Flow Visualization of the Three-dimensional Mixed Convection in a Horizontal Square Channel with Heated and Cooled Side Walls

In this work mixed convection in a horizontal channel with the lower wall heated at uniform heat flux is studied numerically. A three dimensional problem is modeled and solved by means of the FLUENT code. The domain is made of a principal channel and two channels with adiabatic walls, one upstream the principal channel and the other downstream. The principal channel is formed by a uniformly heated horizontal wall, a parallel wall located above and two adiabatic vertical side walls. The aim of this paper is to investigate the effect of Reynolds and Rayleigh numbers on thermal and fluid dynamic behavior in mixed convection in a horizontal channel heated from below. The analysis is carried out in transient regime in order to evaluate the thermal and fluid dynamic parameters as functions of the time. The Reynolds and Rayleigh numbers investigated are between 5 and 500 and 1.37×106 and 2.75×106 respectively. The corresponding Richardson number, Ri = Gr/Re2, holds values in the range 7.76 – 1.55 × 105. Wall temperature distributions and profiles along longitudinal and transversal coordinates are reported for different time values. Air velocity and temperature in the principal channel are presented along the longitudinal and transversal sections for some time values.

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Numerical Simulation of Laminar Flow and Heat Transfer Over a Blunt Flat Plate in Square Channel

Journal of Heat Transfer ◽

10.1115/1.1420715 ◽

2001 ◽

Vol 124 (1) ◽

pp. 8-16 ◽

Cited By ~ 13

Author(s):

Hideki Yanaoka ◽

Hiroyuki Yoshikawa ◽

Terukazu Ota

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Flat Plate ◽

Stokes Equations ◽

Three Dimensional ◽

Flow Region ◽

Recirculation Region ◽

Square Channel ◽

Flow And Heat Transfer ◽

Side Walls

Three-dimensional simulations of laminar separated and reattached flow and heat transfer over a blunt flat plate in a square channel are presented. Numerical calculations of Navier-Stokes equations and energy equation are carried out using the finite difference method. Results of three-dimensional calculation are compared with two-dimensional ones and effects of the side walls are described. It is clarified from the present results that the reattachment length increases with an increase of Reynolds number and the flow in the recirculation region becomes three-dimensional. The reattachment line is curved by the side wall effects. Two-dimensionality of the flow is reduced as Reynolds number increases. The horseshoe-vortex formed near the side walls has great effects upon the heat transfer in the redeveloping flow region. The separated shear layer around the center of plate becomes unstable with a further increase of Reynolds number and the vortices are periodically shed from the reattachment flow region. Such vortices exhibit a hairpin-like structure and greatly influence the heat transfer.

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Effects of Gaps Between Side-Walls and60∘Ribs on the Heat Transfer and Rib Induced Secondary Flow Inside a Stationary and Rotating Cooling Channel

International Journal of Rotating Machinery ◽

10.1155/s1023621x01000379 ◽

2001 ◽

Vol 7 (6) ◽

pp. 425-433

Author(s):

Robert Kiml ◽

Sadanari Mochizuki ◽

Akira Murata

Keyword(s):

Heat Transfer ◽

Flow Visualization ◽

Secondary Flow ◽

Three Dimensional ◽

Local Heat Transfer ◽

Local Heat ◽

Cooling Channel ◽

Three Dimensional Flow ◽

Side Walls ◽

Visualization Experiments

The present study investigates the effects of gaps between the side-walls and60∘ribs on the local heat transfer distribution between two consecutive ribs. The heat transfer and flow visualization experiments were carried out inside a straight rib-roughened duct with the ribs mounted on two opposite side walls with and without the gaps. The results showed that the existence of the gaps appreciably enhances the Nu in the area between two consecutive ribs. It is caused by (1) the introduction of the fresh air through the gaps into this region, and (2) the improvement of the three-dimensional flow structure in the area between the two ribs.

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Influence of the Gap Size Between Side Walls and Ribs on the Heat Transfer in a Stationary and Rotating Straight Rib-roughened Duct

International Journal of Rotating Machinery ◽

10.1155/s1023621x00000245 ◽

2000 ◽

Vol 6 (4) ◽

pp. 253-263 ◽

Cited By ~ 1

Author(s):

R. Kiml ◽

S. Mochizuki ◽

A. Murata

Keyword(s):

Heat Transfer ◽

Flow Visualization ◽

Flow Direction ◽

Three Dimensional ◽

Side Wall ◽

Local Heat Transfer ◽

Local Heat ◽

Wall Region ◽

Side Walls ◽

Cooling Passage

The objective of this study is to investigate a heat transfer phenomenon in a straight ribroughened duct which represents a cooling passage of a modern gas turbine blade. Experiments were performed for ribs mounted perpendicularly to the main flow direction on two opposite sides of the duct for the following cases: (1) with no gaps, (2) with gaps=0.33hand (3) with gaps=1hbetween the side walls and ribs (wherehis the rib height). The heat transfer results revealed significant differences among these three cases, showing that the existence of gaps increases the heat transfer. Particularly, the local heat transfer on the wall between the consecutive ribs is higher in the near-side wall region than in the central region. To shed some light on this phenomenon, flow visualization was conducted using the particle tracer method. The flow visualization results revealed the effect of gaps on the three-dimensional flow structure between the ribs. It was concluded that this structure caused the heat transfer enhancement in the near-side wall region.

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