Flow and heat/mass transfer in a wavy duct with various corrugation angles in two dimensional flow regimes
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Abstract
In this study, two dimensional heat/mass transfer characteristics and flow features were investigated in a rectangular wavy duct with various corrugation angles. The test duct had a width of 7.3 mm and a large aspect ratio of 7.3 to simulate two dimensional characteristics. The corrugation angles used were 100°, 115°, 130°, and 145°. Numerical analysis using the commercial code FLUENT, was used to analyze the flow features. In addition, the oil-lamp black method was used for flow visualization. Local heat/mass transfer coefficients on the corrugated walls were measured using a naphthalene sublimation technique. The Reynolds number, based on the duct hydraulic diameter, was varied from 700 to 5,000. The experimental results and numerical analysis showed interesting and detailed features in the wavy duct. Main flow impinged on upstream of a pressure wall, and the flow greatly enhanced heat/mass transfer. On a suction wall, however, flow separation and reattachment dominantly affected the heat/mass transfer characteristics on the wall. As the corrugation angle decreased (it means the duct has more sharp turn), the region of flow stagnation at the front part of the pressure wall became wider. Also, the position of flow reattachment on the suction wall moved upstream as the corrugation angle decreased. A high heat transfer rate appeared at the front part of the pressure wall due to main-flow impingement, and at the front part of the suction wall due to flow reattachment. The high heat/mass transfer region by the main-flow impingement and the circulation flow induced at a valley between the pressure and suction walls changed with the corrugation angle and the Reynolds number. As the corrugation angle decreased, the flow in the wavy duct changed to transition to turbulent flow earlier.
Keywords
Reynolds Number Sherwood Number Pressure Wall Stagnation Flow Longitudinal VortexList of symbols
- AR
aspect ratio (W/H)
- Cp
pressure coefficient in Eq. 5
- Dh
hydraulic diameter
- Dnaph
naphthalene vapor diffusivity in air
- dy
naphthalene sublimation depth
- f
friction factor in Eq. 6
- H
duct height
- hm
local mass transfer coefficient in Eq. 1
- L
duct length
- \( \dot m \)
mass flux
- Ps
static pressure on the wall
- Patm
atmospheric pressure
- P.F.
performance factor in Eq. 7
- \( Re_{{D_{h} }} \)
Reynolds number based on hydraulic diameter
- Sh
Sherwood number in Eq. 2
- \( \overline {{\text{Sh}}} _{{{\text{span}}}} \)
spanwise-averaged Sherwood number in Eq. 3
- \( \overline{\overline {{\text{Sh}}}} \)
overall averaged Sherwood number in Eq. 4
- dt
time interval during experiment
- U0
average duct inlet velocity
- W
duct width
- x
- streamwise coordinate (Fig. 1)Fig. 1
Details of test wavy duct
- y
vertical distance from the center (Fig. 1)
- z
spanwise coordinate (Fig. 1)
Greek symbols
- α
corrugation angle
- ρ
density of air
- ρs
density of solid naphthalene
- ρv,w
naphthalene vapor density on the surface
- ρv,∞
naphthalene vapor density in bulk air
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