Research Papers

Experimental Investigation of Heat Transfer and Friction Characteristics of Arc-Shaped Roughness Elements Having Central Gaps on the Absorber Plate of Solar Air Heater

[+] Author and Article Information
Navneet Kumar Pandey

Department of Mechanical Engineering,
JSS Academy of Technical Education,
Noida, Uttar Pradesh 201301, India

Vijay Kumar Bajpai

Department of Mechanical Engineering,
National Institute of Technology, Kurukshetra,
Kurukshetra, Haryana 136119, India

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received July 26, 2014; final manuscript received April 5, 2016; published online May 5, 2016. Assoc. Editor: Werner Platzer.

J. Sol. Energy Eng 138(4), 041005 (May 05, 2016) (8 pages) Paper No: SOL-14-1215; doi: 10.1115/1.4033402 History: Received July 26, 2014; Revised April 05, 2016

Thermal performance of solar air heater does not take into account the energy loss due to friction for propelling air through the duct. In this work, an experimental investigation has been carried out to study the effect of heat transfer and friction characteristics of turbulent flow of air passing through rectangular duct which is roughened by circular arcs having gaps of 2 mm in between arranged in angular fashion, and the roughened wall is uniformly heated. The thermal and friction characteristics are governed by duct aspect ratio (W/H), hydraulic diameter (D), and relative roughness pitch (P/e), angle of attack of angular arc (α), and Reynolds number (Re). Experiments encompassed the Reynolds number ranges from 3600 to 15,100, P/e ranges from 6 to 20, and angle of attack of angular arc of flow over the protrusions ranges from 15 deg to 75 deg. The results have also been compared to W-shaped roughness inclined at 45 deg. The maximum enhancement in heat transfer and friction factor is 3.15 and 3.93 times as compared with smooth duct. Arc with gaps have also been observed to be better than their W-shaped counterparts. These experimental results have been used to study their influence on Nusselt number and friction factor, and empirical relations have been derived using regression analysis.

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Fig. 5

Variation of Nusselt number with Reynolds number

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Fig. 4

Variation of friction factor versus Reynolds number factor for smooth duct

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Fig. 2

Schematic diagram of experimental setup

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Fig. 1

Sectional view of the duct used in experimental setup

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Fig. 6

Variation of Nusselt number with Reynolds number for smooth and rough geometries (arc-shaped)

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Fig. 7

Variation of friction factor for smooth and rough shaped geometries

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Fig. 8

Variation of Nusselt number with Reynolds number for different geometries

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Fig. 9

Variation of friction factor with Reynolds number for different geometries




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