Contributors: Warith Al-Anbiyaa University, Karbala, Iraq.; Laboratoire de Génie Civil et Géo-Environnement (LGCgE) - ULR 4515 (LGCgE); Université d'Artois (UA)-Université de Lille-Ecole nationale supérieure Mines-Télécom Lille Douai (IMT Lille Douai); Institut Mines-Télécom Paris (IMT)-Institut Mines-Télécom Paris (IMT)-JUNIA (JUNIA); Université catholique de Lille (UCL)-Université catholique de Lille (UCL); Refrigeration and Air-conditioning Department, Technical Engineering College, The Islamic University, Najaf; Department of Mechanical Engineering, Faculty of Engineering, Kufa University, Najaf; Mechanical Engineering Department, University of Technology - Baghdad; Lebanese International University (LIU); International University of Beirut (BIU); Laboratoire de Thermique et d’Energie de Nantes (LTeN); Centre National de la Recherche Scientifique (CNRS)-Nantes Université - Ecole Polytechnique de l'Université de Nantes (Nantes Univ - EPUN); Nantes Université - pôle Sciences et technologie; Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ)-Nantes Université - pôle Sciences et technologie; Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ); Institut Terre Environnement Strasbourg (ITES); École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS); École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES); Gulf University for Science and Technology (GUST)
Abstract: International audience ; Recovering low-to-medium grade waste heat from diesel-engine exhaust to preheat domestic hot water (DHW) can reduce auxiliary heating demand; however, published exhaust-to-water recovery studies commonly emphasize first-law gains while providing limited second-law quantification under coupled variations of flow conditions and concentric-tube geometry, and rarely integrate pumping-power penalties with discounted economic indicators and life-cycle-based environmental metrics in a unified framework. To address this gap, this work proposes a comprehensive 4E (energy–exergy–exergoeconomic–exergoenvironmental) assessment of a counter-flow heat-recovery concentric-tube heat exchanger (HR-CTHE) integrated upstream of an auxiliary water heater. The thermo-hydraulic model combines a validated overall-U correlation with developing-flow correction and a counter-flow ɛ–NTU formulation with temperature-dependent properties, alongside regime-dependent pumping-power prediction. A broad parametric sweep is conducted over exhaust inlet temperature (Th,i=500–900 K), Reynolds numbers (Reh,Rec=103–2×104), inner diameter (Di=0.03–0.15 m), and diameter ratio (Do/Di=1.25–3), for DHW setpoints of 338–365 K and a 4 m exchanger. Results show that recovered heat rate is primarily governed by Th,i and hot-side turbulence (increasing Reh yields the strongest gains), whereas the temperature lift of the recovered stream is maximized at moderated cold-side flow rates; thus, conditions that maximize q do not necessarily maximize the recovered-water outlet temperature. Exergetic efficiencies remain intrinsically low for this low-grade recovery application and deteriorate when Rec is increased excessively due to amplified entropy generation and pumping penalties, highlighting the importance of hot-side strengthening combined with cold-side moderation. The discounted economic analysis (annual savings, NPV, and discounted payback over 10 years at 10% discount rate) indicates that profitability is substantially higher when ...
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