# Numerical Simulation of Heat Transfer Performance of a Dimpled Tubular Heat Exchanger
###### Abstract  
The processing of dimple on the outer wall of tube will produce corresponding protrusion dimple on the inner wall. The turbulent flow and heat transfer performance of a tubular heat exchanger containing a dimpled inner tube is studied numerically. The results show that the main reason for the enhancement of heat transfer ability of the dimple is the flow vortex in the concave dimple and the shock to the wall induced by the protrusion dimple. Compared with the smooth wall of the tube, the maximum enhancement of heat transfer was 1.94 times in concave dimple and 2.74 times in protrusion dimple. By comparing the heat transfer performance, flow resistance, and comprehensive heat transfer factor of the tube and shell of different sizes of exchange heat pipe, it is determined that the combination of inner and outer wall dimple size of 10-15 mm is a structure with better comprehensive heat transfer performance.  
dimple; tubular heat exchanger; heat transfer performance +
Footnote †: journal: Applied Sciences  
transfer capacity, the dimpled heat exchange tube had smaller flow resistance and better comprehensive heat transfer performance. The numerical calculation research on circular cross section pipelines containing concave dimple was carried out by [PERSON] et al. [6] The influence of concave dimple on heat transfer effect of pipelines under different arrangement of structural parameters were analyzed. The results showed that the structure of concave dimple should be reasonably designed to avoid the influence of vortex dead zone on heat transfer effect. [PERSON] et al. [7] used the Realizable k-\(\epsilon\) model to numerically simulate the heat transfer of protruded oval dimpled pipes, focusing on analyzing the influence of the number and distribution of dimple on the flow and heat transfer characteristics of the pipes. [PERSON] et al. [8] carried out numerical simulation of the spiral protrusion dimple tube. The reasons for enhanced heat transfer of the protrusion dimple were analyzed from the perspective of flow field structure. The optimal relative depth (H/d) range of the dimple were determined by analyzing the comprehensive heat transfer coefficient. experiments and numerical simulations on tube heat exchangers containing dimple and rough surface heat exchange tubes were carried out by [PERSON] [9] et al. The results showed that compared with the smooth tube of the same size, the heat transfer capacity of the heat transfer tube combined with the rough wall surface can be increased by more than 200%, and the comprehensive heat transfer coefficient can reach more than 1.5. Through the above-mentioned literature and experiment, dimple will cause considerable increase in pressure drop. How to enhance the heat transfer with limited pressure-drop increase has become the focus of research.  
In the processing process of the dimpled tube, the protrusion dimple will be formed on the inner wall during the processing of the concave dimple on the outer wall. Due to the influence of wall thickness, the size of protrusion dimple is often larger than the corresponding concave dimple. Previous studies generally only considered the influence of the protrusion dimple or concave dimple structure on the heat transfer performance of the pipe. According to the results of previous studies, dimple enhances the heat transfer effect and also increases the flow resistance. Whether the change of flow field will affect each other and then affect the comprehensive heat transfer effect of the heat exchange tube when protrusion dimple and concave dimple coexist remains to be further studied. Therefore, based on the structure of tubular heat exchangers in petrochemical enterprises, this paper uses the CFD software Fluent to analyze the influence of the inner tubes with different sizes of dimple concave and protrusion on the heat transfer capacity of both tube side and shell side of tubular heat exchangers. A comprehensive evaluation of the heat transfer performance of dimpled heat exchange tubes is carried out.