Thermal Conduction Lab

Conduction Lab Planning Day

Safety Concerns

In this lab, the resistor inside the box enclosure will be dissipating heat and may get hot enough to cause skin burns.

Materials

  • DC power supply with current display
  • Test leads with clips
  • Multimeter
  • Power resistor
  • Enclosure

Planning

Devise a plan to measure the conductive behavior a small enclosure.

q = UA \Delta T

Note that even though this enclosure has three dimensions and six sides, we can treat it as one-dimensional steady-state conduction.

Our tools so far:

  • Power supplies
  • Thermometers
  • Resistors

Consider these questions:

  • What tools can we use?
  • Which of the variables in the equation can we control?
  • Which can we measure directly?
  • Which can we measure indirectly?
  • What other heat transfer mechanisms should we consider?
  • How would you tabulate your data?
  • What could we graph?
    • Would we observe a slope or an area?
  • Under what conditions would \Delta T vary for the same power input? (this is the key to the steady-state assumption)

Sketch a labeled diagram of the different pieces and indicate how they relate to the equation.

Devise a plan to determine how well our small model home adheres to our equation for heat conduction:

Steady-State

Note that our equation for conduction is only valid if no energy is being converted. That is when the energy in equals the energy out. When we start applying power, some of the energy is heating up the box and the air inside the box. This is energy conversion.

Data Collection

  • Group up into teams
  • Revisit your data collection plan
    • You are taking temperature difference and power observations at steady-state
  • Select a model home box to measure
  • Plan to take data at 2, 4, and 6 watts of power
    • using your resistor value, estimate the voltage for your power levels
    • use the power supply to tune your power if your estimate is slightly off
  • Take careful data and notes
  • Take photos of your apparatus
  • Take a photo of your notes

Tips:

  • as the temperature increases, take periodic readings to better visualize the leveling off of the temperature
  • use Ohm’s Law and the equation for electrical power to set your voltage for the resistor.

Data Analysis

  • Review your collected data
  • Decide in your group how you will plot your data
  • Explain to each other what parts of the graph relate to the experiment and the equation
  • Quantify the UA value of this box
  • We will share results in class

Exercises

1 Conduction Fundamentals Notes

Read the notes on conduction fundamentals and answer the following questions:

  • What are the direct measurements we could make when observing one-dimensional steady-state conduction?
  • What are the indirect measurements we could make?

2 Proposed Procedure

Write up a procedure that you will follow to set up an experiment, collect data, analyze the data, and interpret the result.

3 Final Graph and UA Estimation

Turn in a scan of your notebook. It should show:

  • your graph of temperature vs power
  • the calculation of the slope
  • how the slope was used to calculate of your UA value.

4 After Analysis Reflection

Please write a short essay (at least 50 words) covering the following questions.

  • What new things did you learn?
  • What surprised you?
  • What was key for your understanding?