Brownian Motion-Based Model For Enhanced Thermal Conductivity Of Nanofluids

Nanofluids are a new class of heat transfer fluids which are engineered by dispersing nanometer-sized solid particles in conventional fluids. This is a rapidly emerging interdisciplinary field where nanoscience, nanotechnology, and thermal engineering meet. Since the novel concept of nanofluids was coined in 1995, this research topic has attracted tremendous interest from researchers worldwide due to their exciting thermal properties and potential applications in numerous important fields. Although research works have shown that nanofluids exhibit significantly higher thermal conductivity compared to their base fluids, the underlying mechanisms for the enhancement are still debated and not thoroughly understood. Despite considerable theoretical efforts devoted to the development of model for the prediction of the effective thermal conductivity of nanofluids, there has been little agreement among different studies and no widely accepted model is also available due to inconclusive heat transfer mechanisms of nanofluids. Nevertheless, fundamental understanding of the underlying mechanisms and development of a unanimous theoretical model are crucial for exploiting potential benefits and applications of nanofluids. In this chapter, a new and improved Brownian motion-based model is introduced for the prediction of the enhanced thermal conductivity of nanofluids. In addition to the Brownian motion of nanoparticles, this model also takes into account several other important factors such as particle size and interfacial nanolayer that contribute to the enhancement of the effective thermal conductivity of nanofluids. The conventional kinetic theory-based Brownian motion term has been renovated using effective diffusion coefficient concept. The present model shows reasonably good agreement with the experimental results of various aqueous nanofluids and gives better predictions compared to classical and other recently developed models. Besides providing a brief review on theoretical studies and various heat transfer mechanisms of nanofluids, details of the present model development and its validation with the experimental results are also discussed in this chapter. © 2012 by Nova Science Publishers, Inc. All rights reserved