*5.6. Effect of Hot Fluid Mass Flow Rate on First and Second Law Characteristics*

*5.6. Effect of Hot Fluid Mass Flow Rate on First and Second Law Characteristics*  The effect of the hot fluid mass flow rate and volume fraction on first and second law characteristics of hybrid nanofluids with OS-shaped nanoparticles is presented in Figure 14. The hot fluid mass flow rate varies at 10 kg/h, 20 kg/h and 30 kg/h. The performance index increases with the volume fraction for the same hot fluid mass flow rate because of higher dominance of the heat transfer increase compared to the pumping power increase as the volume fraction increases. Moreover, the steepness of the increasing trend of the performance index with the volume fraction becomes sharp at the higher hot fluid mass flow rate. For the same volume fraction, the performance index decreases with an increase in the hot fluid mass flow rate because the dominance of the increase in the pumping The effect of the hot fluid mass flow rate and volume fraction on first and second law characteristics of hybrid nanofluids with OS-shaped nanoparticles is presented in Figure 14. The hot fluid mass flow rate varies at 10 kg/h, 20 kg/h and 30 kg/h. The performance index increases with the volume fraction for the same hot fluid mass flow rate because of higher dominance of the heat transfer increase compared to the pumping power increase as the volume fraction increases. Moreover, the steepness of the increasing trend of the performance index with the volume fraction becomes sharp at the higher hot fluid mass flow rate. For the same volume fraction, the performance index decreases with an increase in the hot fluid mass flow rate because the dominance of the increase in the pumping power is superior compared to the increase in heat transfer with an increase in the hot

increases by 3.99%, 9.43% and 12.27% for hot fluid mass flow rates of 10 kg/h, 20 kg/h and 30 kg/h, respectively, as the volume fraction increases from 0.5% to 2.0%. The performance index of Al2O3/Cu with OS-shaped nanoparticles decreases by 39.37%, 38.29% and 36.20% as the hot fluid mass flow rate increases from 10 kg/h to 20 kg/h, and that decreases by 70.31%, 69.51% and 67.94% as the hot fluid mass flow rate increases from 10 kg/h to 30 kg/h for volume fractions of 0.5%, 1.0% and 2.0%, respectively. The thermal entropy generation rate increases with an increase in the hot fluid mass flow rate for all volume fractions, due to increase in the temperature gradient and heat transfer. Similarly, the heat transfer enhances with the volume fraction, which results in an increase in the thermal entropy generation rate with an increase in the volume fraction for all hot fluid mass flow rates. However, the increasing trends of thermal entropy generation rates with volume fractions are not steep for higher hot fluid mass flow rates. The pressure drop and average temperature have both increased with an increase in volume fraction and hot fluid mass flow rate. With an increase in volume fraction, the increase in average temperature is more

fluid mass flow rate. The performance index of Al2O3/Cu with OS-shaped nanoparticles increases by 3.99%, 9.43% and 12.27% for hot fluid mass flow rates of 10 kg/h, 20 kg/h and 30 kg/h, respectively, as the volume fraction increases from 0.5% to 2.0%. The performance index of Al2O3/Cu with OS-shaped nanoparticles decreases by 39.37%, 38.29% and 36.20% as the hot fluid mass flow rate increases from 10 kg/h to 20 kg/h, and that decreases by 70.31%, 69.51% and 67.94% as the hot fluid mass flow rate increases from 10 kg/h to 30 kg/h for volume fractions of 0.5%, 1.0% and 2.0%, respectively. The thermal entropy generation rate increases with an increase in the hot fluid mass flow rate for all volume fractions, due to increase in the temperature gradient and heat transfer. Similarly, the heat transfer enhances with the volume fraction, which results in an increase in the thermal entropy generation rate with an increase in the volume fraction for all hot fluid mass flow rates. However, the increasing trends of thermal entropy generation rates with volume fractions are not steep for higher hot fluid mass flow rates. The pressure drop and average temperature have both increased with an increase in volume fraction and hot fluid mass flow rate. With an increase in volume fraction, the increase in average temperature is more dominant than the increase in pressure drop, hence the friction entropy generation rate decreases as the volume fraction increases for all hot fluid mass flow rates. This decreasing trend becomes steeper with the volume fraction at the higher mass flow rates. On the other side, with the increase in the hot fluid mass flow rate, the increase in the pressure drop is dominating compared to the increase in average temperature; therefore, the friction entropy generation rate is high at a higher mass flow rate and vice versa for all volume fractions. Based on the trends for the thermal and friction entropy generation rates with volume fractions and hot fluid mass flow rate, the Bejan number is evaluated. The Bejan number increases with the increase in volume fraction and decrease in the hot fluid mass flow rate. The thermal entropy generation increases, and the friction entropy generation decreases with the increase in volume fraction, which results in an increase in the Bejan number with an increase in the volume fraction. The thermal and friction entropy generation rates have both increased with the increase in the hot fluid mass flow rate but the increasing rate of the friction entropy generation rate is significantly higher than the thermal entropy generation rate. Therefore, the Bejan number decreases with the increase in the hot fluid mass flow rate for each volume fraction. The Bejan number of the Al2O3/Cu nanofluid with OS-shaped nanoparticles increases by 0.21%, 0.73% and 1.74% for hot fluid mass flow rates of 10 kg/h, 20 kg/h and 30 kg/h, respectively, as the volume fraction increases from 0.5% to 2.0%. The Bejan number of Al2O3/Cu with OS-shaped nanoparticles decreases by 3.06%, 2.89% and 2.57% as the hot fluid mass flow rate increases from 10 kg/h to 20 kg/h, and that decreases by 10.72%, 10.24% and 9.37% as the hot fluid mass flow rate increases from 10 kg/h to 30 kg/h for volume fractions of 0.5%, 1.0% and 2.0%, respectively. Soroush and Chamkha have also shown that the first and second law characteristics of single-particle nanofluids enhances as the volume fraction increases for all nanoparticle shapes [30]. The contributions of thermal and friction entropy generation rates for Al2O3/Cu with OS-shaped nanoparticles at various hot fluid mass flow rates are depicted in Figure 15.
