DRLL module

Calculation of heat transfer and pressure drop in flow through corrugated tubes

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When liquids and gases flow through pipes, heat transfer and pressure loss depend not only on the properties of the fluid and the type of flow but also on the structure of the heat-transferring surface.

To improve heat transfer, corrugated tubes are suitable, which ensure early laminar turbulent flow change, better condensate discharge or targeted formation of liquid films.

The heat transfer increases more than the pressure loss, resulting in smaller heat exchangers and lower operating costs.

At the same time, the self-cleaning effect of the corrugated tubes reduces the tendency to fouling.

On the basis of experimental approaches, the DRLL module calculates the heat transfer coefficient α [1] and the resistance coefficient ζ or pressure loss Δp [2] in flow-through corrugated tubes.

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Literature

[1] Wärmeübergang in einphasig durchströmten Drallrohren, Wärmetechnische Information der hde Metallwerk GmbH, Menden, 1994

[2] Druckabfall bei Strömungen in einseitig- und kreuzgedrallten Rohren, Wärmetechnische Information der hde Metallwerk GmbH, Menden, 1992

Comparative calculation for a heat exchanger with plain or corrugated tubes

Corrugated tubes can be used in heat exchanger design, as long as the contamination tendency of the medium allows it and the heat transfer in the tubes is to be improved during the given task.

The following sample calculation shows the differences between corrugated and plain tubes.

  • Water is heated from 90°C to 110°C with 2 bar steam.
  • A pipe register with 8 rows of 30 pipes each and 3 tube-side passes is considered.
  • Tubes with an outside diameter of ⌀ 13.5 x 0.7 mm are used.
  • There is a requirement of 15% reserve, i.e. performance number 1.15.

The calculation is carried out with the program package AC and module DRLL as an extension.

Result:

With corrugated tubes, the tube length for the flow rate range under consideration is 14% to 17% shorter. The pressure drop is slightly lower.

For the final decision, a cost comparison must be made by comparing tube costs and operating costs.

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Dieser Beitrag ist auch verfügbar auf: Deutsch (German)