Fish schooling as a basis for vertical axis wind turbine farm design

Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the high power coefficient (mechanical power output divided by the power of the free-stream air through the turbine cross-sectional area) of an isolated turbine. However when in close proximity to neighbouring turbines, HAWTs suffer from a reduced power coefficient. In contrast, previous research on vertical axis wind turbines (VAWTs) suggests that closely-spaced VAWTs may experience only small decreases (or even increases) in an individual turbine's power coefficient when placed in close proximity to neighbours, thus yielding much higher power outputs for a given area of land. A potential flow model of inter-VAWT interactions is developed to investigate the effect of changes in VAWT spatial arrangement on the array performance coefficient, which compares the expected average power coefficient of turbines in an array to a spatially-isolated turbine. A geometric arrangement based on the configuration of shed vortices in the wake of schooling fish is shown to significantly increase the array performance coefficient based upon an array of 16x16 wind turbines. Results suggest increases in power output of over one order of magnitude for a given area of land as compared to HAWTs.Comment: Submitted for publication in BioInspiration and Biomimetics. Note: The technology described in this paper is protected under both US and international pending patents filed by the California Institute of Technolog

Boundary layer analysis for nonlinear singularly perturbed differential equations

This paper focuses on the boundary layer phenomenon arising in the study of singularly perturbed differential equations. Our tools include the method of lower and upper solutions combined with analysis of the integral equation associated with the class of nonlinear equations under consideration

Novel crosslinkers for high performance poly-AMPS-based proton exchange membranes for fuel cells

Polymer electrolyte fuel cells (PEFC) gained a lot of interest in recent years as a potential solution for an eco-friendly energy. Proton exchange membranes (PEM) are one of the main components of PEFCs and require mechanical and chemical stability to ensure high proton conductivity and effective separation of anode and cathode under challenging conditions. Best commercial membranes made from sulfonated fluoropolymers, such as Nafion®, are rather expensive. To improve fuel cell performance at a lower cost, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was investigated recently. 1 Since polyAMPS (PAMPS) excessively swells or even dissolves in water, we investigated several commercial crosslinkers and new multifunctional monomers (Fig. 1) to decrease swelling by crosslinking. AMPS, crosslinker and photoinitiator were dissolved in water and N-methyl-2-pyrrolidone (NMP), respectively. To facilitate conductivity measurements and handling of crosslinked PAMPS formulations after UVinitiated radical polymerization, they were constrained within a porous membrane using a procedure described by Zhou et al. 2 We tested several commercial crosslinkers and according to these results we developed new crosslinkers with enhanced hydrolytical stability and conductivity. In contrast to the commercial crosslinkers, where conductivity increased with increasing amount of crosslinker, our new acrylamide based crosslinkers needed only very low concentrations. They could achieve more than 2.5 times the conductivity of Nafion with only 5 wt% crosslinker. We used this novel crosslinkers to integrate them into asymmetric membranes with interpenetrating proton-conducting morphology for enhanced methanol barrier properties. 3 First results of their performance compared to Nafion will be presented. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. The authors would like to thank 3M for PP membrane samples and Ciba SC, Huntsman, Ivoclar Vivadent and Sartomer for samples of photoinitiator and crosslinker. 1 a) Qiao, J., et al., Journal of Materials Chemistry 2005, 15 (41), 4414-4423. b)Diao, H., et al., Macromolecules 43 (15), 6398-6405. 3 Zhou, J., et al., Journal of Membrane Science 2005, 254 (1-2), 89-99. 4 Radovanovic, P., et al., Journal of Membrane Science 2012, 401-402, 254-261

Photopolymerization of crosslinked proton conducting membranes

Several monomers and crosslinker in a broad range of concentrations in water and 1-Methyl-2-pyrrolidone (NMP) respectively were screened for their mechanical properties, water uptake and conductivity in porous membranes by photo polymerization with a polar photo initiator. As conductive polymer, primarily poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and poly(2-sulfoethyl methacrylate) (PSEM) respectively as well as polymers of phosphonic acid containing monomers or newly synthesized monomers were used. The conductive monomers were crosslinked with varying hydrophobic and hydrophilic multifunctional monomers like N,N'-methylene bisacrylamide (MBA), 2-Propenoic acid, 2-methyl-, 1,1'-(1,10-decanediyl) ester (D3MA) or polyethyleneglycol diacrylates with two varying chainlengths (PEG-DA700, PEG-DA330). The advantage of several different building blocks with known characteristics is the possibility to tune the polymer to special needs of an application. For example, some polymer compositions have good conductivity at lower temperatures whereas other polymers develop better properties at elevated temperatures. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat and with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. We thank 3M for providing us with samples of the PP membrane. 1/ Hamrock, S.J. and M.A. Yandrasits, Proton Exchange Membranes for Fuel Cell Applications. 2006. 46(3): p. 219 - 244. 2/ Hoogers, G., Membranes and Ionomers, in Fuel Cell Technology Handbook G. Hoogers, Editor. 2002, CRC Press. p. 36

Novel crosslinkers for high performance poly-AMPS-based proton exchange membranes for fuel cells

Polymer electrolyte fuel cells (PEFC) gained a lot of interest in recent years as a potential solution for an eco-friendly energy. Proton exchange membranes (PEM) are one of the main components of PEFCs and require mechanical and chemical stability to ensure high proton conductivity and effective separation of anode and cathode under challenging conditions. Best commercial membranes made from sulfonated fluoropolymers, such as Nafion®, are rather expensive. To improve fuel cell performance at a lower cost, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was investigated recently. 1 Since polyAMPS (PAMPS) excessively swells or even dissolves in water, we investigated several commercial crosslinkers and new multifunctional monomers (Fig. 1) to decrease swelling by crosslinking. AMPS, crosslinker and photoinitiator were dissolved in water and N-methyl-2-pyrrolidone (NMP), respectively. To facilitate conductivity measurements and handling of crosslinked PAMPS formulations after UVinitiated radical polymerization, they were constrained within a porous membrane using a procedure described by Zhou et al. 2 We tested several commercial crosslinkers and according to these results we developed new crosslinkers with enhanced hydrolytical stability and conductivity. In contrast to the commercial crosslinkers, where conductivity increased with increasing amount of crosslinker, our new acrylamide based crosslinkers needed only very low concentrations. They could achieve more than 2.5 times the conductivity of Nafion with only 5 wt% crosslinker. We used this novel crosslinkers to integrate them into asymmetric membranes with interpenetrating proton-conducting morphology for enhanced methanol barrier properties. 3 First results of their performance compared to Nafion will be presented. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. The authors would like to thank 3M for PP membrane samples and Ciba SC, Huntsman, Ivoclar Vivadent and Sartomer for samples of photoinitiator and crosslinker. 1 a) Qiao, J., et al., Journal of Materials Chemistry 2005, 15 (41), 4414-4423. b)Diao, H., et al., Macromolecules 43 (15), 6398-6405. 3 Zhou, J., et al., Journal of Membrane Science 2005, 254 (1-2), 89-99. 4 Radovanovic, P., et al., Journal of Membrane Science 2012, 401-402, 254-261

Asymmetric proton-conducting membrane made by photopolymerization

Proton-conducting membranes with interpenetrating polymer network morphology have been frequently considered in recent years for potential replacement of standard Nafion membranes in direct methanol fuel cells. Asymmetric membranes comprising protonconducting channels of cross-linked sulfonic acid functionalized ionomers embedded within a matrix of thermally-resistant, glassy polymer were prepared by photopolymerization starting from a polymer solution and evaluated in our laboratories. These membranes have an integral top skin layer with fine proton-conducting channels, which serves as a barrier against methanol crossover, on top of a coarser proton-conducting support. Conductivity of asymmetric membranes over a range of initial polymer concentrations and ion-exchange capacities (IEC) was just slightly lower than for the corresponding symmetric membranes. Methanol barrier properties of asymmetric proton-conducting membranes were better than that of the state-of-the art Nafion 115 membrane. The crosslinking agent functionality had a major effect on membrane conductivity. Use of trifunctional crosslinking agents resulted in significantly higher conductivities than those obtained with bifunctional agents, even surpassing the conductivity of Nafion membranes

Asymmetric sol-gel proton-conducting membrane

Proton-conducting membranes with interpenetrating polymer network morphology have gained attention in recent years for potential replacement of standard Nafion membranes in direct methanol fuel cells. These membranes generally consist of fine interpenetrating domains of proton-conducting and mechanically-supporting polymer phases, which often leads to improvements in mechanical strength and methanol barrier properties. Asymmetric sol-gel membranes comprising proton-conducting channels of cross-linked sulfonic acid functionalized ionomers embedded within a matrix of thermally-resistant, glassy polymer were prepared by photopolymerization starting from a polymer solution and evaluated in our laboratories. These membranes have an integral top skin layer with fine biomimetic proton-conducting channels, which provides a barrier against methanol crossover, on top of a coarser proton-conducting support. Conductivity of asymmetric membranes over a range of initial polymer concentrations and ion-exchange capacities (IEC) was just slightly lower than for the corresponding symmetric membranes. Methanol barrier properties of asymmetric sol-gel membranes were better than that of Nafion 115 membrane. The crosslinking agent functionality had a major effect on membrane conductivity. Use of trifunctional crosslinking agents resulted in significantly higher conductivities than those obtained with bifunctional agents, even surpassing the conductivity of Nafion membranes

High performance proton conducting membranes for fuel cells made by photopolymerization of hydrolytically stable monomers

Proton conducting membranes were prepared by photopolymerization of 2- acrylamido-2-methylpropane sulfonic acid solutions within the pores of polypropylene membranes. Several commercial and novel multifunctional monomers synthesized in IAS lab were investigated as suitable crosslinking agents for this application. Some membranes made with synthesized crosslinkers at low crosslinker concentrations exceeded 2.5 times the conductivity of Nafion® 115 membrane, while exhibiting a good hydrolytical stability, in contrast to the commercial crosslinkers based on multifunctional (meth)acrylates

Proton conducting membranes based on photopolymerizable monomers

The proton exchange barrier or Proton Exchange Membrane (PEM) is the critical part of a fuel cell. The basic function of the membrane is to enable proton transport, while being simultaneously impermeable for electrons and gas. Typically, membranes for the PEM fuel cells (PEMFC) are made of perfluorocarbon-sulfonic acid monomers. The best known material of this class is Nafion which has a unique interpenetrating structure of hydrophobic perfluorocarbon regions providing thermal and chemical resistance, mechanical strength and diffusional resistance combined with hydrophilic regions of water clusters surrounding charged sulfonic acid groups which allow selective proton transport. For these reasons, Nafion is still considered the benchmark against which most of the new materials are compared [1]. At the molecular level, proton transport may follow two principal mechanisms: (a) diffusion mechanism via H3O+ ion as a carrier and (b) proton hopping mechanism (Grotthuss transport) [2]. Contemporary PEMFCs are exclusively based on the vehicle mechanism. PEMFCs produce water as a by-product and H+ ions moving from the anode to the cathode pull water molecules by an electro-osmotic drag force. In addition, membrane suffers from evaporation of water at working temperatures of 60-90ºC. Nafion effectively conducts protons only when imbibed by water within a narrow range, which limits the operating temperature of PEM fuel cells to around 80oC. However an operating temperature above 100ºC is a highly desirable goal. PEM membranes are not dimensionally stable since the material significantly swells upon water absorption. Therefore the aim of our proton conducting membrane is a rigid polymer with perpendicular nano channels which are filled with a conducting sulfonic polymer where conductivity is mainly achieved by the Grotthuss mechanism. Several monomers and crosslinker in a broad range of concentrations in water and 1-Methyl-2-pyrrolidone (NMP) respectively were screened for their mechanical properties, water uptake and conductivity in porous membranes by photo polymerization with a polar photo initiator. As conductive polymer, primarily poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and poly(2-sulfoethyl methacrylate) (PSEM) respectively as well as polymers of phosphonic acid containing monomers or newly synthesized monomers were used. The conductive monomers were crosslinked with varying hydrophobic and hydrophilic multifunctional monomers like N,N'-methylene bisacrylamide (MBA), 2-Propenoic acid, 2-methyl-, 1,1'-(1,10-decanediyl) ester (D3MA) or polyethyleneglycol diacrylates with two varying chainlengths (PEG-DA700, PEG-DA330). The advantage of several different building blocks with known characteristics is the possibility to tune the polymer to special needs of an application. For example, some polymer compositions have good conductivity at lower temperatures whereas other polymers develop better properties at elevated temperatures. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat and with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. We thank 3M for providing us with samples of the PP membrane. 1/Hamrock, S.J. and M.A. Yandrasits, Proton Exchange Membranes for Fuel Cell Applications. 2006. 46(3): p. 219 - 244. 2/ Hoogers, G., Membranes and Ionomers, in Fuel Cell Technology Handbook G. Hoogers, Editor. 2002, CRC Press. p