Spiral baffle, jacket with

At a given Reynolds number, heat transfer coefficients of coils, particularly with turbulent flow, are higher than those of long, straight pipes, due to friction. This also applies to flow through an annular jacket with spiral baffling. 

A jacketed, agitated reactor consists of a vertical cylinder 1.5 m diameter, with a hemispherical base and a flat, flanged, top. The jacket is fitted to the cylindrical section only and extends to a height of 1 m. The spacing between the jacket and vessel walls is 75 mm. The jacket is fitted with a spiral baffle. The pitch between the spirals is 200 mm. 

Annular jacket with 210 < NRe <10,000 spiral baffling Use the above equations depending on the value of NRe. 

Chapter 7, Reactor Design, discusses continuous and batch stirred-tank reactors and die packed-bed catalytic reactor, which are frequently used. Heat exchangers for stirred-tank reactors described are the simple jacket, simple jacket with a spiral baffle, simple jacket with agitation nozzles, partial pipe-coil jacket, dimple jacket, and the internal pipe coil. The amount of heat removed or added determines what jacket is selected. Other topics discussed are jacket pressure drop and mechanical considerations. Chapter 7 also describes methods for removing or adding heat in packed-bed catalytic reactors. Also considered are flow distribution methods to approach plug flow in packed beds. 

Figure 7.3 compares calculated overall heat-transfer coefficients for several reactor heat exchangers, using water for both the jacket and reactor fluid. The figure shows that the highest heat-transfer coefficient is obtained with internal coils and the lowest with the simple jacket (called the conventional jacket in Figure 7.3) without a spiral baffle or agitation. It is assumed that the flow rate for the internal coil is the coil flow rate and not the jacket flow rate, as plotted in Figure 7.3. Heat-transfer coefficients for the half-pipe coil, agitated, and baffled jackets are conparable.

This design is a variation of the conventional jacket. The internal, spiral baffle allows for high flow velocities to be reached. Some clearance must be allowed for between the baffles and the inside of the jacket, to allow for assembly, fabrication and tolerances. Although this clearance may be small, the total leakage area per baffle turn may be substantial when compared with the cross sectional flow area of the baffle passage. Thus, the actual velocity may only be a fraction of the calculated value. To compensate for this leakage around the baffles it is recommended that a 10% allowance be applied to either the total area required or total heat required. 

For design purposes, the half pipe coil and conventional jackets with spiral baffles are treated as coils. This procedure converts the shape of the passageway into an equivalent diameter pipe coil. 

Figure 2-48. Types of Jacket Construction (a) Plain Jacket (b) Jacket with Spiral Baffle (c) Pipe Coil Welded to Shell...

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