Q1: Sewage sludge is an example of the __________ fluid.

ANS:A - Bingham plastic

A Bingham plastic is a type of non-Newtonian fluid that exhibits a behavior similar to both solids and liquids under different conditions of stress. Here are the key characteristics and properties of a Bingham plastic fluid:

1. Yield Stress: A Bingham plastic fluid behaves like a solid at low stresses because it requires a certain amount of stress, known as the yield stress (τy\tau_yτy​), to begin flowing. Below this yield stress, the fluid behaves as if it is solid and does not deform or flow.
2. Linear Viscosity: Once the yield stress is exceeded, the fluid flows like a Newtonian fluid, meaning its viscosity remains constant with respect to shear rate. Above the yield stress, the shear rate and shear stress are linearly related by a viscosity coefficient, similar to Newtonian fluids.
3. Flow Behavior: The flow behavior of a Bingham plastic fluid can be described by the Bingham plastic model: τ=τy+μγ˙\tau = \tau_y + \mu \dot{\gamma}τ=τy​+μγ˙​ where:
   • τ\tauτ is the shear stress,
   • τy\tau_yτy​ is the yield stress (the minimum stress required to initiate flow),
   • μ\muμ is the viscosity of the fluid when it flows (sometimes called plastic viscosity),
   • γ˙\dot{\gamma}γ˙​ is the shear rate.
4. Applications: Bingham plastics are found in various industrial and natural contexts. For example, drilling muds, certain food products (like ketchup), and slurries of certain types behave as Bingham plastics. Understanding their flow behavior is crucial for applications such as pipeline transport, where the ability to predict when flow will occur (based on yield stress) and the subsequent behavior under flow conditions is important.

In summary, a Bingham plastic is characterized by its yield stress, which distinguishes it from Newtonian fluids where viscosity decreases continuously with increasing shear rate, and from pseudoplastics where viscosity decreases with increasing shear rate but without a yield stress threshold.