Heat transfer characteristics in two-pass rectangular channels with inclined partition wall

Serpentine channels with a sharp 180 degrees turn are often used in compact heat exchangers. The local heat transfer characteristics in such channels are very complex, because the secondary flow arises in the turning flow, and the flow separation and reattachment occur around the sharp turn. In most studies conducted on this subject, the partition (inner) wall of the channel was settled parallel to the outer walls. If the partition wall is inclined with respect to the outer walls, the local heat transfer characteristics in the channel can be considerably altered from those in the parallel-walled channel. Moreover, it is expected that the heat transfer performance of the channel be improved than the case of the parallel partition wall. We made an experimental study on the heat transfer characteristics in rectangular cross-sectioned two-pass serpentine channels with an inclined partition wall. The channel cross section at the entrance was 50 mm x 25 mm, and the inclination angle of the partition wall was changed from -6 degrees (convergent channel) to +6 degrees (divergent channel) at 2 degrees intervals for three turn clearances of 30 mm, 50 mm, and 70 mm. Distributions of local heat (mass) transfer rates on the long-side wall were measured by the naphthalene sublimation method under a single Reynolds number of 3.5x10(4). In this paper, the influence of the inclination angle of the partition wall on heat transfer characteristics in the channels is discussed. Then, the optimum combination of the inclination angle and the turn clearance is examined from viewpoints of the trade-off between the mean heat transfer rate and pressure loss, and of the uniformity in the distribution of local heat transfer rates.