Heat Transfer and Friction Characteristics of Turbulent Flow through a Circular Tube with Ball Turbulators

Abstract

Abstract:One of the most commonly used methods of heat transfer enhancement is flow turbulization. This effect can be achieved, e.g., by placing special turbulizing elements into the channel. In this paper, the effects of ball turbulators (BTs) on the heat transfer and fluid friction characteristics in a circular tube are investigated through numerical simulation. The Reynolds number (Re) is in the range of 5000-35,000 under a condition of uniform heat-flux. BTs with different diameter ratios (e.g., 0.5, 0.75, and 1) and spacer lengths (40, 51.77, and 62.5 mm) are inserted in the circular tubes. The results show that the heat transfer rates in the tube equipped with BTs are around 1.26-2.01 times that of those in the plain tube. The BTs with a ball diameter ratio of one provide higher friction factors than 0.75 and 0.5 by about 34.6-46.2% and 51.1-63.4%, respectively. A smaller ball diameter ratio is more able to decrease the friction factor. The performance evaluation criterion (PEC) data indicate that the use of a smaller ball diameter ratio (BDR) and a smaller spacer length are preferred. The results also reveal that BTs with a larger diameter ratio and a smaller spacer length yield the highest heat transfer rate as well as the largest pressure loss. Compared with the plain tube, the fluid flow velocity near the tube wall is significantly improved when BTs are used at the same Reynolds number.

Heat transfer enhancement in inserted extruded aluminum finned tubes

“…The resistance coefficient correlation formula is shown in Eq. (10). The correlation coefficient R 2 of the multiple linear regression fitting is 0.9233.…”

“…Jin Z [1] and Zaid S. Kareem [2,3] studied the heat transfer and resistance characteristics of hexagonal star, triangle, and two-angle threaded pipes; Zachár [4] and Jayakumar [5] studied the heat transfer and resistance characteristics of threaded coils; Aroonrat [6] and Lu G et al [7][8][9] proposed the heat transfer coefficient correlation formula of pressed threaded coils smoke tubes by experimental means, the Nusselt number of the threaded smoke pipe is 80% -130% higher than that of the smooth tube at the same Reynolds number and Prandtl number. Wei Y [10], Frédéric J. Lesage [11], Alberto García [12], and others studied the heat transfer and resistance characteristics of various spoilers added to the smoke pipe. The two strengthening methods of the thread and inner spoiler do not increase the effective heat exchange area, and the total strengthening capacity is limited.…”

Special Issue “Active Flow Control Technologies for Energy and Propulsive Systems”

“…In reference [17], the effects of ball turbulators (BTs) on the heat transfer and fluid friction characteristics in a circular tube are investigated through numerical simulation. The performance evaluation criterion (PEC) data underline that the use of a smaller ball diameter ratio and a smaller spacer length are preferred.…”

Numerical Studies on Thermo-Hydraulic Characteristics of Turbulent Flow in a Tube with a Regularly Spaced Dimple on Twisted Tape

“…The effect of artificial roughness on heat transfer enhancement was studied by García et al, [21]. In a circular tube fitted with ball turbulators at a Reynolds number range of 5000-35000, the heat transfer and friction factor characteristics of turbulent water flow are investigated by Yuan et al, [22] through numerical simulation and the Nusselt number increases and the friction factor decreases as the number of Reynolds increases in a tube with BTs. For an improved tube, the Nusselt number is about 1.26-2.01 times as much as that of the plain tube, while the friction factor raises sharply by about 3.74 to 10.27 times.…”