Numerical study of the heat transfer characteristics of two distinct spiral coil configurations with the insertion of twisted tape in a shell and tube heat exchanger
Mohammed Al-Mosallam, Ali B.M. Ali, Sana M. Shrama, Mohammad N. Fares, Seyed Hossein Hashemi Karouei, Dheyaa J. Jasim, Mehdi Alinia-kolaei
Abstract
The incorporation of a spiral coil, rather than a conventional plain coil, into a shell and coil heat exchanger results in superior heat transfer performance. This improvement is attributed to the spiral coil's capacity to increase fluid circulation and turbulence, along with its ability to accommodate longer tube lengths in a limited space. In addition, the spiral geometry can provide benefits such as reduced fouling and reduced maintenance requirements through a self-cleaning mechanism. Promoting a more uniform flow distribution ensures optimal utilization of the heat exchanger surface area and reduces areas of reduced flow. The outstanding thermal performance of the specific spiral coil configuration discussed here, especially when combined with nanohybrid fluids, demonstrates its significant potential to enhance the development of compact heat exchangers in various engineering fields, including process and power generation industries, renewable energy systems, and heating, ventilation, and air conditioning applications. The performance of a shell and coil heat exchanger with two specific designs and two types of water-based hybrid nanofluids was investigated. This study first compares two types of spiral coils with and without external spiral fins and with water as the working fluid at different Reynolds numbers. This comparison is made by the dimensionless parameter Performance Evaluation Criterion (PEC), which is the ratio of the Nusselt number to the friction factor. The results show that both types of spiral coils equipped with external spiral fins induce significant flow mixing, which leads to a significant increase in heat transfer. The results clearly show the superiority of the spiral coil with a specific design and equipped with external spiral fins (case (A)) in achieving higher heat transfer rates and further performance improvements, especially in case (A). The results in the first part also showed that at Reynolds number 250, cases (A), (B), and (C) have 152 %, 97 %, and 58 % efficiency increase compared to case (D), respectively. In the second part of this study, the findings showed that the PEC values for Al2O3_MWCNT/water and water/Ag_HEG were 79 % and 21 % higher than the pure water case, respectively.