explain the construction and working of a box type solar cooker with the help of a labelled diagram?
Answers
The main parts of a box type solar cooker are:
- An insulated metal box painted black from inside.
- A glass sheet.
- A plane mirror as reflector.
It is well known fact that a black coloured surface absorbs more heat than a white surface. So, the inner walls and bottom of metallic box to be used for making solar cooker are painted black to increase absorption of heat. This box is covered by a thick transparent sheet of glass. When the box with glass cover is placed in the sunlight, the glass cover allows the infra red rays present in sunlight to pass into the box. Most of these infra red rays are then absorbed by black surface of the box and the box becomes hot. But, after sometime when the black surface becomes hot it starts radiating out heat in the form of infra red rays. But, the glass sheet cover placed over the box does not allow the heat radiated by the black surface to go out from the box. In this way, the glass cover enables the cooker to entrap the heat inside it.
Usually, a plane mirror reflector is also attached on the top of the box. The plane mirror reflector increases the efficiency of solar cooker by reflecting more and more sunlight inside the box.
It should be noted that the temperature inside box type solar cooker can go from 1000C to 1400C within 2 to 3 hours when placed in sunlight. So, this type of solar cooker is used to cook only those food materials which require gentle heating.
Answer:
image
A device that utilises solar energy for cooking purposes is called a solar cooker. The most commonly used form of solar cooker is known as box-type solar cooker. A box-type solar cooker is shown in the figure.
Construction of a box-type solar cooker: A box-type solar cooker consists of the following components:
Box (B): This is an insulated metal or a wooden box. It is painted black from inside because black surface absorbs more heat. The box may be provided with four roll-wheels.
Glass cover (G): A cover made of two sheets of toughened glass held together in an aluminium frame is used as a cover of the box B.
Plane mirror reflector ®: A plane mirror reflector fixed in a frame is fixed to the box B with the help of hinges. The mirror reflector can be positioned at any desired angle to the box. The mirror is positioned so as to allow the reflected sunlight fall on the glass cover of the box.
Cooking containers ©: A set of containers made of aluminium and blackened from outside are kept in the box B. These containers are also painted black because black surface absorbs more heat.
Working: The food is cooked in a shallow vessel of the container. The box has a transparent covering of glass sheet over it. The solar cooker is placed in sunlight and reflector (plane mirror) is adjusted in such a way that a strong beam of sunlight enters the box through the glass sheet. The blackened metal surfaces in the wooden box absorb infra-red radiations from the beam of sunlight and heat produced raises the temperature of blackened metal surface to about 100°C.
The food absorbs heat from the black surface and gets cooked. The thick glass sheet does not allow the heat produced to escape and thus, helps in raising the temperature in the box to a sufficiently high degree to cook the food.