Static mixers heat transfer

Since the static or motionless mixer promotes radial flow of both momentum and heat, it will significantly enhance the heat transfer rate. Figure 7-30 shows static mixer heat transfer packing installed in the tubes of a multitube heat exchanger. 

Static mixers are used ia the chemical iadustries for plastics and synthetic fibers, eg, continuous polymeri2ation, homogeni2ation of melts, and blending of additives ia extmders food manufacture, eg, oils, juices, beverages, milk, sauces, emulsifications, and heat transfer cosmetics, eg, shampoos, hquid soaps, cleaning Hquids, and creams petrochemicals, eg, fuels and greases environmental control, eg, effluent aeration, flue gas/air mixing, and pH control and paints, etc. 

Static mixing of gas—Hquid systems can provide good interphase contacting for mass transfer and heat transfer. Specific interfacial area for the SMV (Koch/Sulzer) mixer is related to gas velocity and gas holdup ( ) by the following ... 

Heat transfer in static mixers is intensified by turbulence causing inserts. For the Kenics mixer, the heat-transfer coefficient b is two to three times greater, whereas for Sulzer mixers it is five times greater, and for polymer appHcations it is 15 times greater than the coefficient for low viscosity flow in an open pipe. The heat-transfer coefficient is expressed in the form of Nusselt number Nu = hD /k as a function of system properties and flow conditions. 

The static mixer is also useful for direct contact heat transfer between fluids, nvo phase contacting, and other useful applications such as mass transfer. 

Static mixer length, in., or length of pipe in ft Thickness of heat transfer wall, ft Mass How rate, Ib/hr... 

L = Static mixer length, in., or length of pipe in ft IAt = Thickness of heat transfer wali, ft M = Mass flow rate, lb/hr m = Function of fluid properties, such as u, k and cp N, = Shaft speed of rotation, revolutions per second Ne = Newton number, depends on design NF = Force number, consistent units, dimensionless = F/(PN2D4)... 

To address these problems, Phoenix has manufactured bromonitromethane using continuous processing technology in a plant that was engineered to fit the chemistry. The bromination was carried out in low-volume static mixer tubes, allowing efficient heat transfer and accurate process control. 

Commercially available static mixer reactors (SMR) as large as 1.8 m in diameter are operating in the production of nylon, silicones, polystyrene, polypropylene, and other polymers. Removing heat from a highly exothermic reaction in a static mixer equipped with a simple cooling jacket is limited by heat transfer to small diameters, typically less than 6 in. A new type of static mixer has been developed to overcome laminar heat-flow transfer problems. It is called the SMR mixer-heater exchanger-reactor (Mutsakis et al, 1986). 

Visser, J.E., Rozendal, P.F., Hoogstraten, H.W. and Beenackers, A.A.C.M. (1999), Three-dimensional numerical simulation of flow and heat transfer in the Sulzer SMX static mixer, Chem. Eng. Sci., 54, 2491-2500. 

Because motionless mixers continuously interchange fluid between the walls and the center of the conduit, they also provide good heat transfer, especially with the twisted-element style of mixers. Sometimes, high-viscosity heat exchange is best accomplished with a static mixer. 

Static in-line mixers were developed for the intimate mixing of many mixtures, from solutions to heterogeneous mixtures (such as two immiscible liquids or gases in liquids) to viscous fluids, such as peanut butter [19], Commercial in-line mixers are tubes as small as 0.8 in. outside diameter by 6 in. long. Inside the tubes stationary elements are positioned to blend the components of the mixture in primarily a radial manner. By providing a reactor with a high surface-area-to-volume ratio, efficient heat transfer is allowed. Static mixers are used for reactions where good... 

Endothermic reactions, such as steam reforming, are usually carried out in long narrow tubes filled with catalysts and externally heated by flames. The heat could be provided more uniformly and more accurately at the necessary level by a combustion catalyst coated on the outside of the tubes, and heat transfer rates could be further improved by coating the endothermic reaction catalyst on the inner wall of the tube. In this way, the heat of combustion is transferred to the heat sink (the endothermic reaction) through the solid wall, avoiding solid-gas heat transfer resistances. However, the tubular geometry is not most efficient for this application because of the difficulty to coat the inside of the tubes and the need to include static mixers to facilitate mass transfer to the catalytic surfaces. 

Qi, Y. Kawaguchi, Y. Christensen, R.N. Zakin, J.L. Enhancing heat transfer ability of drag reducing surfactant solutions with static mixers and honeycombs. Int. J. Heat Mass Trans. 2003, 46, 5161-5173. 

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