Abstract:

A novel twisted tube coaxial heat exchanger was developed, and its heat transfer and flow characteristics were experimentally tested. Correlation formulas for Nusselt number (Nu) and friction factor (f ) criteria for the tube and shell passes were derived. The experimental results indicate that the total heat transfer coefficient and flow resistance increase with higher flow velocities. Within the test range of 0.1—1.5 m/s, the total heat transfer coefficient increased by approximately 34%, while the flow resistance increased from 37 Pa to 6033 Pa, representing a nearly 120-fold increase. The shell flow resistance increased from 361 Pa to 130761 Pa. For Reynolds numbers between 1000 and 10000, the performance evaluation factor ($\eta$) of the twisted tube coaxial heat exchanger exceeds 1, and reaches a maximum of 2.3. However, for Reynolds numbers between 10000 and 30000, $\eta$ is less than 1. The overall comprehensive performance of the twisted tube coaxial heat exchanger is the best within a tube flow rate range of 0.1—0.5 m/s and a shell flow rate range of 0.1—0.4 m/s, indicating that it is suitable for small refrigeration and air conditioning equipment as well as application scenarios with low Reynolds numbers.

Key words: heat transfer, laminar flow, turbulent flow, flow resistance, coaxial casing heat exchanger

摘要：

开发一种新型扭曲管同轴套管换热器，对其传热和流动特性进行实验测试，并拟合管程及壳程的Nusselt数（$Nu$）和摩擦因子（$f$）关联式。实验结果表明：随着流速的增大，总传热系数和流阻升高。在测试范围内（0.1~1.5 m/s），总传热系数增幅约为34%，管程流阻从37 Pa升高约120倍至6033 Pa，壳程流阻从361 Pa升高至130761 Pa。当1000<$Re$$\le$10000时，扭曲管同轴套管换热器综合评价因子（$\eta$）>1，最高为2.3；当10000<$Re$<30000时，η<1。在管程流速为0.1~0.5 m/s、壳程流速为0.1~0.4 m/s的范围内，扭曲管同轴套管换热器的整体综合性能最佳，说明扭曲管同轴套管换热器适用于小型制冷空调设备，适合Reynolds数较低的应用场景。

关键词: 传热, 层流, 湍流, 流动阻力, 同轴套管换热器