Two of the most useful experimental devices are strain gauges and thermocouples. In this lab you actually construct
a K-type thermocouple by soldering together a Ni-Cr and a Ni-Al wire to form a junction. You will learn how to attach
your junction to a specimen, such as a metal object, to obtain a compensated, true temperature reading in C or F. You will
read the junction with a digital multimeter that establishes 0 C as the reference, and you will learn how to log data at
various sample rates.
In this experiment 2 thermocouples are made by the student team then mounted on a rectangular metal plate. One end of the
metal plate is heated for a few minutes by a torch then left to cool in air. The rise and fall of temperature at the two locations
is logged. In the Heat Transfer lecture course, transient, 2-D modelling in Excel is being studied at this time. The student is encouraged
to attempt to model the observed results with the lecture theory.
Lab 3 Analysis Suggestions
- Describe the construction of the thermocouple
- Describe the mounting on the test specimen
- Discuss calibrating the voltmeters
- Describe the test done and how the measurements were made
- Organize the data
- Discuss converting the voltages to temperatures
- Plot temperature vs time for the 2 locations
- Determine the exponential rise and fall of the temperature wrt time
- What is the time constant, how does it compare to rhocpV/hA as given on page 166 for various values of h?
- Can formula 5-3, page 165, describing Lumped Heat-Capacity Systems be applied to the cooling portion of the data making some rough assumptions of boundary conditions, ie make a guess for the temperature of the heated side and for the unheated sides. Consider convection occurring from all unheated surfaces.
- Try modelling the heating and cooling phases according to example 5-14 on page 210.
- Discuss problems with the experiment and what could be done better next time such as using radiation thermometry to measure the temperature of the gas flame and of the heated surface.
- Discuss organization of the team approach, ie what assignments and responsibilities were given to the team members?
