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Optimum flow rates in indirect systems.

Author(s) : GRANRYD E.

Summary

Indirect systems are often used in heat pumps and in refrigeration applications. In such systems the fluid flow rate in the secondary loop can be chosen relatively freely: a large flow rate reduces the temperature differences but has the disadvantage that that the pumping power for circulating the fluid increases with increasing flow rates. The effects of these parameters in system operation will be illustrated by examples. It is shown that there are two optima for the flow rate, one resulting in minimum total energy demand and another giving maximum net cooling capacity in a refrigeration system. General relations for the pumping power that gives a minimum total energy demand in a given system will be shown, as well as the optimum for maximum net cooling capacity. Simple solutions are given for both these criteria in a dimensionless form as the ratio of the pumping power demand, in relation to the transferred heat rate. It is also possible to establish relations for optimum flow velocities in heat exchangers, representing the two optima for "energy efficiency", and "maximum net cooling capacity". For heat pump applications the solutions are slightly different compared to those used for refrigeration systems.

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Pages: ICR07-B1-1376

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Details

  • Original title: Optimum flow rates in indirect systems.
  • Record ID : 2007-2630
  • Languages: English
  • Source: ICR 2007. Refrigeration Creates the Future. Proceedings of the 22nd IIR International Congress of Refrigeration.
  • Publication date: 2007/08/21

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