Design and analysis of a heat exchanger for a small-scale gas turbine

A gas turbine is classified as a continuous combustion internal combustion engine. Small scale gas turbines are gas turbines with an output of up to 500 kW. These internal combustion engines unlike the traditional Otto and Diesel engines, work following the Brayton cycle. For these engines to achieve high efficiencies values of about 50%, with an electrical efficiency of about 35%, they need to be run with a recuperated energy cycle of varying configurations. Thus, the objective of this work is to design a heat exchanger for a small-scale gas turbine. In this work, we are aiming at increasing the efficiency of an already existing small-scale gas turbine. This will be done by incorporating it with a Plain-Fin Compact Heat Exchanger (PFCHE). This PFCHE is of rectangular fins and a crossflow fin arrangement. The material of construction is steel due to its high thermal resistance. The design of the heat exchanger was done based on the algorithm given by Shah et al. This design was then implemented using an appropriate CAD tool. From the design, simulation tests were run using a full adaptive and automatic meshing algorithm. These simulation results were then analysed. It was found that there was a 32% rise in the temperature of the air entering the combustion chamber of the turbine. Also, a 50% reduction in the fin height can cause as much as an 18% increase in the fin efficiency of the heat exchanger, while a 50% increase in the effectiveness value can cause as much as a 40% increase in the outlet temperature.