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Name: Colleen
Status: student
Grade: 6-8
Location: N/A 
Country: N/A
Date: 1/30/2005


Question:
Why does a heat sink work? I know that one material takes the heat away from another material so that material does not expand. I did a butter experiment with this and the butter fell off of each type of metal after a number of seconds then we added a bulldog clip and it took longer. But why does this work?


Replies:
One of the laws of thermodynamics is that there is an desire for equilibrium between two different temperature areas (a very simplified explanation). That is to say, if you have on area that has a higher temperature next to an area that has a lower temperature, the heat will "flow" to the cooler region to help raise its temperature while simultaneously cooling itself off and eventually they will both be the same temperature. Your butter experiment is exactly what is going on. The butter is cooler and the metal is warmer. The metal will give up some of its heat to the butter raising the temperature of the butter while cooling the temperature of the metal. When you add the heat sink to the metal, you have created a third area into which the metal gives its heat. Now instead of all the heat flowing to the butter, some of the heat is going to the butter AND the heat sink.

Heat sinks aren't just for stopping the expansion of metals, they are instrumental in whisking heat away from devices that are very sensitive to heat problems. Electronics are the best example. Processor chips in you computer are very sensitive to heat. If they see too much heat, they will start to loose their number crunching abilities, so designers put heat sinks along with fans on the processor to whisk heat away. That is one reason you always hear a fan going when you turn you computer on. Hope this helped explain things a little better. Thanks for using Newton.

Christopher Murphy, P.E.
AFRL


Heat sinks are used for the purpose of preventing something from getting too hot. A typical example is an integrated circuit chip in a computer or a transistor. The chip is small but dissipates a considerable amount of power for its size (tens of watts).

If the chip were simply connected to the rest of the computer with wires, it would get hot and fail. Instead, the chip is connected by special glue or bonding onto a metal heat sink plate that makes a good connection to the chip. The purpose of the heat sink is to spread the heat over a larger area enabling it keep cooler. The heat flows from the chip to the large heat sink (which might be cooled by air from a fan.)

Powerful super computers might have liquid-cooled heat sinks that the chips are bonded to.

When people think of heat sinks they commonly think of a metal device that has no moving parts, and the item that you want cooled is clamped onto it.

There are other types of cooling systems, some of which may have parts or be electrical, and these have other names.

A "sink" is also a concept in science. In science, if you want to say that there is a drain or a way out for something, you might call it a "sink." You might have a sink for electrons, a sink for heat, or a sink for positrons. You can even refer to a "phonon sink" in physics.

Bob Erck


Not really my field. But, my layman's opinion. You hit the nail on the head, with the diversion statement. Since heat is not visible to the naked eye, imagine the heat as water. My experience with a heat sink was in soldering. You place the sink beyond the piece you are soldering. The idea to protect the items, further down the line. So, let us assume the heat is water. You would place a diversion pipe. The heat, or water flowing from the soldering gun, is bypassed, thus protecting the items further along the line.

Now, the way the heat sink works, it is a material that absorbs heat easily. I would guess its molecules and composition have more room. So, with the water analogy, it would be like a sponge at the end of the pipe. So, you can see, it is not a sure thing, there would be a limit. With the sponge, it becomes full and loses some to the air, but ultimately, the path is reformed. The folks at the Alamo held off Santa Anna, but were overwhelmed. If you solder too long, you either have to add more heat sinks, or wait to let the heat dissipate to the air etc. It appears your experiment showed there was a limit.

James Przewoznik


There are many kinds of heat sinks. In photosynthesis experiments, my students use a heat sink involving nothing more than a one gallon aquarium filled with water. The light used in the experiment often is an incandescent bulb and the heat from the bulb will effect the results. The aquarium water acts to absorb the heat from the light bulb so only the light reaches the experiment. This is generally how all heat sinks work in simple terms.

Steve Sample


There are 2 factors to consider in heat sinks. how much heat can the heat sink absorb, and how much heat can it dissipate.

The heat capacity of a piece of metal depends not only on how large it is (large objects tend to be harder to change the temperature of), but also what kind of metal it is. Aluminum for example, takes a lot more energy to heat up than copper or iron. So part of the heat that was previously going straight to the butter is now working to heat up the heat sink instead. So imagine the difference between filling up one 5 gallon bucket with water, or filling up two 5 gallon buckets from the same hose.

Dissipate just means "get rid of" Heat sinks used in computers have to be very good at getting rid of heat, and usually the only way to do that is to heat the air around them instead. So an object with a lot of surface area touches a lot of air, and will be getting rid of heat as well as absorbing it itself. (Now imagine one of your buckets has holes in it.)

Ryan Belscamper


In the simplest case, it is all about sharing: you have some total amount of energy, and it is going to be shared by all the molecules that are physically in contact. If you have more molecules, they each get less energy, naturally. [Think of ten kids with one bag of candy. Now add a few more kids.]

In more complicated cases, it is also important to consider the rate at which heat energy moves through materials. Suppose you did not actually attach the bulldog clip, but only put it near the hot metal. You would still have a heat sink -- an object that will want its share of the total energy -- but the heat energy would have to travel through air to get to the bulldog clip, and air is relatively poor conductor of heat. In this case, the bulldog clip would get a smaller share of the energy. [Think of ten kids, with ten straws, drinking from one glass of water. Now add a few more kids, but give the new kids really narrow straws.]

Tim Mooney



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