Numerical analysis of heat transfer and fluid flow in rotary regenerative air pre-heaters

The Ljungstrom rotary air pre-heater is a regenerative heat exchanger used for preheating the combustion air, mainly in steam boiler plant. The hot gas and cold air ducts are arranged to allow both the flue gas and the inlet air to flow simultaneously through the machine. The hot flue gas heats the rotor material and as the rotor rotates, the hot rotor section moves into the flow of the cold air and preheats it. Existing simulations of regenerative air pre-heaters are mainly based on empirical approximations where some of the effects of the process are neglected. Although this usually gives reasonably acceptable results, it was thought that CCM analysis of such devices, which stands for Computational Continuum Mechanics, would result in a better understanding of the process features, such as the fluid-solid interaction. A grid interface was developed to transfer the geometry of such a Ljungstrom air pre-heater to a finite volume numerical mesh which is later used for the calculation of unsteady fluid-solid interactions. Results were obtained by use of the commercial CCM solver "Comet" of Star CD. In this paper the results are presented in the form of diagrams of the velocity and temperature fields as functions of time and space. The results of both the one- and three-dimensional calculations and field measurements are compared and good agreement was achieved. The result of this study is the development of an effective procedure for computer calculation of processes in a Ljungstrom air pre-heater to optimise its parameters, which can be used either for research and development or in everyday engineering practice.