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Chemical Engineering Fluid Flow, Heat Transfer and Mass Transfer - VOLUME 1 - Sixth Edition by J. M. COULSON and J. F. RICHARDSON with J. R. BACKHURST and J. H. MARKER.
Students of chemical engineering soon discover that the data used are expressed in a great variety of different units, so that quantities must be converted into a common system before proceeding with calculations.
Standardisation has been largely achieved with the introduction of the Systeme International d'Unites (SI)(1' 2) to be discussed later, which is used throughout all the Volumes of this series of Chemical Engineering books.
This system is now in general use in Europe and is rapidly being adopted throughout the rest of the world, including the USA where the initial inertia is now being overcome.
Most of the physical properties determined in the laboratory will originally have been expressed in the cgs system, whereas the dimensions of the full-scale plant, its throughput, design,
And operating characteristics appear either in some form of general engineering units or in special units which have their origin in the history of the particular industry.
This inconsistency is quite unavoidable and is a reflection of the fact that chemical engineering has in many cases developed as a synthesis of scientific knowledge and practical experience.
Familiarity with the various systems of units and an ability to convert from one to another are therefore essential, as it will frequently be necessary to access literature in which the SI system has not been used.
In this chapter the main systems of units are discussed, and the importance of understanding dimensions emphasised.
It is shown how dimensions can be used to help very considerably in the formulation of relationships between large numbers of parameters.
The magnitude of any physical quantity is expressed as the product of two quantities; one is the magnitude of the unit and the other is the number of those units.
Thus the distance between two points may be expressed as 1 m or as 100 cm or as 3.28 ft. The metre, centimetre, and foot are respectively the size of the units, and 1, 100, and 3,28 are the corresponding numbers of units
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