Lesson 8 - Control of Fluid Flow 1
This lesson will consider two main classifications of pumps: centrifugal and positive displacement. These will be introduced together, with aspects of their design and operation. The lesson will also pull together various fluid mechanics concepts from previous lessons, such as the Darcy-Weisbach equation and the use of loss-coefficient to calculate pressure drops in pipe systems. It will use this information to then size pumps for particular pipe systems.
Preface
So far in our study of fluid mechanics, we have considered various elements of both fluid statics and dynamics. This has allowed us to quantify aspects of pressure and pressure drops within a tank and tank-and-pipe system. Now is the time to consider the piece of equipment which, in most industrial situations, is used to promote flow and overcome the pipeline pressure drop – the pump.
We will consider two classes of pump: centrifugal and positive displacement pumps, their design and operation, how we operate them in practice, and how we go about sizing a pump for a particular operation.
Transporting liquids
As we have discussed, it is an inherent need of the brewing and packaging processes to transport liquids. Although it is possible to transport liquids without pumps, through the use of gravity or gas pressure, these approaches are not widely practised. There is a need to build a brewery vertically, or on a hillside in the case of gravity feed. We must also consider the cost and controllability issues of gas-driven transport.
In the case of gravity to induce flow, this can be done by elevating the process to provide the head to distribute fluid through the site. Even in situations such as this, there is an inherent disadvantage with gravity feed. The maximum flow rate possible is governed by the height of feed tanks above the intended point-of-use. In practice, a larger flow rate may be required, and in such cases, pumps will be essential.
Do some further reading on tower breweries if you wish. These are types of plants which are part of the rich history of brewing, and in some cases still in use today. They utilise gravity to assist in the downward flow of brewing water, and wort, etc.
In most practical situations, pumps are the foundation of the brewery with regards to transporting liquids. A pump can be defined as a machine that converts mechanical shaft work into principally kinetic energy of a liquid. The mechanical energy is usually (we will consider some exceptions) transmitted via a rotating shaft, and although a huge variety of pump types are available, they can generally be placed into one of two categories:
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Centrifugal pumps (rotodynamic pumps)
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Positive displacement pumps
Let us look at these categories in turn, starting with centrifugal pumps.