A glossary

Chemical engineering glossary

Here is a collection of concepts on chemical engineering stuff

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Actuatuor. It refers to a mechanism to move or control a part of an electrical component or other type of devices, such as valves. Electromagnets or motors are examples of electrical actuators.

Button. Mechanical manual device to close or open a circuit, by means of the contacts.

Closed control loop. An automated control loop. In other words, without the intervention of an operator.

Contact. (Electrical) It refers to two short metal strips attached to the ends of a wire so that it may work as mechanism to allow or stop the flow of electricity through them to to energize or de-energize the circuit these are connected to.

Control loop. It is an arrangement of four elements connected to each other aiming to keep the process controlled variable as closed as possible to a set-point by manipulating another process variable (the manipulated process variable).

Controlled variable. It is the same as the process variable and is pointed out as the one to be controlled.

Dry basis moisture content. This is a companion of the wet basis moisture content. For drying operations it is usually called X (as a fraction) or 100X (as percentage moisture) and its units would be kg moisture/kg wet solid.

Humidity. It can be defined as the ratio of mass of a substance A to the mass of a substance B. There are different variations, such as: absolute humidity (for humidification operations) or dry basis humidity (for drying operations), for example.

Latching. It refers to a position in which the contact remains in hold or locked position.

Manipulated variable. It is a variable that will indirectly change a controlled variable. It is not a process variable but changes in time and one should be able to measure it. Examples of manipulated variables are flow rate and driver speed.

Open control loop. A non-automated control loop. In other words, one in which an operator performs a task as part of the loop.

Process variable. It is a, physical or chemical, parameter of a chemical process that has the following features: it changes in time, it can be measured or exist an instrument to measure it or exist a chemical technique to determine it, proper process/equipment operation may require real time or periodical monitoring of this variable and proper process/equipment operation require adjustments (control) of this variable.

Set point. It refers to the controlled process variable value at which desired process conditions are attained.

Switch. Automatic mechanism, driven by pressure, temperature or position among other variables, for close or open an electric circuit, by means of the contacts.

Valve. A device whose techonology may be mechanical, pneumatic, electrical, magnetic or of other nature and whose aim is to regulate or stop the flow of a fluid.

Wet basis moisture content. This is in fact a form of humidity. It is defined as the moisture (solvent) content of a solid or solution or suspension in terms of weight %. For drying operations it is usually given in % and its units would be kg moisture/kg wet solid ( kg moisture/(kg dry solid + kg moisture) ).