Class 2 (2nd Engineer) MEKG 📅 Jan 2017

Exam Question

With reference to mult-tubular heat exchangers explain:

(a) How and where impingement attack is likely to occur in the tubes

(b) Why is it desirable that coolant flow rate should not exceed that required to maintain correct fluid temperature

(d) Partial obstruction of tube is a common cause of tube failure

Reference Answer

(a) Impingement attack is a form of material degradation resulting from the erosive action of high-velocity fluid impacting a surface. The high-velocity fluid flow creates localised zones of high stress and turbulence, leading to material removal. The most susceptible locations for impingement attack are:
Tube bends : High-velocity flow changes direction, leading to material erosion.
Tube entrances : Sharp fluid acceleration causes localized erosion.
Heat exchanger shell in front of fluid entrance : Direct impingement of the incoming fluid can damage the shell.

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