Heat Recovery System Research Articles

Structural, electronic, vibrational, optical and thermoelectric properties of 1T-Na2O monolayer via MD and DFT study

Abstract Density Functional Theory (DFT) was implemented to determine the physical properties of the 1T-Na2O monolayer with the aid of WIEN2k software. To determine the electronic property exchange correlation such as GGA and hybrid functionals were implemented. The electronic property studies unveiled the 1T-Na2O monolayer as a direct bandgap semiconductor that has band gap values of 1.68 eV and 2.75 eV with GGA and hybrid correlation functionals. The dynamical stability of the 1T-Na2O monolayer was established by harnessing Phonon dispersion analysis, while the thermal stability was established by harnessing the Ab-initio Molecular Dynamics (AIMD). The optical properties investigation revealed that the 1T-Na2O monolayer shows an excellent absorption coefficient in the UV region and has a potential application in optoelectronic applications. The 1T-Na2O monolayer shows promise for waste heat recovery systems due to its thermoelectric properties, with a figure of merit of 0.82 at 400 K. The effective masses of electrons and holes (charge carriers) are determined. The relative ratio was estimated to determine the recombination rate of charge carriers and was found to be limited.

Feedstock Characterization for Enhanced Heat Recovery from Composting Processes: A Review

Compost Heat Recovery Systems (CHRS) sustainably capture heat from composting waste biomass, helping reduce greenhouse gas emissions and fossil fuel reliance. The choice of feedstock affects the performance of CHRSs as it controls the microbial activities and the amount of heat generated. This review evaluates plant-based, animal-derived, and non-agricultural feedstocks to optimize CHRS energy recovery. A systematic review of 244 studies, published from 1996 to 2023 and available on Scopus, Web of Science, and external databases, categorized feedstocks based on properties like carbon-nitrogen ratio (C/N), moisture content, bulk density, and heating value to assess their impact on energy recovery and compost quality. The review followed the PRISMA guidelines, excluding irrelevant documents and those that lacked quantitative data. Animal-based materials, which have high levels of moisture and nutrients, such as nitrogen (14.50–32.20 g/kg TS) and phosphorus (13.0–13.5 g/kg TS), promote rapid growth of microbes and consistent heat production supported by their stable carbon content (353.8–450.0 g/kg TS) and optimal C/N ratios (5.90–28.90). On the other hand, plant-based materials that are rich in volatile solids (327.2–960.0 g/kg TS) and lignin (36.7–290.0 g/kg TS) offer a steady and prolonged release of heat but decompose more slowly.

Renovating Post-First-Energy-Regulation Housing: Achieving Nearly Zero-Energy buildings under typical and extreme warm conditions in a temperate European city

Decarbonising the built environment is essential for achieving the 2050 European objectives. Multi-family buildings comprise nearly half of Europe’s building stock, yet there is no regulation mandating all housing renovations to be Nearly Zero-Energy Buildings (NZEBs). This paper highlights the role of NZEB renovation for residential buildings constructed between the first energy regulations, after the first oil crisis, and the EPBD 2002 implementation (post-first-energy-regulation housing), as a pivotal factor towards energy transition. In Spain, this period (1980–2006) encompasses approximately 45% of existing dwellings. A case study was conducted in a city with a Cfb temperate climate, focusing on the most representative residential typology of the target period: the linear block. The study evaluates its current state and defines potential measures to meet NZEB requirements, achieving zero consumption when renovation of thermal envelope is combined with heat recovery systems, heat pumps, and PV panels.This research is based on energy simulations for two climate scenarios: the typical meteorological year (TMY, official series 1970–2000) and the most extreme warm year (EWY, 2022) in Spain. Results indicate active cooling systems are necessary for NZEB renovations in Spanish Cfb climates. Furthermore, low-temperature radiators significantly reduce heating consumption, while splits are the most suitable cooling systems. This study shows Spain is not adequately preparing its housing stock to face climate change, as most typical renovation works are based on official weather files that need updating to reflect harsher summer conditions. Finally, the study aims to encourage new policies and enhance existing regulations to address rising temperatures and heatwaves.

Performance prediction and operating conditions optimization for aerobic fermentation heat recovery system based on machine learning

Performance prediction and operating conditions optimization for aerobic fermentation heat recovery system based on machine learning

Thermodynamic modeling and AI-enhanced optimization of a novel tri-level waste heat recovery system for industrial processes

Thermodynamic modeling and AI-enhanced optimization of a novel tri-level waste heat recovery system for industrial processes

Exploring energy efficiency and savings potential of a horizontal domestic drain water heat recovery system in high-rise apartment buildings

In residential buildings, domestic hot water (DHW) used for showering and handwashing produces significant amounts of hot drain water (DW), which is typically wasted. This study proposes a horizontal drain water heat recovery (DDWHR) unit to capture waste heat from DW and improve overall DHW system efficiency with the focus on thermal exchange in a compact installation suitable for high-rise apartment buildings. Experiments under different operating conditions were conducted to evaluate the DDWHR unit’s thermal performance and energy-saving potential. Results showed that the proposed DDWHR unit achieved energy efficiency of 90–95%, depending on operating conditions, due to high heat recovery rates. In the entire DHW system, the DDWHR unit demonstrated approximately 15% heating energy savings compared to conventional DHW setups. Also, nationwide adoption of the DDWHR unit in two-person apartments could reduce gas costs by about 14% annually. The findings of this study indicate that the horizontal DDWHR unit can effectively promote sustainable DHW use in high-rise residential buildings and offers a promising solution for improving energy efficiency in DHW systems.

Comprehensive study on waste heat recovery from gas turbine exhaust using combined steam rankine and organic rankine cycles

Waste heat recovery technology has proven to be an effective approach for enhancing energy efficiency, reducing greenhouse gas emissions, and lowering energy costs. This study assesses the performance of different waste heat recovery systems from thermodynamic, exergy destruction, economic, and environmental perspectives. Using the DWSIM software, the study simulated a waste heat recovery cycle powered by a high-temperature heat source (508.99 °C) to maximize recovery power and determine the optimal system configuration, including standalone Organic Rankine Cycle (ORC), standalone Steam Rankine Cycle (SRC), and combined systems like SRC with series ORC (SRC + S-ORC), cascade ORC (SRC + C-ORC), and a combination of both (SRC + S-ORC + C-ORC). Among these configurations, the SRC + S-ORC + C-ORC configuration delivered the best performance, achieving a net power output of 3,532.14 kW and a thermal efficiency of 17.09 %. Economically, it demonstrated strong results with a net present value of €1.478 million, a payback period of 8.01 years, and a benefit-cost ratio of 1.32. This configuration also had the highest environmental impact, reducing CO2 emissions by 12,452.48 metric tons per year, equivalent to annual earnings of approximately €999,933.85 through carbon credits trading. The study also found that the evaporator experienced the most significant exergy destruction, suggesting opportunities for improving the highest exergy destruction area, leading to an increase in overall system efficiency. In conclusion, the SRC + S-ORC + C-ORC configuration offers the most promising combination of thermodynamic, economic, and environmental benefits for waste heat recovery systems.

Experimental and Numerical Study for a Horizontal Wastewater Heat Recovery System

This study aims to numerically and experimentally investigate the performance of a drain water heat recovery device. Consequently, a heat exchanger prototype was developed to integrate with classic rectangular shower trays of small dimensions. The proposed drain water heat recovery (DWHR) system was tested using a specially designed experimental stand. In addition, the experimental data were compared to numerical results based on Computational Fluid Dynamics (CFD) simulations. The values of effectiveness and Number of Transfer Units (NTU) achieved for the proposed DWHR system, based both on experimental and numerical data, are similar to those from the literature for analogous configurations of horizontal DWHR systems. Consequently, the heat exchanger prototype analyzed could represent a pertinent solution for heat recovery from drain shower water with minimum investment costs.

Optimization of Heat Recovery System Based on Different Types of Finned Tube Heat Exchangers

Optimization of Heat Recovery System Based on Different Types of Finned Tube Heat Exchangers

A System to Store Waste Heat as Liquid Hydrogen Assisted by Organic Rankine Cycle, Proton Exchange Membrane Electrolyzer, and Mixed Refrigerant Hydrogen Liquefaction Cycle

ABSTRACTThis study proposes a system to store waste heat as liquid hydrogen using a proton exchange membrane electrolyzer (PEME) and a mixed refrigerant hydrogen liquefaction cycle. The novelty of this study lies in proposing a waste heat recovery system that stores electricity as liquid hydrogen, consuming less power due to the improved exergy efficiency of the components. The proposed system is analyzed to achieve better efficiency in terms of thermal and exergy efficiencies. Waste heat is used to generate power by an organic Rankin cycle (ORC), produced electricity is utilized in the PEME unit and compressors of liquefaction cycle to produce and liquefy hydrogen, respectively. Codes are written in EES software to simulate the system. Thermodynamic analysis is done in order to achieve better thermal efficiency for the proposed model. Membrane potential at different values of current density is calculated and compared with validate the simulated model. The exergy efficiency of the liquid hydrogen production process is 57%. The exergy efficiency, rate of power produced in ORC, and rate of hydrogen production by the electrolyzer increase significantly by increasing the isentropic efficiency of the turbine. At a temperature of 340 K for the evaporator, the thermal efficiency of ORC is obtained at 8.5%, which is approximately 3% higher compared with that of the previous similar process.

Estimating the potential for thermal energy efficiency in the industrial sector: A hybrid model integrating exergy analysis and long-term technology diffusion scenarios

Thermal energy for heating and cooling accounts for a significant portion of the total energy consumed in the industrial sector, and is predominantly provided by fossil fuels. Thus, effective thermal energy management is essential for reducing overall energy consumption, operational costs, and emissions in the industrial sector. While previous studies have explored energy efficiency in this sector, there is a lack of research specifically addressing the challenges of modeling thermal energy efficiency in industry. Therefore, this study proposes a novel hybrid methodological approach that integrates macroeconomic perspectives with detailed end-use analysis and exergy considerations, allowing for a more accurate assessment of recoverable energy in industrial processes in alternative technology diffusion scenarios over a long-term horizon. An empirical study focusing on the pulp and paper subsector in Brazil demonstrated the applicability of the proposed model and revealed significant potential for thermal energy efficiency improvements. The model identified that through optimal technology diffusion scenarios, the sector could achieve up to 25 % reduction in thermal energy consumption by 2050, with heat recovery systems accounting for approximately 40 % of these savings. Cost-effective technology adoption curves indicated that 60 % of this potential could be realized through economically viable investments with payback periods under 3 years. Overall, this study contributes to the field of industrial energy efficiency by offering a hybrid methodological approach that can be adapted to different industrial settings, and can help policymakers and industry stakeholders develop effective strategies to improve thermal energy efficiency and reduce emissions in the industrial sector.

Utilizing supercritical water gasification for hydrogen production combined with a waste heat recovery system for domestic households

Hydrogen from food waste can provide sustainable energy. Food waste can be gasified into clean, efficient hydrogen gas using cutting-edge techniques. This study is about the gasification of food waste under different settings to determine gas production and efficiency. The supercritical water gasification (SCWG) method was used in experiments at 400 °C, 450 °C, and 500 °C with reaction durations of 30, 60 and 90 min. The results showed peak values of CO2, CO, CH4, H2 at 90 min, equivalent to 6.2 % and 7.9 % hydrogen efficiency (HE) and cold gas efficiency (CGE). Peak CGE and HE were 6.7 % and 9.2 % at 500 °C, whereas peak CE and total gas output were 6.8 % and 8.6 %. To generate heat and power, a PEM cell was added. Gasification-generated hydrogen was warmed and fed in the PEM circuit at 0.7, 1 and 1.5 m/s. The peak velocity indicates a 23.1 % waste heat recovery rate and a higher hydrogen temperature difference of roughly 8.1 °C. At the temperature of peak gasification (500 °C), the values of CO2, CO, CH4, and H2 are approximately 3.6 mol/kg, 0.3 mol/kg, 2.6 mol/kg, and 4.7 mol/kg, respectively. At the peak gasification temperature (500 °C), As a result, the suggested system is ideal for combining hydrogen production to generate both power and heat energy for use in heating small homes or buildings (the proposed system can deliver that much energy or at least partially fulfill it).

Fuzzy TOPSIS optimization of MHD trihybrid nanofluid in heat pipes

Heat pipes have the potential to benefit from nanofluid flow between coaxial cylinders. Heat is effectively transferred from one place to another by means of heat pipes. Heat pipes can be used for electronics cooling, spacecraft thermal management, and heat recovery systems by adding nanofluids, which enhances the heat pipe's thermal conductivity and heat transfer capability. This work aims to discover an approximate solution for the flow of a trihybrid nanofluid (THNF) consisting of graphene, copper, and silver between two coaxial cylinders in magneto-hydrodynamics, taking into account the broad variety of applications. The nanomaterial is tested in a system with a fixed inner cylinder and a rotating outer cylinder. It contains graphene, copper, silver, and kerosene oil as the base fluid. For examining the flow characteristics, magnetic field is applied along radial direction of the cylinder, while inner cylinder is fixed, and outer cylinder is rotating. Moreover, temperature of the outer cylinder is higher than the lower cylinder. The objective of this study is to develop a mathematical model of the problem and solve the governing equation numerically using the MATLAB built-in routine called bvp4c. Additionally, we identify the most effective physical parameter to optimize the heat transfer rate using Fuzzy Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). Using a variety of factors, we calculate fluid velocity, skin friction, temperature, and Nusselt number graphically. According to the study, higher Brinkman numbers (Br) and magnetic parameter (M) characteristics lead to higher temperatures. Furthermore, Fuzzy TOPSIS shows that alternative A11 (ϕ=(0.9,1.0,1.0),M=(0.5,0.7,0.9),Br=(0.9,1.0,1.0)) has the maximum heat transfer rate, while another A8 (ϕ=(0,0,0.1),M=(0,0,0.1),Br=(0,0,0.1)) has the lowest.

Analysis of the Heat Content of Exhaust Gases from a Heavy-Duty Diesel Engine under Real-world Driving Conditions and Cold Start Operation

Abstract European Commission is currently working on defining new Euro 7 standards for light and heavy-duty vehicles, which will set severe restrictions on emissions in real driving conditions, and under cold-start operations. It is well known that about 60% of fuel energy converted in a diesel engine is lost in exhaust flow, coolant, and other forms of loss. A more efficient vehicle usage can be achieved by exploiting such dissipated energy content to produce additional mechanical or electrical energy. Several solutions can be adopted for Waste Heat Recovery (WHR) systems. Among them, exploiting the synergy between Organic Rankine Cycles (ORCs), thermal storage with Phase Change Materials (PCM), and electric hybridization is the solution adopted in the research project IRIDESCENT (biodIesel hybRID Electric buS with waste heat reCovEry aNd sTorage). The efficacy of recovering heat content from exhaust gases in reducing fuel consumption has already been demonstrated under stationary conditions. However, one of the challenges in applying WHRs to the powertrain of road vehicles is the fast dynamics of the engine load that determines fast variations in the flow rate and temperature of the exhaust gases. This makes it difficult to optimize energy recovery and explains the need to adopt PCM thermal storage systems. In this framework, the goal of the present work is to characterize the variability of temperature and flow rate in the exhaust gases of a diesel engine for heavy-duty applications under real-world driving conditions. To this end, a dataset of information retrieved from the scientific literature for the Isuzu FTR850 truck was used. The dataset consists of twenty-eight trips performed with the same driver over the same route. It includes both hot-start and cold-start trips and three different values of trailer load (0, 1500, 3000 kg). For each trip, data from GPS, ambient sensors, onboard diagnostics (OBD) systems, and portable emissions measurement systems are made available with a frequency of 1 Hz. In this investigation, a statistical analysis of the data set and a preliminary selection of the ORC and PCM technologies are performed.

Model based design of a turbo-compound bottomed to internal combustion engine exhaust gas

Abstract The transportation sector is living a new era, where the conventional powertrains based on thermal engines are flanked by innovative ones, based on electric and hybrid systems. This revolutionizes the behaviour and the driving habits, as well as the figure of the whole propulsive system, which should integrate different energy sources on board and the energy demand for propulsion, auxiliaries, ancillary components, vehicle needs, etc. But, for heavy-duty vehicles, it is very difficult to abandon in the short and mean term the reciprocating combustion engine technology. Also, for passenger cars and light duty vehicles, the pure electric propulsion seems to put in more evidence limits not only technological. In this panorama, the development of very high efficiency engines is mandatory to fit the emissions targets, both referred to pollutant emission and CO2. In this regard, waste heat recovery into mechanical or electrical energy is one of the most promising options to reduce fuel consumption. It is of particular interest for heavy duty engines, where the operation does not suffer so much the transient phases, and hybrid powertrains, where the energy recovered can be stored in electrical form and used for all the necessities of the vehicles. In this paper, a waste heat recovery system based on an additional turbine placed in the exhaust line of a turbocharged internal combustion engine has been studied. The auxiliary turbine is designed thanks to a model-based approach. The performance map of the turbine has been calculated referring to the thermodynamic conditions of the engine exhaust gases as input parameters. The so-designed component is then integrated with an engine model, and the benefits of a turbo-compound technology bottomed to the engine were assessed. In this way, the potential power recoverable from the turbine is evaluated under design and off-design conditions. The integration with engine model allowed to estimate the side effects related to backpressure increase on the engine exhaust manifold (which leads to an overconsumption or an underrating of the engine torque), as well as the equilibrium change on the turbocharger shaft. Definitively, the final overall engine performances are assessed including the need for a bypass which, in certain engine working conditions, must exclude the recovery.

Impact of the type of heat exchanger on the characteristics of low-temperature thermoacoustic heat engines

Thermoacoustic technologies are considered an effective solution for harnessing low-temperature heat, whether from waste or renewable sources. However, in practice, developing and implementing high-performance thermoacoustic systems is a complex challenge. In real waste heat recovery systems, heat exchange between thermoacoustic engines (TAEs) and external heat sources is facilitated by auxiliary systems, such as circulation loops that include recuperative heat exchangers. It is evident that the upper power limit of a TAE is constrained by the thermal performance of its internal heat exchangers. This article investigates the energy transfer processes between the internal recuperative heat exchangers of a TAE and its matrix, and presents a mathematical model describing the interactions between the matrix and the heat exchangers. The model accounts for the effects of temperature inhomogeneities on the surface of the recuperative heat exchangers, which influence the temperature distribution within the TAE matrix. The use of liquid-gas recuperative heat exchangers in TAEs introduces temperature heterogeneity within the components of the thermoacoustic core. This study shows that such temperature variations can reduce the matrix gain factor for additional acoustic energy by a factor of 1.1 to 1.3. Therefore, when designing low-temperature thermoacoustic systems, it is essential to consider the type and characteristics of the heat exchangers used. The analysis indicates that recuperative heat exchangers can reduce the efficiency of thermoacoustic machines, whether they function as engines or refrigerators.

High-efficiency waste heat recovery systems integrated with thermal energy storage for sustainable Data Centres.

Abstract This paper proposes an advanced energy recovery system for Data Centres (DCs), highly energy-intensive facilities that can be effectively coupled with eco-sustainable technologies to meet the Green New Deal targets. In this context, this study aims to assess the opportunities of recovering the waste heat produced by a DC to satisfy the energy heating demand of some office buildings. The evaluation was carried out by a simulation model developed in MATLAB-Simulink environment. The considered DC was cooled with rear door and CPU cold plate heat exchangers coupled with two chillers and a water TES. The parametric analysis showed how an average 53 kW DC placed in south Sardinia (Italy) can effectively meet the heating needs for office building volumes from 20000 to 40000 m3. Since the recovered energy never exceeds 60% of the available energy from the DC, the payback time is always higher than 10 years. Further analysis, considering more demanding utilities, as hospitals, district heating or industrial processes, could make this solution more profitable.

Research on green manufacturing process optimization based on thermal efficiency optimization and LCA technology

In the context of sustainable development and increasing awareness of environmental protection, the manufacturing industry faces the dual challenge of improving resource efficiency and reducing environmental impact. This study aims to explore the optimization scheme of green manufacturing process through the combination of thermal efficiency optimization and life cycle assessment (LCA) technology, and promote the sustainable development of manufacturing industry. In this paper, a combination of experimental and theoretical analysis is used to first evaluate the thermal energy utilization rate in the current manufacturing process and identify the existing energy waste. Subsequently, the thermal efficiency was improved by introducing an improved heat recovery system and optimizing process parameters. Using LCA technology, the environmental impact assessment of the manufacturing process before and after optimization is carried out to quantify the effect of the optimization measures. Studies have shown that through thermal efficiency optimization, energy consumption in manufacturing processes is reduced and greenhouse gas emissions are significantly reduced.

Monitoring the heating energy performance of a heat wheel in a direct expansion air handling unit

This study presents an on-site examination of the heating energy performance of a real ventilation system, running on the flat roof of a shopping complex building in Hungary. The main focus of this study is to delve into the heating energy efficiency of specific air handling elements, such as the air-to-air rotary heat wheel and the direct expansion heating coil supplied by a variable refrigerant volume outdoor unit under real operation conditions. Additionally, an investigation was carried out during the heating season to scrutinize the potential occurrence of CO2 transfer from the exhaust airflow to the supply airflow within the heat wheel, which issue highlights a notable limitation of the heat recovery system. Based on the monitored and measured data, the energy saving impact of the heat wheel was 20.5 % on the electric power consumption of the variable refrigerant volume outdoor unit throughout the entire heating period, compared to operation without heat wheel. Furthermore, the relative average of CO2 cross-contamination is recorded as 3.8 % in the investigated heating season.

Enhanced Energy Harvesting from Thermoelectric Modules: Strategic Manipulation of Element Quantity and Geometry for Optimized Power Output

Rising environmental concerns and increasing electricity generation costs have sparked significant interest in waste heat recovery systems, particularly thermoelectric modules. Given the challenge of breakthroughs in thermoelectric materials, improving module structure has become a key strategy for enhancing efficiency. This study examines the commercially available TGM1-127-1.0-0.8 thermoelectric module through comparative simulation of flat plate and annular configurations. By maintaining consistent conditions across designs—including total volume of thermoelectric material, element geometry, heat source contact area, temperature differential, and connecting copper plate volume—we investigated the relationship between thermoelectric element quantity and module performance. Results demonstrate that the number of thermoelectric elements not only determines the open-circuit voltage but also significantly influences output power. Notably, the output power trend remains consistent across temperature differentials, independent of load resistance variations, suggesting a fundamental relationship between element quantity and module efficiency.