Heat transfer surface jackets

Commonly used heat-transfer surfaces are internal coils and external jackets. Coils are particularly suitable for low viscosity Hquids in combination with turbine impellers, but are unsuitable with process Hquids that foul. Jackets are more effective when using close-clearance impellers for high viscosity fluids. For jacketed vessels, wall baffles should be used with turbines if the fluid viscosity is less than 5 Pa-s (50 P). For vessels equipped with cods, wall baffles should be used if the clear space between turns is at least twice the outside diameter of the cod tubing and the fluid viscosity is less than 1 Pa-s (10... 

The flow of heat across the heat-transfer surface is linear with both temperatures, leaving the primaiy loop with a constant gain. Using the coolant exit rather than inlet temperature as the secondaiy controlled variable moves the jacket dynamics from the primaiy to the secondaiy... 

The fluidfoil impellers (shown in Fig. 18-2) usually give more flow for a given power level than the traditional axial- or radial-flow turbines. This is also thought to be an advantage since the heat-transfer surface itself generates the turbulence to provide the film coefficient and more flow should be helpful. This is true to a limited degree in jacketed tanks (Fig. 18-34), but in helical coils (Fig. 18-35), the... 

Scraped-Surface Crystallizer For relatively small-scale apph-cations a number of ciystallizer designs employing direct neat exchange between the shiny and a jacket or double wall containing a cooling medium have been developed. The heat-transfer surface is scraped or agitated in such a way that the deposits cannot build up. 

The factors that can affect the rate of heat transfer within a reactor are the speed and type of agitation, the type of heat transfer surface (coil or jacket), the nature of the reaction fluids (Newtonian or non-Newtonian), and the geometry of the vessel. Baffles are essential in agitated batch or semi-batch reactors to increase turbulence which affects the heat transfer rate as well as the reaction rates. For Reynolds numbers less than 1000, the presence of baffles may increase the heat transfer rate up to 35% [180]. 

Figure 17.19. Reactors for the oxidation of sulfur dioxide (a) Feed-product heat exchange, (b) External heat exchanger and internal tube and thimble, (c) Multibed reactor, cooling with charge gas in a spiral jacket, (d) Tube and thimble for feed against product and for heat transfer medium, (e) BASF-Knietsch, with autothermal packed tubes and external exchanger, (f) Sper reactor with internal heat transfer surface, (g) Zieren-Chemiebau reactor assembly and the temperature profile (Winnacker- Weingartner, Chemische Technologie, Carl Hanser Verlag, Munich, 1950-1954).

The flow of heat across the heat-transfer surface is linear with both temperatures, leaving the primary loop with a constant gain. Using the coolant exit temperature as the secondary controlled variable as shown in Fig. 8-55 places the jacket ( mamics in the secondary loop, thereby reducing the period of the primary loop. This is dynamically advanti reous for a stirred-tank reactor because of the slow response of its large heat capacity. However, a plug flow reactor cooled by an external heat exchanger lacks this heat capacity and requires the faster response of the coolant inlet temperature loop. 

Heat transfer surfaces—helical coils, harp coils, or platecoils—are often installed inside the vessel and jackets (both side wall and bottom head) so that the vessel wall and bottom head can be used as heat transfer surfaces. Figure 10.1 gives a suggested geometry for helical coils and harp coils. 

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