Thermohydraulic design of heat exchangers for direct-cycle integrated gas turbine plants

Closed gas turbine plants coupled directly to a gas-cooled nuclear reactor consist of two kinds of main heat exchangers. The heat leaving the process at its low-temperature end is transferred from the gas to an intermediate water circuit by coolers. Heat transfer at an intermediate temperature range from the low-pressure to the high-pressure gas takes place in the recuperator. Integration of the gas turbine cycle in a single prestressed concrete pressure vessel requires compact design and special arrangement of all components including the heat exchangers. In this paper some general correlations for the dimensions of heat exchangers with longitudinal flow are given and discussed with respect to optimum design of recuperator and cooler. The dimensions considered are flow cross-section, length and heat transfer area of the apparatus. Minimizing the pod diameter in the concrete pressure vessel is important, and gives an advantage to longitudinal flow heat exchangers as compared to cross-flow types. Different types of heat transfer surfaces such as smooth, rough and finned walls are compared and criteria for the determination of optimum surface extension are given. The experimental results available indicate that a reduction of length can be achieved by the use of finned or rough surfaces. (author)