By Ryan Strand Vice President of Operations at Wisconsin Oven Distributors
Recalling her experience in WW2, a nurse named Audrey wrote this about the unsanitary conditions she observed, “Limbs and torsos were encased in very thick, hastily applied plaster of Paris. In many cases, suppurating wounds and gangrene lay beneath.” The importance of sterilization was well known at the time, but not universally implemented. A few years later in 1947, the United States Pharmacopeia (USP) revised it’s chapter on sterilization to include the following instructions for dry heat sterilization: > 1 hour at > 170 °C.1
That same year, our German manufacture Memmert was commissioned by the Red Cross to create a simple hot air sterilizer to avoid the danger from infections and epidemics. Founder Willi Memmert used the science of thermostatics to develop an oven using recycled aluminum from old aircraft parts. The basic idea behind this development was simple — the accurate measurement and regulation of temperature.
For many years Memmert and Memmert USA have been manufacturing and distributing equipment to the United States. Everything we sell and service today — including climate & stability chambers, storage chambers, Peltier cooled units, water and oil baths, and vacuum ovens — is relatively simple and revolves around the basic principles of science incorporated into our thermostatic equipment. Thermostatics is the branch of science concerned with thermal equilibrium, “the condition under which two substances in physical contact with each other exchange no heat energy.”2 As technology has advanced and our product line has grown, the concepts underlying our equipment are still simple and are still based on science.
Vacuum Oven Science
For example, vacuum ovens are used in various industries for drying powders, curing epoxy coatings, and extracting moisture or chemicals from implants that go into the human body. The simple scientific principle in play is the combination of temperature and pressure. In order for something to dry, moisture must evaporate or turn from liquid into gas. If the pressure on an object is decreased below atmospheric levels, as occurs in a vacuum oven, water can evaporate at a lower temperature which means that it dries faster. It also makes it possible to pull moisture out of places where it is trapped.
Why does the vacuum oven work so well? Imagine you have a sponge in your hand saturated with water and you want the sponge to be dry. There are several ways you can do this.
- Let the sponge sit out in ambient conditions. The water will evaporate naturally and eventually the sponge will be dry. This method takes the most time.
- Dry the water out of the sponge using heat alone, as would happen in a residential clothes dryer or a standard Memmert oven. This method is faster than the first one, but not the fastest method possible.
- Squeeze the water out of the sponge and heat the sponge so that it becomes completely dry. This is the quickest method.
Option three is how a vacuum oven works on an object placed inside the unit. The object is heated when it is placed on the thermoshelf and the moisture is squeezed out of it when the pump draws the pressure down to a certain level inside the chamber. Simple science.
Finally, there is the question about what happens to the moisture after it is removed from the object in the vacuum oven. Looking at the wet sponge again, if you tried to dry it by putting it in a bucket and squeezing the sponge, the water would soak right back into it if you didn’t remove the water from the bucket. Similarly, the water from the object in the vacuum oven goes into the atmosphere of the oven. If it’s not removed using a purge cycle, it will cook in its own moisture or remain saturated. Once again, it’s simple science that tells us moisture must have a place to go once it is removed from an object.
Climate Chamber Science
A second example of simple science can be found in climate chambers. A climate chamber, or environmental test chamber, “artificially replicates conditions which machinery, materials, devices or components might be exposed to. It is also used to accelerate the effects of exposure to the environment”.3 What is the science behind a climate chamber? It is the combination of temperature and humidity. Today we can control the humidity inside our climate chambers from 10% to 98% relative humidity.
Why would you want to test objects inside of a climate chamber at various temperatures and levels of humidity? An object placed in a chamber at a specific temperature, humidity level, and time period will have different characteristics if the conditions of temperature, humidity and time are changed. You can also test how the chemical makeup of objects changes if the temperature and humidity are continuously changing. These studies are particularly useful in understanding how a product might break down or change over time. It’s simple science.
The effects of temperature and humidity can be observed with items placed outside for extended periods of time. In early autumn, people visit pumpkin patches and select the best ones to bring home. A pumpkin is at its freshest when it is first displayed on the front porch. If the fall is cold, as it usually is in Wisconsin, with slightly below average temperatures and relatively low humidity, the pumpkins can be displayed for a long period of time without molding, rotting or breaking down. The change in temperature and humidity levels dictate how long the pumpkin will last. If fall is warm and humid, or if there are multiple changes in the temperature and humidity, the pumpkin won’t last quite as long. It is simple science.
Every object on earth today has a life expectancy and will break down over time. The life expectancy of objects can be simulated and tested inside Memmert climate chambers. You can create multiple different temperature and humidity levels for long or short periods of time. Or you can add different ramp rates to simulate actual or extreme conditions and observe the effects on the object over time. You can add light to simulate day and night. Eventually over time the item will change and will breakdown. These experiments can be performed on anything from car tires to CDs to food. It is simple…It is science.
Everything that we do today in the thermostatic industry is based on science. When a customer has a question or cannot figure out why something is not working properly we fall back on the simple principles of science: temperature, atmosphere, humidity, pressure, condensation, or a combination thereof.