Heat Recovery System Research Articles

Energy and exergy analysis of a thermoelectric generator system for automotive exhaust waste heat recovery

Thermoelectric generators are a viable solution for recovering and producing energy utilizing wasted energy in automotive exhaust. Exergy analysis can help identify irreversible losses that occur during the transfer of exhaust energy, which is essential for comprehending and developing exhaust thermoelectric generator systems. In this study, we proposed a model based on thermodynamic of the exhaust thermoelectric generator and conducted energy and exergy analyses. The results indicate that convective heat transfer exergy loss and PN junction thermal conductivity exergy loss are the primary exergy losses of the exhaust thermoelectric generator, accounting for more than 52.0 % of the total. Increasing the temperature of exhaust can boost the performance of systems, but it may also reduce the proportion of available energy obtained by the cooling water. When the exhaust heat transfer coefficient is increased to 300, the convective exergy losses of the exhaust can be reduced to 17.6 %, resulting in an overall exergy efficiency of 38.8 %. Furthermore, by increasing the exhaust flow rate from 10 g/s to 50 g/s, the power generation capacity has increased by a factor of 6.87, with little change in exergy losses. These findings are valuable for developing high-efficiency exhaust power generators.

“Hospital’s Thermo-neutral Zone for Patient Safety and Climate Change Sustainability

The efficacy of Iraq's direct heat recovery system is influenced by the nation's architectural design, particularly in view of the escalating climate conditions. There is an increasing worry on the necessity to openly address the local building patterns in Iraqi cities due to the challenging task of mechanically cooling buildings in the absence of electricity. The model was built using data obtained from field research carried out from January 2021 to March 2022. The field measurements of microclimatological parameters were carried out between March and August 2022 in order to evaluate the accuracy of the models. This methodology showcases the potential to make accurate predictions of future air temperatures by utilising variables as low as 5 percent. The air temperature decreases by 0.5 °C for every G increase across an area of 0.03-0.20 m2/m2, which is equivalent to a Leaf Area Index (LAI) of 4.5 m2/ha. This work introduces a standardized approach for assessing thermal comfort in real-world settings. The study examines the continuous use of hybrid ventilation systems at Kadhimiya Teaching Hospital to ensure a consistent air quality in the wards. Installing temperature control systems in these sites is vital to provide thermal comfort, as it serves as a potentially effective but expensive measure to address the impacts of climate change. Installing fans in military fortifications in Iraq seems to be a cost-efficient and uncomplicated approach to enhance their resilience against the escalating heat caused by the projected effects of global warming. However, when assessing the thermal comfort of buildings in Iraq's present and future climates, the established method proves to be considerably more advantageous.

Innovative Integration of Phase Change Materials and Conceptional Design of Test Cases – New Products for the Building Envelope

The building sector contributes to a great part of energy consumption and has a major impact on climate in Europe. Development of climate-friendly and energy-efficient products is required to reach low and net-zero energy buildings and to facilitate the energy transition. The building envelope is critical in defining the demand for space heating and cooling as well as ensuring thermal comfort and indoor environmental quality through proper ventilation. This paper presents the conceptual test cases integrating phase change materials (PCMs) in the building envelope. PCM absorbs, stores, and releases the heat energy in a controlled manner taking advantage of the temperature difference between night and day. Hence PCM can support the thermal management of the building by minimizing unwanted heat gains and losses while integrated into walls or support the energy efficiency of ventilation while supplying fresh air. Smart ventilated heat harvesting windows and multifunctional sandwich panels are developed within the EU-funded iclimabuilt project. Additionally, commercial air-guided PCM storages are presented as ready-to-install products for decentralized ventilation and heat recovery systems.

Design and Thermodynamic Analysis of Waste Heat Recovery System of Sludge Hydrothermal Carbonization

This paper proposes a new type of sludge hydrothermal carbonization waste heat recovery system, which transfers the heat in the sludge hydrothermal carbonization to the combustion air of the boiler through total heat exchange to achieve waste heat recovery. The waste heat recovery system makes full use of the heat in the steam and improves the calorific value of the sludge entering the incinerator. With the increase of combustible matter content in sludge, the exergy efficiency of waste heat recovery system increases. Due to the improved steam quality and the use of small turbines to do work, the operating economy is improved.

Techno-economic and environmental analysis of high temperature heat pumps integration into industrial processes: the ammonia plant and pulp mill cases

Heat pumps will play an important role in improving the performance of the industrial processes aiming to decarbonize their heating requirements. Yet, defining the best operating conditions of those devices may be a challenging task, as they are embedded in larger energy conversion systems and in direct competition with fired and electric heaters and other waste heat recovery systems. The costs of the energy inputs also influence the selection of either a heat pump or a gas boiler, which affects the overall efficiency and the incremental cost of the final solution. Thus, a systematic analysis must be applied in order to determine the best option to supply the heating requirement, without considerably impacting the operational feasibility of the overall plant. In this work, the base-case performance of two industrial applications with intensive heating demand, namely, the solvent regeneration process of a carbon capture unit and the black liquor concentration process of a kraft pulp mill, are compared to that of the scenarios in which a high temperature heat pump or a mechanical vapor recompression unit are integrated, aiming to reduce the energy consumption and the environmental impact. The benefits of the integration of a heat pump or a mechanical vapor recompression unit over a conventional reboiler and a multiple effect evaporation system are discussed in the light of thermodynamic, economic and environmental indicators. As a result, the alternative approaches remain competitive vis-à-vis the conventional solutions in terms of energy consumption and operating costs. In addition, the emissions associated to the heating applications could be reduced by 45% if a high temperature heat pump is integrated. The optimized solution using a heat pump has an overall exergy efficiency 9% higher compared to the typical configuration of the ammonia plant. In pulp mills, the integration of mechanical vapor recompression systems slightly affects the performance compared to the conventional scenario with a multiple effect evaporation system.

Experimental examination of the effect of thermal barrier coating in a 2-stroke gasoline engine on recovery performance in exhaust waste heat recovery system with thermoelectric generator and engine performance

In internal combustion engines, while the decrease in in-cylinder wall temperature increases the amount of energy passing towards the cooling system, it decreases temperature and pressure at the end of compression and accordingly reduces thermal efficiency of the engine. Moreover; combustion chamber elements are exposed to chemical corrosion and deformation as a result of uncompleted combustion in the cylinder. With thermal barrier coating application, the energy lost in cooling system will decrease and exhaust temperatures will increase in 2-stroke engines. Placement of a waste heat recover system with thermoelectric generator into the exhaust system can provide exhaust waste heat recovery and increase thermal efficiency of the engine. There is no study in the literature, which examines waste heavy recovery systems with thermal barrier and thermoelectric generator altogether. In this article, yttria stabilized zirconia coating has been applied by means of plasma spraying method in the combustion chamber of a 2-stroke gasoline engine, and effect of thermal barrier coating application on engine performance and exhaust waste heat recovery system has been examined experimentally. According the results of the experiment, maximum engine power has increased by 6.23%, maximum engine torque has increased by 6.02%, and specific fuel consumption decreased by 5.56%. While the exhaust temperatures have increased by 78.5 °C at maximum by means of thermal barrier coating application; by means of thermal barrier coating application with waste heat recovery system with thermoelectric generator, a higher waste heat recovery has been obtained by 64.8%.

Performance Optimization and Exergy Analysis of Thermoelectric Heat Recovery System for Gas Turbine Power Plants.

Thermoelectric (TE) waste heat recovery has attracted significant attention over the past decades, owing to its direct heat-to-electricity conversion capability and reliable operation. However, methods for application-specific, system-level TE design have not been thoroughly investigated. This work provides detailed design optimization strategies and exergy analysis for TE waste heat recovery systems. To this end, we propose the use of TE system equipped on the exhaust of a gas turbine power plant for exhaust waste heat recovery and use it as a case study. A numerical tool has been developed to solve the coupled charge and heat current equations with temperature-dependent material properties and convective heat transfer at the interfaces with the exhaust gases at the hot side and with the ambient air at the heat sink side. Our calculations show that at the optimum design with 50% fill factor and 6 mm leg thickness made of state-of-the-art Bi2Te3 alloys, the proposed system can reach power output of 10.5 kW for the TE system attached on a 2 m-long, 0.5 × 0.5 m2-area exhaust duct with system efficiency of 5% and material cost per power of 0.23 $/W. Our extensive exergy analysis reveals that only 1% of the exergy content of the exhaust gas is exploited in this heat recovery process and the exergy efficiency of the TE system can reach 8% with improvement potential of 85%.

Performance of a Compost Aeration and Heat Recovery System at a Commercial Composting Facility

Performance of a Compost Aeration and Heat Recovery System at a Commercial Composting Facility

Modeling and economic evaluation of deep geothermal heat supply systems using the example of the Wealden near Hannover, Germany

Germany desires to become climate-neutral in its heat supply by 2045. From 2024 onward communities are legally required to develop a plan documenting how the objective will be achieved. Geothermal resources can be a major building block to reach the aspirational target if they can be developed at competitive costs. To evaluate the economic potential of geothermal resources is time and money consuming. Questions which need to be addressed in the context of such evaluations are: how can an economic recovery of geothermal heat be achieved, how can subsurface risks associated with an exploration be managed, and how competitive is a deep geothermal energy recovery compared to other options of heat supply? These questions are key to a development of deep geothermal heat, especially if the geothermal conditions are not as prominent as in already realized projects, but less favorable as in the deep clastic sediments of the North German Basin. With this contribution a procedure is presented and used to determine net present values and the associated levelized costs for deep hydrothermal heat recovery systems. It consists of modelling the geothermal cycle, sizing all necessary components, costing them, and calculating net present value and levelized cost. The thermal model is verified by comparing the modelled state variables pressure and temperature at relevant state points of the thermal cycle with actual data of a geothermal project. The cost model is validated with biding results and cost information from actual projects and modified as appropriate. In applying the model to a setting in the Hannover–Celle area with temperatures of around 70 °C, conditions are determined, which lead to positive net present values. The degree of their influence is determined in sensitivity analyses allowing a systemic optimization. The results show that for a coupled heat plant with geothermal heat supplied at baseload conditions, levelized costs of approx. 8 cents/kWh are achievable. The presented thermodynamic and cost models are considered helpful instruments for developing preliminary conceptual estimates, strategies for optimization, and portfolio management.

Thermal Comfort Temperature Evaluation in Hospital Wards for Patient Safety and Climate Change Sustainability

The quality of Iraq's direct heat recovery system is affected by the country's construction design, particularly in light of the warming climate Reference Minimum 26.6 C Reference Average Air Temperature38.6 C,. There is growing concern that the local building patterns need to be addressed openly because the lack of electricity makes the mechanical cooling of buildings difficult in Iraqi cities. This methodology demonstrates the capability to generate precise forecasts of forthcoming air temperatures by using variables as little as 5 percent. This paper presents a standardized methodology for evaluating thermal comfort in the field. The study analyzes the hybrid ventilation systems utilized by Kadhimiya Teaching Hospital round-the-clock to maintain the constant air quality in the wards. Installing climate control is crucial in these locations to maintain thermal comfort as a potentially powerful but costly response to climate change. Adding fans to military fortifications in Iraq appears to be a cost-effective and simple method to improve their resistance to the extreme heat that is anticipated to become more common due to global warming. However, in evaluating the thermal comfort of buildings in Iraq's current and future climates, the established method is significantly more useful.

Waste heat recovery of air conditioning on thermal efficiency enhancement of water heater

Air conditioning units are used to deliver comfortable air in households for the daily life of humans. This generates waste heat into the surroundings, that can cause global warming. This study investigated the thermal performance of water heaters recovering waste heat from air conditioners. A double-tube heat exchanger was installed between the compressor and the condenser to recover heat from the air conditioner. The inlet water temperature ranges from 15 °C to 40 °C, mass flow rates range from 2.5 L/m – 12.5 L/m, and water heater power input of 880 W – 3520 W is investigated. The results showed that water heaters have high thermal efficiency at low water mass flow rates. The waste heat of the air conditioner was recovered, which increased the thermal efficiency of the water heater by 12 % – 180 %, higher than the conventional type by approximately 50 %. The inlet water temperature ranges from 15 °C to 25 °C, and the input power range from 880 W to 1760 W has a significant impact on the thermal efficiency of the water heater. The energy consumption of the air conditioner decreased significantly when it was integrated with the heat recovery system. In addition, the water mass flow rate affected the energy consumption of the air conditioner. This study provides guidelines for improving the thermal efficiency of water heaters to reduce carbon dioxide emissions and heat rejection from air conditioners, leading to a reduction in global warming.

Packed bed thermal energy storage for waste heat recovery in the iron and steel industry: A cold model study on powder hold-up and pressure drop

Waste heat recovery in the energy intensive industry is one of the most important measures for the mitigation of climate change. The present study examines the integration of a packed bed thermal energy storage for waste heat recovery in the iron and steel industry. Along with the highly fluctuating availability of excess heat the main difficulty of waste heat recovery in industrial processes is the high amount of powder that is transported by the hot exhaust gases. Therefore, the experimental investigations in this study focus on the powder hold-up and pressure drop in a packed bed thermal energy storage that is operated with a gas-powder two phase exhaust gas as heat transfer fluid. The ultimate goal is, to assess its suitability and robustness under such challenging operational conditions. The results indicate, that 98% of the powder that is introduced into the system with the heat transfer fluid during charging accumulates in the packed bed. Remarkably, most of the powder hold-up in the packed bed is concentrated near the surface at which the heat transfer fluid enters the packed bed. When reversing the flow direction of the heat transfer fluid to discharge the storage with a clean single phase gas, this gas is not contaminated with the powder that has been accumulated in previous charging periods. The entirety of these findings reinforces the suitability of packed bed thermal energy storage systems for waste heat recovery in the energy intensive industry.

Thermo-Economic Performance of Organic Rankine Cycle-Based Waste Heat Recovery for Power Generation at a Wide Range of Operating Conditions

This study assesses the performance of organic Rankine cycle-based waste heat recovery systems under different working fluids and operating conditions. The basic ORC (BORC) and ORC with recuperator (RORC) are investigated for power generation and economy using toluene and benzene. Thermodynamic and economic indicators are studied at various expander inlet temperatures, expander inlet pressure, evaporation temperature, and condensation temperature. RORC achieves higher ηth by reducing heat source in the evaporator whereas BORC recovers more waste heat and improves Pnet. With toluene, BORC improves Pnet when increasing the expander inlet temperature and pressure. The lowest LCOE of 0.0532 US$/kWh is from BORC operated with toluene at a Pnet of 349 kW and decreases with an increase in expander inlet temperature. The addition of a recuperator adds to the costs of initial investment and LCOE and slightly improves the performance of the ORCs for waste heat recovery.

Thermo-economic optimization of an ORC system for a dual-fuel marine engine

The Organic Rankine Cycle (ORC) is one of the most promising systems to recover the waste heat sourced from internal combustion engines. In this study, thermodynamic, economic and environmental analyses of the scavenge air cooling water-driven Waste Heat Recovery System (WHRS) based on the organic Rankine cycle are conducted for a dual-fuel marine engine integrated with exhaust gas recirculation (EGR) system. Zero ozone-depleting and low global warming potential working fluids; R245fa, R236ea from hydrofluorocarbons, R600a, R601a from hydrocarbons, R1234ze and R1234yf from hydrofluoroolefins are selected for the low-grade WHRS. In addition to the thermal analyses, the mass and volume of the system along with the safety factors of the working fluids are evaluated to judge the physical applicability of the system for ships. Thermo-economic performances of the fluids are analyzed, optimized and compared under various engine loads, Tier II and Tier III modes to reveal the effects of different engine operating conditions on the parameters. According to the results, scavenge air has a significant amount of waste heat at medium and heavy loads and switching the engine mode remarkably affects the performance of the WHRS. R601a shows the best thermo-economic performance, however, considering the applicability of the system R236ea is the most suitable working fluid for the ORC WHRS. The overall thermal efficiency of the power generation system can be increased by about 2.8%.

Numerical investigation of the performance of a PCM-based renewable and exhaust heat recovery system for building applications

A hybrid device consisting of a PCM-based photovoltaic/thermal system and a heat recovery wheel is introduced and its performance is examined analytically. This device is designed with the aim of supplying the heating load, cooling load and electrical load of a building and reducing the building's dependence on the air handling unit. The performance of the device at different hours on two days that represent the hot and cold days of a year, in different months and during a year for the weather conditions of Kermanshah, Iran, is investigated and then, the effect of the effective parameters on the annual yield of the device is checked. The investigation showed that by using the hybrid device, it is possible to provide 4.12–11.31 °C of pre-heating and 0.60–9.22 °C of pre-cooling of the outside air on January 15th and August 15th, respectively. Also, it was revealed that except in the three months of January, February and December, in the rest of the months the hybrid device is able to supply the entire thermal load required by the building. Finally, the total annual useful thermal power and electric power produced by the hybrid device was reported as 24776.49 kWh and 7747.66 kWh, respectively.

Exergy and environmental analysis of SOFC-based system including reformers and heat recovery approaches to establish hydrogen-rich streams with least exergy loss

Building total CO2 emissions must decline by more than 95 % from 2020 to 2050. Statistical studies affirm that 84 % of the fuel cell applications in the world are attributed to the residential market and are limited to the range of 0.5–5 kW. In this study, defining a building-based fuel cell, the first and second law of thermodynamics were approved for the hybrid system consisting of SOFC enhanced with an internal reformer and microturbine. In addition, an external reformer along with two heat recovery systems are integrated to change methane to hydrogen. Based on the exergy balance equation, 37 The installation of heat recoveries was very effective in hybrid system irreversibility reduction so they were able to reduce exergy losses by 38 %. The most irreversibility was related to chemical reactions that occurred in the external reformer (share of 37.3 %) and combustion chamber (share of 32 %) while the share of the fuel cell was only 10.7 %. The calculations of the second law showed that the hybrid system with heat recovery can convert 57.6 % of the input exergy into useful work. The environmental analysis revealed that establishing a hybrid system with a higher temperature is more effective than that with higher pressure. The CO2 emissions of the hybrid system at the lowest and highest temperature were 1.946 kg/kW and 0.81 kg/kW.

Progress and Prospects for Research and Technology Development of Supercritical CO2 Thermal Conversion Systems for Power, Energy Storage, and Waste Heat Recovery

CO2 is an environmentally friendly heat transfer fluid and has many advantages in thermal energy and power systems due to its peculiar thermal transport and physical properties. Supercritical CO2 (S-CO2) thermal energy conversion systems are promising for innovative technology in domestic and industrial applications including heat pump, air-conditioning, power generation, renewable energy systems, energy storage, thermal management, waste heat recovery and others. Both S-CO2 and transcritical CO2 thermodynamic cycles have been extensively investigated in order to improve the efficiencies of thermal and power systems and achieve net zero carbon emissions. This paper focuses on the progress and prospects for current research and technology development of S-CO2 thermal energy conversion systems and their applications including power generation, energy storage and waste heat recovery. First, the CO2 thermal transport and physical properties and benefits using CO2 as a heat transfer fluid in thermal energy and power systems are discussed. Then, classification of CO2 thermodynamic systems is presented. Next, S-CO2 for power generation, energy storage and waste heat recovery systems are presented. Finally, research needs of subcritical and supercritical CO2 heat transfer, fluid flow and heat exchangers for the development of various thermal energy and power systems are discussed.

Study on the process technology of energy saving and consumption reducing for municipal sludge-based biochar

Taking the production process of sludge-based biochar as the research object, based on the measured data of engineering field operation, the thermal balance models of sludge carbonization and cooling conveying system, pyrolysis gas incineration and waste heat recovery system, flue gas treatment and deodorization system were established respectively. The energy loss points in the process of operation were determined and calculated. The results show that the energy consumption loss of sludge-based biochar production process is 23550 MJ/h under the field operation conditions of feeding 2920 kg/h of dry sludge (moisture content 30 %), 19.65 kg/h of natural gas and 67 kg/h of fresh water, producing 1500 kg/h of sludge-based biochar (moisture content 4.5 %) and carbonization temperature 450 °C. Compared with the sludge drying incineration process, it can save energy and reduce consumption by 52.2 %, and the calorific value of sludge-based biochar is 7.04 MJ/kg, which is 49.6 % higher than that of dry sludge.

Cold Climate Challenges: Analysis of Heat Recovery Efficiency in Ventilation Systems

As building energy consumption gains ever-increasing attention worldwide, the focus on addressing it through the examination and optimization of efficient heat recovery solutions continues to intensify. With well-insulated and airtight buildings, the proportion of heating needs attributed to ventilation is growing, leading to the widespread integration and optimization of heat recovery solutions in mechanical ventilation systems. Heat recovery in ventilation is a highly efficient strategy for reducing heat losses and conserving energy. This study involves the investigation of a ventilation unit installed in an apartment situated in Riga, Latvia, as a practical examination of heat recovery system efficiency within the Latvian climate conditions, representing a cold climate region. The objective of this study was to examine the heat recovery efficiency of the ventilation system in the Latvian climate with variable outdoor and exhaust air parameters, given that the dry heat recovery efficiency is different from the actual heat recovery efficiency. The ventilation unit was equipped with a plate heat exchanger at an airflow rate of 105 m3/h. To evaluate heat recovery efficiency, extensive measurements of air temperature and relative humidity were conducted. The collected data was analyzed, employing statistical regression analysis to ensure measurement reliability and assess correlations. The findings indicated a strong correlation between variables such as heat content, moisture content, and sensible air parameters. It was observed that the actual heat recovery efficiency was 6% higher than the calculated dry efficiency, emphasizing the importance of considering real-world conditions in heat recovery assessments. Additionally, regression analysis demonstrated a positive linear correlation with a coefficient of 0.77, highlighting the dependency between actual measurements and the theoretical model. These quantitative outcomes provide essential insights for optimizing heat recovery systems and enhancing energy-efficient ventilation practices, especially in cold climate environments. Moreover, this study highlights the strong correlation between variables such as heat content, moisture content, and sensible air parameters. Findings offer essential insights for optimizing heat recovery systems and enhancing energy-efficient ventilation practices, especially in cold climate environments.

Study on the heat recovery behavior of horizontal well systems in the Qiabuqia geothermal area of the Gonghe Basin, China

Geothermal energy, as a highly regarded renewable energy source, holds vast potential for widespread applications. However, the methods of geothermal energy extraction need to be optimized and improved according to specific geological conditions. This study aims to provide a multi-level horizontal branch well heat recovery system for the Qiabuqia geothermal field in the Gonghe Basin. To begin, this study systematically investigated the influence of various engineering parameters on production temperature and establishes mathematical models to depict the relationships among these parameters. Subsequently, we unveiled the precise numerical correlation between well length and the limit injection rate, utilizing multiple production indexes to comprehensively characterize the practical production characteristics and effectiveness of the multi-level heat recovery system. Finally, a comprehensive economic evaluation of the system was conducted. The research findings indicate that there exists a linear relationship between production temperature and injection temperature, while a second-order polynomial relationship is observed between production temperature and injection rate, wellbore size, and well length. In single-well heat recovery systems, the ratio of well length to the limit injection rate is 4000, whereas in multi-level branch well system, the limit injection rate is 88 % of that in single-well systems. Furthermore, branch wells located farther from the injection end exhibit greater heat recovery capacity but relatively higher production costs. Nonetheless, overall, the production cost for 1000-m-long branch wells can be reduced to around $0.05 $/kWh, demonstrating significant economic feasibility. These research findings provide momentum for the sustainable development and utilization of hot dry rock resources, simultaneously offering more precise guidance for the design and operation of hot dry rock power generation projects.