Liquid metals, heat transfer references

In general, there are many open questions concerning liquid-metal heat transfer, and the reader is referred to Refs. 13 and 23 for more information. 

For turbulent flow, the thermal entrance region is shorter than for laminar flow (with the exception of liquid metals which have a very low Prandtl number), and thus the fully developed values of the Nusselt number are frequently used directly in heat transfer design without reference to the thermal entrance effects. The turbulent fully developed Nusselt number in a smooth channel can be expressed as a function of the Reynolds number and of the Prandtl number. 

Conduction drying is usually carried out using hot cylinders, which are rotating metallic cans that are heated using steam or special heat-transfer liquids. When steam is used, the drying system is often referred to as steam cans, which are shown schematically in Figure 34.6. The energy requirements removed are typically around 4700 kJ/kg, which is usually lower than that of other thermal dryers. 

Film Heat Transfer Coefficient Value Most of the experimental data for liquid metals in forced convection have been obtained for round tubes. Since a large fraction of heat transfer to liquid metals in forced convection is by molecular and electronic conduction, the velocity and temperature distribution of the fluid in the channel is expected to have a noticeable effect. Until data are obtained for the reference channel, however, the data for round tubes is used with the equivalent diameter of the channel replacing the diameter of the tube. Most of the round tube data fall below the L.yon-Martinelli theoretical prediction, and therefore 85% of the Lyon-Martinelli Nusselt Number is used as the best average value in the range of Peclet Number of interest (500-1000). The factor shown in Table X represents the expected accuracy of experimental data. 

The furnaces are designed so that combustion of the fuel gas or liquid occurs around the reaction tubes. Temperatures of the combustion gases are often as high as 1200°C in the immediate vicinity of the tubes. Most heat is transferred by radiation, and the portion of the furnace in which the reaction tubes are located is often referred to as the radiant zone. The maximum permissible temperature for the metal in the tubes depends on the type of... 

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