Browsing by Author "Arunachala, U.C."

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Efficient design of an artificially roughened solar air heater with semi-cylindrical side walls: CFD and exergy analysis
(Elsevier Ltd, 2020) Nidhul, K.; Yadav, A.; Anish, S.; Arunachala, U.C.
Solar air heater (SAH) with semi-cylindrical sidewalls and W-baffles is analyzed for energy and exergy efficiency in the turbulent flow regime. Computational fluid dynamics (CFD) analysis is carried out for a fixed baffle inclination (?) and varying the relative baffle height (Rh = e/D) and relative baffle pitch (Rp = P/D) in the range 0.046–0.115 and 0.46–1.15, respectively. For Reynolds number (5000 < Re < 17,500), the numerical methodology is substantiated using experimental and theoretical correlations obtained from the literature. Smaller vortices near the sharp corners are removed by rounding the sharp edges, allowing the flow of fluid from inside and horizontal walls of the duct towards the semi-cylindrical sidewalls. This increases the overall turbulent kinetic energy. A peak augmentation of 3.24 and 4.03 times is obtained for Nusselt number (Nu) and friction factor (f), respectively, in contrast to conventional SAH. With a maximum enhancement of 127% in the effectiveness parameter relative to smooth SAH, this novel SAH design is evidently energy efficient. Based on CFD results, new correlations are developed in terms of Rh and Rp, which predicts the values with an absolute deviation of 4% and 7.4%, respectively. With lower exergy destruction, maximum enhancement in thermal and exergetic efficiency is obtained as 40.7% and 95.4%, respectively, for the proposed SAH relative to conventional SAH. Upon comparison with ribbed rectangular duct SAH configurations, the present design with semi-cylindrical side walls outperforms at all flow Re. © 2020 International Solar Energy Society
Stability improvement in natural circulation loop using tesla valve an experimental investigation
(2019) Arunachala, U.C.; Rajat, A.C.; Shah, D.; Sureka, U.
Natural circulation loop works on the basic principle of thermosiphon effect, which doesn t require any external force to drive the fluid in a loop. Hence they are highly applicable in power industries where there are a source and a sink. However, the flow pattern in a single-phase natural circulation loop is quite unstable especially the horizontal heater horizontal cooler configuration which results in lower loop effectiveness. A lot of research has been carried out to study these instabilities and find a way to curb them. Techniques such as tilting of loop, use of nanofluids, adding flow resistances etc. have shown promising results. But they have their own practical constraints. Hence in the present experimental study, a Tesla-type passive valve is incorporated in natural circulation loop. Due to its presence, not only stability period is reduced (at least 90 s compared to non-Tesla loop) but also unidirectional flow is achieved. The Tesla valve performed better for a broad range of heater power (90-170W) and was also able to provide noticeable resistance to the flow when the loop was inclined by 2.5 in the opposite direction. TJPRC Pvt. Ltd.
Stability improvement in natural circulation loop using tesla valve – an experimental investigation
(Transstellar Journal Publications and Research Consultancy Private Limited (TJPRC) editor@tjprc.org, 2019) Arunachala, U.C.; Rajat, A.C.; Shah, D.; Sureka, U.
Natural circulation loop works on the basic principle of thermosiphon effect, which doesn’t require any external force to drive the fluid in a loop. Hence they are highly applicable in power industries where there are a source and a sink. However, the flow pattern in a single-phase natural circulation loop is quite unstable especially the horizontal heater horizontal cooler configuration which results in lower loop effectiveness. A lot of research has been carried out to study these instabilities and find a way to curb them. Techniques such as tilting of loop, use of nanofluids, adding flow resistances etc. have shown promising results. But they have their own practical constraints. Hence in the present experimental study, a Tesla-type passive valve is incorporated in natural circulation loop. Due to its presence, not only stability period is reduced (at least 90 s compared to non-Tesla loop) but also unidirectional flow is achieved. The Tesla valve performed better for a broad range of heater power (90-170W) and was also able to provide noticeable resistance to the flow when the loop was inclined by 2.5° in the opposite direction. © TJPRC Pvt. Ltd.
Thermo-hydraulic and exergetic performance of a cost-effective solar air heater: CFD and experimental study
(Elsevier Ltd, 2022) Nidhul, K.; Yadav, A.K.; Anish, S.; Arunachala, U.C.
An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of secondary flow strengthening the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6–1 to obtain the optimum baffle pitch for 6000 p. A maximum thermo-hydraulic performance of 2.69 is obtained for the gap at the trailing apex. The proposed design has a higher collector efficiency, 55–70%, compared to the ribbed rectangular SAH design exhibiting 30–55%. With lower exergy losses, the present SAH design has higher exergetic efficiency (1.5%–2.2%)than ribbed rectangular SAH (0.9%–1.7%) for the range of Re studied. Further, at low Re, the present SAH design has a higher coefficient of performance, indicating that it is cost-effective than ribbed rectangular SAH designs. © 2021 Elsevier Ltd