3.4 Conversion Constants
A significant amount of a practicing engineer’s time is spent in converting data and equations from one set of units to another. As long as scientists provide data and information in grams and centimeters while engineers calculate in terms of pounds and feet, this confusion in terminology will continue to exist. For the most part, the units in this text are consistent with those adopted by the engineering profession in the United States.
The physical, biological, and chemical properties of materials are important considerations in any study of desalination. To promote a better understanding of such properties, many of which are covered in Chapter 04, some definitions are briefly introduced in this section. Equations used in engineering as well as in the physical sciences are dimensional equations. The choice of the fundamental system of units determines the magnitude of the quantity described. Since the choice is optional, it is usually made to suit the convenience of a certain segment of the scientific community. For example, astronomers measure distance in light years, nuclear physicists employ angstroms, engineers use feet, etc. Engineers in the United States generally employ English units, but technical individuals need to be able to convert from one system of units to another.
Information on conversion constants (sometimes referred to as conversion factors) for length, mass, time, force, pressure, volume, energy, power, concentration, viscosity, and heat capacity are provided in Table 3.2. Commonly used water and water-related conversion constants, as they relate to volume and volumetric flowrate, are provided in Tables 3.3 and Table 3.4, respectively.
Table 3.2 Conversion constants.
| To convert from | To | Multiply by |
| Length | ||
| m | cm | 100 |
| m | mm | 1000 |
| m | microns (µm) | 106 |
| m | angstroms (Å) | 1010 |
| m | in | 39.37 |
| m | ft | 3.281 |
| m | mi | 6.214 x 10-4 |
| ft | in | 12 |
| ft | m | 0.3048 |
| ft | cm | 30.48 |
| ft | mi | 1.894 x 10-4 |
| Mass | ||
| kg | g | 1000 |
| kg | lb | 2.205 |
| kg | oz | 35.24 |
| ton | 2.268 x 10-4 | |
| kg | grains | 1.543 x 104 |
| lb | oz | 16 |
| lb | ton | 5 x 10-4 |
| lb | g | 453.6 |
| lb | kg | 0.4536 |
| lb | grains | 7,000 |
| Time | ||
| s | min | 0.01667 |
| s | hr | 2.78 x 10-4 |
| s | day | 1.157 x 10-7 |
| s | week | 1.653 x 10-6 |
| s | yr | 3.171 x 10-8 |
| Force | ||
| N | kg-m/s2 | 1 |
| N | dynes | 105 |
| N | g-cm/s2 | 105 |
| N | lbf | 0.2248 |
| N | lb-ft/s2 | 7.233 |
|
lbf
|
