CFD simulation of irreversibilities for laminar flow of a power-law nanofluid within a minichannel with chaotic perturbations: An innovative energy-efficient approach

• Published in: Energy conversion and management 2017-07, Vol.144, p.374-387
• Main Authors: Bahiraei, Mehdi, Gharagozloo, Khashayar, Alighardashi, Masoud, Mazaheri, Nima
• Format: Article
• Language: English
• Subjects: Chaotic geometry; Energy efficiency; Entropy; Entropy generation; Fluid dynamics; Fluid flow; Heat transfer; High Reynolds number; Laminar flow; Laminar mixing; Minichannel; Nanofluids; Non-Newtonian nanofluid; Reynolds number; Second law of thermodynamics; Simulation; Thermal boundary layer; Thermodynamics; TiO2 nanoparticles
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2017.04.068

•Irreversibilities for a power-law nanofluid in a chaotic minichannel are examined.•Increasing either concentration or Re number rises frictional entropy generation.•Increasing either concentration or Re number reduces thermal entropy generation.•An optimal point by concentration rise is found for entropy generation at high Re.•Total entropy generation in chaotic channel is lower than that in straight channel. The irreversibilities caused by heat transfer and friction for a power-law nanofluid in a minichannel having chaotic perturbations are examined through calculation of entropy generation rates. Chaotic advection, or Lagrangian chaos, is a flow regime in which chaos is developed in the physical domain. It can intensify mixing in laminar flows and therefore, increase heat transfer. The simulations are also carried out in a straight channel. An increase in either concentration or Reynolds number augments frictional entropy generation while decreasing thermal entropy generation. By increasing concentration in the chaotic channel, total entropy generation (i.e., frictional plus thermal) decreases at low Reynolds numbers, however, a minimum (optimal) point occurs at a high Reynolds number, which is very important based on the second law of thermodynamics. Due to intense mixing in the chaotic channel, thermal boundary layer cannot grow and consequently, thermal entropy generation in this channel is much less than that in the straight channel. Therefore, although frictional entropy generation in the chaotic channel is greater than that in the straight channel, total entropy generation in the chaotic channel is smaller, which shows a lower level of irreversibility. Moreover, compared to the straight channel, the chaotic channel is of a lower Bejan number.