Reactant pressure differential control for fuel cell gases

A pair of spool valves are described which are balanced between pressures of reactant gases supplied to a fuel cell power plant. The pressure differences are controlled between the gases so as to maintain those pressures substantially in the proportions necessary for operation of the fuel cell

Turbulence and secondary motions in square duct flow

We study turbulent flows in pressure-driven ducts with square cross-section through direct numerical simulation in a wide enough range of Reynolds number to reach flow conditions which are representative of fully developed turbulence. Numerical simulations are carried out over extremely long integration times to get adequate convergence of the flow statistics, and specifically high-fidelity representation of the secondary motions which arise. The intensity of the latter is found to be in the order of 1-2% of the bulk velocity, and unaffected by Reynolds number variations. The smallness of the mean convection terms in the streamwise vorticity equation points to a simple characterization of the secondary flows, which in the asymptotic high-Re regime are found to be approximated with good accuracy by eigenfunctions of the Laplace operator. Despite their effect of redistributing the wall shear stress along the duct perimeter, we find that secondary motions do not have large influence on the mean velocity field, which can be characterized with good accuracy as that resulting from the concurrent effect of four independent flat walls, each controlling a quarter of the flow domain. As a consequence, we find that parametrizations based on the hydraulic diameter concept, and modifications thereof, are successful in predicting the duct friction coefficient

Temperature and finite-size effects in collective modes of superfluid Fermi gases

We study the effects of superfluidity on the monopole and quadrupole collective excitations of a dilute ultra-cold Fermi gas with an attractive interatomic interaction. The system is treated fully microscopically within the Bogoliubov-de Gennes and quasiparticle random-phase approximation methods. The dependence on the temperature and on the trap frequency is analyzed and systematic comparisons with the corresponding hydrodynamic predictions are presented in order to study the limits of validity of the semiclassical approach.Comment: 9 pages, 4 figure

Materials for Teaching Lean Accounting

Lean production and lean management practices are becoming more widespread, and conventional accounting methods may be incompatible with lean management. Lean accounting methods and performance measures have been developed that support lean management, but these methods receive very little coverage in cost and managerial accounting courses. One reason for the lack of lean accounting coverage is a lack of availability of classroom materials for teaching lean accounting. The Lean Accounting Content Depository hosted by the American Accounting Association has been created to address the lack of lean accounting teaching materials. The material available from the Lean Accounting Content Repository is described. Suggestions for incrementally increasing coverage of lean accounting in cost and managerial courses are presented, and a semester long course devoted entirely to lean accounting is outlined. Selected lean accounting materials suitable for classroom use available from other sources are described

Study of fuel cell powerplant with heat recovery

It was shown that heat can be recovered from fuel cell power plants by replacing the air-cooled heat exchangers in present designs with units which transfer the heat to the integrated utility system. Energy availability for a 40-kW power plant was studied and showed that the total usable energy at rated power represents 84 percent of the fuel lower heating value. The effects of design variables on heat availability proved to be small. Design requirements were established for the heat recovery heat exchangers, including measurement of the characteristics of two candidate fuel cell coolants after exposure to fuel cell operating conditions. A heat exchanger test program was defined to assess fouling and other characteristics of fuel cell heat exchangers needed to confirm heat exchanger designs for heat recovery

Public crowdsensing of heat waves by social media data

Abstract. Investigating on society-related heat wave hazards is a global issue concerning the people health. In the last two decades, Europe experienced several severe heat wave episodes with catastrophic effects in term of human mortality (2003, 2010 and 2015). Recent climate investigations confirm that this threat will represent a key issue for the resiliency of urban communities in next decades. Several important mitigation actions (Heat-Health Action Plans) against heat hazards have been already implemented in some WHO (World Health Organization) European region member states to encourage preparedness and response to extreme heat events. Nowadays, social media (SM) offer new opportunities to indirectly measure the impact of heat waves on society. Using the crowdsensing concept, a micro-blogging platform like Twitter may be used as a distributed network of mobile sensors that react to external events by exchanging messages (tweets). This work presents a preliminary analysis of tweets related to heat waves that occurred in Italy in summer 2015. Using TwitterVigilance dashboard, developed by the University of Florence, a sample of tweets related to heat conditions was retrieved, stored and analyzed for main features. Significant associations between the daily increase in tweets and extreme temperatures were presented. The daily volume of Twitter users and messages revealed to be a valuable indicator of heat wave impact at the local level, in urban areas. Furthermore, with the help of Generalized Additive Model (GAM), the volume of tweets in certain locations has been used to estimate thresholds of local discomfort conditions. These city-specific thresholds are the result of dissimilar climatic conditions and risk cultures

Impact of different thermal zone data simplification for model calibration on monitored-simulated performance gaps

The paper analyses the impact of different simplification approaches for model verification purposes considering a reference demo case of a municipality school located in Torre Pellice (Italy), which has been monitored with room detail since April 2021. The target variable of the calibration process is the indoor air temperature: firstly, results validity is checked on an unoccupied free-running period; secondly, occupied standard behaviours and adapted to real-use ones are adopted to test the simplification choices impact on indoor thermal comfort indicators (e.g. the Adaptive Comfort Model). Several model simplification actions on both building-level construction and zoning approaches are considered. Results of this demo case demonstrate the usability of simplified models, which can be adopted instead of more detailed and time-consuming full models for performance gap detections and other analyses

Comparing different approaches to define shading control threshold via a new automatic building simulation platform

Active shading systems are essential to prevent heat gains in buildings and reduce the risk of overheating phenomena. The control logic must avoid overheating while allowing solar gains during heating hours. In general, smart control is based on a temperature and/or solar irradiation threshold; however, innovative informatics tools now allow optimising these thresholds based on specific building and climate characteristics. The paper presents a new building energy dynamic simulation platform used here to define optimal shading control thresholds for free-running and mechanically cooled spaces. Several shading control approaches are applied and compared, considering fixed hourly schedules, controls based on standard thresholds, and optimised thresholds with the tool. The analysis is performed considering the sole summer. The approach shows how the developed platform and the proposed methodology can optimise shading control thresholds, considering the specific building characteristics and the local climate conditions, consequently reducing energy needs or thermal discomfort conditions

Smartphone-based photogrammetry for the 3D modeling of a geomorphological structure

The geomatic survey in the speleological field is one of the main activities that allows for the adding of both a scientific and popular value to cave exploration, and it is of fundamental importance for a detailed knowledge of the hypogean cavity. Today, the available instruments, such as laser scanners and metric cameras, allow us to quickly acquire data and obtain accurate three-dimensional models, but they are still expensive, require a careful planning phase of the survey, as well as some operator experience for their management. This work analyzes the performance of a smartphone device for a close-range photogrammetry approach for the extraction of accurate three-dimensional information of an underground cave. The image datasets that were acquired with a high-end smartphone were processed using the Structure from Motion (SfM)-based approach for dense point cloud generation: different image-matching algorithms implemented in a commercial and an open source software and in a smartphone application were tested. In order to assess the reachable accuracy of the proposed procedure, the achieved results were compared with a reference dense point cloud obtained with a professional camera or a terrestrial laser scanner. The approach has shown a good performance in terms of geometrical accuracies, computational time and applicability