The Graetz heat-transfer problem in a double-pass parallel-plate heat exchanger for a power-law flow subject to hybrid boundary conditions was investigated theoretically and verified experimentally. An impermeable plate with negligible thermal resistance was placed between two parallel plates to conduct double-pass operations, and the performance of the device was significantly improved. The mathematical model was solved analytically using the separation of variables along with the superposition principle and an orthogonal expansion of the power series. The present study was aimed at developing a high-performance heat exchanger with hybrid boundary conditions, such as a constant temperature at the lower wall and a uniform flux at the upper wall. A dimensionless number (β) was defined to characterize the relative magnitude of the two different boundary conditions. From the average Nusselt number, the boundary condition with a constant heat flux at the upper wall could play a more important role in the heat transfer than the constant temperature at the lower wall. The heat-transfer efficiency enhancement was higher for the power-law fluid with a larger power index. However, the double-pass device in this study was more suitable for power-law fluids with a small power index when considering both heat-transfer efficiency and power consumption.
關聯:
Journal of Applied Science and Engineering 22(1), p.57-68
