Turbulent heat transfer coefficients in an isothermal-walled tube for either a built-in or free inlet

Local heat transfer coefficients were determined for turbulent flow in an isothermal-walled circular tube whose inlet was either built into a large wall or was supported so as to be in free space. In either case, the sharp-edged nature of the inlet induced flow separation and subsequent reattachment just downstream of the inlet, and these processes were found to have a dominant influence on the thermal entrance region. At the point of reattachment of the flow, the heat transfer coefficients for the case of the built-in inlet ranged from 4.15 to 2.4 times the corresponding fully developed values over the Reynolds number range from 5000 to 88 000. The length of the thermal entrance region was also increased by the presence of the inlet-induced separation. With the tube inlet built into a large wall or baffle plate, the heat transfer coefficients in the immediate neighborhood of the inlet were found to be lower than those for a tube with a free inlet, the differences being in the range of 10%.