Design of Novel Heat Recovery Systems from Diesel Generator Exhaust Using Phase Change Materials

Abstract

The global energy crisis demands a fast transition to sustainability. A sustainable circular economy emphasizes the development of recovery solutions for future generations. This paper proposes the encapsulation of phase change materials (PCMs) within two designs. The first design features a coiled heat exchanger with paraffin PCM embedded within the coil, while the second design utilizes three concentric tubes to encapsulate the paraffin between the shell and inner tubes. What sets these designs apart is their ability to harness the energy carried by exhaust gases from diesel engines through a dual-process system. During the charging phase, the PCM stores part of the thermal energy extracted from the exhaust gases, while a heat transfer fluid (HTF) is simultaneously circulated to be heated for immediate applications. Throughout this study, a numerical approach was adopted using ANSYS Fluent software to optimize the performance of this system under different parameters. These parameters include the initial temperature and mass flow rate of the exhaust gases, the type and mass flow rate of the HTF, and the melting temperature range of the PCM. It was found that at a higher exhaust inlet temperature of 600K and a mass flow rate of 0.01 m3/s and using air as HTF with a lower inlet mass flow rate of 0.0001 m3/s, both systems achieve complete melting of the paraffin in a shorter period with a high outlet air temperature. Interestingly, variations in paraffin type had negligible effects on system dynamics, highlighting the robustness of the proposed designs. Following the numerical optimization, both prototypes were tested for selected boundary conditions and available testing conditions, demonstrating a successful alignment between experimental and numerical outcomes. Furthermore, numerical simulations of the discharge phase for the optimal design demonstrate an extended solidification duration of 2.5 hours during which air temperature rises from 300K to 317K. These findings underscore the potential of PCM-integrated systems in addressing energy challenges while optimizing performance and efficiency.