Materials for severe erosion and cavitation in homogenizer components:

• Standard austenitic stainless steel (AISI 304/316) is too soft to withstand intense cavitation, high-velocity liquid erosion ($100\text{--}200\text{ m/s}$), and particle impact at $200\text{--}250\text{ bar}$.
• High carbon steel lacks necessary corrosion resistance in food-contact acid/cleaning environments.
• Stellite (a non-ferrous cobalt-chromium-tungsten superalloy) or tungsten carbide is standardly used for fabricating homogenizer valves, valve seats, and impact rings due to its exceptional resistance to abrasive wear, erosion, and cavitation fatigue.
• Nichrome steel is an electrical resistance heating alloy, not a wear-resistant structural alloy.

In centrifugal disc-stack cream separators, the conical metal discs are stacked inside the bowl at an angle of inclination of $45^\circ$ to $60^\circ$ relative to the horizontal. This specific conical angle allows denser skim milk and sediment to slide down along the underside of the upper disc outward while lower-density fat globules coalesce and glide upward along the upper surface inward.

Option analysis:

• $11^\circ - 20^\circ$: Too shallow, sediment would stall and clog the disc channels.
• $45^\circ - 60^\circ$: Correct, optimal industrial range for self-clearing disc separation.
• $25^\circ - 40^\circ$: Sub-optimal inclination angle.
• $70^\circ - 80^\circ$: Excessively steep, drastically reduces sedimentation path area.

Mechanical separations (such as filtration, sedimentation, centrifugal separation, and sieving) are physical unit operations based purely on mechanical forces and differences in physical properties (particle size, shape, density). They are applicable strictly to heterogeneous mixtures containing distinct, physically separated phases.

Option analysis:

• Heterogeneous mixture: Correct, mechanical separation requires discrete physical phases to segregate.
• Homogeneous mixture: Requires thermodynamic/diffusional separation operations such as distillation or evaporation.
• Colloidal mixture: Generally requires membrane filtration or destabilization rather than coarse mechanical separation.
• True solutions: Single molecular phase, cannot be separated mechanically.

During high-pressure homogenization, nearly all hydraulic pumping energy is dissipated as frictional heat in the homogenizing valve. The empirical thermodynamic rule for milk homogenization is that temperature rises by approximately $1^\circ\text{C}$ for every $40\text{ bar}$ ($4\text{ MPa}$) pressure drop across the valve:

$$\Delta P = P_{\text{inlet}} - P_{\text{outlet}} = 205\text{ bar} - 5\text{ bar} = 200\text{ bar}$$ $$\Delta T = \frac{200\text{ bar}}{40\text{ bar/}^\circ\text{C}} = 5^\circ\text{C}$$ $$T_{\text{outlet}} = T_{\text{inlet}} + \Delta T = 64^\circ\text{C} + 5^\circ\text{C} = 69^\circ\text{C}$$

Option analysis:

• $66^\circ\text{C}$: Underestimates temperature rise.
• $69^\circ\text{C}$: Correct, exact calculated outlet temperature.
• $70^\circ\text{C}$: Incorrect.
• $72^\circ\text{C}$: Overestimates rise.