Experimental Study and Conjugate Heat Transfer Simulation of Turbulent Flow in a 90° Curved Square Pipe

Abstract

This paper discusses the turbulent flow and heat transfer from a uniform air flow with high temperature to the outside through a 90° curved square pipe. Both conjugate heat transfer (CHT) simulation and experiments of temperature field measurements at cross sections of the pipe are performed. A straight pipe is investigated and compared with the 90° curved pipe. The temperature of the air flow at the inlet of the pipe is set at 402 K, and the corresponding Reynolds number is approximately 6 × 104. To obtain the spatial average temperature at each cross section, the temperature fields are measured along the streamwise of the pipes and in the circumferential direction using thermocouples at each cross section from the inlet to the outlet of both the straight and curved pipes. Furthermore, the simulation is performed for turbulent flow and heat transfer inside the pipe wall using the Re-normalization group (RNG) k-ε turbulence model and CHT method. Both the experimental and numerical results show that the curvature of the pipe result in a deviation and impingement in the high-temperature core and a separation between the wall and air, resulting in a secondary flow pattern of the temperature distribution.

Heat Transfer Characteristics of Turbulent Flow in Double-90°-Bend Pipes

“…The large amount of heat dissipated to the pipe wall at the first bend is transferred upstream and downstream through the inside of the pipe by thermal conduction. The tendency for heat transfer enhancement to occur at the first bend is consistent with previous results by Guo [23] and Liberto et al [29].…”

“…Figure 9b shows that for the double-bend pipe, the high-temperature core, which is at the center of the first bend entrance (z = 40 D), shifts to the outside (−x side) at the first bend exit (z = 42.4 D). This shift may be due to compressive heating of the fluid on the outside of the bend by centrifugal forces, as suggested by Guo et al for their single-bend pipe [23]. The distribution after the entrance to the second bend (z = 47.4 D ~53.7 D) shows that the hot core, which was biased toward the −x side, gradually shifts toward the +x side.…”

“…From the middle of the second bend, the local Nu number decreases significantly, indicating that the heat transfer enhancement is not significant. Figure 19 also shows the experimental results of Guo et al [23], who evaluated the heat transfer characteristics of a single-bend pipe under the same flow conditions. In the experiment of Guo et al, the local Nusselt number also increased in the middle of the first bend, a trend that is consistent with the simulation in the present study.…”

“…They found that the heat transfer was mostly greater on the outside of the bend than on the inside of the bend, and that the difference decreased with an increasing Reynolds number. Guo et al [23] measured the cross-sectional temperature profile of a pipe with a 90 • bend, finding that the heat flux was higher on the outside of the bend as the hot core of the fluid was biased outward by the bend. Other studies on bend geometries have mainly investigated coil-type and U-shaped pipes.…”

“…As described above, various studies have investigated the heat transfer characteristics of bent pipes, but few studies [23] have experimentally evaluated heat transfer characteristics by measuring the in-plane temperature distribution. The heat transfer characteristics of pipes with single bends and U-shaped bends and coil-type piping have been actively studied for applications such as heat exchangers, but there has been a lack of research on the heat transfer characteristics of turbulent flow in S-shaped double bends.…”