Performance analysis of the thermoelectric device as the internal heat exchanger of the trans-critical carbon dioxide cycle

Although the thermoelectric device (TED) has recently been studied as a sub-cooler of the trans-critical CO₂ cycle, setting the TED to uniquely be an internal heat exchanger (i.e. TED-IHX) is an implementation that is yet to be well studied. Therefore, this paper's objective is to study the potential of integrating the TED – internal heat exchanger (TED-IHX) component into the trans-critical CO₂ cycle for increasing the cycle's coefficient of performance (COP). The TED-IHX is studied both as a thermoelectric generator (TEG) to generate additional electricity from the internally exchanged heat, or as a thermoelectric cooler (TEC) to accelerate the internal heat transfer rate. To achieve this analysis, a 1-D finite element thermodynamic model of the TED-IHX is developed, and this is then integrated into the overall cycle model to evaluate the cycle COP. Simulation results demonstrated that although operating the TED-IHX as a TEG offered a COP improvement of up to 5%, the improvement is inferior over the direct IHX. This occurred because the heat transfer effectiveness is lowered by the TED's thermal resistance. Moreover, while operation as a TEC significantly reduces the compressor power requirement, the increased TEC power consumption negates this benefit.