Study of the Mechanical Properties of Highly Efficient Heat Exchange Tubes

Abstract

Highly efficient heat exchange tubes are special tube shapes that are widely used in heat exchangers to enhance heat transfer. In this study, experimental measurements and numerical simulations were carried out on two types of highly efficient heat exchange tubes, namely, spirally grooved tubes and converging–diverging tubes, to investigate changes in their mechanical properties after rolling from smooth tubes. It was found that, unlike the smooth tubes, all axial, circumferential, and radial stresses exist at the two types of tubes under axial loading, and the maximum axial stress is much larger than that at the smooth tubes. Compared to the smooth tubes, the yield strength and ultimate strength of the highly efficient heat exchange tubes increase while the axial elastic stiffness decreases. Although the capability of resisting fatigue fracture of the highly efficient heat exchange tubes is less than that of smooth tubes, they still meet the requirements of the heat exchanger under fatigue loading. Axial stress concentration factors and stiffness equivalent factors for the highly efficient heat exchange tubes are regressed as a function of the structural parameters for engineering applications.

Mechanical Properties and Heat Transfer Performance of Conically Corrugated Tube

“…The results are shown in Figure 3. Axial stiffness [24] refers to the axial deformation of the tube under the action o axial tensile or compressive load at the linear elastic stage. So, the slope of the stress-s curve in the online elastic stage represents the stiffness of the tubes.…”

“…Several groups of tensile tests showed that the axial stiffness of the con corrugated tubes was 38-43% that of the smooth tubes, and the axial stiffness of the cally corrugated tubes was about 57-62% that of the smooth tubes. However, the Axial stiffness [24] refers to the axial deformation of the tube under the action of unit axial tensile or compressive load at the linear elastic stage. So, the slope of the stress-strain curve in the online elastic stage represents the stiffness of the tubes.…”

“…To evaluate the influence of the surface discontinuities of the conically corrugated tubes on the fatigue strength of the tubes, fatigue tests were also performed. The maximum load F max for the fatigue tests is determined as follows [24,30]:…”

“…Wang et al [21] analyzed and studied corrugated tubes using numerical simulation and obtained the relationship with stiffness. Qian et al [22][23][24] studied the twisted pipe, bellows, spiral grooved pipe, and zoom pipe using experimental and numerical simulation methods, and proposed and calculated the stiffness equivalent coefficient of high-efficiency pipe. Shen et al [25] studied the titanium tube in a condenser by using an experimental method.…”