Car Tube Solar Cooker

Objective

To demonstrate that
a. Radiant heat can be trapped and used for beneficial applications, like boiling rice.
b. Air acts as an insulator.

Outcome

Students will
a. Comprehend the amount of radiant heat to be battled by AC’s inside a glass building in order to cool occupants.
b. Understand that air is not an efficient medium of cooling due to its insulating properties

Requirements

Car tube, 2 nos of black painted vessel with lid, metal box, glass pane (to cover the car tube from top), infrared thermometer, rice, water, salt and a small clay/mud brick enclosed space for the cooker to fit in.

Prerequisites

A. Conceptual knowledge of heat transfer processes.

B. Knowledge of how to conduct temperature measurement using infrared thermometer.

Procedure

Step 1: On a hot sunny day, gather with students on the rooftop around 11 am.

Step 2: Place the inflated car tube in a well sunlit area 

Step 3: Add rice and water in the vessel and place it inside the cavity of the car tube

Step 4: Cover the assembly with the glass pane. Make sure it is airtight. 

Step 5: Leave the assembly undisturbed for two hours.

Step 6: With the help of an infrared thermometer, note the temperature of the vessel at every 30 minute interval. 

Step 7: Open the lid of the vessel after two hours, boiled rice is ready to be served!

Step 8: Simultaneously repeat the same procedure by placing the other vessel inside a metal box

Step 9: Repeat the same procedure by placing the third vessel inside a brick/mud enclosed space and cover it from the top, making it airtight.

Step 10: Measure intermittent temperature values for the vessel in both the cases at every 30 minute interval

Step 11: Compare temperature readings for both scenarios and compare them 

Indulge in a dialogue with students, by asking the following questions:

Step 12: The intermittent temperature values of car tube solar will be greater than metal box solar cooker. Ask students 

1. The reason for this temperature difference:
   Ans: An air filled car tube around the cooking vessel inhibits the loss of heat (trapped by the glass on top) from the cooker to the surroundings. If a metal box is used instead of a car tube, heat gain is quicker but so is the heat loss due to conduction. Hence temperature attained by the solar cooker will be lower, resulting in an increase in cooking time. In the case of brick/mud enclosure, heat gain process is slower and the temperature attained is much lower.
2. If air is a poor conductor of heat, why is air used to cool buildings instead of other cooling mediums?
3. If Brick/mud takes longer to cool, why is glass and metal used in buildings that are made today?

Table

Reference Images

Metal Box

Car Tube Solar Cooker