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Copper Nanoparticles To Thermal Properties Of Nanofluids Engineering Essay

In this project, the analysis study concentrated on thermal performance of double pipe heat exchanger. The analyses were based on the test condition stated in previous chapter.

In this section, the analyses of the thermal properties of nanofluids have been carried out. The thermal properties of nanofluids included the thermal conductivity, density, specific heat and viscosity. The thermal properties in this study were calculated using the correlation developed by Vasu et al. (2008) as shown in equation (3.8)-(3.12). The input data added are diameter of copper particle, thermal conductivity and density of particle for copper, temperature coolant inlet, constant C, Boltzmann constant and properties for base fluid such as density and specific heat. The results are illustrated in Figure 4.1 to Figure 4.4.

Figure 4.1 shows the thermal conductivity of copper water based nanofluids at 30oC with different volume fraction. The thermal conductivity of nanofluids was found to be slightly higher than water. The thermal conductivity of the nanofluids has been increased with the increase of the volume fraction of copper nanoparticles. At 2.0% volume fraction of copper nanoparticles, the thermal conductivity of nanofluids achieved the increments about 26.18%. The increment of the thermal conductivity occurred by suspended copper nanoparticles in water. The nanofluids show higher thermal conductivity due to increase in Brownian motion, formation of nanolayer and nanoparticles clustering. Therefore, the thermal conductivity of nanofluids was depended to the volume fraction percentage. Similar result reported by Mintsa et al. (2009).

The density and viscosity of the nanofluids increased with the increasing of volume fraction of copper nanoparticles. The increasing occurred because of the adding of nanoparticles in a base fluid. These parameters were calculated using Equation (3.10) and Equation (3.12). The results are illustrated in Figure 4.2 and Figure 4.4.

Figure 4.3 shows that the specific heat of the coolant decreased gradually when the nanoparticles were added. The specific heat was calculated using Equation (3.11). From this equation, as the density of nanofluids increased, the specific heat decreased. In other word, the denser of substance, the lower of the specific heat. In addition, the specific heat depended almost linearly on the volume fraction of the particles in the suspension. Similar result was reported by Namburu et al (2009).

Figure 4.1 Thermal conductivity of water based copper nanofluids at 30oC with different volume fraction

Figure 4.2 Density of water based copper nanofluids at 30oC with different volume fraction

Figure 4.3 Specific heat of water based copper nanofluids at 30oC with different volume fraction

Figure 4.4 Viscosity of water based copper nanofluids at 30oC with different volume fraction

4.3 Influence of volume fraction of copper nanoparticles to thermal performance of double pipe heat exchanger.

In this analysis, the mass flow rate was determined by Equation (3.15). The coolant mass flow rate was influenced by nanofluids viscosity as the higher viscosity, higher the coolant mass flow rate. It also can be explained from Equation (4.1).

(4.1)

In this equation, was varied due to different value of particle volume fraction and other parameters were kept constant. The result is demonstrated in Figure 4.5. Coolant Prandtl number was calculated using equation (3.16) and the thermal conductivity was an influential parameter for Prandtl number. The higher thermal conductivity of nanofluids will lead to lower value of Prandtl number. These relationships are shown in Figure 4.6. Figure 4.7 shows lower coolant Nusselt number with the increasing of copper nanoparticles based on Equation (3.14). The decreasing in the Nusselt number was due to the decreasing in Prandtl number at varies concentrations. Similar result reported by Xuan and Li (2003).

Figure 4.5 Effect of copper volume fraction to coolant mass flow rate at constant Reynolds number

Figure 4.6 Effect of copper volume fraction to nanofluids Prandtl number at constant Reynolds number

Figure 4.7 Effect of copper volume fraction to nanofluids Nusselt number at constant Reynolds number

This analysis also found that the water based copper nanofluids demonstrated higher coolant heat transfer coefficient as calculated using Equation (3.13). The relationship is shown in Figure 4.8 where coolant heat transfer coefficient increased with copper nanoparticles. For 2.0% copper nanofluids based water achieved 2963.25 W/m2K of heat transfer coefficient compared to 2553.01 W/m2K for the base fluids which is about 16.1% increment. The relation is illustrated in Figure 4.8. The same trend is demonstrated in Figure 4.9 for overall heat transfer coefficient for coolant side. The overall heat transfer coefficient for coolant side increased with copper nanoparticles. For instance, the overall heat transfer coefficient achieved about 62.47 W/m2K for 2.0% volume fraction of copper nanoparticles compared to 62.23 W/m2K for base fluids.

Heat transfer rate was found increasing as the volume fraction of copper nanoparticles increased as shown in Figure 4.10. This improvement was calculated using Equation (3.22). The overall heat transfer coefficient, density and specific heat of the nanofluids had influenced with the increasing of the heat transfer rate. For 2.0% copper nanofluids based water achieved 18.9% increasing of heat transfer rate compare to base fluids.

Figure 4.8 Effect of copper volume fraction to coolant heat transfer coefficient at constant Reynolds number

Figure 4.9 Effect of copper volume fraction to nanofluids overall heat transfer coefficient at constant Reynolds number

Figure 4.10 Effect of copper volume fraction to nanofluids heat transfer rate at constant Reynolds number

4.4 Influence of coolant inlet temperature to thermal conductivity of nanofluids

In this analysis, coolant inlet temperature were varied from 30oC to 40oC. Figure 4.11 showed the thermal conductivity of copper water based nanofluids at 30oC, 35oC and 40oC with different volume fraction. The thermal conductivity of nanofluids was found to be slightly high when the temperature increased. The thermal conductivity of the nanofluids also had been increased with the increased of the volume fraction of copper nanoparticles. At 40oC, for 2.0% volume fraction of copper nanoparticles, the thermal conductivity of nanofluids achieved 0.816 W/mK compared to 0.776 W/mK at 30oC for the same volume fraction. The increment of the thermal conductivity occurred by suspended copper nanoparticles in water. The higher temperature increased the Brownian motion. Therefore, temperature also was an influence in determining the higher thermal conductivity. Similar result reported by Vasu et al. (2008).

Figure 4.11 Comparison of nanofluids thermal conductivity with different coolant inlet temperature at varies volume fraction

4.5 Influence of coolant inlet temperature to thermal performance of double pipe heat exchanger

This analysis also found that the copper nanofluids based water demonstrated higher coolant heat transfer coefficient as the increasing of inlet temperature. This result was calculated using Equation (3.13). It was observed from Figure 4.12 and found that coolant heat transfer coefficient increased with the increased copper nanoparticles due to higher thermal conductivity of the nanofluids. This results also shown that the heat transfer coefficient decreased with the increasing of operating inlet temperature. At 40oC, for 2.0% copper nanofluids based water resulting 2877.83 W/m2K of heat transfer coefficient compared to 2963.25 W/m2K at 30oC for the same volume fraction which was about 2.96% decreasing. The same trend is demonstrated in Figure 4.13 for overall heat transfer coefficient for coolant side. The overall heat transfer coefficient for coolant side increased with copper nanoparticles. This results also shown that the overall heat transfer coefficient decreased with the increasing of operating inlet temperature. For instance, the overall heat transfer coefficient achieved about 62.43 W/m2K at 40oC for 2.0% volume fraction of copper nanoparticles compare to 62.47 W/m2K at 30oC for the same volume fraction.

The heat transfer rate clearly decreased with operating inlet temperature rise since the cooling temperature difference was being reduced. However, heat transfer rate found increasing as the volume fraction of copper nanoparticles increased as shown in Figure 4.14. This result was calculated using Equation (3.22). At 40oC, for 2.0% copper nanofluids based water achieved 21.9% decreasing of heat transfer rate compare to at 30oC for the same volume fraction.

Figure 4.12 Comparison of nanofluids heat transfer coefficient with different coolant inlet temperature at varies copper volume fraction

Figure 4.13 Comparison of nanofluids overall heat transfer with different coolant inlet temperature at varies copper volume fraction

Figure 4.14 Comparison of nanofluids heat transfer rate with different coolant inlet temperature at varies copper volume fraction

4.6 Influence of coolant Reynolds number to thermal performance of double pipe heat exchanger

This section presents the effect of coolant Reynolds number on the thermal properties of nanofluids. Coolant Reynolds number plays important role in determining the thermal performance of double pipe heat exchanger. From this analysis, it indicated that as the coolant Reynolds number increased, the heat transfer coefficient and the overall heat transfer coefficient also increased. The results of the analyses are illustrated in Figure 4.15 and Figure 4.16.

Nanofluids with higher copper volume fraction generates higher overall heat transfer coefficient compared to base fluids. Same scenario happened for heat transfer rate where it was proportional to coolant Reynolds number. For instance, with the addition of 2.0% copper nanoparticles, 49% improvement of heat transfer rate had been achieved at 15000 Reynolds number for coolant. It was also observed that the double pipe heat exchanger thermal performance increased with the increased of coolant Reynolds number. Figure 4.17 shows the heat transfer rate of the double pipe heat exchanger using nanofluids was higher than that double pipe heat exchanger using water.

Figure 4.15 Effect of coolant Reynolds number and copper volume fraction to heat transfer coefficient

Figure 4.16 Effect of coolant Reynolds number and copper volume fraction to overall heat transfer coefficient based on coolant side

Figure 4.17 Effect of coolant Reynolds number and copper volume fraction to heat transfer rate

4.7 Influence of oil Reynolds number to thermal performance of double pipe heat exchanger

This section presents the effect of oil Reynolds number on the thermal properties of nanofluids. A coolant’s mass flow rate, Nusselt number and Prandtl number did not experienced any change since the coolant Reynolds number was kept fixed at 13000. Only oil Reynolds number volume fraction of copper nanoparticles was varied in this section. With the increase of oil Reynolds number, the oil heat transfer coefficient was increased as shown in Figure 4.18. At 2.0% volume fraction of copper nanoparticles, the heat transfer increased about 34.1% with the increasing of oil Reynolds number. Substituting higher value of oil heat transfer coefficient into Equation (3.2), overall heat transfer coefficient based on oil side of the double pipe heat exchanger was obtained and shown in Figure 4.19. From this analysis, it indicated that as the oil Reynolds number increased, the heat transfer coefficient and the overall heat transfer coefficient also increased.

Figure 4.18 Effect of oil Reynolds number and copper volume fraction to heat transfer coefficient

Figure 4.19 Effect of oil Reynolds number and copper volume fraction to overall heat transfer coefficient based on oil side

4.8 Comparison of coolant pressure drop and pumping power

In this section, the analysis focused on the coolant pressure drop and pumping power of the double pipe heat exchanger at varying copper nanoparticles volume fraction. The Reynolds number (13000) was substituted into Equation (3.15) to determine the mass flow rate value. The mass flow rate value substituted into Equation (3.18) to determine coolant mass velocity. The pressure drop had been calculated by using fanning friction factor based on Equation (3.20), which then substituted into Equation (3.17).

It was observed that the coolant pressure drop increased with the addition of copper nanoparticles. The result revealed that a pressure drop of 7789.58 Pa was obtained by adding 2.0% copper nanoparticles compared to a pressure drop of 4683.52 Pa for a base fluids. Due to this extra pressure drop, a higher coolant pumping power was needed. The pumping power was calculated using Equation (3.21). The efficiency of the pump was taken 0.8. Calculated results also indicated that about 2.34 kW pumping power was obtained by adding 2.0% copper nanoparticles compared to 1.18 kW pumping power for a base fluids. This showed that the adding of nanoparticles required higher pumping power due to higher mass flow rate. These trends were shown in Figure 4.21 and Figure 4.22. The increasing in density and viscosity increased the pressure drop and pumping power of flowing liquids.

Figure 4.20 Influence of copper volume fraction to coolant pressure drop at fixed coolant mass flow rate

Figure 4.21 Influence of copper volume fraction to coolant pumping power at fixed coolant mass flow rate

4.9 Effect of nanofluids to size of the double pipe heat exchanger

In this analysis, the effect of nanofluids to size double pipe heat exchanger was studied. The analysis needed to show the reduction of size double pipe heat exchanger when using nanofluids. For length reduction, the pressure drop is was fixed at 4500 Pa. The Equation (3.17) was manipulated in order to the determine the length of the double pipe. It can also be explained from Equation (4.2 ).

(4.2)

40% of the length is reduced when using nanofluids at 2.0% copper nanoparticles. The calculation results are illustrated in Figure 4.22. Therefore, at the same thermal performance, the size of double pipe heat exchanger can be reduce and more capability and efficiency to use in small area.

Figure 4.22 Influence of copper volume fraction to inner length of the double pipe heat exchanger at fixed pressure drop

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