Operating Pressure Ratio Research Articles

Upgraded one-dimensional code for the design of a micro gas turbine mixed flow compressor stage with various crossover diffuser configurations

Abstract Micro Gas Turbine (MGT) designers often have the need for a design tool, capable of rapidly providing feasible design options. The upgrade of such an existing MATLAB® based mixed flow compressor design application (1D App) is discussed. In MGT engines, diffuser design largely influences the compressor stage performance. Crossover diffusers provide superior efficiency and pressure ratio performance compared to legacy type diffusers, albeit at the expense of operating range. The reduced operating range attributed to single vane crossover diffusers can be alleviated by splitter vane, tandem vane, and combined configurations. Therefore, the 1D App is updated to allow the user the ability to design these additional crossover diffuser configurations. Performance results are verified using Numeca/FINE™ Turbo CFD software. It is shown that the upgraded 1D App provides predicted performance results within 1 % of CFD results for both total-to-total efficiency and pressure ratio.

Turning Data Center Waste Heat into Energy: A Guide to Organic Rankine Cycle System Design and Performance Evaluation

This study delves into the adoption of the organic Rankine cycle (ORC) for recovering waste heat from data centers (DCs). Through a literature review, it examines energy reuse with a focus on electric power generation, the selection of working fluids, and system design principles. The objective is to develop a thorough framework for system design and analysis, beginning with a quantity and quality investigation of waste heat available. Air cooling systems, chosen often for their simplicity, account for about 70% of used cooling methods. Water cooling demonstrates greater effectiveness, albeit less commonly adopted. This study pays close attention to the selection of potential working fluids, meticulously considering the limitations presented by the available sources of heat and cold for vaporization and condensation, respectively. It reviews an ORC-based system setup, incorporating fluid streams for internal processes. The research includes a conceptual case study where the system is designed and simulations are conducted in the DWSIM environment. The simulation model considers hot air or hot liquid water returning from the data center cooling system for ORC working fluid evaporation. Ambient water serves for condensing, with pentane and isopentane identified as suitable organic fluids. Pentane assures ORC net electric efficiencies ranging between 3.1 and 7.1% when operating pressure ratios increase from 2.8 to 6.4. Isopentane systems, meanwhile, achieve efficiencies of 3.6–7.0% across pressure ratios of 2.7–6.0. Furthermore, the investigation provides key performance indicators for a reference data center in terms of power usage effectiveness (PUE), energy reuse factor (ERF), energy reuse effectiveness (ERE), and greenhouse gas (GHG) savings. This study concludes with guidelines for system analysis, including exergy considerations, and details the sizing process for evaporators and condensers.

Composite membranes based on ether oxygen-rich polyimide with superior CO2/N2 separation properties prepared by interfacial polymerization

Ether oxygen-rich polymeric membranes emerge as promising membranes in CO2 separation due to the high affinity between CO2 molecules and ethylene oxide segments. However, there is a massive challenge in developing asymmetric membranes with high CO2 permeation performance and CO2/light gas separation performance. This work revealed composite membranes with ether oxygen-rich polyimide separation layers were developed by interfacial polymerization between 1,2,4,5-benzenetetracarbonyl tetrachloride and commercial diamines named o,o'-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol followed by thermal imidization. The influences of the polymerization time and monomer concentrations on the gas transport and separation properties of the composite membranes were studied based on single-gas permeation. The optimum membrane possessed a superior high ideal CO2/N2 separation factor of 429 accompanied with a moderate permeance of 150 GPU for CO2 at 25oC and 0.2 MPa. The performance stability was studied by operating the membrane at various pressures and temperatures. The result showed the composite membrane possessed excellent plasticization resistivity at high pressures. The separation property of composite membranes for CO2/N2 binary mixture was also evaluated. The influences of the operation parameters, including stage-cut and pressure ratio on the product purity and recovery were investigated. The results showed great practical application potential in efficient separation of flue gas.

Effect of Engine Design Parameters on the Climate Impact of Aircraft: A Case Study Based on Short-Medium Range Mission

The climate impact of aviation is considerably different from that of other transport modes. The turbofan engine’s efficiency can be increased by increasing the Operating Pressure Ratio (OPR), bypass ratio (BPR) and Turbine Inlet Temperature (TIT), thereby reducing CO2 and H2O emissions. However, this may have an adverse effect on the secondary emissions, such as NOx, soot, etc. Taking a holistic view in evaluating the climate impact of engine development trends considering all the climate forcers is imperative for design trends in the future. This research investigates the impact of some key engine design parameters on climate. The emission changes due to design variations in the CFM56-5B are estimated using in-house engine performance and emission prediction tools. Accordingly, the changes in the species’ Average Temperature Response for 100 years (ATR100) are analyzed using a climate assessment tool, AirClim. The results show that the overall climate impact increases by 40% when increasing OPR from 25 to 40. Meanwhile, the Twin Annular Premixed Swirler (TAPS-II) combustor reduces the total ATR100 drastically, in the range of 52–58%, due to lean combustion.

An innovative S–CO2 recompression Brayton system and its thermodynamic, exergoeconomic and multi-objective analyses for a nuclear spacecraft

An innovative layout of a recompression supercritical carbon dioxide (S–CO2) cycle for nuclear spacecraft was proposed in this work. Thermodynamic and exergoeconomic analysis of the innovative cycle have been performed to study the effect of essential operating parameters on the split ratio, maximum operating pressure ratio, minimum operating temperature, maximum operating temperature, and compressor C4 inlet pressure based on the first and second laws of exergoeconomics and efficiency. Finally, the innovative power cycle is optimized with high efficiencies, low cost and lightweight. The results show that the optimization progress is based on the thermodynamic and exergoeconomics method; the minimum operating temperature can significantly improve efficiencies and reduce circular investment cost; then after the multi-objective optimization progress, the thermal efficiency (ηth), exergy efficiency (ηex) and mass of Brayton turbomachinery unit (MBTU) improved by 2.71 %, 3.69 %, and 2.8 %; total capital cost rate (total) and levelized cost of electricity (LCOE) reduced by 0.88 % and 4.55 %, respectively.

Characterization of cavitation zone in cavitating venturi flows: Challenges and road ahead

Dynamic features of a cavitating venturi have been a topic of investigation for the past few decades. This review presents state-of-the-art of experimental and numerical studies in cavitating venturi to address the challenges in understanding flow behavior and developing reliable numerical models. Many experimental studies have shown that two strongly coupled mechanisms, namely, Re-entrant Jet and the bubbly shock influence the cavitation zone behavior. We provide pointers from the past and recent studies to the influence of geometry and operating conditions, introducing changes in cavity oscillation. From an operational viewpoint, the modeling studies need to predict four crucial parameters related to its steady and dynamic operation: choked mass flow rate, operating pressure ratio range, cavitation length, and frequency of cavity oscillations. In this paper, we discuss the possible ways to properly configure a one-dimensional (1D) model, which can be a handy tool for extracting the key integral parameters. Realistic predictions require direct numerical simulations, which is not always an economically viable option. Recent three-dimensional (3D) simulations with compressible formulations for flow field and a cavitation model coupled with large eddy simulations to handle turbulence have achieved some success in predictions. Many simplified approaches have been popular. In this paper, we systematically bring out the predictability limits of popularly used mixture models coupled with cavitation and turbulence in more commonly studied two-dimensional (2D) and fewer three-dimensional geometries. Two-fluid models could provide answers, but further studies are required to mitigate the modeling challenges and to enable realistic predictions of the steady and dynamic features of this elegant flow control device for a chosen application.

Experimental characterization of cavitation zone and cavity oscillation mechanism transitions in planar cavitating venturis

Cavitating venturi is a passive flow rate anchoring device used in varied industrial applications. The dynamics of the cavitation zone can be of interest to ascertain the controlled operation of cavitating venturi under varying pressure ratios. In the current work, we present the results of the complete characterization of three planar cavitating venturis with different divergent angles. Quasi-steady experiments are conducted for a pressure ratio range of 0.39–0.95 and an inlet Reynolds number range of 7.3 × 104–1.28 × 105. Shadowgraphy and high-speed imaging are used to obtain the cavitation zone length and the oscillation frequencies. Spectral proper orthogonal decomposition and discrete Fourier transform are used to assess the dynamics of the cavitation zone. The cavitation zone behavior has been delineated into three specific zones (named R1, R2, and R3 in this work) during the operation when the cavitation is fully contained within the divergent section. Two Strouhal number ranges (based on the inlet dimensions), StD,in≥ 0.1 for large-scale cloud shedding and StD,in≤ 0.05 for small-scale oscillations of the attached cavity, are ascertained as a primary indicator of the dynamic behavior. The current work confirms that the dynamics is governed by re-entrant jet at high cavitation numbers in R1 and the combined action of the re-entrant jet and the bubbly shock wave (collapse-induced) at low cavitation numbers in R3. The transition in the cavitation zone behavior in R2 primarily causes a shift in the sensitivity of the cavitation zone and the dominant frequencies over the operating pressure ratios. In the present work, we show that the span of the transition region (R2) decreases with an increase in the divergent angle.

Thermodynamic Performance Comparisons of Ideal Brayton Cycles Integrated with High Temperature Fuel Cells as Power Sources on Aircraft

Developing hybrid electric aircraft is propitious to reducing carbon dioxide emissions and fuel consumption. Combustion engines coupled with solid oxide fuel cells are proposed for aircraft propulsion systems, where the compressor is powered by fuel cells instead of turbines. The thermal cycle of the new engine is obviously different from that of conventional combustion engines and can be characterized in the temperature entropy diagram under some reasonable assumptions, which were analyzed and investigated. Performance parameters, such as the specific thrust, are derived and can be expressed by several fundamental thermal parameters. Three different cycles integrating Brayton cycles and SOFC are shown. The main conclusions are as follows: (1) The maximum operating pressure ratio of the Brayton cycles integrated with fuel cells is 32. The maximum thermal efficiency of the cycle at the lowest combustion temperature is 82.2%, while that of the BC is 65.1% at the high combustion temperature. (2) The new cycles can not work if the combustion temperature is lower than 1350 K. Otherwise, the fuel utilization will be too huge.

Flametube Evaluation of a Lean-Lean Combustor Concept Developed for Supersonic Cruise Aircraft

Abstract Gaseous emissions were measured in single-cup flametube tests of an advanced low-NOx combustor concept at simulated supersonic cruise conditions. The combustor concept is a low technology readiness level (TRL), lean front-end design developed under the NASA Fundamental Aeronautics/Supersonics project to minimize NOx emissions at supersonic cruise. The flametube conditions matched or approached combustor conditions at supersonic cruise, with combustor inlet temperatures up to 920 K, inlet pressures up to 19 bar, and combusted gas temperatures up to 2,120 K. Whether these conditions met or just approached supersonic cruise conditions depended on the type of engine the combustor would be installed in. Two types of engines were considered here: a “derivative” engine based on a current technology and an “advanced” engine with a higher operating pressure ratio and higher temperature limits. For the “derivative” engine, the combustor is expected to be at least close to meeting the NASA NOx emissions goal of 10 g-NOx/kg-fuel at supersonic cruise. However, with the higher combustor inlet and flame temperatures of the advanced engine, NOx emissions are expected to be well above the goal.

Superiority analysis of the cooled cooling air technology for low bypass ratio aero-engine under typical flight mission

The cooled cooling air technology (CCA technology) is beneficial to increase the aero-engine operating pressure ratio and turbine inlet temperature, while its influence mechanism during the full flight envelope is still ambiguous. A comparative analysis has been completed in this study to assess the flight performance of an aircraft engine with or without CCA technology. Based on the aircraft and aero-engine integrated technique, a novel analytical model is developed by combining the propulsion requirement analysis model with the engine design/off-design point analysis model. The precise submodules of the heat exchanger and the turbine blade in engine model improve the -practicability of analysis, which considers the influence of the flight mission on the heat transfer performance. This literature suggests that CCA technology could enhance the fuel weight at take-off phase, the weight-specific surplus power, the load factors, and the supersonic cruising Mach number by approximately 3–4.85% with re-optimizing the cycle parameters. The inlet temperature of turbine Tt4 rises by around 3% without the turbine blade temperature exceeding the limitation. This work further analyzes the most influential structural factor of the total engine performance and the transverse tube pitch is discovered as a noteworthy feature. Additionally, it is well known that the heat transfer and pressure drop of the CCA heat exchanger (CCA-HEX) change dramatically during the whole flight mission. Our findings provide valuable insights into a better understanding of the mechanisms of CCA-HEX characteristic change, in which poor heat transfer occurs at low altitudes and high Mach numbers, whereas the largest flow resistance appears in the high-altitude and low-Mach-number regionsin theopposite manner. In conclusion, CCA technology is a cost-effective method to improve the propulsion performance of the aircraft engine for flight mission.

Flexible operation strategy for formic acid synthesis providing frequency containment reserve in smart grids

The demand-side contribution to grid frequency regulation is becoming increasingly important due to the growing penetration of renewable energy in the power system. Among energy-intensive industrial loads, chemical plants have a high potential to offer grid balancing services due to their existing control infrastructure and storage capabilities. However, applying fast ramp rates and providing time-critical grid services is not straightforward due to strict constraints and the nonlinear dynamics of chemical systems. Therefore, adaptive operating approaches are required to increase the process’s flexibility and facilitate the fast demand response operation. This work proposes a flexible operating strategy for the cooperative operation of a Polymer Electrolyte Membrane (PEM) electrolyser and multi-stage compression systems in a chemical process to provide Frequency Containment Reserve (FCR). This strategy aims to realise the desired power regulation dynamics on the grid side while maintaining the reactor’s optimal operating conditions, i.e., temperature, pressure and flow rate ratio. A techno-economic analysis is performed to obtain optimal operating points. The techno-economic analysis shows that operating the process at a baseload of 73% while offering the remaining capacity as a power reserve can create additional revenue and improve the economic profit by around 10%. The proposed approach is validated by dynamic simulations of a Carbon Capture and Utilisation (CCU) process for formic acid production. The results show that the proposed strategy can enhance the process’s operational flexibility and enable FCR provision with a limited impact on reactor efficiency (<1%).

Estimation of radial shaft seal, oil drag and windage loss in twin screw oil injected compressor

The objective of this paper is to study the mechanical power loss arising from radial shaft seal, oil drag, and windage within the twin-screw oil-injected screw compressor. The previous papers in the series presented the evaluation of power loss due to the gears and bearings where it was found that the calculated total power loss was underestimated when compared to the experimental results for different sizes of compressors and different operating conditions. This indicates that few additional contributing elements were missing and needed due consideration to enhance the prediction. Literature review of the basic fluid dynamics and transmission gears confirms that oil drag loss and windage loss can also contribute to the power loss considerably.This paper presents a review of a few methods for the prediction of the radial shaft seal, oil drag, and windage loss. Predictions with the use of these methods and their comparison with the experimental results are analysed in this paper. Experimental results of three different sizes of the compressors tested in laboratory conditions were taken as reference for the comparison at different operating speeds and pressure ratios. The analysis helps to understand the contribution of each element of the power loss which can help a designer to optimally design a screw compressor.

Parametric modeling of a solid state Ericsson cycle heat engine

The Johnson Thermoelectric Converter (JTEC) operates as an approximation of an Ericsson cycle thermodynamic heat engine with no moving parts. During operation, hydrogen flows from a high-temperature high-pressure region to a low-pressure region by way of a membrane-electrode assembly. In passing through the assembly, the hydrogen is stripped of its electrons which flow through the circuit and reform with protons to the recover hydrogen on the low-pressure side. Some of the electrical power extracted is used to electrochemically “pump” the hydrogen back to the low-temperature high-pressure side and sustain the pressure differential. The objective of the work presented here was to mathematically characterize a JTEC system and to develop the coupled relationships between design goals like efficiency, net power production, and power density; and design parameters like high versus low operating temperatures and pressures, device geometry, and thermophysical properties of the device materials and working fluid. Power production is related to the operating pressure ratio, the ratio of high to low device operating temperatures, the high operating temperature, and the effective heat transfer area of the hot end. The efficiency is related to several non-dimensional and dimensional number groups (especially the recuperator effectiveness). The power density or volume of the device is related to a different recuperator parameter, the high temperature of the heat addition source, the cold temperature of the thermal rejection source, and the internal device geometry. Even with reasonable simplifications and assumptions, the design space contains a large number of variable parameters. The model equations were exercised over the large parametric trade space.

A Software Tool for the Design and Operational Analysis of Pressure Vessels used in Offshore Hydro-pneumatic Energy Storage

Despite the breakthroughs and rapid growth in the global installed offshore wind capacity over the last two decades, a prevailing major challenge is the intermittent nature of the wind resource itself. Consequently, co-locating energy storage systems with wind turbines deployed out at sea is perceived as a key component that will help to overcome this crucial challenge and address the mismatch between the supply of green energy and actual energy demand in real time. Of particular interest are hydro-pneumatic energy storage solutions that can deliver a safer and more reliable operation for a longer life span when compared to electro-chemical storage solutions.This paper presents a smart software tool named SmartPVB, which has been specifically developed for the optimisation of the design of pressure vessel bundles used in offshore hydro-pneumatic energy storage systems. The optimised design parameters obtained through the software SmartPVB help drive the material requirements to a minimum. A sensitivity study to analyse the influence of various parameters on a hydro-pneumatic energy storage system mounted on the seabed at a water depth of 200 m is also outlined. Results suggest that the optimal operating pressure ratio to minimise steel requirments for the pressure vessel bundle lies between 2.4 and 2.6. Furthermore, it is shown that the overall mass of the pressure vessel bundle per unit of storage capacity increases with sea depth, while it decreases with increasing peak operating pressures up to 200 bar.

Fluid Dynamics of a Bistable Diverter Under Ultrasonic Excitation—Part I: Performance Characteristic

Abstract This paper investigates an ultrasonically driven bistable fluidic diverter at inlet nozzle Mach numbers of up to Mn = 0.3 and operating pressure ratios of up to Pr = 1.1. Part I examines the switching characteristics with respect to nondimensional parameters of excitation amplitude, frequency, required energy, switching time and inlet total pressure. It is shown that to promote switching at turbulent jet Mach numbers of up to Mn = 0.3 it is necessary to excite a jet preferred mode of St = 0.45 which differs from previously reported laminar jet operation of the similar device. For the reference case the switching time amounts to 1.2 ms suggesting oscillation frequencies of up to 500 Hz. Part II is a combined experimental and numerical study that examines the triggered instability modes in the free shear layer using large eddy simulations (LES) and visualizes the flow field using Particle Image Velocimetry (PIV).

Numerical Study of the Flow Uniformity Inside the High-Pressure Side Manifolds of a Cooled Cooling Air Heat Exchanger

To maintain efficiency in advanced aero-engines, it is crucial to set high limits for the Operating Pressure Ratio (OPR) and Turbine Entry temperature (TET). This can be achieved using a Cooled Cooling Air (CCA) heat exchanger, which precools the compressed air with the bypass stream before the compressed air enters the turbine to cool the blades. The aim of the present study was to improve the aero-thermal performance of CCA heat exchangers by enhancing the uniformity of flow through its high-pressure (HP) side manifolds. The development of the new manifolds was constrained by their manufacturability, as well as the pressure drop across the heat exchanger. The inlet and outlet manifold geometries are parameterised, and Computational Fluid Dynamic (CFD) simulations are carried out for Maximum Take-Off (MTO) conditions. Shape changes were performed using the mesh morphing tool, which enabled the intermediate remeshing steps to be skipped. By means of regression analysis, it was possible to find inlet and exit manifolds with improved flow uniformity; the heat transfer, structural integrity, and weight of the baseline and new manifolds were then evaluated. The new manifolds were structurally sound, and showed an 18.8% improvement in uniformity, a 10.6% reduction in pressure drop, a 0.4% increase in heat transfer rate, and a 22.5% decrease in weight.

Numerical Optimization of an Ejector for Waste Heat Recovery Used to Cool Down the Intake Air in an Internal Combustion Engine

Abstract In the present paper, a numerical investigation of a jet-ejector is carried out using a real gas model of R1234yf. The prototype under investigation works with specific operating conditions of a jet-ejector refrigeration system intended for waste heat recovery in an internal combustion engine (ICE). In the first instance, the geometry optimization involving nozzle exit diameter, mixing chamber diameter, and nozzle exit position (NXP) is performed. Once the optimum geometry has been obtained, the jet-ejector prototype is tested with different operating pressure ratios to determine its off-design performance. The flow structure in relevant cases has been examined with an emphasis on critical and subcritical modes. The flow phenomena occurring during expansion, entrainment, and mixing processes are discussed so performance degradation can be directly related to physical processes. The analysis has been completed fitting simulated points to critical and subcritical planar surfaces. The results in terms of goodness of fit are satisfactory so the jet-ejector performance in off-design operating conditions can be reflected through simple mathematic models. When the overall cycle is assessed by using previous computational fluid dynamics (CFD) maps, it is observed that the achievable cooling drops significantly when an ambient temperature of 31 °C is exceeded.

Performance characteristics comparison of major types of mechanical cryocoolers for aerospace applications

The three major types of mechanical cryocoolers in aerospace applications, namely reverse-Brayton cryocoolers, Stirling/pulse tube cryocoolers and Joule-Thomson cryocoolers, have significantly different performance characteristics. Some of these differences are due to the nature of their thermodynamic cycles; others come from their drastic differences in mean operating pressures and pressure ratios. This paper first provides an overview of the performance characteristics of these three types of cryocoolers, their unique performance benefits and main applications. It then derives an analytical expression for a cryocooler’s Carnot efficiency, considering the effects of the system pressure ratio drop from the warm end to the cold end and heat leak due to the convective flow and axial conduction. The convective heat leak is related to the pressure drop and the figure of merit of the heat transfer surface using the Colburn-Chilton analogy. Based on this result, the paper discusses the key control parameters affecting the size and mass of the heat exchanger and thus the overall cooler system in each type of cryocooler.

Investigation on reverse flow characteristics in UTSGs with coupled heat transfer between primary and secondary sides

Under natural circulation conditions, the reverse flow phenomenon may occur within some U-tubes. This will result in the flow resistance coefficient of the steam generator (SG) obviously larger than that under forced circulation conditions, and the decrease of nature circulation capability in the primary circuit (PC). The heat transfer characteristics between the secondary circuit (SC) and PC in the SG are very complicated. Expressly, there is an obvious preheating section due to a certain fluid under-heat degree at the inlet of the ascending passage in the SC. In this paper, a type of marine SG is studied and a theoretical model of the SC single channel is established for the preheating sections (PS) corresponding to the ascending section (AS) and the descending section (DS) of U-tubes. Based on this model, the reverse flow characteristics of U-tubes are researched, and the influence of SC operating pressure, U-tubes pitch and circulation ratio on the U-tube reverse flow characteristics are calculated and analyzed. The results show that compared with the existing reverse flow calculation methods, the temperature distribution in the PS of SC increases exponentially and remains unchanged in the boiling section, and the critical flow rate is relatively higher. The increase of SC operating pressure and U-tubes pitch will decrease the mass flow rate of reverse flow, and the influence of circulation ratio has the opposite conclusion.

The application of nanofiltration membrane for recovering lithium from salt lake brine

In the current study, the applicability of nanofiltration membrane for recovering lithium from salt lake brine with a high magnesium-to-lithium mass ratio was evaluated under different operating pressure, temperature, multi-ion presence, and concentration ratio conditions. The results showed that the yield of lithium and its separation from magnesium increase with pressure, with the rejection of magnesium reaching 92% at 3.5 MPa. The maximum membrane flux of 50 L/m2 h is achieved at 313 K, while the separation efficiency decreases with increasing temperature. Furthermore, the existing sodium and potassium compete with lithium to pass through the nanofiltration membrane. The yield of lithium reaches 99% when the concentration ratio is 4. However, membrane flux and separation efficiency decrease with increasing concentration ratio. Ionic fractionation is found to be governed by the special properties of the ions, dielectric exclusion, and steric hindrance. Our results indicate that DK membrane shows considerable promise as a means to separate magnesium and lithium and to recover lithium from salt lake brine with high magnesium-to-lithium mass ratios.