Transport phenomena heat transfer

Celata GP, Cumo M, Gugliehni M, Zummo G (2000) Experimental investigation of hydraulic and single phase heat transfer in 0.130 mm capillary tube. In Proceedings of the international conference of heat transfer transport phenomena microscale, Begell House, pp 108-113... 

Gritzo, L. A, et al., 1995a, Heat Transfer to the Fuel Surface in Large Pool Fires, Transport Phenomenon in Combustion, S. H. Choa (ed.), Taylor and Francis Publishing, Washington, DC. 

The driving forces, or driving potentials, for transport phenomena are (i) the temperature difference for heat transfer (ii) the concentration or partial pressure difference for mass transfer and (iii) the difference in momentum for momentum transfer. When the driving force becomes negligible, then the transport phenomenon will cease to occur, and the system will reach equilibrium. 

The primary motivation for predicting the electrochemical properties of the coolant circuits of water-cooled nuclear power reactors has been that of explaining and predicting tenacious operating problems that include SCC and CF, mass transport of corrosion products and subsequent fouling of heat transfer surfaces, activity transport due to the movement of neutron-activated radionuclides from the core to out-of-core surfaces that are not shielded, and, in the case of PWRs, the axial offset anomaly (AOA). This latter phenomenon results from the deposition of boron... 

The transfer of heat in a fluid may be brought about by conduction, convection, diffusion, and radiation. In this section we shall consider the transfer of heat in fluids by conduction alone. The transfer of heat by convection does not give rise to any new transport property. It is discussed in Section 3.2 in connection with the equations of change and, in particular, in connection with the energy transport in a system resulting from work and heat added to the fluid system. Heat transfer can also take place because of the interdiffusion of various species. As with convection this phenomenon does not introduce any new transport property. It is present only in mixtures of fluids and is therefore properly discussed in connection with mass diffusion in multicomponent mixtures. The transport of heat by radiation may be ascribed to a photon gas, and a close analogy exists between such radiative transfer processes and molecular transport of heat, particularly in optically dense media. However, our primary concern is with liquid flows, so we do not consider radiative transfer because of its limited role in such systems. 

Most of you will take a heat transfer or a transport phenomenon class during your third year where you will learn in more detail about various modes of heat transfer. You will also learn how to estimate heat transfer rates for various situations, includii the coolit of electronic devices and the design of fins for transformers or motorcycle and lawn mower ei ne heads and other heat etchai rs, like the radiator in your car or the heat exchangers in furnaces and boilers. The intent of this seexion was to briefly introduce you to the concept of heat transfer and its various modes. 

Correlations for Boiling Heat Transfer Nucleate boiling is a complex phenomenon. Several mechanisms have been proposed to explain the boiling process, such as latent heat transport, microconvection, vapor-liquid exchange, wake flow, enhanced convection, and microlayer evaporation, details of which can be found in Ginoux (1978). 

Thermal conduction is the phenomenon by which heat is transported from high- to low-temperature regions of media that are in intimate contact. The ability of a material to transfer heat is described by thermal conductivity, which is a... 

Microscale thermal transport phenomenon involves complex transfer mechanism of free electrons and phonons. The molecular dynamics and processes are not significant in most of the microscopic engineering applications. However, scale effects become extremely important in system with sudden high heat flux irradiation by laser pulses and some other dimensionally space- and time-governed problems. Anisimov etal. (1974) proposed the first two-step model for microscale conduction as... 

In order to incorporate the shape of the p>articles (e.g. cylinders) and the interaction between the particles, extensions of this Maxwell model were later developed by (Hamilton and Grosser, 1962) and (Hui et al., 1999). However, these classical models were found to be unable to accurately predict the anomalously high thermal conductivity of nanofluids (Murshed et al., 2008a). Thus, researchers have proposed several mechanisms to explain this phenomenon. For example, (Kebflnski et al., 2002) systematized the four different mechanisms for heat transfer to explain these enhancements, namely (i) Brownian motion of the nanoparticles (ii) liquid layering at the liquid/ particle interphase, (iii) the nature of the heat transport in the nanoparticles and (iv) the effect of nanoparticle clustering. From the analysis made in an exhaustive review paper on nanofluids (Murshed et al., 2008a) and other publications cited, therein, it is our belief that the effect of the particle surface chemistry and the structure of the interphase partide/fluid are the major mechanisms responsible for the unexpected enhancement in nanofluids. 

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