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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

Specific heat vs. temperature subject to the influence of MWNT/water nanofluid at 0.1 vol.%.
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Figure 6: Specific heat vs. temperature subject to the influence of MWNT/water nanofluid at 0.1 vol.%.

Mentions: In addition to thermal conductivity, the specific heat also affects the performance of nanofluid. The specific heat of city water (tap water) is 4.383 J/g K at 20°C (4.373 J/g K at 25°C). The specific heat of D.I. water is 4.456 J/g K at 20°C (4.454 J/g K at 25°C). The specific heat of MWNT is 0.6 J/g K at 20°C. On the other hand, the specific heat of MWNT/city water nanofluid is 4.398 J/g K at 20°C (4.389 J/g K at 25°C). Therefore, the specific heat of MWNT/city water nanofluid at 0.1 vol.% is higher than that of city water. The specific heat is increased to be about 0.4% at 20°C shown in Figure 6. This indicates that the total amount of heat that can be absorbed by MWNT/city water is increased. However, the specific heat of MWNT nanofluid at 0.1 vol.% is lower than that of D.I. water. It is generally observed that the heat capacity is decreased with the addition of nanoparticles. From the measured experimental data for CuO nanofluids, Zhou et al. [23] also reported that the specific heat capacity of CuO nanofluid decreases gradually with increasing volume concentration of nanoparticles.


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)

Specific heat vs. temperature subject to the influence of MWNT/water nanofluid at 0.1 vol.%.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Specific heat vs. temperature subject to the influence of MWNT/water nanofluid at 0.1 vol.%.
Mentions: In addition to thermal conductivity, the specific heat also affects the performance of nanofluid. The specific heat of city water (tap water) is 4.383 J/g K at 20°C (4.373 J/g K at 25°C). The specific heat of D.I. water is 4.456 J/g K at 20°C (4.454 J/g K at 25°C). The specific heat of MWNT is 0.6 J/g K at 20°C. On the other hand, the specific heat of MWNT/city water nanofluid is 4.398 J/g K at 20°C (4.389 J/g K at 25°C). Therefore, the specific heat of MWNT/city water nanofluid at 0.1 vol.% is higher than that of city water. The specific heat is increased to be about 0.4% at 20°C shown in Figure 6. This indicates that the total amount of heat that can be absorbed by MWNT/city water is increased. However, the specific heat of MWNT nanofluid at 0.1 vol.% is lower than that of D.I. water. It is generally observed that the heat capacity is decreased with the addition of nanoparticles. From the measured experimental data for CuO nanofluids, Zhou et al. [23] also reported that the specific heat capacity of CuO nanofluid decreases gradually with increasing volume concentration of nanoparticles.

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