First Law Analysis of Control Volumes

2008 ◽

Author(s):

Sanggyu Kang ◽

Kyoungdoug Min

Keyword(s):

Energy Balance ◽

Thermal Management ◽

Dynamic Modeling ◽

Management System ◽

Mass Conservation ◽

Cell System ◽

Operating Conditions ◽

Automotive Application ◽

Thermal Management System ◽

Control Volumes

Water and thermal management are crucial factors in determining the performance of PEMFC for automotive application. In order to investigate the effect of cell humidity and temperature on the performance of PEMFC, a dynamic model of a PEMFC system for automotive application has been developed by using Matlab/Simulink®. The model is composed of a PEM unit cell, membrane humidifier, and thermal management system (TMS). At first, fuel and air are well hydrated by the shell and tube humidifier, then humidified fuel and air flow into the PEMFC for electrochemical reaction. PEMFC temperature was maintained at a constant level by the thermal management system. The active area of PEM model is 240 cm2. The cell was discretized into several control volumes in the through-plane to resolve energy balance and species diffusion. The membrane humidifier model is also discretized into three control volumes in the through-plane to resolve the mass conservation and energy balance. Fuel and air are hydrated by the diffusion of the water through the membrane. The thermal management system consists of radiator, fan and pump. De-ionized water cools down the temperature of PEMFC. In order to validate the model, the model was compared with a corresponding experiment. Comparison shows that simulation results are in good agreement with experiments. And the dynamic response of PEMFC with regard to the change of current was also investigated. The model is useful to elucidate the relationships between operating conditions such as air relative humidity, temperature, etc. It is expected that this dynamic modeling of PEMFC system can contribute to the design optimization of PEM fuel cell system for vehicle application.

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Stand-Alone Containment Analysis of the PHÉBUS FPT-1 Test With the ASTEC and the MELCOR Codes

Volume 4: Computational Fluid Dynamics (CFD) and Coupled Codes; Decontamination and Decommissioning, Radiation Protection, Shielding, and Waste Management; Workforce Development, Nuclear Education and Public Acceptance; Mitigation Strategies for Beyond Design Basis Events; Risk Management ◽

10.1115/icone24-60184 ◽

2016 ◽

Author(s):

Bruno Gonfiotti ◽

Sandro Paci

Keyword(s):

State Of The Art ◽

External Environment ◽

Fission Products ◽

Severe Accident ◽

Sensitivity Analyses ◽

Complex Task ◽

Primary Coolant ◽

Control Volumes ◽

Coolant System

The estimation of Fission Products (FPs) release from the containment system of a nuclear plant to the external environment during a Severe Accident (SA) is a quite complex task. In the last 30–40 years several efforts were made to understand and to investigate the different phenomena occurring in such a kind of accidents in the primary coolant system and in the containment. These researches moved along two tracks: understanding of involved phenomenologies through the execution of different experiments, and creation of numerical codes capable to simulate such phenomena. These codes are continuously developed to reflect the actual SA state-of-the-art, but it is necessary to continuously check that modifications and improvements are able to increase the quality of the obtained results. For this purpose, a continuous verification and validation work should be carried out. Therefore, the aim of the present work is to re-analyze the Phébus FPT-1 test employing the ASTEC (F) and MELCOR (USA) codes. The analysis focuses on the stand-alone containment aspects of the test, and three different modellisations of the containment vessel have been developed showing that at least 15/20 Control Volumes (CVs) are necessary for the spatial schematization to correctly predict thermal-hydraulics and the aerosol behavior. Furthermore, the paper summarizes the main thermal-hydraulic results, and presents different sensitivity analyses carried out on the aerosols and FPs behavior.

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Vorticity transport in the leading-edge vortex on a rotating blade

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.18 ◽

2014 ◽

Vol 743 ◽

pp. 249-261 ◽

Cited By ~ 68

Author(s):

Craig J. Wojcik ◽

James H. J. Buchholz

Keyword(s):

Leading Edge ◽

Quasi Equilibrium ◽

Transport Mechanisms ◽

Leading Edge Vortex ◽

Rotating Blade ◽

Edge Vortex ◽

Rotation Motion ◽

Vorticity Transport ◽

Control Volumes ◽

Quiescent Fluid

AbstractVorticity transport is analysed within the leading-edge vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the leading-edge vortex. An initial global analysis between the $25$ and $50\, \%$ spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the leading-edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the $25$ and $50\, \%$ spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the leading-edge vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of leading-edge-vortex circulation. Thus, it provides an important condition for maintenance of an attached leading-edge vortex on the inboard portion of the blade.

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Defining the Thermodynamic Efficiency in a Wave Rotor

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4033508 ◽

2016 ◽

Vol 138 (11) ◽

Cited By ~ 4

Author(s):

Shining Chan ◽

Huoxing Liu ◽

Fei Xing

Keyword(s):

Gas Turbine ◽

Control Volume ◽

Thermodynamic Efficiency ◽

Wave Rotor ◽

Wave Rotors ◽

Compression And Expansion ◽

Efficiency Estimation ◽

Parametric Analyses ◽

Control Volumes ◽

Thermodynamic Processes

A wave rotor enhances the performance of a gas turbine with its internal compression and expansion, yet the thermodynamic efficiency estimation has been troubling because the efficiency definition is unclear. This paper put forward three new thermodynamic efficiency definitions to overcome the trouble: the adiabatic efficiency, the weighted-pressure mixed efficiency, and the pressure pre-equilibrated efficiency. They were all derived from multistream control volumes. As a consequence, they could correct the efficiency values and make the values for compression and expansion independent. Moreover, the latter two incorporated new models of pre-equilibration inside a control volume, and modified the hypothetical “ideal” thermodynamic processes. Parametric analyses based on practical wave rotor data demonstrated that the trends of those efficiency values reflected the energy losses in wave rotors. Essentially, different thermodynamic efficiency definitions indicated different ideal thermal cycle that an optimal wave rotor can provide for a gas turbine, and they were recommended to application based on that essence.

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Numerical prediction of the performance of gas-lubricated spiral groove thrust bearings

Proceedings of the Institution of Mechanical Engineers Part J Journal of Engineering Tribology ◽

10.1243/1350650971542363 ◽

1997 ◽

Vol 211 (2) ◽

pp. 117-128 ◽

Cited By ~ 9

Author(s):

Y Yue ◽

T. A. Stolarski

Keyword(s):

Control Volume ◽

Numerical Procedure ◽

Operating Conditions ◽

Hydrodynamic Bearings ◽

Thrust Bearings ◽

Flow Balance ◽

Control Volumes ◽

Volume Method ◽

Spiral Angle ◽

Spiral Grooves

The objective of this paper is to develop an accurate numerical procedure for the analysis of nominally flat contacts with spiral grooves lubricated by gases. The numerical procedure, which is based on the control-volume method, enables the solutions of the non-linear Reynolds equation to be obtained without limitation in geometry and operating conditions. Satisfactory flow balance was achieved on the control volumes as well as on the whole boundary and the method was proved to be very accurate. Convergence of the method was quick for any compressibility number. Three types of contact with spiral grooves were analysed. They were hydrodynamic bearings without interior chambers, hydrodynamic bearings with interior chambers and hybrid bearings. The effects of spiral angle, groove geometry (length, depth and width) and compressibility on performances were investigated for all possible designs.

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Morphodynamic stability and characteristic length scales of bifurcations and confluences loops

10.5194/egusphere-egu21-8017 ◽

2021 ◽

Author(s):

Niccolò Ragno ◽

Marco Redolfi ◽

Marco Tubino

Keyword(s):

Froude Number ◽

Water Surface ◽

Characteristic Length ◽

Coupled Model ◽

Surface Elevation ◽

Momentum Balance ◽

Water Surface Elevation ◽

Control Volumes ◽

Almost All ◽

Fluvial Environments

<p>The morphodynamics of multi-thread fluvial environments like braided and anastomosing rivers is fundamentally driven by the continuous concatenation of channel bifurcations and confluences, which govern the distribution of flow and sediment among the different branches that are reconnecting further downstream. Almost all studies performed to date consider the two processes separately, although they frequently appear as closely interconnected. In this work, we tackle the problem of analyzing the coupled morphodynamics of such bifurcation-confluence systems by studying the equilibrium and stability conditions of a channel loop, where flow splits into two secondary anabranches that rejoin after a prescribed distance. Through the formulation of a novel theoretical model for erodible bed confluences based on the momentum balance on two distinct control volumes, we show that the dominating anabranch (i.e. that carrying more water and sediment) is subject to an increase of the water surface elevation that is proportional to the square of the Froude number. This increase in water surface elevation tends to reduce the slope of the dominating branch, which produces a negative feedback that tends to stabilize the bifurcation-confluence system. A linear analysis of the coupled model reveals that the stabilizing effect of the confluence depends on the ratio between the length of the connecting channels and the average water depth, independently of the channel slope and Froude number. Furthermore, the effect of the confluence is potentially able to stabilize the channel loop in conditions where the classic stabilizing mechanism at the bifurcation (i.e. the topographical effect related to the gravitational pull on the sediment transport) is very weak, as expected when most of the sediment is transported in suspension. The identification of a characteristic length scale that produces a coupling between the confluences and bifurcations opens intriguing possibilities for interpreting the self-adjustment of the planform scale of natural multi-thread rivers.</p>

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Numerical simulation of fire in road tunnel. Selection of calculation grid

Pozharnaia bezopasnost` ◽

10.37657/vniipo.pb.2021.72.64.005 ◽

2021 ◽

pp. 47-54

Author(s):

И.А. Болодьян ◽

С.В. Пузач ◽

А.С. Барановский

Keyword(s):

Field Tests ◽

Field Method ◽

Research Field ◽

Computational Grids ◽

Maximum Temperature ◽

Road Tunnel ◽

Road Tunnels ◽

The Masses ◽

Control Volumes ◽

Calculation Grid

Рассматривается вопрос выбора расчетной сетки при моделировании пожара в тоннеле с помощью полевого метода и проводится оценка возможного влияния размеров ячеек сетки, а также граничного условия постоянства давления на результаты расчета. Выполнено моделирование пожара для четырех размеров расчетной сетки. Обоснована возможность применения наиболее грубой из используемых сеток с точки зрения инженерных расчетов, в том числе с оговоркой относительно постановки граничного условия. The issue of fire safety of road tunnels is currently an urgent task. Road tunnels are usually not standard typical facilities, but the unique structures. Therefore, it is necessary to study the influence of various parameters on the development of fire in order to take into account the characteristics of a particular object and make decisions on its effective fire protection. Implementation of field tests in this case is expensive and time-consuming. In this regard, numerical modeling is one of the most effective methods of such research. Field models are the most common and currently used for numerical calculations. These models are based on the numerical solution of the system of conservation equations for small control volumes of the calculation grid. This paper examines the issues of selection the calculation grid when modeling a fire in tunnels using the field method is considered and the possible influence of the size of the grid cells is estimated. The mathematical model used in this work is based on a set of differential equations of hydrodynamics, heat transfer, as well as the equation of conservation of the masses of components. Four computational grids were selected for a horizontal (without slope) model tunnel to determine the optimal cell size. As a result of conducted calculations it was established the following: the size of calculated grid is not fundamental for the initial stage of the fire; the use of smaller grid may be preferable at further development of fire, accompanied by increase of combustion capacity to the maximum; the maximum temperature values, especially in the far sections, are obtained on the coarsest grid. The use of such a grid for estimated engineering calculations can be allowed.

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Application and Research of Rotate-Lookup-Summation in Robot Motion

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.467-469.186 ◽

2011 ◽

Vol 467-469 ◽

pp. 186-191

Author(s):

Hao Bin Shi ◽

Wen Jie Dong

Keyword(s):

Control Volume ◽

Dimensional Space ◽

Control Variable ◽

Control Process ◽

Controlling Factors ◽

Dimensional Control ◽

Control Factors ◽

Look Up Table ◽

New Research ◽

Control Volumes

How to exercise reasonable motion control on robot becomes a new research focus in robot technology research. This paper proposes the Rotate-Lookup-Summation according to the deficiency of traditional look-up table. This method first confirm the controlling factors P1，P2….Pn that would affect the control volume Z, and then the multi-dimensional control volumes and multi-dimensional control factors would be projected to sub-dimensional space. Finally, the same controlling factors of different sub-dimensional space would be rotated to a single sub-dimensional space and establish a corresponding table. According to the single sub-dimensional space value of the controlling factors, the corresponding control variable could be found in table and eventually complete the control process. Experiments show that the method could ensure the integrity and accuracy of table, reduce the table memory capacitance and lookup time, so as to realize the control of look-up table in micro-device.

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