Flow Reversal in Opposing Mixed Convection Flow in Inclined Pipes

1989 ◽  
Vol 111 (1) ◽  
pp. 114-120 ◽  
Author(s):  
A. S. Lavine ◽  
M. Y. Kim ◽  
C. N. Shores
Keyword(s):  
Mixed Convection ◽  
Tilt Angle ◽  
Maximum Flow ◽  
Flow Reversal ◽  
Transition To Turbulence ◽  
Convection Flow ◽  
Periodic Behavior ◽  
Tube Cross Section ◽  
High Reynolds ◽  
Inclined Pipe

An experimental investigation of opposing mixed convection in an inclined pipe has been conducted. Dye injection reveals the existence of flow reversal regions. There is an optimal tilt angle that yields maximum flow reversal length. Flow reversals are seen to cause early transition to turbulence. Temperature profiles are measured across the tube cross section near the entrance to the heated section, and show the effect of tube inclination. Temperature measurements exhibit periodic behavior in the flow reversal region under some conditions, generally characterized by low tilt angle and moderate to high Reynolds and Grashof numbers. Flow visualization indicates that this periodic behavior is due to the intermittent breakdown of the flow reversal region.

scholarly journals MHD Mixed Convection Micropolar Fluid Flow through a Rectangular Duct

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Mekonnen Shiferaw Ayano ◽  
Stephen T. Sikwila ◽  
Stanford Shateyi
Keyword(s):  
Magnetic Field ◽  
Differential Equations ◽  
Mixed Convection ◽  
Applied Magnetic Field ◽  
Flow Reversal ◽  
Convection Flow ◽  
Temperature Profiles ◽  
Rectangular Duct ◽  
Micropolar Fluid Flow ◽  
Flow Through

Mixed convection flow through a rectangular duct with at least one of the sides of the walls of the rectangle being isothermal under the influence of transversely applied magnetic field has been analyzed numerically in this study. The governing differential equations of the problem have been transformed into a system of nondimensional differential equations and then solved numerically. The dimensionless velocity, microrotation components, and temperature profiles are displayed graphically showing the effects of various values of the parameters present in the problem. The results showed that the flow field is notably influenced by the considered parameters. It is found that increasing the aspect ratio increases flow reversal, commencement of the flow reversal is observed after some critical value, and the applied magnetic field increases the flow reversal in addition to flow retardation. The microrotation components flow in opposite direction; also it is found that one component of the microrotation will show no rotational effect around the center of the duct.

Flow and Mixed Convection Heat Transfer in a Divergent Heated Vertical Channel

1996 ◽  
Vol 118 (3) ◽  
pp. 606-615 ◽  
Author(s):  
C. Gau ◽  
T. M. Huang ◽  
W. Aung
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Flow Reversal ◽  
Forced Flow ◽  
Vertical Position ◽  
Convection Flow ◽  
Reversed Flow ◽  
Buoyancy Parameter ◽  
Divergent Channel

This paper concerns an experimental study of the mixed convection flow and heat transfer inside a divergent channel formed by two plane walls. One of the side walls is oriented vertically and is heated uniformly, and the opposite wall is tilted at an angle of 3 deg with respect to the vertical position and is insulated. The ratio of the height to wall spacing at the flow inlet, which is at the smaller opening of the channel is 15. The Reynolds number of the main forced flow ranges from 100 to 4000 and the buoyancy parameter, Gr/Re2, varies from 0.3 to 907. Flow reversal is found to occur for both assisted and opposed convection. The effect of channel divergence on the occurrence and structure of the reversed flow and the heat transfer is presented and discussed. It is found that the divergence of the channel decelerates the mainstream such that flow reversal is initiated at a much lower buoyancy parameter. The adverse pressure gradient tends to push the reversed flow upstream and leads to a deeper penetration of the reversed flow into the channel The destabilization effect of the divergent channel can lead to breakdown of vortices and to transition to turbulent flow. This can significantly enhance the heat transfer. Temperature fluctuation measurements at different locations are used to indicate oscillations and fluctuations of the reversed flow. The effect of the buoyancy parameter on the Nusselt number and the reversed flow structure is discussed. The average Nusselt number is determined and correlated in terms of relevant nondimensional parameters for pure forced and mixed convection, respectively.

An Experimental Study of Transition to Turbulence in Vertical Mixed Convection Flows

1989 ◽  
Vol 111 (1) ◽  
pp. 121-130 ◽  
Author(s):  
R. Krishnamurthy ◽  
B. Gebhart
Keyword(s):  
Experimental Study ◽  
Natural Convection ◽  
Mixed Convection ◽  
Boundary Region ◽  
Transition To Turbulence ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Downstream Location ◽  
A Value ◽  
Convection Parameter

Results are reported from an experimental study of a mixed convection flow, that is, combined forced and natural convection, undergoing transition to turbulence, adjacent to a vertical, uniform-heat-flux surface. Small and aiding forced convection effects were studied. The measurements, in air, were made at pressure levels ranging from 4.4 bars to 8 bars, at flux levels q″ in the range 14–1300 W/m2. The imposed free-stream velocities U∞ were around 5 cm/s. One objective was to determine any quantitative parameters that would predict the bounds of the transition region. Another was to measure disturbance growth characteristics during transition. Results show that, at a given U∞, the beginning of transition is not correlated by the local Grashof number Grx* alone. An additional dependence on both the downstream location and pressure level was found. Thermal and velocity transitions were found to begin when the mixed convection parameter εM reached a value of 0.18. Transition was found to be complete when the nondimensional convected energy in the boundary region, βq″x/5k, reached a value of 7.10. These experimental results confirm the prediction of linear stability analysis, that aiding mixed convection stabilizes the flow, compared to pure natural convection flow. The data also support a physical explanation of these mechanisms.

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