Thermal Image Contest

2023 Thermal Image Contest

What is your password?

When I was going to use my thermal camera outside for inspiration, it started raining, so I had to go back to my room. Right before entering my room, I tried taking a photo of the keypad using thermal camera and saw fingerprints on it after I had entered the passcode (they’re shifted slightly upward). This gave me an idea. A few days later, me and my friend went to his room to work. I told him that I could guess his password. He did not believe it but still wanted me to try, so he entered the room first. I took a picture of the keypad and saw the numbers 3, 5, 7. Since his phone number ended with 5375 and the password had four digits, I used that as my guess and managed to get in. He changed his passcode the very next day.

Wait, is this a speaker?

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

At first glance, it looks similar to the speaker with an electric wire. Surprisingly, it is the thermal image of an air conditioner outdoor unit! During hot summer, you may have felt a sudden warm air blowing into you while walking near a building. It's because of this unit. When the air conditioner runs, the refrigerant absorbs heat from the inside by evaporation and emits heat to the outside by condensation. The refrigerant flows through the pipe (internal flow), and convection occurs between the fluid and the pipe. The fins are attached to the pipe like a heat exchanger. Material with high thermal conductivity is used to facilitate conduction, such as copper. Thanks to the fin and the fan, the heat is efficiently removed by forced convection, and the cooled refrigerant goes back inside. As shown in the image, the refrigerant pipe to the inside is cold, showing 11.0 degrees.

The Thermal Flower and the Thermal Fairy

I took a picture of five lights hanging side by side. In our naked eyes, we cannot notice that the corresponding area near each light also has a higher temperature than the ambient. However, the lights emit heat radially and it heats the area of the ceil near it. We can guess that free convection occurs around the light so that the hot air arises toward the ceil, and also the electromagnetic waves with visible range wavelength will be emitted from the light.

I have drawn some lines to show the image reminded with the picture. The corresponding heated area of each light looks like a flower in a forest and the lights themselves resemble a scrumptious fruit hanging on a green bush, and I imagined a fairy sitting on the middle fruit with a white dress, which is the heat source of the lamp in reality.

It is not how it looks – reflectivity and absorptivity

The image initially resembling a crime scene actually portrays a knife coated with water from an ice bath. The knife was briefly submerged in the water, aligning its temperature with the ambient room temperature of approximately 27℃ at the time of the image capture. However, thermal camera readings indicate temperatures of 34.3℃ and 11.0℃ for two distinct regions on the knife, prompting an explanation for this discrepancy.

The lower temperature region (11.0℃) is actually the temperature of the water from the ice bath. Water exhibits high absorption in the Infrared (IR) spectrum, rendering it opaque within this range, in contrast to its transparency in visible light.

Conversely, the higher temperature region (34.3℃) appears hotter than it truly is due to the stainless steel's high reflectivity. My close proximity to the knife, coupled with the surrounding irradiation, caused a lot of IR radiation to be reflected from the knife's surface.

The “Not So Hot” Band Performance

This image captures a band performance in KAIST. From bare eyes, the insides of the hall can be quite dark. However, the thermal camera is able to constantly “see” by detecting IR, visible and UV waves (mainly IR) emitted through radiation from the surroundings. 

The air-con appears cold (dark blue) due to cooling by forced convection of cold air being pumped out from the outlet vanes; While the spotlights and people appear hot (bright, orange & yellow) due to heat emitted by radiation. 

Temperature of human is about 37⁰c, but the predicted temperature is much lower. This is because human not a blackbody, and the emissivity of the human body and the reference emissivity of the thermal camera is different. The same goes for the air-con (different actual temperature). 

The crowd was excited because the band was “on fire”. However, the thermal camera proved that it’s not true. 

What Color We Need to sit, in Hot Summer

The image above shows that the brighter the color of the brick, such as white, the higher the temperature, and the different the temperature of the brick. This is deeply related to the absorptivity and reflectivity of heat transfer. This means that for the wavelength range of visible light, the closer to black, the relatively high absorptivity, the lower the reflectivity, and the closer to white, the lower the absorptivity and the higher the reflectivity. Therefore, the higher the absorptivity or the lower the reflectivity, the more heat is transferred to the object, and the hotter the surface is measured. If we had to sit somewhere outside on a hot day, we wouldn't have to sit on a black object, or on a floor, or on a brick, but rather on an object as bright as possible or as white as possible to avoid the heat.

Exploring the window’s left-right thermal contrast

The pictures are the left and right window cross sections of my dormitory room, taken by opening the window to the edge. The ambient outside temperature was 22°C.

On the left side, where the inside wall temperature is 27.9°C and the outside surface temperature is 15.3°C, this temperature difference is due to the different thermal properties of the materials involved. The thicker brick outside the surface acts as insulation, hindering the heat transfer from the outside environment to the inside of the room. The inside wall has a higher temperature due to the warmer indoor air.

On the right side, where the inside temperature is almost the same as the other side and the outside surface temperature is 19.3°C the absence of a brick exterior surface allows more rapid heat transfer between the outside environment and the window frame. Thus, the outside temperature is closer to the ambient temperature.

2022 Thermal Image Contest

The criminal always leaves a trace
– thermal footprint


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? 


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


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


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


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


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


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


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!


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


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


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!


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 


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.