Abstract
In this paper, the numerical simulation was used to study the flow and heat transfer characteristics for twisted oval and two-start twisted helically wound tubes with Reynolds numbers 4000–16,000. The significant factors that affect the flow and heat transfer characteristics were analyzed. The range of twist pitch p is 0.02–0.10 m, and ellipse ratio r is 1.2–2 for twisted oval tube, the groove depth e is 0.4–2 mm for two-start twisted tube. The result showed that the relative friction coefficient and Nusselt number increased with the increase of ellipse ratio r and decreased with the increase of twist pitch p for twisted oval helically wound tube. With the growth of Reynolds number, the effects of twist pitch p and ellipse ratio r on the flow characteristics decreased. In addition, the average level of the thermal enhancement factor TEF of the two-start twisted was higher than that of the twisted oval helically wound tube. The maximum enhancements factor TEF of 1.1312 is obtained with groove depth of 2.0, twisted pitch of 0.02, and Reynolds number of 4000 for the two-start twisted tube. Finally, new empirical formulas for flow and heat transfer in helically wound tubes were proposed for two kinds of enhanced tubes.
Highlights
Enhanced heat transfer technology can improve the efficiency of heat exchangers, making the equipment more compact and energy-efficient.[1]
The results showed that the effect of secondary flow for twisted oval tubes enhanced the convective heat transfer, and the enhancement factor increased with the increase of ellipse ratio, while it decreased with the increase of pitch
The effects of significant factors on the flow and heat transfer characteristics of twisted oval and two-start twisted helically wound tubes are studied by numerical simulation
Summary
Enhanced heat transfer technology can improve the efficiency of heat exchangers, making the equipment more compact and energy-efficient.[1] Generally, there are three forms of enhanced heat transfer technology, namely active heat transfer, passive heat transfer and composite heat transfer.[2] Passive heat transfer technology is widely used because it does not need additional energy input,[3] which can change the flow characteristics and increase heat transfer efficiency. Tubes made with rough surface technology are often known as enhanced tubes. The convex surface in the tube can produce. Advances in Mechanical Engineering secondary flow and disturb the fluid boundary layer, which increases the heat transfer area and improve heat transfer coefficient. These factors improve the heat transfer performance
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