Half-pipe 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. 

To reduce the pressure drop, a batch reactor with a half-pipe jacket of length L and flowrate W can be partitioned into a two-zone jacket, each with a length L/2 and each supplied with W jacket flowrate. This doubles the jacket flow at a lower pressure drop in each zone. The flow in each zone can then be increased to increase the outside and overall heat transfer coefficients, which is similar to those of the single-zone jacket. 

Half-pipe jackets are formed by welding sections of pipe, cut in half along the longitudinal axis, to the vessel wall. The pipe is usually wound round the vessel in a helix Figure 12.72c. 

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

Heat transfer rate required select a spirally baffled or half-pipe jacket if high rates are required. 

If the larger reactor has a larger size half-pipe jacket, the jacket flow... 

The size of the half-pipe jacket is identical at both scales, that is, k = 1.0... 

So, half-pipe jackets would be used for high pressure. 

Vertical Vacuum Pan Dryers. The agitated vertical dryer (Fig. 3.) has been designed for drying many different products which may come from centrifuges or filters. Generally, the body is formed by a vertical cylindrical casing with a flat bottom flanged to the top cover head. The unit is fully heated by an outside half-pipe jacket welded on the cylindrical wall, the bottom and the top head. 

They are cheaper than the half pipe jacket for low internal pressures. 

For either a dimple jacket design or a half pipe jacket, the pressure drop will be higher flian that of an equivalent conventional jacket, due to flie increased turbulence. 

---