Transient Spatial Response of Various Solids Using Thermocouples

Labortory 1 Outline
Transient Spatial Response of Various Solids Using Thermocouples
By
Brad Peirson
EGR 468 – Heat Transfer
Instructor: Dr. Sozen
School of Engineering
Padnos College of Engineering and Computing
Grand Valley State University
January 31, 2008

1.0 Introduction
The general energy balance from thermodynamics applies to both blocks. Equation 1 shows the
energy balance as applied in this experiment with no internal energy sources.
2.0 Background
The experimental setup consisted of two K type thermocouples inserted into solid blocks of two
different materials. The first material tested was aluminum. The second was a potato cut into a
similar sized block. Both blocks had two thermocouples inserted into them: one located in the block
near the surface of the material and the other was located near the center of the material. The
thermocouples were connected to a PC through a National Instruments CA 1000 connector
assembly enclosure and a National Instruments Hi-Precision temperature and volt-meter. The
blocks were placed into a bath of boiling water and the computer was used to chart the
temperature at both locations in each block over time.
3.0 Experimental Results
Figure 1 shows the resulting Excel plot of the temperature of each block with time.
Figure 1: Temperature versus Time for the Aluminum and Potato Block

4.0 Discussion
Figure 1 shows that for both blocks the centerline temperature increased much less rapidly than the
surface temperature. This is a direct result of more material between the center and the water than
between the surface of the water. It would require significantly more heat (i.e. time) to heat the
block through the center than it would to change the surface temperature.
Figure 1 also shows that for both the center and the surface temperatures, the aluminum block’s
temperature raised much more rapidly than the potato. This is a result of the composition of each
material. The aluminum block has a thermal capacity of 0.896 kJ/kg°C [1]. The potato is mostly
made of water, which has a thermal capacity of approximately 4.2 kJ/kg°C [1]. A higher thermal
capacity implies that at a given surrounding temperature it will require more time to raise the
internal temperature of the potato than the aluminum. This conclusion is supported in the
experimental results.
5.0 Conclusions
The experiment was conducted in a bath of boiling water. This condition provides a certain measure
of control that a similar experiment using ice water would not. At room temperature the blocks
would naturally be above the temperature of the ice water bath. When lowered into the bath the
temperature of the water closest to the blocks would be raised slightly as heat is transferred into
the water. This would cause a natural convection at the surface with variations in the fluid
temperature immediately surrounding the block.
At room temperature the blocks are naturally cooler than the boiling water. However as long as the
water is kept boiling it is in phase change, therefore the temperature will remain constant. This
allows the system to be modeled with isothermal boundary conditions as opposed to convection
boundary conditions.
6.0 References
1. Holman, J.P., Heat Transfer, Ninth Edition. McGraw Hill, New York, 2002.