Heat Transfer and Friction Characteristics for Turbulent Flow of Dimpled Tubes

Abstract

The hydrodynamic and heat transfer characteristics of dimpled tubes with different arrangements were investigated in this paper. The dimples on the tube are outward-facing, raised, with aligned and staggered arrangements. The experiments were carried out in counter-current flow patterns with cold air along the tube inside and hot water around the outside of the tube. The Reynolds numbers of air flow were in the range of 1.6·10 4 to 5.4·10 4 . By comparing the performances among three tubes (smooth tube, dimpled tube with aligned arrangement, and dimpled tube with staggered arrangement), we could find that the dimpled tubes enhanced the Nusselt number by about 18.6∼22.7 %, while the friction factors of the dimpled tubes increased by 18.6∼25.9 % for the aligned arrangement and by 14.3∼29.8 % for the staggered arrangement. The test results also showed that different dimple arrangements have very little effect, which is always within 5 %. By the integrated performance evaluation of (Nu a /Nu s )/(f a /f s ) 1/3 , the maximum of the heat transfer enhancement with the same friction penalty, about 19 %, could be achieved by optimization of the dimpled-tube design.

Thermal and exergetic evaluation of parabolic trough collectors with finned absorbers operating with air

“…18,19 Munoz and Abanades 20 proved that the use of internal fins in the PTC absorber increases its thermal performance up to 2% when it is operating with Syltherm 800. Wang et al 21 proved that the use of dimples in the PTC absorber leads to Nusselt enhancement up to 23% when the collector operates with air. Recently, Bellos et al 22 examined the impact of longitudinal fins in PTC absorber for operation with carbon dioxide, air, and helium.…”

Measurement of quasi-local friction factor of gas flow in a micro-tube

“…The experimental results are 12-20% higher than the values predicted from the Blasius formula. The friction factors obtained by Morini et al, 8 Celata et al, 9 and Yang et al 10 are also plotted in Figure 11 for comparison. Morini et al 8 measured the inlet and outlet pressures of a long PEEK tube and obtained the average friction factors between the inlet and the outlet.…”

“…Yang et al 10 measured the inlet and outlet pressures of long steel tubes to obtain the average friction factor with an assumption of the isothermal flow. The relative surface roughness of the tubes ranges from 0.08 to 0.22%.…”

“…Yang et al 10 also measured the inlet and outlet pressures of three long steel micro-tubes with inner diameters of 85.6, 308.4, and 920.1 mm to obtain the average friction factor between the inlet and the outlet. The length-to-diameter ratios of those tubes are 1125, 581, and 197, respectively.…”

Numerical Study on Heat Transfer Enhancement in a Receiver Tube of Parabolic Trough Solar Collector with Dimples, Protrusions and Helical Fins

“…It turned out that heat transfer enhancements can reach factors of 2 or more and the associated friction factor multipliers in the range of 4 to 6. Wang et al [11] experimentally investigated the hydrodynamic and heat transfer characteristics of dimpled tubes with aligned and staggered dimple arrangements. The Reynolds number of air flow is from 1.6 10 4 to 5.4 10 4 .…”