Boundary layer redevelops with mesh cylinder inserts for heat transfer enhancement. (June 2017) - Tu, Wenbin
Highlights: Mesh cylinder insert can achieve a heat transfer enhancement of 1.8–3.6 times that of smooth tube. Inserts with P = 0.2 mm brings the best heat transfer performance among the open area rate samples. The shortest spacer length ( S / D = 50/12) achieved the worst heat transfer performance. It is valuable to adopt a short insert length ( L / D = 25/12) in the design of heat exchanger. Abstract: In this paper, mesh cylinder inserts were adopted to enhance the convective heat transfer in a circular tube. The effect of open area rate ( P = 0.1 mm, P = 0.2 mm, P = 0.4 mm), inlet closed type, spacer length ( S / D = 50/12, S / D = 75/12, S / D = 100/12) and insert length ( L / D = 25/12, L / D = 50/12, L / D = 100/12) on heat transfer performance were numerically investigated at the Reynolds number of 280–1800. The results show that mesh cylinder inserts has an excellent heat transfer performance in the laminar regime. It was mainly due to the high Nu number produced by boundary layer redevelopment at the inlet and the complex flow at the annular region also contributes to the high heat transfer rate. The excellent heat transfer performance is obtained at the cost of high flow resistance. To avoid sharply increase in the flow resistance, a small hole is cut in the closed inlet of mesh cylinder inserts, which can greatly decrease the friction factor without sharply decrease the heat transfer rate. The open area rate has little impact on the heat transfer rate and the best heat transfer performance is resulted from inserts with P = 0.2 mm. Heat transfer performance of mesh cylinder inserts is also affected by the spacer length, insert length. A relatively long spacer length ( S / D = 100/12) and a short insert length ( L / D = 25/12) are recommended in the design of heat exchanger in this work.