Excel

7. The possibility of a typo increases as the formula to be entered getsmore

complex. Sometimes, it is advisable to break the problem into steps and

obtain answers in which you have confidence. Then, you can attempt to

code the problem in a simple formula. We will look at an example.

An engineer working with a gas-sparging system needs to compute

Pm from the equation:

log10

Pm

Pmo

� � ¼ 192

Dl

DT

� �4:38 D2 l N

v

!0:115 DlN

2

g

� �1:96 Dl DT

� � Q

ND3 l

� �

Make a worksheet similar to Figure 2.28 by computing the four

variable terms on the right-hand side of the equation separately in

1 2 3 4 5 6 7 8 9

A B C D E Gas-Sparge System Pmo 794 (Dl/DT)^4.38 0.004768 Dl 0.36 (Dl²N/v)^0.115 4.415957 DT 1.22 (DlN²/g)^1.96(Dl/Dt) 0.486494 N 2.8 (Q/NDl³) 0.031844 v 8.93E-07 Right side 0.06263 g 9.81 Pm 917 Q 0.00416 Computed Pm 917

n FIGURE 2.28

34 CHAPTER 2 Basic Operations Chapter 2 Problems

E2:E5. They are combined with the 192 constant in E6 and Pm is

computed in E7. You should check each term with a hand calculator.

Then, in B9, enter a single formula to compute Pm. In a real-life

situation, once agreement has been reached between B9 and E7, the

range D2:E7 could be deleted.

8. *When a person stands in the wind, the air feels colder than when the

air is still. The apparent temperature is called the wind chill (Twc) and

is computed from the formula shown in Figure 2.29 where Ta is the

air temperature. The values shown for parameters a through d are for

degrees Celsius computations. Ta is the air temperature and V the

wind velocity. For Fahrenheit computations, use 35.74, 0.6215,

�35.75, and 0.4275 for the parameters and express V in mph. The

cells B4:B7 have been named by the letters to the right.What formula

can be used in E5 such that it can be filled down and across to make

the table? Be careful with the name for the cell B6. Can you easily

modify your worksheet for Fahrenheit work?

13. Recursion may be used to solve certain mathematical problems.

The Babylonian (also called Heron’s) method to find square roots is

summarized by the recursive equation: xi+ 1 ¼ 1

2 xi +

N

xi

� � : Or in

words, (1) make a guess, (2) divide your original number by your

guess, (3) find the average of these two numbers, and (4) use this

average as your next guess. Make a worksheet similar to that in

Figure 2.33 and test it for various values of N. Later, we shall meet

the SQRT function.

37Play It Again, Sam