ANALYSIS OF A HEAT EXCHANGER FOR A COGENERATION UNIT USING COMPUTATIONAL FLUID DYNAMICS

A cogeneration unit is a device for the production of electricity and heat. Waste heat is used in the cogeneration (Combine Heat and Power or CHP) process. This process increases the efficiency of the whole cogeneration unit system. One of the most important parts of a cogeneration unit is the exhaust heat exchanger, where waste heat is recovered. The objective of this applied research is to examine the properties of a shell-and-tube heat exchanger for a CHP unit of up to 200 kW manufactured by TEDOM a.s. The computations presented in this article are the results of computations where the influence of the composition of flue gas entering the computation in comparison with measured quantities were examined. The article contains a comparison of the influence of the flue gas, represented by CO2, N-2 and air as an ideal gas. The results include an analysis of the character of the flow in the heat exchanger, especially in the input volume of the flue gas, where, apart from the influence of the flue gas properties, the influence of the construction on the flue gas mass flow rate distribution into the tubes was also examined. The advantage of this extensive computation lies in the possibility of a detailed analysis of particular parts of the heat exchanger as well as the possibility of detecting potential construction imperfections, which could negatively influence heat transfer and hence the total efficiency of the heat exchanger and the CHP unit.