Plate-type cooler:

• Construction: A stack of corrugated metal plates (gasketed) clamped in a frame, with alternate flow passages for the two fluids.
• Design: High heat-transfer coefficient due to the corrugations and thin plates; compact and light; large surface area in a small volume.
• Operation: The two fluids flow in alternate passages (counter-flow); the plates can be added/ removed to change capacity.
• Efficiency: Very high heat-transfer efficiency; low approach temperature.
• Suitability: Ideal for clean fluids (fresh water, oil, low-fouling) and where space/ weight is limited; not ideal for heavily fouling or high-pressure/ high-temperature fluids (gasket limits).

Tube-type cooler:

• Construction: A shell with a bundle of tubes (straight or U-tube), with the tube-side fluid flowing through the tubes and the shell-side fluid around them.
• Design: Lower heat-transfer coefficient than plate type; larger and heavier for the same duty.
• Operation: The fluids flow through the tubes and shell; the tube bundle can be removed for cleaning.
• Efficiency: Good but lower than plate type; higher approach temperature.
• Suitability: Suitable for high-pressure/ high-temperature fluids, heavily fouling fluids (sea water), and where robustness is required; used for main engine jacket water, sea water coolers, etc.

• Fluid type and fouling: Plate type for clean fluids; tube type for sea water/ heavily fouling fluids.
• Pressure and temperature: Tube type for high pressure/ temperature; plate type limited by gasket rating.
• Space/ weight: Plate type where space/ weight is limited.
• Heat-transfer efficiency: Plate type where high efficiency/ low approach is needed.
• Maintenance/ cleaning: Consider ease of cleaning (plate type is easy to dismantle; tube type requires tube cleaning).
• Cost: Plate type is often cheaper for a given duty but has gasket replacement cost.
• Corrosion/ material: Consider the materials compatible with the fluids.
• Capacity/ flexibility: Plate type allows adding/ removing plates; tube type is fixed.

• Purpose: Backflushing reverses the flow through the cooler to dislodge and flush out fouling (marine growth, sludge, debris) that has accumulated on the plate surfaces and in the passages, restoring heat-transfer efficiency and reducing pressure drop.
• Procedure: With the cooler in service (or isolated), the flow is reversed using the backflushing valves/ arrangement for a short period, flushing the fouling out. The flow is then returned to normal.
• How it helps: Backflushing removes the fouling layer, restoring the heat-transfer efficiency and reducing the pressure drop, so the cooler operates at its design performance and the need for frequent dismantling/ cleaning is reduced. It is a quick, low-cost maintenance action that maintains efficiency and prevents severe fouling.