Hydrothermal performance and entropy production rate of rGO-CO3O4/H2O hybrid nanofluid in corrugated-converging pipes

Abstract

The ever-growing interest in developing more effective and compact heat exchangers necessitates the investigation of combined passive solutions. Despite the diverse related literature, there are no studies on corrugated-converging pipes. This work examines the effect of Reynold's number (5.0×103≤Re≤5.0×104), diameter ratio (1≤DR≤2), and concentration of nanoparticle (0≤VR≤0.2%), on the Poiseuille number (fRe), average Nusselt number (Nu), performance evaluation criterion (PEC), and EPR of rGO−CO3O4/ H2O hybrid nanofluid (NF) flowing in corrugated-converging pipes of different orientations (inwardly and outwardly) and smooth converging pipes in turbulent flow regime. The k−ω and discrete phase models were used to simulate the turbulent hybrid NF flow by Ansys Fluent. The results revealed that the Nu in the corrugated converging pipe is higher than that of a smooth pipe, but this is accompanied by a higher pressure drop (dP). The argumentation of Nu is attributed to flow acceleration, thinning of the thermal boundary layer (TBL), and an increase in the rate of mixing as a result of the relative increase in turbulence introduced by the presence of corrugation. In addition, it was noted that the modified pipes have lower EPR due to temperature gradient (TEPR) compared with straight pipe. However, the opposite is the case for EPR due to fluid flow (VEPR). The lower TEPR and higher VEPR are attributed to a relative increase in flow turbulence. Quantitatively, the normalized values (referencing smooth pipe) of Nu, (fRe), TEPR, and VEPR at Re=5×103 in inwardly and outwardly corrugated converging pipes and smooth converging pipes of DR = 2 are {2.24, 8.15×101, 4.13×10−1, and 8.62×101}, {1.94, 4.45×101, 4.78×10−1, and 4.15×101} and {1.03, 3.1×101,9.20×10−1, and 3.17×101}, respectively. PEC increases with increasing VR. For instance, across the range of VR considered (0 % ≤ VR ≤ 0.2 %), the values of PEC increase by 20.69 %. Consequently, it can be presented as a promising heat transfer enhancement technique in terms of energy saving. Consequently, corrugated-converging pipes can be presented as a promising heat transfer enhancement technique in terms of energy saving.