Internally rifled boiler tubes

Internally rifled boiler tubes are used to evaporate water into steam inside boilers of thermal power plants. Because of their internally rifled shape, they are more efficient. The boiling crisis takes place later, thus allowing for greater heat transfer between the pipe and the fluid inside the pipe. Costs of this type of tube are generally higher than plain tubes. Current research into these tubes is being conducted due to their potential to increase efficiency of power plants.

History

These tubes are sometimes called Serve tubes after the name of their French inventor. However, Serve's tubes were for use in fire-tube boilers rather than the water-tube boilers used in modern power stations and were lobed or finned rather than rifled.[1] Later on Siemens came up with the research project and introduced the name SLMF (Siemens Low Mass Flux).[2]

Working

The internally rifled (also known as ribbed) tubes are used in boilers and heat exchangers for efficient results in terms of heat transfer. The internal ribs of rifles introduce the centrifugal force inside the tubes.[3] The flowing media ( which commonly is a mixture of steam and water) as a result of this centrifugal force, separates water from the steam mixture and forces water towards the wall and there is no steam-film formation.[4] This process increases the surface area for the maximum heat transfer when compared to the smooth tubes.[5]

Advantages
  1. Higher heat transfer rate at higher steam quality levels.[5]
  2. Better heat transfer at lower mass flux levels.[5]
  3. Reduction in the mean metal temperature of the tube walls.[5]
  4. Ability to increase the heat transfer by optimizing rifle geometry.[5]

Disadvantages
  1. The manufacturing and installation costs as compared to the normal tubes are higher.
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References
  1. Typically French accessories
  2. Johansen, Axel Ohrt. "Modelling of rifled boiler tubes". Denmark Teknikal Universiti. University of Denmark. Retrieved 12 April 2013.
  3. Yue, Guangxi (2009). Proceedings of the 20th International Conference on Fluidized Bed Combustion. USA: Springer. pp. 181–182. ISBN 9783642026829.
  4. Viswanathan, Ramaswamy (1989). Damage Mechanisms and Life Assessment of High Temperature Components. USA: ASM International. p. 190. ISBN 9780871703583.
  5. Spliethoff, Hartmut (2010). Power Generation from Solid Fuels. USA: Springer. pp. 129–131. ISBN 9783642028564.


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