Ideal Cycle Research Articles

Simulation of an operation of nested Halbach cylinder arrays in regenerative magnetic cooling cycles: The way to maximum thermal span

In this study, a numerical model of the Active Magnetic Regenerator (AMR) cycle, implemented in the reciprocal demonstrator, was developed using COMSOL Multiphysics. A nested Halbach cylinder (NHC) array served as the magnetic field source. Additional simulation of an operation of the NHC array was carried out. To eliminate the discrepancies between the heat exchange duration of the heat transfer medium (HTM) and the hot and cold ends of the regenerator, an adequate time dependence of the inner cylinder rotation angle was calculated. The latter provides the symmetrical sinusoidal form of time dependence of the magnetic flux density in the gap of NHC array, which is important for enhancing the performance of a magnetic refrigerator. It was established that in order to achieve a maximal temperature span, it is necessary to shift the phases of the magnetic field insertion/removal and heat transfer fluid pumping processes by nearly half of the operating cycle period. The latter brings the simulated cycle closer to the ideal AMR cycle.

Thermochemical production of ammonia via a two-step metal nitride cycle - materials screening and the strontium-based system.

Ammonia synthesis via the catalytic Haber-Bosch process is characterized by its high pressures and low single-pass conversions, as well as by the energy-intensive production of the precursors H2 and N2 and their concomitant greenhouse gas emissions. Alternatively, thermochemical cycles based on metal nitrides stand as a promising pathway to green ammonia production because they can be conducted at moderate pressures without added catalysts and be further driven by concentrated solar energy as the source of high-temperature process heat. The ideal two-step cycle consists of the nitridation of a metal to form a metal nitride, followed by the hydrogenation of the metal nitride to synthetize NH3 and reform the metal. Here, we perform a combined theoretical and experimental screening of mono-metallic nitrides for several candidates, namely for Sr, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, Li, and Al. For the theoretical screening, Ellingham diagrams and chemical equilibrium compositions are examined with thermodynamic data derived from density function theory computations. For the experimental screening, thermogravimetric runs and mass balances supported by on-line gas analyses are performed for both steps of the cycle at ambient pressure and over the temperature ranges 100-1000 °C for nitridation and 100-500 °C for hydrogenation. The strontium-based cycle is selected as a reference for detailed examination and shown to synthetize NH3 at 1 bar by effecting the nitridation at 407 °C (at peak rate) and the hydrogenation at 339 °C (at peak rate). The co-formation of metal hydrides (SrH2) and metal imides (Sr2HN) are shown to help close the material cycle.

Thermodynamic analysis of a heat engine: experiments with the Stirling cycle

This paper presents a practical thermodynamic analysis of a desktop Stirling engine to demonstrate some of the fundamental principles involving the conversion of heat to work as part of an introductory undergraduate course. Experimental measurements of temperature, pressure and volume using an Arduino microcontroller allows for the construction of P-ν and T-s process diagrams from thermodynamic relationships. By comparing the quantitative data from actual and ideal cycles, the Stirling engine represents an effective teaching tool for reinforcing core content with students.

Thermodynamic evaluation of thermomagnetic motors with first and second order transition magnetocaloric materials

Thermomagnetic motors serve as energy harvesters by converting low-grade thermal wastes into useful mechanical power. This paper proposes a mathematical model based on the first law of thermodynamics for assessing the specific work produced by thermomagnetic motors utilizing first and second-order magnetocaloric materials. After initial verification of the results against data from open literature for the ideal Ericsson and Brayton cycles, the model then explores the impact of losses and irreversibilities on the output work. It was found that internal demagnetizing fields reduce the available work up to 42% for the simulated conditions, while heat losses and magnetic hysteresis are complex to implement and show minor impacts. Thermal hysteresis, in turn, may enhance the specific work, but prolong cycle periods. The model provides a cost-effective means to compare magnetocaloric materials and evaluate motor performance, aiding in component selection for thermomagnetic motors.

Pool boiling performance of R32/R290 and R32/R1270 blends as potential alternatives to R410A

The implementation of the climate change agreement intensified the actions of government agencies and industries to phase out refrigerants with high global warming potential (GWP). This study investigated refrigerant blends as possible low GWP alternatives for R410A in a refrigerating application. The cycle efficiency and flammability of binary and ternary blends among 19 pure refrigerants were evaluated based on an ideal vapor compression refrigeration cycle model with application conditions of water chillers. The mixtures R32/R290 and R32/R1270 were selected based on the acceptable efficiency and availability. Further investigation of the pool boiling performance of the two mixtures with various mass fractions was conducted. The results showed that the heat transfer coefficient deteriorated as the temperature glide and the vapor–liquid fraction difference became larger, and increased with the increasing of the vapor pressure and thermal conductivity. Meanwhile, the heat transfer coefficient of the two mixtures did not deteriorate at the mass fraction of R32 near 70 wt%, where the near-azeotropic mixtures were formed. The results show that the pool boiling heat transfer performances of R32/R290 (70/30 wt%) and R32/R1270 (70/30 wt%) were 2.23% lower and 8.67% higher than that of R410A, respectively, and R32/R1270 (70/30 wt%) has 9.3% higher performance than pure R32 at low heat flux. Six correlations were compared against the present data. None of the correlations can accurately predict both the R32/R290 and R32/R1270 mixtures. A modified correlation based on three of the six previous correlations was developed taking account the vapor–liquid fraction difference, temperature glide, heat flux, and system pressure. The prediction performances of the modified correlation were improved for both mixtures with the mean absolute deviation of 5.95 % and 6.58 % for R32/R290 and R32/R1270, respectively, and most of the data points within the deviation band of 15 %.

Operating characteristics of an adsorption chiller with heat and mass recovery scheme for low-grade heat source

Waste heat recovery from data center is regarded as one of the most promising application of adsorption refrigeration in the future. To better understanding of the system, the operating characteristics, including temperature, pressure and heat exchange capacity, of the adsorption chiller for such low-grade heat source should be revealed. Unfortunately, they have not been detailedly reported yet. In this paper, lab experiments on a silica gel-water adsorption chiller prototype with heat and mass recovery scheme are implemented. The results show that this chiller can achieve 3.17 kW of average cooling power and 0.482 of coefficient of performance under the conditions of 60 °C hot water inlet temperature, 30 °C cooling water inlet temperature and 22 °C chilled water inlet temperature. The temperature and pressure characteristics reveal that adsorbent bed desorption phase results in the worsening of the deviation from ideal cycle when compared to its adsorption phase. Hence, the heat and mass transfer performance of bed in desorption phase is prioritized to be enhanced. The analysis on heat exchange capacity indicates that mass recovery operation is more beneficial to the adsorption reaction. The optimal heat recovery time is found to be 24 s while the heat recovery efficiency is 0.711.

A novel cycle engine for low-grade heat utilization: Principle, conceptual design and thermodynamic analysis

Efficient engine technologies to convert low-grade heat to electricity are urgently desired. In this work, a conceptual structure of engine for a novel cycle or one-way oscillating flow cycle (OOFC), which consists of two isochoric and two adiabatic processes, is described for low-grade heat utilization. Characteristics of OOFC allows for the working fluid temperature glide to be matched to the decrease in temperature of low-grade heat. Then, thermodynamic model is developed for evaluating the performance. Theoretical simulation results show that maximum specific output works are in the range of 12.2 kJ kg−1 – 79.7 kJ kg−1. Compared to Stirling cycle system, maximum specific output work in OOFC system could be improved by 16.2 %–24.8 %. Compared to ideal Carnot cycle engine system, maximum specific output works in OOFC system is nearly the same and 1.8 %–2.6 % lower. As Carnot cycle engine is ideal while thermodynamic cycle loss and heat transfer loss in cold heat exchangers are considered in OOFC engine, the ratios of maximum specific output work demonstrate that OOFC system could be very promising for low-grade heat utilization as a result of well-matched temperature profile in hot heat exchanger.

A Novel Second Harmonic Voltage Suppression Control for PSFB Converter in Dual-Stage Single-Phase Rectifier

The inherent second harmonic power pulse in single-phase grid-connected rectifiers leads to a noticeable output voltage ripple and thus results in the degradation of the system. A novel second harmonic suppression control is introduced in this paper to address this issue. The key point of the proposed control lies in the real-time prediction of the phase-shifted full-bridge (PSFB) converter’s desired duty cycle through accurate PSFB converter modeling. By accurately predicting the ideal duty cycle, the proposed control facilitates a significant enhancement in the control loop’s gain specifically at the second harmonic frequency, thereby improving the overall system performance. To validate the theoretical analysis, a series of simulations and experiments were conducted. The results demonstrate the effectiveness of the proposed second harmonic suppression control in mitigating second harmonic output voltage ripple.

Theoretical thermal efficiencies of ideal, supercharged and gasoline engine cycles

This paper updated the perception of theoretical thermal efficiencies of reciprocating engine cycles by the analysis of six ideal cycles (Diesel, Joule-Brayton, Otto, Atkinson, Sabathe and Song). It was theoretically elucidated that more available energy remains in exhaust gas at higher load than at lower one, testifying that the exhaust waster energy recovery is more important at higher load than at lower one. A supercharged cycle was theoretically demonstrated to have lower thermal efficiency than its counterpart naturally-aspirated one, while supercharged engines had been always considered to have higher thermal efficiency. The thermal efficiencies of gasoline engines were first derived, testifying that a homogeneous spark-ignition gasoline engine at part-load has less thermal efficiency than its corresponding Otto cycle and can achieve a higher thermal efficiency by retarding (or advancing) inlet valve closing than by throttling intake flow.

Primary investigation on Ram-Rotor Detonation Engine

The study presents a new type of detonation engine called the Ram-Rotor Detonation Engine (RRDE), which overcomes some of the drawbacks of conventional detonation engines such as pulsed detonation engines, oblique detonation engines, and rotating detonation engines. The RRDE organizes the processes of reactant compression, detonation combustion, and burned gas expansion in a single rotor, allowing it to achieve an ideal detonation cycle under a wide range of inlet Mach numbers, thus significantly improving the total pressure gain of the propulsion system. The feasibility and performance of RRDE are discussed through theoretical analysis and numerical simulations. The theoretical analysis indicates that the performance of the RRDE is mainly related to the inlet velocity, the rotor rim velocity, and the equivalence ratio of reactant. Increasing the inlet velocity leads to a decrease in the total pressure gain of the RRDE. Once the inlet velocity exceeds the critical value, the engine cannot achieve positive total pressure gain. Increasing the rim velocity can improve the total pressure gain and the thermodynamic cycle efficiency of RRDE. Increasing the equivalence ratio can also improve the thermodynamic cycle efficiency and enhance the total pressure gain at lower inlet velocities. While at higher inlet velocities, increasing the equivalence ratio may reduce the total pressure gain. Numerical simulations are also performed to analyze the detailed flow field structure in RRDE and its variations with the inlet parameters. The simulation results demonstrate that the detonation wave can stably stand in the RRDE and can adapt to the change of the inlet equivalence ratio within a certain range. This study provides the preliminary theoretical basis and design reference for the RRDE.

Theoretical helium liquefaction rate based on the temperature-distributed refrigeration method in regenerative refrigerators

Helium liquefaction is important for applications of cryogenic engineering, helium recovery and purification, and so on. Regenerative refrigerators are generally applied for small-scale applications because of their relatively high efficiency, competitive compactness, etc. However, the liquefaction efficiency (the ratio of the input power of the ideal liquefaction cycle to that of the practical cycle) of helium is low. In this paper, a novel method called temperature-distributed refrigeration to improve the performance of helium liquefiers by utilizing distributed refrigeration power is proposed. The theoretical liquefaction efficiency by applying this method in the regenerative cycle is analyzed. The analysis assumes that there is no radial thermal resistance during the transmission of refrigeration power. The working pressure of helium in the refrigerator is in a wide reduced pressure range of 4.0–61.7, with the liquefied helium maintained at 0.1 MPa. The results indicate that the theoretical maximum liquefaction rate reaches 50.5 L/d (1.5 W at 4.2 K). This liquefaction rate is 2–3 times that of liquefying with only the cold ends. Meanwhile, the liquefaction efficiency increases with the working pressure, reaching a theoretical maximum of 44.5 % at a reduced pressure of 61.7. It is the highest possible efficiency for a two-stage regenerative refrigerator. This method should provide a reference for the optimization of small-scale helium liquefaction systems.

A numerical procedure to obtain ideal piston trajectories and key design parameters for a hydrogen-fuelled resonating free piston generator

A new numerical procedure is presented to enable a hydrogen-fuelled two-stroke resonating free-piston generator target ideal Otto cycles to provide tracking paths for feedback control to maximise efficiency. Piston trajectories and design parameters are obtained for specified power, compression-ratio, and air-fuel-ratio. These parameters include scavenge port locations, heat release position, equivalent bottom-dead-centre position, and an electrical machine constant which is generally power-switched to take two values within a cycle. The main objectives of the paper are to develop the numerical procedure, and to demonstrate its use in finding a generator with maximum efficiency, and a generator with a single electrical machine constant, avoiding in-cycle power switching. To develop the procedure, a multi-physics generator model provides kinematics to an energy equation, culminating in a novel two-stage procedure. Stage-1 involves iteration and minimisation; Stage-2 just involves minimisation. Testing by simulation involves a 14-kW generator case study with compression ratio of 9, lean air-fuel equivalence ratio of 0.4, plus friction and electrical machine losses. An overall maximum generator efficiency of 54.9% is obtained using the procedure, compared to 51.3% without power switching. Computationally, the two-stage procedure proves highly efficient, typically taking around 11 min in total to complete on a desktop computer. The novelty of the procedure is its ability to optimally design and operate a hydrogen-fuelled resonating free-piston generator to meet a target specification, thereby offering a potentially inexpensive way to decarbonize transport, particularly in heavy duty applications.

Design and analysis of an ideal scramjet flowpath

The current work presents a novel conceptual framework for the fluid and gasdynamics that govern the design and performance of an ideal scramjet flowpath. These include a theoretical comparison between ram and scram modes, the physics of thrust loss during inlet unstart, and the design of an optimal scramjet flowpath. We present a unique explicit, closed-form relation for the wall divergence of an ideal scramjet combustor. The accompanying derivations and discussions, which leverage this formulation, seek to address uncertainties and misconceptions regarding the dominant fluid processes present in these engines. It is shown that scram and ram modes exhibit theoretical similitude for maximum thrust potential at conditions beyond the one-dimensional Rayleigh choking limit but can diverge below the global choking threshold. Additionally, it is shown that even for an ideal scramjet heat engine cycle, thermodynamic efficiencies at various flight conditions deviate from those of the classical Brayton cycle. These insights and accompanying theoretical analyses are meant to establish a foundation for the thermodynamics and gasdynamics relevant to the performance of dual-mode scramjet engines. The resulting work offers an intuitive technical perspective on supersonic combustion and the fundamentals of dual-mode scramjet operation that can be applied across a wide range of scramjet-related experimental and computational studies and design efforts in the future.

Rapid quantitative PCR equipment using photothermal conversion of Au nanoshell

The emergence of infectious diseases worldwide necessitates rapid and precise diagnostics. Using gold nanoshells in the PCR mix, we harnessed their unique photothermal properties in the near-infrared regime to attain efficient heating, reaching ideal photothermal PCR cycle temperature profile. Our photothermal PCR method expedited DNA amplification while retaining its detection sensitivity. Combining photothermal quantitative PCR with real-time fluorometry and non-invasive temperature measurement, we could amplify the target DNA within just 25 min, with a minimum detectable DNA amount of 50 picograms. This innovation in photothermal qPCR, leveraging the photothermal properties of gold nanoshells, will pave the way for immediate point-of-care diagnostics of nucleic acid biomarkers.

Contrasting responses of relationship between solar-induced fluorescence and gross primary production to drought across aridity gradients

Satellite solar-induced chlorophyll fluorescence (SIF) can provide valuable insights on terrestrial gross primary production (GPP) and its response to climate from region to global scales. However, the relationship between SIF and GPP under different climate conditions (such as drought) is not yet fully understood and remains a topic of debate in the literature. Here we examined the responses of the SIF–GPP relationship (i.e., the slope k of the linear SIF–GPP relationship, GPP = k × SIF) to drought along the aridity gradient using seven satellite SIF datasets, three GPP products, and 62 flux towers. The results revealed divergent SIF–GPP relationships under different aridity and drought conditions based on different SIF and GPP datasets. Overall, we found that with increasing aridity index (AI) (more humid), k derived from SIF with afternoon overpass (dailySIFPM) decreased, while k from SIF with morning overpass (dailySIFAM) increased. When there is a drought, for arid and semi-arid regions with AI from 0 to 0.4, kPM (the slope of dailySIFPM–GPP) increased, but kAM (the slope of dailySIFAM–GPP) decreased. The dailySIFPM also showed larger decreases than dailySIFAM and GPP during the drought. The contrasting responses among two groups of SIF may result from different SIF overpass time which detected different levels of water stresses on photosynthesis. The dryland ecosystems may exhibit strong midday and afternoon depression in photosynthesis under stress, which led to underestimation of daily SIF that was converted from midday/afternoon-observed SIF by assuming ideal symmetrical diurnal cycle of solar radiation. Our study highlights that in addition to multiple previously reported factors, different observation time of SIF may also affect the SIF–GPP relationship.

Hydrogen Storage System Attained by HCOOH-CO2 Couple: Recent Developments in Pd-Based Carbon-Supported Heterogeneous Catalysts

The present review revisits representative studies addressing the development of efficient Pd-based carbon-supported heterogeneous catalysts for two important reactions, namely, the production of hydrogen from formic acid and the hydrogenation of carbon dioxide into formic acid. The HCOOH-CO2 system is considered a promising couple for a hydrogen storage system involving an ideal carbon-neutral cycle. Significant advancements have been achieved in the catalysts designed to catalyze the dehydrogenation of formic acid under mild reaction conditions, while much effort is still needed to catalyze the challenging CO2 hydrogenation reaction. The design of Pd-based carbon-supported heterogeneous catalysts for these reactions encompasses both the modulation of the properties of the active phase (particle size, composition, and electronic properties) and the modification of the supports by means of the incorporation of nitrogen functional groups. These approaches are herein summarized to provide a compilation of the strategies followed in recent studies and to set the basis for a hydrogen storage system attained using the HCOOH-CO2 couple.

Теоретическая оценка эффективности применения одноступенчатых длинноходовых поршневых компрессоров в холодильной технике и системах сжижения углеводородов

The analysis of the main modern technologies for obtaining low temperatures and liquefying hydrocarbons using compressor equipment is presented and the most significant results of research in the field of low-flow compressors based on low-speed, long-stroke piston stages are presented. A method for calculating an ideal vapor-compression refrigeration cycle is presented, adapted to the object under consideration, taking into account the possibility of implementing quasi-isothermal compression. A comparative computational analysis of temperature conditions and thermodynamic efficiency of a two-stage refrigeration cycle and single-stage refrigeration cycles is carried out during adiabatic and quasi-isothermal compression processes in the boiling temperature range 278 K ... 198 K. It is shown that in terms of the discharge temperature and coefficient of performance, a single-stage vaporcompression ammonia refrigeration machine based on a low-speed quasi-isothermal stage is comparable to a similar two-stage machine based on adiabatic stages. This allows, in relation to actual objects — small refrigeration machines and installations, to predict both the energy and technical advantages of using a single-stage scheme based on low-speed, long-stroke piston compressors. In addition, it has been shown that the effective use of such a compressor is also possible in hydrocarbon liquefaction systems, while ensuring their safe temperature conditions in a wide range of atmospheric temperatures.

Preventive Maintenance Policy to Improve the Effectiveness of XYZ Machine

PT ABC which is a manufacturing company that produces steel pipes. The last period there was an XYZ machine that often downtime and disrupted the production process. The breakdowns indicate the ineffectiveness of machine. It was necessary to identify and analyze the problems that occurred and the factors that caused the problem. Measurement of machine effectiveness dan it caused is carried out using the OEE method. To avoid the recurrence of machine ineffectiveness, machine maintenance is carried out in a preventive manner according to the spare parts classification (there are 3 classifications of spare parts based on price, namely A under Rp.250,000, B between Rp.250,000 -Rp.500,000 and C above Rp.500,000). The results obtained for the average value of OEE for 1 year is 68%, which shows a value below the ideal OEE standard (85%) and needs to be evaluated. From the calculation of the largest losses value is in the reduce speed losses factor of 67%, it is necessary to minimize the difference in ideal cycle time with actual time (operation time). The best scheduling results is using the preventive maintenance policy method with the schedule of maintenance are: for classification A spare parts the maintenance every 3 months, class B every 5 months, and class C every 6 months.

Real-Time Management for an EV Hybrid Storage System Based on Fuzzy Control

Following the European Climate Law of 2021 and the climate neutrality goal for zero-emission transportation by 2050, electric vehicles continue to gain market share, reaching 2.5 million vehicles in Q1 of 2023. Electric vehicles utilize an electric motor for propulsion powered by lithium batteries, which suffer from high temperatures caused by peak operation conditions and rapid charging, so hybridization with supercapacitors is implemented. In this paper, a fuzzy logic controller is employed based on a rule-based scheme and the Mamdani model to control the power distribution of the hybrid system, driven by the state of charge and duty cycle parameters. An active topology with one bi-directional DC-to-DC converter at each source is exploited in the MATLAB/Simulink environment, and five power states like acceleration and coasting are identified. Results show that the ideal duty cycle is within 0.40–0.50 as a universal value for all power states, which may vary depending on the available state of charge. Total efficiency is enhanced by 6%, sizing is increased by 22%, leading to a more compact layout, and battery life is extended by 20%. Future work includes testing with larger energy sources and the application of this management strategy in real-time operations.

Optimization of a novel drive mechanism approaching the ideal cycle for beta type Stirling engines

Stirling engines are capable in the renewable energy gain and the recovery of waste heat, both of which are important issues today. Existing studies revealed that the piston trajectories convergent to the Stirling cycle provide more power than traditional crank mechanism. In this study, a hypocycloid drive mechanism not used in the literature was optimized on the ideal piston trajectories for beta type Stirling engines. Optimization was realized to improve the isochoric heating and cooling processes as well as the isothermal compression and expansion. The cyclic work was treated as another objective succession. The optimal results taking into account these five objectives were obtained with the gear ratios of 5 and 4 for displacer piston and power piston, respectively. The piston dwells provided the enough objective succession not only for the both isochoric processes but also for the isothermal compression process, while failed in the isothermal expansion. In comparison with crank mechanism, a cyclic work increment of 10% was achieved in the near-ideal piston trajectories, but the maximum increment of 14% eventuated in some out of ideal.