Influence of thermal shock on fouling of smooth, rough and finned tubes

• Surface roughness assists deposit formation and development of the fouling layer.
• ​The induction period in case of rough tubes is less than smooth tubes by almost 22%.
• The fouling layer resistance in case of rough tubes is double that of smooth tubes.
• The thermal shock blows off the fouling layer in case of plain tubes.
• The thermal shock ceases in removing the fouling layer in case of finned tubes.

Deposits of salts and extraneous materials occur during water desalination by heating, forming an insulating layer, which is known as fouling. Fouling reduces the rate of heat transfer between the heating medium and the water, subsequently decreases the desalination efficiency gradually and sometimes can lead to operation failure. The thermal shock is a fouling mitigation technique in water desalination units, which could be due to sudden decrease or increase in the heat transfer process. The objective of this research is to study the removal of fouling layers by the thermal shock in case of (i) smooth tubes, (ii) rough tubes and (iii) finned-rough tubes. It has been found that it is possible to remove the fouling layer by the thermal shock technique in case of smooth and rough tubes, but not in case of finned tubes. The thermal shock blows off the fouling layer in case of plain tubes, and the fouling process resumes after the thermal shock without any delays, i.e. no more induction period. Fins assist the sticking of crystals to the heat exchanger tubes and prevent its removal by thermal shock. Fins act as a heat sink during the thermal shock, which reduces the dissipation of heat to the surrounding water, i.e. cooling of the tubes, and prevent cracking of the fouling layer.