Abstract

The heat transfer performance (HTP) of an improved elastic tube bundle (IETB) was analyzed using a bi-directional fluid-structure interaction calculation method. The vibration-enhanced HTP of heat exchangers with different inlet velocities (Uin) and row number N were studied. The results show that the amplitude gradually increases as the Uin increase with a maximum increase of 309.98%. The amplitude with fixed shell side length (FL-heat exchanger) is generally higher than that with variable shell side length (VL-heat exchanger) under different row numbers. The average amplitude of the three directions increased by 4.55%, 11.54%, and 7.41%, respectively. The heat transfer coefficient (h) is directly proportional to Uin, and the comprehensive HTP gradually decreases with the increase of Uin. With the increase in the row numbers, h generally showed a downward trend. For the VL-heat exchanger, h decreases as the row number increases, which increases from N=6 to N=9, and h decreases by 13.85%. For the FL-heat exchanger, h first increases and then gradually decreases. The comprehensive HTP also maintained the same trend. Compared VL-heat exchanger and FL-heat exchanger, reducing the spacing between tube rows increases heat transfer per unit volume, leading to improved comprehensive HTP of the IETB heat exchanger.

Introduction

Heat exchangers [1–۳] are commonly used devices for exchanging energy in industries such as aerospace, chemical, and refrigeration production. When the traditional tubular heat exchanger works, its internal rigid heat transfer elements begin to vibrate under the impact of fluid, which can result in fatigue damage and decreased heat exchanger service life [4,5]. Shell and tube heat exchangers [6,7] are currently the most widely used in industrial production. The study of enhanced heat transfer in heat exchangers has become a hot topic of current research [8]. To reduce the influence of fluid shock, utilizing the vibration-enhanced heat transfer principle, an elastic tube bundle heat exchanger is proposed [9,10]. The material of the heat transfer element was replaced from steel to copper to achieve small amplitude vibration of the internal tube bundle at the low frequency, this improvement not only improves the heat transfer coefficient (h), but also uses the vibration deformation to remove the scale on the heat transfer surface, reduce the thermal resistance, and finally realize the composite heat transfer enhancement. However, due to the disadvantages such as poor comprehensive heat transfer performance (HTP) of elastic tube bundles, it is essential to improve the structure to obtain better comprehensive HTP.

Conclusion

Based on the bi-directional fluid-structure interaction calculation method, the effect of Uin and row number N on vibration and HTP of the IETB heat exchanger are studied. According to the results above, the key conclusions follow.

(۱) The average amplitude of IETBs in different row numbers gradually increases with the rising of Uin. The vibration uniformity of the IETBs is better at low Uin. Besides, the difference in amplitude among different IETBs becomes larger and larger. And the amplitude in the FL-heat exchanger is generally higher than the VL-heat exchanger. For the VL-heat exchanger, when the row number is increased, the average amplitude decreases gradually. For the FL-heat exchanger, it decreases first and then increases.

(۲) The average heat transfer coefficient ha/hva of IETBs is directly proportional to Uin and comprehensive HTP decreases gradually with the rising of Uin. With the increase of tube number i, the ha/hva presents a general trend of decline. And ha/hav in the FL-heat exchanger is generally greater than that VL-heat exchanger. In addition, the hva is always greater than h, which indicates that vibration facilitates the achievement of heat transfer enhancement.