Flow and Heat Transfer Characteristics in Small Diameter Tube Bundles with a Staggered Layout: an experimental study

An experimental research on flow and heat transfer characteristics of staggered tube bundles with different tube diameters (2mm, 3mm and 5mm) is conducted. In the experiment, the number of rows (4-12), the mass rate of the air (0.06kg/s-0.18kg/s), and the transverse tube pitch (S1/d=2, S1/d=3) are variables to study the characteristics of the airside flow resistance and heat transfer. The three main conclusions of the experimental results are as follows: (1) Under the same conditions, the smaller tube diameter leads to the larger airside convective heat transfer coefficient. Besides, the deviation between the Nusselt number of the experiment and the empirical correlation of Žukauskas is in the range between -14% and -10%; (2) The effect of transverse distance on heat transfer is not obvious, but the convective heat transfer coefficient increases significantly with the increase of row number; (3) The external pressure drop of the tube exhibits an exponential increase with the air flow rate. Particularly in the experimental samples with smaller diameters, the outflow resistance of the tube is noticeably higher compared to other tubes. Finally, new empirical correlations of the airside convection heat transfer for the small-diameter staggered tube bundles are fitted according to the experimental data, and it is hoped to provide a reference for the more accurate design of tube bundle heat exchangers.