- CONDUCTION: Is when heat is transferred from one molecule to another though a substance, in other words it's the flow of heat through solids. An example of this would be when one end of a nail is under a flame over a period of time till the other side of the nail will be hot as well. This is because of conduction.
The time it takes for the other side of the nail to become hot depends if it's the material is a heat conductor or insulator. If it's a conductor then heat can easily be transfer, but if it's a insulator heat is difficult to be transmitted.
- CONVECTION: Is the transfer of heat by a movement of liquid and gas due to different density levels which is caused by the difference in temperature. An example of this would be when a kettle is being heated up by a stove. The bottom of the kettle is heated first then the heat rises to the top and the cooler water flows down to be heated. This continues to circulate making the heat in the kettle transfer throughout the liquid.
- THERMAL RADIATION: Is electromagnetic radiation created by thermal motion. Radiation is something that emits energy through waves, electromagnetic radiation is just a type of wave that sustains electric and magnetic components. Hence thermal motion produces energy in the form of waves that maintain electric and magnetic substances.
Tuesday, 7 May 2013
WHAT IS THE PURPOSE OF A THERMOS?
The purpose of a thermos is to retain the temperature in a container by allowing heat to flow out or in so that its contents are kept cold or hot depending on the liquid in the container. Heat can only flow from hot surfaces to cold ones by three ways.
HOW ARE CURRENT THERMOSES CONSTRUCTED?
A typical thermos would have a flask (inner chamber inside of an outer chamber.) The inner layers (glass and vacuum) would be coated with mercury to allow heat rays to enter the flask and be reflected between the two layers; this prevents the transfer of heat.
Sometimes modern thermoses are made of stainless steel-Inside and out, so it does not shatter. It's naturally reflective so a reflective coating sometimes doesn't need to be added. Although other thermoses have a shiny interior coat insulator such as metal, to expel thermal radiation because it causes heat loss.
Thermoses often use rubber or cork material to make bottle stoppers, this prevents the glass container from touching the the outer container surrounding the flask so that conduction doesn't occur.
Sometimes modern thermoses are made of stainless steel-Inside and out, so it does not shatter. It's naturally reflective so a reflective coating sometimes doesn't need to be added. Although other thermoses have a shiny interior coat insulator such as metal, to expel thermal radiation because it causes heat loss.
Thermoses often use rubber or cork material to make bottle stoppers, this prevents the glass container from touching the the outer container surrounding the flask so that conduction doesn't occur.
WHAT MATERIALS ARE CURRENTLY USED TO MAKE A THERMOS AND WHY?
Often current thermos are made out of two layers (Glass & Vacuum) to decrease the amount of heat escaping, a rubber support so that conduction doesn't occur, and a shiny interior coat around the outside layer of the bottle. The shiny coat is used to lessen the amount of thermal radiation. Some other materials that could be used to make a thermos could be,
http://answers.yahoo.com/question/index?qid=20100107222756AALF6q1
- 2L Bottle
- Plastic bottle
- Tin foil
- Foam layer
- Duct tape
- Steel wool
- Sock
- Rice
- Clay
- Bubble
- Wrap
- These two layers are nestled together at the neck and all the air in between them is evacuated.
- A reflective coating is added to the surfaces of both layers so that radiative heat loss can be minimized.
Tin foil: The tin foil will be going inside the 2L bottle and around the plastic bottle so that the heat keeps circulating and the heat content isn’t being lost but reflected.
Foam layer & Steel wool: The foam layer and steel wool will act as the main insulator. The foam layer can’t conduct air because of its plastic pockets, thus heat/cold temperatures can’t be release easily. Steel wool is used in many industrial places for high heat insulation; this proves that steel wool can retain heat as it’s been tested and used numerous times.
Duct tape: To keep everything together as well as add extra insulation
Rice: To secure materials together, and get rid of extra crevices that is not needed.
- This material could be used for the bottom of the thermos to prevent conduction
Cotton sock: to maintain the steel wool or any other materials and to add extra insulation. Cotton traps air which build up in heat.
Bubble Wrap: Contains patches of trapped air which is a good insulator, as temperatures can’t be transferred.
http://wiki.answers.com/Q/How_is_bubble_wrap_a_good_insulator
http://wiki.answers.com/Q/How_is_bubble_wrap_a_good_insulator
Clay: The minerals in clay have low thermal conductivity so it’s a good heat insulator. Which is why we choose this for the top cover of our thermos.
- Since most of the heat loss in a thermos occurs through the neck and opening of the flask, the openings are usually stoppered with cork, polyethylene plastic or rubber that is attached to the lid to prevent any additional heat loss.
http://answers.yahoo.com/question/index?qid=20100107222756AALF6q1
Monday, 6 May 2013
Day 5: [TROUBLESHOOTING AND RE-TESTING]
After the thermos was rebuild our initial focus was on troubleshooting. Once the testing took place again for the second time, now with the requirements, it occurred to us that the thermos wasn't retaining all the heat as the bottle still felt warm. There was only a certain spot that was maintaining the heat which was the bottom of the bottle, that held rice. The reason for this is because in current thermoses they hold a rubber support at the bottom which prevents the flask from touching the outer layer. When the flask isn't touching the outer layer, heat isn't being transferred because of the insulation (rubber) between them. In this case, the thick layer of rice at the bottom of our thermos acted as a good heat insulator based on our experience.
Therefore we applied the same method by adding bubble wrap which is a thicker layer of insulation inside of the 2L bottle to surround the plastic bottle, and furthermore having tin foil and tape entwine outside of the 2L bottle to insure extra insulation. We decided to keep the plastic lid of the bottle as it is, because from our research we found out that plastic is a good head insulator and it's a easy material to cut though so we can insert our thermos in. The very last detail we added was a piece of clay for the lid to prevent the heat coming out of the hole that was made for the thermos. The clay would just be placed on top without being glued or taped on so that it can be removed when liquid is needed to be poured in the thermos. Clay is also a good heat insulator because the minerals that it's made out of are low in thermal conductivity.
Friday, 3 May 2013
Day 4: [BACK TO THE DRAWING BOARD]
Even though the top of the thermos wasn't completed and the thermometer was not in place, we decided to start testing anyways to check the durability of the thermos. The thermos was generally able to retain the heat, but the plastic bottle which we had placed inside the 2L bottle was more than 500 mL, which did not meet the requirements because we needed to use 500 mL or less. Trouble-shooting began as more adjustments are being made and further research was being done. Some of the ideas we shared were, to use a Styrofoam cup or coffee cup for the inside of the 2L bottle as they were both small so would probably use less then 500 ml Luckily enough a plastic bottle was given to us that met the requirements so we started rebuilding using it right away. Another thing we changed besides the bottle was the sock which was switched to a thicker cotton sock because it's a better insulator as it can trap air from being transferred.
(http://wiki.answers.com/Q/Why_cotton_is_a_good_insulator#page2)
(http://wiki.answers.com/Q/Why_cotton_is_a_good_insulator#page2)
Thursday, 2 May 2013
Day 3: [IDEAS PUT INTO ACTION]
We have started constructing our thermos and are adding improvements along the way; another layer of duct tape was added around the steel wool, rice was added in the 2L bottle to insulate the empty spaces, and a wool sock was used to contain the steel wool. We also discovered the aluminum covering would not work, due to the fact that it's too hard, and not flexible which makes it difficult to shape. We have contemplated on what to material to use as the lid, but haven't come up with a conclusion yet. Another adjustment we made to our design is instead of covering the entire 2L bottle in tin foil we decided to add some inside the bottle, but also shape some into small balls to secure the near top of the bottle. This way the foil will apply weight on the rice, and compresses it so it doesn't become loose and fall out. The use of a metal bottle was ditched because we were unable to find the right requirements and later on we found out that metal is not a good insulator but a conductor of heat. As the period reaches its end, our thermos is almost complete, the only thing left to add is the covering for the top and the thermometer.
http://answers.yahoo.com/question/index?qid=20080210210142AAxsxzk
http://answers.yahoo.com/question/index?qid=20080210210142AAxsxzk
Wednesday, 1 May 2013
Day 2: [DEVELOPING RESEARCH & IDEAS]
As our research is progressing, and ideas are developing. We came up with a new and improved design and discussed for any farther improvements that could be made, based on our research. The previous designs created contained only one container that would have a layer of insulators, from our research we realized that current thermoses are made with a inner and outer chamber (Glass bottle & vacuum). Henceforth for our thermos we choose a metal bottle for the inner chamber and a plastic bottle for the outer chamber. We also decided who was responsible for obtaining each of the materials that the teacher won't be providing.
Subscribe to:
Posts (Atom)