Liquid-metals heat transfer coefficients

Lyon, R. E., 1955, Liquid Metal Heat Transfer Coefficient, Trans. AIChE47 75-79. (4)... 

R. N. Lyon, Liquid-Metal Heat Transfer Coefficients, Chem. Eng. Progr. 47(2), 75-79 (1951). 

Temperature difference metal surface to boiling liquid (K) Heat transfer coefficient metal surface to boiling liquid (kW/m2 K)... 

A liquid boils at 340°K on the inside of a metal surface heated by condensing steam on the outside (constant steam to metal heat transfer coefficient of 11 kW/m °K). The metal s thickness is 3 mm, and its thermal conductivity is 42 W/m °K. The inner heat transfer coefficients (i.e., metal surface to boiling liquid) are functions of the temperature differences (metal to boiling liquid) as shown below ... 

Gauges used for measuring the liquid level in vessels may be of semitransparent and even nontransparent materials. Figure 3.2 illustrates a simple level gauge on a steel vessel used for liquid ammonia storage. As shown, a narrow strip of insulation is taken away from the vessel s shell to expose the bare metal. Consequently, the heat transfer coefficient from the... 

An organic liquid is boiling at 340 K on the inside of a metal surface of thermal conductivity 42 W/m K and thickness 3 mm. The outside of the surface is heated by condensing steam. Assuming that the heat transfer coefficient from steam to the outer metal surface is constant at 11 kW/m2 K, irrespective of the steam temperature, find the value of the steam temperature to give a maximum rate of evaporation. 

For liquid metals the superiority of nucleate boiling heat transfer coefficients over those for forced-convection liquid-phase heat transfer is not as great as for ordinary liquids, primarily because the liquid-phase coefficients for liquid metals are already high, and the bubble growth period for liquid metals is a relatively short fraction of the total ebullition cycle compared with that for ordinary fluids. In the case of liquid metals, the initial shape of the bubbles is hemispheric, and it becomes spherical before leaving the heating surface. This is because of very rapid... 

Summary of experimental data Film boiling correlations have been quite successfully developed with ordinary liquids. Since the thermal properties of metal vapors are not markedly different from those of ordinary liquids, it can be expected that the accepted correlations are applicable to liquid metals with a possible change of proportionality constants. In addition, film boiling data for liquid metals generally show considerably higher heat transfer coefficients than is predicted by the available theoretical correlations for hc. Radiant heat contribution obviously contributes to some of the difference (Fig. 2.40). There is a third mode of heat transfer that does not exist with ordinary liquids, namely, heat transport by the combined process of chemical dimerization and mass diffusion (Eq. 2-162). 

The overall heat transfer coefficient is normally made up of several terms arising from the various resistances to the flow of heat. In the simple example mentioned above, there will be terms for heat transfer through the liquid by conduction and convection, for conduction through the metal wall of the tank and through any layers of insulating material and for heat loss from the outer skin to the surrounding air. 

Traditionally, production of metallic glasses requires rapid heat removal from the material (Fig. 2) which normally involves a combination of a cooling process that has a high heat-transfer coefficient at the interface of the liquid and quenching medium, and a thin cross section in at least one-dimension. Besides rapid cooling, a variety of techniques are available to produce metallic glasses. Processes not dependent on rapid solidification include plastic deformation (38), mechanical alloying (7,8), and diffusional transformations (10). 

Heat exchangers may be termed, for example, a condenser (where condensing a process vapor) or an evaporator (where vaporizing a liquid), and they are, of course, designed with a variety of metals and alloys having high heat-transfer coefficient U values, such as copper-based alloys. 

Extensive data on liquid metals are given in Ref. 13, and the heat-transfer characteristics are summarized in Ref. 23. Lubarsky and Kaufman [14] recommended the following relation for calculation of heat-transfer coefficients in fully developed turbulent flow of liquid metals in smooth tubes with uniform heat flux at the wall ... 

Liquid metals constitute a class of heat-transfer media having Prandtl numbers generally below 0.01. Heat-transfer coefficients for liquid metals cannot be predicted by the usual design equations applicable to gases, water, and more viscous fluids with Prandtl numbers greater than 0.6. Relationships for predicting heat-transfer coefficients for liquid metals have been derived from solution of Eqs. (5-38a) and (5-38b). By the momentum-transfer-heat-transfer analogy, the eddy conductivity of heat is = k for small IVp,. Thus in the solu-... 

Product Quality Considerations of product quality m require low holdup time and low-temperature operation to avoid thermal degradation. The low holdup time eliminates some types of evaporators, and some types are also eliminated because of poor heat-transfer characteristics at low temperature. Product quality may also dictate special materials of construction to avoid metallic contamination or a catalytic effect on decomposition of the product. Corrosion may also influence evaporator selection, since the advantages of evaporators having high heat-transfer coefficients are more apparent when expensive materials of construction are indicated. Corrosion and erosion are frequently more severe in evaporators than in other types of equipment because of the high liquid and vapor velocities used, the frequent presence of solids in suspension, and the necessary concentration differences. 

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