Conversion of units

Conversion of units from one system to another is simply carried out if the quantities are expressed in terms of the fundamental units of mass, length, time, temperature. Typical conversion factors for the British and metric systems are  

Force 1 pound force = 32.2 poundal = 4.44 x 10 dyne = 4.44 N Other conversions are now illustrated. 

Convert 1 poise to British Engineering units and SI units. 

Conversion factors to SI units from other units are given in Table 1.2 which is based on a publication by Mullin  

The conversion of units is easy. We show this for the velocity. Suppose we want to convert kmh into m s -So what is a velocity of 90 km h in ms We simply insert the conversion factor in the units itself 

Therefore, 90 kmh = 90 x 1000 m(3600 s) . Finally we gather the numbers which arose in the expression and obtain 

The conversion of units does not take place in balancing an equation. If we write 

We show this for the pressure. If we want to convert mmHg into Pa, then a little bit more effort is needed. The unit mm Hg looks like a length but refers to a pressure that is exhibited by a column of mercury at 0 °C and standard earth acceleration g [ms ]. 

Without thinking about details, how heavy such a column might be, we start with a formal procedure. We regard now mmHg as a length as such. We convert at first mm Hg in m Hg, because we need the height in meters  

A measured quantity can be expressed in terms of any units having the appropriate dimension. A particular velocity, for instance, may be expressed in ft/s, miles/h, cm/yr, or any other ratio of a length unit to a time unit. The numerical value of the velocity naturally depends on the units chosen. 

The equivalence between two expressions of the same quantity may be defined in terms of a ratio  

Ratios of the form of Equations 2.2-1,2.2-2, and 2.2-3 are known as conversion factors. 

To convert a quantity expressed in terms of one unit to its equivalent in terms of another unit, multiply the given quantity by the conversion factor (new unit/old unit). For example, to convert 36 mg to its equivalent in grams, write 

If you are given a quantity having a compound unit [e.g., miles/h, cal/(g °C)], and you wish to convert it to its equivalent in terms of another set of units, set up a dimensional equation write the given quantity and its units on the left, write the units of conversion factors that cancel the old units and replace them with the desired ones, fill in the values of the conversion factors, and carry out the indicated arithmetic to find the desired value. (See Example 2.2-1.) 

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Since data have been collated from a variety of sources, and tend to be presented in mixed units, and because rapid conversion of units is an advantage in many on-site situations, conversion tables are included in Chapter 18. Finally, since safety with chemicals cannot be addressed exhaustively in a handbook, selected sources of reliable current information on chemical hazards and their control are listed in Chapter 19. 

The quotient 1 L/1000 cm3, which is called a conversion factor, is multiplied by 536 cm3. Because the conversion factor equals 1, this does not change the actual volume. However, it does accomplish the desired conversion of units. The cm3 in the numerator and denominator cancel to give the desired unit liters. 

That is, we use a factor to change the units (mol to g) for one substance (A) or we use a factor to express the ratio of substances (B to A) in terms of the same unit (mol). If we follow the diagrams in the figures in this chapter, do we ever use one factor to make both a conversion for substance and a conversion of units simultaneously ... 

You supplied the result on data line A. You need only nake the proper conversion of units ... 

The following problems illustrate conversions of units. Note that in all such computations it is important to include the dimensions of numbers, just as stressed in Chapter 3, and that the use of these dimensions helps to avoid errors. 

Example 6.3 is an exercise in conversion of units of the energy balances. 

Under such conditions, the focus of retrofitting and revamping existing units will be optimizing middle-distillate production. Consequently, to meet higher quality requirements for middle distillates, E.U. refiners are projected to invest in hydrocracking capacity. Such investments may include standalone units and moderate conversion of units upstream of the FCC.15 Refiners will also raise hydrotreating capability. 

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