II notice your with your dryer that you apply the principal of lowering the boiling point of water by reducing the atmospheric pressure. This is ok but two points:
- You are using hot moist air to convey the material to the process from the dryer.
- Nothing is actually sweeping the moisture from the granule chamber at the reduced pressure. Unless you continually circulate fresh air at the reduced pressure through the drying vacuum chamber.
Can you tell me what dew point you were able to reach for polyethyleneterephthalate. granules, and in particular have you recorded results in the tropics where ambient air is at 30 celsius with near 100% relative humidity? (i.e. some days the ability of the air even at elevated temperatures to have greater moisture content is at best poor.)
Thank you for your inquiry into our vacuum dryer. Keep in mind that vacuum has been used to dry resin for decades. Many industries use vacuum to dry materials (food, pharmaceuticals, chemicals). Some resin manufacturers use vacuum to dry material prior to being packaged in sealed bags and shipped to processors. They use very large vacuum vessels to dry thousands of kilos of material at a time. We have developed a dryer that is practical, affordable and easy to use for any processor of plastic. It is correct that we are using hot, moist air to elevate the temperature of the resin. The theory is when vacuum is applied at a minimum of 25 inches or 635 mm of mercury, all moisture in the vacuum chamber vaporizes. The moisture vapor must be "swept" from the chamber. We have developed a proprietary purging technique which removes the moisture from the vacuum chamber. Since desiccant is not used, dew point has nothing to do with how resin dries in a vacuum dryer. The key criteria to vacuum drying are temperature and proper level of vacuum for an appropriate period of time. Our testing shows that once the pellets are at the proper temperature, 20 minutes of vacuum is sufficient to reach material supplier recommended levels of moisture. We have tested the unit in fully saturated air simulating 100% humidity and have found that it has little or no affect on the performance of the dryer. We are drying in a vacuum so ambient conditions have no affect.
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