“…In this section, the relationship between the local heat transfer coefficients and the local gas–liquid slip velocities in a pilot‐scale bubble column with diameter of 0.44 m and height of 3.65 m is investigated. Al‐Dahhan and coworkers 20,21 had studied the effect of superficial gas velocities, radial and axial positions on the local heat transfer coefficients in bubble columns. They found that the local heat transfer coefficients increased with the increase of superficial gas velocities while decreased with increasing the r / R in the fully developed region, 20,21 as shown in Figure 5.…”
Section: Resultsmentioning
confidence: 99%
“…To explore the relationship between the local gas–liquid slip velocities and the local heat transfer coefficients, the local heat transfer coefficients in pilot‐scale bubble columns measured by Al‐Dahhan and coworkers 20,21 are used in this work. The geometry of the air–water bubble columns and the superficial gas velocities in the research of Al‐Dahhan and coworkers 20,21 are presented in Table 2.…”
Section: Modeling and Simulationsmentioning
confidence: 99%
“… In experiments, the dynamic liquid height in the References 20 and 21 is 2.67 and 3.20 m, respectively. …”
Section: Modeling and Simulationsmentioning
confidence: 99%
“…Al‐Dahhan and coworkers 20 provided a comprehensive summary on the developed models for calculating the heat transfer coefficients. The influence of some hydrodynamic properties (e.g., bubble velocity, bubble pass frequency, bubble chord length, and gas holdup) on the heat transfer coefficients in bubble columns had been investigated by previous studies 20‐24 . However, the relationship between the local gas–liquid slip velocities and the local heat transfer coefficients in bubble columns has not been explored.…”
The knowledge of the local gas–liquid slip velocity distribution can offer a better understanding for the complex transport phenomena in bubble columns. In this work, CFD–PBM simulations are carried out to investigate the effect of superficial gas velocities, axial positions, and scale of bubble columns on the time‐averaged radial profiles of gas–liquid slip velocities. Furthermore, the relationship between local slip velocities and local heat transfer coefficients in pilot‐scale bubble columns at superficial gas velocities of 0.05 m/s, 0.20 m/s, and 0.35 m/s is studied. The results indicate that the slip velocities decrease with the increase of r/R (r‐radial position, R‐column radius), while increase with increasing superficial gas velocities in general. In the fully developed region, the axial positions have small impact on the local slip velocities. A strong linear relation between heat transfer coefficients and slip velocities in the fully flow developed region is observed.
“…In this section, the relationship between the local heat transfer coefficients and the local gas–liquid slip velocities in a pilot‐scale bubble column with diameter of 0.44 m and height of 3.65 m is investigated. Al‐Dahhan and coworkers 20,21 had studied the effect of superficial gas velocities, radial and axial positions on the local heat transfer coefficients in bubble columns. They found that the local heat transfer coefficients increased with the increase of superficial gas velocities while decreased with increasing the r / R in the fully developed region, 20,21 as shown in Figure 5.…”
Section: Resultsmentioning
confidence: 99%
“…To explore the relationship between the local gas–liquid slip velocities and the local heat transfer coefficients, the local heat transfer coefficients in pilot‐scale bubble columns measured by Al‐Dahhan and coworkers 20,21 are used in this work. The geometry of the air–water bubble columns and the superficial gas velocities in the research of Al‐Dahhan and coworkers 20,21 are presented in Table 2.…”
Section: Modeling and Simulationsmentioning
confidence: 99%
“… In experiments, the dynamic liquid height in the References 20 and 21 is 2.67 and 3.20 m, respectively. …”
Section: Modeling and Simulationsmentioning
confidence: 99%
“…Al‐Dahhan and coworkers 20 provided a comprehensive summary on the developed models for calculating the heat transfer coefficients. The influence of some hydrodynamic properties (e.g., bubble velocity, bubble pass frequency, bubble chord length, and gas holdup) on the heat transfer coefficients in bubble columns had been investigated by previous studies 20‐24 . However, the relationship between the local gas–liquid slip velocities and the local heat transfer coefficients in bubble columns has not been explored.…”
The knowledge of the local gas–liquid slip velocity distribution can offer a better understanding for the complex transport phenomena in bubble columns. In this work, CFD–PBM simulations are carried out to investigate the effect of superficial gas velocities, axial positions, and scale of bubble columns on the time‐averaged radial profiles of gas–liquid slip velocities. Furthermore, the relationship between local slip velocities and local heat transfer coefficients in pilot‐scale bubble columns at superficial gas velocities of 0.05 m/s, 0.20 m/s, and 0.35 m/s is studied. The results indicate that the slip velocities decrease with the increase of r/R (r‐radial position, R‐column radius), while increase with increasing superficial gas velocities in general. In the fully developed region, the axial positions have small impact on the local slip velocities. A strong linear relation between heat transfer coefficients and slip velocities in the fully flow developed region is observed.
“…Bubble‐column reactors belong to the important multiphase gas‐liquid contactors, which are widely applied in various industries, such as chemical processing, biochemical and biotechnology, petrochemical and refining, gas processing industries, etc. 1–10. The heat and mass transfer characteristics are the key design parameters which influence conversion level, productivity output, and economic operation expenses.…”
Bubble dispersion characteristics play an important role in heat and mass transfer of bubble-liquid two-phase turbulent flows in bubble-column reactors. In order to quantitatively describe the influence of operation conditions and sparger design on two-phase turbulent hydrodynamics in terms of a computational fluid dynamics approach, a second-order moment bubble-liquid twophase turbulent model was developed to predict the effects of superficial gas velocity, liquid and gas density, liquid dynamic viscosity, and sparger nozzle configuration on bubble-liquid hydrodynamics, e.g., bubble volume fraction, turbulent kinetic energy, and turbulent kinetic energy dissipation. Bubble dispersion behavior was found to be a complex function of industrial operations and sparger configuration parameters.
The flow regime transitions in a gas-solid fluidized bed were studied for the first time using a micro-foil heat flux sensor. The time series of heat flux signals was analyzed by statistical and state space methods. The experimental measurements were performed in a lab-scale gas-solid fluidization column. Four different flow regimes, i.e., fixed-bed flow regime, bubbling-flow regime, slugging-flow regime, and turbulent-flow regime, and three intermediate transition velocities, i.e., minimum fluidizing velocity or minimum bubbling velocity, minimum slugging velocity, and minimum turbulent velocity, were successfully identified. The method based on the analysis of heat flux sensor measurements allowed to determine accurately the different flow regimes and the transition velocities.
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