After about 40 minutes of driving, this thermal image captures the engine bay of a car. On the left side, the bright yellow container is the coolant reservoir, indicating that the coolant temperature is quite high after extended engine operation. The strong yellow and white colors in this region show intense heat, confirming significant thermal buildup in the cooling system. At the very top of the second image, you can see a straight pipe running through the radiator. Notably, the brightness decreases as you move along the radiator, which clearly indicates that a temperature gradient exists across the radiator, demonstrating efficient heat transfer, which is critical for engine protection.

Thanks to my friend Seunghyun Ha. This figure shows a person wearing glasses with showing forehead with his hand. Since the infra-red ray cannot penetrate glasses, the camera cannot receive heat emission from near eyes. We can observe that the forehead appears warmest region in face since it has thin skin and lots of blood vessels under the skin, so more heat can reach the surface. Also, you can see cheeks and jaw look cooler than the forehead, and this happens because of several factors. One of the factors is angle. The forehead viewed perpendicularly, so the camera takes 100% heat from it. However, cheeks and jaw have angles, so the emissivity drops, and it looks cooler than the forehead. Another factor is physiological differences, such as skin thickness and vascular activity difference. So, we can expect that cheeks and jaw have thicker skin than the forehead.

The tablet PC is running its own processor while charging its battery. It is shown that the center of the screen has the highest temperature, due to electrical heating. Since the note application is not performance-demanding, we can conclude that the generated heat is most from charging the battery. Therefore, the location of the battery and its charging circuit should be the center of the device. The charging cable also shows electrical heating, and the jacket of the cable reduces the surface temperature (conduction on a tube wall). Also, the edge of the device shows higher temperature than that of the adjacent screen, due to the higher thermal conductivity of aluminum.

On the other hand, the energy drink can (mandatory for homework) and the black ceramic cup are both subjected to the radiation of the tablet PC. The measurement shows that the can has higher reflectivity than the cup.

Have you ever wondered what is behind the walls of the bathroom? Where do the pipelines go? Where does the water come from? This thermal image shows a bathroom sink shortly after hot water usage. You can see that aside from the pipe that is connected to the drainage hole of the basin, there is another yellow line that starts from the basin and goes across the floor. This is the pipeline that supplies hot water to the faucet, which is hidden behind the walls. The hot water transfers heat to the pipe by convection, which again heats the wall and floor next to it by conduction.

 Another fact you can observe is that the faucet on top of the basin glows the brightest. This is because the faucet is made of steel, which has a higher conductivity than the ceramic basin, making it the hottest part in the picture.

This photo shows iced tea made at a school festival. The contrast with the hot temperature outside is visible, and at the same time, the water and ice are transparent to our eyes, and the hot background behind them is rendered in a cool purple hue, confirming that the water and ice are not transparent in the infrared.

This is a picture of my friend and her reflection. It's straightforward, right? However, it could be seen in a deeper aspect. As we can see, the temperature of her reflection differs from her body temperature even though her reflection and herself look alike. Why? Because the mechanism of the FLIR camera is detecting infrared radiation, emitted from a heat source (thermal radiation) while the image reflection is the work from visible light (optical phenomenon). The image is virtual so what the camera detects is the thermal radiation from a mirror which is a different heat source with a different surface from a person's body.

It reminds me that even the person I see in the mirror is not really me. Besides, my feelings when I see myself in the mirror always change every time. I feel like it's hard to find the answer to the question, "Who am I?"

While studying in N7, I felt cold and noticed that the window was only half closed. Its outer pane was shut, but the inner one remained open. After closing the inner pane, the room warmed up. Before leaving, I took the thermal image of the space in between the windows.

At first, the image might not seem interesting, since it shows that surfaces have similar temperature – a problem case we’ve solved earlier in the semester. However, what stood out was the lower temperature between the two panes, indicating a small gap in the frame that allows cold air to enter. In this case, the inner pane prevents cold airflow from reaching the room. It traps the air, reducing mass flow into the room, and therefore heat transfer. If the gap was fully sealed, a single, isolated window might be enough.

So, double window secret: the inner pane improves isolation by stopping cold airflow.

The temperature of the wheels of a car that has just been parked after driving is higher than that of the wheels of a car that has been parked on a day when the surface temperature is about 40 degrees. In addition, while the temperature distribution of the wheels of a parked car is generally uniform in a state of thermal equilibrium, a car that has just been parked has a higher temperature in contact with the surface and is lower toward the center. The degree of temperature drop will increase toward the center. The reason is that the same boundary condition is the same at the same r, because heat is less transferred in a circular motion situation.

This thermal image captures the moment a hairdryer was turned on atop a desk. The bright white and yellow zone at the nozzle tip represents a high-temperature stream of air reaching nearly 57.4°C, shooting out in a distinct cone-shaped path. The surrounding cooler environment is shown in purple, highlighting a clear boundary between heated and unheated air.

The heat transfer here is dominated by forced convection, as the electric motor blows hot air rapidly forward. You can also observe how the air closest to the nozzle is the hottest, gradually cooling as it spreads out, which reflects both advection and heat dissipation through mixing with ambient air.

Interestingly, the heat path resembles a torch or “invisible flame,” emphasizing how everyday appliances like a hairdryer manipulate thermal energy in a highly directional and visual way — if only we could always see it this clearly.

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.

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.

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. 

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.

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.

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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.