Abstract:

An experimental study was carried out on the boiling heat transfer of R22 flowing inside three internal thread tubes with different geometrical parameters. Three enhanced tubes have the same inner and outer diameters, which are 6.9 mm and 7.92 mm respectively. The outside surface of the tube is smooth, while the inside enhanced structure is different. The variation range of the helix angle is from14° to18°, the thread height is between 0.15 mm and 0.22 mm, and the thread width is from 0.1 mm to 0.2 mm. The relationship between the heat transfer performance and the mass velocity in three enhanced tubes and a smooth tube was tested by changing the mass velocity of refrigerant under given condition of import and export of refrigerant, and their performance is compared. Experimental results indicate that the heat transfer coefficients of three internal thread tubes are 60%—80%, 80%—120% and 80% higher than that of smooth tube. Analysis suggests that the larger helix angle is advantageous to the heat transfer,when fluid is on laminar flow or the transition of laminar flow and annular flow, and more of thread amount is advantageous to the heat transfer,when the fluid is on annular flow.

Key words: thermodynamics, heat transfer, gas-liquid flow, boiling, internal thread tube

摘要：

对3种不同螺纹结构的强化管的管内沸腾换热性能进行对比实验研究, 采用R22为实验工质。3种强化管的内径和外径相同, 分别为6.9 mm和7.92 mm;管外均为光滑表面, 管内的强化结构参数则不同:螺纹的螺旋角变化范围为14°~18°, 螺纹高为0.15~0.22 mm, 螺纹槽宽度为0.1~0.2 mm。在给定进口和出口制冷剂的状态下, 通过改变管内工质的质量流速, 测试3根强化管的换热特性与质量流速的关系, 并进行性能对比。实验结果表明:3种螺纹管管内沸腾传热系数分别比光管高出60%~80%, 80%~120%和80%。分析认为, 当流动处于层状流或者层状流与环状流的过渡区时, 较大的螺旋角有利于换热;当流体处于环状流时, 较多的螺纹头数有利于换热。

关键词: 热力学, 传热, 气液两相流, 沸腾, 内螺纹管