Stirring heat transfer characteristic

Example 20 Heat transfer characteristic of a stirring vessel... 

The dimensional analysis performed with the dimensional system M, L, T, delivers, for the heat transfer characteristic of a stirring vessel, the following 6-para-metric pi-set ... 

In the optimization of stirrers for an optimal heat transfer, it may not be forgotten that the removable heat flow, Q [kW], increases according to the heat transfer characteristic with Re2/3 n2/3, whereas the thereby associated stirrer power (stirring heat)... 

Garg, R. Gattinara, A. Godbole, P. Ho, J. Roberts, M. Witulski, F. Shelukar, S. Reynolds, S. Heat transfer characteristics and performance of stirred media milling for pharmaceutical applications. Int. Fine Particle Res. Inst. Ann. Con. Holland, July 2000. 

In the laminar flow range Re < 10 the heat conduction dominates (which is periodically disturbed by the stirring device rotating past in the neighborhood of the wall) and the effect of density and viscosity disappears entirely. Then the following relationship applies for the heat transfer characteristic ... 

Many modifications to the basic stirred autoclave design have been made to improve its heat transfer characteristics those commonly used in polyolefin production processes include the use of external coolers, overhead condensers or internal cooling coils. 

The general characteristics of a batch reactor (BR) are introduced in Chapter 2, in connection with its use in measuring rate of reaction. The essential picture (Figure 2.1) in a BR is that of a well-stirred, closed system that may undergo heat transfer, and be of constant or variable density. The operation is inherently unsteady-state, but at any given instant, the system is uniform in all its properties. 

Maintenance of proper temperature is a major aspect of reactor operation. The illustrations of several reactors in this chapter depict a number of provisions for heat transfer. The magnitude of required heat transfer is determined by heat and material balances as described in Section 17.3. The data needed are thermal conductivities and coefficients of heat transfer. Some of the factors influencing these quantities are associated in the usual groups for heat transfer namely, the Nusselt, Stanton, Prandtl, and Reynolds dimensionless groups. Other characteristics of particular kinds of reactors also are brought into correlations. A selection of practical results from the abundant literature will be assembled here. Some modes of heat transfer to stirred and fixed bed reactors are represented in Figures 17.33 and 17.18, and temperature profiles in... 

Homopolymerization. The free-radical polymerization of VDC has been carried out by solution, slurry, suspension, and emulsion methods. Slurry polymerizations are usually used only in the laboratory. The heterogeneity of the reaction makes stirring and heat transfer difficult consequently, these reactions cannot be easily controlled on a large scale. Aqueous emulsion or suspension reactions are preferred for large-scale operations. The spontaneous polymerization of VDC, so often observed when the monomer is stored at room temperature, is caused by peroxides formed from the reaction of VDC with oxygen, fery pure monomer does not polymerize under these conditions. Heterogeneous polymerization is characteristic of a number of monomers, including vinyl chloride and acrylonitrile. 

In stirred-tank reactors, the characteristic time for heat transfer can be related to geometric parameters and fluid properties as follows ... 

To quantify the variation of dissipated mechanical power, the intensified reactor (subscript 2) operating at higher stirring speed is compared with the original reactor (subscript 1). The ratio of the characteristic heat-transfer times can then be expressed as follows ... 

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