Regenerative Cycle Research Articles

Energetic Analysis of Low Global Warming Potential Refrigerants as Substitutes for R410A and R134a in Ground-Source Heat Pumps

The European building sector is responsible for approximately 40% of total energy consumption and for 36% of greenhouse gas emissions. Identifying technological solutions capable of reducing energy consumption and greenhouse gas emissions is one of the main objectives of the European Commission. Ground source heat pumps (GSHPs) are of particular interest for this purpose, promising a considerable reduction in greenhouse gas emissions of HVAC systems. This paper reports the results of the energetic analysis carried out within the EU research project GEO4CIVHIC about the performance of geothermal heat pumps working with low-GWP refrigerants as alternatives for R134a and R410A. The work has been carried out through computer simulations based on base and regenerative reverse cycles. Several heat sink and heat source temperature conditions have been considered in order to evaluate the GSHPs’ performance in the whole range of real conditions that can be found in Europe. Particular attention has been paid to the evaluation of compression isentropic efficiency and its influence on the overall cycle performance when dealing with steady-state heat pump simulations. To do so, five different scenarios of isentropic efficiency calculation have been studied and discussed.

A novel self-condensing transcritical CO2 power cycle with a vortex tube: Thermoeconomic assessment study and comparison

The low critical temperature of carbon dioxide (CO2) requires low-temperature heat sinks for condensation, which limits the application of the transcritical carbon dioxide (tCO2) power cycle system. This paper proposes a novel self-condensing tCO2 power cycle system with a vortex tube, which uses the vortex tube to achieve CO2 condensation without an external low-temperature heat sink. Firstly, the detailed thermodynamic and economic models of the proposed tCO2 power cycle system are established and verified. Then, the effects of decision variables on the thermoeconomic performances of the system are studied through parametric analysis. Finally, the performances of the self-condensing tCO2 power cycle system and the simple regenerative supercritical carbon dioxide (sCO2) power cycle are optimized and compared by single-objective and multi-objective optimizations. The single-objective optimization results reveal that the optimal thermal efficiency, exergy efficiency, and the levelized cost of electricity of the self-condensing tCO2 power cycle system are 41.42%, 69.01%, and 0.0739 $/(kW·h), which are 3.06%pt (percentage point) higher, 3.89%pt higher and 3.90% lower than those of the simple regenerative sCO2 power cycle system. The multi-objective optimization results show that compared with the simple regenerative sCO2 power cycle system, the self-condensing tCO2 power cycle system improves the thermal and exergy efficiencies by 1.81%pt and 2.41%pt at the expense of 3.37% higher in the levelized cost of electricity. Exergy destruction analysis reveals that the high temperature recuperator has the largest exergy destruction, which should be improved first.

Thermodynamics and Structural Optimization of Organic Rankine Cycle Plant for Clean Energy Access Using Artificial Bee Colony and Multi-Criteria Decision-Making Algorithms

The quest to decarbonize the energy space to avert the negative climate change consequences calls for using low/zero-carbon energy conversion technologies in the energy generation space. The Organic Rankine Cycle is a low/zero-carbon energy conversion technology for recovering waste heat from low to medium-temperature heat sources and for biomass conversion. Therefore, this paper presents the thermodynamic optimization, with an artificial bee colony algorithm, of different ORC configurations, including simple organic Rankine cycle, Regenerative Organic Rankine Cycle, Cascade Organic Rankine Cycle, Organic Rankine Cycle with Superheat, Organic Rankine Cycle with Superheat and Reheat, Regenerative-Superheat Organic Rankine Cycle, Regenerative-Reheat Organic Rankine Cycle and Two Complementary ORC using twelve (12) different working fluids. The thermodynamic optimization was followed by structural optimization using a multi-criteria decision approach. The modified-TOPSIS multi-criteria decision-making analysis was used to perform the structural optimization. The overall optimization study shows that the Regenerative-Reheat Organic Rankine Cycle, operating with an isopentane of 0 GWP and ODP, was selected as the best ORC configuration. The Regenerative-Reheat Organic Rankine Cycle has the following performance; thermal efficiency of 49.5%, maximum power output of 0.4 MW, condenser pressure of 90 kPa, and turbine pressure of 3.37 MPa. The results presented in this work will support clean energy developers in the clean energy access sector, especially in the agrarian community with huge agro-waste generation potentials.

Energy Conversion Characteristics and Modeling of Supercritical Hydrocarbon Fuel in Regenerative Cooling

During the cracking process of hydrocarbon fuel, the heat would be converted into internal energy and chemical energy. It is necessary to study the conversion relationship between internal energy and chemical energy in the above-mentioned energy conversion process, which is of great significance for the efficient use of fuel heat sinks in the regenerative cooling process. Therefore, the influences of pressure, mass flow rate, wall heat flux, and heating rate on the energy conversion were investigated, and an empirical prediction model was developed. The numerical results revealed that the influence of pressure on heat sink mainly focuses on the low and medium conversion. The chemical heat sink decreases with the increase of the mass flow rate and the heating rate, while the chemical heat sink increases with the increase in the wall heat flux. In addition, based on the analysis of the numerical data, an energy conversion correlation is developed by the Buckingham PI theorem, and most of the data calculated by this correlation can satisfy the deviation bandwidth of .

Primary Umbilical Endometriosis: A Rare Entity

Primary umbilical endometriosis is a rare benign gynaecological disorder caused by ectopic endometrial tissue in the umbilicus. The disease typically manifests as a painful umbilical nodule associated with cyclic bleeding or discharge during menstruation. Here, a 46-year-old woman with low parity and without previous history of abdominal surgery has been reported who presented with cyclical per-umbilical bleeding and pain in the umbilical region during menstruation without any palpable umbilical nodule. The patient responded well to initial medical management, but symptoms recurred on discontinuation of the medication. Though clinically, there was no palpable nodule, and ultrasonography revealed a hypoechoic lesion in the lower umbilical region suggestive of endometrial deposition. On resuming medical management, her symptoms abated. J Bangladesh Coll Phys Surg 2023; 41: 173-176

Application Of Finger Hand Relaxation To Reduce Post Laparotomy Operation Pain In Bilateral Chocolate Cyst Patients

Chocolate cyst or what is often called endometriosis is a functional endometrial condition that experiences cyclic bleeding. Treatment of endometriosis can be done by laparotomy. One of the nursing problems that often arises in post-laparotomy patients is severe pain or acute pain. Pain can affect various things, such as physical, behavioral, and also affect daily activities. Thus it is necessary to handle it so as not to give a negative influence. One of the relaxation techniques that can be used to reduce postoperative pain is the finger hold relaxation technique or often called the finger hold. This type of research is a case study research, which was conducted on 1 patient, namely Mrs. N. She is the first day postoperative laparotomy patient. The focus of this study is the application of finger-hold relaxation therapy to reduce post-laparotomy pain in chocolate cyst patients. Finger hold therapy is taught and carried out 2 times a day, at least 4 hours after administration of analgesic drugs, namely in the morning before taking the medicine and in the afternoon after lunch. Before and after being given the finger-hold relaxation intervention, the patient's perceived pain scale was measured. Measurement of the pain scale using the Verbal Descriptive Scale" and "Wong Baker Pain Rating Scale". The results of this study showed that finger-hold relaxation therapy for 2 times a day in 2 days showed that the results of finger-hold relaxation could reduce the scale of postoperative laparotomy pain, from moderate pain to mild pain. Nurses are expected to apply finger-hold relaxation therapy as a management procedure in postoperative laparotomy patients with chocolate cysts.

Sensitivity analysis and multi-objective optimization of the energy, exergy and thermo-economic performance of a Brayton supercritical CO2-ORC configurations

The following research compared some energy, exergetic and thermo-economic indicators of a supercritical CO2 simple Brayton cycle integrated with a simple organic Rankine cycle (SORC), and a regenerative organic Rankine cycle (RORC). A thermodynamic model was developed to determine the net power, thermal efficiency, the fuel consumption, and the exergy destruction of all the components of the system. Also, a thermo-economic model was developed to determine some economic indicators such as the levelized cost of energy (LCOE), the payback period (PBP) and specific investment cost (SIC). A sensitivity analysis was carried out to study the influence of the primary turbine inlet temperature (TIT), the high-pressure in the compressor (PHigh), the evaporator pinch point temperature difference (PPT), and the pressure ratio (Pr) on the indicators performance. Three different working fluids were selected in this study: acetone, toluene and cyclohexane. The results showed that cyclohexane had the best energy performance giving an efficiency of 48.02% for the RORC system. Besides, it presented the best thermo-economic results for the LCOE (0.26 USD/kWh), SIC (2626.75 USD/kWh), and a PBP (11.2 years). Finally, a multi-objective optimization was developed based on energy, exergy and thermo-economic performance parameters as objective functions to obtain a technical and economic feasible solution able to implement them in industrial applications.

A Whole-Course-Repair System Based on Neurogenesis-Angiogenesis Crosstalk and Macrophage Reprogramming Promotes Diabetic Wound Healing.

Diabetic wound (DW) therapy is currently a big challenge in medicine and strategies to enhance neurogenesis and angiogenesis have appeared to be a promising direction. However, the current treatments have failed to coordinate neurogenesis and angiogenesis simultaneously, leading to an increased disability rate caused by DWs. Herein, a whole-course-repair system is introduced by a hydrogel to concurrently achieve a mutually supportive cycle of neurogenesis-angiogenesis under a favorable immune-microenvironment. This hydrogel can first be one-step packaged in a syringe for later in situ local injections to cover wounds long-termly for accelerated wound healing via the synergistic effect of magnesium ions (Mg2+ ) and engineered small extracellular vesicles (sEVs). The self-healing and bio-adhesive properties of the hydrogel make it an ideal physical barrier for DWs. At the inflammation stage, the formulation can recruit bone marrow-derived mesenchymal stem cells to the wound sites and stimulate them toward neurogenic differentiation, while providing a favorable immune microenvironment via macrophage reprogramming. At the proliferation stage of wound repair, robust angiogenesis occurs by the synergistic effect of the newly differentiated neural cells and the released Mg2+ , allowing a regenerative neurogenesis-angiogenesis cycle to take place at the wound site. This whole-course-repair system provides a novel platform for combined DW therapy.

Novel regenerator design for caloric cycles using artificial neural network — Genetic algorithm method and additive manufacturing

The regenerator is a key component to determine the performance of the active regenerative caloric cycle. Although the geometry of the regenerator is an important factor, very limited geometries have been used in prototypes due to the limitations of conventional manufacturing. Therefore, this study proposed a new type of regenerator with a high heat transfer rate for the caloric cycle, which is a packed rod bed, using additive manufacturing. In order to ensure a systematic approach for the new design of the regenerator, a new design optimization using an artificial neural network — genetic algorithm with the help of computational fluid dynamics was introduced. Artificial neural network models were used to predict the j and f factors of the packed rod bed and showed a mean relative error of less than 2.0% for the j factor, and a mean relative error of less than 7.5% for the f factor. The accurate results of artificial neural networks contribute to improving the optimization process. The regenerator optimized through the artificial neural network — genetic algorithm method increased the system efficiency by 4.7% and the cooling capacity by 13.0% compared to the baseline caloric cycle using a parallel plate matrix. Considering that caloric cycles are still in the development stage due to the lack of performance of the magnetocaloric cycle, this eventually may contribute to the commercialization and energy saving of the magnetic refrigeration cycle while the design optimization might also help to improve the performance of other caloric cycles.

Clinical Pattern and Spectrum of Atypical Endometriosis: A Series of 5 Cases

Endometriosis refers to the extrauterine presence of hormonally active endometrial glands and stroma. This ectopic endometrial tissue exhibits cyclic bleeding, inflammation, fibrosis and leads to formation of adhesions. Endometriosis affects about 10% to 15% of women between 15 to 45 years of age. Clinical presentations vary from infertility, dysmenorrhoea, chronic pelvic pain, deep dyspareunia and even bleeding at external sites like the umbilicus. Besides involving fallopian tubes, bowel, liver, thorax, pericardium, pleura etc, the most commonly affected areas in the gastrointestinal tract are the descending colon, rectosigmoid, appendix, and ileo-caecum in descending order of frequency. This case series highlights some unusual presentations of endometriosis along with co-existence of other ovarian pathologies which are not frequently encountered in clinical practice. This series also highlights the role of preoperative radiology for an adequate clinical diagnosis and complete surgical excision.

A Comprehensive Comparative Analysis of Energetic and Exergetic Performance of Different Solar-Based Organic Rankine Cycles

In this work, a comprehensive energetic and exergetic comparative assessment is presented for the simple solar organic Rankine cycle (SORC), regenerative solar organic Rankine cycle (RORC), and dual-loop solar organic Rankine cycle (DORC), considering parameters such as the net power produced, exergy destruction, exergy, and energy efficiency in four zones located in Colombia due to their high solar irradiation potential. The energetic and exergetic balances were applied for each system component, using toluene as the working fluid. The RORC system showed a 2% increase in efficiency over the SORC, while the DORC cycle was lower than the SORC (45.85%) and RORC (46.90%) systems. Finally, for the exergy analysis, the results revealed that the SORC (5.3%) and RORC (5.2%) systems had the highest efficiency compared to DORC systems. Additionally, the highest exergy destruction (89%) was related to the collector, followed by the evaporators (1–2%), pumps (0.1%), and turbines (1.12%).

Comparative investigation of six layouts of S-CO2 cycles based on advanced exergy analysis

In the present research, a comparative and comprehensive investigation is performed on the six different layouts of the supercritical carbon dioxide cycle based on conventional and advanced exergy. The effect of different layouts on the exogenous exergy destruction of each component is also investigated in this study for the first time. Performing the advanced exergy analysis presents different priority suggestions from conventional exergy analysis to the improvement of components of each cycle. It is worth noting that the intercooling cycle has the lowest exergy destruction value among the other layouts. The reducible value of exergy destruction in the intercooling cycle, the pre-compression cycle, the recompression cycle, the dual regenerative cycle, the partial cooling cycle, and the simple regenerative cycle, according to the results of advanced exergy analysis, is 42.20 %, 49.49 %, 38.78 %, 37.77 %, 33.45 %, and 36.88 %, respectively. As a result, the pre-compression cycle offers the most possibility for development. The highest layout’s impact on the exogenous exergy destruction is related to the partial cooling cycle, followed by the recompression and intercooling cycles.

One-way heat exchange regenerative cooler: Principle, conceptual design and thermodynamic analysis

Distinctive characteristics of thermodynamic cycle consisting of two isochoric and two adiabatic processes have not been clarified and no specialized coolers have been developed for such cycle. In this work, the distinctive characteristics of such cycle were analyzed and obtained. Based on proposed concept of one-way heat exchange in oscillating flow’s heat exchangers, conceptual design of such cycle cooler was introduced. Then, both analytical and second-order models without considering losses of heat transfer and flow were developed to obtain the practicalcoefficient of performance (COP) for such cycle cooler at room temperature conditions. Also, COP of Stirling cooler and vapor compression refrigeration systems were investigated and obtained for comparisons. Degrees of thermodynamic perfection defined as the ratio of practical COP over ideal COP were employed for compatible performance comparisons between different coolers at various conditions. The results showed that the values for such cycle cooler were 54.1%∼84.6% for cooling and 60.8%∼89.7% for heating respectively. The values for Stirling cooler were 14.7%∼73.9% for cooling and 16.7%∼79.3% for heating respectively. And the values for R32 systems were 69.1%∼89% for cooling and 63.5%∼89.5% for heating respectively, while the values for R1234yf systems were 73.1% ∼85.9% for cooling and 66.4%∼86.2% for heating respectively. As there was temperature glide heat exchange in such cycle cooler, the values based on lowest cold temperature or highest hot temperature could be up to 90.3%∼99.4% and 91.9%∼99.4% for cooling and heating respectively. Thus, degrees of thermodynamic perfection show that the irreversibility in such cycle cooler over Stirling cooler is largely reduced. And it also indicates that such cycle coolers have huge potential as an alternative for vapor compression refrigeration systems.

Multi-objective design optimization of an integrated regenerative transcritical cycle considering sensitivity in Pareto-optimal solutions

Small modular nuclear reactors (SMRs) are an emerging technology with many potential benefits to cost, manufacturing, and safety over more traditional reactor designs. The NuScale Power Module (NPM) is a pressurized water SMR that uses natural convection to circulate its coolant. Variations of steam Rankine cycles have been the predominant design for power cycles in the nuclear energy space for decades, but ongoing research has suggested promising alternatives to be used in future designs. Previous works have suggested that a transcritical Rankine cycle with an organic working fluid like ethanol or methanol could have superior thermal efficiency compared to comparable steam Rankine cycles for mid-temperature applications. This study presents a design optimization and sensitivity analysis of an organic transcritical Rankine cycle (ORTC) with methanol as a working fluid, with a model of the NPM used as the primary cycle. Multi-objective optimization is used to analyze the trade-off between thermal efficiency and levelized cost of energy (LCOE) for this cycle design. All of the optimal designs identified in the multi-objective optimization show improvements in LCOE compared to the benchmark regenerative steam Rankine cycle at comparable thermal efficiencies, with LCOE being reduced by as much as 19.1% by using the ORTC. In the Pareto front, higher efficiency solutions use regenerative cycle designs, while lower LCOE solutions do not utilize regenerators. A sensitivity analysis of the optimal design points reveals that regenerative design points have greater sensitivity in both LCOE and thermal efficiency to the variation in the design parameters.

Thermodynamic analysis of combined cycle system based on supercritical CO2 cycle and gas turbine with reheat and recuperation

ABSTRACT The gas turbine combined cycle (GTCC) system has the advantages of high power density, high efficiency, and fast start-stop control, which will occupy an important position in the next-generation power system. In this paper, two groups of reheat cycle gas turbines with different thermal parameters are compared and the reheat and recuperative cycle is constructed by adding a recuperator to the recommended reheat cycle. Two typical sCO2 cycles are selected to construct a combined cycle system with simple cycle, reheat cycle, reheat, and recuperative cycle, respectively. In the range of gas turbine pressure ratio of 32–56, the parameters of GTCC with turbine inlet temperature of 1750°C are optimized based on the system calculation method of total physical properties, and the thermodynamic performance of the GTCC system was evaluated. The research shows that the reheat cycle with a TRIT (inlet temperature of the turbine after reheat) of 1250°C has higher efficiency and lower specific net work than the reheat cycle with a TRIT of 1750°C, and the relatively low exhaust temperature is more suitable for the sCO2 bottoming cycle. In addition, compared with the simple cycle, the optimal topping cycle thermal efficiency of the reheat and regenerative cycle is only reduced by 0.1%, but the exhaust temperature is higher. Under the same sCO2 cycle form, the combined cycle efficiency is improved by 1.5–2.0%. The thermal efficiency of the reheat and regenerative cycle gas turbine combined cycle (RCRHCC) studied in this paper can reach up to 67.53%, which has the potential to become the next generation of GTCC units.

Thermo-economic and environmental optimization using PSO of solar organic Rankine cycle with flat plate solar collector

The use of solar energy is considered a potential strategy for the production of electrical energy through thermal heat sources. This article portrays a study framed to be energetic, economic, and environmental fields. This study was carried out in two thermal configurations: the Regenerative Rankine Cycle (RORC) and the Simple Organic Rankine Cycle (SORC), which use solar energy to supply electrical power to a building. The thermodynamic and economic models were proposed for each subsystem of the thermal process, allowing hourly simulations to know the economic indicators such as the payback period (PBP), the levelized cost of energy (LCOE), the specific investment cost (SIC), and the initial investment cost (CInv). The effect of operational variables such as the pressure ratio (rp), the evaporator pinch point temperature (Ap), the condensation pinch point temperature (Tcond), and the solar collector area (Ac) on the Relative Annual Benefit (RAB) were studied. Finally, the Particle Swarm Optimization (PSO) algorithm was implemented to optimize the economic indicators and the environmental impact of the thermal configurations. Results showed that the RORC configuration presented a better performance in terms of generation, purchase, and hourly sale of energy. However, in terms of RAB, the SORC (39,833 USD/year) showed better results in contrast to the RORC (39,604 USD/year) for an evaporator pinch point temperature of 35 °C. Finally, the application of the PSO optimization algorithm allowed the reduction of the LCOE (11.64%), SIC (11.67%), and PBP (11.81%) thermo-economic indicators from the base condition for the SORC, and the reductions obtained in the RORC were LCOE (18.11%), SIC (10.67%), and PBP (11.11%). However, the decrease in environmental Impact for both systems was less than 1% as a consequence of the high contribution of thermal oil in the construction phase of the system.

Proposal and application of supercritical steam Rankine cycle using supercritical reheating regeneration process and its comparison between S-CO2 Brayton cycle

Compared with the steam Rankine cycle, high efficiency is one of the core advantages of the supercritical carbon dioxide (S-CO2) Brayton cycle. However, the steam Rankine cycle still has the possibility of breaking its efficiency limit. This paper originally proposes the supercritical reheating regeneration process and constructed the supercritical regenerative Rankine cycle. It's found that the supercritical regeneration process can not only heat the feedwater, but also heat the reheated steam. then the thermal efficiency of the Rankine cycle can be further increased. Meanwhile, under the framework of the Carnot cycle, the average temperature at which heat is added (Tave,h) and the average temperature at which heat is rejected (Tave,c) are set as the optimization value, to perform a comparative study between the S-CO2 Brayton cycle and the supercritical steam Rankine cycle. Through analysis, by applying the supercritical regeneration process, Tave,h of the Rankine cycle is significantly increased. It can reach or exceed Tave,h of the S-CO2 cycle. Meanwhile, the heat-rejection process in the condenser of the Rankine cycle is the isothermal process, and its Tave,c is significantly lower than that of the Brayton cycle, which is a non-isothermal heat rejection process. Thus, the thermal efficiency of the steam Rankine cycle can surpass the S-CO2 cycle. When the turbine inlet parameter is 30 MPa/620 °C, the thermal efficiency and average temperature at which heat is added are 55.65 % and 573.6 °C for RRRC + RH and 54.72 % and 568.8 °C for TC + RH, respectively. Based on the supercritical regeneration process, the Rankine cycle overcomes the existing efficiency bottleneck, and has the potential to surpass the thermal efficiency of the S-CO2 cycle.

Design and numerical simulation of radial inflow turbine of the regenerative Brayton cycle using supercritical carbon dioxide

Carbon dioxide is abundant on earth and has a high density in the supercritical phase so that the turbomachinery size can be small. Thus the turbine, compressor, and alternator can be made compact. The advantage of the Brayton Cycle is using a regenerator on the exit side of the turbine for heat recovery. The S–CO2 radial inflow turbine is suitable for systems ranging from 0.1 MW to 25 MW. Turbomachinery can have high power densities for smaller-scale energy generation because to the low flow rates of the high-density working fluids. Small-modular heliostat fields, thermal storage, and radial inflow turbines with a power output of around 1 MW are appropriate for solar base-load energy systems in rural and isolated places, particularly in Indonesia. However, the experimental research is costly, time-consuming, and may pose security threats, whereas CFD modeling improves the design process and greatly saves time and money.This study aims to design a radial inflow turbine for the Regenerative Brayton Cycle. The turbine has designed to work at 70,000 RPM with a net power target of 40 kW. Regenerative Brayton Cycle with supercritical carbon dioxide working fluid (S–CO2) designed for turbine inlet temperature is 800 K, the compressor inlet temperature is 320 K, and the pressure ratio in turbine 1.63. Based on the cycle's design, the turbine and compressor powers are 113.84 kW and 60.53 kW, respectively. The geometric design has been carried out with an approach by some of the literature related to this research. Computational Fluid Dynamics (CFD) simulations are then performed on the results of the design of the turbine. The CFD simulation results of the radial inflow turbine show that can produced is 113.28 kW, and the total to total turbine efficiency is 81.63% at 70,000 RPM and 2.0 kg/s. However, in this study the turbine's design is targeted in around 40 kW. So, according to CFD simulation results, the net power and the efficiency of the Brayton cycle generated is 53.75 kW and 18.74%, respectively.

Energy and Exergy Analysis of a Geothermal Sourced Multigeneration System for Sustainable City

The issue of depleting fossil fuels has emphasized the use of renewable energy. Multigeneration systems fueled by renewables such as geothermal, biomass, solar, etc., have proven to be cutting-edge technologies for the production of different valuable by-products. This study proposes a multigeneration system using a geothermal source of energy. The main outputs include power, space heating, cooling, fresh and hot water, dry air, and hydrogen. The system includes a regenerative Rankine cycle, a double effect absorption cycle and a double flash desalination cycle. A significant amount of electrical power, hydrogen and fresh water is generated, which can be used for commercial or domestic purposes. The power output is 103 MW. The thermal efficiency is 24.42%, while energetic and exergetic efficiencies are 54.22% and 38.96%, respectively. The COPen is found to be 1.836, and the COPex is found to be 1.678. The hydrogen and fresh water are produced at a rate of 0.1266 kg/s and 37.6 kg/s, respectively.

Thermal convective effect on the performance of thermally regenerative electrochemical cycle against self-discharge

The effect of convective heat transfer on low-grade heat recovery in thermally regenerative electrochemical cycles (TRECs), which were operated on the basis of electric double-layer capacitors, was investigated at varying flow rates of fluid flowing from thermal reservoirs. Although the TREC performance is primarily determined by the magnitude of an open-circuit voltage rise driven by a temperature difference, it can be significantly restricted by spontaneous charge losses due to self-discharge. To investigate the convective heat transfer effect against self-discharge, cycle performance was evaluated through experiments at flow rates ranging from 56 to 184 mL/min, and further estimated at extended lower flow rates to 14 mL/min through numerical calculations. When TRECs were operated between 20 and 60 °C, the highest net work was obtained to be 81.3 μJ at 184 mL/min, corresponding to 34 % conversion efficiency relative to the Carnot efficiency. Unlike the high flow rate conditions, the TREC performance below 56 mL/min significantly decreased with reduced the flow rate due to the considerable charge loss by self-discharge. This shows the stronger flow dependence of the TREC performance. This study provides a novel approach to estimate energy loss through a time constant analysis, thereby enabling better TREC designs concerning energy efficiency.