Computational Fluid Dynamics Simulation of a Tubular Aerosol Reactor for Solar Thermal ZnO Decomposition

2007 ◽  
Author(s):  
Christopher Perkins ◽  
Alan W. Weimer
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Surface ◽  
High Surface Area ◽  
Dynamics Simulation ◽  
Base Case ◽  
Reactor Wall ◽  
Conductive Heat ◽  
Sensitive Material ◽  
Aspect Ratios

Computational fluid dynamics simulations were performed to model solar ZnO dissociation in a tubular aerosol reactor at ultra-high temperatures (1900 K–2300 K). Reactor aspect ratios ranged between 0.15 and 0.45, with the smallest ratio base case corresponding to a reactor diameter of .02286 m. Gas flowrates were set such that the Ar:ZnO ratio was greater than 3:1 and the system residence time was below 2 s. The system was found to exhibit highly laminar flow in all cases (Re ∼ 10), but gas velocity profiles did not seriously affect temperature profiles. Particle heating was nearly instantaneous, a result of the high radiation heat flux from the wall. There was essentially no difference between gas and particle temperatures due to the high surface area for conductive heat exchange between the phases. Calculation of ZnO conversion showed that significant conversions (>90%) could be attained for residence times typical of rapid aerosol processing. Particle sizes larger than 1 μm negatively affected conversion, but sizes of 10 μm still gave acceptable conversion levels. Simulation of reaction of product oxygen with the reactor wall showed that a reactor constructed of an oxidation-sensitive material would not be a viable choice for a high temperature solar reactor.

Computational Fluid Dynamics Simulation of a Tubular Aerosol Reactor for Solar Thermal ZnO Decomposition

2007 ◽  
Vol 129 (4) ◽  
pp. 391-404 ◽  
Author(s):  
Christopher Perkins ◽  
Alan Weimer
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Gas Flow ◽  
High Surface ◽  
Dynamics Simulation ◽  
Base Case ◽  
Reactor Wall ◽  
Conductive Heat ◽  
Sensitive Material ◽  
Aspect Ratios

Computational fluid dynamics simulations were performed to model solar ZnO dissociation in a tubular aerosol reactor at ultrahigh temperatures (1900–2300K). Reactor aspect ratios ranged between 0.15 and 0.45, with the smallest ratio base case corresponding to a reactor diameter of 0.02286m. Gas flow rates were set such that the Ar:ZnO ratio was greater than 3:1 and the system residence time was below 2s. The system was found to exhibit highly laminar flow in all cases (Re∼10), but gas velocity profiles did not seriously affect temperature profiles. Particle heating was nearly instantaneous, a result of the high radiation heat flux from the wall. There was essentially no difference between gas and particle temperatures due to the high surface area for conductive heat exchange between the phases. Calculation of ZnO conversion showed that significant conversions (>90%) could be attained for residence times typical of rapid aerosol processing. Particle sizes of >1μm negatively affected conversion, but sizes of 10μm still gave acceptable conversion levels. Simulation of reaction of product oxygen with the reactor wall showed that a reactor constructed of an oxidation-sensitive material would not be a viable choice for a high temperature solar reactor.

scholarly journals Computational Fluid Dynamics Simulation and Experimental Study of Key Design Parameters of Solar Thermal Collectors

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
James Allan ◽  
Zahir Dehouche ◽  
Sinisa Stankovice ◽  
Alan Harries
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Thermal Efficiency ◽  
Thermal Contact ◽  
High Surface ◽  
Heat Removal ◽  
Solar Thermal ◽  
Dynamics Simulation ◽  
Low Flow ◽  
Design Parameters

Numerical simulation enables the optimization of a solar collector without the expense of building prototypes. This study details an approach using computational fluid dynamics (CFD) to simulate the performance of a solar thermal collector. Inputs to the simulation include; heat loss coefficient, irradiance, and ambient temperature. A simulated thermal efficiency was validated using experimental results by comparing the calculated heat removal factor. The validated methodology was then applied to five different inlet configurations of a header–riser collector. The most efficient designs had uniform flow through the risers. The worst performing configurations had low flow rates in the risers that led to high surface temperatures and poor thermal efficiency. The calculated heat removal factor differed by between 4.2% for the serpentine model and 12.1% for the header–riser. The discrepancies were attributed to differences in thermal contact between plate and tubes in the simulated and actual design.

scholarly journals Fire Propagation Study in Naturally Ventilated Buildings using Computer Simulation

2019 ◽  
Author(s):  
Raja Singh
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Natural Ventilation ◽  
The Other ◽  
Dynamics Simulation ◽  
Small Cells ◽  
Base Case ◽  
Fire Propagation ◽  
Naturally Ventilated Buildings ◽  
Made In

Fire safety is of imminent concern in buildings since the first building was made. In a fire, the major concerns are evacuation and safety from the smoke and the heat. Smoke and the heat of the fire spreads in the building from one space to the other if there is continuity in space. Naturally ventilated buildings are made with a premise of enhancing this vertical and horizontal continuity in order to create health ventilation and air movement. In case of a fire, these natural ventilation pathways can facilitate the flow of smoke and heat through the spaces. This study aims at verifying using computational fluid dynamics simulation the actual role played by natural ventilation elements in the propagation of fire in buildings. A CFD (Computational Fluid Dynamics) package called FDS(Fire Dynamics Simulator) has been used preceded by a 3D model made in a 3D modelling software. The CFD software uses laws of conservation of mass, momentum and energy to actually evaluate the change in the mass, momentum and energy in small cells. These cells are of which the test space is made up of and is divided into. A test case is made up of a building with conventional design. This is tested against enhanced naturally ventilated buildings with parametric iterations. The first model of the building has one feature and then the feature gets added and tested again in each case. Here, we can compare in real time the effect of each feature against a base case and against the other features provided for enhanced natural ventilation. What is compared in all the results is the slices made at the same location. This gives us an insight on the fire propagation in naturally ventilated buildings and designers can use this to prevent fires from endangering the lives of the inhabitants.

scholarly journals Enhancement of cerebrovascular 4D flow MRI velocity fields using machine learning and computational fluid dynamics simulation data

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
David R. Rutkowski ◽  
Alejandro Roldán-Alzate ◽  
Kevin M. Johnson
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Velocity Fields ◽  
Dynamics Simulation ◽  
Patient Specific ◽  
4D Flow Mri ◽  
4D Flow ◽  
Flow Phase ◽  
Flow Mri ◽  
Trained Network

AbstractBlood flow metrics obtained with four-dimensional (4D) flow phase contrast (PC) magnetic resonance imaging (MRI) can be of great value in clinical and experimental cerebrovascular analysis. However, limitations in both quantitative and qualitative analyses can result from errors inherent to PC MRI. One method that excels in creating low-error, physics-based, velocity fields is computational fluid dynamics (CFD). Augmentation of cerebral 4D flow MRI data with CFD-informed neural networks may provide a method to produce highly accurate physiological flow fields. In this preliminary study, the potential utility of such a method was demonstrated by using high resolution patient-specific CFD data to train a convolutional neural network, and then using the trained network to enhance MRI-derived velocity fields in cerebral blood vessel data sets. Through testing on simulated images, phantom data, and cerebrovascular 4D flow data from 20 patients, the trained network successfully de-noised flow images, decreased velocity error, and enhanced near-vessel-wall velocity quantification and visualization. Such image enhancement can improve experimental and clinical qualitative and quantitative cerebrovascular PC MRI analysis.

scholarly journals Design Considerations for Borehole Thermal Energy Storage (BTES): A Review with Emphasis on Convective Heat Transfer

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-26 ◽  
Author(s):  
Helge Skarphagen ◽  
David Banks ◽  
Bjørn S. Frengstad ◽  
Harald Gether
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Theoretical Calculations ◽  
High Surface ◽  
High Surface Area ◽  
Volume Ratio ◽  
Thermal Recovery ◽  
Conductive Heat ◽  
Geological Environment

Borehole thermal energy storage (BTES) exploits the high volumetric heat capacity of rock-forming minerals and pore water to store large quantities of heat (or cold) on a seasonal basis in the geological environment. The BTES is a volume of rock or sediment accessed via an array of borehole heat exchangers (BHE). Even well-designed BTES arrays will lose a significant quantity of heat to the adjacent and subjacent rocks/sediments and to the surface; both theoretical calculations and empirical observations suggest that seasonal thermal recovery factors in excess of 50% are difficult to obtain. Storage efficiency may be dramatically reduced in cases where (i) natural groundwater advection through the BTES removes stored heat, (ii) extensive free convection cells (thermosiphons) are allowed to form, and (iii) poor BTES design results in a high surface area/volume ratio of the array shape, allowing high conductive heat losses. The most efficient array shape will typically be a cylinder with similar dimensions of diameter and depth, preferably with an insulated top surface. Despite the potential for moderate thermal recovery, the sheer volume of thermal storage that the natural geological environment offers can still make BTES a very attractive strategy for seasonal thermal energy storage within a “smart” district heat network, especially when coupled with more efficient surficial engineered dynamic thermal energy stores (DTES).

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