Hot Air Sterilizer Oven Principles

Hot air sterilizer Hot air or oven is a device in use to sterilizing items that moist should not penetrate. That is items that will damage by exposure to moist heat. Such items include powders, sharp instruments and petroleum products etc. In other words, we use dry heat sterilization for articles for which other methods such as using autoclave are not good. At the same time, hot air ovens are in use for articles that can withstand high temperature.

Hot Air Sterilizer Description
There are two types of hot air oven. One type is electrical home appliance for baking and the other is used in sterilization. In this text, we have more in hot air oven sterilizer. It finds uses in laboratory, pharmacy and in surgery. The oven uses dry heat to sterilize articles. Temperature range for this device is from 50 to 300 °C (122 to 572 °F). It has double wall insulation which keeps the heat in and conserves energy. However, the inner layer is a poor conductor and outer layer is metallic.
However, the internal wall is isolated from the external wall by insulating material which keeps internal high temperature conditions and delays the transfer of heat to the outside.
There is also an air filled space in between to aid insulation. An air circulating fan helps in uniform circulation of the heat. The inner space contains adjustable wire mesh plated trays or aluminium trays and may have an on/off rocker switch. The capacities of these ovens vary. Most hot air sterilizers receives power from electricity. This is either 220 v, 50 Hertz or 110 v, 50 Hertz  depending on the country
Hot Air Sterilizer Principles

The oven produces heat through sets of resistance heating elements, The heat  energy is being transferred to the chamber by natural means as well as by forced convection if there is a fan. The heating elements are located in the at the bottom of the oven

In order to use the sterilizer/oven, first activate the main switch, press the button or dial the knob to set the oven temperature and set the sterilizing timer. The inner chamber of the sterilizer will heat up till the oven reach the set temperature. When the sterilizer reached the set temperature, a thermostat activates the timer and the timer begins to countdown until it reach the set time. At this time, it switch off power to the heating elements. However, the elements continues to work via the thermostat control until the set time.

Hot Air Sterilizer Parts and Functions
Hot air oven controls make use of the following components

There is a thermostat controlling the temperature. The thermostat automatically regulates  and maintains already set temperature. It on or off a device such as an heating element when the temperature reaches a certain set point. Some types are of simple rod thermostat while some are electronic or digital. 

Glass thermometer is an instrument for measuring and indicating temperature. Typical one consist of a narrow, hermetically sealed glass tube marked with graduations and having at one end a bulb containing mercury or alcohol. The mercury or alcohol expands and contracts in the tube with heating and cooling. In our context, the thermometer visually indicate the working temperature of the sterilizer.

Basic Hot Air Sterilizer Circuits Diagram

Hot air sterilizer oven circuit diagram

Use of Hot Air Sterilizer

A complete cycle involves heating the oven to the required temperature.  Likewise, it maintains that temperature for the proper time interval for ‘that temperature’. Then turning the machine off and cooling the articles in the closed oven till they reach room temperature.

The standard settings for a hot air oven are:

  • 1.5 to 2 hours at 160 °C (320 °F)
  • 6 to 12 minutes at 190 °C (374 °F)
We use temperature sensitive tapes or other devices like those using bacterial spores to work as controls, to test for the efficiency of the device in every cycle.

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