The effect of nanoparticle shape on alumina/EG-water (50:50) nanofluids flow within a solar collector: Entropy and exergy investigation

In this paper, the entropy generation (EGen) and exergy of a solar collector (SC) with alumina/ethylene glycol-water (50:50) nanofluid (NFs) flow are calculated. The tubes and the absorber plate of the collector are made of copper and steel, and the results of both materials are compared. Tubes with hexagonal cross section are considered. Nanoparticles (NPs) with four different shapes of platelet, brick, blade, and cylinder are considered, and their effect is evaluated. Volume fraction (ϕ) changes in the range of 0–4%, and mass flow rate varies from 0.25 to 1 kg/s. These parameters as well as the material of collector tubes and the shape of NPs are the variables of this study and their effect on fluid frictional entropy generation (Sg,ff), thermal entropy generation (Sg,th), total entropy generation (Sg,tot), exergy output (Exout), and exergy loss (Exloss) is examined. Proposed relationships and an in-house code in MATLAB software are used for analysis. The results demonstrated that the use of copper tube leads to smaller amounts of Sg,ff, and Sg,tot than steel tube. Besides, the Exout for cooper tubes is higher than that for steel ones. An increment in the flow rate enhances Sg,tot. Increasing the fluid mass flow rate from 0.25 to 1 kg/s increases the values of Sg,tot 7.9 and 8.4 times for the steel and copper collectors, respectively. The addition of NPs reduces Sg,th but enhances Sg,ff at high values of ϕ. The addition of 4% of all shapes NPs intensifies the magnitudes of Exout and Exloss.