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Enhancements of thermal conductivities with Cu, CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system.

Liu M, Lin MC, Wang C - Nanoscale Res Lett (2011)

Bottom Line: Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance.It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime.Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan. ccwang@mail.nctu.edu.tw.

ABSTRACT
In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.

No MeSH data available.


Related in: MedlinePlus

Typical SEM micrographs and HRTEM micrograph of CuO, MWNT, and Cu. (a) Typical SEM micrograph of CuO nanoparticles; (b) typical SEM micrograph of MWNTs; (c) typical HRTEM micrograph of MWNTs; (d) typical SEM micrographs of Cu nanoparticles.
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Figure 3: Typical SEM micrographs and HRTEM micrograph of CuO, MWNT, and Cu. (a) Typical SEM micrograph of CuO nanoparticles; (b) typical SEM micrograph of MWNTs; (c) typical HRTEM micrograph of MWNTs; (d) typical SEM micrographs of Cu nanoparticles.

Mentions: Typical SEM micrograph of CuO nanoparticles is shown in Figure 3a. The morphology and particle size of CuO powders are clearly seen. The CuO powders generally exhibit small particle sizes and a narrow distribution. The agglomerated CuO nanoparticles range from 30 to 50 nm with spherical shape. A typical SEM micrograph of MWNTs is shown in Figure 3b. The randomly oriented fiber-like MWNTs are clearly seen. An individual MWNT is several microns long. Small catalytic, metallic nanoparticles are observed at the tip of the MWNT with diameters of 20 to 30 nm. Figure 3c shows a typical HRTEM micrograph of MWNTs. The HRTEM image clearly shows the characteristic features of MWNTs. The MWNT core is hollow with multiple layers almost parallel to the MWNT axis. Its inner diameters are about 5 to 10 nm, and outer diameters are about 20 to 50 nm, respectively. Typical SEM micrograph of Cu nanoparticles is shown in Figure 3d. Cu nanoparticles synthesized by chemical reduction shows the monodispersed distribution of particle sizes. The agglomerated particle sizes of the Cu nanoparticles range from 50 to 100 nm with spherical and square shapes.


Enhancements of thermal conductivities with Cu, CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system.

Liu M, Lin MC, Wang C - Nanoscale Res Lett (2011)

Typical SEM micrographs and HRTEM micrograph of CuO, MWNT, and Cu. (a) Typical SEM micrograph of CuO nanoparticles; (b) typical SEM micrograph of MWNTs; (c) typical HRTEM micrograph of MWNTs; (d) typical SEM micrographs of Cu nanoparticles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211363&req=5

Figure 3: Typical SEM micrographs and HRTEM micrograph of CuO, MWNT, and Cu. (a) Typical SEM micrograph of CuO nanoparticles; (b) typical SEM micrograph of MWNTs; (c) typical HRTEM micrograph of MWNTs; (d) typical SEM micrographs of Cu nanoparticles.
Mentions: Typical SEM micrograph of CuO nanoparticles is shown in Figure 3a. The morphology and particle size of CuO powders are clearly seen. The CuO powders generally exhibit small particle sizes and a narrow distribution. The agglomerated CuO nanoparticles range from 30 to 50 nm with spherical shape. A typical SEM micrograph of MWNTs is shown in Figure 3b. The randomly oriented fiber-like MWNTs are clearly seen. An individual MWNT is several microns long. Small catalytic, metallic nanoparticles are observed at the tip of the MWNT with diameters of 20 to 30 nm. Figure 3c shows a typical HRTEM micrograph of MWNTs. The HRTEM image clearly shows the characteristic features of MWNTs. The MWNT core is hollow with multiple layers almost parallel to the MWNT axis. Its inner diameters are about 5 to 10 nm, and outer diameters are about 20 to 50 nm, respectively. Typical SEM micrograph of Cu nanoparticles is shown in Figure 3d. Cu nanoparticles synthesized by chemical reduction shows the monodispersed distribution of particle sizes. The agglomerated particle sizes of the Cu nanoparticles range from 50 to 100 nm with spherical and square shapes.

Bottom Line: Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance.It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime.Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan. ccwang@mail.nctu.edu.tw.

ABSTRACT
In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.

No MeSH data available.


Related in: MedlinePlus