Measurement of Combustion Air to a Typical Cyclone Burner With a Common Wind Box and Pressure Loss Effects on the Cyclone Due to Inlet Configuration

2009 ◽  
Author(s):  
Robert O. Brandt
Keyword(s):  
Pressure Loss ◽  
Cross Flow ◽  
Flow Distribution ◽  
Cfd Modeling ◽  
Width Ratio ◽  
Worst Case ◽  
Air Inlet ◽  
Large Length ◽  
Coal Flow ◽  
Case Condition

To maintain proper fuel air ratio and minimize NOx during combustion, air and coal flow into a cyclone burner must be measured. Due to the large length to width ratio of the air inlet to some burners, often greater than 7, accurate measurement has proven to be difficult; in fact, measurement with a ratio greater than 2 to 1 has proven to be difficult. A typical cyclone burner system was analyzed with a premium CFD modeling package, with particular attention being given to the location which would be considered “worst case”. If this location can be measured accurately, then we can assume that the less stringent locations will also be measured accurately. Additionally, a “best case” was also analyzed to compare pressure loss due to the measurement. The worst case location was chosen based on a cross flow condition of the air just going around the corner at the entrance, where the flow velocity is the highest. See Figure A. The “best case” condition was chosen as the air flow entering the inlet normal to the plane of the inlet, although this condition may not actually exist in the example wind box chosen. Three inlet configurations were analyzed, (1) three optimally designed Oval High Betas across the inlet, (2) two optimally designed Oval High Betas across the inlet and (3) the flow distribution across the inlet as is, with no method to break up the large length to width ratio. Of particular interest, once the analysis for both the “worst case” and “best case” were done for the three inlet configurations, one configuration, proved best for both measurement and pressure loss—condition (1), the three optimally designed Oval High Betas.

Simulation of Forward Osmosis Flow in a Two-Dimensional Asymmetric Membrane Channel With Draw Channel Circular Baffle Implementation

2015 ◽  
Author(s):  
James R. L. Koch ◽  
Ramesh K. Agarwal
Keyword(s):  
Osmotic Pressure ◽  
Pressure Loss ◽  
Membrane Filtration ◽  
Concentration Polarization ◽  
Fluid Dynamic ◽  
Forward Osmosis ◽  
Cross Flow ◽  
Cfd Modeling ◽  
Asymmetric Membrane ◽  
Asymmetric Membranes

Forward Osmosis (FO) driven asymmetric membrane filtration is a developing technology which shows promise for seawater desalination and wastewater treatment. Due to the fact that asymmetric membranes are widely used in conjunction with this technology, internal concentration polarization (ICP), a flow-entrainment effect occurring within such membranes, is a significant if not dominant source of overall osmotic pressure loss across the membrane. Accurate modeling of ICP effects is therefore very critical for accurate Computational Fluid Dynamic (CFD) modeling of asymmetric membranes. A related, dilutive effect known as external concentration polarization (ECP) also develops on both the rejection and draw sides of the membrane, further contributing to osmotic pressure loss. In order to increase the overall water flux, circular spacers can be implemented within the draw channel of FO cross-flow membrane exchange units to decrease the effects of ICP and draw ECP. The drawback of spacer inclusions is an increased pressure loss across the length of the feed channel. The system efficiency gained by the decrease in ECP must therefore be weighed against the energy cost of hydraulically making up lost channel pressure. To model the geometry of a FO cross-flow channel, the open source CFD package OpenFOAM is used. A compressible flow model with explicit boundary conditions is developed to simulate the flux transfer and ICP effects present within an asymmetric membrane when exposed to a NaCl solution. Results are validated by comparison with the numerical data generated by earlier models of asymmetric membranes implemented by other investigators using similar simulation conditions.

Simulation of Forward Osmosis Flow in a Two-Dimensional Asymmetric Membrane Channel With Draw Channel Circular Baffle Implementation

2016 ◽  
Author(s):  
James R. L. Koch ◽  
Ramesh K. Agarwal
Keyword(s):  
Osmotic Pressure ◽  
Pressure Loss ◽  
Membrane Filtration ◽  
Concentration Polarization ◽  
Fluid Dynamic ◽  
Forward Osmosis ◽  
Cross Flow ◽  
Cfd Modeling ◽  
Asymmetric Membrane ◽  
Asymmetric Membranes

Forward Osmosis (FO) driven asymmetric membrane filtration is a developing technology which shows promise for seawater desalination and wastewater treatment. Due to the fact that asymmetric membranes are widely used in conjunction with this technology, internal concentration polarization (ICP), a flow-entrainment effect occurring within such membranes, is a significant if not dominant source of overall osmotic pressure loss across the membrane. Accurate modeling of ICP effects is therefore very critical for accurate Computational Fluid Dynamic (CFD) modeling of asymmetric membranes. A related, dilutive effect known as external concentration polarization (ECP) also develops on both the rejection and draw sides of the membrane, further contributing to osmotic pressure loss. In order to increase the overall water flux, circular spacers can be implemented within the draw channel of FO cross-flow membrane exchange units to decrease the effects of ICP and draw ECP. The drawback of spacer inclusions is an increased pressure loss across the length of the feed channel. The system efficiency gained by the decrease in ECP must therefore be weighed against the energy cost of hydraulically making up lost channel pressure. To model the geometry of a FO cross-flow channel, the open source CFD package OpenFOAM is used. A compressible flow model with explicit boundary conditions is developed to simulate the flux transfer and ICP effects present within an asymmetric membrane when exposed to a NaCl solution. Results are validated by comparison with the numerical data generated by earlier models of asymmetric membranes implemented by other investigators using similar simulation conditions.

scholarly journals Modelling of service reservoirs

2001 ◽  
Vol 3 (3) ◽  
pp. 165-172 ◽  
Author(s):  
Hoi Yeung
Keyword(s):  
Plug Flow ◽  
Flow Characteristics ◽  
Flow Distribution ◽  
Tracer Test ◽  
Computational Fluid Mechanics ◽  
Width Ratio ◽  
Dual Function ◽  
Water Age ◽  
Reactor Model ◽  
Increased Risk

Service reservoirs were built to provide the dual function of balancing supply with demand and provision of adequate head to maintain pressure throughout the distribution network. Changing demographics in the UK and reducing leakage have led to significant increases in water age and hence increased risk of poor water quality. Computational fluid mechanics has been used to study the behaviour of a range of service reservoirs with a rectangular plan form. Detailed analysis of flow distribution and water age suggests that tanks with horizontal inlets are better mixed when compared with vertical top water level inlets. With increasing length to width ratio, the flow characteristics of tanks with vertical inlets increasingly resemble plug flow. A new multi-channel reactor model was developed to model the recirculations in service reservoirs. This simple model can be used to characterise the flow characteristics of service reservoirs from tracer test results.

CFD Modeling of Cogeneration Burner Applications and the Significance of Thermal Radiative Heat Transfer Effects

2003 ◽  
Author(s):  
A. F. Tenbusch
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Radiation ◽  
System Design ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Flow Distribution ◽  
Cfd Modeling ◽  
Large Temperature ◽  
Flow Heat

Industrial burners provide process heat for a wide range of applications including cogeneration power production. In such applications a (typically) natural gas fired stationary turbine powers an electric generator and indirectly powers a heat recover steam generator (HRSG). The HRSG steam cycle operates by reclaiming the residual thermal energy of the gas turbine exhaust (GTE) flow. Burners are used to reheat the GTE and increase plant capacity during peak demand periods. CFD modeling is used in the design of burner systems for HRSG applications. GTE flow exiting the turbine unit is passed through a diffuser and then expanded into ductwork where the steam system heat exchangers are located. The expansion of the GTE flow from the turbine diffuser to the full cross section of the ductwork is usually severe and creates an uneven flow distribution. Flow correcting structure may be needed to distribute the flow depending upon the severity of the duct expansion. CFD modeling is used to predict the flow distribution of the GTE and guide the design of any necessary flow correcting structure. Burners are typically installed in an array upstream of the application heat exchanger inlet. CFD combustion, heat transfer, and flow analysis is employed in the burner system design process to locate the burner array, determine any necessary flow baffling, and to ensure and provide a uniform thermal distribution at the downstream heat exchanger inlet. Excessive thermal variation in the GTE flow entering the heat exchanger results in large temperature gradients that can lead to thermal cracking and fatigue of the heat exchanger surfaces. CFD modeling is used to ensure that the burner system design produces a uniform flow and temperature distribution at the heat exchanger inlet region downstream of the burners. This report presents a case study of a CFD flow, heat-transfer, and combustion analysis for a typical HRSG burner application. Two CFD models were constructed for the analysis. The first model included the coupled effects of flow, heat transfer, and combustion for the entire HRSG model volume, but excluded the effects of thermal radiation. The second model included a sub-domain of the HRSG volume near the burner and included the additional effects of thermal radiation, both surface radiation and the effects of the radiatively participating flue gas. Radiative effects were included in the second model by employing the Discrete Transfer Method. Results of the study showed the significant role thermal radiative heat transfer had on the resulting temperature predictions downstream of the flame zone.

CFD modeling of gypsum scaling in cross-flow RO filters using moments of particle population balance

2020 ◽  
Vol 8 (5) ◽  
pp. 104151
Author(s):  
Ashish Uppu ◽  
Abhijit Chaudhuri ◽  
Shyama Prasad Das ◽  
Nitikesh Prakash
Keyword(s):  
Cross Flow ◽  
Population Balance ◽  
Cfd Modeling ◽  
Particle Population ◽  
Gypsum Scaling

scholarly journals Applications of CFD Method to Gas Mixing Analysis in a Large-Scaled Tank

2007 ◽  
Author(s):  
Si Y. Lee ◽  
Richard A. Dimenna
Keyword(s):  
Liquid Surface ◽  
Operating Conditions ◽  
Evolution Rate ◽  
Cfd Modeling ◽  
Local Concentration ◽  
Gas Mixing ◽  
Recirculation Flow ◽  
Air Inlet ◽  
Inlet Conditions ◽  
Vapor Space

The computational fluid dynamics (CFD) modeling technique was applied to the estimation of maximum benzene concentration for the vapor space inside a large-scaled and high-level radioactive waste tank at Savannah River site (SRS). The objective of the work was to perform the calculations for the benzene mixing behavior in the vapor space of Tank 48 and its impact on the local concentration of benzene. The calculations were used to evaluate the degree to which purge air mixes with benzene evolving from the liquid surface and its ability to prevent an unacceptable concentration of benzene from forming. The analysis was focused on changing the tank operating conditions to establish internal recirculation and changing the benzene evolution rate from the liquid surface. The model used a three-dimensional momentum coupled with multi-species transport. The calculations included potential operating conditions for air inlet and exhaust flows, recirculation flow rate, and benzene evolution rate with prototypic tank geometry. The flow conditions are assumed to be fully turbulent since Reynolds numbers for typical operating conditions are in the range of 20,000 to 70,000 based on the inlet conditions of the air purge system. A standard two-equation turbulence model was used. The modeling results for the typical gas mixing problems available in the literature were compared and verified through comparisons with the test results. The benchmarking results showed that the predictions are in good agreement with the analytical solutions and literature data. Additional sensitivity calculations included a reduced benzene evolution rate, reduced air inlet and exhaust flow, and forced internal recirculation. The modeling results showed that the vapor space was fairly well mixed and that benzene concentrations were relatively low when forced recirculation and 72 cfm ventilation air through the tank boundary were imposed. For the same 72 cfm air inlet flow but without forced recirculation, the heavier benzene gas was stratified. The results demonstrated that benzene concentrations were relatively low for typical operating configurations and conditions. Detailed results and the cases considered in the calculations will be discussed here.

scholarly journals Enhancement of Impingement Heat Transfer With the Crossflow Normal to Ribs and Pins Between Each Row of Holes

2018 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Cross Flow ◽  
Experimental Results ◽  
Hole Density ◽  
Impingement Heat Transfer ◽  
The Cross ◽  
Flow Maldistribution

Impingement heat transfer investigations with obstacle (fins) on the target surface were carried out with the obstacles aligned normal to the cross-flow. Conjugate heat transfer (CHT) computational fluid dynamics (CFD) analysis were used for the geometries previously been investigated experimentally. A 10 × 10 row of impingement jet holes or hole density, n, of 4306 m−2 with ten rows of holes in the cross-flow direction was used. The impingement hole pitch X to diameter D, X/D, and gap Z to diameter, Z/D, ratios were kept constant at 4.66 and 3.06 for X, D and Z of 15.24, 3.27 and 10.00 mm, respectively. Nimonic 75 test walls were used with a thickness of 6.35 mm. Two different shaped obstacles of the same flow blockage were investigated: a continuous rectangular ribbed wall of 4.5 mm height, H, and 3.0 mm thick and 8 mm high rectangular pin-fins that were 8.6 mm wide and 3.0 mm thick. The obstacles were equally spaced on the centre-line between each row of impingement jets and aligned normal to the cross-flow. The two obstacles had height to diameter ratios, H/D, of 1.38 and 2.45, respectively. Comparison of the predictions and experimental results were made for the flow pressure loss, ΔP/P, and the surface average heat transfer coefficient (HTC), h. The computations were carried out for air coolant mass flux, G, of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss and surface average HTC for all the predicted G showed reasonable agreement with the experimental results, but the predictions for surface averaged h were below the measured values by 5–10%. The predictions showed that the main effect of the ribs and pins was to increase the pressure loss, which led to an increased flow maldistribution between the ten rows of holes. This led to lower heat transfer over the first 5 holes and higher heat transfer over the last 3 holes and the net result was little benefit of either obstacle relative to a smooth wall. The results were significantly worse than the same obstacles aligned for co-flow, where the flow maldistribution changes were lower and there was a net benefit of the obstacles on the surface averaged heat transfer coefficient.

scholarly journals Investigation of flow non-uniformities in the cross-flow heat exchanger with elliptical tubes

2019 ◽  
Vol 108 ◽  
pp. 01009 ◽  
Author(s):  
Stanisław Łopata ◽  
Paweł Ocłoń ◽  
Tomasz Stelmach
Keyword(s):  
Heat Exchanger ◽  
Measurement Data ◽  
Cross Flow ◽  
Flow Distribution ◽  
Transitional Flow ◽  
Working Fluid ◽  
Elliptical Cross ◽  
Flow Heat ◽  
The Cross ◽  
Inflow Conditions

In heat exchangers, especially those with the cross-flow arrangement, it is nearly impossible to achieve the uniform distribution of the working fluid in the tubular space with the currently used inlet and outlet chambers (in some constructions as well). The improper inflow conditions to individual tubes, including those with an elliptical cross-section - often used because of their favorable features compared to round tubes, is the cause of improper heat transfer. In this respect, transitional flow is of particular importance. This flow regime is complex and challenging to model. Therefore, it is necessary to perform experimental verification. For this purpose, an appropriate stand was built, allowing to investigate the flow of the working fluid (water) to the elliptical tubes in the cross-current heat exchanger. The paper presents the results of measurements for manifold geometry, which are currently used in practice (for heat exchanger constructions). The analysis of the measurement data confirms the nonuniform flow distribution to individual tubes of the heat exchanger.

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