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.

An experimental study of nonlinear disturbance behaviour in natural convection

1973 ◽  
Vol 61 (2) ◽  
pp. 337-365 ◽  
Author(s):  
Yogesh Jaluria ◽  
Benjamin Gebhart
Keyword(s):  
Natural Convection ◽  
Experimental Studies ◽  
Boundary Region ◽  
Base Flow ◽  
Longitudinal Vortex ◽  
Forced Flow ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Mean Flow ◽  
Mean Velocity

An experimental investigation has been carried out to determine the behaviour of three-dimensional disturbances in laminar natural convection flow adjacent to a flat vertical surface with uniform heat flux input. A controlled two-dimensional disturbance, with a superimposed transverse variation, was introduced into the boundary region by a vibrating ribbon. The downstream propagation and amplification of these disturbances were studied in detail. Of principal interest was their nonlinear interaction with the base flow and any secondary mean flows that might arise therefrom. Measurements of the transverse mean velocity component indicate a double longitudinal vortex system. These results also show a distortion of the longitudinal base velocity profile which rapidly increases downstream. An alternate spanwise steepening and flattening of the profile is found to result. These mean flow modifications are found to be in good general agreement with existing theoretical and experimental studies of such flows. Our results are also compared with those obtained for forced flow. Several very important differences and similarities are indicated.

Mixed Convection On a Vertical Plate With an Unheated Starting Length

1976 ◽  
Vol 98 (4) ◽  
pp. 576-580 ◽  
Author(s):  
R. M. Abdel-Wahed ◽  
E. M. Sparrow ◽  
S. V. Patankar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Mixed Convection ◽  
Vertical Plate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Boundary Layer Equations ◽  
A Value ◽  
The Heat Transfer Coefficient ◽  
Convection Parameter

The effect of an unheated starting length on combined forced and natural convection adjacent to a vertical plate has been investigated by solving the nonsimilar laminar boundary layer equations. The solutions were carried out numerically for prescribed values of the governing parameters which include the starting length Reynolds number Re0, a mixed convection parameter gβ(ΔT)ν/U∞3, and the Prandtl number (which was assigned a value of 0.7). The local heat transfer results show that the presence of the unheated starting length can significantly accentuate the effects of buoyancy relative to the case of no starting length. The degree of accentuation of the buoyancy effects is strongly influenced by the magnitude of gβ(ΔT)ν/U∞3. When this parameter is on the order of 10−3, the natural convection contribution to the heat transfer coefficient is markedly increased owing to the starting length. On the other hand, when gβ(ΔT)ν/U∞3 is about 10−5 the buoyancy contribution is essentially unaffected by the starting length. The shape of the velocity profile is also found to be highly responsive to the interaction between the buoyancy and the starting length. As a by-product of the research, the accuracy of a well-known integral momentum/energy solution for pure forced convection with a starting length was established. In addition, velocity profiles for mixed convection without a starting length were compared with those of experiment in order to appraise a proposed explanation for a disparity that had been previously identified in the literature.

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.

Mixed Convection in Air in an Open Ended Cavity With a Moving Plate Parallel to the Cavity Open Surface

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Nicola Bianco ◽  
Vincenzo Naso ◽  
Oronzio Manca
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Mixed Convection ◽  
Plate Motion ◽  
Uniform Heat Flux ◽  
Geometrical Parameters ◽  
Heated Plate ◽  
Open Surface ◽  
Moving Plate ◽  
Plate Temperature

In this study, a numerical investigation of mixed convection in air in an open ended cavity, with a moving plate parallel to the cavity open surface, is carried out. The moving plate has a constant velocity, whereas a vertical plate of the open cavity is heated at uniform heat flux. All the other walls are adiabatic. The numerical analysis is obtained by means of the commercial code FLUENT. Two configurations, assisting and opposing, are analyzed. In the assisting configuration, natural convection is supported by the plate motion, whereas, in the opposing configuration, natural convection and plate motion have opposing effects. The effect of different geometrical parameters, heat flux and moving plate velocity are analyzed. Results in terms of heated plate and moving plate temperature profiles are presented and simple monomial correlation equations for both the configurations are proposed between the terms Nu/Re0.6 and Ri.

Mixed convection flow due to a moving vertical plate parallel to free stream under the influence of Newtonian heating and thermal radiation

2014 ◽  
Vol 5 (3) ◽  
pp. 859-870
Author(s):  
Prabhugouda Patil ◽  
S. Roy
Keyword(s):  
Prandtl Number ◽  
Mixed Convection ◽  
Thermal Radiation ◽  
Vertical Plate ◽  
Free Stream ◽  
Convection Flow ◽  
Mixed Convection Flow ◽  
Newtonian Heating ◽  
Mixed Convection Parameter ◽  
Convection Parameter

The steady mixed convection flow from a moving vertical plate in a parallel free stream is considered to investigate the combined effects of buoyancy force and thermal diffusion in presence of thermal radiation as well as Newtonian heating effects. The governing boundary layer equations are transformed into a non-dimensional form by a group of non-similar transformations. The resulting system of coupled non-linear partial differential equations is solved by an implicit finite difference scheme in conjunction with the quasi-linearization technique. Computations are performed and representative set is displayed graphically to illustrate the influence of the mixed convection parameter ( ), Prandtl number (Pr), the ratio of free stream velocity to the composite reference velocity ( ) and the radiation parameter (R) on the velocity and temperature profiles. The numerical results for the local skinfriction coefficient ( ) and surface temperature ( ) are also presented. The results show that the streamwise co-ordinate  significantly influences the flow and thermal fields which indicate the importance of non-similar solutions. Also, it is observed that the increase of mixed convection parameter causes the increase in the magnitude of velocity profile about 65% for lower Prandtl number fluids (Pr=0.7), while it decreases in the temperature profile about 30%. Present results are compared with previously published work and are found to be in excellent agreement.

Impact of Partial Slip and Heat Source on MHD Mixed Convection Flow of Nanofluid in a Double Lid-Driven Cavity Containing Insulated Obstacle

2020 ◽  
Vol 9 (3) ◽  
pp. 230-241
Author(s):  
M. A. Mansour ◽  
S. Sivasankaran ◽  
A. M. Rashad ◽  
T. Salah ◽  
Hossam A. Nabwey
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Source ◽  
Mixed Convection ◽  
Vertical Wall ◽  
Partial Slip ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Mixed Convection Flow ◽  
Left Wall

The current investigation analyzes the effects of partial slip and heat generation on the mixed convection flow with heat transfer in an inclined double lid-driven square cavity containing centered square adiabatic obstacle in the presence of magnetic field. The used cavity is subjected to constant heat flux and filled with Cu-water nanofluid. The top and bottom horizontal walls are thermally insulated and move with uniform velocity while the right vertical wall is maintained at a constant low temperature. A uniform heat flux is located in a part of th left wall of the cavity while the remaining part of this wall is thermally insulated. Finite volume technique is utilized to solve dimensionless governing equations of the problem. The proposed method is validated with the previous published numerical studies which distinctly offer a good agreement. The obtained results show that changing in the heat source length affects much the flow and thermal fields than the position of heat source. The averag Nusselt number decreases when the aspect ratio of the obstacle and heat source length increases. The heat transfer rate behaves nonlinearly with inclination of the cavity.

Natural Convection From a Horizontal Tube Heat Exchanger Immersed in a Tilted Enclosure

Solar Energy ◽  
2002 ◽  
Author(s):  
Wei Liu ◽  
Jane H. Davidson ◽  
F. A. Kulacki ◽  
Susan C. Mantell
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Horizontal Tube ◽  
Heating System ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Tube Heat Exchanger ◽  
Flux Boundary Conditions ◽  
Solar Water Heating System

Heat transfer rates of a single horizontal tube immersed in a water-filled enclosure tilted at 30 degrees are measured. The results serve as a baseline case for a solar water heating system with a heat exchanger immersed in an integral collector storage. Experiments are conducted for isothermal and stratified enclosures with both adiabatic and uniform heat flux boundary conditions. Natural convection flow in the enclosure is interpreted from measured water temperature distributions. Formation of an appropriate temperature difference that drives natural convection is determined. Correlations for the overall heat transfer coefficient in terms of the Nusselt and Rayleigh numbers are reduced to the form NuD = 0.675RaD0.25 for 106 ≤ RaD ≤ 108.

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