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Sameeksha.

A centrifugal pump adds energy to the fluid using a rotating impeller — kinetic energy is converted to pressure head. Flow varies with the back-pressure (system curve), and it must be primed. Best for high flow, low-to-moderate head, low-viscosity fluids.

A positive displacement (PD) pump traps a fixed volume and forces it out — flow is almost constant regardless of pressure, so it can build very high pressure and handle viscous fluids. It needs a relief valve because dead-heading can burst the line.

Cavitation happens when the local pressure at the pump suction drops below the liquid's vapour pressure, so vapour bubbles form and then collapse violently on the impeller — causing noise ("pumping gravel"), vibration, and erosion damage.

NPSH (Net Positive Suction Head) is the suction-side pressure margin above vapour pressure. To avoid cavitation you need NPSH available > NPSH required. Fix it by raising suction level, lowering temperature, shortening/widening suction piping, or reducing pump speed.

Reynolds number is the ratio of inertial to viscous forces — it tells you whether flow is smooth or chaotic.

• Re < 2100 → laminar (smooth, ordered layers)
• 2100 – 4000 → transition
• Re > 4000 → turbulent (mixing, eddies)

It's dimensionless, so it lets you scale up from lab to plant.

Distillation separates components by difference in volatility (boiling point). Vapour rises and liquid falls through trays (or packing); on each stage they contact and re-equilibrate, so the lighter component concentrates at the top and the heavier at the bottom. A reboiler supplies vapour at the bottom; a condenser condenses vapour at the top.

Reflux ratio = liquid returned to the column ÷ distillate taken out (R = L/D). Higher reflux → better separation (purer product) but more energy and a bigger column. There's a trade-off between number of trays and reflux — that's the McCabe–Thiele idea.

In counter-current flow the two fluids move in opposite directions, keeping a more uniform and larger temperature difference along the whole length. This gives a higher LMTD (log mean temperature difference), so you transfer more heat with less area. It can also cool the hot stream below the outlet temperature of the cold stream — impossible in co-current.

Co-current (parallel) flow has a big ΔT at the inlet that collapses quickly, so it's less efficient — used only when you need to limit the maximum wall temperature.

Absorption is a bulk phenomenon — a substance penetrates into the volume of another phase (e.g. CO₂ gas dissolving into a liquid solvent in a packed column). It's like a sponge soaking up water.

Adsorption is a surface phenomenon — molecules stick to the surface of a solid (e.g. moisture or colour onto activated carbon / silica gel). It's like dust settling on a table.

When a particle falls through a fluid, it accelerates until drag balances gravity (minus buoyancy) — then it falls at a constant terminal / settling velocity. For small particles in laminar flow, Stokes' law applies:

So settling is faster for bigger, denser particles and slower in more viscous fluids. This governs sedimentation tanks, clarifiers and cyclone design.

A PFD (Process Flow Diagram) is the big-picture view — major equipment, main process streams, and key flows/temperatures/pressures. It shows what the process does.

A P&ID (Piping & Instrumentation Diagram) is the detailed engineering drawing — every pipe, valve, instrument, controller, and safety device. It shows how the plant is built, operated and controlled. Operators and maintenance work from the P&ID.

Exothermic releases heat (ΔH negative) — e.g. combustion, neutralisation. Endothermic absorbs heat (ΔH positive). In a reactor, exothermic reactions need cooling and runaway control; endothermic need a heat supply.

A catalyst speeds up a reaction by providing a lower-activation-energy path. It is not consumed and does not change the equilibrium position or ΔH — it only helps you reach equilibrium faster.

• Batch: charged once, no flow in/out during reaction. Flexible, good for small volumes / pharma.
• CSTR (continuous stirred tank): well-mixed, so concentration is uniform and equals the outlet. Composition is low → lower reaction rate, needs larger volume.
• PFR (plug flow): fluid moves like plugs, concentration changes along the length. For the same conversion it usually needs less volume than a CSTR for normal-order reactions.

Mechanical: plate-and-frame filter press, rotary vacuum drum filter, centrifuge, cyclone (gas–solid). Membrane: microfiltration → ultrafiltration → nanofiltration → reverse osmosis in decreasing pore size. The driving force is a pressure difference across the medium; the cake builds up and adds resistance over time.

Choice depends on particle size, slurry concentration, whether you want the cake or the filtrate, and batch vs continuous needs.

• Zeroth: if two bodies are each in thermal equilibrium with a third, they are with each other (basis of temperature).
• First: energy is conserved — ΔU = Q − W. You can't create or destroy energy.
• Second: entropy of an isolated system never decreases; heat flows hot → cold on its own. No 100% efficient engine.
• Third: entropy → a constant (zero for a perfect crystal) as temperature → absolute zero.

It's the electrolysis of brine (saturated NaCl solution). In a membrane cell, a cation-selective membrane separates the anode and cathode compartments:

• At the anode: chloride ions are oxidised → chlorine gas (Cl₂).
• Na⁺ ions migrate through the membrane to the cathode side.
• At the cathode: water is reduced → hydrogen gas (H₂) + OH⁻, which combine with Na⁺ to give caustic soda (NaOH).

So the three products are caustic soda, chlorine and hydrogen. The membrane keeps the chlorine and caustic separate (high purity) and is more energy-efficient and far cleaner than the old mercury or diaphragm cells.

Impurities like calcium and magnesium ions damage and clog the ion-exchange membrane and reduce cell efficiency. So brine is purified (precipitation + ion-exchange resin treatment) to very low hardness before it enters the membrane cells. Clean brine = long membrane life = lower cost.

Chlorine is toxic and corrosive — needs leak detection, scrubbers (caustic scrubbing of Cl₂), and strict PPE. Hydrogen is flammable/explosive — must be kept away from chlorine and ignition sources. Caustic soda is highly corrosive to skin and eyes. So the plant relies on gas detectors, emergency scrubbers, relief systems and rigorous handling procedures.

Caustic soda (NaOH) is one of the most widely used industrial chemicals: viscose/VSF and textiles, soaps & detergents, alumina (Hindalco), pulp & paper, water treatment, and more. Grasim originally built its chemicals business to supply caustic soda to its own VSF plants, then grew into India's largest producer — so it both captures the merchant market and feeds its fibre business.