Abstract:
The transitional flow regime in the pressure drops of tube
with twisted tape inserts is presented in this experimental
investigation. This region of transition has not been previously
identified for friction factors with twisted tape insert. This study
employed the method of area goodness factor in order to
establish this region with twisted tape insert. This experimental
study was conducted at a constant heat flux boundary condition
of 2 kW/m2 using water as working fluid and a twisted tape insert
with twist ratio of 5. The friction factors in a plain circular tube
and tube with twisted tape insert across the fully developed flow
region were determined from the measured pressure drops over
a bulk Reynolds number range of 560 to 10 404 and Prandtl
number range of 3.81 to 6.67. The area goodness factor used to
identify the region of transition with the twisted tape insert was
evaluated by dividing a fully developed local Colburn j-factors
at a length-to-diameter ratio of 141 by the corresponding friction
factors obtained at the same mass flow rate. This method
established a diversion of data in the laminar flow regime from
the data in the turbulent flow regime. The data within the
diversion was classified as the transitional flow regime which
commenced at a bulk Reynolds number of 1 029 and ended at a
bulk Reynolds number of 1 505 for the tube with the twisted tape
insert of twist ratio of 5. A comparative analysis of the friction
factors against Reynolds numbers in the plain tube showed that
the transitional flow regime commenced at a bulk Reynolds
number of 3 041 and ended at a bulk Reynolds number of 3 292.
Description:
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .
