant flow to a thruster is one of the most basic and fundamental requirements for operation of electric propulsion systems, whether they be in the laboratory or on flight spacecraft. Hence, it is important for the electric propulsion community to have a common understanding of typical methods for flow control and measurement. This paper addresses the topic of propellant flow primarily for the gaseous propellant systems that have dominated laboratory research and flight application over the last few decades, although other types of systems are also briefly discussed. Although most flight systems have employed a type of pressure-fed flow restrictor for flow control, both thermal-based and pressure-based mass flow controllers are routinely used in laboratories. Fundamentals and theory of operation of these types of controllers are presented, along with sources of uncertainty associated with their use. Methods of calibration and recommendations for calibration processes are presented. Finally, details of uncertainty calculations are presented for some common calibration methods and for the linear fits to calibration data that are commonly used.

Bubble Tolerant Liquid Management

Initially CMP slurries were hand mixed in small quantities and drawn from buckets at the back of the tool using peristaltic pumps. Batch to batch variations adversely affected yields as did pulsatile dispense. Eventually, automated, batch verified, basement blending and loop distribution systems came into use. These systems reduced batch to batch variation but, still relied upon peristaltic pumps for dispense volume control. Particle generation from tubing and high chemical cost drove a need for a change at sub-micron (90 Nanometer) geometries. Various flow control schemes were evaluated including paddle wheel, turbine and differential pressure based systems ultimately settling on ultrasonic based flow controllers as the preferred technology. However, as feature sizes continue to shrink, the chemistries required to achieve smaller feature sizes becomes more and more exotic. Mixtures including peroxides and hydroxides naturally out-gas which produce bubbles in the dispensed flow streams, and in some cases results in a two-phase flow regime. At comparatively low volumetric void fractions bubble concentrations (less than 10%) can adversely affect measurement accuracy of DP, Paddle Wheel, Turbine or Ultrasonic flow measurement technologies to the extent that many of these flow measurement technologies cease to operate satisfactorily. Malema has developed a mass based, flow controller for slurry and clear chemical dispense applications. Based on Coriolis mass flow rate measurement, the Malema Coriolis Mass Flow Controller (CMFC) is essentially bubble tolerant. Flow meter / flow controller manufacturers used an assortment of software techniques to filter the effects of these entrained bubbles with limited results. Since Coriolis measures mass directly, bubbles have very little effect on measured or dispensed volumes. A brief history of the Coriolis Effect, how it is applied to direct mass flow rate measurements will be presented and discussed including a description of Malema’s family of CMFCs and associated performance data.

Response Characteristics of a Pre-Commercial Mixed Potential Ammonia Sensor in Diesel Engine Exhaust

Advancements in both combustion system design and emission control technologies have allowed more efficient diesel engines to meet stringent exhaust emissions standards. With very stringent emission regulations currently in place, combustion system design and combustion management are used in conjunction with available exhaust after treatment technologies for optimal reduction of emissions to meet regulatory targets. Current diesel vehicles in the US are equipped with a diesel oxidation catalyst (DOC) to control CO and HC emissions, a diesel particulate filter (DPF) to control particulate matter (PM) and selective catalyst reduction (SCR) or lean-NOx trap (LNT) to control NOX emissions. In SCR, NOx is reduced to H2O and N2over a catalyst through the injection of an ammonia source provided by the onboard storage of diesel exhaust fluid (DEF), typically a mixture of urea and de-ionized water. These emission control technologies add significant complexity and cost to a vehicle and some result in additional fuel penalty needed for their operation. Meeting the EPA Tier 3 emissions reduction requirements while simultaneously increasing fuel economy to meet new CAFE standards will require optimization of advanced combustion strategies and emissions control technologies as well as their state of operation under transient vehicle operation. NH3 sensors are needed to monitor DEF injection and prevent NH3 slip—a condition under which unreacted ammonia from the SCR is emitted in the tailpipe exhaust. Ideally, both NH3 and NOxsensors would be incorporated into a closed-loop system to maintain ammonia close to stoichiometry in the SCR system, and could also serve to monitor engine out and tailpipe out emissions in order to ensure regulatory compliance. Mixed-potential sensors are electrochemical devices that develop a non-Nernstian potential due to differences in the redox kinetics of various gas species at each electrode/electrolyte gas interface1,2. The difference in the steady-state redox reaction rates between the “fast” and “slow” electrodes gives rise to the measured mixed potential response. A patented LANL sensor design incorporates dense electrodes and a porous electrolyte and reproducible and stable sensors are prepared using a high temperature ceramic co-fire approach3. The use of dense electrodes minimizes deleterious heterogeneous catalysis, and the increased morphological stability of dense electrodes yields a robust electrochemical interface, increasing lifetime durability4. The use of a dense gold-alloy working electrode (e.g. the slow electrode), imparts preferential selectivity to NH3, and avoids the stability problems one finds when using thin film, porous Au electrodes5. Previously, we reported on the response of an experimental, tape-cast version of a mixed potential ammonia sensor to simulated diesel exhaust in a high-flow bench reactor at the Oak Ridge National Laboratory (ORNL) National Transportation Research Center (NTRC)7. In this work, we present recent results from evaluating the performance of a pre-commercial form of a mixed potential-based NH3 sensor in engine exhaust conditions at the NTRC using a GM 1.9L CIDI diesel engine. A planar NH3 sensor with a protective porous overcoat was tested in diesel engine exhaust gas (20 L/min) sampled downstream of the engine’s DOC. In order to simulate NH3 slip from a full SCR emissions control system, NH3 was injected immediately upstream of the sensor using a calibrated mass flow controller. The sensor response quantitatively tracked levels of injected NH3 and transients measured via Fourier transform infrared (FTIR) analyzer, using a calibration curve derived from an ammonia staircase response measured in the engine exhaust at low NOx and HC concentrations (<20 ppm) and steady-state engine conditions. Exhaust gas recirculation (EGR) switching and EGR sweeps were used to evaluate the NH3 sensor response under different amounts of total NOx. This calibration curve was used to directly compare the [NH3] calculated from sensor response to the gas phase composition measured via FTIR. References J. W. Fergus, Journal of Solid State Electrochemistry 15 (5), 971-984 (2010).F. H. Garzon, R. Mukundan and E. L. Brosha, Solid State Ionics 136-137, 633-638 (2000).P.K.Sekhar et. al., Sensors and Actuators B: Chemical 144, 112 (2010).R. Mukundan, E. L. Brosha and F. H. Garzon, Journal of The Electrochemical Society 150 (12), H279 (2003).J. Tsitron et. al., Sensors and Actuators B 192 (2014) 283-293.E. L. Brosha et al., “Response Characteristics of a Stable Mixed Potential NH3 Sensor in Simulated Diesel Exhaust,” 228th Meeting of the ECS, Phoenix, AZ, October 2015. Acknowledgments The authors would like to thank Roland Gravel and the DOE Vehicle Technology Office for providing funding for this work. Engine-based studies were conducted at the National Transportation Research Center User Facility at Oak Ridge National Laboratory. Figure 1

Chromium(VI) reduction in aqueous medium by means of catalytic membrane reactors

A novel method for catalytic reduction of chromium(VI) to chromium(III) in model and real water is proposed in this work. Hydrogen was used as a reducer. Three different catalytic membrane reactors were prepared and employed in the studied reaction. The catalytic membrane reactors were prepared using commercial corundum hollow fiber membranes. The active phases, palladium, cerium oxide, iron oxide or combinations of them, were incorporated by incipient wetness impregnation of the corresponding water-soluble salts followed by calcination and reduction. The catalytic tests were performed in semi-batch mode at ambient conditions. A mass flow controller was used to supply hydrogen to one end of the membrane whilst the other end was kept closed. The reactors were submerged into a vessel containing the chromate solution. The concentration of the chromate was continuously monitored following a standard analytical method. The initial chromate concentration was varied between 0.5 and 18mgL−1. In order to completely reduce the Cr(VI) to Cr(III), it was necessary to decrease the pH of the solution to 3. In the end of the tests the final solutions were neutralized to pH 8 and filtered. The content of chromium in the final solutions and in the precipitates was determined by inductively coupled plasma (ICP) technique. It was demonstrated that for the studied reaction the presence of palladium is essential. In all experiments, with synthetic and real water adjusted to pH 3, the catalytic membrane reactors containing palladium (0.3–0.9w/w%) effectively reduced the chromium to levels below 0.03mgL−1 without losing activity in repetitive runs. The results from ICP analyses demonstrated that the chromium can be completely eliminated from the water after neutralization and filtration.

Direct determination of cadmium in foods by solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry using a tungsten coil trap

In this work, a solid sampling device consisting of a tungsten coil trap, porous carbon vaporizer and on-line ashing furnace of a Ni–Cr coil was interfaced with inductively coupled plasma mass spectrometry (ICP-MS). A modified double gas circuit system was employed that was composed of carrier and supplemental gas lines controlled by separate gas mass flow controllers. For Cd determination in food samples using the assembled solid sampling ICP-MS, the optimal ashing and vaporization conditions, flow rate of the argon–hydrogen (Ar/H2) (v:v=24:1) carrier gas and supplemental gas, and minimum sampling mass were investigated. Under the optimized conditions, the limit of quantification was 0.5pg and the relative standard deviation was within a 10.0% error range (n=10). Furthermore, the mean spiked recoveries for various food samples were 99.4%–105.9% (n=6). The Cd concentrations measured by the proposed method were all within the certified values of the reference materials or were not significantly different (P>0.05) from those of the microwave digestion ICP-MS method, demonstrating the good accuracy and precision of the solid sampling ICP-MS method for Cd determination in food samples.

Modeling, state estimation and nonlinear model predictive control of cathode exhaust gas mass flow for PEM fuel cells

Polymer electrolyte membrane fuel cells are efficient energy converters and provide electrical energy, water and oxygen depleted air with a low oxygen content as exhaust gas if fed with air. Due to their low emission of greenhouse gases and noise they are investigated as replacement for auxiliary power units currently used for electrical power supply on aircraft. Oxygen depleted air, called ODA-gas, with an oxygen concentration of 10–11% and a low humidity can be used for tank-inerting on aircraft. A challenging task is controlling the fuel cell system for generation of dehumidified ODA-gas mass flow while simultaneously keeping bounds and gradients on control inputs. This task is attacked by a nonlinear model predictive control. Not all system states can be measured and some states measured exhibit a significant time delay. A nonlinear state estimation strategy builds the entire system state and compensates for the delay. The nonlinear model predictive control and the state estimation are derived from the system model, which is presented. Simulation and experimental results are shown.

A fabrication of colorimetric sensor using pH indicator for determination of toxic gases

Event Abstract Back to Event A fabrication of colorimetric sensor using pH indicator for determination of toxic gases Sung Yeol Kim1, Joon Woo Chon1, Jong Hyun Ko1 and Dong June Chung1 1 Sungkyunkwan University, Department of polymer science & engineering, Korea Critical toxic gases have been used in the several industrial plants. So workers were exposed to many kinds of toxic gases without proper safety guard in the field. Low concentration of toxic gases injures the eyes, nose, and respiratory organs and cause allergic reaction [1]. These gas leaks emerged as a social issue, because Exposure of toxic gases was fatal for the long term. The World Health Organization(WHO) has set a safe exposure stand respectively [2]. Colorimetric detection of gases has been used for years. They are based on the change in color of pH indicators incorporated in a porous matrix [3]. There were many researches of sensor detecting toxic gases used by pH indicators [4], but there were many disadvantages during the measurement. Expensive analytical instruments are needed, and it takes a long time to obtain the results [5]. In this study we found that it is better and easier to use simple pH indicators to detect toxic gases. We made convenient pH indicator-based films for detecting 4 types of toxic gases easily. Using polymeric binder, the pH indicators were embeded in a polymeric film. To improve sensitivity and reactivity, we added other additive for enhancement. So we could be observed by naked eyes without aid of analytical devices, and decrease the response time. As a result, we made films which reacted with toxic gases and which were faster than commercialized ones. To make pH indicator-based film sensors, we adopted a method of dip coating. Main substrate was non-woven fabric wiper(WW-2109), polymeric binder was a sodium alginate and cross linking agent was calcium chloride. To improve reactivity, benzoquinone was a additive as electron transfer agent. At first, we made a solution which added sodium alginate(1wt%), benzoquinone, and pH indicator(0.1wt%). Prepared films were impregnated again in the above solution. Then they were impregnated in a calcium chloride solution(10wt%) again. After finish to make sensor, toxic gases(20, 10ppm) was exposed constantly by mass flow controller(MFC). To observe degree of the color change, Spectrophotometer was used and the graph of ΔE*a*b* was drew every 5 seconds. Sodium alginate can use to crosslink with calcium chloride by ionic linkage. There was a good resistance to washing pH indicator in wet environment. From adding benzoquinone, the film`s color changed to the other color in the 10, 20ppm concentration of gases, and it reacted completely with in a minute. When colorimetric sensors contacted toxic gases exposed by MFC, they changed color from blue to yellow or yellow to blue, because of movement of proton. Benzoquione help a movement of proton. The change started after 10 seconds, when films contacted with toxic gases. Humidity is a important requirement. If humidity was high, its reactivity was more faster. After exposure of toxic gases, we used a spectrophotometer to confirm the degree of color change. Spectrophotometer digitize a image from using L*a*b* color coordinate. When we compared with before and after, we could know degree of the color change. Without crosslinking reaction, dye will get out of the wiper, but using the a crosslinking of calcium alginate, we improve water repellency of films in wet environment. By coating pH indicators and benzoquinone on films, it is possible to make films with more faster reactivity with in a minute. In the field, we can determine a gas leak by naked eye within a minute, and prevent unexpected accidents with this films. This work was supported by Fundamental Technology R&D Program for Society of the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning (Grant NO. 2013M3C8A3075845).

Long Bubble Penetration through Viscoelastic Fluids in a Suddenly Contracting and Expanding Tube

This study investigated the properties of long bubbles penetrating viscoelastic fluids in a suddenly contracting and expanding tube. Injection gas flow is controlled by a mass flow controller (MFC). Some of dimensionless parameters, such as the capillary number (Ca), the Reynolds number (Re), the fractional ratio (m), and the Weissenberg number (Wi), are discussed herein. The experimental results showed that bubble velocity, Ca, and Wi increase as shear viscosity increases under a constant gas flow by MFC. However, as shear viscosity increases, bubble diameter decreases, andmincreases. When gas flow is 200 mL/min and shear viscosity increases, the bubble front is sharper in the contraction tube, and the bubble front shape is blunter in the sudden expansion tube. When gas flow is 600 mL/min and shear viscosity increases, the bubble front is blunter in the contraction tube and exhibits a torch shape in the sudden expansion tube.

Reactant Control System for Proton Exchange Membrane Fuel Cell

The Proton Exchange Membrane Fuel Cell (PEMFC) has been a focus in many fuel cell studies for tremendous commercialization. It generates an efficient and reliable power with a suitable system to ensure its electrochemical reaction operates well. In this paper, a reactant system is being discussed. Significant parameters such as reactant pressure, flow rate and stoichiometric ratio are the major factors for a reliable performance. A fuel cell owning a complex structure with traditional reactant requirement generally gives an unsatisfactory performance when facing dynamic loading instances. Fuel starvation usually occurs especially during transients where the reactants consumed are higher than being supplied. This in turn causes a problem to the MEA components such as platinum particles agglomeration, carbon corrosion and even cell reversal problem that lead to degeneration of fuel cell. Hence, excess stoichiometric ratio need to be supplied to prevent this issue and ensure a dynamic operation at the same time avoid the wastage issues. A development of a system identification and control strategy for reactant system is significant to ensure a reliable performance of power production and longer life span of the fuel cell. Hydrogen was controlled according to the load variation and the reactant control system compensates the loading transient variation that meets the design requirements and produces a reliable performance. The Mass Flow Controller (MFC) meter used with the current input range between 0.004 to 0.020 A and was changed for the suitable supply of fuel flow accordingly. A Zigler-Nicholes method used to tune the PID controller using a parameter of Kc = 23,385, Ti = 0.011 and Td = 0.002. An optimum consumption of hydrogen observed with an average error from the overall reaction is 0.000423 A. From the result shown, the reactant control system build is competence to fulfill the loading demand.

Measurements of Air Velocities in Polymer Electrolyte Membrane Fuel Cell Channels Using Electrochemical Impedance Spectroscopy

In this work, air velocities in the channels of an operating polymer electrolyte membrane fuel cell are measured using electrochemical impedance spectroscopy (EIS). From the equations of the oxygen transport in fuel cell channels, we derive an analytical expression of the channel impedance at low frequencies which is a function of the operating conditions, the channel geometry and air velocity only. Air velocities are computed using a nonlinear curve fitting of the analytical channel impedance to the single cell impedance measured at current densities ranging from 0.16 to 0.5 A/cm2 under various air stoichiometries. Our results show less than 13% of relative error between the theoretical air velocities given by the mass flow controller and those measured from the fuel cell impedance for current densities lower than 0.42 A/cm2. A direct application of this work is the real-time diagnostic of fuel cell channel clogging in stack configuration.

Glow-discharge radio frequency plasma polyether and fluoropolyether coated substrates prevent IgG protein adsorption

Event Abstract Back to Event Glow-discharge radio frequency plasma polyether and fluoropolyether coated substrates prevent IgG protein adsorption Marvin M. Mecwan1* and Buddy Ratner1* 1 University of Washington, Bioengineering, United States Introduction: Protein-based pharmaceuticals present unique challenges in processing, packaging and delivery. All proteins rapidly adsorb to solid surfaces, essentially irreversible, and frequently leads to denaturation or aggregation of the protein. Also, there are concerns with substances from the packaging leaching out and affecting proteins. This study examines fundamental aspects of protein interactions with surfaces, particularly using glow discharge plasma-treated surfaces which can be readily applied to delivery devices, packaging and processing equipment [1],[2] and may lead to a new generation of surfaces effective for protein manufacture, storage and delivery. This research particularly focuses on plasma tetraglyme (TG), acrylic acid (AA), perfluoropropylene (C3F6), and perfluoromethyl vinyl ether (C3F6O) plasma treated glass, stainless steel, and cyclic olefin polymer (COP) substrates and their interaction with IgG. Methods: Glass and COP (8mm φ discs), and 316L stainless steel (7 x 7 mm2) substrates were sequentially cleaned with DCM, acetone, and methanol in a sonication bath for 10 mins x 2. RF-Plasma deposition and delamination: Substrates were loaded into the reactor, and argon etched (40W for 5 min). Using a mass flow controller, the monomer of choice was introduced into the chamber and were plasma deposited. Plasma-treated samples (n=3/group) were washed using DI water x 3 over 24 hours to assess whether coatings would delaminate. ESCA analyses were done using an S-Probe ESCA (with monochromatic Al K-alpha X-rays focused to 800µm spot size) using survey and detailed C1s scans. Data was analyzed using ESCA analysis software. IgG adsorption studies: Bovine IgG was tagged using an ICl method. Plasma-treated samples (n=3/treatment group) were immersed in 0.1mg/mL I-125 tagged bovine IgG solution in 1x cPBS with sodium iodide (cPBSI) for 1 hr. Samples were rinsed with cPBS x 3 and counted for 10 mins using a gamma counter. Cytotoxicity studies: Plasma-coated samples were eluted in complete growth medium for 24 hrs (370C, 5% CO2­ incubator). ~80% confluent NIH-3T3 fibroblasts were exposed to eluates from the plasma coated substrates, and observed over 48 hrs using an inverted microscope. ISO 10993-5 guidelines were used for cytotoxic evaluation. Results and Discussion: ESCA scans of plasma-treated substrates showed absence of substrate associated peaks (such as Fe or Si), suggesting that coatings did not delaminate; also implies that plasma coatings on substrates are at least 10 nm thick (ESCA resolution is 100Å). Furthermore, experimental and theoretical elemental compositions of the surfaces align well. Protein adsorption studies show that tetraglyme and acrylic acid plasma coatings are essentially non-fouling (<2 ng/cm2) as compared to C3F6 and C3F6O plasma coatings which adsorbed proteins in the range of 10-14 ng/cm2. Furthermore, all plasma treated substrates show reduced protein adsorption compared to untreated controls. Moreover, fibroblasts exposed to all plasma coating eluates remained viable after 48 hours. Conclusions: The data demonstrate that plasma-treated polyether and fluoropolyether substrates can create a new generation of surfaces that can be used for contact with protein therapeutic agents.Future studies will be aimed at investigating the strength of bonding of IgG to these surfaces, as well as protein aggregation studies. Winston Ciridon; Xia Dong, PhD