Brayton Refrigeration Cycle Research Articles

Thermodynamic and technoeconomic limitations of Brayton refrigeration for air conditioning{fr}Limites thermodynamiques et technoéconomiques de la réfrigération Brayton pour la climatisation

With global cooling demand increasing, there is a need for refrigeration cycles that use low global warming potential (GWP) refrigerants. Researchers have flirted with the idea of using the Brayton cycle for refrigeration over the years, but it has yet to prove competitive in performance or cost when compared to the widely used vapor compression cycle. The recent development of an electrochemical Brayton refrigeration cycle has renewed interest in the thermodynamics of Brayton refrigeration. This work provides a parametric study of the COP of a Brayton cycle air conditioner (either mechanical or electrochemical in nature) as a function of the characteristics of the cycle components (thermal conductances and isentropic efficiencies). When the isentropic efficiencies of the adiabatic components (i.e., the compressor and turbine in the mechanical Brayton cycle) are 90%, the cycle COP is limited to a value of ∼1. Furthermore, a thermodynamic comparison to the vapor compression cycle reveals that the Brayton refrigeration cycle generates ∼8 × more entropy, and that the thermodynamic favorability of the vapor compression cycle is due to the presence of phase change.

Device Model for a Solid‐State Barocaloric Refrigerator

Solid‐state refrigeration represents a promising alternative to vapor compression cooling systems. Solid‐state devices based on magnetocaloric, electrocaloric, and elastocaloric effects have demonstrated the ability to achieve high‐efficiency, reliable, and environment‐friendly refrigeration. Cooling devices based on the barocaloric (BC) effect—entropy change due to applied hydrostatic pressure, however, has not yet been realized despite the significant promise shown in material‐level studies. As a step toward demonstrating a practical cooling system, this work presents a thermodynamic and heat transfer model for a BC refrigerator The model simulates transient thermal transport within the solid refrigerant and heat exchange with hot and cold thermal reservoirs during reversed Brayton refrigeration cycle operation. The model is used to evaluate the specific cooling power (SCP) and coefficient of performance (COP) of the device comprising nitrile butadiene rubber (NBR) as a representative BC refrigerant. Experimentally validated BC properties of NBR are used to quantify the contribution of different operating parameters including cycle frequency, applied pressure, operating temperatures, and heat transfer coefficient. The results show that a BC refrigerator operating with a temperature span of 2.4 K and 0.1 GPa applied pressure can achieve an SCP of 0.024 W g−1 at 10 mHz cycle frequency and a COP as high as 5.5 at 1 mHz cycle frequency—exceeding that of conventional vapor compression refrigerators. In addition, to identify key refrigerant properties, the effect of bulk modulus, thermal expansion coefficient, heat capacity, and thermal conductivity on device performance are quantified. The results highlight the trade‐off between different material properties to maximize the BC response, while minimizing mechanical work and improving thermal transport. This work demonstrates the promise of solid‐state cooling devices based on soft BC materials and provides a framework to quantify its performance at the device‐level.

Comparative energy and exergy analysis of ortho-para hydrogen and non-ortho-para hydrogen conversion in hydrogen liquefaction

This study reports the comparative energy and exergy analysis of ortho-para hydrogen and non-ortho-para hydrogen conversion in hydrogen liquefaction process. Two cases were simulated, case A – hydrogen liquefaction with ortho-parahydrogen conversion and case B – hydrogen liquefaction without ortho-parahydrogen conversion. This is the first study that presents a comparative energy and exergy analysis between such two cases. In this research, a hydrogen liquefaction process was designed adopting cascaded five-stage Brayton refrigeration cycle. The process was simulated in Aspen PLUS. The process used a mixed refrigerant (of liquefied natural gas) refrigeration cycle to precool the gaseous hydrogen feed from 26 °C temperature to −192 °C temperature, and mixed refrigerant (of nelium) was subsequently used to further deep-cool the the hydrogen stream from −192 °C temperature to −245.99 °C temperature in the cryogenic section of the process. Liquefaction was achieved by expanding the hydrogen through Joule-Thomson valve at −248.37 °C and 1 bar. The simulated results of the two cases showed the specific energy consumption of case A to be 8.45 kWhr/kgLH, and that of case B to be 15.65 kWhr/kgLH respectively. The results also indicated a total exergy efficiency of 92.42% in case A and 87.18% in case B. The research results showed that the hydrogen liquefaction designed with configuration of ortho-parahydrogen conversion has better performance indicators than the liquefaction without ortho-parahydrogen conversion. Therefore, hydrogen liquefaction with ortho-parahydrogen conversion can be considered in the design and development of new hydrogen liquefaction plants. Process optimization is recommended to further enhance the specific energy consumption and exergy efficiency of both processes.

Exergetic efficiency and exergy-based ecological function performance optimizations for two irreversible simple Brayton refrigeration cycle models

Air (Brayton) refrigerator has some application potentials nowadays. Based on two irreversible models of constant- and variable-temperature heat reservoir simple Brayton refrigerators established in previous references, this paper further derives exergetic efficiencies and ecological functions, and provide exergy-based comprehensive comparative analyses and optimizations for the two cycle models. Comparative studies among coefficient of performance (COP), cooling load, exergetic efficiency and ecological function characteristics are performed, including general performance analyses for fixed effectivenesses of heat exchangers and performance optimization by optimizing heat conductance distribution and optimizing heat capacity rate marching between heat-reservoir and working substance. For constant-temperature heat reservoir cycle, when select optimal pressure ratio, exergetic efficiency indicator is more reasonable than cooling load and ecological function indicators. When optimizing heat conductance distribution, cooling load indicator is almost the same as exergetic efficiency indictor. For variable-temperature heat reservoir cycle, the reasonable range of pressure ratio is that slightly larger than optimal one at maximum COP. For fixed pressure ratio, the difference between two optimal heat conductance distributions corresponding maximum cooling load and maximum exergetic efficiency is small. Various fixed design parameters have their influence features on the general performances and optimal performances of the cycle models, they should be considered specifically and pointedly. The major difference comparing with classical thermodynamic analysis is the consideration of heat-transfer loss in heat exchangers herein.

An energy-saving hydrogen liquefaction process with efficient utilization of liquefied natural gas cold energy

Storage and transportation of hydrogen in liquid form offers considerable advantages, but the high energy consumption of hydrogen liquefaction processes needs to be addressed. In this study, a novel hydrogen liquefaction process integrated with a dual-pressure organic Rankine cycle (DORC) is proposed. It offers significant energy-saving by efficiently utilizing the cold energy of liquefied natural gas (LNG). The key parameters in the proposed process are investigated, and the results are combined with an improved genetic algorithm for efficient optimization of the process. The optimal exergy efficiency of the proposed process is 48.7%, and the minimal energy consumption is 6.29 kWh/kgLH2. Thanks to the power output (381.3 kW) of the DORC and the energy saved by the cryogenic compression of nitrogen (586.6 kW), energy consumption of the proposed process is reduced by approximately 3.1% compared to that of the process without a DORC. Moreover, an improved helium Brayton refrigeration cycle for hydrogen cryo-cooling is simpler, but less the refrigerant usage and energy consumption compared to the previously proposed cycles. The proposed process demonstrates excellent performance in terms of energy saving and efficiency improvement, providing a low-cost scheme to produce liquid hydrogen.

Quantum Brayton Refrigeration Cycle with Finite-Size Bose–Einstein Condensates

We consider a quantum Brayton refrigeration cycle consisting of two isobaric and two adiabatic processes, using an ideal Bose gas of finite particles confined in a harmonic trap as its working substance. Quite generally, such a machine falls into three different cases, classified as the condensed region, non-condensed phase, and regime across the critical point. When the refrigerator works near the critical region, both figure of merit and cooling load are significantly improved due to the singular behavior of the specific heat, and the coefficient of performance at maximum figure of merit is much larger than the Curzon–Ahlborn value. With the machine in the non-condensed regime, the coefficient of performance for maximum figure of merit agrees well with the Curzon–Ahlborn value.

Integrated hydrogen liquefaction process with a dual-pressure organic Rankine cycle-assisted LNG regasification system: Design, comparison, and analysis

Improving the efficiency and reducing the cost of hydrogen liquefaction systems have become a subject of importance nowadays. Through the comparison and analysis of existing processes, a hydrogen liquefaction system that can enhance the utilization efficiency of liquefied natural gas (LNG) cold energy is developed. The system includes a dual-pressure organic Rankine cycle (DORC)-assisted LNG regasification process and improved cascade Joule-Brayton refrigeration cycles. To assess the performance of the proposed process, two forms of ORC and three Brayton refrigeration cycles are compared, respectively. The genetic algorithm is applied to optimize the proposed process. The coefficient of performance, exergy efficiency, and specific energy consumption of the proposed process is 0.20, 46.9%, and 6.61 kWh/kgLH2, respectively. Owing to the efficient utilization of LNG cold energy, the power output of the DORC is 16.2% higher than that of a regular ORC. Furthermore, the improved cryo-cooling process exhibits a significant performance enhancement. Compared to two existing processes, the UA value of the heat exchangers in the proposed cryo-cooling process is reduced by 47.6% and 8.3%, respectively, and the required mass flow rate of helium is reduced by 45.3% and 8.6%, respectively. Moreover, the exergy analysis performed on the system indicates that the exergy utilization rate of the hydrogen pre-cooling process is 80.2%, while that of the cryo-cooling process is only 48.7%.

Modified Brayton refrigeration cycles for forced-flow cooling of HTS fusion system

A thermodynamic study is performed to identify the suitable refrigeration cycles for emerging application to HTS (high-temperature superconductors) fusion system. According to the recent reports on compact and efficient fusion system, the HTS magnets are supposed to operate around at 20 K by forced-flow cooling of helium gas. In addition to the main cryogenic load for magnets, there are other cooling requirements, including the refrigeration of thermal shield and current leads. In order to compose a closed refrigeration system without liquid-nitrogen supply or any boil-off loss, modified Brayton cycles are designed to cover the cooling loads with a circulation loop of coolant for magnets, thermal shield, and current leads. Innovative design is also proposed to integrate the cooling loop with the refrigeration cycle, as helium gas is used as coolant and refrigerant. A variety of modified cycles with forced-flow cooling are optimized through iterative analysis with process simulator (Aspen HYSYS) and the real-gas properties of helium. It is verified that the integrated refrigeration cycles with cooling loop could have a great merit in thermodynamic efficiency as well as the simpler operation without any cryogenic pumping device. It is also demonstrated that a single refrigeration cycle could be designed to fully cover all the cooling requirements for HTS fusion system.

Study on Performance Comparison of Two Hydrogen Liquefaction Processes Based on the Claude Cycle and the Brayton Refrigeration Cycle

Hydrogen liquefaction is an essential section for efficient storage and transportation of hydrogen energy. Both the Claude cycle and Brayton refrigeration cycle are available for large-scale hydrogen liquefaction systems. Two large-scale hydrogen liquefiers with the liquefaction capacity of 120 t/d based on the Brayton refrigeration cycle and the Claude cycle, respectively, are analyzed and compared in this study. Sensitivity analysis is used to optimize the parameters of two liquefaction systems in HYSYS. According to the results, the exergy loss and specific energy consumption of the Claude liquefier are 18.98 MW and 5.62 kWh/kgLH, which are 6.6% and 4.4% less than those of the Brayton liquefier, respectively. Exergy analysis reveals the exergy loss of compression and expansion systems in the Claude liquefier is less than that of the Brayton liquefier, while the exergy loss of the throttle valve in the Claude liquefier is more notable. In addition, the molar flow rate of hydrogen used as refrigerant in the Claude liquefier is 10.6% less than that of refrigerant in the Brayton liquefier. Owing to the smaller size requirements of equipment and the lower specific energy consumption, the Claude cycle is more suitable for large-scale hydrogen liquefaction processes.

Effect of pressure on heat and mass transfer performance in spray drying tower with low inlet temperature

• Pressure effect on spray-drying tower used in wastewater treatment is studied. • A three-stage single droplet model is developed and used in spray drying simulation. • Wastewater treatment using spray-drying tower under low pressure is tested. • Guidance on selection of optimal operating pressure for spray drying is provided. • The optimum pressure is due to increased mass transfer and reduced residence time. The spray drying tower is an important device of the air circulation evaporation-separation electroplating wastewater treatment system based on Brayton refrigeration cycle, which can acquire the optimum system performance by controlling the operational pressure. In order to explore the optimum pressure in the tower, the heat and mass transfer performances of the spray drying tower under different pressures are investigated. The experimental results show that the evaporation rate increases with the decrease of the pressure. The effect of pressure on tower height and inlet air temperature required for droplet to be completely dried is simulated to use the model verified by experimental data. A three-stage heat and mass transfer model for single-droplet is developed in the simulation. The simulation results show that there is an optimal pressure corresponding to the lowest required tower height. The optimal pressure is increased with the increase of inlet air temperature. When the tower height is fixed, the inlet air temperature required for drying droplet firstly decreases and then increases with the increase of pressure. In addition, through analyzing heat and mass transfer, it is found that the decrease of pressure results in the increase of not only the mass transfer driving force but also the air velocity, thus the droplet residence time is decreased, which leads to the existence of optimal pressure. It is feasible to achieve complete drying in spray drying process by reducing the pressure in the tower with low inlet temperature.

Experimental Assessment of a Reverse Brayton Cycle Based On Automotive Turbochargers and E-Chargers for Cryogenic Applications

Abstract The utilization of automotive engine components for the development of a reverse Brayton cycle is shown in this study. The well-known characteristics of turbochargers and electrical centrifugal compressors commonly used in the automotive industry is a starting point for developing an experimental cycle configuration of a reverse Brayton refrigeration cycle with the ability to achieve up to 115 K after a multi-stage compression with intermediate cooling and a single-stage expansion in a radial turbine using air (R-729) as working fluid. The use of a variable nozzle turbine allows to evaluate the optimum rack position for each operating point, while having control over refrigeration capacity. Studies over the minimum cycle pressure at the inlet of the first stage of compression have been performed to assess the possible benefit of creating vacuum or pressurize the working fluid. A 1 m^3 cooling chamber was attached to the installation to test the ability of cooling different thermal loads working under different operation ways, open or closed cycle, this is, letting the working fluid to interact with the thermal load or cooling it through a heat exchanger. The evaluation of thermodynamic parameters allows to obtain the coefficient of performance (COP) of the installation and the efficiency of each component. The analysis of turbomachinery performance will allow identifying weak points to improve cycle performance, and the coupling model between rotatory machines as well as to adapt the size of the installation to the refrigeration capacity required for different applications.

Investigation on the regenerative Brayton refrigeration cycle performances using novel Mn-Fe-P-Si composite material with thermal hysteresis as the working medium

MnFeP(As, Ge, Si) series compounds are three kinds of MnFe-based magnetocaloric materials, which have giant magnetocaloric effect. In this work, the experimental characteristic curves of new style Mn-Fe-P-Si materials, numbered as 1: Mn1.32Fe0.67P0.52Si0.49, 2: Mn1.37Fe0.63P0.5Si0.5, and 3: Mn1.35Fe0.66P0.5Si0.5 are presented. Based on the experimental data of these component materials and thermodynamic analysis method, a novel composite material is put forward. The optimal molar mass ratios of the composite material are obtained and they are 0.22, 0.33, 0.45, respectively. A regenerative Brayton refrigeration cycle employing the optimal composite material with thermal hysteresis as the working medium is built. By numerical calculation, the influences of thermal hysteresis on the main thermodynamic quantities are evaluated. The results show that the thermal hysteresis of the working medium results in a decrease of 13.6%, 14.6%, 18.8%, and 16.1% of the cooling quantity, net cooling quantity, optimally working temperature range, and coefficient of performance, respectively. These conclusions are beneficial to the optimal parameter design and performance improvement of active magnetic refrigerators.

Design and performance analysis of a hydrogen liquefaction process

Based on the improved Claude precooling cycle combined with Joule–Brayton refrigeration cycle, a hydrogen liquefaction process with high efficiency and mixed refrigerants is developed. Four independent refrigeration cycles with nitrogen and three different mixed refrigerants are used. By this process, 288.92 tons gaseous hydrogen (25 °C, 21 bar) can be transferred into liquid hydrogen (−253.4 °C, 1.3 bar), and the coefficient of performance (COP), specific energy consumption (SEC) and exergy efficiency are 0.1574, 5.85 kWh/kgLH2 and 55.30%, respectively. Based on the sensitivity analysis, the SEC is reduced to 5.742 kWh/kgLH2, the COP increases to 0.1602, and their variations account for 1.85% and 1.78%, respectively. This study has a guiding significance for the design and optimization of large-scale hydrogen liquefaction process.

Hydrogen liquefaction process with Brayton refrigeration cycle to utilize the cold energy of LNG

A thermodynamic process is investigated and designed for hydrogen liquefaction system to utilize the cold energy of liquefied natural gas (LNG). This study is an initial effort of newly launched five-year governmental project in Korea, aiming at efficient hydrogen liquefiers. Since Korea is a major LNG import country, the cold energy is abundantly available and could be useful in reducing the liquefaction cost. Hydrogen gas at ambient temperature is pre-cooled by LNG and then fed into a closed-cycle Brayton refrigerator. Rigorous thermodynamic analysis is carried out on the process with standard or modified Brayton cycles for the optimal condition to minimize the power consumption. It is revealed that LNG at atmospheric pressure is much more effective in pre-cooling than pressurized LNG (for pipeline distribution), because of the temperature pinch problem in heat exchanger. By taking into consideration the efficiency and other factors such as safety, compactness, and simplicity of operation, 2-stage expansion cycle with LNG pre-cooling is identified as most suitable for the pilot system with a capacity of 0.5 ton/day. Full details of liquefaction process are presented with the optional use of catalysts for ortho-para conversion.

Zero methane loss in reliquefaction of boil-off gas in liquefied natural gas carrier ships by using packed bed distillation in reverse Brayton system

Reverse Brayton refrigeration cycle with nitrogen as working fluid is widely used in reliquefaction of boil-off gas generated in LNG tanks onboard. These reliquefiers allow venting of some vapour that has methane in it. This entails a loss of energy and release of greenhouse gas into the environment. As the boil-off gas contains low-boiling temperature nitrogen, its complete reliquefaction is possible only by decreasing the pressure at the turbine outlet that makes the reliquefaction system bulkier. In this paper, two proposed modifications have succeeded in achieving zero methane loss without any reduction of turbine outlet pressure. In one modification, the vent gas is recycled and completely reliquefied with the boil-off gas. In other modification, a distillation column purifies the vent gas to less than a part per million of methane in it and near-pure nitrogen is fed back to the system. Rational exergy efficiency of vent-recycled and distillation column systems are higher than the basic system by 14.9% and 8.7% respectively albeit with some increase in mass flow rate of nitrogen compressor and the size of heat exchangers. The period of return on investment reduces by one month and increases by six months in vent-recycled and column system respectively.

Thermoeconomic performance optimization of an irreversible Brayton refrigeration cycle using Gd, Gd0.95Dy0.05 or Gd0.95Er0.05 as the working substance

An irreversible regenerative Brayton refrigerator cycle is established, in which the nonperfect regenerator, regenerative time, heat leak, and irreversible adiabatic processes are taken into account. The mathematical expressions of the refrigeration rate, coefficient of performance, and thermoeconomic function of the refrigeration cycle are derived and the thermoeconomic function is optimized. Moreover, choosing Gd, Gd0.95Dy0.05 and Gd0.95Er0.05 as the working substances respectively, we discussed in detail the influences of the thermoeconomic and thermodynamic parameters on the optimal thermoeconomic and thermodynamic performances. The results show that the thermoeconomic performance of the refrigeration cycle using Gd or Gd0.95Dy0.05 as the working substance is better than that using Gd0.95Er0.05 and the thermoeconomic performance of the refrigeration cycle using Gd0.95Dy0.05 as the working substance is better than that using Gd in the situation with the lower adiabatic magnetization.

A Thermo-Environmental Evaluation of a Modified Combustion Gas Turbine Plant

This paper reports the comprehensive thermodynamic modeling of a modified combustion gas turbine plant where Brayton refrigeration cycle was employed for inlet air cooling along with evaporative after cooling. Exergetic evaluation was combined with the emission computation to ascertain the effects of operating variables like extraction pressure ratio, extracted mass rate, turbine inlet temperature (TIT), ambient relative humidity, and mass of injected water on the thermo-environmental performance of the gas turbine cycle. Investigation of the proposed gas turbine cycle revealed an exergetic output of 33%, compared to 29% for base case. Proposed modification in basic gas turbine shows a drastic reduction in cycle's exergy loss from 24% to 3% with a considerable decrease in the percentage of local irreversibility of the compressor from 5% to 3% along with a rise in combustion irreversibility from 19% to 21%. The environmental advantage of adding evaporative after cooling to gas turbine cycle along with inlet air cooling can be seen from the significant reduction of NOx from 40 g/kg of fuel to 1 × 10−9 g/kg of fuel with the moderate increase of CO concentration from 36 g/kg of fuel to 99 g/kg of fuel when the fuel–air equivalence ratio reduces from 1.0 to 0.3. Emission assessment further reveals that the increase in ambient relative humidity from 20% to 80% causes a considerable reduction in NOx concentration from 9.5 to 5.8 g/kg of fuel while showing a negligible raise in CO concentration from 4.4 to 5.0 g/kg of fuel.

Parametric study of an integrated organic Rankine/reverse Brayton refrigeration cycle and multiple-effect desalination unit

Parametric study of an integrated organic Rankine/reverse Brayton refrigeration cycle and multiple-effect desalination unit

A theoretical investigation on exergy analysis of a gas turbine cycle subjected to inlet air cooling and evaporative after cooling

A thermodynamic investigation based on energy and exergy analyses was carried out for the gas turbine cycle utilising Brayton refrigeration cycle for inlet air cooling and water injection for evaporative after cooling. Combined application of inlet air cooling and evaporative after cooling enhanced cycle's exergetic output from 29% to 33% and reduces the exergy loss from 24% to 3%. This arrangement in gas turbine also changed the percentage of local irreversibility of the cycle components considerably. At a given ambient relative humidity of 60%, proposed modification in basic gas turbines boost the cycle first and second law efficiency by 3.7% and 4.2%, respectively. The results obtained reveal that application of reverse Brayton refrigeration cycle for inlet air cooling along with evaporative after cooling could be a most promising option for performance enhancement of gas turbines operated in hot and humid climatic regions.

A novel hydrogen liquefaction process configuration with combined mixed refrigerant systems

A novel large-scale plant for hydrogen liquefying is proposed and analyzed. The liquid hydrogen production rate of the proposed plant is 100 tons per day to provide the required LH2 for a large urban area with 100,000–200,000 hydrogen vehicles supply. In the pre-cooling section of the process, a new mixed refrigerant (MR) refrigeration cycle, combined with a Joule–Brayton refrigeration cycle, precool gaseous hydrogen feed from 25 °C to the temperature −198.2 °C. A new refrigeration system with six simple Linde–Hampson cascade cycles cools low-temperature gaseous hydrogen from −198.2 °C to temperature −252.2 °C. The process specific energy consumption (SEC) is 7.69kWh/kgLH2 which minimum value is 2.89kWh/kgLH2 in ideal conditions. The exergy efficiency of the system is 39.5%, which is considerably higher than the existing hydrogen liquefier plants around the world. However, assuming more efficiency values for the equipment can improve it. The energy analysis specifies that coefficient of performance (COP) of the process is 0.1710 which is a high quantity of its kind between other similar processes. Effect of various refrigerant components concentration, discharge pressure of the high pressure compressors of the pre-cooling section, and hydrogen feed pressure on the process COP, exergy efficiency, and SEC are investigated. After that, a new MR will be offered for the cryogenic section of the plant. The system improvements are considerable comparing to current hydrogen liquefying plants, therefore, the proposed conceptual system can be used for future hydrogen liquefaction plants design.