scholarly journals Edge Cooling of a Fuel Cell during Aerial Missions by Ambient Air

Micromachines ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1432
Author(s):  
Lev Zakhvatkin ◽  
Alex Schechter ◽  
Eilam Buri ◽  
Idit Avrahami
Keyword(s):  
Fuel Cell ◽  
Numerical Model ◽  
Wind Tunnel ◽  
Boundary Conditions ◽  
Air Temperature ◽  
Numerical Models ◽  
Heat Removal ◽  
Ambient Air ◽  
Experimental Setup ◽  
Good Agreement

During aerial missions of fuel-cell (FC) powered drones, the option of FC edge cooling may improve FC performance and durability. Here we describe an edge cooling approach for fixed-wing FC-powered drones by removing FC heat using the ambient air during flight. A set of experiments in a wind tunnel and numerical simulations were performed to examine the efficiency of FC edge cooling at various flight altitudes and cruise speeds. The experiments were used to validate the numerical model and prove the feasibility of the proposed method. The first simulation duplicated the geometry of the experimental setup and boundary conditions. The calculated temperatures of the stack were in good agreement with those of the experiments (within ±2 °C error). After validation, numerical models of a drone’s fuselage in ambient air with different radiator locations and at different flight speeds (10–30 m/s) and altitudes (up to 5 km) were examined. It was concluded that onboard FC edge cooling by ambient air may be applicable for velocities higher than 10 m/s. Despite the low pressure, density, and Cp of air at high altitudes, heat removal is significantly increased with altitude at all power and velocity conditions due to lower air temperature.

Long-term thermal two- and three-dimensional analysis of roller compacted concrete dams supported by monitoring verification

2010 ◽  
Vol 37 (4) ◽  
pp. 600-610 ◽  
Author(s):  
Vladan Kuzmanovic ◽  
Ljubodrag Savic ◽  
John Stefanakos
Keyword(s):  
Thermal Analysis ◽  
Boundary Conditions ◽  
Thermal Field ◽  
Numerical Models ◽  
Three Dimensional ◽  
Roller Compacted Concrete ◽  
Rcc Dam ◽  
Field Investigations ◽  
Good Agreement

This paper presents two-dimensional (2D) and three-dimensional (3D) numerical models for unsteady phased thermal analysis of RCC dams. The time evolution of a thermal field has been modeled using the actual dam shape, RCC technology and the adequate description of material properties. Model calibration and verification has been done based on the field investigations of the Platanovryssi dam, the highest RCC dam in Europe. The results of a long-term thermal analysis, with actual initial and boundary conditions, have shown a good agreement with the observed temperatures. The influence of relevant parameters on the thermal field of RCC dams has been analyzed. It is concluded that the 2D model is appropriate for the thermal phased analysis, and that the boundary conditions and the mixture properties are the most influential on the RCC dam thermal behavior.

A Numerical Model for Thermal Performance of an Unglazed Transpired Solar Collector

2011 ◽  
Author(s):  
Saeed Moaveni ◽  
Patrick A. Tebbe ◽  
Louis Schwartzkopf ◽  
Joseph Dobmeier ◽  
Joseph Gehrke ◽  
...  
Keyword(s):  
Numerical Model ◽  
Air Temperature ◽  
Thermal Performance ◽  
Solar Collector ◽  
Energy Savings ◽  
Ambient Air ◽  
Solar Collectors ◽  
Heating Unit ◽  
Plate Temperature ◽  
Building Wall

In this paper, we will present a numerical model for estimating the thermal performance of unglazed transpired solar collectors located on the Breck School campus in Minneapolis, Minnesota. The solar collectors are installed adjacent to the southeast facing wall of a field house. The collectors preheat the intake air before entering the primary heating unit. The solar collector consists of 8 separate panels (absorber plates). Four fans are connected to the plenum that is created by the absorber plates and the adjoining field house wall. All fresh air for the field house is provided by the solar collectors before being filtered and heated by four, independent two stage natural gas fired heaters. Moreover, the following data were collected onsite using a data acquisition system: indoor field house space temperature, ambient air temperature, wind speed, wind direction, the plenum exit air temperature, the absorber plate temperature, and the air temperatures inside the plenum. The energy balance equations for the collector, the adjacent building wall, and the plenum are formulated. The numerical model is used to predict the air temperature rise inside the plenum, recaptured heat loss from the adjoining building wall, energy savings, and the efficiency of the collectors. The results of the numerical model are then compared to the results obtained from the onsite measurements; which are in good agreement. The model presented in this paper is simple yet accurate enough for architects and engineers to use it with ease to predict the thermal performance of a collector.

Effects of Operating Conditions on the Heat Management of a Microscale Fuel Cell

2019 ◽  
Author(s):  
Liyong Sun ◽  
Adam S. Hollinger ◽  
Jun Zhou
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Waste Heat ◽  
Heat Removal ◽  
Current Collector ◽  
Ambient Air ◽  
Operating Conditions ◽  
Heat Management ◽  
Fuel Flow ◽  
Fuel Stream

Abstract Higher energy densities and the potential for nearly instantaneous recharging make microscale fuel cells very attractive as power sources for portable technology in comparison with standard battery technology. Heat management is very important to the microscale fuel cells because of the generation of waste heat. Waste heat generated in polymer electrolyte membrane fuel cells includes oxygen reduction reaction in the cathode catalyst, hydrogen oxidation reaction in the anode catalyst, and Ohmic heating in the membrane. A novel microscale fuel cell design is presented here that utilizes a half-membrane electrode assembly. An ANSYS Fluent model is presented to investigate the effects of operating conditions on the heat management of this microscale fuel cell. Five inlet fuel temperatures are 22°C, 40°C, 50°C, 60°C, and 70°C. Two fuel flow rate are 0.3 mL/min and 2 mL/min. The fuel cell is simulated under natural convection and forced convection. The simulations predict thermal profiles throughout this microscale fuel cell design. The exit temperature of fuel stream, oxygen stream and nitrogen stream are obtained to determine the rate of heat removal. Simulation results show that the fuel stream dominates heat removal at room temperature. As inlet fuel temperature increases, the majority of heat removal occurs via convection with the ambient air by the exposed current collector surfaces. The top and bottom current collector removes almost the same amount of heat. The model also shows that the heat transfer through the oxygen channel and nitrogen channel is minimal over the range of inlet fuel temperatures. Increasing fuel flow rate and ambient air flow both increase the heat removal by the exposed current collector surfaces. Ultimately, these simulations can be used to determine design points for best performance and durability in a single-channel microscale fuel cell.

Modeling of Heat Removal in a Single-Channel Microscale Fuel Cell

2017 ◽  
Author(s):  
Liyong Sun ◽  
Adam S. Hollinger
Keyword(s):  
Fuel Cell ◽  
Heat Generation ◽  
Single Channel ◽  
Waste Heat ◽  
Heat Removal ◽  
Ambient Air ◽  
Reduction Reaction ◽  
Membrane Electrode ◽  
Cell Design ◽  
Fuel Temperature

Considerable waste heat is generated via the oxygen reduction reaction in polymer electrolyte membrane fuel cells. Consequently, heat generation and removal in conventional fuel cell architectures has been carefully investigated in order to achieve effective thermal management. Here we present a novel microscale fuel cell design that utilizes a half-membrane electrode assembly. In this design, a single fuel/electrolyte stream provides an additional pathway for heat removal that is not present in traditional fuel cell architectures. The model presented here investigates heat removal over a range of inlet fuel temperatures. Heat generation densities are determined experimentally for all inlet fuel temperatures. The simulations presented here predict thermal profiles throughout this microscale fuel cell design. Simulation results show that the fuel stream dominates heat removal at room temperature. As inlet fuel temperature increases, the majority of heat removal occurs via convection with the ambient air. The model also shows that heat transfer through the oxidant channel is minimal over the range of inlet fuel temperatures.

scholarly journals Fixed Grid Numerical Models for Solidification and Melting of Phase Change Materials (PCMs)

2019 ◽  
Vol 9 (20) ◽  
pp. 4334 ◽  
Author(s):  
José Henrique Nazzi Ehms ◽  
Rejane De Césaro Oliveski ◽  
Luiz Alberto Oliveira Rocha ◽  
Cesare Biserni ◽  
Massimo Garai
Keyword(s):  
Numerical Model ◽  
Boundary Conditions ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Change Materials ◽  
Source Term ◽  
Numerical Models ◽  
Fixed Grid ◽  
Numerical Studies ◽  
The Impact

Phase change materials (PCMs) are classified according to their phase change process, temperature, and composition. The utilization of PCMs lies mainly in the field of solar energy and building applications as well as in industrial processes. The main advantage of such materials is the use of latent heat, which allows the storage of a large amount of thermal energy with small temperature variation, improving the energy efficiency of the system. The study of PCMs using computational fluid dynamics (CFD) is widespread and has been documented in several papers, following the tendency that CFD nowadays tends to become increasingly widespread. Numerical studies of solidification and melting processes use a combination of formulations to describe the physical phenomena related to such processes, these being mainly the latent heat and the velocity transition between the liquid and the solid phases. The methods used to describe the latent heat are divided into three main groups: source term methods (E-STM), enthalpy methods (E-EM), and temperature-transforming models (E-TTM). The description of the velocity transition is, in turn, divided into three main groups: switch-off methods (SOM), source term methods (STM), and variable viscosity methods (VVM). Since a full numerical model uses a combination of at least one of the methods for each phenomenon, several combinations are possible. The main objective of the present paper was to review the numerical approaches used to describe solidification and melting processes in fixed grid models. In the first part of the present review, we focus on the PCM classification and applications, as well as analyze the main features of solidification and melting processes in different container shapes and boundary conditions. Regarding numerical models adopted in phase-change processes, the review is focused on the fixed grid methods used to describe both latent heat and velocity transition between the phases. Additionally, we discuss the most common simplifications and boundary conditions used when studying solidification and melting processes, as well as the impact of such simplifications on computational cost. Afterwards, we compare the combinations of formulations used in numerical studies of solidification and melting processes, concluding that “enthalpy–porosity” is the most widespread numerical model used in PCM studies. Moreover, several combinations of formulations are barely explored. Regarding the simulation performance, we also show a new basic method that can be employed to evaluate the computing performance in transient numerical simulations.

scholarly journals THE NUMERICAL MODELLING OF TIDES IN A SHALLOW SEMI-ENCLOSED BASIN BY A MODIFIED ELLIPTIC METHOD

2018 ◽  
Vol 21 ◽  
pp. 1-47
Author(s):  
Mulia M. Sidjabat
Keyword(s):  
Numerical Model ◽  
Numerical Modelling ◽  
Boundary Conditions ◽  
Coefficient Of Friction ◽  
Iterative Scheme ◽  
Linear Equations ◽  
Tidal Constituent ◽  
Non Linear ◽  
Non Linear Equations ◽  
Good Agreement

A numerical model which renders possible the numerical solution of the nonlinear tidal equations by obtaining a solution for each individual tidal component is developed. For this purpose, a set of time independent non-linear equations for each tidal constituent is constructed. Each of these sets of equations is interrelated through the non-linear frictional terms, the approximation of which is accomplished by an iterative scheme. The method is tested for several models before it is applied to the real basin (Bight of Abaco). In order to evaluate the model and to construct the boundary conditions along the opening, a series of tidal observations were undertaken. The viability of the method is indicated by the fact that the results of computations using a coefficient of friction r = 0.0034 give good agreement with observations for all components and  over  all stations.

scholarly journals DIC in Validation of Boundary Conditions of Numerical Model of Reinforced Concrete Beams Under Torsion

2018 ◽  
Vol 64 (4) ◽  
pp. 31-48 ◽  
Author(s):  
B. Turoń ◽  
D. Ziaja ◽  
L. Buda-Ożóg ◽  
B. Miller
Keyword(s):  
Reinforced Concrete ◽  
Numerical Model ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Experimental Research ◽  
Concrete Beams ◽  
Numerical Models ◽  
Experimental Tests ◽  
Reinforced Concrete Beams ◽  
Image Correlation

AbstractThe paper presents the experimental research and numerical simulations of reinforced concrete beams under torsional load. In the experimental tests Digital Image Correlation System (DIC System) Q-450 were used. DIC is a non-contact full-field image analysis method, based on grey value digital images that can determine displacements and strains of an object under load. Numerical simulations of the investigated beams were performed by using the ATENA 3D – Studio program. Creation of numerical models of reinforced concrete elements under torsion was complicated due to difficulties in modelling of real boundary conditions of these elements. The experimental research using DIC can be extremely useful in creating correct numerical models of investigated elements. High accuracy and a wide spectrum of results obtained from experimental tests allow for the modification of the boundary conditions assumed in the numerical model, so that these conditions correspond to the real fixing of the element during the tests.

A Numerical Model for Solid Oxide Fuel Cells

2006 ◽  
Author(s):  
N. Massarotti ◽  
F. Arpino ◽  
A. Carotenuto ◽  
P. Nithiarasu
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Numerical Model ◽  
Energy Conversion ◽  
Numerical Models ◽  
Species Conservation ◽  
Catalyst Layer ◽  
Energy Conversion Systems ◽  
Channel Electrode ◽  
Characteristic Based Split

Fuel cells have been very much studied in the last few years as promising future energy conversion systems. In fact, these systems have a number of advantages with respect to more traditional energy conversion systems, such as, for instance, higher potential efficiency, flexibility for distributed generation, and reduced emissions. Accurate and physically representative numerical models are essential for the future development of energy conversion systems based on fuel cell technology. In the present paper, a general and detailed numerical model is proposed, in which all the quantities of interest are calculated locally, on the basis of general governing equations for the phenomena involved. The model proposed in this work is based on the solution of the appropriate set of partial differential equations that describe the phenomena that occur in the different parts of the fuel cell: 1) anodic compartment, which includes fuel channel, electrode and catalyst layer; 2) electrolyte; and 3) cathode compartment. To solve the momentum, energy and species conservation equations in the anodic and cathodic compartments, a finite element procedure is employed, based on the Characteristic Based Split (CBS) algorithm. The CBS, thanks to its generality and modularity, is able to successfully predict fuel cell performances. The results obtained from the simulations show a good agreement with other data available in the literature.

scholarly journals Analysis of a Tubular Torsionally Resonating Viscosity–Density Sensor

Sensors ◽  
2020 ◽  
Vol 20 (11) ◽  
pp. 3036
Author(s):  
Daniel Brunner ◽  
Joe Goodbread ◽  
Klaus Häusler ◽  
Sunil Kumar ◽  
Gernot Boiger ◽  
...  
Keyword(s):  
Numerical Model ◽  
Numerical Models ◽  
Experimental Results ◽  
Static Case ◽  
Flow Loop ◽  
Actual Measurement ◽  
Wide Range ◽  
Laminar And Turbulent Flow ◽  
The Impact ◽  
Good Agreement

This paper discusses a state-of-the-art inline tubular sensor that can measure the viscosity–density ( ρ η ) of a passing fluid. In this study, experiments and numerical modelling were performed to develop a deeper understanding of the tubular sensor. Experimental results were compared with an analytical model of the torsional resonator. Good agreement was found at low viscosities, although the numerical model deviated slightly at higher viscosities. The sensor was used to measure viscosities in the range of 0.3–1000 mPa·s at a density of 1000 kg/m3. Above 50 mPa·s, numerical models predicted viscosity within ±5% of actual measurement. However, for lower viscosities, there was a higher deviation between model and experimental results up to a maximum of ±21% deviation at 0.3 mPa·s. The sensor was tested in a flow loop to determine the impact of both laminar and turbulent flow conditions. No significant deviations from the static case were found in either of the flow regimes. The numerical model developed for the tubular torsional sensor was shown to predict the sensor behavior over a wide range, enabling model-based design scaling.

scholarly journals AUTOMATIC CALIBRATION OF NUMERICAL TIDAL MODELS

1980 ◽  
Vol 1 (17) ◽  
pp. 144
Author(s):  
K.P. Holz ◽  
U. Januszewski
Keyword(s):  
Numerical Model ◽  
Numerical Models ◽  
Calibration Method ◽  
Trial And Error ◽  
Elbe River ◽  
One Dimensional ◽  
Tidal Waves ◽  
Standard Tool ◽  
The Elbe River ◽  
Good Agreement

Numerical models for the simulation of tidal waves in estuaries have "become a standard tool of coastal engineers. Before they can he applied to practical problems, they have to be calibrated against nature. The basis for calibration is normally a representative set of tidal curves (natural field data), which has to be reproduced by the numerical model. Generally, the calibration is performed by empirically tuning certain parameters, until a fairly good agreement between measured and calculated quantities is obtained. In most cases, this is a "trial-and error" process which may become very time-consuming, and which strongly depends on the intuition and experience of the user. In order to make the process of calibration more effective, and to ensure that the best possible agreement between nature and numerical model is achieved, a calibration method has been developed to determine the parameters of the numerical model automatically by means of a mathematical method of optimization. The method is applied to a one-dimensional numerical model of the Elbe River.

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