The heat exchanger thermal performance factor (h) is defined as
the increased convective heat transfer coefficient (hE) to the nonincreased
convective heat transfer coefficient (hNE) ratio at an
identical pumping power which can be expressed as Thermal performance factor was calculated based on the
annulus friction factor and the results are presented in Fig. 11. The
main scope of the present study was to compare a double pipe heat
exchanger made of corrugated inner tube and smooth outer tube
with a double pipe heat exchanger made of corrugated inner tube
and corrugated outer tube. By determining the results of the heat
exchanger made of smooth outer tube and corrugated inner tube as
the references, the employment of corrugated tube for outer tube of
heat exchanger, increases the thermal performance factor about
26e38%. It means that the outer tube corrugations have significant
effect on performance of the double pipe heat exchanger.