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Experimental and CFD-based thermal performance prediction of solar air heater provided with chamfered square rib as artificial roughness

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Abstract

An experimental and two-dimensional computational fluid dynamics (CFD) analysis of a solar air heater has been carried out using chamfered square rib as artificial roughness on the absorber plate. The relative roughness pitch (P/e = 7.14–17.86), chamfer angle (α = 0°–40°), Reynolds number (Re = 3800–18,000) and relative roughness height (e/D = 0.042) are chosen as design variables for analysis. A uniform heat flux of 1000 W/m2 is maintained on the surface of absorber plate. CFD code, ANSYS FLUENT 14.5 with renormalization group k-ε model was chosen. An enhancement in Nusselt number and friction factor with decrease in relative roughness pitch (P/e) is presented and discussed with reference to experimental and CFD analysis. The effect of chamfer angle and Reynolds number on enhancement of Nusselt number and friction factor is also presented. Optimum configuration of roughness element for artificially roughened solar air heater has been determined in terms of thermo-hydraulic performance parameter. The chamfer angle of 20° on square rib and relative roughness pitch of 7.14 provide best thermo-hydraulic performance of 2.047 considering the maximum heat transfer and minimum pressure drop.

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Abbreviations

D :

Equivalent or hydraulic diameter of duct (mm)

e :

Rib height (mm)

w :

Rib width (mm)

h :

Heat transfer coefficient (W/m2 K)

H :

Depth of the duct (mm)

k :

Thermal conductivity of air (W/mK)

u :

Air flow velocity in x-direction (m/s)

v :

Air flow velocity in y-direction (m/s)

W :

Width of the duct (mm)

l :

Length of test section (m)

ΔP o :

Pressure drop across the orifice meter (Pa)

ΔP :

Pressure drop across test length (Pa)

c p :

Specific heat of air (J/kg K)

L 1 :

Inlet length of duct (mm)

L 2 :

Test length of the duct (mm)

L 3 :

Outlet length of duct (mm)

P :

Pitch (mm)

U :

Mean airflow velocity in the duct (m/s)

Q u :

Rate of heat flow gained by air (W)

e/D :

Relative roughness height

f :

Friction factor

l/s :

Relative length of grit

Pr :

Prandtl number

P/e :

Relative roughness pitch

Re :

Reynolds number

W/H:

Duct aspect ratio

Nu:

Nusselt number

μ :

Dynamic viscosity (Ns/m2)

μ t :

Turbulent viscosity (Ns/m2)

ρ :

Density of air (Kg/ m3)

K :

Turbulent kinetic energy (m2/s2)

β :

Thermal diffusivity

υ :

Kinematic viscosity (m2/s)

Γ :

Molecular thermal diffusivity

Γ t :

Turbulent thermal diffusivity

ε:

Dissipation rate

α :

Chamfer angle

S:

Smooth

R:

Roughened

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Authors and Affiliations

  1. Department of Mechanical Engineering, Visvesvaraya National Institute of Technology, Nagpur, India

    Vipin B. Gawande, A. S. Dhoble & D. B. Zodpe

  2. Department of Mechanical Engineering, D.I.T University, Dehradun, India

    Sunil Chamoli

Authors
  1. Vipin B. Gawande
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  2. A. S. Dhoble
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  3. D. B. Zodpe
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  4. Sunil Chamoli
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Corresponding author

Correspondence to Vipin B. Gawande.

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Technical Editor: Francis HR Franca.

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Gawande, V.B., Dhoble, A.S., Zodpe, D.B. et al. Experimental and CFD-based thermal performance prediction of solar air heater provided with chamfered square rib as artificial roughness. J Braz. Soc. Mech. Sci. Eng. 38, 643–663 (2016). https://doi.org/10.1007/s40430-015-0402-9

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  • DOI: https://doi.org/10.1007/s40430-015-0402-9

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