Trends in the Development of Machinery and Associated Technology ” TMT 2008 , Istanbul , Turkey , 26-30 August , 2008 INFLUENCE OF ROTATIONAL SPEED UPON HEAT TRANSFER IN A ROTARY REGENERATIVE HEAT EXCHANGER
Ljungström air preheater is a regenerative heat exchanger which is mainly used in steam boiler plants for preheating of the combustion air. The hot gas and cold air ducts are arranged in such a way to allow both 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. Simulations of regenerative heat exchanger described in open literature are mainly based on the empirical approach where some of the effects to the process are simplified or neglected. Although this may give reasonably good and in many cases acceptable results, a more comprehensive mathematical model based on differential equations of continuity, momentum and energy is applied here for analysis of the flow and heat transfer in such a device for better understanding of its process features. Using that, an effective procedure was developed for calculation of processes in rotary heat exchanger for optimisation of its parameters, which can be used either in research and development purposes or in the common industrial practice. An analysis based on such a mathematical model is applied in this paper to allow rotational speed to vary and quantify its influence upon heat transfer in the rotary air preheater to show hat optimal conditions exist for which the heat transferred passes through its maximum.