An Investigation of Steady Wall-Ceiling and Partial Enclosure Fires

1984 ◽  
Vol 106 (1) ◽  
pp. 221-228 ◽  
Author(s):  
C.-P. Mao ◽  
A. C. Fernandez-Pello ◽  
J. A. C. Humphrey
Keyword(s):  
Numerical Model ◽  
Laminar Flow ◽  
Radiation Transport ◽  
Turbulent Transport ◽  
Qualitative Description ◽  
Significant Discrepancy ◽  
Fire Hazards ◽  
First Case ◽  
Flame Sheet ◽  
Prediction Approach

A numerical model has been developed to: (a) study the buoyancy-driven combusting flows of partial enclosure fires and (b) to help assess the fire hazards of different burning materials. The calculations provide the flow patterns and distributions of velocity, temperature, species concentration, and flame location in the flow. The model assumes steady laminar flow and makes use of the flame sheet approximation to describe the gas-phase chemical reaction. In corresponding experiments, photographic determinations of flame location were made. Two different cases were studied: (i) a fire occurring in a wall-ceiling configuration with variable pyrolyzing length (of PMMA material); and (ii) a partial enclosure fire with variable soffit and pyrolyzing lengths (the latter of PMMA or POM materials). Good agreement was obtained between measurements and calculations of the flame location for the first case. However, a significant discrepancy was found for the second case and is attributed to the neglect of turbulence and radiation transport in the model. Notwithstanding these limitations, it is found that a simple laminar flow model provides a correct qualitative description of the evolution of partial enclosure fires. For example, stratified (layered) motions, recirculation zones and the so-called “firewind” are correctly predicted as a function of pyrolysis and soffit lengths. The present approach, of incorporating physico-chemical parameters and boundary conditions of practical systems into a numerical model for assessing fire hazards, is very attractive due to its relative ease of execution. The accuracy of the numerical prediction approach can be improved by including radiation and turbulent transport.

Hot-Wire Measurements of Turbulence Correlations in a Triangular Duct

1962 ◽  
Vol 29 (4) ◽  
pp. 609-614 ◽  
Author(s):  
C. J. Cremers ◽  
E. R. G. Eckert
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Cross Section ◽  
Circular Tube ◽  
Turbulent Transport ◽  
Circular Cross Section ◽  
Hot Wire ◽  
Round Tube ◽  
Flow Through ◽  
Hot Wires

Previous studies by flow visualization have indicated that the flow through a duct of triangular cross section is in its characteristics quite different from flow through a duct with circular cross section. They revealed among others that purely laminar flow exists in the corners of the duct even though the bulk of the fluid moves in turbulent motion. Heat-transfer measurements in such a duct appear to indicate that the turbulent transport in the direction of the height of the duct is considerably smaller than expected from circular tube measurements. The present paper reports the measurements of turbulent correlations for turbulent flow through such a duct. These measurements have been made with hot wires of very small dimensions. They again reveal the existence of a laminar corner region. In the bulk of the fluid, the differences of the correlations to those in a round tube turned out to be smaller than originally suspected.

Towards transition modelling for supersonic laminar flow control based on spanwise periodic roughness elements

2005 ◽  
Vol 363 (1830) ◽  
pp. 1079-1096 ◽  
Author(s):  
Meelan Choudhari ◽  
Chau-Lyan Chang ◽  
Li Jiang
Keyword(s):  
Boundary Layer ◽  
Laminar Flow ◽  
Flow Control ◽  
Leading Edge ◽  
Design And Optimization ◽  
Supersonic Aircraft ◽  
Laminar Flow Control ◽  
Key Enabling Technologies ◽  
Novel Concept ◽  
Prediction Approach

Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University (ASU) has led to a novel concept for passive LFC, which employs distributed leading edge roughness to limit the growth of naturally dominant crossflow instabilities in a swept-wing boundary layer. Predicated on nonlinear modification of the mean boundary-layer flow via controlled receptivity, the ASU concept requires a holistic prediction approach that accounts for all major stages within transition in an integrated manner. As a first step in developing an engineering methodology for the design and optimization of roughness-based supersonic LFC, this paper reports on canonical findings related to receptivity plus linear and nonlinear development of stationary crossflow instabilities on a Mach 2.4, 73° swept airfoil with a chord Reynolds number of 16.3 million.

scholarly journals A qualitative description of shallow groundwater effect on surface temperature of bare soil

2009 ◽  
Vol 13 (9) ◽  
pp. 1749-1756 ◽  
Author(s):  
F. Alkhaier ◽  
R. J. Schotting ◽  
Z. Su
Keyword(s):  
Numerical Model ◽  
Soil Temperature ◽  
Skin Temperature ◽  
Soil Profile ◽  
Land Surface ◽  
Shallow Groundwater ◽  
Soil Surface ◽  
Qualitative Description ◽  
Groundwater Depth ◽  
Daily Minimum Temperature

Abstract. Whether or not shallow groundwater affects skin temperature (the temperature of soil surface) is important to detect depth and extent of shallow groundwater by dint of remote sensing and important for land surface modelling studies. Although few studies have been conducted to investigate that effect, they have yielded contradicting conclusions and they stopped in 1982. To determine that shallow groundwater affects skin temperature, we measured soil temperature at two different depths (5 and 10 cm) in seven places with variable water table depths every ten minutes and for six days. After that, we correlated the minimum, maximum and average daily temperatures to average groundwater depth. We also built a simple numerical model using a differential equations solver, Flex PDE, to simulate heat transfer into soil profile and used it to simulate groundwater effect on skin temperature. We found quite high negative correlation between the maximum and average daily soil temperature and groundwater depth. Contrarily, we could hardly find any correlation between the daily minimum temperature and groundwater depth. Numerical simulations, though simple, were useful in showing that groundwater shifted skin temperature curves up in the winter and down in the summer without affecting the shape of the curve. We conclude that shallow groundwater affects skin temperature directly by its distinctive thermal properties in the soil profile and indirectly by affecting soil moisture which in turn has many different and contradictory effects on skin temperature. This study recommends building a comprehensive numerical model that simulates the effect of shallow groundwater on skin temperature and on the different energy fluxes at land surface.

scholarly journals Effects of Bridge-Shaped Microchannel Geometry on the Performance of a Micro Laminar Flow Fuel Cell

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 822
Author(s):  
Muhammad Tanveer ◽  
Kwang-Yong Kim
Keyword(s):  
Fuel Cell ◽  
Numerical Model ◽  
Laminar Flow ◽  
Cross Section ◽  
Cross Sections ◽  
Three Dimensional ◽  
Narrow Channel ◽  
Navier Stokes ◽  
Cross Sectional ◽  
Square Channel

A laminar flow micro fuel cell comprising of bridge-shaped microchannel is investigated to find out the effects of the cross-section shape of the microchannel on the performance. A parametric study is performed by varying the heights and widths of the channel and bridge shape. Nine different microchannel cross-section shapes are evaluated to find effective microchannel cross-sections by combining three bridge shapes with three channel shapes. A three-dimensional fully coupled numerical model is used to calculate the fuel cell’s performance. Navier-Stokes, convection and diffusion, and Butler-Volmer equations are implemented using the numerical model. A narrow channel with a wide bridge shape shows the best performance among the tested nine cross-sectional shapes, which is increased by about 78% compared to the square channel with the square bridge shape.

A Numerical Model to Simulate Diffuse Effects in Microfluidic Fuel Cells

2010 ◽  
Author(s):  
Isaac B. Sprague ◽  
Prashanta Dutta
Keyword(s):  
Fuel Cell ◽  
Numerical Model ◽  
Laminar Flow ◽  
Ion Transport ◽  
Double Layer ◽  
Electric Double Layer ◽  
Double Layers ◽  
Algebraic Equations ◽  
Microfluidic Fuel Cell ◽  
Volume Method

A 2D numerical model is developed for a laminar flow fuel cell considering ion transport and the electric double layer around the electrodes. The Frumkin-Butler-Volmer equation is used for the fuel cell kinetics. The finite volume method is used to form algebraic equations from governing partial differential equations. The numerical solution was obtained using Newton’s method and a block TDMA solver. The model accounts for the coupling of charged ion transport with the electric field and is able to fully resolve the diffuse regions of the electric double layer in both the stream-wise and cross-channel directions. Different operating phenomena, such as laminar flow separation and the development of the depletion boundary layers and electric double layers are obtained. These numerical results demonstrate the model’s ability to capture the complex behavior of a microfluidic fuel cell which has been ignored in previous 1D models.

scholarly journals A qualitative description of shallow groundwater effect on surface soil temperature

2009 ◽  
Vol 6 (2) ◽  
pp. 2129-2152
Author(s):  
F. Alkhaier ◽  
R. J. Schotting ◽  
Z. Su
Keyword(s):  
Numerical Model ◽  
Soil Temperature ◽  
Skin Temperature ◽  
Soil Profile ◽  
Land Surface ◽  
Shallow Groundwater ◽  
Qualitative Description ◽  
Groundwater Depth ◽  
Daily Minimum Temperature ◽  
Modelling Studies

Abstract. Whether or not shallow groundwater affects skin temperature is important to detect depth and extent of shallow groundwater by dint of remote sensing and important for land surface modelling studies. Although few studies have been conducted to investigate that effect, they have yielded contradicting conclusions and they stopped in 1982. To determine that shallow groundwater affects skin temperature, we measured soil temperature at two different depths (5 and 10 cm) in seven places with variable water table depths every ten minutes and for six days. After that, we correlated the minimum, maximum and average daily temperatures to average groundwater depth. We also built a simple numerical model using a differential equations solver, Flex PDE, to simulate heat transfer into soil profile and used it to simulate groundwater effect on skin temperature. We found quite high negative correlation between the maximum and average daily soil temperature and groundwater depth. Contrarily, we could hardly find any correlation between the daily minimum temperature and groundwater depth. Numerical simulations, though simple, were useful in showing that groundwater shifted skin temperature curve up in the winter and down in the summer without affecting the shape of the curve. We conclude that shallow groundwater affects skin temperature directly by its distinctive thermal properties in the soil profile and indirectly by affecting soil moisture which in turn has many different and contradictory effects on skin temperature. This study recommends building comprehensive numerical model that simulate the effect of shallow groundwater on skin temperature and on the different energy fluxes at land surface.

scholarly journals Choosing an optimal <i>β</i> factor for relaxed eddy accumulation applications across vegetated and non-vegetated surfaces

2021 ◽  
Vol 18 (18) ◽  
pp. 5097-5115
Author(s):  
Teresa Vogl ◽  
Amy Hrdina ◽  
Christoph K. Thomas
Keyword(s):  
Detection Limit ◽  
Land Surface ◽  
Turbulent Transport ◽  
Atmospheric Stability ◽  
Forest Site ◽  
Relaxed Eddy Accumulation ◽  
First Case ◽  
Wide Range ◽  
Scalar Similarity ◽  
Method Model

Abstract. Accurately measuring the turbulent transport of reactive and conservative greenhouse gases, heat, and organic compounds between the surface and the atmosphere is critical for understanding trace gas exchange and its response to changes in climate and anthropogenic activities. The relaxed eddy accumulation (REA) method enables measuring the land surface exchange when fast-response sensors are not available, broadening the suite of trace gases that can be investigated. The β factor scales the concentration differences to the flux, and its choice is central to successfully using REA. Deadbands are used to select only certain turbulent motions to compute the flux. This study evaluates a variety of different REA approaches with the goal of formulating recommendations applicable over a wide range of surfaces and meteorological conditions for an optimal choice of the β factor in combination with a suitable deadband. Observations were collected across three contrasting ecosystems offering stark differences in scalar transport and dynamics: a mid-latitude grassland ecosystem in Europe, a loose gravel surface of the Dry Valleys of Antarctica, and a spruce forest site in the European mid-range mountains. We tested a total of four different REA models for the β factor: the first two methods, referred to as model 1 and model 2, derive βp based on a proxy p for which high-frequency observations are available (sensible heat Ts). In the first case, a linear deadband is applied, while in the second case, we are using a hyperbolic deadband. The third method, model 3, employs the approach first published by Baker et al. (1992), which computes βw solely based upon the vertical wind statistics. The fourth method, model 4, uses a constant βp, const derived from long-term averaging of the proxy-based βp factor. Each β model was optimized with respect to deadband size before intercomparison. To our best knowledge, this is the first study intercomparing these different approaches over a range of different sites. With respect to overall REA performance, we found that the βw and constant βp, const performed more robustly than the dynamic proxy-dependent approaches. The latter models still performed well when scalar similarity between the proxy (here Ts) and the scalar of interest (here water vapor) showed strong statistical correlation, i.e., during periods when the distribution and temporal behavior of sources and sinks were similar. Concerning the sensitivity of the different β factors to atmospheric stability, we observed that βT slightly increased with increasing stability parameter z/L when no deadband is applied, but this trend vanished with increasing deadband size. βw was unrelated to dynamic stability and displayed a generally low variability across all sites, suggesting that βw can be considered a site-independent constant. To explain why the βw approach seems to be insensitive towards changes in atmospheric stability, we separated the contribution of w′ kurtosis to the flux uncertainty. For REA applications without deeper site-specific knowledge of the turbulent transport and degree of scalar similarity, we recommend using either the βp, const or βw models when the uncertainty of the REA flux quantification is not limited by the detection limit of the instrument. For conditions when REA sampling differences are close to the instrument's detection limit, the βp models using a hyperbolic deadband are the recommended choice.

scholarly journals Thermal Assessment of Laminar Flow Liquid Cooling Blocks for LED Circuit Boards Used in Automotive Headlight Assemblies

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1202
Author(s):  
Muhsin Kilic ◽  
Mehmet Aktas ◽  
Gokhan Sevilgen
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Mass Flow ◽  
Thermal Performance ◽  
Cover Plate ◽  
Coolant Fluid ◽  
Liquid Cooling ◽  
Flow Rates ◽  
Mass Flow Rates

This research work presents a comparative thermal performance assessment of the laminar flow cooling blocks produced for automotive headlight assembly using a high power Light Emitting Diode (LED) chip. A three-dimensional numerical model with conjugate heat transfer in solid and fluid domains was used. Laminar flow was considered in the present analysis. The validation of the numerical model was realized by using the measured data from the test rig. It was observed that substantial temperature variations were occurred around the LED chip owing to volumetric heat generation. The cooling board with lower height performs better thermal performance but higher pressure drop for the same mass flow rates. The cooling board with the finned cover plate performs better thermal performance but results in an increased pressure drop for the same mass flow rates. Increasing the power of the LED results in higher temperature values for the same mass flow rates. The junction temperature is highly dependent on the mass flow rates and LED power. It can be controlled by means of the mass flow rate of the coolant fluid. New Nusselt number correlations are proposed for laminar flow mini-channel liquid cooling block applications.

scholarly journals Numerical study of new techniques drag reduction: application to aerodynamic devices

2021 ◽  
Vol 12 ◽  
pp. 16
Author(s):  
Amine Agriss ◽  
Mohamed Agouzoul ◽  
Abdeslem Ettaouil ◽  
Abdessamad Mehdari
Keyword(s):  
Laminar Flow ◽  
Drag Reduction ◽  
Numerical Study ◽  
The Body ◽  
Test Cases ◽  
Ansys Fluent ◽  
New Techniques ◽  
Reduction Techniques ◽  
First Case ◽  
Naca 0012

In the present study, new drag reduction techniques applied to aerodynamic structures have been developed. The test cases have been numerically performed using three simplified models. Simulations have been performed by using the CFD software Ansys fluent. The first case deals with a laminar flow over a flat plate. Drag reduction is obtained by corrugating the shape of the plate. The second case treats a laminar flow over a NACA 0012 airfoil. By the addition of a device fixed on the flow separation point, the drag could be reduced. The last case concerns a turbulent flow over the Ahmed body. Drag reduction is obtained by the perforation of a conduit leading a part of the flow from the front to be injected at the rear of the body.

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