Comprehensive review, categorization, and practical insights on heat recovery from hot air and exhaust gas in engineering applications

In recent years, there has been a significant focus on energy management on a worldwide scale, with particular attention given to the development of waste heat recovery (WHR) technologies. These systems aim to capture and use the waste heat energy found in hot fluids produced by many engineering applications, such as exhaust gases, hot air, cooling water, and radiative heat. These applications can be categorized into four primary areas, namely iron and steel industries, energy, and power generation, automotive and transportation, and building and construction. While prior literature has examined many facets of WHR, this study presents an innovative methodology by offering an extensive and comprehensive analysis that focuses on WHR systems linked to exhaust emissions and hot air inside these industries. This study classifies the subdomains within each sector and conducts an in-depth examination of the processes and results associated with the integration of WHR technology into these sectors. Analytical schematics resulting from the reviewed results are given, together with tabulated summaries of WHR systems for each subdomain. It highlights significant advancements in exhaust gas recovery and air conditioning technologies, showcasing innovations such as thermoelectric generators (TEGs), organic Rankine cycles (ORCs), advanced heat exchangers, and environmentally friendly refrigerants. Furthermore, the paper proposes a comprehensive analysis of the data to improve understanding of the efficacy and improvements of WHR systems. Finally, the present manuscript constitutes a useful reference guide for researchers, policymakers, and industry stakeholders in the energy management field, particularly heat recovery (HR).