Thermal Image Contest

The criminal always leaves a trace – thermal footprint

A12

  • "Best title" by peer students

  • "Best message delivery (tie)" by peer students

  • "Best creativity" by peer students

When I came into the room, I noticed that the snacks on my desk were missing. The suspects are friends in the room. I quickly got a thermal footprint image using a thermal imaging camera, and I was able to find the suspect scientifically.
When standing on the floor, a conductive heat transfer occurs from the foot to the floor because the temperature of the person’s body is relatively high than that of the floor.
After the foot is released, a convective heat transfer occurs due to the difference between ambient air temperature and floor temperature. The temperature difference decreases over time. In the image, we can find out that the most recent thermal footprint shows a relatively higher temperature.
These footprints cannot be found with our naked eyes. However, the criminal always leaves a trace. I was able to get important clues at the scene using thermal imaging camera.

Why do we need huge grill for internal combustion car?

A3

  • "Best message delivery (tie)" by peer students

I was wondering why do we have large grill in front of car. And how we eliminate this in EV? This picture is my car right after driving. The engine is hot due to the combustion of fuel, but the bonnet has lower temperature compare to engine. Generated heat from engine is cooled by 2ways; coolant and air flow through the grill. Therefore, engine has heat loss to maintain its temperature and prevent overheating for stability and efficiency issues. This heat transfer is convection with external flow. In aspect of air flow, the faster car moves, the larger the air flow intake relatively. That’s why we have extra huge airduct for super cars. Even the car accelerates rapidly, the engine can maintain its temperature. In EV, we have electric motor instead of combustion engine, the temperature relatively lower so we can maintain the temperature without the grill.

Heat Transfer of Ceramic vs Plastic Drippers for Brewed Coffee

A1

How the heat transfer affects our brewed coffee when using different materials for the “dripper”. When pouring hot boiling water to the plastic cone it heats up quickly and produces a very hot cup, but the opposite happens with the ceramic cone that produced a less hot cup. This is due to the heat resistance and thermal mass. Ceramic has a higher thermal mass and heat resistance so in brewing coffee process it produces colder cup than the plastic. As the ceramic absorbs some of the heat. In other words, when pouring boiling water, the heat from the water transfers to the plastic much quicker so the resulted temperature of the coffee is higher.

No title

A2

I took a picture of my tablet and om phone. It clearly shows the heat distribution in the devices and the location of the battery. The phone temperature is higher than the tablet because of the location of the battery and due to the material in the phone. Also, the components in the phone is more closer, so the heat transfer much easily in the phone.

Forced convection over an iced body

A4

This picture is not - as it can look like - an image obtained in a wind tunnel to illustrate your fluid mechanics textbook.
Indeed, on this picture we can see an ice block that is plunged in a bath of agitated and tempered water. So, the water surrounding the ice block creates forced convection other the piece of ice. A boundary layer made of cold water issued from the ice melting is created and we can observe the boundary layer separation forming marginal vortices.
In fact, the temperature gradient between the surrounding water and the ice engenders thermal diffusion or conduction and the bulk motion of the previously agitated water engenders advection. The ice is melting due to this phenomenon of convection and cold water is carried by the velocity boundary layer. This cold water allows us to “see” the boundary layer separation through the thermal camera.

Parking lot cars and their temperatures

A5

Everyday when I visit places with a lot of cars parking the temperature inside is more than the outside, So today I visited one of the parking areas to test the thermal camera and as we can see the difference between each car temperature. The one on the left looks like it just arrived to the mall and also he might left his car in the sun because crossing by the car can make you feel how hot is it, the car in the middle might parked there for more than an hour because it’s not that warm. The last car on the right side looks a bit strange that there is no heat coming from it which implicates that the owner didn’t go out recently or the car might be left by the owner and no one is using it. In conclusion, Testing the camera was so fun.

A two-layer coffee

A6

My friend is drinking an Einspänner from Cafe dream. It is a hot coffee with cold cream foam at the top. We can see in the circle that the coldest point is right at her mouth (where the foam is), while the hottest is at the center of the hot liquid coffee. The foam is at 14.4°C (Point Min in the circle) while the atmosphere is at 22°C (Point 1). There are two things to say here:
1. The hottest point is at the center because hot liquids emit heat from the edges first, which are directly in contact with colder structures.
2. The foam acts like an insulation wall to the coffee. Indeed, the foam can be seen as a solid structure, which makes the heat transfer rate to and from the hot liquid lower. At the end, the cold foam helps the coffee to stay hot.

Another me outside the window

A7

I saw another me outside the window by taking a picture with thermal camera. But he definitely had a lower temperature than me. (Look at the picture above. He is cooler than my bookshelf!)
Thermal radiation makes another me like this. Heat transfers from my body to the surrounding by radiation.
Heat flux reaches to window and some part of it absorb to window, some part of heat transmit through the window. And some of it reflect to window and come back to me or detect to the thermal camera. At this moment, the heat measured by thermal camera is less than the heat emitted from my body, thus the measured temperature is also smaller than the temperature of my body.

Same water, different plumes!

A8

3 different cups, from the first, thermos bottle, stainless cup, paper cup contain hot water(all 70 degrees Celsius, 20 degrees Celsius ambient air, identical water volumes). Because ambient air temperature is lower than the water, convection heat transfer occur and plumes appear. Thus, as we learned in free convection, we can see the 3 cases as hot circular plates place at the bottom cases. Friction coefficients are different and first case provide constant heat flux which is zero(thermos bottle), while other provide constant heat flux(approximately) with nonzero(higher for second one because of larger k) values. These differences lead first, third picture have larger and smoother, thicker temperature at the edges, and friction coefficient will affect plume complexity(first has lower C_f, so smoother plumes). Additionally, although only for second case, heat transfer occurs at the bottom surface, we can ignore this effect because we observe only the top sections.

Heat solution of Nintendo Switch

A9

A thermal photo of Nintendo Switch after stress test of 1 hour. The system become steady state at highest temperature of 42degree Celsius. The main source of heat exchange between the Nintendo and outside is convection. Passive convection between the entire body and Main body was done. Also, forced convection with a fan can be observed through the thermal camera. We can see buoyant jet is generated at the middle top of the Nintendo. use heat pipe (Yellow part in the photo) with high k to deliver heat generated by chip to cooler. There are thin lines with low k at both end of main body, providing some insulation to the controller at both sides so that controller part (purple part in the photo) remained about 30degree Celsius to prevent user from burn.

How to choose the color of your car

A11

  • "Best relevance" by peer students

Relevance refers that the image and the text contain interesting features of heat transfer.

In thermal image, the brighter the color the hotter the surface. Which is corresponding to our knowledge from the heat transfer course respect to reflectivity. For opaque surface, 𝛒 + 𝛂 = 𝟏(𝛒:refelctivity, 𝛂: absorptivity). Assume all the conditions of above situation is identical in three different cars, such as surface condition(emissivity) and irradiation, except the surface color. Also, as we all know that white color reflect all the wavelength of visible range while black color can’t reflect any of the wavelength of visible range(refer to Figure 12.22). Gray color is somehow in between white and black. Which means that in visible range, which covers most of the solar radiation range, 𝛒white > 𝛒gray > 𝛒balck <=> 𝜶black > 𝜶gray > 𝜶white. And larger absorptivity means that the heat transfer to the system is become higher which makes hotter surface. So if you are very sensitive to the heat, choose the white color car.

This Fin is Too Big!

A13

I decided to take a picture of my nearby apartment that can be seen from outside the window. The temperature was about 26-30 degrees Celsius on the road(yellow), and it was about 19 degrees Celsius on the building(purple). If we consider the apartment as a huge fin(assuming there is no heating within because of weather) extending upward from the bottom parking lot surface(lecture part 3-2), we can see that the convection and conduction of the extended surface leads to lower temperatures. Assuming one-dimensional, steady-state conduction in an extended surface of constant conductivity and uniform cross-sectional area , with negligible generation and radiation, the fin equation is of the form: d^2T/dx^2 – hP/kA_c*(T – Tinf) = 0. If we let m = sqrt(hP/kA_c), for the infinite fin(since the height of the apartment is high) theta = theta_B*exp(-mx). The comparison between the temperature on the parking lot surface and the apartment is quite apparent

Thermal Inspection for Heat Transfer of a Refrigerator Compartment In Severe Heat Surroundings

A10

  • "Best expalantion" by peer students

A thermal image of an open refrigerator compartment is showing a striking contrast of temperatures. The darker bluish areas are depicting a cold environment of -4℃ to -6.8℃ inside, whereas the outer boundary of the refrigerator compartment is brightly lit at 37.7℃.
Refrigerators work on a refrigeration cycle which is the converse of a heating cycle. In a refrigerator the ability to maintain low temperatures inside, by insulating heat transfer from outside environment is important. The fridge compartment is opaque and sealed off to minimize heat transfer due to convection and radiation. After stable operation of refrigerator, its electrical power consumption was monitored using multimeter. Considering electrical efficiency of compressor and thermal efficiency of usual refrigerators, the heat flux was calculated as 319 W/m2.
With thermal gradient of 700.8 K/m through fridge boundary, the heat conduction coefficient is 0.45 W/m.K corresponding to effective insulators like wood and PVCs etc.