Heat Transfer

For the inquiry, I decided to use four coffee mugs from my set of dishes. I chose these four mugs because they are the same size, shape, and thickness and are made from the same material. They were as identical as possible which made them a constant in the activity. I selected four different insulators consisting of Styrofoam, a dishcloth, newspaper, and plastic wrap. I chose Styrofoam because it is the material used in to-go coffee cups. The Styrofoam cups limit the heat transfer so that the coffee consumer does not get burned through the cup. For this reason, I thought Styrofoam would prove to be the best insulator. For the second insulator, I decided to try a cotton dishcloth folded in half. I was thinking of the quilt on my bed when I chose the dishcloth. The quilt keeps me warm at night when we have the windows open. I could not cut my quilt down to fit the cup, so I used the dishcloth, which was sewn in a similar manner as the quilt. The next insulator was newspaper. I have seen homeless people sleeping on park benches with newspaper as covers. I have also read about people stuffing their clothes with newspaper in order to keep warm on cold days. I selected plastic wrap for my fourth insulator because I use plastic wrap to protect food, and I wanted to see how well it insulates against heat transfer. I figured the plastic wrap would be the worst insulator of the four insulators tested because it is relatively thin.

 To begin the inquiry, I poured 3/4 of a cup of water into each coffee mug. I placed the mugs inside the microwave oven on a glass turntable. The mugs were placed in a circle the same distance apart with the handles pointing out from the center of the circle. By heating all four cups on the turntable at the same time, I maintained an even heating of the water in each mug. I heated the water in the mugs for two minutes. While the mugs were in the microwave, I cut a circle from a Styrofoam plate and folded the dishcloth, newspaper, and plastic wrap in half. At the end of the two minutes, I used a thermometer to measure the water temperature. The water was heated to 46°C. I used two rubber bands to attach a circle of Styrofoam to the top of the first mug and set the mug on the counter. I attached the dishcloth, newspaper, and plastic wrap to each of the remaining three mugs using one rubber band around each mug. I placed the three mugs on the counter next to the first mug and set a timer for 30 minutes. When the 30 minutes were up, I removed the Styrofoam from the first mug and measured the temperature of the water. The water temperature had dropped from 46°C to 38°C, a difference of 8°C. I repeated the procedure with the remaining mugs. The water in the mug with the dishcloth was also 38°C. The water in the mug with the newspaper dropped to 37°C, and the water in the mug with the plastic wrap dropped to 36°C.  

The results were somewhat unexpected. I predicted the Styrofoam would be the best insulator, so I was surprised that the water in both the Styrofoam and the dishcloth mugs dropped 8°C. I expected the Styrofoam to be a better insulator than the cotton dishcloth because Styrofoam contains air pockets. Heat does not transfer quickly through the air because the molecules in the air are further apart than molecules in solids (Tilley, et. al, 2008). I believed newspaper would be an adequate insulator. Since the water in the mug with the newspaper on top dropped only one degree lower than the water with the Styrofoam and the dishcloth, my belief in newspaper as an acceptable insulator was correct. I also accurately predicted the plastic wrap would be the worst insulator because it does not have air pockets to slow the heat transfer. The water temperature in the mug with the plastic wrap dropped the most in the inquiry.

The heat transfer inquiry provided several insights into heat transfer and insulators. During the inquiry, I experienced the effects of all three forms of heat transfer.  According to Wisc-Online (2012), when I used the microwave oven to heat the water in the mugs, I used radiation.  The electromagnetic waves generated by the microwave oven came in contact with the mugs and the water in the mugs.  Heat was transferred from the electromagnetic waves to the mugs and the water in the mugs causing them to heat up.  I felt the effects of convection when I touched the insulators at the top of the mugs and felt the warmth.  The warmth I felt was due to the energy moving from the heated water, through the air above the water and into the insulators.  I noticed the effects of conduction when I felt the heat on the outside of the mug.  Energy transferred from the water through the ceramic mug to my fingers.  I also learned different materials insulate in varying degrees.  As previously mentioned, heat transfer occurs slowly through the air because the air molecules are further apart than the molecules in liquids or solids.  I examined the Styrofoam with a magnifying glass and discovered I could see the air pockets contained in the material.  The dishcloth was folded in half which allowed a layer of air between the two dishcloth layers. The newspaper was also folded in half, so air was trapped between the newspaper layers as well.  Less heat escaped from the first three materials.  The plastic wrap was also folded in half, but due to the nature of plastic wrap, very little air was trapped between the plastic wrap layers, and more heat escaped.  The activity proved the importance of air pockets in insulators.

I would like to repeat the experiment with bubblewrap. Bubblewrap has a lot of trapped air, so I wonder how well it will do as an insulator.  I would also like to try a piece of carpeting just to see what type of insulator it is since we use it on our floors.  I did not try any solids in my experiments, so I would like to see the results using a piece of wood or a brick.  I know metal would be a poor insulator as metal is a great conductor of heat.  It would be interesting to see how fast heat escapes when using a piece of metal.  I wanted to use aluminum foil in my experiment, but we did not have any.

I would like to test oatmeal and coco wheats to see how the density of the material affects cooling.  I think the oatmeal would take the longest to cool because it is thicker than coco wheats and water. Water should cool the fastest because it is less dense.