A study on the direct leakage of rotary air preheater with multiple seals

The direct leakage of rotary air preheater was studied both experimentally and numerically. We have tested different seal structures from single to triple seals cases, which are used in real air preheater equipments to control the direct leakage. To describe the effect of the gap width and inlet pressure on the orifice coefficient and in terms of the air leakage engineering modifying factor, some improved relationships were obtained, which are superior over the traditional ones because of their better accuracy. The main factors that affect the air leakage are the air flow expansion, inlet velocity at the seal gap entrance, and the flow boundary conditions on the seal plate surface. The first upstream seal accounts for most of the total pressure drop on the entire multiple-seal system. The simulation results on the multiple-seal system show that the system of triple seals is better in controlling the leakage than that of the double seals when the seal gap is small; however, when the seal gap increases up to a critical value, the difference between the double- and triple-seal becomes negligible.