Half-welded coils

For the calculation of the heat transfer coefficient of the external film, some models are also available [2], describing the hydraulics of the flow in the jacket or in the half-welded coils. The results depend strongly on the technical design of the equipment. Thus, the direct experimental determination is mostly preferred. 

B - Cast iron vessel with integral steel tubes C - Welded helical coil with intercolated copper plates D - Welded half pipe coil... 

The outside coefficient, ho, is quite low for water in a simple open jacket. It can be increased by using agitation nozzles, a spiral baffle in the jacket, or a half-pipe coil welded to the tank [1,2]. The wall resistance is usually negligible for a steel tank, but it may be significant for a thick stainless steel wall or for a glass-lined reactor. 

This design is not used frequently due to the minimal contact area between the shell and coil. It does however alleviate one of the problems of constructing a half-pipe coil. That is the cutting of the coils in half and the subsequent wastage. Some techniques have been developed to form flat ships into half pipe coils to save wastage and labor. There is just as much welding required for attaching a full pipe coil as there is with the half pipe. 

Spiral Half Pipe Coil welded to the shell... 

The heat exchange area (A) may vary with time due to the volume increase by the feed. This variation is determined by the geometry of the reactor, especially by its height covered by the heat exchange system (jacket, internal coils, or welded half-coils). In case there is a significant change in the physical chemical properties of the reaction mixture, the overall heat exchange coefficient (U) will also be a function of time. 

Preparation of ethyl monochloride. Ethyl monochloride is synthesised (Fig. 107) in synthesis reactor 1, which is a steel cylindrical enameled apparatus with a welded spherical bottom and removable lid, fashioned with cooling coil 4 and an agitator. There are two synthesis reactors 1. They operate ahead of each other by the time equal to half of the duration of the whole operation. 

Welding of supports shall not be half complete before loading in internals such as trays, tower packings, catalysts on trays, internal cooling coils, and provision of external fittings and connecting gas and liquid pipes. 

Figure 4.10.23 Typical devices for cooling stirred tank reactors (a) double jacket, (b, c) half or full pipe welded on external surface, and (d) internal coil. Adapted from Dittmeyer et o/. (2003).

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