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Waste heat air-source heat pump water heater (WH-ASHPWH) systems have been widely used to provide water heating in buildings due to their advantages of high efficiency and low environmental impact. It is important to determine reasonable operating conditions for WH-ASHPWH systems to improve their heating efficiency, especially for systems using industrial waste heat. In this study, a semiempirical parametric model of a WH-ASHPWH system was established to simulate heating performance under different working conditions and determine the optimum operating range of the system. A new discrete model for a tube-in-tube condenser was also generated. Taking the equipment of a pharmaceutical factory as an example, the heat exchanger model was first calibrated; then, the global model was used to study the effects of different air-side and condenser-side waste heat conditions on the heating performance of the system. According to the simulation results, the coefficient of performance (COP) reached a maximum value of 4.5 under the optimum working conditions. The deviation between the COP simulation data and experimental values was less than 8.28%, and the simulation time was less than 8 min. These metrics indicate that the model is reasonable and efficient. [ABSTRACT FROM AUTHOR]

In this study, a fluid–thermal–electrical multiphysics numerical model was developed for the thermal and electrical analyses of a heat sink-based thermoelectric generator (TEG) in a waste heat recovery system used for casting a bronze ingot mold. Moreover, the model was validated based on experimental data. Heat sinks were installed on the hot side of the TEG module to recover the waste heat from the flue gas generated in the casting process. The numerical results of the thermal and electrical characteristics of a plate fin (PF)-based TEG showed good agreement with the experimental findings. Numerical simulations of heat sinks with three different fin structures—PF, cylinder pin fin (CPF), and rectangular pin fin (RPF)—were conducted. The simulated system pressure drop, hot- and cold-side temperature difference in the TEG module, TEG power output, and TEG efficiency were compared for the differently designed fin structures. The results showed that for the same fin area, the CPF heat sink-based TEG system achieved a lower pressure drop, higher power output, and higher efficiency than the other two designs. This was particularly true when the velocity of the flue gas and the fin height exceed 5 m/s and 28.6 mm, respectively. Therefore, for low and high flue gas velocities, PF and CPF heat sinks are recommended as the best choices, respectively. [ABSTRACT FROM AUTHOR]

A significant amount of energy in the form of heat is lost in industrial processes once it is used in specific processes. Among different technologies, high-temperature heat pumps (HTHP) are a valuable method of recovering low-temperature waste heat in the industry in a very efficient way that can be activated using clean electricity. As a recently investigated technology, they are not yet spread in industrial processes, where traditional technologies are preferred. Therefore, this work shows an HTHP computer program (named HeatPack) to be used as a simulator by the university or technical students of courses included in applied thermodynamics engineering. This interactive and user-friendly platform allows the modification of different operating and design parameters and the working fluid. As outputs, the program provides the rest of the operating parameters and the energy performance of the cycle (quantified by the coefficient of performance, COP). The proposed HTHP and a gas boiler are compared by the program and the energetic, carbon footprint, and economic savings are displayed. Students, as the main target of users of the program, can observe how this technology can provide benefits. For instance, emission reductions in comparison with fossil fuel-based boilers, under which situation the energy performance of the HTHP is higher, and which alternative low global warming potential (GWP) refrigerants can provide more advantages. In addition to the educational use, this software can be used to design and study the integration of HTHPs in existing industrial needs to evaluate the feasibility. [ABSTRACT FROM AUTHOR]

This paper proposes a real-time capable augmented control scheme for a parallel evaporator organic Rankine cycle (ORC) waste heat recovery system for a heavy-duty diesel engine, which ensures efficient and safe ORC system operation. Assuming a time constant separation between the thermal and pressure dynamics, a nonlinear model predictive control (NMPC) is designed to regulate the mixed working fluid (WF) outlet temperature and the differential temperature between the two parallel evaporator outlets. Meanwhile, the evaporator pressure is regulated by an external PID control. The NMPC is designed using a reduced order, moving boundary control model of the heat exchanger system. In the NMPC formulation, state feedback is constructed from the estimated state via an unscented Kalman filter based on temperature measurements of the exhaust gas and WF at the evaporator outlet. The performance of the proposed control scheme is demonstrated in simulation over an experimentally validated, high fidelity, and physics-based ORC plant model during a transient constant speed and variable load engine drive cycle. The performance of the proposed control scheme (NMPC plus PID) is further validated via comparison with a conventional, multiple-loop PID controlling both the mixed evaporator outlet WF temperature, and the evaporator pressure. The simulation results demonstrate that the proposed control scheme outperforms a multiple-loop PID control in terms of both safety and total recovered thermal energy by up to 12% and 9%, respectively. [ABSTRACT FROM AUTHOR]

Two supercritical CO 2 (sCO 2) Brayton cycles for waste heat recovery in a solid oxide fuel cell (SOFC)-based plant are assessed and compared from thermodynamic and economic perspectives. One cycle considered is a simple sCO 2 cycle with recuperation, while the other is the supercritical recompression CO 2 (srCO 2) cycle. To provide a fair comparison between the performances of the SOFC-sCO 2 integrated plants, the flue gas is considered to exit at the same temperature in both cases, through a heating unit to generate hot air. The findings indicate that designing an efficient SOFC-sCO 2 integrated plant for cogenerating electricity and a by-product, e.g., heat, is not solely a question of selecting the most efficient sCO 2 layout as the bottoming power cycle. Rather, it is a tradeoff between the exergetic performance of the sCO 2 layout and its potential to absorb heat from upper SOFC system. It is shown that, at the optimized condition, the capability of a simple sCO 2 cycle for recovering heat from the SOFC is 30.86% higher than a srCO 2 layout. However, the exergy efficiency of the SOFC-srCO 2 integrated cogeneration plant is 0.64% higher than that of the SOFC-sCO 2 , with a corresponding increase in the average unit cost of products of 3.06%. • Simple and modified supercritical CO 2 Brayton cycles are compared for WHR of SOFC. • Thermodynamic and thermoeconomic analyses are implemented for cogeneration plants. • Using efficient SCO 2 layout does not guarantee high waste heat to power conversion. • Employing a simple SCO 2 cycle instead of a SRCO 2 layout raises power production. • The SOFC-SRCO 2 integrated cogeneration plant has a 0.64% higher exergy efficiency. [ABSTRACT FROM AUTHOR]

• Study of energy and exergy of a dual-loop organic Rankine cycle combining with engine. • Study the effect of both engine and cyclic parameters simultaneously. • The dual-loop cycle produces 310 kW power, which is 31% of the engine brake power. • Evaluation of the adequacy of the developed RSM models by the ANOVA tables. In this paper, which is the part 1 of this study, the energy and exergy characteristics of a dual-loop organic Rankine cycle (ORC) combining with a heavy-duty diesel engine were investigated. The proposed cycle is driven by the waste heat of the exhaust gases, intake air, and the coolant. Central composite design (CCD), which is a standard response surface methodology (RSM) technique, was applied to design of experiments (DoE) and to investigate the influence of both the engine and cyclic parameters such as the engine speed, the start of injection (SOI), the higher pressure of the high-temperature loop, and the higher pressure of the low-temperature loop. Adequacy of the developed RSM models has been evaluated by the ANOVA tables. The results revealed an increase in whether the engine or cycle parameters led to an enhance in the produced power of the system. As a comparison, the variation in engine variables has more impact on the produced power. On the opposite side, a change in the engine speed and SOI have a minor effect on the thermal efficiency of the system. The maximum produced power of the dual-loop ORC system was identified as 310 kW, which was resulted at the engine speed of 1800 RPM, and 0.0 degrees of CA bTDC for SOI; while the higher pressures of the HT and LT loops were in 2400 and 2100 kPa, respectively. This obtained power is 31% of the engine brake power. The maximum values for the thermal and exergy efficiencies were observed as 9.5% and 43%, respectively. Also, the exergy analysis demonstrated that the highest exergy destruction rate of the system is determined to be 500 kW. [ABSTRACT FROM AUTHOR]

Looking at the waste heat potential made available by industry, it can be noted that there are many sectors where small scale (< 100 kWe) organic Rankine cycle (ORC) plants could be applied to improve the energy efficiency. Such plants are quite challenging from the techno-economic point of view: the temperature of the primary heat source poses a low cutoff to the system thermodynamic efficiency. Therefore, high-performance components are needed, but, at the same time, they have to be at low cost as possible to assure a reasonable payback time. In this paper, the design of a two-stage radial in-flow turbine for small ORC industrial plants is presented. Compared to commonly applied mono-stage expanders (both volumetric and dynamic), this novel turbine enables plants to exploit higher pressure ratios than conventional plants. Thus, the theoretical limit to the cycle efficiency is enhanced with undoubted benefits on the overall ORC plant performance. The design process involved 1D/2D models as well as 3D Computational Fluid Dynamic ones. After the design of the preliminary configuration, sensitivity analyses were carried out varying the most relevant geometric parameters for design performance improvement. Thereafter, the stages were both analyzed in off-design conditions giving their performance maps. Moreover, a stage stacking procedure was applied to obtain the overall turbine behavior. [ABSTRACT FROM AUTHOR]