Heat transfer in a straight tube situated downstream of a bend

Abstract

The axial variation of the local heat transfer coefficient in a straight tube situated downstream of a bend is measured by a mass transfer technique for parametric values of the Reynolds number (5000–85000), bend turn angle (0, 30, 60, and 90°), and flow condition at the bend inlet. For one flow condition, the bend inlet is fed by a hydrodynamically developed tube flow. In a second case, the bend is fed from a large upstream plenum through a sharp-edged inlet. The Schmidt number for the mass transfer is 2.5 (naphthalene sublimation in air). It is found that the presence of a bend fed from a plenum through a sharp-edged inlet gives rise to a decrease in the mass (heat) transfer coefficients in the downstream tube compared with those for the no-bend case. On the other hand, a bend fed with a developed flow generally tends to decrease the coefficients in the downstream tube at lower Reynolds numbers while increasing the coefficients at higher Reynolds numbers. For both bend inlet configurations, there is clear evidence of laminarization of the flow at the lower Reynolds numbers and larger bend turn angles.