Cooling Cycle times

With the cooling capability of water, cooling cycle times can be reduced in the WAIM and the crystalhzation occurs difficultly at the process condition. 

Shorter cycle times produce smaller bed sizes. The minimum cycle time is usually dictated by the minimum regeneration time required to heat and cool the bed. Systems of greater than two beds provide some flexibiUty in regeneration time but add to investment costs. 

Extrusion blow moulding of bottles has been successfully accomplished in reeent years by attention to the points mentioned above. It is to be noted here that UP VC has a much lower average specific heat between the proeessing temperature and room temperature than polyethylene and, being essentially amorphous, no latent heat of fusion. This leads to much less heat needing to be removed on cooling of mouldings and very short cycle times are possible. 

Assume that in Example 7-10, the overall cycle time for a batch reaction is 8 hrs. The cycle time will include 2 hrs for heat-up and 3 hrs for cool-down. The batch will be heated from 20°C to the reaction temperature of 60°C, then cooled to 35°C. Using a hot-water jacket temperature of 80°C, it took 15 min to heat the batch from 20°C and 30°C. Calculate the jacket temperatures required for heat-up and cool-down. 

Since any background heaters must now be allowed to operate during the cooling cycle their control must be set below the lower limit for the conditioned space. Interlock with the main plant may be included. These features should be checked and noted at this time. 

The cycle time is controlled by the heating and cooling rates, which in turn depend on the following factors the temperature of the heaters and the cooling medium, the initial temperature of the sheet, the effective heat transfer coefficient, the sheet thickness, and thermal properties of the sheet. 

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