Tag Archives: convection

European scientists use Energy2D to simulate submarine eruptions

The November issue of the Remote Sensing of Environment published a research article "Magma emission rates from shallow submarine eruptions using airborne thermal imaging" by a team of Spanish scientists in collaboration with Italian and American scientists. The researchers used airborne infrared cameras to monitor the 2011–2012 submarine volcanic eruption at El Hierro, Canary Islands and used our Energy2D software to calculate the heat flux distribution from the sea floor to the sea surface. The two figures in the blog post are from their paper.

According to their paper, "volcanoes are widely spread out over the seabed of our planet, being concentrated mainly along mid-ocean ridges. Due to the depths where this volcanic activity occurs, monitoring submarine volcanic eruptions is a very difficult task." The use of thermal imaging in this research, unfortunately, can only detect temperature distribution on the sea surface. Energy2D simulations turn out to be a complementary tool for understanding the vertical body flow.

Their research was supported by the European Union and assisted by the Spanish Air Force.

Although Energy2D started out as an educational program, we are very pleased to witness that its power has grown to the point that even scientists find it useful in conducting serious scientific research. We are totally thrilled by the publication of the first scientific paper that documents the validity of Energy2D as a research tool and appreciate the efforts of the European scientists in adopting this piece of software in their work.

Using Energy2D to simulate solar updraft towers

The day/night cycle of an SUT
The solar updraft tower is a new-concept clean energy power plant for generating electricity from the sun. Sunshine falling on a greenhouse collector structure around the base of a tall chimney heats the air within it. The resulting convection causes air to rise up in the tower, driving wind turbines to produce electricity. In 2011, a plan of building a massive solar updraft tower in Arizona was announced (for more information, see this CNN report: Can hot air be the free fuel of the future?).

Compared with other solar technologies, solar updraft towers have many significant advantages. For example, it does not require water; it can be built in barren areas; it can still generate electricity after dark; its lifetime is much longer than solar panel arrays; and so on. Engineering-wise, it is a sound concept. The rest is a political will to get it banked and constructed. Let's hope it wouldn't take too long.
Streamline analysis of air intake

Instead of waiting for it to come true, why not go to our Energy2D website and see a bunch of simulations? You can even start to investigate it with our powerful Energy2D software. For example, you can turn the sunlight on and off to investigate how the heat absorbed during the day can still be released at night to drive the turbines. You can adjust the height of the tower to get an idea of why engineers want to build an insanely tall tower that rivals the height of Burj Khalifa in Dubai, the tallest building in the world. You can even use Energy2D's comprehensive analysis tools to study what happens when you block one of the air intake entrances.

The opportunities of inquiry with Energy2D are practically endless. You don't have to wait for someone to erect a solar updraft tower to explore about the technology -- you can do it now and the concept of a new technology is only a few mouse clicks away from you. Why not show these simulations and your investigations to your students to get them interested in clean energy today?

Using Energy2D to simulate Trombe walls

A Trombe wall is a sun-facing wall separated from the outdoors by glass and an air space. It consists a solar absorber (such as a dark surface) and two vents for air in the house to circulate through the space and carry the solar heat to warm the house up. In a way, a Trombe wall is like a machine that uses air as a convey belt of thermal energy harvested from the sun. Trombe walls are very simple and easy to make and are sometimes used in passive solar green buildings.

Hiding sophisticated power of computational fluid dynamics behind a simple graphical user interface, our Energy2D software can easily simulate how a Trombe wall works. The two images in this blog post show screenshots of a Trombe wall simulation and its closeup version. You can play the simulation on this page and download the models there. If you open the models using Energy2D, you should be able to see how easy it is to tweak the models and create realistic heat flow simulations.

Solar chimneys operate based on similar principles. Energy2D should be able to simulate solar chimneys as well. Perhaps this would be a good challenge to you. (I will post a solar chimney simulation later if I figure out how to do it.)

A simple IR experiment to prove that the North Carolina Sea Level Rise Bill is just flat wrong

Last month, North Carolina's Senate passed a bill that would have required the state's Coastal Resources Commission to base predictions of future sea level rise along the state's coast on a steady, linear rate of increase. This has sparked controversies across the nation amid the record heat waves in many states.

If the lawmakers had done our very simple IR experiment on visualizing thermohaline in a cup, published in the July issue of last year's Journal of Chemical Education (see the image to the left), they would have had a better understanding about the possibility of the nonlinear acceleration of ice shelf melting: The less salty the seawater is, the faster the ice shelf above it melts. And the faster ice melts, the less salty the seawater will become. This creates a positive feedback loop that accelerates the melting process. If the speed of ice melting in systems as simple as a cup of saltwater is not as nice as the "steady, linear" rate some of the lawmakers would like to see, who can be sure that systems as complex as the Earth would follow a "steady, linear" trajectory of change?

If you bother to read on, this experiment uses just a cup of tap water, a cup of salt water, and some ice cubes. The two cups are placed next to each other on a table for comparison. (a) An IR image right after an ice cube was added to a cup of freshwater (left) and a cup of saltwater (right). (b) An IR image taken after four minutes showing a downwelling column in the freshwater. (c) An IR image taken after nine minutes showing the tabletop was cooled significantly near the freshwater cup. (d) An IR image taken after 16 minutes showing that the bottom of the freshwater cup became cooler than the top whereas the bottom of the saltwater cup remained warmer than the top.

To see the entire process caught under an IR camera, you can watch the embedded YouTube videos in this blog post. Feel free to send these videos to your representatives if you happen to live in the coastal area of North Carolina. Or send to a science teacher in North Carolina in the hope that the bill will be revised in the future to consider the possibility of nonlinear acceleration.

Note that these videos do not represent any political view and should not be considered as in support of any agenda, my purpose is only to provide a humble scientific demonstration to prove that things do not always go smoothly as we wish.

Comparing convection and conduction using Energy2D

The following are two Energy2D simulations that compare convection and conduction, which should run within this page if you have installed Java and Java applets are enabled with your browser. The first one shows the case of natural convection. The second one shows the case of forced convection.

Instruction: Click inside a simulation window. Press 'R' to  start or stop, 'T' to reset, 'L' to reload the initial configurations, and 'G' to open or close a graph. The virtual temperature sensors can be moved around, though most other pieces are locked to their positions. Right-click on the windows for more actions.

Natural convection (driven by thermal buoyancy):

Forced convection (driven by airflow):

A Von Kármán vortex street.
The following screenshot shows a typical Von Kármán vortex street produced from the second simulation. Energy2D is also capable of producing other interesting fluid patterns such as mushroom cloudsBernard's Cell, and the Kelvin–Helmholtz instability.

More generally, Energy2D is a Java application that allows users to create interactive, real-time simulations of heat and mass flow. A simulation you create can be easily placed on the Internet just like what you saw above.

On a separate note, below are two results for conduction simulations using Energy2D that illustrate the circuit analogy: Ohm's Law is the electrical analogy of Fourier's Law of Heat Conduction. It is interesting to note that Ohm actually drew considerable inspiration from Fourier's work on heat conduction in the theoretical explanation of his work (see Ohm's Law in Wikipedia). Ironically, today's students seem to be more familiar with Ohm's Law than Fourier's Law. So the circuit analogy is used in textbooks to help students understand heat conduction.

The analogy to a parallel circuit.
The analogy to a series circuit.

Visualizing convection without using ink

Figure 1. A top view of a floating ice cube.
If you have done a convection demo using a container of water and some ink, you may have had to change the water after each demo since the ink had diffused everywhere, which may make the convection pattern less easy to observe. Depending on the size of your container, that is some work to do and some water and ink to waste.

Here is a greener and better way to do it--using an infrared (IR) camera. An IR camera shows hot and cold (typically) in red and blue colors, which can be considered as "IR ink" that can be seen only through an IR camera. With the tool, all you can do is to add some ice cubes or hot water to a container of water every time you need to do a demo. There is no need to change the water.
Figure 2. A side view of a floating ice cube showing "cold fingers." 

One thing to notice is that you should not use a glass container--because it reflects off IR rays that will get into the image. A clear plastic one is the best as it does not reflect much and it allows you to observe what happens inside (if anything visible) with naked eyes.

Figure 3. A view from another side
showing the the cooling at the
Figure 4. An IR image after hot water was added to room temperature water in a container showing hot water tended to float atop.
Figure 5. An IR image of a fish tank showing a clear pattern of temperature stratification.