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The design of solid oxide fuel cells (SOFC) using biogas for distributed power generation is a promising alternative to reduce greenhouse gas emissions in the energy and waste management sectors. Furthermore, the high efficiency of SOFCs in conjunction with the possibility to produce hydrogen may be a financially attractive option for biogas plants. However, the influence of design variables in the optimization of revenues and efficiency has seldom been studied for these novel cogeneration systems. Thus, in order to fulfill this knowledge gap, a multi-objective optimization problem using the NSGA-II algorithm is proposed to evaluate optimal solutions for systems producing hydrogen and electricity from biogas. Moreover, a mixed-integer linear optimization routine is used to ensure an efficient heat recovery system with minimal number of heat exchanger units. The results indicate that hydrogen production with a fuel cell downstream is able to achieve high exergy efficiencies (65–66%) and a drastic improvement in net present value (1346%) compared with sole power generation. Despite the additional equipment, the investment costs are estimated to be quite similar (12% increase) to conventional steam reforming systems and the levelized cost of hydrogen is very competitive (2.27 USD/kgH2).

The photovoltaic-thermal collector is one of the most interesting technology for solar energy conversion, combining electric and thermal energy production in a single device. Vapour-compression heat pump is already considered the most suitable clean technology for buildings thermal energy needs. The combination of these two technologies in an integrated ”photovoltaic-thermal solar-assisted heat pump” (PVT-SAHP) system allows reaching a high fraction of the building thermal needs covered by renewable energy sources and to improve the performances of both the photovoltaic-thermal collector and the heat pump. The first is cooled down increasing its energy conversion efficiency, while providing low-temperature thermal energy to the second, which benefits from a higher evaporation temperature. The review study presents the state-of-art of photovoltaic-thermal solar-assisted heat pump systems intended to cover thermal energy needs in buildings, with a particular focus on the integration methodologies, the possible configurations, the use of different sources and the design of sub-system components. These issues are addressed by much scientific research, to improve the reliability and applicability of this technology, as an option for the building decarbonization. This study aims to present PVT-SAHP systems in an organic and critical way to propose a useful tool for future research developments. More in detail, the work highlights the fact that the integration of photovoltaic-thermal collectors as evaporator of the heat pump in direct-expansion systems allows the highest heat recovery and performances. However, the distinction of the two circuits lead to more reliable, flexible and robust systems, especially when combined with a second heat source, being able to cover both heating and cooling needs. The implementation of real-time control strategy, as well as the continuous development of the compressor and refrigerant industries is positively influencing this technology, which is receiving more and more attention from scientific research as a suitable solution for nearly zero energy buildings.

In the present work, the performance improvement of a waste heat recovery system is investigated by applying a fuel cell and thermoelectric generator. With the use of energy, exergy, exergo-economic, and environmental analyses (4E analysis), the performance of the improved system is evaluated. A mathematical simulation in the Engineering Equation Solver (EES) is developed for basic and modified systems. Comparative analysis is carried out to demonstrate the benefit of the suggested system. The logical and correct combination of appropriate subsystems can lead to the maximum exploitation of an energy source, which is the innovation of the present work. The comparison of suggested system (PR/FC-TEG) with the CHP system indicates that the net output power of the PR/FC-TEG system is 3881 kW compared with 958.4 kW for the CHP system. However adding fuel cell to the PR/FC-TEG system increase output power by about 2162 kW, and it imposes 4823 kW exergy destruction rate to the system. The exergy destruction rate of the PEM FC, regenerator, and vapor generator are about 88.96% of the total exergy destruction rate, which infers the importance of these components in the PR/FC-TEG system improvement. Parametric analysis on the PR/FC-TEG performance with changing four influencing parameters is performed. Results indicate that increasing the turbine 1 inlet temperature by about 1.1% increases the cost of generated electricity from 72.92 to 73.88 $/GJ and decreases the sustainability index from 1.68 to 1.65. The multi-objective optimization of the developed system can be a promising option for future study.

This paper deals with the exergy analysis of two experimental prototypes consisting of indirect evaporative cooling systems with different constructive characteristics. Both prototypes have been designed and manufactured in the Thermal Engineering Laboratory of the University of Valladolid. They are made of polycarbonate hollow panels of different cross section and connected into a heat recovery cycle. Each prototype has been tested at 4 levels of outdoor air volume flow (from 125 to 400 m3·h−1) and 4 levels of dry bulb temperature (from 25 to 40 °C). For each of the 16 different operating conditions the exergy destructed by each prototype has been calculated. Results show that the higher the dry bulb temperature at the primary air inlet, the higher the exergy destruction and the exergy losses. The exergy destruction increases when the wet bulb depression temperature of the secondary air inlet decreases, leading to more inefficient configurations. The value of the exergetic efficiency is in the order of 2–12 %. The optimum combination of operating conditions at any inlet temperature of the primary air can be proposed as: 300 m3h−1 and 200 m3h−1. for the wide and narrow plates prototype, respectively.

This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system, which use CaCl2 as the working medium. The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator. Through direct contact with the solution in the absorber, the flue gas is going to carry out gas, liquid heat transfer between heat exchanger, realization of sensible heat and latent heat step by step. As the key part of the system, absorber is established by one-dimensional steady-state heat transfer and mass transfer model. This paper uses the finite difference method to model the discrete numerical methods, and analyzes the characteristics of heat and mass transfer in the absorber. We obtain the concentration curves of the three kinds of working medium's temperature and flow along the height direction. We also analyze the influence of CaCl2 solution parameters changes on the absorption process, parsing the reason of the temperature change by analyzing the three working medium's energy flow trend. We found that the temperature change of flue gas is non-monotonic, which decreases gradually in the range of absorption tower height 0–0.9 m, and then increases gradually. The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution. Although such a change has an impact on the efficiency of the system, it prevents the "white smoke" from condensing in the air, which effectively protects the environment. Compared with conventional LiBr absorption heat pump, the system constructed in this paper has certain advantages in latent heat recovery, flue gas heat energy utilization, energy conservation and emission reduction and economy.

This chapter describes a system which recovers waste heat to be used for baking, improving the fuel efficiency of the oven by at least 15%. The heat recovery system uses heat from the burner flues. This may be used to heat one or two final zones of the oven. These zones would not require burners, giving a saving in capital and running costs.

This chapter builds on Chapters 2 and 4 and describes more advanced concepts, representations, procedures and graphical diagrams related to the analysis and design of heat recovery systems for both grassroots and retrofit situations. The grassroots case is extended to add more industrial realism, and to bring investment costs into the discussion. Key elements of the grassroots component are Multiple Utilities, Heat Transfer Area considerations, additional design tools beyond the Pinch Design Method, forbidden matches and an introduction to the use of optimisation for heat exchanger network design. Key elements of the retrofit part are procedures for Targeting, Design and Optimisation, where in all these stages focus is on maximum utilisation of existing equipment, making the task very different from the grassroots case. The Network Pinch concept will also be described, which as the name indicates is a feature of the Heat Exchanger Network (HEN), while the Heat Recovery Pinch is a feature of the stream data.

Endüstride ve birçok atık ısı tesislerinde kullanılan atık ısı geri kazanım üniteleri gerekli temiz havanın ön ısıtılmasında kullanılan sistemlerdir. Bu çalışmada ısı değiştiricisi ısı borusu olan bir ısı geri kazanım ünitesinin performansının iyileştirilmesi ve böylece çalışma sıcaklık aralığının arttırılması amacıyla oluşturulan deney düzeneği üzerinde uygulamalı bir çalışma yapılmıştır. Çalışmanın özgün yanı ısı değiştiricisi olarak kullanılan ısı borularında son yıllarda pek çok uygulama olanağı bulan nanoakışkanların kullanılması hedeflenmiştir. ZnO/Su ve ZnOAl2O3/Su nanoakışkanları ısı borusunda çalışma akışkanı olarak kullanılmış ve temel akışkan suya göre ısı geri kazanım ünitesi ısıl performansındaki iyileşme oranları belirlenmeye çalışılmıştır. Soğuk hava bölgesinde (kondenser), soğuk hava hızı 0.437m/s ve Re=7100 olduğunda ZnOAl2O3 ve ZnO nanoakışkanları için sırasıyla %90 ve %80 oranında iyileşme elde edilmiştir.

Numerous intersected rock fractures constitute the fracture network in enhanced geothermal systems. The complicated convective heat transfer behavior in intersected fractures is critical to the heat recovery in fractured geothermal reservoirs. A series of three-dimensional intersected fracture models is constructed to perform the flow-through heat transfer simulations. The geometry effects of dead-end fractures (DEFs) on the heat transfer are evaluated in terms of intersected angles, apertures, lengths, and the connectivity. The results indicate that annular streamlines appear in the rough DEF and cause an ellipse distribution of the cold front. Compared to plate DEFs, the fluid flow in the rough DEF enhances the heat transfer. Both the increment of outlet water temperature ΔTout and the ratio of heat production Qr present the largest at the intersected angle of 90° while decline with the decrease of the intersected angle between the main flow fracture (MFF) and the DEFs. The extension of the length of intersected DEFs is beneficial to heat production while enhancing its aperture is not needed. Solely increasing the number of intersected DEFs induces a little increase of heat extraction, and more significant heat production can be obtained through connecting these DEFs with the MFF forming the flow network.

In this study an investigation of Turkey's overall industrial waste heat potential is conducted, and possible power and hydrogen conversion technologies are considered to produce useful energy such as power and hydrogen. The annual total industrial waste heat was has a 71 PJ in 2019 and is expected to double by 2050. The temperature range of the waste heat differs by sector at a large range of 50 °C–1000 °C. Absorption power cycle (APC), Organic Rankine Cycle (ORC), Steam Rankine cycle (SRC) and Gas Turbine (GT) systems are adapted for power production based on the waste heat temperature while electrochemical and electro-thermochemical hydrogen production systems are adapted for hydrogen generation. Proton Exchange Membrane, Alkaline, and high temperature steam electrolysis methods are selected for pure electrochemical conversion technologies and Hybrid Sulfur (HyS), Copper Chlorine (CuCl), Calcium–Bromine (CaBr), and Magnesium Chlorine (MgCl) cycles are utilized as hybrid thermochemical technologies. Many cases are formed, and best temperature matching power-hydrogen system couples are selected. It is possible to produce enough hydrogen to compensate up to 480 million m3 natural gas equivalents of hydrogen annually with selected technologies which corresponds to ~5% of residential natural gas consumption in Turkey. Economic analysis reveals that lowest hydrogen generation cost belongs to the GT-HyS system. When hydrogen is used for heating applications by a certain mixture fraction to NG pipelines, it may reduce more than 720 thousand tons of CO2 reduction annually due to natural gas use.

The present study deals with the performance analysis of thermochemical energy storage system based on four different working pairs, namely LaNi4.85Sn0.15-MmNi4.6Al0.4, LaNi4.75Sn0.25-MmNi4.6Al0.4, LaNi4.65Sn0.35-MmNi4.6Al0.4 and LaNi4.55Sn0.45-MmNi4.6Al0.4. The first law and second law performance parameters are considered to evaluate the performance of the energy storage system. The temperature of heat storage and heat recovery for the four different working pairs are in the range of 93–140 °C and 105–165 °C respectively. Recovering the heat at higher temperature than that of storage is called heat upgradation. Highest degree of heat upgradation is 24 °C, and it is obtained for the working pair of LaNi4.55Sn0.45-MmNi4.6Al0.4. The theoretical highest energy storage density and COP are 129 kJ/kg and 0.54 respectively for the working pair of LaNi4.65Sn0.35-MmNi4.6Al0.4. From the second analysis, the lowest exergy loss and highest second law efficiency are 2.57 kJ and 96.4% respectively for the working pair of LaNi4.75Sn0.25-MmNi4.6Al0.4. Based on the first law analysis, the working pair, LaNi4.65Sn0.35-MmNi4.6Al0.4, is taken as best pair and based on the second law analysis, the working pair, LaNi4.75Sn0.25-MmNi4.6Al0.4, is taken as best pair. However, suitable working pair need to be selected based on the type of application.

The customarily discarded exhaust from the fossil fuel-based power plants of the off-grid mines holds the thermal potential to fulfill the heating requirement of the underground operation. This present research fills in an important research gap by investigating the coupling effect between a diesel exhaust heat recovery and an intake air heating system employed in a remote mine. An integrative approach comprising analytical, numerical, and experimental assessment has been adapted. The novel analytical model developed here establishes the reliability of the proposed mine heating system by providing comparative analysis between a coupled and a decoupled system. The effect of working fluid variation has been examined by the numerical analysis and the possible improvement has been identified. Experimental investigations present a demonstration of the successful lab-scale implementation of the concept and validate the numerical and analytical models developed. Successful deployment of the fully coupled mine heating system proposed here will assist the mining industry on its journey towards energy-efficient, and sustainable mining practices through nearly 70% reduction in fossil fuel consumption for heating intentions.

A novel solid oxide fuel cell (SOFC) multigeneration system fueled by biogas derived from agricultural waste (maize silage) is designed and analyzed from the view point of energy and exergy analysis. The system is proposed in order to limit the greenhouse gas emissions as it uses a renewable energy source as a fuel. Electricity, domestic hot water, hydrogen and cooling load are produced simultaneously by the system. The system includes a solid oxide fuel cell; which is the primary mover, a biogas digester subsystem, a cascaded closed loop organic Rankine cycle, a single effect LiBr-water absorption refrigeration cycle, and a proton exchange membrane electrolyzer subsystem. The proposed cascaded closed-loop ORC cycle is considered as one of the advanced heat recovery technologies that significantly improve thermal efficiency of integrated systems. The thermal performance of the proposed system is observed to be higher in comparison to the simple ORC and the recuperated ORC cycles. The integration of a splitter to govern the flue gas separation ratio is also introduced in this study to cater for particular needs/demands. The separation ratio can be used to vary the cooling load or the additional power supplied by the ORC to the system. It is deduced that net electrical power, cooling load, heating capacity of the domestic hot water and total energy and exergy efficiency are 789.7 kW, 317.3 kW, 65.75 kW, 69.86% and 47.4% respectively under integral design conditions. Using a parametric approach, the effects of main parameters on the output of the device are analyzed. Current density is an important parameter for system performance. Increasing the current density leads to increased power produced by the system, decreased exergy efficiency in the system and increased energy efficiency. After-burner, air and fuel heat exchangers are observed to have the highest exergy destruction rates. Lower current density values are desirable for better exergy-based sustainability from the exergetic environmental impact assessment. Higher current density values have negative effect on the environment.

Health Canada's cross-Canada residential radon survey from 2012 demonstrated roughly 7% of Canadian homes contain radon levels above the national guideline of 200 Bq/m3. British Columbia (BC) is the first province in Canada to mandate a full stack passive soil depressurization (PSD) system installed within homes in radon prone areas. All other provinces within Canada require a sealed and capped rough-in pipe. In this study, PSD systems were installed in fifteen new construction homes and retrofitted in six existing homes across three provinces in Canada. This study demonstrated the potential of well-designed PSD systems to reduce radon exposure in Canadian homes, reducing indoor radon concentration below 200 Bq/m3 in all 21 homes during multiple 30-day periods. During the winter, the PSD system was less effective in several new construction homes, whereas it appeared to operate more consistently in retrofitted existing homes. Further investigation revealed homes with a heat recovery ventilator (HRV), a ground floor bathroom, or no stack insulation were susceptible to degradation in the PSD system performance from the shoulder to winter season. Such performance degradation might be attributed to 1) HRV defrost mode causing a reduction in the ventilation air supply, 2) unsealed ground floor cut outs for the bathroom increasing the building stack effect and inducing more radon ingress through the floor slab during the winter, and 3) stacks without insulation causing frost and restricting the airflow within the stack.

Ammonia/salt absorption refrigeration cycle has advantages of low grade heat recovery, excellent thermal performance and simple construction, which may play an important role in refrigeration and air-conditioning fields for energy saving and emission reduction. The present paper introduces a prototype of absorption refrigeration system driven by exhaust heat operating with NH3/LiNO3 and NH3/LiNO3+H2O, which is composed of commonly used devices with the advantages of low cost and simple manufacture. Comprehensive experiments on the prototype were carried out with varying operating conditions (exhaust-gas temperature, chilled-water temperature, cooling-water temperature) to evaluate their influences on performance parameters. The NH3/LiNO3 system was driven by gaseous exhaust heat in the range of 150.1°C∼325.1°C, the minimum evaporating temperature reached -25.29°C, the cooling capacities varied between 0.60kW and 3.00kW, the electrical coefficient of performance varied between 3.30 and 16.52, and the overall coefficient of performance varied between 0.263 and 0.584. The NH3/LiNO3+H2O system was driven in the range of 125.8°C∼330.1°C, the minimum evaporating temperature reached -22.56°C, the cooling capacities varied between 0.92kW and 3.91kW, the electrical coefficient of performance varied between 4.65 and 20.30, and the overall coefficient of performance varied between 0.310 and 0.566. The experimental results were compared with that of NH3/NaSCN system by authors’ previous work, it is found that three ammonia/salt working fluids have respective advantages and optimal working condition ranges. The experimental evaluation and comparison provide significant references for the optimization and practical application of the ammonia/salt absorption refrigeration systems.

Gerekli temiz havanın ön ısıtılmasında kullanılan sistemler; sanayide ve birçok atık ısı tesislerinde kullanılan atık ısı geri kazanım üniteleridir. Bu çalışmada havadan havaya ısı geri kazanım sistemlerinde saf su ve nanoakışkanlar kullanılarak ısı borulu ısı geri kazanım sisteminin ısıl performansının iyileştirilmesi hedeflenmiştir. Son zamanlarda bayağı uygulama alanı bulan nanoakışkanların deney düzeneğinde kullanılmış olması, çalışmaya özgünlük değeri katmıştır. Çalışma akışkanı olarak MgO+CuO/Su hibrit nanoakışkanı ve MgOAl2O3/Su nanoakışkanı ısı borulu ısı değiştiricisinde kullanılmıştır. Bu nanoakışkanların kullanılmasıyla, saf suya göre ısı geri kazanım sisteminin ısıl performanstaki iyileşme oranları tespit edilmiş ve bunlara yorum getirilmeye çalışılmıştır. Isı borularının alt kısmı olan kondenser bölgesinde, soğuk hava hızı 0.751 m/s ve Re=12300 iken, MgO+CuO/Su hibrit nanoakışkanı için % 77 oranında ve MgOAl2O3/Su nanoakışkanı için % 91 oranında iyileşme olduğu ölçülmüştür.

The effects of water depth, flow rate and preheating using heat exchanger were investigated experimentally on solar still. The best performance indicated for shallowest depth and lowest inlet flow ...

In this paper, design and development of an energy-efficient oil-fired tilting furnace with an innovative recuperator are reported. During the melting of metals, it is reported that around 50% of the total energy is lost in flue gases. Therefore, there is always a need to improve upon the efficiency of the furnaces. The design of the recuperator is based upon the application of all the three basic modes of heat transfer to preheat the incoming air. Financial and environmental aspects were also evaluated after upgradation with the recuperator. The internal hollow pipe of the proposed recuperator is so designed that at its exterior cylindrical surface, multiple turns of a guide way are welded in a spiral fashion. This increases the heat transfer between the flue gas and ambient air to the burner. The study shows that the efficiency of the oil-fired tilting furnace got enhanced by 50% after implementing the proposed recuperator. Specific fuel consumption without the recuperator was 0.166 kg/kWh, which was reduced to 0.138 kg /kWh with the recuperator. The principle of increasing thermal efficiency and limiting fuel consumption was based on heat recovery from the combustion products to preheat the cold incoming fuel mixture. Therefore, this study focuses on the relations between combustion and heat exchanges on a large scale. The exergy evaluation technique was used constructively to estimate the furnace’s efficiency since the exergy efficiency is an additional sustainable appraisal in real situations. A channel for flue gases is provided in the developed furnace, which helps to divert hazardous gases away from the working environment.

Hydrogen fuel cell vehicles pave a promising technological pathway to achieve carbon neutrality. Conventional electric air-conditioning greatly increases hydrogen consumption and thus reduces the driving range. To recover waste heat for vehicle air-conditioning, this study proposes an integrated proton exchange membrane fuel cell (PEMFC) and microchannel membrane-based absorption cooling (MMAC) system. Using a validated model, the PEMFC-MMAC system is characterized under different vital parameters. The PEMFC parameters affect the performance of both PEMFC and MMAC. The coupled performance of the PEMFC-MMAC system increases under a higher operating temperature, a higher operating pressure, or a higher doping level. The MMAC parameters mainly affect the performance of MMAC. The coupled performance of the PEMFC-MMAC system increases under a lower microchannel width or a lower microchannel height. In the covered PEMFC and MMAC parameter ranges, the combined energy efficiencies are improved by 202–273% while the equivalent power efficiencies are improved by 11.4–14.8% with heat recovery. The cooling-to-electrical ratio is 2.02–2.73, the cooling capacity per volume is 129.4–345.9 kW/m3, while the cooling capacity per mass is 0.0439–0.1132 kW/kg. Compared to the existing falling-film absorption cooling technology, the MMAC improves the compactness by 165.1%, reduces the weight by 51.3%, and enhances the COP by 2.6%. This study can facilitate the development of highly-compact, light-weight, energy-efficient, and zero-GWP technology for waste-driven air-conditioning in hydrogen vehicles.

Internal combustion engines have a very important place in biogas production facilities to convert biogas energy to electricity. Unfortunately, although intense studies on improving internal combustion engine efficiencies by operational optimisation methods, serious progress is not achieved yet. However, there are many ways to improve the performance of these engines apart from structural optimisation meth-ods. One of the most important ways is to utilize by integrating jacket water used to cool the biogas fuelled internal combustion engines into the new generation low-temperature heat recovery systems like organic Rankine cycles. In the present study, simple and regenerative organic Rankine cycles were optimised to improve the overall performance of an biogas fuelled internal combustion engine by using the jacket water which is released into the atmosphere after cooling the engine. Also, the energy, exergy and environmental aspect of these systems are evaluated. Finally, exergoeconomic analysis for both sys-tems are conducted, and then payback periods of both systems are determined. As a result of the study, the maximum net power, thermal and exergy efficiencies of the simple organic Rankine cycle was cal-culated as 42.14 kW, 11.47 % and 63.27 % respectively, while the maximum net power, thermal and exergy efficiencies of the regenerative organic Rankine cycle are found as 45.3 kW, 12.34 % and 68.02 %. In addition, it is observed that the maximum power production obtained from the regenerative organic Rankine cycle corresponded to nearly 630 kg CO2/h emission reduction. The best payback period value is also calculated as 7.37 years in the simple organic Rankine cycle. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Efficiently utilizing the low-grade heat contributes to improving energy consumption structure and energy utilization efficiency, as well as preventing environmental deterioration. To harvest low-grade heat below 80 °C, advanced adsorption-based osmotic heat engines are constructed, which consist of an adsorption-based desalination module for thermally separating the salt solution into concentrated and diluted streams, and a reverse electrodialysis module for converting produced salinity gradient into electricity. Two different heat recovery configurations are employed to improve the heat-to-electricity performance: one is that the cooling power generated in the evaporator is used to cool the condenser and the other is that evaporator is coupled inside the condenser. The transient responses are analyzed and the effects of adsorption/desorption time, switching time, working concentration and heat source temperature on the heat-to-electricity performance are discussed. The efficiency with respect to Carnot efficiency is also presented to provide information on effectively utilized level of the available exergy. Compared with original configuration, the reduced effective condensing temperature in Configuration I and the pressurization effect in Configuration II significantly elevate the working capacity, thus to boost the work extracted. At lower working concentrations and adsorption times, the electric efficiency can be improved via Configuration II, while at higher working concentrations and adsorption times, the advanced configurations hinder the electrical efficiency. In Configuration II, compared with original configuration, the electric power and efficiency are improved by 68.3% and 15.2%, respectively, at a heat source temperature of 333.15 K with 2 mol/kg NaCl solution. While with 7 mol/kg NaCl solution, the electric power is augmented by 11.8% while the electric efficiency is decreased by 19.8%. This study may contribute to designing advanced adsorption-based osmotic heat engines to achieve an upgraded heat-to-electricity performance.

In coal-fired power plants, most of the working fluids used in a mid–low-temperature flue gas waste heat recovery system (FGWHRS) are low-temperature boiler supply air or condensate water in the flue gas condenser. This is prone to cause low-temperature corrosion, as the system temperature is lower than the acid dew point of the flue gas. In this study, an experimental apparatus was set up at the entrance of the desulfurization tower of a 330 MW unit in Xinjiang, China, which uses the technology of high-temperature boiler feed water (above 80 °C) to recover the waste heat of mid–low-temperature flue gas. The heat exchange performance of the mid–low-temperature FGWHRS was evaluated under different working conditions, and the optimal input parameters of the system for each considered working condition are given based on the analysis. It was found that the low-temperature corrosion in the system could be avoided using this technology. To eliminate low-temperature corrosion, the lowest temperature for the inlet water was predicted to be 69 °C in our study via curve fitting based on the experimental data. The results could provide a theoretical basis and engineering guidance for determining the best heat recovery strategy of mid–low-temperature FGWHRS.

During steel production, the impurities in the hot metal react with the fluxes forming the steel slag. Chemical constituents of this steel slag (SS) are relevant to iron/steelmaking or blended cement manufacture. Harmful impurities present in it, however, limit its recycling to these applications. Japan, Europe, and the US consume a significant amount of their SS, but more than 50% end up in low-end applications such as aggregates, etc. Massive generation and limited usage have resulted in huge SS accumulation in China and India (the top two steel-producing countries). This paper takes a critical look at the developments toward steel slag recycling and utilization, leading to resource conservation and greenhouse emission control. Various approaches toward eliminating the inhibiting factors for recycling the SS in iron/steelmaking and blended cement manufacture are critically analyzed. Based on the analysis, the authors present a holistic approach toward steel slag utilization beyond the conventional application areas like aggregates, landfilling, etc. This approach involves heat recovery from the molten slag, optimal, and efficient materials recovery/recycling, and carbon capture. Energy recovery conserves fossil fuel consumption (with a consequent reduction in CO2 emission). The energy recovery processes inching toward commercial application yield a granulated glassy slag suitable for further recycling. Indirect benefits from these include a reduction in the environmental and ecological impacts of mining and related activities. Such endeavors will enable the steel industry to circumvent stringent environmental regulations and achieve energy efficiency.

Open absorption heat pump (OAHP) system is more viable option to recover waste heat from moist gas as compared to the traditional condensation methods. This promising technology has great potential for latent heat recovery from moist gas, drying process in paper and other industrial heating applications. This study presents the process modelling and comparative analysis of OAHP system in Aspen Plus using two different solutions by adopting part regeneration technique. The promising potassium formate-water (HCOOK/H2O) which has lower causticity, lower costs and better crystallization characteristics is used as an alternative to the caustic lithium bromide-water (LiBr/H2O) solution in this study. Process model of the system is established in Aspen Plus and, the properties validity is confirmed with published experimental and Engineering Equation Solver (EES) library data. A detailed comparative parametric study is carried out to evaluate the effect of influencing parameters on coefficient of performance (COP), water recovery (φ) and heat recovery (ζ) efficiencies. The performance of OAHP system is found to be very similar using different concentrations as 2.13 COP value for 50% LiBr/H2O and 2.19 for 70% HCOOK/H2O solution over design conditions. Similarly, φ is found to be 0.701, 0.688 while ζ as 0.716 and 0.705 for both the absorbents. Moreover, the system’s operational concentration range is 45-61.3% for LiBr/H2O and 55-82.1% for HCOOK/H2O at 135 °C regeneration heat input. Potassium formate solution having quite similar properties to the aqueous lithium bromide is also confirmed to have similar performance trends using 50% and 70% concentrations.

Heat recovery technology using thermoelectric has attracted many research intentions mainly for its ability to generate power passively. The automotive engine usually produces waste heat ranging from 30-40% due to the thermodynamic limit. The use of thermoelectric generator (TEG) for waste heat recovery and power generation could increase the efficiency of the internal combustion engine system. This research developed and investigated a heat recovery system using a thermoelectric generator (TEG) for power generation. A thermoelectric generator (TEG) consisted of thermoelectric modules, hexagonal pipe connector and heat sinks was built and connected to an exhaust pipeline. A theoretical model was developed to access the thermal and electrical performance of the TEG system. The theoretical model consisted of the heat transfer mechanism including the thermal resistance networks from the flue gas to TEG and the heat sink. The electrical power output was determined using the Seebeck principle. The early stage of finding reveals that the system was able to produce an open circuit voltage of 0.13 V for a small temperature gradient of 3ᵒC between the cold and hot surface of the TEG. The further improvement of the system is currently under investigation for producing higher power. In the future, this system hopefully could replace the car battery for charging the alternator as well as increasing the overall efficiency of the engine system.

In this work, the industrial case study of effluent drying with a direct and hybrid heat recovery configuration is investigated for the purpose of improving heat recovery potential and understandin...

In this study, a model of a variable refrigerant flow (VRF) heat pump is developed that combines multiple physical equations into only one characteristic equation. The parameters of the characteris...

Thermal management of metal hydride (MH) hydrogen storage systems is critically important to maintain the hydrogen absorption and release rates at desired levels. Implementing thermal management arrangements introduces challenges at system level mostly related to system's overall mass, volume, energy efficiency, complexity and maintenance, long-term durability, and cost. Low effective thermal conductivity (ETC) of the MH bed (~0.1–0.3 W/mK) is a well-known challenge for effective implementation of different thermal management techniques. This paper comprehensively reviews thermal management solutions for the MH hydrogen storage used in fuel cell systems by also focusing on heat transfer enhancement techniques and assessment of heat sources used for this purpose. The literature recommended that the ETC of the MH bed should be greater than 2 W/mK, and heat transfer coefficient with heating/cooling media should be in the range of 1000–1200 W/m2K to achieve desired MH's performance. Furthermore, alternative heat sources such as fuel cell heat recovery or capturing MH heat during charging and releasing it back during discharging have also been thoroughly reviewed here. Finally, this review paper highlights the gaps and suggests directions accordingly for future research on thermal management for MH systems.

This article presents a general overview of the heat recovery systems used in the ceramic tile production sector and gives an introduction into the outputs of the European research project DREAM developed in the frame of the EU Horizon 2020 program. DREAM stands for 'Design for Resource and Energy efficiency in cerAMic kilns' and has the aim of studying new techniques for reducing consumption and environmental impacts in the ceramic production cycle.

This paper presents experimental results on the study of the effects of ejector adiabatic absorber on heat and mass transfer of binary nanofluid with heat transfer additives (2-ethyl-1-hexanol and gum Arabic). In this case, H2O/lithium bromide-alumina nanofluid was suggested due to a growing interest in absorption heat transfer working fluid for solar energy application. An experimental setup — ejector test rig — was designed to study the absorption, heat, and mass transfer rate as a result of refrigerant vapour mass flow entrained by the ejector adiabatic absorber. The study was carried out at different solution mass flowrate (0.051 to 0.17 kg/s) with three prepared sample solutions, which include pure LiBr solution, LiBr-Alumina nanofluid without heat transfer additives, and LiBr-Alumina nanofluid with heat transfer additives. The absorption rate, mass transfer coefficient, heat transfer rate, and heat transfer coefficient for the three samples were reported. On the other hand, the percentage enhancements for all the parameters — at a suitable flow rate of 0.085 kg/s — due to the addition of alumina without and with heat transfer additives were recorded. The absorption rate enhancements were 25% and 96%, the enhancement rates of mass transfer coefficient recorded were 20% and 82%, the heat transfer rate enhancements were 85% and 183%, and the heat transfer coefficient enhancements obtained were 72% and 156% with addition of alumina nanoparticles only and alumina nanoparticles with heat transfer additives respectively. Material mass balance analysis suggests that mass inflow in the ejector equals to the mass outflow from the ejector, indicating a complete absorption of the entrained refrigerant vapour beyond which falling film absorption can occur due to concentration. This article also presents experimental evidence of the capability of ejector as strong adiabatic absorber, heat, and mass transfer component, which were earlier reported using numerical models.

The results of studies of the effectiveness of using the air method of preventing condensation formation in the gas-exhaust ducts for anticorrosive protection of chimneys of gas-fired heating boiler plants are presented. This method is used in heat-recovery systems of boiler plants, characterized by deep cooling of gases (below the dew point temperature of water vapor contained in exhaust-gases). The essence of this method is to change the thermal and humidity characteristics of exhaust-gases after heat-recovery by mixing dry and heated air in front of the chimney. Schematic solutions of heat-recovery systems using two options for using the air method are presented. The first option corresponds to the use of the air method when mixing air from the heater of boiler plant. In the second option, for the implementation of the air method, air heated in the heat-recovery system itself is used. To assess the efficiency of the air method, computational studies were carried out to determine the thermal and moisture characteristics of flue gases at the mouth of different types of chimneys under different operating modes of the boiler during the heating period. The studies were carried out for two proposed options for using the air method when using air with a change in its temperature over a wide range. The values of the dew point of the flue gases at the mouth of the chimney and the temperature of its inner surface were calculated at various proportions of the mixed air. The parameters of flue gases and mixed air were determined, ensuring the absence of condensation in the chimneys. Based on the values of the obtained parameters, a comparative analysis of the effectiveness of the considered options for using the air method was carried out. It is shown that for heating boilers the use of this method is the most effective in complex heat-recovery systems when using recovered heat for heating return heat-network water and combustion air. Key words: gas-fired boilers, exhaust-gases, deep cooling, air method, thermal and humidity condition, chimney, anticorrosive protection

The new German Radiation Protection Act (StrlSchG) of 31 December 2018 established a reference value of 300 Bq m−3 for the annual average radon activity concentration in buildings with recreation and living rooms, as well as in workplaces. It is expected that the reference value will be exceeded in a vast number of buildings throughout Germany and that radon protection measures will become indispensable. A simple and inexpensive radon protection measure for existing buildings is ventilation. In the scope of a joint project, ventilation systems with zone control and heat recovery are to be extended by the control parameter radon activity concentration. A highly sensitive, miniaturized radon monitor will be developed for this purpose, which can be integrated wirelessly into ventilation systems. Radon measurements were carried out in 13 apartments of an unoccupied heated apartment block in Germany over a period of three weeks in the wintertime. High radon activity concentrations were found on all three floors. The maximum values were 14000 Bq m−3 on the first floor, 6000 Bq m−3 on the second floor, and 2000 Bq m−3 on the third floor. Ventilation experiments were carried out in an apartment with high radon activity concentration. Two decentralized ventilation systems with heat recovery were installed in each of the two opposite outside walls. The controlling device of the system was activated wirelessly depending on the radon activity concentration. The radon activity concentration was reduced from 8000 Bq m−3 to 800 Bq m−3 in a first experiment in the living room.