China
Africa
Explore chapters and articles related to this topic
Characteristics and Behavior of Nanofluids
Published in C. Anandharamakrishnan, S. Parthasarathi, Food Nanotechnology, 2019
S.K. Vimala Bharathi, Sayantani Dutta, J.A. Moses, C. Anandharamakrishnan
The thermal conductivity of nanofluids can be measured using techniques such as the cylindrical cell method, temperature oscillation method, steady-state parallel-plate method, 3 w method, thermal constants analyzer method, thermal comparator method, and transient hot-wire method. Among these techniques, the transient hot-wire method is adopted by many researchers because of its accuracy, repeatability, feasibility, and possibility of measuring instantaneously (Sridhara and Satapathy, 2011; Paul et al., 2010). Having said that, thermal conductivity is a turnkey aspect of nanofluids, and it is therefore quintessential to better exploit the merits of these special fluids in designing thermally durable equipment, and/or process kinetics. This non-classical behavior could be especially made to use in miniature thermal approaches that have been in demand for quite some time, and therefore the augmented ability of nanofluids could support such developmental projects.
Nanoscale Thermal Phenomena
Published in C. B. Sobhan, G. P. Peterson, Microscale and Nanoscale Heat Transfer, 2008
Patel et al. (2003) found that the enhancement of the effective thermal conductivity did not increase linearly with the temperature, for the same volume fraction of nanoparticle suspensions composed of Au-thiolate nanoparticles with 10–20 nm diameters and a base fluid of water and toluene. The enhancement ratio in this investigation was found to be 5% to 21% in the temperature range of 30°C–60°C at a volume ratio of 0.00026 in toluene, and 7% to 14% for Au particles stabilized with a monolayer of octadecanethiol, even for a loading of 0.001% in water. This nonlinear variation is quite similar to findings by Wang et al. (2003), who utilized SiO2 nanoparticle suspensions. In both these investigations, the transient hot-wire method was used to measure the effective thermal conductivity.
Experimental Studies on the Influence of Metal and Metal Oxide Nanofluid Properties on Forced Convection Heat Transfer and Fluid Flow
Published in Alina Adriana Minea, Advances in New Heat Transfer Fluids, 2017
Viswanatha Sharma Korada, Seshu Kumar Vandrangi, Subhash Kamal, Alina Adriana Minea
The thermal conductivity of nanofluids has a significant influence on HTC. It has been identified from experimental studies that nanofluid thermal conductivity is a function of material properties, base fluid, volume fraction, temperature, size, shape, pH value, and dispersion (Eapen et al. 2010). The transient hot wire method is commonly used for the measurement of thermal conductivity due to fast response time, in addition to high accuracy. Early studies for the determination of effective thermal conductivity of nanofluids are based on the Maxwell (1881) model for two-phase solid–liquid mixtures, given by keff=kbfkp+2kbf+2(∅/100)(kp−kbf)kp+2kbf−(∅/100)(kp−kbf) Researchers such as Bruggeman (1935), Hamilton and Crosser (1962), Wasp (1977), and Jeffrey (1973) proposed improved equations. Further, studies on the interfacial layer (Every et al. 1992; Davis and Artz 1995; Xue 2003; Yu and Choi 2004; Xie et al. 2005; Xue and Xu 2005; Prasher et al. 2006a; Jang and Choi 2007; Murshed et al. 2008) and theoretical models on Brownian motion were also proposed (Keblinski et al. 2002; Koo and Kleinstreuer 2004, 2005; Prasher et al. 2006a; Jang and Choi 2007; Murshed et al. 2009).
Transient heat transfer in fibrous multi-scale composites: A semi-analytical model and its numerical validation
Published in Numerical Heat Transfer, Part A: Applications, 2020
Adam Dobri, Yanwei Wang, T. D. Papathanasiou
One common application requiring the understanding of the transient thermal response of a composite is materials characterization. The Transient Hot Wire method is a common characterization method to measure the thermal conductivity by fitting the increase in temperature to the increase predicted by analytical solutions for an effective material [25]. More modern iterations of the method use FEM to model the response of the wire, silicone contact paste and the sample [26]. The thermal conductivity of the sample is estimated, iteratively, until the difference between the sample response and the modeled response is within a desired tolerance. In composite materials, local non-equilibrium conditions can occur between the two phases, due to the phases having different properties or the presence of a thermal interfacial resistance [16]. In these cases, the local equilibrium assumption, used when considering the composite as a single effective material, is no longer valid. A two-equation model has been proposed to deal with non-equilibrium conditions [17] and will be used in the development of the semi-analytical approach.
An alternative sensitivity method for a two-dimensional inverse heat conduction-radiation problem based on transient hot-wire measurements
Published in Numerical Heat Transfer, Part B: Fundamentals, 2018
The transient hot-wire method is the most widely used in the industrial field for the determination of the thermal conductivity. It is simple and fast as is based on transient measurements of the temperature rise in a medium surrounding a uniformly heated wire. This method uses an ideal theory assuming the hot-wire as an infinitely thin and long line heat source, and considering the sample as an infinite medium. Based on the Fourier diffusion law, the hot-wire method applies only to purely conductive media and could theoretically not be used for materials including radiative heat transfer [12]. In practice, the heated wire should be long enough to satisfy the assumption of one-dimensional heat transfer required by the method. Due to the radiation phenomenon, the influence of the edge effects is more pronounced [1, 12]. In this case, longer wires should be used, which decreases the interest of the method.