Numerical Investigation of Natural Convection in a Mono-Span Greenhouse

2012 ◽  
Author(s):  
Sunita Kruger ◽  
Leon Pretorius
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Natural Convection ◽  
Pitch Angle ◽  
Design Tool ◽  
Design Parameters ◽  
Two Dimensional ◽  
Cfd Model ◽  
Indoor Climate ◽  
Contour Plots

In this paper, the use of computational fluid dynamics is evaluated as a design tool to investigate the indoor climate of a confined greenhouse. The finite volume method using polyhedral cells is used to solve the governing mass, momentum and energy equations. Natural convection in a cavity corresponding to a mono-span venlo-type greenhouse is numerically investigated using Computational Fluid Dynamics. The CFD model is designed so as to simulate the climate above a plant canopy in an actual multi-span greenhouse heated by solar radiation. The aim of this paper is to investigate the influence of various design parameters such as pitch angle and roof asymmetry and on the velocity and temperature patterns inside a confined single span greenhouse heated from below. In the study reported in this paper a two-dimensional CFD model was generated for the mono-span venlo-type greenhouse, and a mesh sensitivity analysis was conducted to determine the mesh independence of the solution. Similar two-dimensional flow patterns were observed in the obtained CFD results as the experimental results reported by Lamrani et al [2]. The CFD model was then modified and used to explore the effect of roof pitch angle and roof asymmetry at floor level on the development of the flow and temperature patterns inside the cavity for various Rayleigh numbers. Results are presented in the form of vector and contour plots. It was found that considerable temperature and velocity gradients were observed in the centre of the greenhouse for each case in the first 40mm above the ground, as well as in the last 24mm close to the roof. Results also indicated that the Rayleigh number did not have a significant impact on the flow and temperature patterns inside the greenhouse, although roof angle and asymmetry did. The current results demonstrate the importance of CFD as a design tool in the case of greenhouse design.

CFD-BASED RESEARCH ON THE LOAD-BEARING CAPACITY OF ASYMMETRIC TEXTURE WITH DIFFERENT REYNOLDS NUMBER

2013 ◽  
Vol 20 (05) ◽  
pp. 1350043 ◽  
Author(s):  
YUNCAI ZHAO ◽  
LEI HAN
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Bearing Capacity ◽  
Two Dimensional ◽  
Hydrodynamic Load ◽  
Cfd Model ◽  
Load Bearing Capacity ◽  
Load Bearing ◽  
Computational Fluid Dynamics Cfd

A two-dimensional computational fluid dynamics (CFD) model was developed to study the load-bearing capacity of asymmetric texture under the state of fluid lubrication. The effects of asymmetric parameter H and the Reynolds number Re on hydrodynamic load-bearing capacity of the oil film were discussed. It was found that a decrease in asymmetric parameter H may significantly improve the load-bearing capacity, but an increase in Reynolds number Re may reduce this effect. For example, with a Re at 20, the load-bearing capacity increases by 73.44% with the H varying from 4 to 0.2. However, with a Re at 160, it has only an increase of 4.68% at the same conditions. In addition, the numerical results also showed that the load-bearing capacity will increase with the increase of Re in certain texture.

Computational Fluid Dynamics Modeling of a Catalytic Flat Plate Fuel Reformer for On-Board Hydrogen Generation

2013 ◽  
Vol 10 (6) ◽  
Author(s):  
Susanta K. Das ◽  
Kranthi K. Gadde
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flat Plate ◽  
Catalytic Combustion ◽  
Cocurrent Flow ◽  
Design Parameters ◽  
Practical Implementation ◽  
Channel Height ◽  
Two Dimensional ◽  
Wgs Reaction

A catalytic flat plate fuel reformer offers better heat integration by combining the exothermic catalytic combustion reaction on one side and the endothermic catalytic reforming reaction on the other side. In this study, steam reforming of natural gas (methane) coupled with a methane catalytic combustion in a catalytic flat plate reformer is studied using a two-dimensional model for a cocurrent flow arrangement. The two-dimensional computational fluid dynamics (CFD) model makes the predictions more realistic by increasing its capability to capture the effect of various design parameters and eliminates the uncertainties introduced by heat and mass transfer coefficients used in one-dimensional models. In our work we simulated the entire catalytic flat plate reformer (both reforming side and combustion side) and carried-out studies related to important design parameters such as channel height, inlet fuel velocities, and catalyst layer thickness that can provide guidance for the practical implementation of such fuel reformer design. The simulated transverse temperature profiles (not shown here due to page limitation) show that there is virtually no heat loss across the plate at the reformer exit. Introduction of a water gas shift (WGS) reaction at the reformer side along with our optimized reformer design parameters decreases the amount of carbon monoxide (CO) almost 90%–98% in the final reformate exiting the reformer as compared to without the WGS reaction. The CFD results obtained in this study will be very helpful to understand the optimization of design parameters to build a first generation prototype.

scholarly journals A Computational Fluid Dynamics Modeling and Experimental Study of the Mixing Process for the Dispersion of the Synthetic Fibers in Wet-Lay Forming

2008 ◽  
Vol 3 (1) ◽  
pp. 155892500800300 ◽  
Author(s):  
Melur K. Ramasubramanian ◽  
Donald A. Shiffler ◽  
Amit Jayachandran
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wire Mesh ◽  
Spherical Particles ◽  
Design Parameters ◽  
Mixing Process ◽  
Cfd Model ◽  
Discrete Phase Model ◽  
Dynamics Modeling ◽  
Synthetic Fibers

In this paper, we present results from a computational fluid dynamics (CFD) model for the mixing process used to disperse synthetic fibers in wet-lay process. We used CFD software, FLUENT, together with the MIXSIM user interface to accurately model the impeller geometry. A multiple reference frame (MRF) model and standard k-e turbulence model were used to model the problem. After obtaining a converged solution for the mixing tank with water, a discrete phase model was constructed by injecting spherical particles into the flow. A mixing tank with baffles and a centrally located impeller was used in experiments. PET fibers (1.5 denier, 6.35, 12.7, and 38.7 mm) at a concentration of 0.01% were mixed in water for the study. In regions behind the baffles, where the model predicted higher concentration of particles, experimental results showed a 34% higher concentration relative to the region in the high turbulence zone near the center. Instantaneous sheets were formed by rapidly dipping and removing a flat wire mesh strainer into the tank at two different locations to assess the state of dispersion in the tank. The sheets were transferred onto a blotting paper and examined under a microscope to count defects. Results show that the number of rope defects was 43% higher in sheets drawn from the region behind the baffles than in the sheets drawn from regions near the center of the tank. Changing baffles from a rectangular to a triangular cross section decreased the number of rope defects, but increased the number of log defects in the sample sheets at the same location. The CFD model can be used to optimize mixing tank design for wet lay fiber dispersion. The model provides further insight into the mixing process by predicting the effect of changes in design parameters on dispersion quality.

Development of a Two-Dimensional Computational Fluid Dynamics Approach for Computing Three-Dimensional Honeycomb Labyrinth Leakage

2004 ◽  
Vol 126 (4) ◽  
pp. 794-802 ◽  
Author(s):  
Dong-Chun Choi ◽  
David L. Rhode
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Three Dimensional ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Two Dimensional ◽  
Cfd Model ◽  
Resource Requirement ◽  
Three Dimensional Flow ◽  
Dimensional Flow

A new approach for employing a two-dimensional computational fluid dynamics (CFD) model to approximately compute a three-dimensional flow field such as that in a honeycomb labyrinth seal was developed. The advantage of this approach is that it greatly reduces the computer resource requirement needed to obtain a solution of the leakage for the three-dimensional flow through a honeycomb labyrinth. After the leakage through the stepped labyrinth seal was measured, it was used in numerically determining the value of one dimension (DTF1) of the simplified geometry two-dimensional approximate CFD model. Then the capability of the two-dimensional model approach was demonstrated by using it to compute the three-dimensional flow that had been measured at different operating conditions, and in some cases different distance to contact values. It was found that very close agreement with measurements was obtained in all cases, except for that of intermediate clearance and distance to contact for two sets of upstream and downstream pressure. The two-dimensional approach developed here offers interesting benefits relative to conventional algebraic-equation models, particularly for evaluating labyrinth geometries/operating conditions that are different from that of the data employed in developing the algebraic model.

Dynamic Instability Analysis of a Spring-Loaded Pressure Safety Valve Connected to a Pipe by Using Computational Fluid Dynamics Methods

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Fengjie Zheng ◽  
Chaoyong Zong ◽  
Chao Zhang ◽  
Xueguan Song ◽  
Fuzheng Qu ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Dynamic Instability ◽  
Design Parameters ◽  
Wave Forces ◽  
Cfd Model ◽  
Pressure System ◽  
System Pressure ◽  
Computational Fluid Dynamics Cfd ◽  
And Performance

Abstract As the ultimate protection of a pressure system, pressure safety valves (PSV) can respond in an unstable manner in the form of flutter and chatter, which will affect service life, reliability, and performance. In order to study the dynamic instability caused by multisource forces including the flow force, the spring compression force, and the pressure wave forces, a high-fidelity computational fluid dynamics (CFD) model of the system is proposed. A complete CFD model, incorporating the PSV, connected pipes, and the pressure vessel, is developed, in which advanced techniques in Fluent using User Defined Function (UDF) and Dynamic Layering method are combined to allow the PSV to be coupled to the system dynamics. Based on this model, the valve's opening and reclosing process is monitored to examine the influence of design parameters on the dynamic instability of the PSV. Specifically, the propagation of pressure waves along the connecting pipes is successfully captured, helping to assess the instability mechanism and provide the ability to optimize the design and setup of pressure relief systems.

A Two-Dimensional CFD Simulation for Different Spacers of Spiral Wound Moudles

2012 ◽  
Vol 557-559 ◽  
pp. 2249-2252 ◽  
Author(s):  
Song Lin Xu ◽  
Wen Qiang Mi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Fluid Flow ◽  
Cfd Simulation ◽  
Two Dimensional ◽  
Cfd Model ◽  
Visual Method ◽  
Unsteady Fluid Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Unsteady Fluid

A computational fluid dynamics (CFD) model was used to simulate unsteady fluid flow in a two-dimensional channel. The flow was computed for several different geometries and velocity. Calculations show different flow patterns of the cavity spacer, the submerged spacer and the zigzag spacer. Applications of two-dimensional CFD simulation give a visual method to determine the advantages of each spacer type.

Points to Note in Modeling Fire With Computational Fluid Dynamics

2012 ◽  
Author(s):  
L. Qu ◽  
W. K. Chow
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Three Dimensional ◽  
Design Tool ◽  
Performance Based Design ◽  
Cfd Model ◽  
Fire Dynamics ◽  
Design Fire ◽  
Computational Fluid Dynamics Cfd ◽  
Three Dimensional Simulations

Computational Fluid Dynamics (CFD) is a popular design tool in many projects for ensuring fire safety through performance-based design. However, there are always challenges on the quality and uncertainties of the CFD simulated results. Two points raised are on the grid size and free boundary conditions. A simple corridor fire with a small design fire is taken as an example to address these two points in this paper. The CFD model Fire Dynamics Simulator (FDS) version 5 was taken as the simulation tool Two-dimensional and three-dimensional simulations are compared. The geometry is proposed to outside for better description on minimizing opening boundary.

scholarly journals Design of Road-Side Barriers to Mitigate Air Pollution near Roads

2021 ◽  
Vol 11 (5) ◽  
pp. 2391
Author(s):  
Jose I. Huertas ◽  
Javier E. Aguirre ◽  
Omar D. Lopez Mejia ◽  
Cristian H. Lopez
Keyword(s):  
Fluid Dynamics ◽  
Air Pollution ◽  
Computational Fluid Dynamics ◽  
Sulfur Hexafluoride ◽  
Computational Domain ◽  
Cfd Model ◽  
Near Surface ◽  
The Road ◽  
Pollutant Concentrations ◽  
Highly Correlated

The effects of using solid barriers on the dispersion of air pollutants emitted from the traffic of vehicles on roads located over flat areas were quantified, aiming to identify the geometry that maximizes the mitigation effect of air pollution near the road at the lowest barrier cost. Toward that end, a near road Computational Fluid Dynamics (NR-CFD) model that simulates the dispersion phenomena occurring in the near-surface atmosphere (<250 m high) in a small computational domain (<1 km long), via Computational Fluid Dynamics (CFD) was used. Results from the NR-CFD model were highly correlated (R2 > 0.96) with the sulfur hexafluoride (SF6) concentrations measured by the US-National Oceanic and Atmospheric Administration (US-NOAA) in 2008 downwind a line source emission, for the case of a 6m near road solid straight barrier and for the case without any barrier. Then, the effects of different geometries, sizes, and locations were considered. Results showed that, under all barrier configurations, the normalized pollutant concentrations downwind the barrier are highly correlated (R2 > 0.86) to the concentrations observed without barrier. The best cost-effective configuration was observed with a quarter-ellipse barrier geometry with a height equivalent to 15% of the road width and located at the road edge, where the pollutant concentrations were 76% lower than the ones observed without any barrier.

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