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*Values listed are for moderate nonproximity agitation. CS = carbon steel.

*Values listed are for moderate nonproximity agitation. CS = carbon steel.

In Eqs. (11-53a) and (11-53&), NRe is based on particle diameter and superficial fluid velocity.

Zenz and Othmer (see "Introduction: General References") give an excellent summary of fluidized bed-to-wall heat-transfer investigations.

Solidification involves heavy heat loads transferred essentially at a steady temperature difference. It also involves the varying values of liquid- and solid-phase thickness and thermal diffusivity. When these are substantial and/or in the case of a liquid flowing over a changing solid layer interface, Siegel and Savino (ASME Paper 67-WA/Ht-34, November 1967) offer equations and charts for prediction of the layer-growth time. For solidification (or melting) of a slab or a semi-infinite bar, initially at its transition temperature, the position of the interface is given by the one-dimensional Newmann's solution given in Carslaw and Jaeger (Conduction of Heat in Solids, Clarendon Press, Oxford, 1959).

Later work by Hashem and Sliepcevich [Chem. Eng. Prog., 63, Symp. Ser. 79, 35, 42 (1967)] offers more accurate second-order finite-difference equations.

The heat-transfer rate is found to be substantially higher under conditions of agitation. The heat transfer is usually said to occur by com-

TABLE 11-8 External Coils; Typical Overall Coefficients*

TABLE 11-8 External Coils; Typical Overall Coefficients*

Type of coil

Coil spacing, in.T

Fluid in coil

range, °F.

m without cement

U with heat-transfer cement

r in. o.d. copper tubing attached

0 0

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