To accommodate for this, we need 3 tests. A properly design plant would have considered this as break downs / power cuts can be expected from time to time. Regarding break downs there are many who simply does not account for this during the design which leaves customers to make some quite interesting solutions when the pipes are blocked after an emergency break down. It may also be difficult to reach pressures on positive pumps as they need this to minimize slip in the pump. However, this will usually result in high investment costs, and a plant which doesn’t running smoothly afterwards. The most common misunderstanding regarding viscosity is using the viscosity at no shear as the production viscosity.
During a breakdown we have no movement, are losing temperature and time is at the essences. During production we have a lot of shear, usually elevated temperature and constant movement. The two scenarios are fundamentally different. When designing a plant for high viscous products we basically need to know a) what is the viscosity during production, b) what is it in case of a break down and c) how fast should we react in case of a breakdown? Once the fluids stop it will slowly recover the initial viscosity (i.e. These are characterized by having a high viscosity when standing still, which decreases once in motion (due to shear forces). Within the food industry the most common non-Newtonian fluid is shear-thinning, time dependent relations also called thixotropic fluids. The reality is much more complicated, and as viscosity increases, we need to take these things into account. I recall myself from the time at university that we most of the time assumed the fluids to be Newtonian, and thus only changed with temperature. When it comes to viscous fluids, there are a lot of misunderstandings and mystery, especially when we talk shear sensitive fluids.
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