| A numerical study is carried out to predict the velocity and temperature distributions in fully developed, constant property, laminar flows in tubes containing twisted-tape inserts. The tape inserts are characterized by the twist ratio y (ratio of 180° twist pitch of the tape H to the tube inner diameter d), and the ratio of tape thickness delta to the tube diameter, delta/d. The swirl flow is simulated by following the helically twisted flow path in the partitioned tube represented by a semi-circular cross-section geometry. In this model, the tape thickness is neglected (delta = 0), which is a reasonable first-order approximation as delta/d ∼ O[10 -2] for most inserts used in practice.;Results for the variations in the velocity and temperature fields with flow Reynolds number Re and tape twist ratio y are presented; the temperature distributions also reflects the influence of fluid Prandtl number Pr. The twisted-tape induced swirl flow field is characterized by a single longitudinal vortex that breaks up into two counter-rotating helical vortices with increasing Re or decreasing y. Correspondingly, both the friction factor f and Nusselt number Nu increase substantially; in the case of heat transfer, Nusselt number also increases with Pr. The results for f and Nu are found to agree very well with the respective Manglik and Bergles (1993) correlations. This verifies the scaling of swirl flow effects by the parameter Sw (=Res/ y ) as proposed by them. (Abstract shortened by UMI.)... |
