Numerical investigation of heat transfer and flow resistance characteristics of interpenetrated flying-wing finned tubes

In the present study, three possible interpenetration modes named vertical insertion, horizontally staggered shift, and streamwise staggered shift are proposed to improve the compactness of the flying-wing finned tube heat exchanger. Also, the effects of these modes on heat transfer and flow resistance characteristics of the finned tubes are numerically analyzed in the Reynolds number range of 1500–3000. It was found that a large vertically embedded depth (L_v), which in the present study has a maximum value of 3.4 mm, creates an acute-angled slit in the fin gradual contraction region. This slit weakens the convective heat transfer. However, the flow resistance characteristic is improved to a certain extent with increasing L_v. It was also found that the monotonous characteristic curves obtain a local inflection point in the range of 2.35–3.05 mm of L_v. An equivalent insertion coefficient is proposed to simplify the comparison of heat transfer rate (Φ). When the envelope size of the heat exchanger core, finned tube number, and pressure drop (Δp) are fixed, the overall thermal-hydraulic characteristics (Φ versus Δp) of the interpenetrated flying-wing finned tube heat exchanger are most significantly improved with L_v equal to 2.7 mm by 6.5% on average. Finally, two interpenetration correction factors are proposed to quantify the effect of interpenetration on the thermal-hydraulic characteristics.