Convection current analysis

Arrows indicate the movement of water. Colour indicates pressure.

I wrote previously about a very simple simulated environment I had created, which was basically a rectangular body of water, split into discrete sectors. Each sector of water had a number of particles (molecules of water) and a temperature. Based on these values, the particles moved between sectors; the more particles or the higher the temperature, the more particles would leave a sector. Gravity also acted to move particles downwards, which particles with a higher energy (temperature), would be more likely to avoid. To close the system, the water was surrounded by invisible sectors of air on top and rock on the sides and bottom, which had a fixed temperature (which allowed the system to lose energy when I later heated up a block).

If the simulation was left for a while, the result was that sectors lower down were colder and more dense (contained more particles), as one would expect I have since added the ability to arrows that indicate the net direction and amount of water moving between each neighbouring sector, so currents can be seen. If a single sector of rock is heated to about four times the temperature than the water, a convection current is induced, as the image above shows. In fact, at first what happens is that there is an explosion, as shown in the video clearly demonstrates. I guess this is quite a realistic simulation of what would happen if you could instantaneously heat the bottom of a pool of water to four times the surrounding temperature.

N.B. The video shows temperature, while the picture at the top shows pressure, hence the different appearance.

Building simulation actually helped me to better understand a few principles of physics I assumed that I already understood, such as the concept that heat rises. The question is: why? I had thought it was because the particles have more energy, and are therefore more likely to overcome the pull of gravity compared to colder particles, which is true. However, when you heat a sector of water, you increase the number of particles moving in all directions. In fact, there will be a greater increase in the number of particles moving sideways than there are moving up. The reason, the simulation ends up with a net movement of particles upwards rather than sideways is because the pressure of the sectors on either side is much higher, whereas the pressure of sectors above are lower. The reason for this is of the particles moving upwards, more are likely to have a high energy than those moving sideways. I’m not sure how well I’ve explained this, but I feel than in simulating this simple phenomenon I have gained a much deeper understanding of what is going on at a molecular level.

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