Search

Abstract Limited experimental research has been conducted on organic Rankine cycle (ORC) systems that use wet working fluids. Therefore, the present study examined how the performance of an ORC system that uses a wet working fluid (R134a) was affected by the superheat degree ratio (SDR) under various scroll rotation speeds. The SDR is the dimensionless ratio between superheat degree and evaporation temperature at a given heat source temperature. Experimental results indicated that at scroll rotation speeds of 900, 1350, and 1800 rpm, the maximum output power of the aforementioned system was 1103, 1464, and 1537 W, respectively, with SDRs of 0.49, 0.49, and 0.54, respectively. The maximum net efficiencies at these speeds were 5.87%, 5.91%, and 5.32%, respectively, which occurred at SDRs of 0.61, 0.49, and 0.48, respectively. This level of system performance was attributable to the high enthalpy at the expander inlet and the high mass flow rate at the high evaporation pressure under an SDR of approximately 0.5. Although increasing the SDR did not enhance the scroll expander's isentropic efficiency, this efficiency decreased considerably when the SDR fell below 0.2. These findings emphasize the importance of optimizing the SDR of ORC systems to improve their performance.

Various design versions of the rotor of hydro-steam turbines (HSTs) and their application fields are reviewed. It is shown that the design with nozzles arranged over the periphery has certain shortcomings resulting in a decreased energy efficiency, including a thermodynamically unjustified increase of pressure at the nozzle inlet, which results in excessively high velocities in the nozzle "throat," a short period of time for which the evaporating medium resides in the nozzle divergent part, and poor aerodynamic characteristics of the peripheral area, which cause increased friction losses during the impeller rotation in a two-phase medium. A hydro-steam turbine impeller design with helical nozzle-channels is proposed. Such design has features that create prerequisites for increasing the turbine efficiency, including a longer time for which the medium resides in the nozzle, a possibility to obtain aerodynamically smooth lateral and peripheral surfaces of the impeller, and better conditions for moisture separation from the medium surrounding the rotating impeller. The conditions under which superheated water enters the impeller are considered, and statements on shaping the impeller profile part are formulated. A procedure for determining the nozzle-channel divergent part's camber line shape is proposed proceeding from the minimal force interaction between the liquid phase fragments and channel walls. An algorithm for determining the areas of the channel divergent part's cross sections when the velocity increase and pressure decrease patterns become monotonic in nature as the flow moves from the inlet to the outlet is developed. A solid-state 3D model of the HST four-nozzle impeller obtained in designing the turbine is presented. [ABSTRACT FROM AUTHOR]

The reverse electrodialysis heat engine (REDHE) represents a transformative innovation that converts low-grade thermal energy into salinity gradient energy (SGE). This crucial form of energy powers reverse electrodialysis (RED) reactors, significantly changing wastewater treatment paradigms. This comprehensive review explores the forefront of this emerging field, offering a critical synthesis of key discoveries and theoretical foundations. This review begins with a summary of various oxidation degradation methods, including cathodic and anodic degradation processes, that can be integrated with RED technology. The degradation principles and characteristics of different RED wastewater treatment systems are also discussed. Then, this review examines the impact of several key operational parameters, degradation circulation modes, and multi-stage series systems on wastewater degradation performance and energy conversion efficiency in RED reactors. The analysis highlights the economic feasibility of using SGE derived from low-grade heat to power RED technology for wastewater treatment, offering the dual benefits of waste heat recovery and effective wastewater processing. [ABSTRACT FROM AUTHOR]

Limited experimental research has been conducted on organic Rankine cycle (ORC) systems that use wet working fluids. Therefore, the present study examined how the performance of an ORC system that uses a wet working fluid (R134a) was affected by the superheat degree ratio (SDR) under various scroll rotation speeds. The SDR is the dimensionless ratio between superheat degree and evaporation temperature at a given heat source temperature. Experimental results indicated that at scroll rotation speeds of 900, 1350, and 1800 rpm, the maximum output power of the aforementioned system was 1103, 1464, and 1537 W, respectively, with SDRs of 0.49, 0.49, and 0.54, respectively. The maximum net efficiencies at these speeds were 5.87%, 5.91%, and 5.32%, respectively, which occurred at SDRs of 0.61, 0.49, and 0.48, respectively. This level of system performance was attributable to the high enthalpy at the expander inlet and the high mass flow rate at the high evaporation pressure under an SDR of approximately 0.5. Although increasing the SDR did not enhance the scroll expander's isentropic efficiency, this efficiency decreased considerably when the SDR fell below 0.2. These findings emphasize the importance of optimizing the SDR of ORC systems to improve their performance. [ABSTRACT FROM AUTHOR]

This study delves into the adoption of the organic Rankine cycle (ORC) for recovering waste heat from data centers (DCs). Through a literature review, it examines energy reuse with a focus on electric power generation, the selection of working fluids, and system design principles. The objective is to develop a thorough framework for system design and analysis, beginning with a quantity and quality investigation of waste heat available. Air cooling systems, chosen often for their simplicity, account for about 70% of used cooling methods. Water cooling demonstrates greater effectiveness, albeit less commonly adopted. This study pays close attention to the selection of potential working fluids, meticulously considering the limitations presented by the available sources of heat and cold for vaporization and condensation, respectively. It reviews an ORC-based system setup, incorporating fluid streams for internal processes. The research includes a conceptual case study where the system is designed and simulations are conducted in the DWSIM environment. The simulation model considers hot air or hot liquid water returning from the data center cooling system for ORC working fluid evaporation. Ambient water serves for condensing, with pentane and isopentane identified as suitable organic fluids. Pentane assures ORC net electric efficiencies ranging between 3.1 and 7.1% when operating pressure ratios increase from 2.8 to 6.4. Isopentane systems, meanwhile, achieve efficiencies of 3.6–7.0% across pressure ratios of 2.7–6.0. Furthermore, the investigation provides key performance indicators for a reference data center in terms of power usage effectiveness (PUE), energy reuse factor (ERF), energy reuse effectiveness (ERE), and greenhouse gas (GHG) savings. This study concludes with guidelines for system analysis, including exergy considerations, and details the sizing process for evaporators and condensers. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The thermo-osmotic energy conversion (TOEC) process harnesses low-grade waste heat for electricity generation. Key to TOEC is selecting membrane materials, with polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) being common choices. This study provides the first life cycle assessment (LCA) of PTFE and PVDF membranes, assessing both lab-scale and large-scale production. It identifies key chemical contributors to their environmental impact and cumulative energy demand (CED). PTFE has a lower CED in regions with renewable energy, while PVDF may be viable in areas reliant on non-renewable biomass. These insights can inform decision-makers in strategizing the implementation of TOEC processes for sustainable development.

Environmental issues shift energy production from conventional methods to new and more efficient alternatives. One of these alternatives is the use of organic Rankine cycles (ORC) in low-grade heat sources to generate both heat and power at small scales. Among different technologies available for this purpose, ORC-based systems seem to be the most suitable and promising option due to their simplicity and versatility. Thus, such systems have been investigated intensively. However, current studies often focus on only one aspect of these systems due to the massive research scale in this field. Therefore, this study aims to provide a fundamental and holistic overview to evaluate ORC-based low-heat sourced and small-scale applications from multiple perspectives. As a result, the basic operating principles and application areas of ORCs, selection and design criteria of their working fluids and all other system components, methods of improving their performance, and other thermodynamic cycles that can be ORC alternatives are examined in detail. The results of this study show that ORC applications can enable small-scale combined heat and power generation, while geothermal and solar energy sources have the potential to scale the size of such applications up to kW capacities. The results also showed that dry & isentropic fluids and vane & scroll expanders are the most suitable refrigerant and expander types, respectively, for small-scale ORC applications. Furthermore, the implications of all findings are critically discussed. [ABSTRACT FROM AUTHOR]

Highlights Solvation engineering toward dual-salt electrolyte by fluorosurfactant additive is proposed, which implements the stable interface of electrode/electrolyte coupled with fast ion thermodiffusion, improving the durability and capability of lithium-ion thermoelectrochemical cell. By combining the optimized electrolyte with functional electrodes, as-constructed device exhibits high Seebeck coefficient and energy density based on hybrid mechanisms, which can be extended as self-power supply for smart electronics.

Employing electric double-layer (EDL) capacitors to harvest low-grade heat (LGH) is a novel technique in the high-efficiency energy absorption field. This work reports the fabrication of a vertical thermoelectric cell, based on a nanoporous graphene electrode immersed in low-concentration saline solution, for use as thermo-charging supercapacitors to convert LGH to electricity via thermally induced voltage. Because of a large specific area and a large number of micropores of nanoporous graphene films, the effective thermoelectric coefficient of the thermoelectric cell containing 0.01 M KCl solution can reach as high as 4.73 mV/°C. However, many factors, such as electrode materials, electrolyte solutions, and energy conversion device components, determine the efficiency of a thermoelectric conversion device. In summary, the device has a lower internal resistance and higher output voltage when the concentration of KCl solution is 0.05 M, and demonstrates higher thermoelectric conversion efficiency. Moreover, improving the conductivity of the electrolyte solution without affecting the device output voltage is also a way to reduce the internal power consumption of the device. The specific power and thermoelectric conversion efficiency of the device are increased by several orders of magnitude when uniformly dispersed silver nanoparticles are added to the potassium chloride solution to enhance the conductivity of the solution. The specific power underwent an increase from 0.50 mW g−1 to 42.37 mW g−1, and the thermoelectric conversion efficiency also increased from 0.0022% to 0.1358%.

Energy drives the growth, transformation, and economic development of every nation. The vitality of human existence and progress hinges on the accessibility of both energy and water resources. As freshwater resources are diminishing, therefore, desalination needs have increased. In solar membrane distillation systems, the key challenge is maintaining the intake water temperature in the membrane distillation system with fluctuating solar radiation intensity which affects the distillate water quantity and quality. The objective of this study is to enhance and optimize a mathematical model for analyzing a cutting-edge solar-integrated PV/T-DCMD system. In this innovative integration, the direct contact membrane distillation intake water temperature is derived from the photovoltaic thermal output. The integration of direct contact membrane distillation with photovoltaic thermal systems represents a cost-effective and technologically advantageous concept. As the water temperature increases, there is a notable improvement in the evaporation efficiency of PV/T-DCMD systems, with an increase from 35.08% to 42.01%. Additionally, there is a reduction in specific thermal energy consumption, decreasing from 1,192 to 1,386 kWh/m³ as a consequence of the elevated feed water temperature. [ABSTRACT FROM AUTHOR]

Highlights: Solvation engineering toward dual-salt electrolyte by fluorosurfactant additive is proposed, which implements the stable interface of electrode/electrolyte coupled with fast ion thermodiffusion, improving the durability and capability of lithium-ion thermoelectrochemical cell. By combining the optimized electrolyte with functional electrodes, as-constructed device exhibits high Seebeck coefficient and energy density based on hybrid mechanisms, which can be extended as self-power supply for smart electronics. Lithium-ion thermoelectrochemical cell (LTEC), featuring simultaneous energy conversion and storage, has emerged as promising candidate for low-grade heat harvesting. However, relatively poor thermosensitivity and heat-to-current behavior limit the application of LTECs using LiPF6 electrolyte. Introducing additives into bulk electrolyte is a reasonable strategy to solve such problem by modifying the solvation structure of electrolyte ions. In this work, we develop a dual-salt electrolyte with fluorosurfactant (FS) additive to achieve high thermopower and durability of LTECs during the conversion of low-grade heat into electricity. The addition of FS induces a unique Li+ solvation with the aggregated double anions through a crowded electrolyte environment, resulting in an enhanced mobility kinetics of Li+ as well as boosted thermoelectrochemical performances. By coupling optimized electrolyte with graphite electrode, a high thermopower of 13.8 mV K−1 and a normalized output power density of 3.99 mW m–2 K–2 as well as an outstanding output energy density of 607.96 J m−2 can be obtained. These results demonstrate that the optimization of electrolyte by regulating solvation structure will inject new vitality into the construction of thermoelectrochemical devices with attractive properties. [ABSTRACT FROM AUTHOR]

This study delves into the adoption of the organic Rankine cycle (ORC) for recovering waste heat from data centers (DCs). Through a literature review, it examines energy reuse with a focus on electric power generation, the selection of working fluids, and system design principles. The objective is to develop a thorough framework for system design and analysis, beginning with a quantity and quality investigation of waste heat available. Air cooling systems, chosen often for their simplicity, account for about 70% of used cooling methods. Water cooling demonstrates greater effectiveness, albeit less commonly adopted. This study pays close attention to the selection of potential working fluids, meticulously considering the limitations presented by the available sources of heat and cold for vaporization and condensation, respectively. It reviews an ORC-based system setup, incorporating fluid streams for internal processes. The research includes a conceptual case study where the system is designed and simulations are conducted in the DWSIM environment. The simulation model considers hot air or hot liquid water returning from the data center cooling system for ORC working fluid evaporation. Ambient water serves for condensing, with pentane and isopentane identified as suitable organic fluids. Pentane assures ORC net electric efficiencies ranging between 3.1 and 7.1% when operating pressure ratios increase from 2.8 to 6.4. Isopentane systems, meanwhile, achieve efficiencies of 3.6–7.0% across pressure ratios of 2.7–6.0. Furthermore, the investigation provides key performance indicators for a reference data center in terms of power usage effectiveness (PUE), energy reuse factor (ERF), energy reuse effectiveness (ERE), and greenhouse gas (GHG) savings. This study concludes with guidelines for system analysis, including exergy considerations, and details the sizing process for evaporators and condensers.

Energy drives the growth, transformation, and economic development of every nation. The vitality of human existence and progress hinges on the accessibility of both energy and water resources. As freshwater resources are diminishing, therefore, desalination needs have increased. In solar membrane distillation systems, the key challenge is maintaining the intake water temperature in the membrane distillation system with fluctuating solar radiation intensity which affects the distillate water quantity and quality. The objective of this study is to enhance and optimize a mathematical model for analyzing a cutting-edge solar-integrated PV/T-DCMD system. In this innovative integration, the direct contact membrane distillation intake water temperature is derived from the photovoltaic thermal output. The integration of direct contact membrane distillation with photovoltaic thermal systems represents a cost-effective and technologically advantageous concept. As the water temperature increases, there is a notable improvement in the evaporation efficiency of PV/T-DCMD systems, with an increase from 35.08% to 42.01%. Additionally, there is a reduction in specific thermal energy consumption, decreasing from 1,192 to 1,386 kWh/m3 as a consequence of the elevated feed water temperature.

Thermal-driven refrigeration technologies, e.g., absorption- or adsorption-type, are gathering momentum since they can utilize low-grade heat from industrial, solar or geothermal energy. However, heat sources and end users are usually mismatched, which could lead to potential heat pollution and increased carbon emissions. Long-distance thermal energy transportation is good for district heating and cooling, which is of great significance if it can achieve a high energy-transportation density and low heat loss. In this paper, a compression-assisted chemisorption chiller driven by a low-temperature heat source for cold transportation is initially proposed, which aims to transport liquid ammonia with chemical potential and generate a cooling effect for end users. A feasibility analysis of the compression-assisted chemisorption chiller is preliminarily performed for 2 km cold transportation. The results show that the highest theoretical coefficient of performance and the energy efficiency of the compression-assisted adsorption chiller using a sodium bromide–ammonia working pair can reach 0.46 and 0.25, respectively, when the evaporation temperature is 20 °C. Among the three selected low-temperature salts, ammonium chloride–ammonia shows the best performance, which is up to about 40% higher than those of sodium bromide–ammonia and barium chloride–ammonia. It is demonstrated that compared with common absorption chillers, a compression-assisted adsorption system has a reasonable working efficiency to transport cold energy when the low- or ultralow-temperature heat source, e.g., lower than 60 °C, is required to be utilized. [ABSTRACT FROM AUTHOR]

Low-grade heat energy from resources below 100 °C is readily available in massive quantities worldwide. However, existing technologies face challenges in converting this heat power into usable forms of energy, such as electricity. This is primarily due to temperature fluctuations in these heat sources and the limited temperature gradient with the surrounding environment. To address this issue, a recently developed technology called thermo-osmotic energy conversion (TOEC) offers a promising solution for harvesting electrical energy from low-grade heat sources. In the TOEC method, a hydrophobic membrane facilitates the transfer of water vapor molecules from a moderately hot aqueous solution to a cold water stream. The resulting hydraulic pressure in the compressed water on the cold side can be harnessed using a hydro-turbine. Despite the many interesting features of TOEC technology, a comprehensive analysis of its performance under various operating conditions and membrane properties is currently lacking in the literature. In this study, we conducted a theoretical evaluation of the TOEC process based on mass and heat transfer phenomena, and we validated our findings with experimental data. Our results indicate that employing membranes with smaller pore size, low thickness, and high porosity, along with higher feed temperature and flowrates, can significantly enhance energy efficiency and power density. Specifically, we demonstrate that the utilization of hydrophobic membranes with nanometer-sized pores, coupled with hydraulic pressures ranging from 6.2 bar to 11.8 bar, enables us to achieve power densities exceeding 5 W/m2, given a 20 °C heat sink and a heat source temperature above 65 °C. Furthermore, we have determined that an applied hydraulic pressure of 9.4 bar yields the maximum energy efficiency value of 0.016%.

Energy-saving technologies are among the priority development lines of Russia's power industry. In recovering the rejected heat from geothermal sources, especially those located in cold climatic zones in which there is no access to service cooling water resources, it is profitable to use organic coolants, e.g., CFC refrigerants, as working fluid for dry cooling towers. The properties of such coolants have, as a rule, been studied to a sufficient detail in the region of low temperatures, because they are mainly used as working fluids for refrigeration systems at moderate heat fluxes. To obtain data on the boiling of organic coolants on a tube bundle for taking into account the influence of bundle lower tubes on the heat transfer in the upper tubes, a vapor generator mockup with a horizontal tube bundle was developed. High-pressure water served as the heating medium; and electric heaters were provided for additionally heating the CFC refrigerant to a level close to the saturation temperature. The tube bundle includes twelve tubes arranged in three rows along the height: the central row consists of four measurement tubes, and two lateral rows consist of auxiliary tubes. Eight thermocouples are installed at the top and bottom in the slots of the central row heat-transfer tubes for measuring the surface temperature. For the lower and upper rows in the bundle, boiling heat-transfer coefficients were obtained in a wide range of specific heat fluxes. It is shown that the boiling on the upper rows is significantly more (by 30–35%) intense than it is on the lower rows. [ABSTRACT FROM AUTHOR]

The absorption refrigeration system can recover low-grade heat and produce cooling capacity, which can realize low-carbon refrigeration. However, due to the constant-temperature evaporation, the conventional system fails to provide efficient cooling for temperature-distributed heat load with large temperature spans, including process cooling, mixture liquefaction and ice slurry making. In this paper, a modified ammonia-water absorption refrigeration system with two pairs of evaporation and absorption processes at different pressure levels is proposed, in order to enhance the temperature matching with the temperature-distributed heat load and promote the absorption heat recovery. A process model is developed and validated, and comparison and parametric studies are conducted to illustrate the advantages of the new system and optimize operating conditions. Results show that the proposed system is suitable for the cooling process with temperature-distributed heat load with large temperature span, and the exergy destruction during the cooling process with temperature-distributed heat load decreases by nearly 40%. Moreover, the system internal heat recovery is improved by harvesting absorption heat. As a consequence, the COP increases by 31% and reaches 0.75, when providing cooling capacity with temperature below -10 °C. It is hoped that this study raises concerns about the characteristics of temperature-distributed heat load and provides feasible approach for efficient cooling with large temperature span. [ABSTRACT FROM AUTHOR]

Abstract Developing redox electrolytes with high thermopower is the key to making efficient thermogalvanic batteries for harvesting low‐grade heat. This work applies molecular dynamics simulations to predict the thermopower (i.e. thermogalvanic temperature coefficient) α of the redox pairs Fe(CN)63−/Fe(CN)64− and Fe3+/Fe2+, showing excellent agreement with experimental values. We showed that α of the Fe3+/Fe2+ redox pair can be increased from 1.7±0.4 mV/K to 3.8±0.5 mV/K with the increased acetone to water fraction. We discovered a significant change in the variance of solvent dipole orientation between Fe3+ and Fe2+, which can serve as a microscopic indicator for large α. In mixed acetone‐water solvent, α of Fe3+/Fe2+ showed a rapid increase at high acetone fractions, due to the intercalation of acetone molecules into the first solvation shell of the Fe2+ at high acetone fractions. Our discovery provides insights into how solvation shell order can be engineered to develop electrolytes with high α.

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The ever-increasing energy demand and global warming caused by fossil fuels push for the exploration of sustainable and eco-friendly energy sources. Waste thermal energy has been considered as one of the promising candidates for sustainable power generation as it is abundantly available everywhere in our daily lives. Recently, thermo-electrochemical cells based on the temperature-dependent redox potential have been intensely studied for efficiently harnessing low-grade waste heat. Despite considerable progress in improving thermocell performance, no attempt was made to develop electrode materials from renewable precursors. In this work, we report the synthesis of a porous carbon electrode from mandarin peel waste through carbonization and activation processes. The influence of carbonization temperature and activating agent/carbon precursor ratio on the performance of thermocell was studied to optimize the microstructure and elemental composition of electrode materials. Due to its well-developed pore structure and nitrogen doping, the mandarin peel-derived electrodes carbonized at 800 °C delivered the maximum power density. The areal power density (P) of 193.4 mW m−2 and P/(ΔT)2 of 0.236 mW m−2 K−2 were achieved at ΔT of 28.6 K. However, KOH-activated electrodes showed no performance enhancement regardless of activating agent/carbon precursor ratio. The electrode material developed here worked well under different temperature differences, proving its feasibility in harvesting electrical energy from various types of waste heat sources. [ABSTRACT FROM AUTHOR]

A newly developed technology, thermo‐osmotic energy conversion (TOEC), is supposed to convert low‐grade heat into power. However, the performance of existing TOEC experiments is deficient. This paper discusses the feasibility of strengthening TOEC by applying negative pressure to the feed liquid, which can reduce air pressure in the membrane pores and molecular diffusion resistance. Theoretical calculation shows that when the cooling and heating temperatures are 40 and 80 °C, respectively, and the transmembrane pressure difference is 5.0 MPa, the TOEC system with a negative pressure of 0.5 bar at the feed side can approach an efficiency of 3.01% and a power density of 16.85 W m−2, which increases by 20% and 27% compared with no negative pressure, respectively. Given the nonuniformity in the real system, computational fluid dynamics simulation is used to obtain the correction factor, which is then used to revise the theory prediction results for the first time. Moreover, a lab‐scale experiment also proves that a negative pressure at the feed benefits the performance of the TOEC device. Overall, this research presents a feasible method to enhance a TOEC system, which may promote the development of a more‐efficiently TOEC system for low‐grade heat utilization. [ABSTRACT FROM AUTHOR]

Technical capacities of petro thermal energy complex usage in heat-cold supply systems and for generation at a low-grade heat medium turbine by means of absorption heat pump are described.

Abstract A newly developed technology, thermo‐osmotic energy conversion (TOEC), is supposed to convert low‐grade heat into power. However, the performance of existing TOEC experiments is deficient. This paper discusses the feasibility of strengthening TOEC by applying negative pressure to the feed liquid, which can reduce air pressure in the membrane pores and molecular diffusion resistance. Theoretical calculation shows that when the cooling and heating temperatures are 40 and 80 °C, respectively, and the transmembrane pressure difference is 5.0 MPa, the TOEC system with a negative pressure of 0.5 bar at the feed side can approach an efficiency of 3.01% and a power density of 16.85 W m−2, which increases by 20% and 27% compared with no negative pressure, respectively. Given the nonuniformity in the real system, computational fluid dynamics simulation is used to obtain the correction factor, which is then used to revise the theory prediction results for the first time. Moreover, a lab‐scale experiment also proves that a negative pressure at the feed benefits the performance of the TOEC device. Overall, this research presents a feasible method to enhance a TOEC system, which may promote the development of a more‐efficiently TOEC system for low‐grade heat utilization.

The electrochemical water splitting to produce clean hydrogen is severely restricted by oxygen evolution reaction (OER) due to the sluggish kinetics of its complicated oxidation process. In this work, the cobalt sulfide nanosheets directly grown on nickel foam (Co–S/Ni 3 S 2 @NF) demonstrated an outstanding OER performance with a potential of 1.57 V (vs. RHE) to achieve a current density of 20 mA cm−2, favorably comparing the performance of the noble metal-based catalyst IrO 2 @NF. The same current density (20 mA cm−2) could be reached at an extremely low potential of 1.35 V (vs. RHE) by adding 0.1 M glycerol, indicating adding chemical mediator is a possible approach to replace the sluggish OER by the corresponding oxidation of chemical mediator. The activation energy comparison of glycerol oxidation reaction (GOR) and OER (21.9 kJ/mol and 28.2 kJ/mol) further proved this conclusion. The solar energy can be captured and utilized to improve OER in the electrochemical water splitting. The anodic current density at ∼1.6 V (vs. RHE) can be increased 10 times by adding glycerol and raising temperature. This work provides solutions to accelerate OER for H 2 production. [Display omitted] • Current density can be increased 10 times by adding glycerol and raising temperatures. • The OER activity of Co–S/Ni 3 S 2 @NF is comparable with the performance of IrO 2 @NF. • The Co–S/Ni 3 S 2 @NF exhibits high catalytic activity and thermal durability for OER. • GOR is a promising candidate to replace OER in electrolysis. • The solar energy can be utilized to improve OER in electrochemical water splitting. [ABSTRACT FROM AUTHOR]

Thermal energy is abundantly available in our daily life and industrial production, and especially, low‐grade heat is often regarded as a byproduct. Collecting and utilizing this ignored energy by low‐cost and simple technologies may become a smart countermeasure to relieve the energy crisis. Here, a unique device has been demonstrated to achieve high value‐added conversion of low‐grade heat by introducing redox‐active organic alizarin (AZ) onto N‐doped hollow carbon nanofibers (N–HCNF) surface. As‐prepared N–HCNF/AZ can deliver a high specific capacitance of 514.3 F g−1 (at 1 A g−1) and an outstanding rate capability of 60.3% even at 50 A g−1. Meanwhile, the assembled symmetric proton capacitor can deliver a high energy density of 28.0 Wh kg−1 at 350.0 W kg−1 and a maximum power density of 35.0 kW kg−1 at 17.0 Wh kg−1. Significantly, the thermally chargeable proton capacitors can attain a surprisingly high Seebeck coefficient of 15.3 mV K–1 and a power factor of 6.02 µW g–1. Taking advantage of such high performance, a satisfying open‐circuit voltage of 481.0 mV with a temperature difference of 54 K is achieved. This research provides new insights into construction of high value‐added energy systems requiring high electrochemical performances. [ABSTRACT FROM AUTHOR]

Liquid‐based thermoelectric cells integrate energy harvesting and storage technology, becoming the focus of energy fields. However, the simultaneous implement of high output voltage and heat‐to‐electricity efficiency is still challenging. Herein, we propose a lithium‐ion thermal charging cell using lithium anode and electrospun zinc vanadate@carbon nanofiber cathode. Benefitting from the superior performance of electrode and the significant difference between the size of cation and anion in electrolyte, such system can continuously realize the harvesting and conversion of low‐grade heat into electricity. Consequently, an open‐circuit voltage of about 2.1 V can be generated at a low temperature gradient of 25 K together with an ultrahigh thermopower of 47.9 mV K−1 and a remarkable power density of 9.2 W m−2. Moreover, an impressive Carnot‐related efficiency (5.2 %) can be achieved under same conditions. This work confirms the superiority of organic thermoelectric system and provides a new insight to develop promising thermal charging cell for sustainable applications. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis of the potential working fluids for a promising thermodynamic cycle (Thermal Power Pump cycle) for the utilisation of low-grade heat. The cycle was analyzed along with nucleate boiling correlations and film condensation analysis for variable heat source temperatures (50–150°C) using nine potential working fluids. The working fluids showed varying degrees of cycle performance and system size requirements. Among the working fluids, cyclopentane seems to be an attractive choice of working fluid, due to its superior cycle performance over the wide range of heat source temperatures with moderate system size requirements. For temperatures above 146°C and below 60°C, water and n-pentane are selected, respectively. Working fluids with stronger molecular forces seem to approach the properties of an ideal working fluid for better performance of the system.

Many regions around the world have limited access to clean water and power. Low-grade thermal energy in the form of industrial waste heat or non-concentrating solar thermal energy is an underutilized resource and can be used for water desalination and power generation. This paper experimentally and theoretically examines a thermoelectric-based simultaneous power generation and desalination system that can utilize low-grade thermal energy. The paper presents concept design and the theoretical analysis of the proposed system followed by experimental analysis and comparison with the theoretical estimations. Experiments were carried out at three heat loads 50, 100 and 150 W to achieve varying temperature gradients across thermoelectric generators. During the experiments, thermoelectric generators were maintained at a hot to cold side temperature difference between 20 to 60 °C. The experiments showed that the power generation flux and freshwater mass flux increased with the increase in the thermal energy source temperature. The power flux varied between 12 to 117 W/m2 of thermoelectric generator area, while freshwater mass flux varied between 4.8 to 23.7 kg/m2⋅h. The specific thermal energy consumption varied between 3.6 to 5.7 MJ/kg of freshwater; this is comparable to the single-stage conventional distillation system. [ABSTRACT FROM AUTHOR]

A thermodynamic model of basic and recuperative transcritical organic Rankine cycles (TRCs) associated with using five pure and six mixed fluids as working fluids has been developed. This model can be employed to investigate the effects of recuperators at inlet expander temperatures (Texp,in) of 150–200°C and inlet expander pressures (Pexp,in) of 3.7–6.9 MPa. The ratio of change (ROC) of the first‐ and second‐law efficiencies (ηI and ηII) was positively correlated with the heat transfer rate of the recuperator and exhibited an opposite trend for a specific volume ratio. ROC was substantially affected by operating parameters and working fluid. However, the recuperator heat transfer rate was negligibly affected by the mixture temperature glide (Tglide). A universal empirical equation of ηI,II was proposed for both TRC configurations. The equation, a function of the specific volume ratio, can predict the system efficiencies for pure and mixed fluids, even if a mixture has an arbitrary mole fraction. As Tglide of R600a‐base mixture and R245fa/R134a was lower than 16 K, they had low error rates and low standard deviations. Finally, the equation was highly accurate in ηII prediction, particularly at a Texp,in of 160°C and 170°C and a Pexp,in of 4.9–5.8 MPa. [ABSTRACT FROM AUTHOR]

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.

The relevance of the study is caused by the need to expand the fuel and energy and mineral resources base through the development of renewable, high-potential mineralized resources of thermal water deposits. However, the exploitation of such deposits is hindered by the high degree of mineralization of natural brines. The use of binary geothermal power plants that implement the Rankine thermodynamic cycle for utilization of thermal energy allows us to solve this problem and obtain relatively cheap electrical energy. There is a need to search and evaluate methods for improving the energy efficiency of thermodynamic cycles, implemented in the development of one of the most promising deposits of thermal waters of Dagestan – Kumukh. A positive assessment of the prospects for development of geothermal resources of the field shows significant potential for improving the economic structure of the region. Purpose: to evaluate the energy efficiency of a binary geothermal power plant, which is based on the organic Rankine cycle in subcritical and supercritical cycles and in different modes of injection of waste coolant for the Kumukh thermal water field; to show the prospects and effectiveness of integrated development of geothermal resources of the field. Object: geothermal systems for electric power development of high potential mineralized thermal waters of the field. The research methods are based on the use of geological exploration, hydrothermal and geochemical research data on the Kumukh thermal water deposit, methods of mathematical modeling and optimization. Results. On the example of a specific thermal water deposit, the technological parameters of the primary circuit of the geothermal power plant were optimized, its energy efficiency was evaluated in subcritical and supercritical organic Rankine cycles with a low boiling secondary coolant. It is shown that the utilization of the low-potential energy of brines in heat pump plants can improve the efficiency of energy cycles in the field. The analysis shows that the creation of integrated technologies for development of high-potential mineralized geothermal resources of the field will significantly improve the economic structure of the region.

A passive membrane-free thermal distiller was used for desalinating hypersaline water. The hypersaline was spontaneously transported under capillary force of the porous and hydrophilic wick, without needing the external driving. Low-grade waste heat such as hot hypersaline water can be worked as the thermal source, and air as the cold source of the distiller. A siphon channel was constructed with the capillary wick and the crystallized salt, which can self-flush the crystallized salt and assure the stability of this passive system. The integrated distiller system can efficiently collect water and salt, achieving zero liquid discharge. [Display omitted] • Zero liquid discharge are achieved with a passive thermal distiller. • A siphon channel is designed to scour the crystalized salt. • The system can stably desalinate 70 g L−1 NaCl solution. • The water yield is 1.33 kg m−2h−1 and salt collection is 0.34 kg m−2h−1 with 60 °C feed solution as thermal source. Membrane distillation of hypersaline solution with low-grade waste heat is particularly outstanding to address the challenge of water-energy nexus. However, the high causticity of hypersaline solution always makes this system complicated and expensive. Here, we design a passive membrane-free thermal distiller for hypersaline desalination with high stability, easy operation and low cost. A siphon channel is constructed with the capillary wick and the crystallized salt, which can self-flush the crystallized salt and assure the stability of this passive system. Together with optimizing heat transfer process to suppress temperature polarization, the integrated distiller system can efficiently collect water and salt, achieving zero liquid discharge. The system can stably desalinate 70 g/L NaCl solution, with the water yield of 1.33 kg m−2h−1 and salt collection of about 0.34 kg m−2h−1 at 60 °C. This passive system is expected to desalinate hypersaline water in large-scale commercial production, for example, integrating with desalination industry. [ABSTRACT FROM AUTHOR]

• Fundamental mechanisms for reactive heat transfer are unravelled. • Endo-/exothermic reactions has limited impact on time-averaged performance. • Instantaneous fluid behaviours are responsible for high heat transfer performance. • Intense and long-lasting heat absorption/release enhance reactive heat transfer. • The role of vortices in heat and mass transfer intensification is elaborated. While fundamental mechanisms of non-reactive jet impingement have been extensively researched, the reactive jet impingement is yet unexplored although it offers the potential to increase further the heat transfer. The present work fills this knowledge gap via high-fidelity numerical simulation of reactive jet impingement invoking the finite rate one-step chemistry. Endo-/exothermic reactions are found to have very limited influence on time-averaged fluid flow, while they induce substantial modifications in heat transfer characteristics. This influence is manifested as discernible changes in the momentary or instantaneous fluid dynamics. Specifically, the primary vortices are responsible for downwashing cold fluid (mostly N 2 O 4) towards the hot plate, posing low local convective heat transfer. The secondary vortices are responsible for extracting heat from the hot plate via the dissociation reaction N 2 O 4 → 2 N O 2 , followed by transporting N O 2 away from the hot plate and towards the upwashing side of the primary vortex. At the upside of the primary vortex, hot N O 2 is cooled by the environment, therefore reforming N 2 O 4 to give out energy. This intense and long-lasting heat absorption and heat release process explains the outstanding performance of reactive jet impingement. [ABSTRACT FROM AUTHOR]

Large amounts of waste heat, below 120 °C, are released globally by industry. To convert this low‐temperature waste heat to power, thermally regenerative flow batteries (TRFBs) have recently been studied. Most analyses focus on either the discharging or the regeneration phase. However, both phases have to be considered to holistically assess the performance of the flow battery. Therefore, a dynamic, open‐access, full‐cycle model of a Cu–NH3 TRFB is developed in Modelica and validated with data from the literature. Based on the validated model, a trade‐off between power density and efficiency is shown that depends only on the discharging strategy of the flow battery. For a sensible heat source with an inlet temperature of 120 °C and heat transfer at a thermodynamic mean temperature of about 90 °C, the power density reaches 38 W m−2 over a complete cycle, and the efficiency reaches 20% of Carnot efficiency. In a benchmarking study, the power production of the flow battery is shown to already achieve 34% of a fully optimized organic Rankine cycle. Thus, TRFBs require further optimization to become a competitive technology for power production and energy storage from low‐temperature waste heat. [ABSTRACT FROM AUTHOR]

Economic expedience of waste heat recovery systems (WHRS), especially for low temperature difference applications, is often questionable due to high capital investments and long pay-back periods. With a simple design, isobaric expansion (IE) machines could provide a viable pathway to utilizing otherwise unprofitable waste heat streams for power generation and particularly for pumping liquids and compression of gases. Different engine configurations are presented and discussed. A new method of modeling and calculation of the IE process and efficiency is used on IE cycles with various pure and mixed working fluids. Some interesting cases are presented. It is shown in this paper that the simplest non-regenerative IE engines are efficient at low temperature differences between a heat source and heat sink. The efficiency of the non-regenerative IE process with pure working fluid can be very high, approaching Carnot efficiency at low pressure and heat source/heat sink temperature differences. Regeneration can increase efficiency of the IE cycle to some extent. Application of mixed working fluids in combination with regeneration can significantly increase the range of high efficiencies to much larger temperature and pressure differences. [ABSTRACT FROM AUTHOR]

Isobaric expansion (IE) technology is a promising solution for mini- and medium-scale low-grade heat utilization. IE engines directly convert heat to mechanical energy and are particularly interesting as direct-acting, vapor-driven pumps and compressors. The elimination of multiple energy transformations, technical simplicity and the ability to use widely available low-grade heat (<100 °C) instead of fossil fuels are attractive features of this technology. The purpose of this paper was to present a new compression technology based on IE Worthington type engines, analyze the process analytically and numerically, and provide a first assessment of its potential. The simplest single- and double-acting schemes were considered for arbitrary low and high pressures of the compressed gas/vapor and driving vapor. In these schemes, the compressor piston was rigidly connected to that of an engine/driver. The vapor use efficiency of the driver process was characterized by the ratio of the network carried out in the cycle to the consumed mass of the driving vapor. The performed thermodynamic analysis showed how the vapor use efficiency depends on the process parameters. It was found that the efficiency of vapor use in the simplest schemes was low in comparison with the efficiency in pumps if the compressor work was much less than the pump work at the same pressure ratio. This occurred because the energy of the driving vapor was spent on the compression of the vapor itself. As a result, the thermal efficiency of the IE engine compressors was lower than that of the IE engine pumps. The difference was very large if the work of the engine feed pump was significant and no heat regeneration is applied. The results obtained are very useful for achieving improvements in this interesting technology, which will be reported in subsequent publications. [ABSTRACT FROM AUTHOR]