Liquid metal flows

The mass flux in the spray scales with liquid metal flow rate. Gas pressure tends to narrow the spray whereas melt superheat tends to flatten the spray)3] By changing the process parameters and/or manipulating the configuration and/or motion of the spray, the mass distribution profile can be tailored to the desired shape. For example, a linear atomizer produces a relatively uniform mass distribution in the spray. The mass flux distribution in the spray generated with a linear atomizer has been proposed to follow the elliptical form of the Gaussian distribution)178]... 

Let us first consider the simple flat plate with a liquid metal flowing across it. The Prandtl number for liquid metals is very low, of the order of 0.01. so that the thermal-boundary-layer thickness should be substantially larger than the hydrodynamic-boundary-layer-thickness. The situation results from the high values of thermal conductivity for liquid metals and is depicted in Fig. 6-15. Since the ratio of 8/8, is small, the velocity profile has a very blunt shape over most of the thermal boundary layer. As a first approximation, then, we might assume a slug-flow model for calculation of the heat transfer i.e., we take... 

Determine an expression for the average Nusselt number for liquid metals flowing over a flat plate. Use Eq. (6-42) as a starting point. 

The process depends on a liquid metal flowing over surfaces to form a fillet between components and into the gap between the components, and then solidifying to form a permanent bond. Thus it is essential that the braze experiences high temperature capillary attraction. Without such attraction, solid braze material placed between components will flow out of the gap, sweat , when it melts. Any residue of non-wetting liquid that remains within the gap will not conform to the microscopic features of the component surfaces but form an array of voids, as illustrated schematically in Figure 10.1, that is mechanically deleterious and should be avoided if at all possible. The size of such voids can be decreased if an external pressure is used to confine a non-wetting liquid braze into a gap but cannot eliminate them because the pressure needed to shrink voids increases as they become smaller. 

Several other ICF reactor concepts use liquid metal walls (Ii W). These include the Los Alamos National Laboratory (LANL) wetted wall concept, the Bechtel concept called EAGLE (which uses a lithium spray in the chamber), the Lawrence Livermore National Laboratory (LLNL) concept called JADE (which uses a fiber-metal structure to control liquid metal flow), and the German/University of Wisconsin concept called HIBALL (which uses carbide "socks" to control liquid metal flow). 

If a liquid metal flows perpendicular to the magnetic field direction (Figure 3), a potential difference across the flow duct is induced in the metal coolant this causes a high electrical current flow when the potential difference is short-circuited by the electrically conducting walls. The relationship between magnetic field (B), electrical current (I), and mechanical force (F), when the I is flowing perpendicular to B,... 

A liquid metal flowing with a uniform velocity V through a pipe of periphery P and cross section A is electrically heated at the rate of u" over a length t of the pipe (Fig. 3P-2). The inlet temperature of the liquid is equal to the ambient temperature Tx. The outside heat transfer coefficient is h. Neglecting the effect of anal conduction . 

Dwyer [113] has developed semiempirical equations for liquid metal flow (Pr < 0.03) in a concentric annular duct (0 < r < 1) with one wall subjected to uniform heat flux and the other... 

Maresca and Dwyer [264] have analyzed the heat transfer of liquid metal flow in a triangular array with uniform longitudinal heat flux. The Nusselt number resulting from their analysis is given in Fig. 5.42. 

Hsu [Int. J. Heat Mass Transfer, 7, 431 (1964)] and Kalish and Dwyer [Int. J. Heat Mass Transfer, 10, 1533 (1967)] discuss heat transfer to liquid metals flowing across banks of tubes. Hsu recommends the equations... 

K. Ho and Y. Zhao. Modelling thermal development of liquid metal flow on rotating disc in centrifugal... 

EXAMPLE 4J-3. Liquid-Metal Heat Transfer Inside a Tube A liquid metal flows at a rate of 4.00 kg/s through a tube having an inside diameter of 0.05 m. The liquid enters at 500 K and is heated to 505 K in the tube. The tube wall is maintained at a temperature of 30 K above the fluid bulk temperature and constant heat flux is maintained. Calculate the required tube length. The average physical properties are as follows n =... 

Borishanskii, V.M., M.A. Gotorsky, and E.V. Firsova. 1969. Heat transfer to liquid metal flowing longitudinally in wetted bundles of rods. Atom. Energy 27 549-568. 

Graber, H. and M. Rieger. 1973. Experimental study of heat transfer to liquid metals flowing in line through tube bundles. Prog. Heat Mass Transfer 7 151-166. 

Similar loops, constructed of stainless steel and operated with radiant heating devices in air, have been used for liquid metal corrosion studies in laboratories around the world (e.g., Refs 16,54). In some cases, removable sample strings are situated in the hot and cold legs to facilitate removal of specimens without inteiruption to liquid metal flow [54]. 

Because forced-convection loops are costly to construct, it is now the usual practice to operate the loops as permanent testing facilities, with corrosion specimens cycled in and out of the facility. Test specimens of various materials are generally placed in the hot leg, and the effect of the flowing liquid on the specimens is determined from changes in weight, dimensions, composition, mechanical properties, and microstructure. Such an approach yields data on maximum corrosion rates as a function of temperature and liquid metal flow rate. Any attempt to elucidate corrosion mechanisms, however, is hampered by the inability to interrelate dissolution and deposition processes. 

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