Effect of the geometry of flattened tube on the thermal performance of a high temperature generator

The present study numerically investigated the effect of the geometry of flattened tube on the thermal performance of a high temperature generator (HTG) with the pre-mixed surface flame burner of the double effect LiBr–water absorption system. The heat transfer tubes of the HTG were consisted with a set of circular and flattened tubes in series. FLUENT, as a commercial code, was applied for estimating the thermal performance of the HTG. Key parameters were the aspect ratio of flattened tubes, rib transversal length, and the rib pitch ratio on the flattened tube of the HTG. The maximum heat transfer rate of the HTG was obtained at the aspect ratio of 6.8 for the flattened tube. The heat transfer rate for the flattened tube was increased by 4.2% as the rib transversal length was increased from 2 mm to 3 mm. The heat transfer rate of the flattened tube with the rib pitch ratio of 15.3 was higher by the maximum 5.8% than that without rib. The heat transfer rate of the HTG with the rib of the rib transversal length of 3 mm and the rib pitch ratio of 15.3 was higher by 3.4% than that without the rib. It led that the exhaust gas temperature of the HTG with the rib was lower by 23 °C than that without the rib.