Dimpled jackets

P). Otherwise the baffles should be located iaside the cod helix. A conventional jacket consists of a vessel outside the main vessel with a gap for the flow of heat-transfer fluid. Half-pipe jackets are usefld for high pressures up to 4 MPa (600 psi). They are better for Hquid than for vapor service fluids and can be easdy 2oned. Dimple jackets are suitable for larger vessels and process conditions up to 2 MPa (300 psi) and 370°C. Internal cods can be either hehcal or baffle cods (Fig. 34). 

The half-pipe jacket is used when high jacket pressures are required. The flow pattern of a liquid heat-transfer fluid can be controlled and designed for effective heat transfer. The dimple jacket offers structural advantages and is the most economical for high jacket pressures. The low volumetric capacity produces a fast response to temperature changes. 

The equivalent diameter D,. in a dimpled jacket equals 0.66 m. the cross-sectional flow area equals 1.98 m." per foot of vessel circumference. 

Figure 12.72. Jacketed vessels, (a) Spirally baffled jacket (b) Dimple jacket (c) Half-pipe jacket (d) Agitation...

Dimpled jackets are similar to the conventional jackets but are constructed of thinner plates. The jacket is strengthened by a regular pattern of hemispherical dimples pressed into the plate and welded to the vessel wall, Figure 2.12b. 

In dimpled jackets a velocity of 0.6 m can be used to estimate the heat transfer coefficient. A method for calculating the heat transfer coefficient for dimpled jackets is given by Makovitz (1971). 

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. 

The jacket temperature, Tj, in Equation 7.4.8, equals the average of the jacket inlet and outlet temperatures. For a coil also use the average of the inlet and outlet temperatures. First, determine if there is sufficient heat-transfer area by assuming a simple jacket. The area of fire jacket is given in Table 7.3. The area will be about the same for simple, pipe coil, and dimple jackets. If the jacket area is insufficient, then determine if coils will provide the additional surface area. The reactor volume should be compensated for the volume occupied by the coils. 

Jackets may be of several types dimpled jackets, patterned plate jackets, and half-pipe coil jackets. Jacketed evaporators are used when the product is somewhat viscous, the batches are small, good mixing is required, ease of cleaning is important, or when glass-lined steel equipment is required. 

Dimpled jacket A dimpled jacket consists of an outer shell having regular indentations of the shell material. These dimples are intended to promote turbulence by creating high local velocities at the dimple. Heat-transfer information concerning dimple-jacketed vessels are proprietary to the fabricators there is a little information in the open literature [77], Other devices There are other special devices such as clamp-on plate coils, weld-on plate coils, etc., that are often used when an unjacketed vessel needs limited heat-transfer capability. 

A reactor is operated according to the system schematic shown in Figure 9.54. Boiling of the carrier that is condensed out of the vapor provides most cooling, and both condensate and uncondensed gas are recycled to the reactor. This reactor has a dimpled jacket. Calculate the heat duty of the jacket under the given conditions. 

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