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Effect of roughness width ratio in discrete Multi v-shaped rib roughness on thermo-hydraulic performance of solar air heater

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Abstract

The artificial roughness on underside of heated surface has been found to be effective technique to improve thermo hydraulic performance of solar air heater duct. In progression to the previous researches, the present study discloses the effect of discrete Multi v-rib on heat transfer and friction in a flow through artificially roughened solar air heater duct. The experimentations were performed to collect the data on heat transfer and friction by varying the Reynolds number (Re) between 2,000 and 20,000, relative width ratio (W/w) from 1 to 10, for the fixed values of relative gap distance Gd/Lv = 0.69, relative gap width g/e = 1.0, relative roughness pitch P/e = 8, relative roughness height e/D = 0.043 and angle of attack α = 60°. The present roughness geometry with relative width ratio (W/w) of 6.0 corresponding to flow Re of 20,000 yields the best thermo hydraulic performance.

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Abbreviations

A p :

Area of absorber plate (m2)

A o :

Cross section area of orifice (m2)

C d :

Coefficient of discharge of orifice

C p :

Specific heat of air at constant pressure (J/kg K)

D :

Hydraulic diameter of duct (m)

e :

Rib height (m)

e/D :

Relative roughness height

f s :

Friction factor of smooth duct

f :

Friction factor of roughened duct

G d :

Gap distance (m)

G d /L v :

Relative gap distance

g :

Gap width (m)

g/e :

Relative gap width

H :

Depth of duct (m)

h :

Convective heat transfer coefficient (W/m2 K)

k :

Thermal conductivity of air (W/m K)

L v :

Length of single v shaped rib (m)

L :

Test section length for pressure drop measurement (m)

m :

Mass flow rate (kg/s)

Nu :

Nusselt number of roughened duct

Nu s :

Nusselt number of smooth duct

(ΔP) o :

Difference of manometric fluid level in U-tube manometer (m)

(ΔP) d :

Difference of water column level in micro-manometer (m)

P :

Pitch of the rib (m)

P/e :

Relative roughness pitch

Q u :

Useful heat gain rate (W)

T f :

Mean temperature of air (K)

T i :

Inlet temperature of air (K)

T o :

Outlet temperature of air (K)

Tam :

Bulk means temperature (K)

Tpm :

Mean plate temperature (K)

u :

Velocity of air (m/s)

W :

Width of duct (m)

w :

Width of single v-shaped rib (m)

W/w :

Relative roughness width ratio

α :

Rib angle of attack (°)

β :

Ratio of orifice diameter to pipe diameter

η :

Thermo-hydraulic performance parameter

ρ :

Density of air (kg/m3)

ρ m :

Density of manometric fluid (kg/m3)

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Authors and Affiliations

  1. Mechanical Engineering Department, Shoolini University, Solan, 174212, Himachal Pradesh, India

    Anil Kumar

  2. Alternate Hydro Energy Centre, Indian Institute of Technology Roorkee, Roorkee, 247667, Uttarakhand, India

    R. P. Saini

  3. Mechanical and Industrial Engineering Department, Indian Institute of Technology Roorkee, Roorkee, 247667, Uttarakhand, India

    J. S. Saini

Authors
  1. Anil Kumar
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  2. R. P. Saini
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  3. J. S. Saini
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Correspondence to Anil Kumar.

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Kumar, A., Saini, R.P. & Saini, J.S. Effect of roughness width ratio in discrete Multi v-shaped rib roughness on thermo-hydraulic performance of solar air heater. Heat Mass Transfer 51, 209–220 (2015). https://doi.org/10.1007/s00231-014-1407-0

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