Local heat transfer and flow distribution in a three-pass industrial heat exchanger

Abstract Local heat transfer from single tubes in an industrial-sized, three-pass heat exchanger of the inline tube bundle type was measured. The transversal and longitudinal pitches were 1.8 D and 1.5 D , respectively, the height of each pass was 30 D and the Reynolds number was 20 000. The measurements were made using an electrically heated cylindrical probe of the metallic film type, an instrument normally used in small-scale laboratory setups to gain detailed information about local heat transfer. The probe was positioned at various tube locations and rotated to yield the circumferential variation of the local heat transfer. Depending on location, local mean heat transfer was less than half or more than twice the nominal mean value. These variations were related to the non-uniform flow distributions present inside the heat exchanger, evidenced by computational fluid dynamics calculations. Also, the calculated velocities were used with an empirical correlation for the Nusselt number, and the results agreed very well with the measured values.