Reverse Brayton Cycle Research Articles

Thermodynamic analysis of a solar-fed heat upgrade system using the reverse air brayton cycle

This analysis focuses on exploiting solar energy to meet industrial energy needs. It is based on upgrading solar heat production using surplus electricity from renewables to generate high-temperature industrial process heat. The approach involves the use of efficient evacuated flat plate solar thermal collectors coupled with a thermal storage tank to power a reverse air Brayton heat pump for high-temperature heat production. A Matlab algorithm has been developed to dynamically analyse energy balances across the system. The analysis is conducted for the location of Komotini, Greece and the results regard the operation of a system for a typical summer week. For the baseline design point with a 1000 m2 collecting area and 50 m3 thermal tank volume, the average daily process heat production for the industry is 8.63 MWh, while the average daily coefficient of performance (COP) for the heat pump is 1.478. Moreover, the present work includes results regarding the parametric performance of the system for different combinations of collecting area and thermal tank volume. It was demonstrated that with the optimization of the solar thermal collector area and thermal tank volume, the daily average COP can be increased up to 23.1 %. Finally, the influence of the units of transfer area of the heat exchangers on the coefficient of performance has been investigated.

Design And Testing of a Compact, Reverse Brayton Cycle, Air (R729) Cooling Machine

Design And Testing of a Compact, Reverse Brayton Cycle, Air (R729) Cooling Machine

Analysis of the thermodynamic performance of the SOFC-GT system integrated solar energy based on reverse Brayton cycle

Efficient power generation systems are an essential way to reduce carbon emissions. To avoid the complex effects of high-pressure conditions on the solid oxide fuel cell (SOFC) and gas turbine (GT) hybrid systems, while further improving energy efficiency. A SOFC-GT hybrid system based on the reverse Brayton cycle (RBC) is proposed, in which the SOFC operates at near atmospheric pressure conditions and GT expands below atmospheric pressure. Solar energy is integrated to further enhance system performance. Rigorous assessments of the novel system and the pressurized system are conducted utilizing energy, exergy and economic analysis. The sensitivity analysis of environmental parameters on the novel system's performance is performed. The results show that the novel system generates power and efficiency better than the conventional system when the GT compression ratio is 3 and 6, respectively. The power generation and exergy efficiency of the novel system at the design point is 60.47 % and 58.57 %, respectively. The largest exergy destruction occurred in the SOFC. The lowest exergy efficient components are the parabolic dish collector (PDC) and heat exchanger 2. The novel system is more cost-effective due to the higher lifetime of the SOFC, with the levelized cost of energy (LCOE) is 0.1418 $/kWh.

Experimental COP optimization procedure in an air-based reverse Brayton cycle for cryogenic applications

Sustainable and efficient refrigerants are essential due to increasing regulatory constraints on traditional high-GWP refrigerants. This study investigates the potential of natural refrigerants, specifically air, in Reverse Brayton Cycles (RBC) for low-temperature applications. Unlike carbon dioxide and ammonia, which pose limitations and safety concerns below -40°C, air offers a safer and more versatile solution due to its excellent thermodynamic properties and availability. An experimental RBC was constructed using automotive components like centrifugal compressors, a radial turbine, and inter-coolers. These cost-effective and accessible components shift the refrigeration paradigm. The RBC was tested to optimize the Coefficient of Performance (COP) at -100°C while dissipating 2 kW, a typical scenario for whole-body cryotherapy (WBC). Key control parameters included the pressure ratio of the centrifugal compressors and the position of the stator vanes in the variable geometry turbine (VGT). The optimization process resulted in a COP increase of up to 28%. Additionally, a 1D gas-dynamic model validated these results, suggesting that different component selections could enhance performance by 17% compared to the experimental optimum point. Air-based RBC systems using automotive components can effectively achieve temperatures below -40°C, offering a viable, eco-friendly alternative to traditional refrigerants. This advancement addresses regulatory challenges and contributes to the scientific community by providing a sustainable refrigeration solution using commercially available components and demonstrating improvements through experimental data.

Thermoeconomic analysis of novel hydrogen liquefaction assisted by absorption refrigeration utilizing heat from Brayton cycle

Abstract Current research presents a novel method for reducing the energy consumption of hydrogen liquefaction through heat recovery of hydrogen liquefier. An ammonia absorption refrigeration cycle on the hydrogen precooling utilizes the heat generated by the compressor intercooler and aftercooler of the reverse Brayton cycle of hydrogen liquefier to precool hydrogen feedstock. The system is analyzed from exergy, energy, and economic perspective. The results are compared with the reference case without a heat recovery system. The proposed system can reduce SEC (specific energy consumption) from 7.37 kWh/kgLH2 to 6.23 kWh/kgLH2 and exergy efficiency improvement from 55.2% to 60.90%. The economic analysis shows that the levelized cost of energy to produce 5.07 tons/day of liquid hydrogen for the reference and novel case is 5.88 USD/kgLH2 and 5.03 USD/kgLH2, respectively. The results imply that the proposed method can be a reference for designing an integrated hydrogen liquefaction system to minimize energy consumption.

A design method of turboexpander-compressors based on multi-objective optimization applied to reverse brayton cycle

This paper presents a new design method for turboexpander-compressors used in air refrigeration. As a key component of the reverse Brayton cycle, the efficiency of the turboexpander-compressor significantly has an impact on the overall cycle performance. The expander section is optimized for multi-objective efficiency at different flow rates using the Imperialist Competitive Algorithm to achieve high performance across all operating conditions. Regarding achieving high utilization efficiency for output power from efficient expanders, the compressor section adopts combined methods involving the jet-wake model and parameter equations. The proposed design is validated through public models, computational fluid dynamics simulations and experiments. Simulations and analysis are conducted on test cases representing comprehensive operational scenarios for both the compressor and the expander, confirming that conclusions drawn based on this method align well with underlying theoretical principles. At the design mass flow, the expander efficiency is 89%, and the compressor utilizes the output power of the expander with an efficiency of 90%. Near the design flow, the expander efficiency is more than 85%, and the compressor utilizes the output power of the expander with an efficiency exceeding 80%. This paper presents a method for turboexpander-compressors applicable to air refrigeration cycles, which achieves a reduction in design costs and an improvement in efficiency under varying loads.

Evaluation of the high-robustness nuclear power cycle against lunar surface environmental threat

Heat sinks exposed to the lunar surface environment cause fluctuations in the energy cycle due to variations in lunar thermal conditions, leading to non-design operations of the energy system. Such suboptimal operations decrease energy efficiency and shorten the lifespan of system components. This paper introduces an innovative design for a highly robust lunar nuclear power cycle that mitigates environmental threats on the lunar surface. A reverse closed Brayton cycle increases the waste heat discharge temperature. Higher waste heat temperatures allow the heat sink panels to have greater heat radiation per unit area, countering the negative disturbances from lunar environmental changes on the energy system. Under the dual threats of lunar dust toxicity and intense solar radiation, the output reduction of this robust nuclear cycle is only 0.96% that of traditional nuclear power cycles with the same thermoelectric parameters. Moreover, even under severe environmental threats, the power quality of this robust nuclear cycle remains 10.8 times better than that of conventional designs with the same nighttime output design baseline. In conclusion, employing a reverse Brayton cycle to increase waste heat emission temperature effectively enhances the robustness of the nuclear power cycle. This paper proposes a new nuclear thermoelectric system framework to withstand threats from the lunar surface environment.

Thermal Performance Design and Analysis of Reversed Brayton Cycle Heat Pumps for High-Temperature Heat Supply

This study examined the performance of reversed Brayton cycle heat pumps to supply heat above 300 °C. The aim was to overcome the current temperature limitations faced by heat pump technology in industrial heat supply sectors by examining the viability of the reversed Brayton cycle. In particular, the effects of the operating conditions on the cycle performance, such as the waste and return heat temperatures, were analyzed through thermal performance analysis. The reversed Brayton cycle heat pumps showed improved performance over conventional vapor compression cycle heat pumps when a heat supply above 215 °C was required. Furthermore, integrating additional heat exchangers into the cycle configuration was proposed in this study as a method to enhance waste heat utilization and recover unused heat from industrial processes. By incorporating preheating and recuperated cycles, these modifications broaden the operational range under the same operating conditions. They also improve the coefficient of performance (COP) of the reference cycle by up to 23% and 27.4%, respectively. This study explored the potential of reversed Brayton cycle heat pumps to supply heat above 300 °C and provided fundamental guidelines for the efficient design and operation of reversed Brayton cycle heat pumps. The results are expected to enhance our understanding of the performance characteristics of reversed Brayton cycle heat pump technology and expand its use as an alternative to fossil-fuel-based heat supply systems.

Utilizing Reversed Brayton Cycle for Enhanced Cooling Tower Technology

This study demonstrates an enhanced cooling tower technology (ECTT) under which the ambient air is precooled and dehumidified to improve the cooling tower efficiency. The reverse Brayton cycle, comprising a compressor, an air cooler, an expander, and a heat and mass exchanger, is used to precondition the ambient air before entering the cooling tower. A plant-scale thermodynamic model is constructed for ECTT, and the system parameters are optimized through genetic algorithm based on the maximum power gained from the system, including the effects of reducing the makeup water for the cooling tower. Compared to conventional cooling towers, the ECTT achieved sub-wet bulb cooling of water, which is 9.5 °C below the wet bulb temperature of ambient air, reduces steam condensation temperature by 34%, and increases steam turbine power output by 4.3%. It also reduces evaporative losses in the cooling tower and reduces the makeup water by 36%. With cooling tower exhaust recirculated in a closed loop, makeup water requirements are further reduced with additional gains in power output.

The design and research of two-stage series-connected helium turbine expanders for hydrogen liquefaction system

The helium turbine expander, is a crucial part of hydrogen liquefaction systems, that determines the overall efficiency of the system. In this paper, a two-stage series-connected helium turbine expanders is designed to achieve a hydrogen liquefaction capacity of 1.7 tonnes per day (TPD). The proposed expander is based on the reverse Brayton cycle and realizes a high pressure ratio of 8.32 to meet the design objective. A dynamic design process in the expansion end is developed and numerically simulated based on the turbine expander design methodology. The off-rated condition performance of the turbine expander is predicted by adjusting the rotational speed and flow rate. The results show that the reasonable rotational speed range of the turbine expander is 46000–54000 RPM, and the reasonable flow coefficient range is 0.6–1.2, which can maintain a high level of efficiency. The internal flow characteristics of the turbine expander are analysed through numerical simulation. The results show that the outlet temperature is suitable for hydrogen liquefaction, and flow loss mainly occurs in the upper-middle part of the impeller and near the tip clearance, followed by the throat of the nozzle. In the prototype tests to verify the rationality of the design of the turbine expanders, the experimental results show that the two turbine expanders can achieve a temperature drop of 31 K, and isentropic efficiencies of 76.8 % and 80.5 %, respectively, which are higher than the design requirements of 75 %. The actual outlet temperature and isentropic efficiency are compared with the numerical simulation results. The errors are less than 4 % and 10 %, respectively, which means that the prototype manufacturing precision meets the system requirements perfectly. Thus, the design of the two-stage series-connected turbine expanders can satisfy the performance design requirements.

Small-scale industrial hydrogen liquefaction and refrigeration

As the hydrogen economy expands, the need for point of use production with smaller liquid hydrogen (LH2) production capacities will increase. Examples of this are transportation hubs in remote locations and numerous other applications where the required LH2 production is less than 5 MT/day. In response to this need, a small-scale industrial 1,000 kg/day hydrogen liquefaction plant is being developed and is planned for operation in 2024. The plant will achieve localized, efficient production, on-demand, in remote locations or any location advantageous for use in transportation, where complicated logistics, with associated transportation costs and tanker evaporative losses are eliminated or minimized. The chief advantages of the design are small size/footprint, safety, reliability, low cost, lack of restrictions on site location, and ability to make practical use of renewable energy. The liquefaction plant utilizes a closed-loop helium reverse-Brayton cycle refrigerator where refrigerant temperatures significantly less than the hydrogen liquefaction temperature cause the hydrogen gas stream to be liquefied. The liquefied hydrogen is maintained in the liquid state via a helium side stream taken from the refrigeration loop routed through the LH2 storage tank. This optional system can maintain LH2 temperatures in the storage tank lower than 18 K to eliminate boiloff and facilitate zero loss transload from tanker trucks and eliminate losses in transfer/dispensing. The hydrogen liquefaction plant does not require liquid nitrogen (LN2) pre-cooling and so can be located in remote areas wherever there is 480 V electricity and hydrogen production capacity available. A slightly modified reverse-Brayton cycle is also used in the refrigeration/storage plants. These plants can facilitate zero loss tanker transload and zero boiloff for LH2 storage plants of virtually any capacity. The smallest of these reverse-Brayton cycle refrigerators, currently in detailed design, refrigeration system RS1500 (1000 W heat lift @ 20K) will be capable of eliminating boiloff losses of the largest storage tanks currently in operation with very low electrical energy consumption.

A compression-free re-liquefication process of LNG boil-off gas using LNG cold energy

Re-liquefying boil-off gas (BOG) of LNG is of great significance for energy conservation and environmental protection. BOG is usually compressed before being liquefied with nitrogen reverse Brayton cycle, which makes the system's capital investment and energy consumption high. A novel compression-free re-liquefication process of BOG using liquid nitrogen (LN2) is proposed. BOG is liquefied with latent heat of LN2, reducing the heat-transfer temperature difference in BOG condenser and the required amount of refrigerant. LN2 is produced using LNG pre-cooled Joule-Thomson cycle. Overall optimization is performed using genetic algorithm. Thermodynamic, economic, and environmental assessments are conducted based on the optimized results. Sensitivity analysis of the principal design parameters is performed. It is found that the proposed process is significantly profitable because it fully utilizes the cold energy of LNG and LN2 and eliminates the required cost for BOG compressor, turbine expander, and LNG regasification process. The minimum specific energy consumption of 0.74 kWh·kg−1 is achieved, and the figure of merit is up to 34.95%. The payback period of total capital investment is only one month. Carbon dioxide emission is reduced by 36242.66 kg·h−1 compared to the direct emission of BOG. Pinch temperature difference of 3∼5 °C is recommended for cryogenic heat exchangers.

Optimization of coalbed methane liquefaction process based on parallel nitrogen reverse Brayton cycle under varying methane contents and liquefaction ratios

The recovery of coalbed methane (CBM) is of significance in preventing coal mining accidents, environmental protection, and energy conservation. Liquefying natural gas purified from CBM, as an efficient storage and transportation technology, provides a convenient way to get CBM products. A CBM liquefaction process based on parallel N2-RBC is investigated to explore the technical feasibility of purifying liquefied natural gas (LNG) from CBM solely through a liquefication process. Sensitivity analysis was conducted to explore the impacts of design parameters on system performance, followed by a global optimization using a genetic algorithm under varying methane contents and liquefaction ratios. Analysis of the optimized results revealed that the specific energy consumption (SEC) and refrigerant flow rate decrease as the discharge pressure of the refrigerant compressor increases, and the decline rate slows down when it exceeds 3000 kPa. SEC decreases with a rise in methane content in CBM, and the decline rate accelerates when methane content in CBM exceeds 60%. SEC and methane recovery rate increase with an increment in liquefaction ratio, while methane concentration in the liquid product decreases. LNG can be feasibly extracted from CBM containing methane content exceeding 70% solely through a liquefaction process while maintaining an acceptable methane recovery rate and SEC.

Optimization of a Reverse-Brayton cycle with inter-cooling and regeneration

A Reverse-Brayton cycle represented by the B787 electrical driven environmental control system is used as the analysis object, including the thermodynamic process of two-stage compression, intercooling, and regeneration. An analytical expression for the thermodynamic performance of the cycle is derived based on the endoreversible thermodynamic analysis model (ETM). Combined with a genetic algorithm, an ETM-based optimization approach (ETM-OA) is proposed. Using this method, it is found that the coefficient of performance is increased by 34.1 % and 48.4 % under two typical flight conditions, respectively, and the corresponding system entropy generation number is reduced by 30.2 % and 51.1 %, respectively. Both ETM-OA and entropy generation analysis show that the electric supercharging module, secondary heat exchanger, and air cycle machine are key components of the system. This study provides a convenient method for obtaining the thermal power conversion mechanism of complex thermal cycles and conducting optimization analysis.

Advanced exergy analysis of a Reverse Brayton cycle using air as working fluid for cryogenic purposes

The global push to reduce greenhouse gas emissions has led to the ban of high global warming potential (GWP) refrigerants in the refrigeration sector, prompting the adoption of low-GWP alternatives. However, as regulations are expected to tighten, technologies like the Reverse Brayton cycles (RBC) are emerging. RBCs can operate with safe fluids and can reach very low temperatures through compressions, regeneration, and expansion, requiring only electricity. This research presents results from an RBC equipped with a radial turbine using natural air (R-729), a hazard-free fluid with zero ozone depletion potential (ODP) and emission potential. The cycle utilizes automotive components, offering a cost-effective, high-tech solution. The study evaluates the cycle COP at a design point and performs an exergetic analysis at 173K. Using a thermal and fluid dynamic model of the cycle, the critical components of the cycle influencing the COP are identified, and potential improvements are explored.

Energy, exergy, economic and environmental (4E) analysis of two-stage cascade, Linder-Hampson and reverse Brayton systems in the temperature range from −120 °C to −60 °C

Cryopreservation in the temperature range from −120 °C to −60 °C is an important way to achieve high-quality food storage. In this paper, an in-depth quantitative thermodynamic comparison of two-stage cascade cycle, Linde-Hampson cycle and reverse Brayton cycle was carried out in the temperature range from −120 °C to −60 °C. Aspen HYSYS was used to invoke advanced genetic algorithm in MATLAB to optimize the system parameters. The two-stage cascade system performs best at the evaporation temperatures above −80 °C, achieving a COP of 0.97 at −60 °C. The Linder-Hampson system performs best when the evaporation temperature is below −90 °C, achieving a COP of 0.35 at −120 °C. In order to further explore the impact of environmental change on the system performance, five typical cities in China were selected to analyze the seasonal performances of the three systems. The seasonal analysis demonstrated that Harbin has the highest latitude and its seasonal energy efficiency ratio is significantly higher than other cities, the performance of the two-stage cascade system fluctuates more obvious within 24-h. What's more, the Linder-Hampson system has the lowest annual investment cost and annual operating cost at the evaporation temperature lower than −90 °C, as well as the lowest emissions of CO2 and SO2.

Experimental investigation on a closed-cycle single-stage turbo-refrigerator for deep freezing

Turbo-refrigerator based on reverse Brayton cycle is an attractive solution for providing refrigeration at ultra-low temperatures below −60 °C for deep freezing. Employing a motor-driven turboexpander compressor (MTEC) not only allows the turbo-refrigerator to achieve high compactness, reliability and flexibility, but also leads to new operating characteristics especially in a closed cycle. This paper aims to investigate the operating characteristics of a closed-cycle single-stage turbo-refrigerator with a MTEC. A high-speed turbo-refrigerator system with the design refrigeration temperature of −86 °C was manufactured and then tested under variable rotating speeds and refrigeration conditions. Test results show that a refrigeration temperature below −96.4 °C was obtained in a pull-down progress. Compared with a fixed-speed operation, variable-speed operation enables the independent control of the refrigeration temperature and the cooling capacity. With the decrease in the refrigeration temperature (or in the cooling capacity), the rotating speed has a greater effect on the COP than that on the cooling capacity (or on the refrigeration temperature). The mass flow rate along with the compression and expansion work shows a decreasing trend as the refrigeration temperature decreases at a fixed speed of the MTEC. The advanced exergy analysis shows a total exergy efficiency of 0.42 (with a COP of 0.62 at refrigeration temperature of −86 °C) could be expected with component improvement in the near future, and it is of the priority to increase the efficiency of the turboexpander.

A novel small-scale biomethane liquefaction process: Assessment through a detailed theoretical analysis

The use of biomethane as fuel in the transport and power generation sectors is widely considered an effective tool to pursue the goals of carbon neutrality and energy security. Therefore, it is very important to promote not only the production and upgrading processes of biomethane from carbon neutral biomass, but also biomethane liquefaction processes, which can allow effective transportation of biomethane, thanks to the fact that the density of the liquid is higher than that of the compressed gas. Biomethane liquefaction plants can benefit from the technologies already used for the liquefaction of natural gas, but the size of biomethane liquefaction plants must be significantly smaller because of the limited quantities of biomethane generated by production and upgrading plants. Biomethane liquefaction plants have still limited diffusion; the most used technologies for the biomethane liquefaction are the Reverse Brayton cycle, the Lynde cycle, and the heat exchange with liquid Nitrogen. Single mixed refrigerant (SMR) processes, which are very effective for the liquefaction of natural gas, have a high potential for the biomethane liquefaction too, but the high specific energy consumption and high plant costs (mainly caused by typical multi-flow heat exchangers employed) are the major issues associated with SMR processes when applied to the very small size of biomethane liquefaction plants, characterised by very low biomethane flow rates. The aim of this paper is to propose a novel SMR process for biomethane liquefaction, which can overcome the above-mentioned issues, contributing towards the implementation of SMR processes for the liquefaction of biomethane and providing a valid alternative to currently used biomethane liquefaction plants; the proposed solution consists in using simple pipe-in-pipe heat exchangers in place of the more complex multi-flow heat exchangers. The validity of this solution is theoretically assessed using a detailed thermodynamic model based on well-stablished equations. Using this tool, it is shown that, by adjusting crucial parameters, such as the molar composition of the refrigerant, the heat exchange is satisfied with an affordable length of the heat exchangers, negligible pressure drops and good levels of the coefficient of performance with reference to such a small-scale application. The predicted specific energy consumption (accounting also for the biomethane compression and pre-cooling) for a biomethane flow rate of 0.03 kg/s is of the order of 0.8 kWh/kgCH4, which is a very good performance level compared to current commercial biomethane liquefaction processes.

Techno-economic analysis on nitrogen reverse Brayton cycles for efficient coalbed methane liquefaction process

Recovery of coalbed methane (CBM) is of great significance for environmental protection, safe production of coal mines, and clean energy supply. To reveal the efficiency difference of different nitrogen reverse Brayton cycles (N2-RBC) for recovering CBM and identify the most efficient N2-RBC in terms of energy consumption and economy, four typical N2-RBCs were studied numerically. Each process was optimized globally by performing genetic algorithm (GA) procedure, using specific power consumption (SPC) per unit product as the objective function. Pinch analysis approach was used to improve N2-RBC. All proposed processes were assessed comprehensively concerning efficiency, exergy loss, and economy. It is found that the slope of the hot/cold composite curve is greatly influenced by the material streams’ mass flow rate while slightly affected by the specific heat except for the region near critical parameters. The parallel arrangement of expanders reaches a better match between hot and cold composite curves than the series. For the liquefaction capacity of 10 tons per day, the liquefaction process using parallel N2-RBC achieves the lowest SPC of 0.72 kWh·kg−1 and the highest figure of merit of 31.11%. It also has the lowest exergy loss of 180.1 kW and a total investment of 4047.76 k$, respectively.

Process design of advanced LNG subcooling system combined with a mixed refrigerant cycle

LNG subcooling system is a conventional system to keep the pressure of an LNG storage tank for LNG carriers, but has a weak point of the low efficiency resulting in a new BOG reliquefaction system. This study suggests a new LNG subcooling system combined with mixed refrigerant cycle (MR-SLNG), which can increase efficiency significantly. The results show the coefficient of performance (COP) of the system becomes 2.5 times higher than that of the conventional LNG subcooling system based on a reverse Brayton cycle (RBC-SLNG). Additionally, MR-SLNG can be a compact system because the volumetric flowrate of the refrigerant compressor decreased to 8.9%, which brings additional benefits to the ship design.