| Experiments were performed to study the effects of a controlled flow imbalance on the heat transfer coefficients in the entrance region of a tube situated in an array of parallel tubes. The array was modeled by two parallel tubes which were set into a large baffle plate to form a sharp-edged inlet, with air being drawn into the tube inlets from a large upstream plenum chamber. Quasi-local heat transfer coefficients were determined at various axial and circumferential locations along the length of the test section tube.;It was found that high degrees of flow imbalance played a decisive role in shaping the axial and circumferential distributions of the heat transfer coefficient in the thermal entrance region. Depending on the measurement site, the heat transfer coefficients were either enhanced or diminished due to the flow imbalance. The fully developed heat transfer coefficients were determined and were in excellent agreement with the well-known results of Petukhov and Popov in the fully turbulent region (Re (GREATERTHEQ) 10000).;The heat transfer coefficients reported here are determined indirectly by the naphthalene sublimation technique, and one of the special achievements of this work was the development of a method for casting naphthalene inside a circular tube.;Auxiliary experiments in which the baffle plate was removed were performed to determine the effect of the baffle plate on the axial distribution of the heat transfer coefficient in the entrance region of a single tube. In general, it was found that the presence of the baffle tends to diminish the heat transfer coefficients.;A preselected, fixed Reynolds number was established in the test section tube while that of the other was varied systematically. Both Reynolds numbers ranged from 5000 to 88000. The separation distance between the tubes varied from 1.5 to 4.5 tube diameters.;The heat transfer experiments were supplemented by the flow visualization experiments using the oil-lampblack technique. The visualization revealed important features of the flow such as flow separation, reattachment, recirculation, and secondary flow, which all were affected by the flow imbalance. Pressure measurements indicated that the flow imbalance did not contribute significantly to the pressure drop. |
