Hot Air Oven - Lecture Notes PDF

Dr. Mohammed tawfiq med. Inst. Eng. Dept. 2nd Year, Lec.7 Hot Air oven ‫كلية المستقبل الجامعة‬ Hot Air Oven page2 med. Inst. Eng. Dept. 2nd Year, Lec.7 ‫كلية المستقبل الجامعة‬...

Dr. Mohammed tawfiq med. Inst. Eng. Dept. 2nd Year, Lec.7 Hot Air oven ‫كلية المستقبل الجامعة‬ Hot Air Oven page2 med. Inst. Eng. Dept. 2nd Year, Lec.7 ‫كلية المستقبل الجامعة‬ Hot Air Oven Introduction: Hot air oven is advice used for heating application such as drying and sterilizing glass wave, surgical tools, so other, this device is thermostatically controlled and electrically heated. Advantages and disadvantages The hot air oven does not require water and there is not much pressure build up within the oven, unlike an autoclave, making them safer to work with. This also makes them more suitable to be used in a laboratory environment. They are much smaller than autoclaves but can still be as effective. They can be more rapid than an autoclave and higher temperatures can be reached compared to other means. As they use dry heat instead of moist heat, some organisms may not be killed by them every time. Hot Air Oven page3 med. Inst. Eng. Dept. 2nd Year, Lec.7 ‫كلية المستقبل الجامعة‬ The parts of oven: 1. Mechanical part. 2. Electric part. Mechanical part : 1. The Coat (outer shield). 2. Fiber glass. 3. The chamber. 4. The shelves (mesh). 1. The coat :The coat is made of aluminum or stainless steel because it is characterized by the following: a) resisting the mechanical shocks b) Resisting the oxidation. c) Rectangular solid shape to be easily placed anywhere in the laboratory. d) The coat consists of several surfaces an isolator material prevents heat from getting outside. 2. Fiber glass : There are two types of fiber glass : a) Brown fiber glass: be somewhat cheap, but it is a dangerous substance because it causes inflammation in respiratory system and should be careful in dealing with. b) Yellow fiber glass: available by variously and it is less dangerous than the brown, the skin is sensitive to it and should wear gloves when dealing with. The Hot Air Oven page4 med. Inst. Eng. Dept. 2nd Year, Lec.7 ‫كلية المستقبل الجامعة‬ advantage of fiberglass is a good insulator of heat and it is used in the oven to prevent the transfer of heat from inside the device to the outside and maintain the internal temperature. 3. The chamber: The chamber is completely made of aluminum or stainless steel because it has the following characteristics: a) Rectangular solid shape to suit dealing with various objects. b) It has thermally insulated from all other parts of the oven to prevent effective on them. c) It has ribs to put shelves in the wanted levels. d) It is made from materials characterized by oxidations' resisting. 4. The shelves (mesh): they are plates on which the objects are placed, the number of shelves is varying according to the number and size of objects, the oven capacity. It characterized by: a) They are made of aluminum which is considered as oxidation resisting material. b) When they are placed in their locations on the ribs some area is lifted to allow movement of air, some shelves contain openings to help this purpose. 1. Electric part : 1. The power supply. 2. The heater. 3. Thermostat. 4. Temperature indicator (thermometer). 5. Timer. 6. Fuses. 7. Control panel. Hot Air Oven page5 med. Inst. Eng. Dept. 2nd Year, Lec.7 ‫كلية المستقبل الجامعة‬ 1. Power supply: The used supply in the oven is 220v – 50Hz transformer and rectifying circuit (AC to DC convert) to run the control panel if the parameters, numeric or other departments in the modern fashion 2. The Heater: The electric heating system is the system in which heating produce by rising of temperature caused by the passing of enough electric current through a conductor to produce the heat. Generally, they can be operated from 50 to 300 °C. The heater element has the following characteristics:  Electrical insulation.  Thermal conductivity. 3. Thermostat : is a component of which senses the temperature of a system so that the system's temperature is maintained near a desired setpoint. The thermostat does this by switching heater on or off, or regulating the flow of the current, to maintain the correct temperature. The most common oven thermostat is gas expansion thermostats. It consists of a gas-filled bulb connected to the control unit by a slender copper tube. The bulb is normally located at the top of the oven. The tube ends in a chamber sealed by a diaphragm. As the thermostat heats up, the gas expands applying pressure to the diaphragm which pulls a lever which disconnects the circuit. 4. Temperature indicator: Two ways are used in temperature indicator there are thermometer and thermocouple & Identified for the internal temperature. 5. Timer: There are two type of timer electrical or mechanical at range 5-60 min given period of time required for sterilization. Hot Air Oven page6 med. Inst. Eng. Dept. 2nd Year, Lec.7 ‫كلية المستقبل الجامعة‬ 6. Fuse: To protect the circuit from high current, high loads, short circuits. 7. Control panel: (oven door) contains several elements and the most important about indicator power lamp usually green & indicator heater lamp usually red & contain switch on-off and timer & knob. Hot Air Oven page7