How To Solve The Problem With Wet Loads


ζ = dryness fraction

ww = mass of water flow (kg, or lb / unit time)

ws = mass of steam (kg or lb / unit time)

If the water content of the steam is 5% by mass, then the steam is said to be 95% dry and has a dryness fraction of 0.95.….(satisfactory dryness fraction is .97)

Once you’ve established that the steam supply is not the source (of excess condensate), it’s time to look more closely at what is being loaded into the vessel, the design of the sterilizer itself and perhaps the operation of the autoclave.
Another common cause of wet loads is the load itself. However tempting it may be to pack the chamber full of product in order to keep up with demand, dense packing is frequently a cause of excessive condensation which cannot then be completely flashed off by subsequent steam injections. Large quantities of hard-goods or even complex packaging can make proper steam circulation a challenge.
Steam enters the chamber and contacts the product, it is essential that the steam collapse (condense) on the product in-order for the heat to be released to the load. But ultimately the water formation must be discharged through condensate management or re- vaporized in order to prevent contamination of the product. Removal of the excess water is crucial to prevention of insulating the load from the steam. That said, too much steam, at too fast a rate can result in excessive water formation which might overwhelm or “swamp” steam traps. Be sure that your steam traps are properly sized.
To “dry” the load after the fact, many users are tempted to employ excessively long deep vacuums at the end of the cycle. Because the chamber is heated (via the jacketing) and the fact that water will “flash off” into steam at a lower temperature under vacuum, this is relatively successful. But what ultimately results is an unnecessarily long cycle time, and potentially a non-sterile load as water can collect in areas, and insulate the intended product from achieving temperature. Deep post-sterilization vacuum “drying” phases are like “closing the barn door after the horses escaped.”
When we are asked to assist under these conditions, we typically look to prevent (or greatly reduce) the formation of condensate by making sure that the load itself is brought up to a certain temperature prior to the introduction of steam.