Effects of Corrugation Angle on Local Heat/Mass Transfer in Wavy Duct of Heat Exchanger

An experimental study is conducted to investigate the effects of duct corrugation angle on heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewalls are determined by using a naphthalene sublimation technique. The corrugation angles(${\alpha}$) of the wavy ducts are 145$^{\circ}$, 130$^{\circ}$, 115$^{\circ}$ and 100$^{\circ}$. And the Reynolds numbers based on the duct hydraulic diameter vary from 300 to 3,000. The results show that at the low Re(Re $\leq$1000), the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, high heat/mass transfer regions are formed on both pressure-side and suction-side walls. At the high Re(Re $\geq$ 1000), these secondary flows are vanished with helping flow transition to turbulent flow and the regions which show high heat/mass coefficients by flow reattachment are formed on suction side. As corrugation angle decreases, the local peak Sh induced by Taylor-Gortler vortices increase at Re $\leq$1000. At high Re(Re $\geq$ 1000), by the existence of different kind of secondary flows called Dean vortices, non-uniform Sh distribution appears along spanwise direction at the narrow corrugation angle (${\alpha}$=100$^{\circ}$). Average Sh also increase by the enhanced effect of secondary vortices and flow reattachment. More pumping power (pressure loss) is required with the smaller corrugation angle due to the enhancement of flow instability.

열교환기 내부 유로의 꺾임각 변화에 따른 국소 열/물질전달 특성 고찰