175,607 research outputs found
Design improvement of circular molten carbonate fuel cell stack through CFD Analysis
Get PDFMolten carbonate fuel cell (MCFC) is a promising technology for distributed power generation. The core of an MCFC power generation unit is the stack, where various fuel cells are connected together in series and parallel in order to obtain the desired voltage and power. Stack geometry and configuration are major engineering topics, as inhomogeneous temperature or mass fractions cause inefficient performances of the fuel cells, as efficiency and power smaller than the expected and shorter lifetime. A detailed model is a useful tool to improve stack performances, through design improvements. In this paper, a 3D model of a stack composed of 15 circular MCFC, considering heat, mass and current transfer as well as chemical and electrochemical reactions is presented. The model validation is conducted using some preliminary experimental data obtained for an MCFC stack developed in the Fabbricazioni Nucleari laboratories. These results are examined in order to improve the stack configuration. It is shown that power density may be increased of about 20% through double side feeding. In addition, the average temperature gradients in the axial direction are reduced of more than 70%. Significant reductions in the temperature gradients, especially in transversal direction, can be achieved by adjusting the mass flow rate of cathodic gas supplied to the various cell
Numerical computation for parallel plate thermoacoustic heat exchangers in standing wave oscillatory flow
Get PDFA simplified computational method for studying the heat transfer characteristics of parallel plate thermoacoustic heat exchangers is presented. The model integrates the thermoacoustic equations of the standard linear theory into an energy balance-based numerical calculus scheme. Details of the time-averaged temperature and heat flux density distributions within a representative domain of the heat exchangers
and adjoining stack are given. The effect of operation conditions and geometrical parameters on the heat exchanger performance is investigated and main conclusions relevant for HX design are drawn as far as fin length, fin spacing, blockage ratio, gas and secondary fluid-side heat transfer coefficients are concerned. Most relevant is that
the fin length and spacing affect in conjunction the heat exchanger behaviour and have to be simultaneously optimized to minimize thermal losses localized at the HX-stack
junctions. Model predictions fit experimental data found in literature within 36% and 49% respectively at moderate and high acoustic Reynolds numbers
Stack, J J, QX8919
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/418729Surname: STACK. Given Name(s) or Initials: J J. Military Service Number or Last Known Location: QX8919. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 8144.242604
Item: [2016.0049.50990] "Stack, J J, QX8919
On Multi-stack Visibly Pushdown Languages
No full textWe contribute to the theory of formal languages of visibly multistack pushdown automata (MVPA). First, we show closure under the main operations and decidability of the main decision problems for the class of MVPA restricted to computations where a symbol can be popped out of a stack S only if it was pushed within the last k contexts of S, for a given k (in a context only one stack can be pushed or popped). In particular, this class turns out to be determinizable. Second, we show the closure under complement of the class of languages accepted by ordered MVPA (where the limitation is that a stack can be popped only if all the lower indexed stacks are empty). This gains decidability of universality, inclusion and equivalence for this class. As a further contribution, we compare the classes of languages accepted by different models of MVPA
Permutations sortable by n-4 passes through a stack
No full textThe subject of pattern avoiding permutations has its roots in computer science, namely in the problem of sorting a permutation through a stack. A formula for the number of permutations of length n that can be sorted by passing it twice through a stack (where the letters on the stack have to be in increasing order) was conjectured by West, and later proved by Zeilberger. Goulden and West found a bijection from such permutations to nonseparable planar maps, and later, Jacquard and Schaeffer presented a bijection from these planar maps to certain labeled plane trees, called beta(1,0)-trees. Using generating trees, Dulucq, Gire and West showed that nonseparable planar maps are equinumerous with permutations avoiding the (classical) pattern 2413 and the barred pattern 41\bar{3}52; they called these permutations nonseparable. We give a new bijection between beta(1,0)-trees and permutations avoiding the dashed patterns 3-1-4-2 and 2-41-3. These permutations can be seen to be exactly the reverse of nonseparable permutations. Our bijection is built using decompositions of the permutations and the trees, and it translates seven statistics on the trees into statistics on the permutations. Among the statistics involved are ascents, left-to-right minima and right-to-left maxima for the permutations, and leaves and the rightmost and leftmost paths for the trees. In connection with this we give a nontrivial involution on the beta(1,0)-trees, which specializes to an involution on unlabeled rooted plane trees, where it yields interesting results. Lastly, we conjecture the existence of a bijection between nonseparable permutations and two-stack sortable permutations preserving at least four permutation statistics
Algorithmic Debugging of Real-World Haskell Programs: Deriving Dependencies from the Cost Centre Stack
Get PDFExisting algorithmic debuggers for Haskell require a transformation of all modules in a program, even libraries that the user does not want to debug and which may use language features not supported by the debugger. This is a pity, because a promising ap- proach to debugging is therefore not applicable to many real-world programs. We use the cost centre stack from the Glasgow Haskell Compiler profiling environment together with runtime value observations as provided by the Haskell Object Observation Debugger (HOOD) to collect enough information for algorithmic debugging. Program annotations are in suspected modules only. With this technique algorithmic debugging is applicable to a much larger set of Haskell programs. This demonstrates that for functional languages in general a simple stack trace extension is useful to support tasks such as profiling and debugging
DESIGN & DEVELOPMENT OF PLANAR SOLID OXIDE FUEL CELL STACK
Get PDFIn the present work, planar anode-supported Solid Oxide Fuel Cell short-stacks have been designed, assembled, tested and characterized. The design of the stacks and its components (frame, housing, interconnect, compressive and bonded seals) required a great attention to the materials properties (i.e. thermal expansion coefficient compatibility, durability, strength and oxidation resistance, conductivity and so on), as well as to the fluid-dynamic analysis focused on flow field and gas distribution. Then, a careful analysis was done based on a multidisciplinary approach to select the stack components materials, geometries, and dimensions; in order to assure a high performing stack at elevated temperatures with cost reduction of materials, parts manufacturing and assembly procedure. The materials selected were: Crofer®22APU for the interconnect and the frame; AISI 316L for bolts and housing; Thermiculite® 866 for the compressive seal placed between the frame and the interconnect plate; Flexible Mica Paper for the compressive seal positioned between the interconnect endplate and the housing; SiO2-CaO-Al2O3-Na2O glass-ceramic sealant for the bonded seal to join the frame with the cell. On the other hand, the stack assembly was focused on the implementation of innovative and simple procedures, which allowed power capacity scale-up in accordance to power requirements. In this work, two different stack configurations were produced: with one cell (for initial testing of the materials and fluid-dynamic selected solutions) and with three cells. It must be mentioned that all developed stacks in this research were assembled with commercial cells "ASC3" from H.C. Starck. Also, calculations at ambient temperature and 800°C were done in the stack compression system to determine the proper tightening torque to be applied: this value was 50N. Although this calculation took into consideration the loss of tightening torque at high temperatures, some marks were found in housing and micas during the stack inspection after disassembly. These marks are a clear indicator of gas leakage. Additionally, a study was carried out related to the effect of the protective Mn1.5Co1.5O4 coating deposited on interconnect surface to prevent the cathode Cr poisoning. This experiment was executed in the stack of one cell configuration. No voltage degradation was observed during the galvanostatic experiment of 360 h at 800°
J. D. Stack, elected January 17, 1923
No full textPortrait of J. D. Stack, member of the Alta Club in Salt Lake City, Utah, elected January 17, 192
Divided we stand: Parallel distributed stack memory management
Get PDFWe present an overview of the stack-based memory management techniques that we used in our non-deterministic and-parallel Prolog systems: &-Prolog and DASWAM. We believe that the problems associated with non-deterministic and-parallel systems are more general than those encountered in or-parallel and deterministic and-parallel systems, which can be seen as subsets of this more general case. We develop on the previously proposed "marker scheme", lifting some of the restrictions associated with the selection of goals while keeping (virtual) memory consumption down. We also review some of the other problems associated with the stack-based management scheme, such as handling of forward and backward execution, cut, and roll-backs
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