Low Compressor Research Articles

Flow Control for Unmanned Air Vehicles

The pervasiveness of unmanned air vehicles (UAVs), from insect to airplane scales, combined with active flow control maturity, has set the scene for vehicles that differ markedly from present-day configurations. Nano and micro air vehicles, with characteristic Reynolds numbers typically less than 105, rely on periodically generated leading-edge vortices for lift generation, propulsion, and maneuvering. This is most commonly achieved by mechanical flapping or pulsed plasma actuation. On larger UAVs, with Reynolds numbers greater than 105, externally driven and autonomous fluidic systems continue to dominate. These include traditional circulation control techniques, autonomous synthetic jets, and discrete sweeping jets. Plasma actuators have also shown increased technological maturity. Energy efficiency is a major challenge, whether it be batteries and power electronics on nano and micro air vehicles or acceptably low compressor bleed on larger UAVs. Further challenges involve the development of aerodynamic models based on experiments or numerical simulations, as well as flight dynamics models.

Experimental Study of a Novel Centrifugal Compressor With Two Successive and Independent Rotors

Abstract This study deals with a low pressure-ratio centrifugal compressor consisting of two counter-rotating rotors called a counter-rotating centrifugal compressor (CRCC). The design method based on the loss model was presented to determine the geometric parameters of the two counter-rotating rotors. According to this method, the rotor of a selected single rotor centrifugal compressor (SRCC) has been redesigned into two counter-rotating rotors (upstream and downstream rotors) by choosing the value of meridional length ratio (LR). The meridional view, the volute shape, and the operating parameters of SRCC are preserved during the design process. In a first step, the counter-rotating mode at a constant rotor speed of 11k rpm has been carried out. The overall characteristics of CRCC are compared to those of SRCC. In a second step, the map characteristic of CRCC is established for seven speed ratios. The results show that CRCC increases up to 4.6% for the pressure ratio and 3.5% for the efficiency compared to SRCC at the same tip-speed. In addition, CRCC can operate at a lower tip-speed by about 2k rpm to produce the same characteristics as SRCC, with better efficiency over a wide range of flow rates. However, the surge margin of the CRCC is shifted to higher flow rates. This disadvantage of the CRCC was solved by choosing the adequate pair of the rotational speeds of the two rotors that will be presented in other publication.

Circumferential Variation of Noise at the Blade-Pass Frequency in a Turbocharger Compressor with Ported Shroud

<div class="section abstract"><div class="htmlview paragraph">The ported shroud casing treatment for turbocharger compressors offers a wider operating flow range, elevated boost pressures at low compressor mass flow rates, and reduced broadband whoosh noise in spark-ignition internal combustion engine applications. However, the casing treatment elevates tonal noise at the blade-pass frequency (BPF). Typical rotational speeds of compressors employed in practice push BPF noise to high frequencies, which then promote multi-dimensional acoustic wave propagation within the compressor ducting. As a result, in-duct acoustic measurements become sensitive to the angular location of pressure transducers on the duct wall. The present work utilizes a steady-flow turbocharger gas stand featuring a unique rotating compressor inlet duct to quantify the variation of noise measured around the duct at different angular positions. The acoustic pressure transducers installed on the rotating duct record time-resolved in-duct acoustic pressure at different azimuthal locations while the compressor is held at a steady operating point. Acoustic measurements are performed across the flow range of a ported shroud compressor at three different rotational speeds. A comparison of sound pressure levels measured at different azimuthal locations reveals the significant contribution of high-frequency BPF noise to the variation in the acoustic pressure around the duct.</div></div>

Advanced exergy and thermoeconomic analysis of the supercritical carbon dioxide recompression cycle: A comparative study

In this paper, the superconducting carbon dioxide cycle is re-examined and compared from the perspective of advanced and thermoconomic exergy analysis to identify real potentials and prioritize the improvement of cycle components. In advanced exergy analysis, in addition to calculating the total exogenous exergy destruction for each component, the contribution and effect of each of the other components and their combination in causing this inefficiency have also been identified. In thermoeconomic analysis of the system, the unit cost of the product, the cost of investment and the cost of destroying the exergy for the components of the system are calculated. Improvements based on advanced exergy analysis are assigned to high temperature recuperator, turbine, compressor 1, preheater, low temperature recuperator, compressor 2 and reactor, respectively. Also, based on thermoeconomic analysis, improving the turbine and reactor is not economically justified. However, the results show that even by abandoning the improvement of these two components, due to their high economic cost and by improving other components of the cycle based on the prioritization of advanced exergy analysis, it is possible to increase the efficiency of the exergy cycle from 4/29/47. There is 63% to 47.4% and cycle energy efficiency from 34.15% to 45.84%.

Solid Oxide Electrolysis System Optimization for Lunar Production of H2 and O2

Remote sensing spacecraft have located extensive surface ice in lunar permanently shadowed regions (PSRs) associated with craters near the poles. Producing H2 and O2 propellants from icy regolith in these regions requires development of integrated, robust electrolysis systems capable of operating in cryogenic environments. This team is demonstrating the feasibility of propellant production from lunar ice using high-temperature solid-oxide electrolysis (SOXE) and an optimized integrated balance-of-plant (BOP). High-temperature steam electrolysis has an efficiency advantage over PEM and alkaline electrolyzers, requiring less than 45 kWhelec kgH2 -1 [1], much less than liquid-phase electrolysis. SOXE systems require efficient steam generation and compression, heat recuperation, and subsequent drying of the H2 product stream. In this study, optimization of a demonstration system using less than 4.0 kWelec is based on OxEon’s SOXE stack that can deliver exceptionally high steam-utilization, (U H2O > 95%) and direct electrochemical O2 compression to facilitate O2 liquification with passive cooling at lunar PSR temperatures. This optimization forms the basis for the implementation of a lab-scale system for testing in a cryo-vac chamber, in order to demonstrate the viability of the optimized system for potential further, flight-scale development.The SOXE stack utilizes rare-earth stabilized zirconia electrolyte similar to technology in the MOXIE (Mars Oxygen In-Situ Resource Utilization Experiment) system [2]. The stack operates at 800ºC to balance trade-offs between area-specific resistance (ASR) and degradation. The 800ºC operating temperature requires efficient thermal integration of BOP to minimize specific energy and mass for reliable operation in the PSRs’ ‘cryo-vac’ conditions, where temperatures can reach as low as 40 K. This study shows how high U H2O enables optimization of the BOP components for system designs that can operate in the cryo-vacuum conditions with specific power w sp < 45 kWhelec kgH2 -1.Figure 1a illustrates principal BOP components including a steam generator, a compressor, cathode and anode heat recuperators, and a H2cooler/dryer. Passive radiative coolers for lunar operation prepare exhaust O2 and H2 product streams for liquification. The team developed a MATLAB-based process model to optimize the system configuration and operation. Performance of the stack, heat exchangers, and compressor are parameterized with both design parameters and system operating conditions that served as optimization variables. The system model is called by the MATLAB function ‘fmincon’ to minimize w sp under constraints that maintain reasonable system mass.The optimization study fixes H2 production rate at 0.075 kg H2 h-1 for the demonstration system in the lab-scale cryo-vac chamber. Optimization variables n this study for this lab-scale prototype system include 1) SOXE stack steam utilization U H2O ; 2) SOXE stack anode electrochemical compression DP a, for the O2 exhaust pressure; 3) steam generator vapor outlet temperature T vap; 4) compressor (scroll) pressure ratio P rat; and 5) inlet steam mass-flow split between recuperators. The SOXE electrolysis stack has a fixed cell area (110.8 cm2) and an experimentally measured area specific resistance (ASR). An electric preheater for the flow out of the cathode recuperator set the inlet steam flow to the 800 ℃ operating temperature, and this preheater added to the power (and thus specific work) required for the system. The SOXE cell operates at the thermoneutral voltage (V tn ≈ 1.28 V/cell @ 800℃) and stack current I tot is proportional to (V tn – V OCV)/ASR, where V OCV, open-circuit voltage, increases with U H2O. Primary BOP power demands include the compressor motor, SOXE stack steam preheater, thermal enclosure heater, and supplemental electric heating for the steam generator, but overall, the stack represented more than 80% of total power demand.Optimization of the system operating at 0.075 kg H2 h-1 shows that w sp had the highest sensitivity to U H2O with values above 0.85 required to achieve w sp < 45 kWhelec kgH2 -1 as shown in the contour plots of Figures 1b and 1c. Minimizing w sp encourages lower compressor pressure ratiosP rat which is limited to a minimum of 2.0. Increasing the steam generator temperature reduces compressor power demand but increases supplemental electrical heating for the steam generation, Thus, steam generator outlet temperature has minimal impact on w sp as shown in Figure 1c. Electrochemical compression of the O2 anode product does not benefit w sp, but it will greatly reduce the O2 passive cooler size which reduces mass/costs for a lunar deployed system. Additional studies are ongoing to look at trade-offs between system mass and system power with an eye toward optimizing both cost and reliability in a full-scale lunar deployed system. References Poszdeich, K. Schwarze, and J. Brabandt, Intl. J. Hydrogen Energy, 44(35), 19089-19101, 2019.Hartvigsen, S. Elangovan, J. Elwell, and D. Larsen, ECS Trans., 78(1), 2953-2963, 2017. Figure 1

Energetic and exergetic performance comparison of an experimental automotive air conditioning system using refrigerants R1234yf and R134a

In this study, the energetic and exergetic performance merits of an automotive air condition-ing (AAC) system using R134a and R1234yf have been investigated. For this aim, a laboratory AAC system was developed and equipped with devices for mechanical measurements. The refrigeration circuit of the system mainly had an evaporator, condenser, liquid receiver, fixed capacity compressor, and thermostatic expansion valve. The tests were performed by changing the compressor speed and air stream temperatures incoming the condenser and evaporator. Based on energy and exergy analysis, various performance parameters of the AAC system for both refrigerants were determined and presented in comparative graphics. It was found that R1234yf resulted in 0.4–10.9% lower refrigeration capacity, 5.5–11.6% lower COP, and 4.7–16.1°C lower compressor discharge temperature, while yielding 9.3–22.3% higher refrig-erant mass flow rate and 1.1–3.5°C higher conditioned airstream temperature in comparison to R134a. Moreover, the components of the R1234yf system usually destructed more exergy, and the total exergy destruction rate per unit refrigeration capacity of the R1234yf system was 4.1–15.3% greater than that of the R134a one.

Experimental studies on direct expansion solar thermal heat pump systems using R430A as a substitute to R134a

The use of halogen-based refrigerants in heat pump applications is restricted because of their high global warming potential (GWP). Therefore, it is necessary to identify a low GWP substitute for heat pump applications. This article presents the energy performance of a direct expansion solar thermal heat pump system (DXSTHPS) using R430A as an environmentally friendly substitute to phase out R134a. The effects of ambient parameters on compressor discharge temperature, compressor energy consumption, condenser heating capacity and coefficient of performance (COP) of a DXSTHPS using R134a and R430A are estimated and compared. Moreover, the total equivalent global warming impacts (TEGWI) of a DXSTHPS using R134a and R430A are evaluated. The results showed that the R430A has 0.7–1.9% lower compressor energy consumption than R134a. The condenser heating capacity and COP of a DXSTHPS using R430A are higher than R134a by 4.6–8.7% and 5.1–10.2%, respectively. The compressor discharge temperature observed in a DXSTHPS using R430A is 5.8 °C higher than R134a. The lubricant physical properties are retained at higher compressor operating temperatures, ensuring compressor reliability. The DXSTHPS using R430A has 4.2–12.9% lower TEGWI due to its lower GWP with lower compressor energy consumption than R134a.

Assessment of thermal performance improvement of GT-MHR by waste heat utilization in power generation and hydrogen production

The Gas Turbine Modular Helium Reactor (GT-MHR) uses two compression stages to compress the helium and a pre-cooler and an intercooler to reduce the compressors inlet temperature, that dissipate around 308.36 MWth at the design operational conditions. This dissipated thermal energy can be used as an energy source to produce hydrogen. An energy analysis is conducted for a proposed system that includes GT-MHR combined with Organic Rankine Cycle (GT-MHR/ORC) and a Proton Exchange Membrane (PEM) electrolyzer (GT-MHR/ORC-PEM) for hydrogen production. The optimum operating parameters values of the new cycle are obtained using the Engineering Equation Solver (EES) software. Thermal efficiency has been improved from 48.6% for the simple GT-MHR cycle to 49.8% for the new combined (GT-MHR/ORC-PEM) cycle including hydrogen production at a rate of 0.0644 kg/s at the same operating conditions. However, the thermal efficiency for the combined GT-MHR/ORC was higher and reaches 50.68%. Moreover, a parametric study is carried out over a wide range of some operating conditions such as turbine inlet temperature, Compressor pressure ratio and compressor inlet temperature to investigate their effect on the new cycle performance. Results revealed that increasing the low-pressure compressor inlet temperature increases the amount of hydrogen produced while decreasing thermal efficiencies for the three cycles. Furthermore, increasing compressor pressure ratio reduces the mass flow rate of hydrogen produced util it reaches a minimum value then it starts to increase slightly, on the contrary, an opposite relationship is observed between thermal efficiencies and compressor pressure ratio. Moreover, at low compressor pressure ratio, the rate of hydrogen produced increases with increasing turbine inlet temperature; however, it decreases by increasing the turbine inlet temperature at high compressor pressure ratio. Nevertheless, a direct correlation is noticed between thermal efficiencies and turbine inlet temperature.

Thermoeconomic Analysis of Vapor Compression Refrigeration System With Dedicated Subcooler for High-Temperature Lift Applications

Abstract A single-stage vapor compression refrigeration system becomes inefficient and impractical when the temperature lift between the evaporator and the condenser becomes large. Under the high-temperature lift, different losses in the system increase, and more refrigerant vapor is formed at the end of the throttling process. The authors have attempted to analyze a vapor compression refrigeration system with a dedicated subcooler for high-temperature lift applications using R134a in the main cycle and four low global warming potential (GWP) refrigerants in the subcooler cycle. The modeling of the proposed system has been carried out in Engineering Equation Solver (EES) considering the energy, exergy, and economic aspects for the simulation of the system. The predicted results show that the use of the proposed system is more beneficial from both performance and economic point of view for high-temperature lift. Nearly 27% improvement in both energetic and exergetic performances are noted whereas cost is reduced by 2% when the proposed system is used instead of a typical refrigeration system. Finally, the present investigation concludes that the use of refrigerant R1234ze is much efficient than the other investigated refrigerants due to its low GWP and compressor discharge temperature, in spite of achieving better thermo-economic performances using R152a as subcooler refrigerant.

Повышение качества проектирования малорасходных ступеней центробежных компрессоров путем создания базы данных виртуальных рабочих колес по результатам CFD-моделирования

Повышение качества проектирования малорасходных ступеней центробежных компрессоров путем создания базы данных виртуальных рабочих колес по результатам CFD-моделирования

Behaviors of Surge Frequencies in Multi-stage Axial Flow Compressors over a Wide Range of Speeds

The fundamental behaviors of deep surge frequencies in axial-flow compressors have come to be described as a rather simple framework for low pressure-ratio compressors, in terms of two essential reduced frequencies concerning resonance frequencies and surge frequencies, on the basis of numerical-experimental results. For high-pressure-ratio multi-stage compressors, however, the frequency behaviors over a wide range of compressor speeds tend to give drastic deviations from the simple framework, including abrupt changes and apparent irregularities. The cause was investigated here by numerical simulations on a nine-stage axial flow compressor. Generally, deep surge frequencies of high-pressure ratio compressors tend to lower gradually, from low speeds toward higher ones. At somewhat below the design speed, the frequencies tend to decrease precipitously, settling to some very low levels of values. The discontinuous drops in the frequencies are shown to result from occurrences of short-term incomplete surge recoveries in the stalling phase of surge. The phenomenon tends to elongate the duration of the stalled phase and the whole surge duration, resulting in the lowered surge frequency. The phenomenon is caused by the flow reversal of high-temperature air in the stalling phase of surge and the re-suction of the hot air in the unstalling phase. The degree of the peak temperature and the intensity of the interferences between the hot-air re-suction phenomenon and the intrinsic surge appear to affect significantly the additional short-term premature stalling of the compressor. It could be strongly related with the high average temperature due to the hot air re-suction, and the duration time of the suction. The complicated behaviors thus become qualitatively explainable, though only by examinations on numerical-simulation results.

Performance improvement of integrated CO2 systems with HVAC and hot water for hotels

Carbon dioxide (R744) systems have emerged as a sustainable and viable alternative to hydrofluorocarbon (HFC) applications within refrigeration. During the past decade, advancements in R744 technology and system architecture have paved the way for new areas of application. Integrated R744 systems for heating and cooling in hotels have demonstrated promising results within a sector characterized by high thermal demands and a large carbon footprint. However, further research is necessary to establish integrated R744 systems as a competitive alternative to traditional HFC systems in hotels. This paper presents the numerical model of an R744 heating and cooling unit installed in Northern Europe. The system is integrated with HVAC and a 6 m3 thermal storage for domestic hot water. A dynamic model of the hotel’s thermal system was created and validated for three seasonal representative weeks using recorded ambient temperatures, heating, and cooling loads. A low load charging strategy, which exploits the thermal storage flexibility, was evaluated as an approach to improve the overall system performance. Simulations demonstrated that charging the thermal storage for longer periods at low compressor loads enhanced the overall efficiency of the system. Energy savings in the range of 5.8–13.2% were achieved based on the different seasonal scenarios. Additionally, peak power usage, operational fluctuations, and ON/OFF cycles were considerably reduced with the low load charging strategy. The proposed strategy can be implemented in similar applications to enhance overall system performance.

Effects of Evaporator and Condenser Temperatures on the Performance of a Chiller System With a Variable Speed Compressor

The operation and performance of heat-pump systems are affected by indoor and outdoor operating conditions. Power consumption and system efficiency are related to evaporator and condenser working pressures. Intelligent controllers such as a proportional integral (PI) controller improve the performance of variable speed refrigeration systems (VSRs) with electronic expansion valve (EEV). Evaporator and condenser pressures affect the system power consumption and efficiency. In this study, the influence of evaporator and condenser temperatures on the performance of a variable speed refrigeration system with an EEV was experimentally investigated at constant cooling load. The experimental system comprises of a rotary compressor, shell-and-coil condenser, EEV, and shell-and-coil evaporator for one-ton cooling capacity with refrigerant R410. Compressor speed and EEV opening are controlled by a PI controller with two control loops and the refrigerant superheat (DS) is maintained at 7°C. The results show that at constant cooling capacity, the refrigerant flow rate rises with the increase in the compressor speed. The coefficient of performance (COP) is improved with low compressor speed. The System COP is increased by 3.3% with increasing evaporator inlet water temperature for 2°C due to the reduction in the compressor speed and compression ratio. High condenser inlet water temperature promotes the refrigerant subcooling.

Sound radiation of the exhaust gas turbocharger as a function of the compressor inflow

The use of exhaust gas turbochargers in modern engine concepts is essential to achieve high efficiencies, low fuel consumption, and low emissions. However, the high rotational speed, a wide range of compression ratios, and dynamic acceleration and deceleration processes cause both tonal and broadband sound radiation. Due to packaging constraints, the intake cycle is often characterized by deflections and cross-section jumps. That leads to a strong secondary flow at the inflow of the compressor. Therefore, in this study, we intensively investigated the influence of disturbed inflow conditions on the sound radiation of the exhaust gas turbocharger. As a result, we found that the flow caused by a 105∘-bend in front of the compressor leads to an increase in broadband flow noise up to 5.5dBA. The decisive factor here is the amount of pre-whirl at the outer radius of the pipe. A high velocity gradient additionally shifts the surge line towards lower flow coefficients and mass flows, respectively. That indirectly reduces the sound radiation due to the greater distance of the operating points to the surge line. However, pre-whirl can counteract this effect. The surge line shifts to larger mass flows due to the decrease of the relative flow angle. In contrast, low turbulence levels and homogeneous compressor inflow lead to reduced flow separation and thus lower broadband sound radiation. The reduction of the secondary flow in the intake of the compressor, e.g. due to pre-guidance devices, therefore represents a promising way of reducing the noise emission of the exhaust gas turbocharger in a passenger car.

Steady-State Performance Prediction for a Variable Speed Direct Expansion Air Conditioning System Using a White-Box Based Modeling Approach

When using a certain type of Heating, Ventilation &amp; Air Conditioning (HVAC) systems, it is primary to obtain their steady-state operating behaviors for achieving a better indoor thermal environment. This paper reports a development of a white-box-based dynamic model for a direct expansion (DX) air conditioning (A/C) system to predict its steady-state operating performance under variable speed operation. The established model consists of five sub-models, i.e., a compressor, an electronic expansion valve, an evaporator, a condenser and a conditioned space. Each sub-model was developed based on partial lumped parameter approach. Using the available data generated from an experimental DX A/C system, both transient and steady-state behaviors predictions agreed well with the experimental ones. With the help of the validated white-box model, the inherent steady-state operating performance expressed in terms of the relationship among total cooling capacity (TCC), equipment sensible heat ratio (E SHR) and coefficient of performance (COP) under various speed combinations of compressor and supply fan were further examined. The results show that a higher COP could be achieved when the DX A/C system was operated at a higher fan speed or a lower compressor speed for dealing with a larger required E SHR. This model could be helpful for A/C system design and controller development.

Parametric Study of Various Thermodynamic Cycles for the Use of Unconventional Blends

This paper aims to conduct a parametric study for five gas turbine cycles (namely, simple, heat exchanged, free turbine and simple cycle, evaporative, and humidified) using a CO2-argon-steam-oxyfuel (CARSOXY) mixture as a working fluid to identify their optimal working conditions with respect to cycle efficiency and specific work output. The performance of the five cycles using CARSOXY is estimated for wet and dry compression, and a cycle is suggested for each range of working conditions. The results of this paper are based on MATLAB codes, which have been developed to conduct the cycle analysis for CARSOXY gas turbines, assuming a stoichiometric condition with an equivalence ratio of 1.0. Analyses are based on the higher heating value (HHV) of methane as fuel. This paper also identifies domains of operating conditions for each cycle, where the efficiency of CARSOXY cycles can be increased by up to 12% compared to air-driven cycles. The CARSOXY heat exchanged cycle has the highest efficiency among the other CARSOXY cycles in the compressor pressure ratio domain of 2–3 and 6–10, whereas, at 3–6, the humidified cycle has the highest efficiency. The evaporative cycle has intermediate efficiency values, while the simple cycle and the free turbine-simple cycle have the lowest efficiencies amongst the five cycles. Additionally, a 10% increase in the cycle efficiency can be theoretically achieved by using the newly suggested CARSOXY blend that has the molar fractions of 47% argon, 10% carbon dioxide, 10% H2O, and 33% oxyfuel at low compressor inlet temperatures, thus theoretically enabling the use of carbon capture technologies.

Energetic and exergetic studies of modified CO2 transcritical refrigeration cycles

Abstract Thermodynamic analysis including energetic and exergetic analysis is carried out employing Engineering Equation Solver for the five modified cycles: dual expansion cycle, internal heat exchanger cycle, work recovery cycle, work recovery with internal heat exchanger cycle and vortex tube expansion cycle. Contours are developed to study the effect of gas cooler temperatures and evaporator temperatures on the system performance and optimum gas cooler pressure. The modified cycle with work recovery turbine offers relatively higher COP and higher exergetic efficiency with lower compressor discharge pressure. The exergy loss in compressor, gas cooler, throttle valve and vortex tube (VT) are considerably higher than that in internal heat exchanger (IHX), evaporator and turbine. It is observed that COP of modified cycle with VT is slightly less than that with IHX, whereas the cycle with work recovery turbine brings the highest COP with the improvement of 25% at the gas cooler exit temperature of 305 K and evaporator temperature of 248 K.

Experimental energy and exergy performance of an automotive heat pump using R1234yf

Various energy and exergy performance parameters of an automotive heat pump (AHP) with R1234yf have been investigated and compared with those of the baseline system with R134a. For this aim, an AHP system was set up from the components of an air-conditioning system employed in a compact car and equipped with instruments for mechanical measurements. It was tested with R1234yf and R134a by changing the compressor speed and air stream temperatures incoming the outdoor and indoor units. Using test data, energy and exergy analyses of the AHP were performed, and its performance parameters were evaluated. The R1234yf system provided conditioned air temperatures in the range of 29.9–59.3 °C, heating capacities in the range of 1.96–3.14 kW and coefficient of performance (COP) values in the range of 2.44–4.56. It yielded 3.3–10.8 °C lower conditioned air temperature, 9.2–15.4% lower heating capacity, 1.6–7.1% lower COP, 13.8–21.6 °C lower compressor discharge temperature, 3.1–19.2% higher total exergy destruction rate per unit heating capacity but significantly less TEWI in comparison with the system with R134a. Moreover, the R1234yf system yielded larger exergy destructions in the outdoor unit, compressor and expansion device but lower exergy destruction in the indoor unit. These findings reveal that R1234yf can be used in AHP systems in expense of less heating capacity, lower COP and higher exergy destruction rate per unit heating capacity in comparison with R134a.

An alternative architecture of the Humphrey cycle and the effect of fuel type on its efficiency

AbstractConventional gas turbines are a very mature technology, and performance improvements are becoming increasingly difficult and costly to achieve. Pressure‐gain combustion (PGC) has emerged as a promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine cycles. The current work analyzes two layouts of the Humphrey cycle for gas turbines with pressure‐gain combustion. One layout replicates the classical layout of gas turbine cycles, whereas an alternative one optimizes the use of pressure‐gain combustion by ensuring the operation of the combustor at stoichiometric conditions. In parallel, both cycle layouts are studied with two different fuels—hydrogen and dimethyl ether—to account for differences in combustion specific heat addition and its effect on cycle efficiency. The current work concludes with an attempt to benchmark the maximum losses of a plenum to achieve efficiency parity with the Joule cycle, for a given pressure gain over a PGC combustor. It is found that the cycle layout with stoichiometric combustion results in an increase in thermal efficiency of up to 7 percentage points, compared to the classic cycle architecture. Moreover, the thermal efficiency of the new layout is less sensitive to the turbine inlet temperature, especially at low compressor pressure ratios. The study of the two fuels has shown that the larger mass specific heat addition leads to higher cycle thermal efficiency and should be considered during the fuel choice. Finally, the maximum allowable plenum pressure loss that results to efficiency parity with the Joule cycle has been computed for a given combustor pressure gain. For turbine inlet temperatures above 1500°C, pressure gain above 1.6 would allow for at least 20% relative pressure drop in the plenum. The respective pressure gain becomes considerably higher for lower turbine inlet temperatures.

Comprehensive Performance Analysis for the Rotating Detonation-Based Turboshaft Engine

The potential advantages of rotating detonation combustion are gradually approved, and it is becoming a stable and controllable energy conversion way adopted to the propulsion devices or ground-engines. This study focuses on the rotating detonation-based turboshaft engine, and the architecture is presented for this form of engine with compatibility between the turbomachinery and rotating detonation combustor being realized. The parametric performance simulation model for the rotating detonation-based turboshaft engine are developed. Further, the potential performance benefits as well as their generation mechanism are revealed, based on the comprehensive performance analysis of the rotating detonation-based turboshaft engine. Comparisons between the rotating detonation turboshaft engine and the conventional one reveal that the former holds significant improvements in specific power, thermal efficiency, and specific fuel consumption at lower compressor pressure ratios, and these improvements decrease with the increase of compressor pressure ratio and increase as turbine inlet temperature increases. The critical compressor pressure ratio corresponding to the disappearance of specific power improvement is higher than that corresponding to the disappearance of thermal efficiency and specific fuel consumption. These critical compressor pressure ratios are positively correlated with flight altitude and negatively correlated with flight velocity. The conductive research conclusion is guidable for the design and engineering application of rotating detonation-based engines.