Cooling down rate

Mechanical Failures Cracks or debonding of the catalyst from the substrate material can occur from thermal stresses as well as dynamic forces on the modules. The catalyst must be carefully handled to prevent premature fracturing. Each requires a warm-up and cool-down rate. 

The modeling of residual stress development during cure can be used to optimize the processing conditions to reduce or control residual stresses. The current process model is used next to assess the effects of several processing conditions on residual stresses. Reduced cure temperature, longer dwell times, slower cool down rate, and the use of novel cure cycles are all feasible for the reduction of residual stresses. 

Cool slowly at Cool-down Rate to End Cure Temperature... 

Start up of a jacketed batch reactor requires control of the heat-up and cool-down rates. This involves determining and setting the jacket heat transfer fluid temperatures. An alternative is to make a trial heat-up and incorporate the results into a time-dependent heat transfer equation ... 

The amount of the applied adhesive and the final bond line thickness must be monitored because they can have a significant effect on joint strength. Curing conditions should be monitored for pressure, heat-up rate, maximum and minimum temperatures during cure, time at the required temperature, and cool-down rate. The primary concerns are to ensure the following ... 

Heat transfer coefficients as high as 300 Btu/hr-ft - F and average heat transfer rates as high as 30,000 Btu/hr-ft were observed during cool-down of our experimental transfer line. The equivalent cool-down rates are limited by the capacity of the system for venting cool-down gas rather than by the heat transfer. It is possible that heat transfer rates could limit the cool-down rate during even a faster cool-down. 

Cure Heat-up (maximum heat-up rate) dwell (time, pressure, temperature) cure (minimum time, pressure, temperature) cool-down (max. cool down rate) tolerances maximum demoulding temperature... 

Cool down rate After the product has been held at the proper temperature for the proper period of time, which will depend on the type of material used, the rate at which the product is cooled is also important. In general, slower cooldown rates will minimize warpage and residual stress in the finished product. However, slower cooldown rates can adversely impact productivity, so a reasonable balance must be identified. In many cases, a slow cooldown through the Tg of the resin system, followed by a somewhat faster cooling rate after the product cools below Tg, represents a good balance of performance and productivity. 

Operation of the system is consistent with reactor coolant system cool down rate limits and consistent with maintaining the component cooling water below design limits during cool down. 

Although two independent trains of ICs are considered as the reference configuration for the Canadian SCWR concept, the required capacity of the ICs varies as the reactor is cooled to prevent mmecessaiily rapid cooling rates. The current two-train configuration may not allow plant operators to adequately control the cool-down rate and would require further subdivision into four independent trains, with one train attached to each of the reactor outlets. Details on the configuration will be established in future design phases. 

The actual cool-down time required is about 65 hr or about 4 K/hr. The 65 hr becomes limited by the refrigerator at lower temperatures, which is a built-in safety feature. The refrigerator and cool-down rate are well matched. 

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