ABSTRACT The present study is carried out to determine the effect of symmetric arc roughness with staggered elements used in solar air heater ducts. The study of arc roughness with staggered elements available in the literature lacks the study of a number of gaps, gap width, staggered pitch, and staggered length in Nusselt number and friction factor evaluation. The studied parameters are number of gaps (Ng ) as 2–5, relative gap width (g/e) as 0.5–2.0, relative staggered pitch (p’/p) as 0.2–0.8, relative staggered length (r/e) as 1.5–4.5, relative roughness height (e/Dh ) as 0.045, arc angle (α) as 30° and relative roughness pitch (p/e) as 10 for Reynolds number (Re) range 3000–14000. Thirteen roughened plates have been evaluated. The highest enhancement in Nusselt number and friction factor recorded is 3.23 and 4.01 times smooth duct, and highest thermohydraulic performance (THP) reported is 2.34. The performance of investigated roughness is compared with the existing best arc roughness geometry.
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