Question

(a) What is the working principle of a plate type cooler on a ship, and what are its main components? How does it differ from other types of heat exchangers used on ships? (6)

(b) What materials are commonly used for the packing in plate type coolers on board ships, and how do these materials impact the efficiency and durability of the cooler? (5)

(c) Describe the process of back flushing a plate type cooler on a ship. Why is back flushing important, and what potential issues can it prevent or mitigate. (5)

Answer 1

(a) Plate type heat exchanger:

A plate type cooler is a compact and highly efficient heat exchanger used on ships to transfer heat between two fluids—typically fresh water, lubricating oil, or seawater—without allowing them to mix.

It works on the principle of counterflow or crossflow heat exchange, where thin metallic plates separate the two fluids.

One fluid flows along one side of each plate while the other flows along the opposite side.
The large surface area of the plates allows efficient thermal energy transfer through conduction and convection.
The corrugation or wavy pattern of the plates promotes turbulence, which enhances the rate of heat transfer and minimizes fouling.

Main Components:

Plates:
- Thin, corrugated metal sheets forming the main heat transfer surface.
- Corrugations increase turbulence and improve heat transfer efficiency.
Frame:
- Provides structural support and holds all plates tightly together.
- Maintains pressure and prevents leakage between the plates.
Gaskets (Packings):
- Rubber or synthetic seals placed between plates.
- Prevent fluid mixing and direct the flow through alternate channels.
Inlet and Outlet Ports:
- Separate connections for the entry and exit of hot and cold fluids.
- Arranged alternately for counterflow or crossflow operation.
Tightening Bolts:
- Used to compress and secure the plates, ensuring proper sealing and pressure integrity.

Differences from Other Types of Heat Exchangers on Ships

Feature	Plate Type Cooler	Shell-and-Tube Cooler
Efficiency (per unit volume)	Significantly higher due to greater turbulence and surface area density.	Lower; relies on flow across tubes.
Size & Weight	More compact and lighter for the same capacity.	Larger and heavier.
Maintenance/Cleaning	Easier to dismantle for mechanical cleaning of the plates.	More difficult to clean the tube surfaces internally.
Fluid Pathways	Plate channels.	Bundle of tubes inside a large shell.

Applications:

Plate type coolers are widely used on ships for:

Lubricating oil cooling
Freshwater cooling
Central cooling systems

Advantages of Plate Coolers on Ships:

Higher thermal efficiency.
Smaller footprint and lighter weight (critical for ship space).
Easier to clean and maintain, making them ideal for systems like lubricating oil coolers and freshwater central coolers.

✓ Verified Model Answer (Text Solution)

(a) Plate type heat exchanger:

Main Components:

Differences from Other Types of Heat Exchangers on Ships

Applications:

Plate type coolers are widely used on ships for: