Effects of Particle Surface Charge, Species, Concentration, and Dispersion Method on the Thermal Conductivity of Nanofluids

Raghu Gowda,Bridgette Budhlall,Fan Gao,Hongwei Sun,Pengtao Wang,Zhiyong Gu,Majid Charmchi

doi:10.1155/2010/807610

Raghu Gowda, Bridgette Budhlall + Show 5 more

Open Access

https://doi.org/10.1155/2010/807610

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Abstract

The purpose of this experimental study is to evaluate the effects of particle species, surface charge, concentration, preparation technique, and base fluid on thermal transport capability of nanoparticle suspensions (nanofluids). The surface charge was varied by changing the pH value of the fluids. The alumina ([Formula: see text]) and copper oxide (CuO) nanoparticles were dispersed in deionized (DI) water and ethylene glycol (EG), respectively. The nanofluids were prepared using both bath-type and probe sonicator under different power inputs. The experimental results were compared with the available experimental data as well as the predicted values obtained from Maxwell effective medium theory. It was found that ethylene glycol is more suitable for nanofluids applications than DI water in terms of thermal conductivity improvement and stability of nanofluids. Surface charge can effectively improve the dispersion of nanoparticles by reducing the (aggregated) particle size in base fluids. A nanofluid with high surface charge (low pH) has a higher thermal conductivity for a similar particle concentration. The sonication also has a significant impact on thermal conductivity enhancement. All these results suggest that the key to the improvement of thermal conductivity of nanofluids is a uniform and stable dispersion of nanoscale particles in a fluid.

Highlights

Due to the low thermal conductivities of most common liquids used in heat exchangers, such as water and ethylene glycol, it has become urgent to look into other advanced alternatives
A recent study shows that the enhancement of thermal conductivity of nanofluids heavily depends on fluid temperature [9, 23] and particle sizes [24, 25]
The effect of surface charge, base fluid, particle species, and dispersion method on thermal conductivity of alumina and copper oxide nanofluids are addressed in a systematic way

Summary

Introduction

Due to the low thermal conductivities of most common liquids used in heat exchangers, such as water and ethylene glycol, it has become urgent to look into other advanced alternatives. A very small concentration of copper nanoparticle (less than 0.3% volume fraction of 10 nm nanoparticles) can enhance the thermal conductivity of base fluid (ethylene glycol) by up to 40% [21]. A recent study shows that the enhancement of thermal conductivity of nanofluids heavily depends on fluid temperature [9, 23] and particle sizes [24, 25]. The recent experimental and theoretical investigation strongly suggests that the nanoparticle aggregation (clusters) plays a significant role in the thermal transport in nanofluids. This research is focused on a systematic investigation of key parameters that affect the thermal conductivity of nanofluids These parameters include surface charge, nanoparticle composition and concentration, base fluids, and preparation techniques. The paper starts with nanofluid preparation and the measurement system, followed with comparisons of the obtained results with those published in open literature and predicted by theory, and the effects of key parameters are discussed and summarized in detail in the end of the paper

Nanofluids Preparation and Experimental Apparatus

Results and Discussion

Conclusions