Working Principle and Construction of Hot Air Oven

Let us see the meaning of a hot air oven and the key points to remember about a hot air oven.

From the name, it is pretty clear that this device uses hot or dry air, and it functions as an insulator chamber, in which the hot air moves continuously within the chamber. The killing action of a hot air oven depends upon the principle of heat conduction in which the dry heat first sterilizes the surface of an object and then the center.

Using a hot air oven, you can sterilize different articles or glasswares like test tubes, Petri plates, flasks, etc. Depending upon the volume of the content needed to be sterilized, the holding temperature ranges between 150 to 180 degrees Celsius. The holding time ranges between 20 to 150 minutes.

The mechanism of dry heat sterilization is the oxidation of the micro-organisms. The organisms are killed by oxidation. Hot air oven manufacturers make use of different materials and insulators to design the hot air oven. Hot air oven is specially designed for rubber industries, oil industries, manufacturing instruments, glassware industries, manufacturing metal equipment, manufacturing medical items, and more.

Construction

Now let us see the construction of a hot air oven by understanding its parts and functions.

Parts and their functions of hot air oven

1. Main Switch

2. Temperature Regulator knob

3. Timer

4. Heat Regulator Knob

5.Asbestos door jacket

6.Thermostat

7.Perforated aluminum tray

8. Double-walled insulated Chamber

1. Main switch - Switch on or switch off the device. The main switch contains a Green Light indicator that Indicates the device is switched on.

2. Temperature regulator knob - Regulates the temperature when you rotate the knob to the right or left.

3. Timer - Sets the time according to the desired temperature.

4. Heat regulator knob - Monitor the flow of heat.

5. Asbestos door jacket - Outer Double-walled door jacket which is made of glassware jacket. Thus, it confines heat within the chamber and also safeguards the instruments against heat damage.

6. Thermostat - This thermostat is placed at the top of the chamber, continuously monitoring the temperature inside.

7. Perforated aluminum tray - Articles like glassware, metals, etc., are kept on the perforated aluminum tray. The perforation allows uniform distribution of the heat to the articles that are kept inside.

8. Double-walled insulated Chamber - Insulates heat within the chamber.

Hence, these are all the parts and their functions of a hot air oven. And we can see that Hot air oven manufacturers designed it exquisitely.

Working principle of hot air oven

Now let's see how it works and how it destroys the micro-organisms. So you would have understood that a hot air oven depends upon dry heat sterilization, but you need to know how it functions or sterilizes the different objects or articles.

So, the hot air oven sterilizes the object via a heat conduction mechanism in which the heat within the chamber first sterilizes the object and then the center of the object.

Let us see how hot airflow inside the chamber:

The electric coil at the bottom of the hot air oven will allow the upward flow of the hot air. The hot air increases towards the top of the chamber, but once it comes in contact with the surface of the chamber, it goes down and moves down the chamber.

Therefore, the hot air flow inside the hot air oven is circular or uniform, which permits uniform heating throughout the chamber.

Description of hot air oven

The chamber or the inner portion of the hot air oven is made of aluminum or stainless steel. It is a double-walled structure. The inner portion of the double wall is filled with glass wool for insulation purposes.

The opening or the door of the hot air oven is made of asbestos. The lining in it prevents the escaping of dry air or hot air from the oven. This opening is also thick-walled, and the inner portion of this opening is filled with glass wool. Glass wool is a type of insulator made from glass filaments. Various Glasswares are placed on the shelves or trays for sterilization purposes.

The procedure to sterilize include:

● First, you need to clean and wash the glassware.

● Then wrap the glassware with aluminum foil.

● Now, place the glassware into the hot air oven and close the door.

● Start the oven by rotating the knob and setting the temperature.

● For an hour, the temperature is set to 160 degrees Celsius and 250 degrees Celsius for half an hour.

● Note the temperature value from the thermometer. Once it reaches the desired temperature, switch off the oven by rotating the knob anticlockwise.

● Now, remove the glassware from the oven carefully.

Practical uses of hot air oven

● Hot air ovens can sterilize metal equipment like scissors, spatula, forceps, etc.

● It is commonly used in practical labs or research labs to sterilize different articles to maintain aseptic conditions.

● As the hot air oven uses dry heat, it can also be used in baking, drying, and curing processes.

● Powders and Non-volatile compounds like sulphonamides, zinc, starch powder, etc., can also be sterilized in the hot air oven.

● Heat-stable glasswares made of a brute-like pipette, burettes, test tubes, flasks, etc., can also be sterilized using a hot air oven.

● A hot air oven is used for dry heat sterilization of glassware, powders, oils in pharmaceutical microbiology labs.

Advantages

● The operation and maintenance of the hot air oven are easy.

● It occupies minimal workspace because of its small size.

● It does not corrode the metal equipment like scissors, forceps, etc., as it uses dry heat.

Disadvantages

● The hot air oven is insufficient to kill the heat-resistant spores like endospores and organisms like prions.

● It can only sterilize the objects that are heat or thermostable.

Conclusion

A hot air oven is a sterilizing appliance that sterilizes many substances. It is used mainly for laboratory purposes and not for food processing purposes. Hence, Hot air oven manufacturers ensure that it stabilizes the operation.