| 1. |
- Chen, J.C., et al.
(författare)
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Heat transfer in fluidized beds: design methods
- 2005
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Ingår i: Powder Technology. ; 150, s. 123-132
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale fluidized beds for commercial processes commonly require heat transfer surfaces. Design then demands that heat transfer coefficients be specified. Empirical correlations are unable to cover the wide range of variables and conditions encountered. Mechanistic models are more reliable, but must be chosen carefully. For bubbling beds, the packet model approach gives reasonable predictions for the convective component of transfer, but further work is required to provide reliable estimates of two required time constants, dependent on the hydrodynamics. For industrial-scale circulating beds, a mechanistic model that incorporates the key factors influencing heat transfer, assumes fully developed transfer, and utilizes results from large-scale units is recommended.
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| 2. |
- Eriksson, M., et al.
(författare)
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Radiation heat transfer in circulating fluidized bed combustors
- 2005
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Ingår i: International Journal of Thermal Sciences. ; 44, s. 399-409
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Tidskriftsartikel (refereegranskat)abstract
- A new model for predicting radiation heat transfer in circulating fluidized bed combustors is proposed. The model assumes two phase structure, the flow at the wall dominated by streamers of clusters traveling mostly downward, interspersed with periods where there is upwards flow of a dilute suspension. Also, the model assumes the intensity distribution to be semi-isotropic in the forward and backward direction. The predictions are in good agreement with the experimental results from the literature. Finally, a parametric study is performed to show the effect of different bed parameters on radiative heat transfer. The results indicate that suspension temperature, wall temperature, wall emissivity, particle emissivity, and suspension density have significant influence on the radiation heat transfer coefficient.
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| 3. |
- Eriksson, Morgan, et al.
(författare)
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Radiative Heat Transfer in Circulating Fluidized Beds
- 2005
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Ingår i: International journal of thermal sciences. - : Elsevier BV. - 1290-0729 .- 1778-4166. ; 44, s. 399-409
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Tidskriftsartikel (refereegranskat)abstract
- A new model for predicting radiation heat transfer in circulating fluidized bed combustors is proposed. The model assumes two phase structure, the flow at the wall dominated by streamers of clusters traveling mostly downward, interspersed with periods where there is upwards flow of a dilute suspension. Also, the model assumes the intensity distribution to be semi-isotropic in the forward and backward direction. The predictions are in good agreement with the experimental results from the literature. Finally, a parametric study is performed to show the effect of different bed parameters on radiative heat transfer. The results indicate that suspension temperature, wall temperature, wall emissivity, particle emissivity, and suspension density have significant influence on the radiation heat transfer coefficient.
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| 4. |
- Ersoy, L., et al.
(författare)
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Circulating fluidized bed hydrodynamics with air staging: an experimental study
- 2004
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Ingår i: Powder Technology. ; 145, s. 25-33
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Tidskriftsartikel (refereegranskat)abstract
- The influence of secondary air injection (SA) on the hydrodynamics of circulating fluidized beds was studied in a 0.23-m ID riser. The secondary to primary air ratio, the vertical position, and the mode of injection (radial, tangential, and 45j entrance) are considered to be the key parameters of SA injection. It was found that the amount and location of SA have direct influence on the solids holdup and the segregation patterns in the riser. The SA divided the riser into two different flow zones: a dense turbulent zone below and a relatively dilute bed above the injection port. The mean solids velocity is found to be upwards with a greater magnitude in the center region. It is downwards with a smaller magnitude along the walls, suggesting core-annular flow structures for both above and below the SA injection region.
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| 5. |
- Farhad, S., et al.
(författare)
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Exergy analysis and performance evaluation of CNG to LNG converting process
- 2008
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Ingår i: Int. J. Exergy. ; 5:2, s. 164-176
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Tidskriftsartikel (refereegranskat)abstract
- A process for converting Compressed Natural Gas (CNG) to Liquefied Natural Gas (LNG) is modelled thermodynamically and effects of design and operating parameters on exergy destruction and performance of the process are studied. Results show that CNG pressure, pressure after Joule–Thomson valve, and temperature of CNG after heat exchanger of refrigerating system have significant effects on optimum design and operation of the process. The results also indicate that the effects of CNG temperature after CNG production section, and pinch temperature of the last heat exchanger of the process are considerable. To determine the effects of natural gas composition on operating the CNG to LNG converting (CLC) process, variation of nitrogen as the most effective content of natural gas on operating the process has been studied and discussed.
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| 6. |
- Koksal, M., et al.
(författare)
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Effect of staged air on heat transfer in circulating fluidized beds
- 2008
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Ingår i: Applied Thermal Engineering. ; 28, s. 1008-1014
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work is to develop a model for bed-to-surface heat transfer in circulating fluidized bed (CFB) risers with secondary air (SA) injection. The heat transfer coefficient is correlated to cross-sectionally averaged solids hold-up. The average solids hold-up is correlated with the operating and design parameters of CFB risers with SA injection. The data used in developing the correlations cover a range of 2.0–8.6 m/s for superficial gas velocity, 5–100 kg/m2s for solids circulation rate, 0–0.6 for secondary to primary air ratio, and 60–300 lm for particle diameter (groups A and B). The predictions obtained with the correlations show good agreement with the experimental data. Furthermore, an experimental correlation, developed in our previous work for prediction of wall-to-bed heat transfer coefficient was used in a parametric study to investigate the effects of design and operating parameters on heat transfer.
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| 7. |
- Mwaba, M.G., et al.
(författare)
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A State of the Art for Magnetic Based Fouling Mitigation Methods
- 2005
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Ingår i: International Journal of Heat Exchangers. ; 6:2, s. 235-266
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Tidskriftsartikel (refereegranskat)abstract
- Fouling mitigation, using magnets, is a technology that promises so much but still remains a mystery. It has been reported that magnets have been successful in controlling scaling, especially that due to calcium carbonate. In this article, the current state of magnetic based fouling mitigation strategies as found in the literature is presented. Experimental results and modeling efforts of magnetic influence on the scaling process are evaluated. The motivation for the evaluation is to identify key issues that require additional research. Evaluation of literature shows that there is an incomplete understanding of how exactly magnetic fields influence fluid systems. Significant knowledge gaps regarding effects of magnetic fields on (a) fluid flow, (b) elementary processes of scaling (nucleation, crystal growth and morphology). It is also evident that there is no clear agreement regarding the right conditions under which magnetic fields are effective in mitigating against fouling. Therefore, it is suggested that priority be placed on fundamental studies of the influence of magnetic fields on properties of the fluid systems under given conditions.
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| 8. |
- Sjosten, J., et al.
(författare)
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Further study on the influence of particle coating on fluidized bed heat transfer
- 2006
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Ingår i: International Journal of Heat and Mass Transfer. ; 49, s. 3800-3806
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Tidskriftsartikel (refereegranskat)abstract
- Heat transfer to an immersed sphere from fluidized uncoated sand particles of different mean size and size distribution is compared with that from coated sand particles of equal size extracted from two full-scale fluidized bed boilers for different superficial gas velocities and mean particle diameters from 350 to 646 lm. The thin coating on the sand bed particles from full-scale boilers was found to have a significant effect on the heat transfer coefficient, while the particle size distributions, as well as coating thickness, had little or no influence on the heat transfer coefficients for the conditions investigated.
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| 9. |
- Yaras, M.I., et al.
(författare)
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Vortex Hydraulic Turbine
- 2007
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Patent (populärvet., debatt m.m.)abstract
- An apparatus for generating electric power from water currents comprises a housing having at least one pair of channel, at least one pair of turbine assemblies and at least one pair of generator assemblies. Each channel of the pair has an axial intake, an axial discharge opening and a side intake. Each side intake extends along a length of the channel and faces in an upstream direction to receive a side inflow of water and directs the side inflow up against an interior surface of the channel to create a vortical flow structure having a low pressure core. The vortical flow structures are produced downstream of the turbine assemblies to effect an increase in a pressure drop across each of the turbine assemblies. The apparatus also has partition extending between the channels near said axial intakes.
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| 10. |
- Zhang, D., et al.
(författare)
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Fluidization Characteristics of Rice Husk in a Bubbling Fluidized Bed
- 2006
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Ingår i: 19th International Conference on Fluidized Bed Combustion.
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Konferensbidrag (refereegranskat)abstract
- The fluidization characteristics of rice husk was investigated experimentally in a 0.17 m ID, 0.9 m high laboratory scale fluidized bed by analyses of mean bed pressure drop, pressure fluctuations, power spectrum of pressure fluctuations, and visual observation with a digital camera. The results show that pure rice husk (rp = kg/m3) cannot be fluidized uniformly due to the occurrence of severe channeling. One of the possible methods to facilitate fluidization is to mix rice husk with an easily fluidizable solid. In this study, mixing 700 mm glass bead particles (rp = 2500 kg/m3) with rice husk improved the fluidization characteristics significantly. The minimum fluidization velocity of the binary mixture decreased and approached to that of glass bead particles as the mass fraction of the rice husk in the mixture was decreased. Power spectrum of pressure fluctuations was used to determine the quality of fluidization and estimate the onset of fluidization for the rice husk-glass beads mixture. Furthermore, it was found that with intermittent (pulsed) supply of fluidization air, the fluidization characteristics of pure rice husk could be substantially enhanced. In a frequency range of 0-10 Hz, flow pulsation resulted in turbulent bed-like behavior with improved gas-solid contact.
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