Fundamental Dimensions and Units

Chemical engineers and scientists will know that the data they use are expressed in a great variety of different units. The length of a rod may be variously described as 12 in, 1 ft, 0.3048 m, 304.8 mm, etc. These lengths are all equivalent. Inch, foot, metre and millimetre define the size of the unit and 12, 1, 0.3048 and 304.8 define the number of the units in each system. There are many useful references in the literature that discuss conversion between units and tabulate conversion factors.1,4,5 

Although the units for each of the measurements above are different, they share the same fundamental dimension, length L. Each of these measurements has the dimensions of length. 

Velocity is the distance travelled per unit time and so has the dimensions of length, L, over time, T, or LT 1. The quantity of material, given by its mass, has the dimensions of mass, M. 

length, L and time, T, are called fundamental dimensions. With heat transfer problems, temperature, , and heat, H, are introduced as fundamental dimensions (see Section 6.7.4). 

Astarita6 presents a brief history of the concept of dimensions and dimensional analysis from Euclid to the present day. 

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