Visualization of flow distribution in rectangular and triangular header geometries

The high heat transfer coefficients and compact sizes of minichannel heat exchangers have become increasingly critical to the development of efficient, inexpensive, and compact thermal systems. In many cases, however, these systems do not work as well as models predict because of unanticipated flow maldistribution. This problem can be mitigated with effective header designs. The present study quantifies the distribution of air-water mixture flows in header geometries relevant to heat exchangers that are important in refrigeration and chemical processing applications. Rectangular and triangular headers connected to microchannels of different diameters are tested to understand the effects of header and tube geometries, operating conditions, and flow patterns on the distribution of the two phases. The inlet quality was varied from 0.05 to 0.35, the inlet mass flux from 50 to 300 kg m−2 s−1, and the outlet channel diameter from 1 to 3 mm. The results show that distribution improves at higher inlet mass fluxes and qualities due to changes in the header flow regime, and in general, the triangular header distributes flow better than the rectangular header.