Abstract: Vertical U-shaped tubes have been used in some waste heat boilers of targe synthetic ammonia plants. In operation, accident of tube failure at the bend due to overheating occurs frequently. The present tests showed that under the action of both centrifugal and gravitational forces, tratification of steam-water flow occurs, leading to heat transfer deterioration on the inner side of the bend. In order to solve the problem, three types of inserted turbulator-a single twisted tape, a double twisted tape and a spiral coil-were tested in a high-pressure electrically heated water-loop experimental installation. Boiling heat transfer and pressure drop characteristics were investigated. The experimental loop consisted of a φ25 × 2 mm stainless steel tube with a 180° bend of 700mm radius, under an operating pressure of 106 × 105Pa. These tests showed that boiling heat transfer deterioration might be eliminated effectively by use of any of the three types of inserted turbulator. The pressure drop of the turbulators were determined, and then the single-phase friction factor relationships were obtained. The Chisholm equation was used to correlate the data of the two-phase pressure drop, and acorrelation for determining the two-phase frictional multiplier was proposed. In order to understand the operating mechanism of the inserted turbulator, flow pattern observations of the single twisted tape were carried out in a transparent tube for air-water flow and an overall flow-pattern map was established in terms of superficial liquid and gas velocities. The single twi-sted tape, which was found to have the lowest frictional pressure drop, is recommended for waste heat boilers.

摘要： 为解决大型合成氨装置U型管高压废热锅炉爆管问题,在P=106×10~5Pa压力下试验了三种管内扰流子结构型式,对消除U型管沸腾传热恶化具有很好的效果.试验确定了三种扰流子型式的阻力特性,得出了单相阻力系数与雷诺数的关系特性,用Chisholm方程求得了两相流摩擦压降倍率与含汽率关系,建立了关联式.在水-空气试验台上进行了扰流子的流型观察试验,建立了流型图.试验得出单头扰流片阻力最小,结构简单,建议用于U型管废热锅炉消除传热恶化,以确保废热锅炉的安全运行.