*5.5. Effect of Hot Fluid Temperature on First and Second Law Characteristics*

The behavior of first and second law characteristics of the Al2O3/Cu nanofluid with OS-shaped nanoparticles for various volume fractions and hot fluid temperatures is presented in Figure 12. The hot fluid temperature varies at 90 ◦C, 80 ◦C, and 70 ◦C and the volume fraction varies at 0.5%, 1.0% and 2.0%. The performance index increases with an increase in the volume fraction as well as hot fluid temperature. The heat transfer and pressure drop both increase with an increase in volume fraction, but the increase in the heat transfer dominates compared to the increase in the pressure drop, hence, as a result, the performance index increases as the volume fraction increases for all hot fluid temperatures. The hot fluid at the higher temperature could transfer more heat compared to hot fluid at a lower temperature. The pressure drop remains almost the same for various hot fluid temperatures, whereas the heat transfer increases with a rise in the temperature, which shows an enhancement in the performance index with an increase in the hot fluid temperature for all volume fractions. The performance index of Al2O3/Cu with OS-shaped nanoparticles increases by 20% and 40% as the hot fluid temperature increases from 70 ◦C to 80 ◦C and 70 ◦C to 90 ◦C, respectively, for each volume fraction. With the increase in volume fraction from 0.5% to 2.0%, the performance index of Al2O3/Cu with OS-shaped nanoparticles enhances by 9.42% for each hot fluid temperature. As elaborated, the heat transfer enhances with an increase in the volume fraction and hot fluid temperature due to an increase in the temperature gradient. Hence, the thermal entropy generation rate increases with an increase in the volume fraction and hot fluid temperature. The increase in the thermal entropy generation rate with the volume fraction is not significantly high, but could not be neglected. The friction entropy generation depends on the pressure drop, but as per the formula, the friction entropy generation rate is evaluated based on the ratio of pressure drop and average temperature. The pressure drop and average temperature both increase as the volume fraction increases, but as explained before, the dominance of the heat transfer is more than pressure drop with an increase in the volume fraction, which leads to a higher increase rate of average temperature than the pressure drop. Therefore, the friction entropy generation rate decreases as the volume fraction increases for all hot fluid temperatures. The pressure drop shows negligible change and heat transfer shows significant enhancement with a rise in the hot fluid temperature. Therefore, the dominance of average temperature rise is higher than the pressure drop as the hot fluid temperature increases, which results in a decrease in the friction entropy generation rate with an increase in the hot fluid temperature for all volume fractions. The Bejan number increases with an increase in the volume fraction and an increase in the hot fluid temperature, because the thermal entropy generation rate increases and the friction entropy generation rate decreases as the volume fraction and hot fluid temperature have increased. The Bejan number is at maximum at the higher hot fluid temperature and higher volume fraction. The Bejan number of Al2O3/Cu with OS-shaped nanoparticles increases by 2.12%, 2.06% and 1.95% as the hot fluid temperature increases from 70 ◦C to 80 ◦C, and that increases by 3.69%, 3.58% and 3.40% when the hot fluid temperature increases from 70 ◦C to 90 ◦C for volume fractions of 0.5%, 1.0% and 2.0%, respectively. As the volume fraction increases from 0.5% to 2.0%, the Bejan number of Al2O3/Cu with OS-shaped nanoparticles increases by 1.01%, 0.85% and 0.73% for hot fluid temperatures of 70 ◦C, 80 ◦C, and 90 ◦C, respectively. Singh and Sarkar have presented the improvement in Nusselt number and reduction in friction factor with an increase in hot fluid temperature [62]. The contributions of thermal and friction entropy generation rates for Al2O3/Cu with OS-shaped nanoparticles at various hot fluid temperatures are depicted in Figure 13.

in Figure 13.

volume fraction from 0.5% to 2.0%, the performance index of Al2O3/Cu with OS-shaped nanoparticles enhances by 9.42% for each hot fluid temperature. As elaborated, the heat transfer enhances with an increase in the volume fraction and hot fluid temperature due to an increase in the temperature gradient. Hence, the thermal entropy generation rate increases with an increase in the volume fraction and hot fluid temperature. The increase in the thermal entropy generation rate with the volume fraction is not significantly high, but could not be neglected. The friction entropy generation depends on the pressure drop, but as per the formula, the friction entropy generation rate is evaluated based on the ratio of pressure drop and average temperature. The pressure drop and average temperature both increase as the volume fraction increases, but as explained before, the dominance of the heat transfer is more than pressure drop with an increase in the volume fraction, which leads to a higher increase rate of average temperature than the pressure drop. Therefore, the friction entropy generation rate decreases as the volume fraction increases for all hot fluid temperatures. The pressure drop shows negligible change and heat transfer shows significant enhancement with a rise in the hot fluid temperature. Therefore, the dominance of average temperature rise is higher than the pressure drop as the hot fluid temperature increases, which results in a decrease in the friction entropy generation rate with an increase in the hot fluid temperature for all volume fractions. The Bejan number increases with an increase in the volume fraction and an increase in the hot fluid temperature, because the thermal entropy generation rate increases and the friction entropy generation rate decreases as the volume fraction and hot fluid temperature have increased. The Bejan number is at maximum at the higher hot fluid temperature and higher volume fraction. The Bejan number of Al2O3/Cu with OS-shaped nanoparticles increases by 2.12%, 2.06% and 1.95% as the hot fluid temperature increases from 70 °C to 80 °C, and that increases by 3.69%, 3.58% and 3.40% when the hot fluid temperature increases from 70 °C to 90 °C for volume fractions of 0.5%, 1.0% and 2.0%, respectively. As the volume fraction increases from 0.5% to 2.0%, the Bejan number of Al2O3/Cu with OS-shaped nanoparticles increases by 1.01%, 0.85% and 0.73% for hot fluid temperatures of 70 °C, 80 °C, and 90 °C, respectively. Singh and Sarkar have presented the improvement in Nusselt number and reduction in friction factor with an increase in hot fluid temperature [62]. The contributions of thermal and friction entropy generation rates for Al2O3/Cu with OS-shaped nanoparticles at various hot fluid temperatures are depicted

**Figure 12.** Behavior of first and second law characteristics of Al2O3/Cu nanofluid with OS-shaped nanoparticles for various volume fractions and hot fluid temperatures. **Figure 12.** Behavior of first and second law characteristics of Al2O3/Cu nanofluid with OS-shaped nanoparticles for various volume fractions and hot fluid temperatures.

**Figure 13.** Contributions of thermal and friction entropy generation rates for Al2O3/Cu with OSshaped nanoparticles at various hot fluid temperatures. **Figure 13.** Contributions of thermal and friction entropy generation rates for Al2O3/Cu with OSshaped nanoparticles at various hot fluid temperatures.
