Heat transfer, direct contact

One disadvantage of fluidized heds is that attrition of the catalyst can cause the generation of catalyst flnes, which are then carried over from the hed and lost from the system. This carryover of catalyst flnes sometimes necessitates cooling the reactor effluent through direct-contact heat transfer hy mixing with a cold fluid, since the fines tend to foul conventional heat exchangers. 

While a superstructure based on the structure in Fig. 16.26 allows for many structural options, it is not comprehensive. Wood, Wilcox, and Grossmanr showed how direct contact heat transfer by mixing at unequal temperatures can be used to decrease the number of units in a heat exchanger network. Floudas, Ciric, and Grossman showed how such features can be included in a heat exchanger network superstructure. Figure 16.27 shows the structure from Fig. 16.26 with possibilities for direct contact heat transfer included. In the... 

Figure 16.27 Possibilities for direct contact heat transfer can be added to the superstructure.

This section describes equipment for heat transfer to or from solids by the indirect mode. Such equipment is so constructed that the solids load (burden) is separated from the heat-carrier medium by a wall the two phases are never in direct contact. Heat transfer is by conduction based on diffusion laws. Equipment in which the phases are in direct contact is covered in other sections of this Handbook, principally in Sec. 20. 

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

The spray-filled tower, Figure 9-100, is also an atmospheric type, containing no fill other than the water sprays and no fans. The water-air contact comes about due to the spray distribution system [144], This design is often used where higher water temperatures are allowed, and the situations where excessive contaminants building up in the water would cause fouling of other direct contact heat transfer surfaces. 

Example 10-26. Determine Contact Stages Actually Required for Direct Contact Heat Transfer in Plate-Type Columns... 

John C. Berg, Andreas Acrivos, and Michel Boudart, Evaporation Convection H. M. Tsuchiya, A. G, Fredrickson, and R. Aiis, Dynamics of Microbial Cell Populations Samuel Sideman, Direct Contact Heat Transfer between Immiscible Liquids Howard Brenner, Hydrodynamic Resistance of Particles at Small Reynolds Numbers... 

Figure 19.5 Nonisothermal mixing carries out direct contact heat transfer.

H. M. Tsuchiya, A. G. Fredrickson, and R. Aris Direct Contact Heat Transfer between Immiscible Liquids... 

The design of devices to promote cocurrent drop flows for heating or cooling a two-phase system, or for direct-contact heat transfer between two liquids, is difficult. The study by Wilke et al. (W7) is typical of the approach frequently used to analyze these processes. Wilke et al. described the direct-contact heat transfer between Aroclor (a heavy organic liquid) and seawater in a 3-in. pipe. No attempt was made to describe the flow pattern that existed in the system. The interfacial heat-transfer coefficient was defined by... 

Nuclear accident scenarios, direct contact heat transfer in, 13 268 Nuclear age, 25 391 Nuclear applications hafnium, 13 89 nitrides in, 17 219... 

Direct Contact Heat Transfer between immiscible Liquids Samuel Sideman... 

Data of direct contact heat transfer are not abundant. The literature has been reviewed by Fair (1972) from whom specific data will be cited. 

The principles of direct-contact heat transfer, treated in the discussions to follow, are presently almost exclusively applied to water cooling and humidification of air. It should be noted, however, that these very same principles can be applied to the cooling or heating of just about any insoluble gas or liquid. 

Distillation and gas absorption are the prime and most common gas-liquid mass-transfer operations. Other operations that are often performed in similar equipment include stripping (often considered part of distillation), direct-contact heat transfer, flashing, washing, humidification, and dehumidification. 

When one is dealing with direct contact heat transfer, the corresponding terms are hLa and hca. Here the driving force is the temperature difference. The L subscript means that we are dealing with a liquid-limited process such as condensing a pure liquid. How to convert kLa data to an hLa value is illustrated by Example 23. 

Converting Liquid Mass-Transfer Data to Direct Contact Heat Transfer Liquid-limited performance measures are much more commonly given for mass-transfer than for heat transfer. Often mass-transfer data are reported as kLa with units of h-1. This can be converted to hLa with units of Btu/(h°F-ft3) by Eq. (14-188). 

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