Investigation of the effect of dimensional and non-dimensional parameters on the performance of pitch-varied staggered arranged dimple solar air heaters

In this study, the efficacy of a single pass, single glazed, five different types of absorber plate incorporated solar air heater (SAH) was experimentally examined in outdoor test conditions on alternative days. The experiment was carried out for flat plate solar air heater (FPSAH) and staggered arranged dimple imprinted absorber plate solar air heater (SDPSAH) maintained at four different pitch ratios (P_t/P_l: 1.0, 1.11, 1.25, and 1.67) by varying the air mass flow rate (m_a) from 0.01-0.05 kg/s (corresponding Re range: 1971.66–10466.45). The results show that the performance of both FPSAH and SDPSAH improves when the m_a increases. For the tested range of m_a, SDPSAH outperforms FPSAH regardless of pitch ratio. SDPSAH, with a pitch ratio of 1.25, on the other hand, has a greater air temperature difference, efficiencies, heat removal factor, collector efficiencies, and averaged Nusselt number (Nu_avg) while having a lower global heat loss coefficient and top loss. The Nu_avg of SDPSAH at a pitch ratio of 1.25 is 1.01–1.17, 1.16–1.24, 1.26–1.57, and 1.44–1.88 times higher than SDPSAH at pitch ratios 1.0, 1.11, 1.67, and FPSAH, respectively. The higher averaged friction factor (f_avg) of 0.0443 is attained for SDPSAH at a pitch ratio of 1.25 due to the presence of the largest number of dimples. The η_th and η_d of SDPSAH at a pitch ratio of 1.25 are 34.5 and 35.5 % higher than those of FPSAH. The global heat loss coefficient of SDPSAH at pitch ratios 1.11, 1.0, and 1.67 is 1.05–1.84, 1.09–2.15, and 1.11–2.92 times higher, respectively, than that of SDPSAH at a pitch ratio of 1.25.