Viscosity and rheology would be the some very important terminologies applied in the field of chemical and process engineering. Despite the fact that both rheology and viscosity usually are related to the fluid properties as well as behavior, however these terminologies do not refer to similar processes. Thus firstly, it is very important to have a clear understanding regarding both of these factors.
The term viscosity is actually the internal level of resistance or the internal frictional factor of the fluid to the external force. It means that when the external force is applied to the fluid, or when the fluid is forced to move, then the inner opposition (viscosity) in the material resist to that applied pressure. The greater is the inner level of resistance in the material (viscosity), more is the concentration of the material. Thus it can be easily stated that this viscosity and the concentration of the fluid are directly proportional to each other. to understand more about the relation between thickness and viscosity, the flow behavior of honey and water can be taken as example. Honey has the higher viscosity then the viscosity of water, thats why thickness of honey is greater then that of water. That is the real reason that when the honey and water both are subjected to external stress; then the water flows much easily then honey.
What Is Rheology?
Rheology is considered as more complex study factor then that of viscosity. The study of rheology involves flow of fluids as well as semi solids too. Those solids that exhibit some extent of flow are also subjected to rheology. The materials having complex structures (like polymers, suspension materials, mud, petrochemicals, sludge, biological materials etc) are usually studied under rheology. However for the handling of complex fluid; only the basic theoretical understanding about what is rheology is not enough as these complex structured materials are usually not described by single value of viscosity, as the viscosity of water, but the viscosity of these complex materials changes with the change of the conditions.