Nanofluids, heat transfer

The concept of nanofluids to further intensify microreactors has been discussed by Fan et al. [17]. The nano-fluids are suspensions of solid nano-partides with sizes typically of 1-100 nm in traditional liquids such as water, glycol and oils. These solid-liquid composites are very stable and show higher thermal conductivity and higher convective heat transfer performance than traditional liquids. They can thus be used to enhance the heat transfer in nanofluids in compact multifunctional reactors. A nanofluid based on Ti02 material dispersed in ethylene glycol showed an up to 35% increase in the overall heat transfer coefficient and a... 

Consolini, L., and Thome J. R., Micro-Channel Flow Boiling Heat Transfer of R-134a, R-236fa, and R-245fa, J. Microfluidics and Nanofluidics, doi 10.1007/ s 10404-008-0348-7 (2008). 

Nanofluids are solid nanoparticles or nanofibers in suspension in a base fluid. To be qualified as nanofluid it is generally agreed that at least one size of the solid particle be less than 100 mn. Various industries such as transportation, electronics, food, medical industries require efficient heat transfer fluids to either evacuate or transfer heat by means of a flowing fluid. Especially with the miniaturization in electronic equipments, the need for heat evacuation has become more important in order to ensure proper working conditions for these elements. Thus, new strategies, such as the use of new, more conductive fluids are needed. Most of the fluids used for this purpose are generally poor heat conductors compared to solids (Fig. 1). 

V. Trisaksri and S. Wongwises, Critical review of heat transfer characteristics of nanofluids. Renewable and Sustainable Energy Reviews, 11, 512-523 (2007). 

S.K. Das, N. Putra, P. Thiesen and W. Roetzel, Temperature dependence of thermal conductivity enhancement for nanofluids, Journal of Heat Transfer, 125, 567-574 (2003). 

W.H. Yu, D M. France, J.L. Routbort and S.U.S. Choi, Review and comparison of nanofluid thermal conductivity and heat transfer enhancements. Heat... 

S.U.S. Choi, Nanofluids From vision to reality through research, J. Heat Transfer, 131, 033106 (2009). 

C.H. Chon and K.D. Kihm, Thermal conductivity enhancement of nanofluids by Brownian motion, J. Heat Transfer, 127, 810 (2005). 

D.H. Yoo, K.S. Hong and H.S. Yang, Study of thermal conductivity of nanofluids for the application of heat transfer fluids, Thermochim. Acta, 455, 66-69 (2007). 

Y. He, Y. Jin, H. Chen, Y. Ding, D. Cang and H. Lu, Heat transfer and flow behaviour of aqueous suspensions of TiOa nanoparticles (nanofluids) flowing upward through a vertical pipe, Int. J. Heat Mass Transfer, 50, 2272-2281 (2007). 

H.U. Kang, S.H. Kim and J.M. Oh, Estimation of thermal Conductivity of nanofluid using experimental effective particle volume, Experimental Heat Transfer, 19, 181-191 (2006). 

B. Wright, D. Thomas, H. Hong, L. Groven, J. Puszynski, E. Duke, X. Ye, and S. Jin, Magnetic field enhanced thermal conductivity in heat transfer nanofluids containing Ni coated single wall carbon nanotubes, Appl. Phy.s Lett., 91,173116 (2007). 

H. Hong, B. Wright, J. Wensel, S. Jin, X. Ye, and W. Roy, Enhanced thermal conductivity by the magnetic field in heat transfer nanofluids containing carbon nanotube, Synth Met., 157,437 (2007). 

Multiphysical transports in electroosmotic flows. Multiphysical transports may accompany the electroosmotic flow, such as heat transfer, oscillation spreading, etc. Some transports may be coupled. Probably the geometry is complex in the real world. The LPBM provides a method though it also faces challenges due to such complicated problems. In most microfluidics and nanofluidics, the... 

In order to provide some physical insight into the dynamics of microchannel heat sinks (MCHS), steady laminar water flow in a smooth single trapezoidal microchannel is discussed and compared with measured data sets. Then the effects of nanofluids on augmented MCHS heat transfer are introduced, employing very simple correlations for the enhanced thermal conductivities of the mixtures. The fluid flow and heat transfer simulations have been carried out with the commercial... 

Nanofluid Flow with Heat Transfer In order to investigate the heat transfer characteristics of a nanofluid in the trapezoidal microchannel, we employed a CuO-water combination as the working fluid. Clearly, the thermal... 

In order to investigate heat transfer enhancement for nanofluids, the average Nusselt numbers... 

Dh = 209.5 pm), the smaller aspect ratio case (A = 0.558) Nuave increases more rapidly when compared to the larger aspect ratio case (A = 0.827). There is a 20-30 % heat transfer enhancement in microchannels when employing nanofluids. The aspect ratio (or hydraulic diameter) measurably influences thermal enhancement when using nanofluids. 

As mentioned, nanofluids exhibit unusual thermal and fluid properties, which in conjunction with microchannel systems provide enhanced heat transfer performance in heat transfer and fluid flow. For example. Wen and Ding [23] reported a considerable convective heat transfer augmentation when employing 7-AI2O3 nanoparticles in water flow in a copper tube based on their experimental results. The test Y-AI2O3 nanoparticles had a size range of 27-56 nm. Figure 9 depicts the local heat transfer coefficient vs. axial distance from the entrance of the test section, which clearly shows that the enhancement of the local heat transfer coefficient... 

Microscale Cooling Devices, Fig. 9 Nanofluid flow application in micFochannel heat sink axial profile of local heat transfer coefficient (Re = 1,050 50) [23]... 

Thus, ongoing research is focusing on the thermal and fluid properties of nanofluids as well as such mixmre flow in microchannels. How to optimize the cooling capabilities of nanofluids in microchannel heat sinks will be a challenging task. Alternative approaches include fluid jet impingement and two-phase, i.e., liquid-vapor, flow with boiling heat transfer. 

Wen D, Ding Y (2004) Experimental investigation into convective heat transfer of nanofluids at the entrance legirai under laminar flow conditions. Int J Heat Mass Transf 47 5181-5188... 

Yang Y, Zhang ZG, Grulke EA, Anderson WB, Wu G (2005) Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow. Int J Heat Mass Transf 48 1107-1116... 

Nanofluids, a concept developed by Choi at Argonne National Laboratory [6], are a new class of heat transfer fluids that are composed of suspended nanosized metallic or nonmetallic sohd particles in liquid media. Nanofluids when properly prepared display significantly enhanced heat transfer capacities relative to those of traditional heat transfer fluids. From the practical application viewpoint, the most critical concerns are the agglomeration and poor suspension stability of the metallic or nomnetallic nanoparticles in a given fluid medium. 

Plasma treatment provides a new approach to functionalize nanoparticle and nanotube surface for heat transfer nanofluid preparation without using stabilizing agents. More experimental investigation is very necessary to optimize the plasma treatment process in terms of plasma chemistry, plasma operating conditions, and proper plasma apparatus design. As pointed out in this entry, besides nanoparticle and nanotube concentration, the enhanced interfacial interactions between nanoparticles and/or carbon nanotubes with base fluids could be another important factor that contributed to the thermal conductivity increase observed in heat transfer nanofluids. A detailed characterization of the nanofluids with the aid of theoretical simulations will help us to understand the fundamental mechanisms for the observed heat transfer enhancement. 

Kim YJ, Ma HB, Yu Q.S (2010) Plasma nanocoatcd carbon nanotubes for heat transfer nanofluids. Nanotechnology 21 295703... 

Lakehal, D., Larrignon, G, and Narayanan, C. 2008) Computational heat transfer and two-phase flow topology in miniature tubes. Microfluid. Nanofluid., 4 (4), 261—271. 

Wamkam CT, Opoku MK, Hong H, Smith P (2011) Effects of pH on heat transfer nanofluids containing ZrO and TiOj nanopaiticles. J Appl Phys 109(2) 024305... 

Wang, X.-Q. and Mujumdar, A.S. (2007). Heat transfer characteristics of nanofluids a review. International Journal of Thermal Sciences, Vol. 46, No. 1, pp. 1-19, January. 

Yue D, Liu Y, Shen Z, Zhang L (2006) Smdy on preparation and properties of carbon nanotubes/ mbber composites. J Mater Sei 41(8) 2541-2544 Yulong D, Hajar A, Dongsheng W, Richard AW (2006) Heat transfer of aqueous susperrsions of carbon nanotubes (CNT nanofluids). Int J Heat Mass Transf 49(2) 240-250 Zaminpayma E (2014) Molecular dynamics simulation of mechanical properties and interaction energy of polythiophene/polyethylene/poly(p-phenylenevinylene) and CNTs composites. Polym Compos... 

This chapter is divided into three parts. In Section 10.2, we discuss the interesting problem of heat transfer in novel materials called nanofluids, which are suspensions of nanoparticles in liquids. Here, the central question is to understand the heat transfer across the interface between a nanoparticle and the surrounding base fluid. We believe that understanding heat transfer across the interface provides crucial insights into the observed enhanced thermal conductivities of nanoparticle suspensions in polar liquids (Choi 2009). We provide an overview of the computation of thermal conductivity for inhomogeneous systems using MD simulations, followed by a discussion on the heat transfer due to radiative heating. 

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