Abstract
The purpose of this experiment is to show the characteristics of the boiling phase change concept. The regions include free convection, nucleate, transition, and film boiling.
The experimental value for maximum heat flux has been calculated to be 1244 W/m^2 and the theoretical value is 137090 W/m^2. This yields a percentage error of 99.1 % which is considered high. From the curves we can see that temperature decreases incrementally as time passes.
The large error in the calculation of the values for the heat flux can be explained by having started the DAQ software before placing the sphere into the liquid nitrogen cylinder and this time was not identical for both spheres. Another possible area of error is the measurement of the diameter of the spheres and it is a very crucial measurement as if affects Volume, Area and the diameter that are all part of important results. Doing several runs of measuring the diameters and averaging it might have yielded better experimental results.
Outline Lab Procedure
1. Measure the diameters of the two spheres.
2. A dewar is filled with liquid nitrogen upto one third of its volume and has two thermocouples attached to it.
3. Choose one of the spheres to have it quenched in a bath of liquid nitrogen.
4, Setup and configure the data acquisition software.
5. Click the manual trigger button on the DAQ prior to inserting the sphere into the dewar of liquid nitrogen and also click the start button to monitor the changes in temperature.
6. Observe the boling phenomenon that occurs in the transient period.
7. Stop the data acquisition software once the minimum temperature has been reached.
8. Remove the sphere from the liquid nitrogen dewar and place it in a dewar filled with water and observe.
9. Data will be automatically exported to Excel and Columns B and C correspond to the temperatures of the two thermocouples.
10. Repeat the experiment for the other sphere.
11. Since this is a short experiment in terms of time duration, do it multiple times to ensure accuracy of results.