Experiment 3 - Lumped Systems Analysis

A 1" brass ball, heated in an oven to 150C, is cooled in a low velocity air stream

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Students were divided into 2 teams. Each team constructed a k-type thermocouple from insulated thermocouple wire which was then soldered into holes drilled into the 1 " solid metal balls. The balls equipped with the thermocouples were heat soaked in an oven at 150 C for 1 hour. At the beginning of the test the heated ball was suspended in an air stream made parallel by a long tube. The air stream velocity was a few m/s. In lumped system analysis the thermal conductivity of the solid is large compared to the heat transfer coefficient from the surface in the air flow so all points in the interior track the exponential surface temperature decay. In this experiment a Radio Shack Digital Multimeter is used along with a K type thermocouple interface. Temperature data is logged to a file in real time for subsequent lumped system analysis.

A student team consisted of (a) team leader responsible for making sure that all tasks of the experiment were accomplished, (b) a member responsible for the thermal soak of the ball in the oven before exposure to the airstream, (b) a member responsible for reading the air flow apparatus manometer for the static and dynamic port pressure, and for the calculation of air flow rate from these values, (c) data takers to make sure the exponential temperature decay experienced by the ball in the airflow was recorded in an electronic log (Radio Shack MeterView) and recorded manually as a back-up, and (d) a member responsible for photography and video tape recording.

A Radio Shack Digital Multimeter with a reference junction thermocouple compensator was used to read the k-type thermocouple embedded in the ball. This meter has an RS232 output which was connected to the experiment laptop running Radio Shack's MeterView software for logging the data at a user-selectable sample rate.