Article

Natural convection in an annulus between two rotating vertical cylinders

Department of Mathematics, Bangalore University, Bengalūru, Karnataka, India
Acta Mechanica (Impact Factor: 1.47). 02/2001; 147(1):173-196. DOI: 10.1007/BF01182360

ABSTRACT A numerical study is conducted to understand the effect of rotation on the axisymmetric flow driven by buoyancy in an annular cavity formed by two concentric vertical cylinders which rotate about their axis with different angular velocities. The inner and outer side walls are maintained isothermally at temperature
c
and
h
, respectively, while the horizontal top and bottom walls are adiabatic. The vorticity-stream function form of the Navier-Stokes equations and the energy equation have been solved by modified Alternating Direction Implicit method and Successive Line Over Relaxation method. Numerical results are obtained for a wide range of the Grashof number, Gr, nondimensional rotational speeds
i
,
o
of inner and outer cylinders and for different values of the Prandtl number Pr. The effects of the aspect ratio,A, on the heat transfer and flow patterns are obtained forA=1 and 2. The numerical results show that when the outer cylinder alone is rotating and the Grashof number is moderate, the outward bound flow is confined to a thin region along the bottom surface while the return flow covers a major portion of the cavity. For a given inner or outer cylinder rotation the temperature field is almost independent of the flow in the annulus for fluids with low Prandtl number, while it depends strongly for high Prandtl number fluids. At a high Grashof number, with moderate rotational speeds, the dominant flow in the annulus is driven by thermal convection, and hence an increase in the heat transfer rate occurs. In the case of unit aspect ratio, the flow pattern is unicellular for the rotation of the cylinders in the same direction, and when they rotate in the opposite direction two or more counter rotating cells separated by a stagnation surface are formed. The rate of heat transfer at the hot cylinder is suppressed when its speed of rotation is higher than that of the cooler cylinder. The computed heat transfer and flow patterns are compared with the available results of a nonrotating cylindrical annulus, and good agreement is found.

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    • "Wang et al. [2012] developed a finite volume model and analyzed transient natural convection in closed ended vertical annuli, with isothermally heated (or cooled) inner surface and insulated horizontal and outer surfaces. Venkatachalappa et al. [2001] conducted a numerical analysis to know the effect of rotation on the axisymmetric flow driven by buoyancy in an annular cavity formed by two concentric vertical cylinders which rotate about their axis with different angular velocities with inner and outer side walls at constant temperatures keeping the horizontal top and bottom walls as adiabatic. The governing equations were solved by Alternating Direction Implicit method and Successive Line over Relaxation method. "
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    ABSTRACT: In this work, transient numerical analysis of two dimensional heat transfer and fluid flow has been carried out for natural convection in an internally heated vertical annulus. The finite volume SIMPLER technique is used for the solution of governing equations on a staggered mesh. The MPI parallel programming technique is used for domain decomposition and parallelization of the code. The results are obtained for an aspect ratio of 10, radius ratio of 2 and Rayleigh number equal to 1000. Prandtl number is varied from 1 to 10. Effects of varying prandtl number on temperature, pressure, axial & radial velocity profiles are evaluated and discussed in detail.
    International Conference on Advancements in Mechanical Engineering (ICAME-2014), Al-Falah University, Dhauj Faridabad (India); 08/2014
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    • "Wang et al. [2012] developed a finite volume model and analyzed transient natural convection in closed ended vertical annuli, with isothermally heated (or cooled) inner surface and insulated horizontal and outer surfaces. Venkatachalappa et al. [2001] conducted a numerical analysis to know the effect of rotation on the axisymmetric flow driven by buoyancy in an annular cavity formed by two concentric vertical cylinders which rotate about their axis with different angular velocities with inner and outer side walls at constant temperatures keeping the horizontal top and bottom walls as adiabatic. The governing equations were solved by Alternating Direction Implicit method and Successive Line over Relaxation method. "
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    ABSTRACT: In this work, transient numerical analysis of two dimensional heat transfer and fluid flow has been carried out for natural convection in an internally heated vertical annulus. The finite volume SIMPLER technique is used for the solution of governing equations on a staggered mesh. The MPI parallel programming technique is used for domain decomposition and parallelization of the code. The results are obtained for an aspect ratio of 10, radius ratio of 2 and Rayleigh number equal to 1000. Prandtl number is varied from 1 to 10. Effects of varying prandtl number on temperature, pressure, axial & radial velocity profiles are evaluated and discussed in detail.
    “International Conference on Advancements in Mechanical Engineering” (ICAME-2014), Al-Falah University, Dhauj Faridabad (India); 08/2014
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    • "Batten et al [29] presented turbulent Taylor vortices between two concentric at a very high radius ratio. Venkatachalappa et al [30] presented a numerical study to understand the effect of rotation on the axi-symmetric flow driven by buoyancy in an annular cavity formed by two concentric vertical cylinders which rotate about their axis with different angular velocities. "
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    ABSTRACT: ___________________________________________________ ABSTRACT The present study aims to investigate experimentally fluid flow and performance characteristics of a double-pipe heat exchanger with rotating inner tube. Parameters that can be used to measure the performance of this type of heat exchanger are also presented, investigated and estimated. The experimental results are reported for the effect of cold and hot water mass flow rates, the heat exchanger arrangement (parallel or counter) and the rotation speed on NTU and effectiveness of the heat exchanger. This study was done for 0 ≤ N ≤ 1000 R.P.M, 0.022 ≤ m c ≤ 0.09 kg/s and 0.022 ≤ m h ≤ 0.09 kg/s. INTRODUCTION Heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air. Heat transfer in rotating systems has been the subject of many experimental and theoretical studies. Many engineering applications involve rotating machinery components with flow in an annulus formed between two concentric cylinders where one or both of the cylindrical surfaces is or are rotating one. Kim and Hwang [1] studied the experimental concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder was stationary and inner one was rotating. Taylor [2, 3] performed analytical and experimental works to predict flow, and thermal fields, stability, heat and mass transfer characteristics, etc., inside the concentric annular space. Mathew and Hegab [4] developed an analytical solution for counter flow micro channel heat exchanger subjected to external heat flux while operating under balanced and unbalanced flow conditions. With the addition of heat from the external heat source, the effectiveness of hot and cold A heat transfer characteristic of laminar flow in a circular annulus with a rotating inner cylinder in the presence of a laminar axial flow was investigated using sublimation techniques by Molki et al. [5]. The work focused on the entrance region of the annulus with simultaneous development of velocity and temperature profiles. Lei et al. [6] studied the existence of hydrodynamic instabilities leads to the formation of Taylor vortices in flows in the annulus between two concentric cylinders with one or both cylinders rotating.
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