ANALYSIS
1. You will graph all three sets of data for the three intervals
using the spreadsheet and use a straight line fit to the data will be made
to determine the mass loss rate during each interval.
Follow the procedure below for all three intervals. Steps 2 and 3 pertain to
Interval #1, but you should repeat them for the other two intervals as well.
2. Use the mouse to select the mass vs. time data for Interval #1 in cells A15:B36.
Click Chart in the toolbar to bring up the chart tools. Then click the Scatter icon from the Toolbar. Then from the submenu, select the Marked Scatter icon: . The chart should appear.
Click on the legend ("Series1") and hit Delete.
Click Chart Layout in the Toolbar.
Select Chart Title and then Title Above Chart from the pull-down menu to create a title box on the chart. Enter your title in the title box.
Use the Axis Titles pull-down menu to create titles for the x and y axes.
Use the mouse to size the chart and to position it on the worksheet.
3. Now that the plot is set up, you will perform a linear (straight-line) fit to the data in order to determine the slope:
Click on any one of the data points.
Select Trendline on the Toolbar and then Trendline Options from the pull-down menu.
Select Type and choose Linear. Select Options and check Display equation on chart. The best straight line fit to the data and its equation will appear on the chart.
Record the slope of the line in cell F29 for Interval #1 (and in cells F60 and F88 for Intervals #2 and #3, respectively).
4. Take the average of the rates for the first and last 10 minute intervals in cells F29 and F88, and record the value in cell F97. Subtract this average from the rate for the middle interval in cell F60 to find the boil-off rate due to the measured power input from the heater. Record this value in cell F99.
5. From the voltage and current data in cells F39:F40, calculate the power using equation (1). Record the value in cell F41 as indicated.
6. Divide the power in cell F41 by the boil-off rate calculated in cell F99, and record the result in cell F100. The resultant value is the heat of vaporization in joules/g. Convert this value to joules/kg and place the answer in cell F101.
7. As displayed in cell F102, the accepted value of the heat of vaporization of nitrogen is 1.992 x 105 joules/kg. How does this compare with the heat of vaporization you measured? Find the percentage error between your results and the accepted value, and enter in cell F103.
8. Print out your Worksheet and submit it to the
lab instructor.