Reverse Brayton Cycle Research Articles

Development of a Simulation Package of Natural Gas Liquefaction System

Gas liquefaction employs refrigeration process to bring feed gas temperature down to enable it to condense. The refrigeration system for natural gas liquefaction consists of some components combined in several configurations. One of those systems is the reversed-Brayton and its modified cycles.A numerical program package was developed to model and analyze the process of small scale natural gas liquefaction with maximum flowrate 1 MTPA or 31.7kg/s. The package was set for the simple 1-stage reversed Brayton cycle and its modified cycle. The process was modelled with assumptions of a steady state condition and natural gas that made of 100% methane. Parameters and variables that may be involved in the simulation are the feed gas flow rate, temperature and pressure, the selection of refrigerants for the cycle, the refrigeration working pressures. The package enable one to calculate the amount of work required for liquefaction process as well as the system's performance in term of its figure of merit.

Modelling of cryogenic cooling system design concepts for superconducting aircraft propulsion

Distributed propulsion concepts are promising in terms of improved fuel burn, better aerodynamic performance, and greater control. Superconducting networks are being considered for their superior power density and efficiency. This study discusses the design of cryogenic cooling systems which are essential for normal operation of superconducting materials. This research project has identified six key requirements such as maintain temperature and low weight, with two critical components that dramatically affect mass identified as the heat exchanger and compressors. Qualitatively, the most viable concept for cryocooling was found to be the reverse-Brayton cycle (RBC) for its superior reliability and flexibility. Single- and two-stage reverse-Brayton systems were modelled, highlighting that double stage concepts are preferable in specific mass and future development terms in all cases except when using liquid hydrogen as the heat sink. Finally, the component-level design space was considered with the most critical components affecting mass being identified as the reverse-Brayton compressor and turbine.

Ground Simulation of High Altitude Test of Turbo-Refrigeration Cycle

Abstract This study proposes a new test approach for a ram air-driven turbo-refrigeration system. The flight performance of the air cycle turbo-refrigerator is indirectly verified through ground tests under various flight conditions, and the actual altitude performance is predicted through dimensional analysis and similarity based on the ground test results. In addition, correction of the Reynolds number is also considered for adequate prediction of performance. This study develops a turbo-refrigerator that consists of a radial turbine and a centrifugal compressor. As this simple system drives the reverse Brayton cycle, it acts as a refrigerator that relieves the heat load. Although the ram air and exhaust conditions are usually simulated in high altitude test facilities, they are very costly and not suitable for prototype development, which often demands requirement and specification changes. The proposed system is designed to deliver a cooling capacity over 2 kW through the heat exchanger at a Mach number of 0.8 and altitude up to 10 km. As a result of current study, the proposed test approach predicts that air cycle turbo-refrigeration system yields sufficient cooling capacity to comply with the requirements for the primary mission flight envelope under the hot day condition, despite slight performance degradation at high altitudes.

Performance evaluation and parametric choice criteria of a Brayton pumped thermal electricity storage system

A more realistic thermodynamic model of the pumped thermal electricity storage (PTES) system consisting of a Brayton cycle and a reverse Brayton cycle is proposed, where the internal and external irreversible losses are took into account and several important controlling parameters, e.g., the pressure ratio and heat flows of the two isobaric processes in the Brayton cycle, are introduced. Analytic expressions for the round trip efficiency and power output of the PTES system are derived. The general performance characteristics of the PTES system are revealed. The optimal relationship between the round trip efficiency and the power output is obtained. The influences of some important controlling parameters on the performance characteristics of the PTES system are discussed and the optimally operating regions of these parameters are determined.

Design of a hydraulically driven compressive elastocaloric cooling system

This article presents the design of elastocaloric cooling system driven by hydraulic actuators. Ni-Ti tubes under axial compressive loading mode are used in the system to provide cooling and heating. Those Ni-Ti tubes are enclosed in four identical beds, which are driven by two one-way hydraulic cylinders. Operated under the single-stage reverse Brayton cycle, the system achieves heat transfer and heat recovery by using a sophisticated heat transfer fluid network controlled by solenoid valves. Two novel designs to improve the system's performance based on the lessons learned from the previous studies are applied to this prototype. Preliminary test results of the material's latent heat at a specific fluid flow rate and temperature difference agree well with the results reported in the literature. System coefficient of performance of 11.0 and temperature lift of 24.6 K are estimated based on a dynamic model developed in the previous study.

A Novel Sensible Heat Pump Scheme for Industrial Heat Recovery

Most industrial heat pumps are based on the reversed Rankine cycle. According to Pinch Analysis, heat pumps should be placed across pinch. A “sharp” pinch with corresponding low temperature lift is required in order to achieve good performance. In addition, as will be demonstrated in this paper, the compression and expansion are not properly placed in the reversed Rankine cycle. A novel sensible heat pump scheme for industrial applications based on the reversed Brayton cycle is developed in this paper. Both compression and expansion are correctly placed above and below pinch, respectively. A systematic methodology for design of the heat pump will be presented. Operating parameters such as inlet temperatures of compression and expansion, heat capacity flow rate of the working fluid, and the pressure ratio for compression are investigated based on thermodynamic and mathematical analyses. Three examples are used to illustrate the design methodology and energy saving potential for using the novel sensible hea...

Thermodynamic analysis and optimization for an irreversible heat pump working on reversed Brayton cycle

This research presents the optimization and performance analysis for irreversible heat pumps operating with reversed Brayton cycle with constant-temperature heat reservoirs via finite-time thermodynamics (FTT) by considering exergetic efficiency as the optimization objective combining exergy model. Moreover, two different strategies in the process of multi-objective optimization are proposed, and the outcomes of each strategy are evaluated separately. The first strategy is proposed to maximize the coefficient of performance (COP), the ecological coefficient of performance (ECOP) and the exergetic efficiency. Furthermore, the second strategy is suggested to maximize the COP, ECOP and Ecological function. All the strategies in the present work are executed via the multi objective evolutionary algorithms based on NSGA|| method. Finally, to govern the final answer in each strategy, three efficient decision makers were executed.

Optimization of UA of heat exchangers and BOG compressor exit pressure of LNG boil-off gas reliquefaction system using exergy analysis

Boil-off gas (BOG) generation and its handling are important issues in Liquefied natural gas (LNG) value chain because of economic, environment and safety reasons. Several variants of reliquefaction systems of BOG have been proposed by researchers. Thermodynamic analyses help to configure them and size their components for improving performance. In this paper, exergy analysis of reliquefaction system based on nitrogen-driven reverse Brayton cycle is carried out through simulation using Aspen Hysys 8.6®, a process simulator and the effects of heat exchanger size with and without related pressure drop and BOG compressor exit pressure are evaluated. Nondimensionalization of parameters with respect to the BOG load allows one to scale up or down the design. The process heat exchanger (PHX) requires much higher surface area than that of BOG condenser and it helps to reduce the quantity of methane vented out to atmosphere. As pressure drop destroys exergy, optimum UA of PHX decreases for highest system performance if pressure drop is taken into account. Again, for fixed sizes of heat exchangers, as there is a range of discharge pressures of BOG compressor at which the loss of methane in vent minimizes, the designer should consider choosing the pressure at lower value.

New insight into regenerated air heat pump cycle

Regenerated air (reverse Brayton) cycle has unique potentials in heat pump applications compared to conventional vapor-compression cycles. To better understand the regenerated air heat pump cycle characteristics, a thermodynamic model with new equivalent parameters was developed in this paper. Equivalent temperature ratio and equivalent isentropic efficiency of expander were introduced to represent the effect of regenerator, which made the regenerated air cycle in the same mathematical expressions as the basic air cycle and created an easy way to prove some important features that regenerated air cycle inherits from the basic one. Moreover, we proved in theory that the regenerator does not always improve the air cycle efficiency. Larger temperature ratio and lower effectiveness of regenerator could make the regenerated air cycle even worse than the basic air cycle. Lastly, we found that only under certain conditions the cycle could get remarkable benefits from a well-sized regenerator. These results would enable further study of the regenerated air cycle from a different perspective.

Performance modeling of air cycle heat pump water heater in cold climate

Air (reverse Brayton) cycle has promising features in cold climate heat pump applications. In this study, an air cycle heat pump water heater (ACHPWH) simulation model considering the off-design performance of components was developed and validated with experimental data from literature. With this model, the performance of ACHPWH was numerically compared with two typical vapor compression heat pump water heaters (VCHPWH) under two different heating schemes, namely instantaneous heating and recirculation heating. For instantaneous heating, the COP of ACHPWH is comparable to that of VCHPWH when supplying high temperature water or operating at low ambient temperature. A significant improvement on annual performance would be achieved as well if higher efficient compressor and expander were applied in ACHPWH system. For recirculation heating, although the COP gap got larger, ACHPWH would save plenty of heating time when operating at low ambient temperature.

Second generation EmDrive propulsion applied to SSTO launcher and interstellar probe

In an IAC13 paper the dynamic operation of a second generation superconducting EmDrive thruster was described. A mathematical model was developed and, in this paper, that model is used to extend the performance envelope of the technology. Three engine designs are evaluated. One is used as a lift engine for a launch vehicle, another as an orbital engine for the launcher and a third as the main engine for an interstellar probe.The engines are based on YBCO superconducting cavities, and performance is predicted on the basis of the test data obtained in earlier experimental programmes. The Q values range from 8×107 to 2×108 and provide high values of specific force over a range of accelerations from 0.4m/s/s to 6m/s/s.The launch vehicle is an “all-electric” single stage to orbit (SSTO) spaceplane, using a 900MHz, eight cavities, fully gimballed lift engine. A 1.5GHz fixed orbital engine provides the horizontal velocity component. Both engines use total loss liquid hydrogen cooling. Electrical power is provided by fuel cells, fed with gaseous hydrogen from the cooling system and liquid oxygen. A 2ton payload, externally mounted, can be flown to Low Earth Orbit in a time of 27min. The total launch mass is 10ton, with an airframe styled on the X37B, which allows aerobraking and a glide approach and landing.The full potential of EmDrive propulsion for deep space missions is illustrated by the performance of the interstellar probe. A multi-cavity, fixed 500MHz engine is cooled by a closed cycle liquid nitrogen system. The refrigeration is carried out in a two stage reverse Brayton Cycle. Electrical power is provided by a 200kWe nuclear generator. The 9ton spacecraft, which includes a 1ton science payload, will achieve a terminal velocity of 0.67c, (where c is the speed of light), and cover a distance of 4 light years, over the 10 year propulsion period.The work reported in this paper has resulted in design studies for two Demonstrator spacecrafts. The launcher will demonstrate the long-sought-for, low cost access to space, and also meet the mission requirements of the proposed DARPA XS-1 Spaceplane. The probe will enable the dream of an interstellar mission to be achieved within the next 20 years.

Thermodynamics cycle analysis and numerical modeling of thermoelastic cooling systems

To avoid global warming potential gases emission from vapor compression air-conditioners and water chillers, alternative cooling technologies have recently garnered more and more attentions. Thermoelastic cooling is among one of the alternative candidates, and have demonstrated promising performance improvement potential on the material level. However, a thermoelastic cooling system integrated with heat transfer fluid loops have not been studied yet. This paper intends to bridge such a gap by introducing the single-stage cycle design options at the beginning. An analytical coefficient of performance (COP) equation was then derived for one of the options using reverse Brayton cycle design. The equation provides physical insights on how the system performance behaves under different conditions. The performance of the same thermoelastic cooling cycle using NiTi alloy was then evaluated based on a dynamic model developed in this study. It was found that the system COP was 1.7 for a baseline case considering both driving motor and parasitic pump power consumptions, while COP ranged from 5.2 to 7.7 when estimated with future improvements.

Study on the matching performance of a low temperature reverse Brayton air refrigerator

A small reverse Brayton cycle air refrigerator was designed and fabricated. Bump-type air journal foil bearing, pressurized thrust gas bearing and centrifugal blower as brake were employed in the turboexpander. Usually, constant brake inlet pressure is set in a reverse Brayton refrigerator. However, the unchanged brake inlet pressure cannot adapt to the changing temperature and expansion ratio during the cooling down process, which could go against the system performance. In this article, the relationship between the turboexpander operation parameters and brake pressure was disclosed through theoretical analysis. The performance curve was analyzed through numerical simulation using CFX. A matching model was established based on the theoretical analysis and numerical simulation. Brake pressure feedback control was then proposed and applied in the experimental study. Thermal performance of the refrigerator was tested under varied operating conditions (different expansion ratios, temperatures and brake pressures). The results indicated that the appropriate brake pressure facilitated system good thermal performance under both design and off-design conditions, and the theoretical results agreed well with the experimental data.

航空機の空調システム設計（第1報：システム作動における高圧除湿系統の機器能力の影響）

The purpose of this study is to clarify the effect of a component for high-pressure water separation, which is included in the air conditioning system of the general commercial aircrafts, on the air-cycle operation (reverse Brayton cycle); the high-pressure water separation consists of water separator and two heat exchangers called reheater and condenser, respectively. This paper briefly describes the typical system configuration of the air-cycle refrigeration progressed with evolutions in turbofan engine. Since nowadays, 4-Wheel air-cycle has been a trend on the aircraft air conditioning system, this paper theoretically shows its advantage on the basis of the thermodynamic cycle study. In the following chapters, an analysis was conducted on the interaction between a reheater and a condenser when each heat transfer performance changes from the baseline operating point. Also, the comparative study was made on the system performances by the 3-wheel and 4-wheel air-cycle. In addition, this paper describes how the heat transfer performance is designed for the reheater and the condenser under the system requirements for the entire air conditioning system.

A new type of refrigerator and its cycle

The world is facing an energy and climate crisis. Globally, the energy sector emits 26 billion tonnes of CO2 each year, and electricity production alone accounts for 41% of emissions (European Wind Energy Association. 2008. Pure Power: Wind Energy Scenarios up to 2030. European Wind Energy Association. p. 6). Currently, reducing CO2 emissions and curbing climate change have become global priorities, and we only have a narrow window of time left in which to act. The new type of refrigerator can offer an immediate and concrete solution to the many energy and climate challenges that we are facing. This is an account of a new type of refrigerator and its cycle for use in the refrigeration industry. For its cycle, the working substance is air or other gases; its cycle is very similar to that of the reverse Brayton cycle (Hou, Y., Zhao, H. L., Chen, C. Z., and Xiong, L. Y. 2006. “Developments in Reverse Brayton Cycle Cryocooler in China.” Cryogenics 46 (5): 403–407). In the cycle of the new type of refrigerator, the isochoric exothermic process and the isothermal exothermic compression process replace the isobaric exothermic compression process of the reverse Brayton cycle. The new type of refrigerator can produce a net electrical energy, and it is not a perpetual motion machine, because the environmental enthalpy and atmospheric pressure can be utilized as the external energy sources, which cannot be performed by any other conventional refrigerators; therefore, the reliability and significance of this new type of refrigerator is self-evident.

Thermodynamic optimization of reverse Brayton cycles of different configurations for cryogenic applications

The thermodynamic optimization of differing Reverse Brayton Refrigeration (RBR) cycle configurations is presented in this study. These cycle configurations include: Conventional 1-stage compression cycle; Conventional 2-stage compression cycle; 1-stage compression Modified cycle with intermediate cooling of the recuperator using an auxiliary cooler; and an Integrated 2-stage expansion RBR cycle. For high pressure ratio applications, multi-stage compressors with intercooling are considered. Analytical solutions for the conventional cycles are developed including thermal and fluid flow irreversibilities of the recuperators and all heat exchangers in addition to the compression and expansion processes. Exergy analysis is performed and the exergy destruction of different components of the RBR cycles for different configurations is presented and the effects of important system parameters on performance are investigated. Thermodynamic optimization of the cycles with intermediate cooling of the recuperator is included. Effects of the 2nd law/exergy efficiency of the auxiliary cooler on the total system efficiencies are presented.

Off-design operating characteristics of an open-cycle air refrigeration system

Air cycle refrigeration based on the reverse Brayton cycle is a potential solution to environmental problems. In this study, the operating characteristics of an open-air cycle refrigeration system were simulated and analyzed. First, optimal design conditions were found through a design parametric study. Then, the operation of the system was simulated using off-design models. Two partial load operating strategies were compared: fixed shaft speed operation and variable speed operation. Fixed shaft speed operation requires a decrease in the refrigeration temperature as the refrigeration capacity decreases. Variable speed operation can operate with any specified refrigeration temperature. Both operations accompany a reduction in the coefficient of performance compared to the design value, but variable speed operation exhibits much less reduction at the same refrigeration capacity. We presented system performance maps and demonstrated that all of the operating conditions, which differ in refrigeration capacity and refrigeration temperature, can be addressed by varying both the speed and target refrigeration temperature simultaneously.

An open Reversed Brayton cylce with Regeneration Using Moist Air for Air Conditioning Cooled by Circulating Water

Abstract This paper presents an open reversed Brayton cycle with regeneration (ORBCR) using moist air for air conditioning cooled by circulating water, and proves its feasibility through performance simulation. Its refrigeration depends mainly on the sensible heat of air and the latent heat of water vapor, its performance is more efficient than a conventional air-cycle, and the utilization of turbo-machinery makes it possible. The adoption of this cycle will make air-conditioned room more comfortable and reduce initial cost because of the very low temperature air obtained. The sensitivity analyses of coefficient of performance (COP) of the cycle without regeneration and the equivalent coefficient of performance (COPE) of the cycle with regeneration to the efficiency of compressor (ηc) and the efficiency of compressor (ηt), and the results of both cycles are also given. The simulation results show that the COPE of this system depends mainly on the temperature before turbine (T7),ηc andηt, and varies with the wet bulb temperature of the outdoor air (Twet). Humid air is a perfect working fluid for central air conditioning and no cost to the user. The ORBCR is more efficient because of the use of the return air to cool water, and then to cool the air before turbine.

Exergetic efficiency optimization for an irreversible heat pump working on reversed Brayton cycle

This paper deals with the performance analysis and optimization for irreversible heat pumps working on reversed Brayton cycle with constant-temperature heat reservoirs by taking exergetic efficiency as the optimization objective combining exergy concept with finite-time thermodynamics (FTT). Exergetic efficiency is defined as the ratio of rate of exergy output to rate of exergy input of the system. The irreversibilities considered in the system include heat resistance losses in the hot- and cold-side heat exchangers and non-isentropic losses in the compression and expansion processes. The analytical formulas of the heating load, coefficient of performance (COP) and exergetic efficiency for the heat pumps are derived. The results are compared with those obtained for the traditional heating load and coefficient of performance objectives. The influences of the pressure ratio of the compressor, the allocation of heat exchanger inventory, the temperature ratio of two reservoirs, the effectiveness of the hot- and cold-side heat exchangers and regenerator, the efficiencies of the compressor and expander, the ratio of hot-side heat reservoir temperature to ambient temperature, the total heat exchanger inventory, and the heat capacity rate of the working fluid on the exergetic efficiency of the heat pumps are analysed by numerical calculations. The results show that the exergetic efficiency optimization is an important and effective criterion for the evaluation of an irreversible heat pump working on reversed Brayton cycle.

Thermodynamic design of methane liquefaction system based on reversed-Brayton cycle

A thermodynamic design is performed for reversed-Brayton refrigeration cycle to liquefy methane separated from landfill gas (LFG) in distributed scale. Objective of the design is to find the most efficient operating conditions for a skid-mount type of liquefaction system that is capable of LNG production at 160l/h. Special attention is paid on liquefying counterflow heat exchanger, because the temperature difference between cold refrigerant and methane is smallest at the middle of heat exchanger, which seriously limits the overall thermodynamic performance of the liquefaction system. Nitrogen is selected as refrigerant, as it is superior to helium in thermodynamic efficiency. In order to consider specifically the size effect of heat exchangers, the performance of plate-fin heat exchangers is estimated with rigorous numerical calculations by incorporating a commercial code for properties of methane and the refrigerant. Optimal conditions in operating pressure and heat exchanger size are presented and discussed for prototype construction under a governmental project in Korea.