مهدی بحیرائی

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.