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MEO Class II: MEKG MEKM MEP MET SC&S SSEP 📊 Trends
Q9 (10 Marks) Machinery & Systems
SSEP • Written Exam

Describe how heat may be transmitted from one source to another and explain with the aid of simple sketches where appropriate how heat transfer from or to the following places is kept to a minimum:

(a) Steam pipes

(b) Meat rooms

(c) Furnace casings

(d) Manoeuvring or control platforms

Appeared In: Dec 2018

✓ Verified Model Answer (Text Solution)

Structured for DG Shipping MEO Class II examination scoring criteria.

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Describe how heat may be transmitted from one source to another and explain with the aid of simple sketches where appropriate how heat transfer from or to the following places is kept to a minimum:

Part (a)

Steam pipes

Part (b)

Meat rooms

Part (c)

Furnace casings

Part (d)

Manoeuvring or control platforms

Heat may be transmitted by three mechanisms:

  • Conduction: heat transfer through a solid material (e.g. through a metal pipe or wall) by the transfer of energy between molecules.
  • Convection: heat transfer through a fluid (liquid or gas) by the movement of the fluid (e.g. hot air rising, or a hot fluid circulating).
  • Radiation: heat transfer by electromagnetic waves (infrared) from a hot surface to a cooler surface, without the need for a medium (e.g. heat radiating from a hot pipe or furnace).
Part (a)

Steam pipes: Heat transfer from the steam pipes is kept to a minimum by lagging (insulation) - a layer of insulating material (e.g. mineral wool, glass fibre, or calcium silicate) is wrapped around the pipe, with a cladding (a metal or canvas covering) to protect it. The insulation reduces conduction (the insulating material is a poor conductor) and convection/radiation (the outer surface is cooler). The lagging is kept dry and in good condition, as wet/damaged lagging loses its insulating value.

Part (b)

Meat rooms (refrigerated spaces): Heat transfer into the meat room is kept to a minimum by:

  • Insulation of the walls, ceiling and floor (a thick layer of insulating material, e.g. polyurethane foam or cork, between the inner and outer linings).
  • A vapour barrier to prevent moisture ingress (which would reduce the insulation).
  • The door is insulated and kept closed, with a good seal.
  • The room is kept at the required low temperature by the refrigeration plant, and the heat load (from the lights, the door opening, and the stored goods) is minimised.
  • The insulation reduces conduction and the vapour barrier prevents condensation.
Part (c)

Furnace casings: Heat transfer from the furnace casing is kept to a minimum by:

  • Insulation (refractory/insulating material) on the inside of the casing, and/or lagging on the outside, to reduce the heat loss and to protect the surrounding structure and personnel.
  • The casing is designed with an air gap or a cooling arrangement (e.g. a water-cooled or air-cooled casing) where necessary.
  • The insulation reduces conduction and radiation, keeping the outer surface at a safe temperature.
Part (d)

Manoeuvring or control platforms: Heat transfer to the control platform (where the operator stands) is kept to a minimum by:

  • Locating the platform away from the hot sources (the engine, exhaust, boiler) where possible.
  • Insulating/lagging the hot pipes and surfaces near the platform.
  • Providing a heat shield or a screen between the platform and the hot source.
  • Ventilating the area to remove the hot air (convection).
  • The platform may be provided with a cool air supply or a water-cooled arrangement.

These measures reduce the heat reaching the operator, providing a safe and comfortable working environment.

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