7.2  Lab Exercise: Radiation and Thermal Imaging

7.2.1 Objectives

1. Become familiar with thermal imaging equipment.
2. Explore heat conduction through different materials.
3. Examine differences between perceived and measured temperature.
4. Investigate temperature changes due to friction.
5. Experiment with thermal visibility in dark environments.

7.2.2 Equipment

• Metal pot
  
• Glass beaker
  
• Ceramic cup
  
• Thermos
  
• Wooden spoon
  
• Eraser
  
• Metal rod
  
• Outdoor jacket
  
• Hot plate
  
• Thermal imaging camera

7.2.3 Calibration

Before performing any temperature measurements with the thermal imaging camera, it is important to configure the device for accurate readings.

1. Power on the camera and allow it to warm up for 2–3 minutes.

2. Emissivity setting:
   Set the emissivity to match the material being imaged. Use the following typical values:

   • Human skin: 0.98
   • Painted or oxidized metal: 0.95
   • Wood or plastic: 0.90–0.95
   • Shiny metal (unpainted): 0.10–0.20 (requires special care)

   Note: You can usually set this via the "Settings" or "Measurement" menu on the Fluke camera. If unsure, leave it at the default of 0.95.

3. Background temperature:
   Set the background (reflected) temperature to room temperature (typically 20–25°C), unless measuring near a radiant heat source.

4. Focus:
   Adjust the focus ring or use the autofocus function (if available) to sharpen the thermal image. Blurry images may give misleading temperature readings.

5. Verify accuracy:

   • Point the imager at a known-temperature surface such as a black electrical tape patch on a room-temperature object.
   • Confirm the reading matches within ±2°C.
   • If not, check emissivity and refocus.

6. Capture reference frame:
   Take a thermal image of a known object (e.g., your hand or a heated mug) and use this as a reference for later comparison.

7. Optional—Thermal alignment test:
   If your camera supports visible-light overlay, verify that the thermal and visual images are aligned by comparing features (e.g., corners, edges).

7.2.4 Activity 1: Conduction Through Materials

1. Pour boiling water into each of the following containers:

   • Metal pot
   • Glass beaker
   • Ceramic cup
   • Thermos

2. Prediction: Rank the containers from coldest to hottest based on how you expect them to appear in the thermal image.

3. Use the thermal imager to inspect each container.

4. Discussion questions:

   • Were your predictions correct?
   • Which material appears hottest in the thermal image? Coldest?
   • Which material conducts heat best? Why?
   • Does the surface of the water appear to be the same temperature as the container walls?

5. Insulation test:

   • Have one team member remove their jacket and let it sit at room temperature for five minutes.
     
   • Then have them put the jacket back on for two minutes.
     
   • Use the thermal imager to inspect the inside and outside of the jacket.

6. Discussion:

   • Is the inside of the jacket a different temperature than the outside?
   • What does this suggest about thermal insulation and body heat retention?

7.2.5 Activity 2: Perceived vs Actual Temperature

1. Touch the wooden spoon and the metal rod with your hands. Predict which one is colder.

2. Measure the temperature of each using the thermal imager.

3. Discussion:

   • Were your predictions correct?
   • Why do some materials feel colder even if they are at the same temperature?

4. Hold each object (wooden spoon and metal rod) in your hands for two minutes.

5. Use the thermal imager to capture the temperature of each object after holding.

6. Discussion:

   • How does the thermal image compare with how the objects feel?
   • What does this suggest about thermal conductivity and heat transfer from your hands?

7.2.6 Activity 3: Friction and Heat

1. Take a thermal image of your palms while they are at rest.

2. Rub your hands together vigorously for 5–10 seconds and take another image.

3. Observation: How has the temperature distribution changed?

4. Rub an eraser on a tabletop while observing it with the thermal imager.

5. Observation:

   • Can you see a heat signature?
   • What does this reveal about heat generation due to friction?

7.2.7 Activity 4: Visibility in Darkness

1. Enter a dark room with the thermal imager. Be careful not to trip!

2. Point it at your classmates.

3. Discussion:

   • Can you see them?
   • How does thermal imaging enable visibility without light?

7.2.8 Analysis and Discussion

1. How did emissivity affect your temperature measurements?
2. Which materials showed the highest thermal contrast and why?
3. What are the advantages and limitations of using infrared cameras in engineering diagnostics?