Abstract:
Vortex generators/turbulent promoters generate the vortices
which reduce the boundary layer thickness and introduce a better
mixing of the fluid to enhance the heat transfer. In this research,
thermal performance of winglets longitudinal vortex generators
(VGs) were investigated experimentally. Delta winglet VGs of
different heights and attack angles were inserted inside a 1 m
length copper tube. The experiments were conducted with VGs
for an air flow range of Reynolds numbers from 6000 to 33000.
The influence of the winglet VGs on heat transfer and pressure
drop was investigated in terms of the Nusselt number and friction
factor. Vortex generators were arranged repeatedly inside the
tube 12 rows (N) with same pitch distance (P=L/N) and each row
consists of 4 VGs in a circular pattern on the inner surface of the
tube. So relative pitch ratio (PR=P/D) is 1.6 and three winglets
blockage ratios (B=H/D) are 0.1, 0.2, 0.3 with respect to three
winglets heights (H=5mm, 10mm and 15mm). Attack angles of
the VGs were maintained 0°, 15°, 35° and 45° for B=0.3. The
objectives of the study were to investigate the heat transfer
enhancement and to identify the parameter which induces the
highest thermal performance augmentation in the circular tube.
Based on the experimental results, the best parameter for
thermal performance enhancement (TPE) (η) is for B=0.1, with
PR=1.6, β=45°. Nusselt number increased 2 times higher than
that of the smooth tube. Friction factor decreased with Reynold
number from 0.13 to 0.06.
Description:
Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016.
