Numerical study of thermal-hydraulic performance enhancement in a shell-and-tube milli-reactor

Sizing-up of microchannels is a promising strategy for microreactor scale-up while heat management is essential in this process. However, thermal-hydraulic performance of shell-and-tube heat exchangers/reactors with milli-channels was seldom studied. In this work, heat transfer performance of this kind of exchanger/reactor was numerically investigated, which can serve as an excellent reference for shell-and-tube milli-reactors design. Initially, straight channels with different diameters were used to showcase the sizing-up effect. By increasing the diameter from 1 mm to 2 mm and from 2 mm to 4 mm, the average heat transfer coefficient (h_ave) dropped by 29.80% and 25.88%, respectively. Main thermal resistance for heat transfer was determined by a comprehensive comparison between the straight and the serpentine channel. The result showed the serpentine channel could effectively increase Nusselt number (Nu) by up to 36%. Furthermore, Box-Behnken design (BBD) was employed and twelve models were developed to study the effect of cavities and protrusions on thermal-hydraulic performance of the straight channel. An increase of Nu was observed with the use of protrusions and the smaller the distance between the two protrusions, the bigger the Nu. However, the performance evaluation criteria (PEC) values for these models were all smaller than one, indicating too much energy was consumed to obtain the corresponding heat transfer enhancement. These two corrugated structures were further used to improve heat transfer of the serpentine channel. Though Nu was increased by 48% to 66%, PEC was decreased by up to 45%. Cavities increased the amount of heat removal while protrusions effectively strengthened heat transfer but resulted in a significant increase of energy loss.