Contributed by the Fluids Engineering Division for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received by the Fluids Engineering Division February 6, 2003; revised manuscript received January 13, 2004. Associate Editor: Y. Tsujimoto and J. Katz.

For sustaining a desired flow rate in a thermo-hydraulic engineering system (channels, ducts etc.), the required pressure-drop is achieved by means of a pump. Reduction in the power required by this pump, without adversely affecting the pressure-drop value, is obviously an important issue, which is given careful thought by the design engineer. Heating a channel for liquid flows reduces the viscosity and by consequence the resulting pressure-drop 1,2. Obviously, one might then consider the benefit of heating the liquid as a means to reduce the viscosity and the pumping power, while maintaining the same pressure-drop 3.

However, as the reduction in the liquid viscosity diminishes for increased temperature...

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