Abstract
The heat transfer of a reactor with improved Intermig impellers was numerically investigated by the finite element method (FEM) simulation software Fluent (V.19). A turbulence model utilized the standard k-ε model, and the turbulent flows in two large vortexes between vertical tubes were collided to form a strong convection. The influence of heat and mass transfer developing from the impeller diameters, the distance between the two impellers (C1), the rotational speed and the installation height of the bottom impeller (C2) were studied. The reactor was equipped with special structure vertical tubes to increase the heat exchange areas. The rate of heat transfer, including criteria such as the convective heat transfer coefficient, the Nusselt number of outside vertical tubes, and the temperature boundary layer thickness, assured the accurate control of the heat exchange mixing state. The experimental testing platform was designed to validate the simulated results, which revealed the influence order of related factors. The Nusselt number Nu was affected by various related factors, resulting in the rotation and diameter of impellers extending far beyond the distance between the two impellers (C1) and the installation height of the impeller (C2). The average temperature boundary layer thicknesses of the symmetrical and middle sections were 3.24 mm and 3.48 mm, respectively. Adjusting the appropriate parameters can accurately control the heat exchange process in such a reactor, and the conclusions provide a significant reference for engineering applications.
Acknowledgements
This project was supported by the National Natural Science Foundation of China (51775262), the Natural Science Foundation of Jiangsu Province of China (BK20161546), the Natural Science Foundation for Colleges and Universities in Jiangsu Province of China (16KJA470001), and the Project of Jiangsu provincial Six Talent Peaks (ZBZZ-014).
Nomenclature
The distance between the two impellers, m
The installation height of the bottom impeller, m
An internal diameter of stirred tank, m
Impeller dimension, m
Liquid level, m
The structural parameters of the improved Intermig blade, m
The thermocouple distribution points of the outer wall of the heat tubes
The thermocouple distribution points of stirring medium temperature measurement
The axis of symmetry and the junction of the vertical tube elbow
The horizontal height of the stirring medium temperature measurement, m
Outside surface area of the vertical tubes, m2
Overall rate of heat transfer, W
Overall heat transfer coefficient, Wm−2 K−1
Mean temperature difference between the heating medium and the material, K
Heating conduction coefficient
Convection coefficient
Radiation coefficient
The internal convection coefficient
The external convection coefficient
Any heat flow through the boundary conditions of the volume control body in the stirred tank, W
The work provided to the control body during the mechanical agitation of the impellers, W
energy accumulated in volume control (kJ)
Nusselt number of outer wall vertical tubes
- Nui
Nusselt number of internal vapors in vertical tubes
Prandtl number
Specific heat capacity of water at the given temperature,
Outside temperature of heating water vapor, K
Inlet temperature of water vapor, K
- Tvapor
The vapor working temperature of internal vertical tubes
Water vapor mass flow, kg/s
Average bath temperature of the agitated liquid medium, K
bulk temperature of cold fluid in tank discretized in time θ (K)
bulk temperature of cold fluid in tank discretized in time θ + n (K)
- θ
Heating time, s
The thermal conductivity at the corresponding temperature, K
The viscosity ratio of the stirring medium in the vessel to the viscosity of the agitating medium near the wall
Reynolds number
Dynamic viscosity of the agitated liquid (heating media) at the mean temperature,
Dynamic viscosity at the inside vertical tubes (heating media) at the wall temperature,
outer diameter of the vertical tubes, m
inside diameter of the vertical tubes, m
Thermal conductivity of stirring fluid at the given temperature, Wm−1 K−1
Thermal conductivity of water vapor at the given temperature, Wm−1 K−1
Combined force of centrifugal force and Coriolis force
Effective viscosity,
Kinematic viscosity,
Turbulent viscosity,
- gi
Gravitational acceleration in the i direction,
Effective thermal conductivity of the stirring cold fluid
Thermal conductivity of stirring cold fluid
Turbulent thermal conductivity of the fluid
- (τij)eff
Stress tensor
Turbulent energy,
Viscosity dissipation rate
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