Compressor Inlet Research Articles

Thermodynamic evaluation and multi-objective optimization of molten carbonate fuel cell-supercritical CO2 Brayton cycle hybrid system

Fuel cell-heat engine hybrid system is a relatively new discipline which proposes to utilize the excess high-temperature heat of the fuel cell as the heat source for the heat engine. This paper is concerned with a thermodynamic analysis of a molten carbonate fuel cell-SCO2 Brayton hybrid system to optimize its performance based on a list of criteria. Four objective functions are considered, including energy efficiency, power density, exergy destruction rate density and ecological function density, to study the influence of four main parameters, including compressor inlet temperature and turbine inlet temperature of the Brayton cycle, and interconnect plate area and current density of the fuel cell, on the performance of the hybrid cycle. The strong conflict between the objective functions necessitates a multi-objective optimization procedure and, therefore, three scenarios are proposed, each takes into account a combination of three of these objective functions. The multi-objective evolutionary method integrated with non-dominated sorting genetic algorithm is used to obtain Pareto optimal frontiers. Finally, three efficient decision-making tools including TOPSIS, LINMAP and Fuzzy are employed by means of which the best answers in each case scenario are selected.Examining the Fuzzy method results for example, in the first scenario, which doesn’t consider power density, ecological function density and exergy destruction rate density meet their optimum values, 1.314 and 0.3864 kW/m2, respectively. However, energy efficiency falls by 10% compared to its maximum, which occurs in the third scenario (0.6676), where ecological function density isn’t included, and power density drops by 25% compared to its own in the second scenario (2.2783 kW/m2), where energy efficiency is not. This indicates the strong confliction between the objective functions and also the necessity of this kind of analysis. However, the first scenario would roughly provide the best condition for the system if one wanted all the objective functions to be optimum all together.

Fluid instabilities in turbocharger compression systems

Turbochargers increase the power density of internal combustion engines, which allows the displaced volume to be reduced and the fuel efficiency to be improved for the same level of performance. However, the demand for turbocharger centrifugal compressors to deliver increasingly elevated boost pressures, over a wide air flow range, results in unfavorable flow fields that generate narrow and broadband noises within the engine air induction system. The present study is a combined computational and experimental effort, focusing on identifying unsteady fluid-flow instabilities in a turbocharger compression system installed on a bench top stand. This work concentrates primarily on prediction of mild and deep surge instabilities, since they limit the low-flow operating range. Surge occurs near the Helmholtz resonance frequency of the compression system (including a compressor inlet duct, centrifugal compressor, compressor outlet duct, plenum, plenum outlet duct, and a valve) and results in low frequency pressure fluctuations throughout the compression system. Additionally, the compressor flow field adapts to operation at reduced flow rates by forming rotating instabilities in the impeller inducer and vaneless diffuser, which contribute to the occurrence of surge and produce noise as they interact with the rotating impeller and stationary volute.

Effect of inertia and compressibility on the pressure drop oscillations of two-phase boiling flows in horizontal parallel channels

In this study, a mathematical model is developed to study Pressure drop oscillations (PDOs) in two horizontal parallel channels using lumped parameter model assuming a homogeneous two-phase flow model. This model investigates the effect of external parameters, such as fluid inertia and compressible gases, on the stability margins of PDOs. Results show that the fluid inertia and compressible gases have high impact on the stability margins of two parallel channels; in fact, increasing the inlet inertia and outlet compressibility increases system stability, while increasing the outlet inertia and inlet compressibility decreases system stability. Thus, increasing the sub-cooling number and inlet resistance coefficient improves stability behavior.

ANALISA KINERJA MESIN REFRIGERASI RUMAH TANGGA DENGAN VARIASI REFRIGERAN

The most important component in the refrigerator is the refrigerant. The refrigerant absorbs heat from one side and throw it to another side through the mechanism of evaporation and condensation. This research aims to develop a refrigeration machine using different refrigerants that can be observed with the performance of the compressor, evaporator performance and COP, and hoped this research can show the installation as a medium of learning in applying the working principle of refrigerator. The research method was experimental at setting 8 refrigeration machine with data collection for the pressure and temperature of R-12 and R-134a were measured at the compressor inlet and outlet for 300 minutes. Determining the value of the enthalpy at any point by using REFPROP program. The use of different refrigerants in a refrigeration machine indicates that the refrigerant R-134a better than R-12. It can be seen after 300 minutes for R-134a, compressor performance 29.4 kJ / kg, the performance of the evaporator is 144.5 kJ / kg, COP 4.9 while for R-12 compressor performance 21.8 kJ / kg, the performance of the evaporator is 12.3 kJ / kg, COP 4.6.

A novel environmental control system facilitating humidification for commercial aircraft

Extreme aircraft cabin air dryness during cruise has aroused wide concern throughout the past 30 years. A new integrated system featuring air supply, pressure regulation, temperature control, water separation, and cabin humidification is proposed based on numerous field investigations, existing cabin humidification methods, and conventional aircraft environmental control systems. Cabin humidification is realized through the injection of purified water into the suction side of cabin environmental control system compressor without changing the original system structure. Another advantage of the new system is the lower demand of ram air benefitted from the decreased temperature of compressor inlet with water injection process. System analysis models and software using enthalpy parameter method are also presented. Verification experiments focused on the core parts of the integrated system show that the system analysis models agree with the experimental data well. System performance characteristic and fuel penalty are evaluated using thermodynamic analysis parameters. Results show that under 5 g/(kg·dry air) humidification, the cabin humidity increased smoothly to about 27.9% during the cruising state. The fuel penalty decreased by 1% under the new integrated system for the lower demand of ram air. The novel integrated system is effective and economy.

Thermodynamic Optimization of Supercritical CO2 Brayton Power Cycles Coupled to Line-Focusing Solar Fields

An opportunity for increasing the parabolic solar power plant efficiency is substituting the actual subcritical Rankine power cycles with the innovative s-CO2 Brayton cycles. In this paper, three configurations are assessed: the recompression cycle (RC), the partial cooling with recompression cycle (PCRC), and the recompression with main compression intercooling cycle (RCMCI), with one reheating stage. The thermodynamic parameters are optimized with three algorithms: SUBPLEX, UOBYQA, and NEWUOA, and the results validated with thermoflow Software. The parabolic troughs and linear Fresnel solar collectors are studied with different heat transfer fluids (HTFs): Solar Salt, HITEC XL, Therminol-VP1, Syltherm 800, and Therminol 75. The dual-loop solar field (SF), combining thermal oil and molten salt (MS) in the same solar plant, is also analyzed. The plant power output and plant energy efficiency are translated into SF aperture area and cost at design point. From the point of view of the plant efficiency and SF cost, the PTC and LF solar collector with Solar Salt as HTF coupled to a s-CO2 Brayton RCMCI cycle is selected as the optimum design solution and compared with the actual PTC Rankine solar plant performance at design point. The total recuperator conductance (UA) plays an important role in optimizing the plant performance, limited by the minimum heat exchangers (HX) pinch point. The UA increment could compensate the HX pressure drop and the compressor inlet temperature (CIT) increment, both impacting very negatively in the s-CO2 plant performance.

Experimental assessment of the open-source SU2 CFD suite for ORC applications

The first-ever experimental assessment of a Computational Fluid Dynamics (CFD) software for Non-Ideal Compressible-Fluid Dynamics (NICFD) flows of interest for ORC applications is presented here. Numerical results using SU2, the open-source suite for multi-physics simulation and design recently extended to deal with complex thermodynamic models of organic fluids, are compared here to experimental results from the Test-Rig for Organic VApours (TROVA) of the Laboratory of Compressible-fluid dynamics for Renewable Energy Applications (CREA), Politecnico di Milano. Experimental results regard supersonic expanding flows of siloxane fluid MDM (Octamethyltrisiloxane, C8H24O2Si3) in non-ideal conditions representative of ORC applications. Three different geometries are considered for the assessment of the CFD solver. The first is a converging-diverging nozzle, representative of ORC supersonic stators, in which the fluid is accelerated to supersonic speed from highly non-ideal conditions, with inlet compressibility factor Z = Pv/(RT), computed using reference Equations Of State (EOS) for MDM fluid, as low as Z ~ 0.81. The second geometry is a diamond-shaped airfoil at a neutral angle of attack. The airfoil is plunged into a supersonic flow at Mach 1.5 and Z ~ 0.9, in mildly non-ideal conditions. Oblique shock waves are observed at the airfoil leading edge and interact with the wind-tunnel walls and the rarefaction fan from the airfoil. This test case is useful to understand the physics of oblique shock-wall and shock-shock interactions in turbine cascades operating in off-design conditions. The third geometry is a supersonic backward facing step, in which the formation of an oblique shock is observed experimentally at the reattachment point past the step. The Mach number is around 1.1 and the compressibility factor Z ~ 0.89. This geometry is representative of the trailing edge of turbine blades and it is useful to study the formation of fish-tail shock waves. These NICFD flows are fairly well captured by the CFD solver, thus confirming the validity of both the thermodynamic models and of the CFD implementation, using both the Euler equations for inviscid flows with negligible thermal conductivity and the full Reynolds-averaged compressible Navier-Stokes equations, for non-ideal compressible turbulent flows. In the considered shocked flows, grid adaptation is found to be key to capture the relevant flow features using a reasonable amount of grid points.

Numerical Investigation of Back Pressure and Free-stream Effects on a Mixed Compression Inlet Performance

Inlet Performance has an important role in the operation of air-breathing propulsion systems. In this study, performance of a supersonic axisymmetric mixed-compression inlet in the supercritical operating condition is numerically studied. The effects of free-stream Mach number and engine-face pressure on performance parameters, including mass flow ratio, drag coefficient, total pressure recovery, and flow distortion are investigated. To this sake, a multi-block density-based finite volume CFD code is developed and Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras one-equation turbulence model is employed. The code is validated by comparing numerical results against other computational results and experimental data for two test cases of inviscid flow in a two-dimensional mixed-compression inlet and flow in an external compression inlet. Finally, the code is utilized for investigation of a specific supersonic mixed-compression inlet with the design Mach number of 2.0 and length to diameter ratio of 3.4. Results revealed that the increment of free-stream Mach number leads to decrease in total pressure recovery and drag coefficient, while mass flow ratio and flow distortion increase. The effects of engine-face pressure on performance parameters showed that by increasing the engine-face pressure, mass flow ratio and drag coefficient remain constant while total pressure recovery increases and flow distortion decreases.

Control of flash gas bypass MAC system with emphasis on start-ups and transients

Most of the previous research on flash gas bypass (FGB) focused on performance improvement in steady state and demonstrated that compared to direct expansion mode (DX), FGB mode have better performance. However, the control strategy of flash gas bypass system and dynamic behavior during start-ups and transients were not yet clearly defined and investigated. In this paper, a novel control strategy has been proposed for an automobile air conditioning system operating in flash gas bypass mode with R134a as the refrigerant. The proposed control strategy utilized an electronic expansion valve (EV) for the control of subcooling from condenser outlet and a bypass valve (BV) for superheat from compressor inlet. Both start-up and transient system behaviors were studied. The experimental results showed that the proposed cycle control strategy was found to be able to provide reliable control to the system. In addition, proper sizing of bypass valve and flash gas bypass tank have also been studied.

Effect of an alternative operating strategy for gas turbine on a combined cooling heating and power system

The off-design performance of a combined cooling heating and power (CCHP) system is of great importance and is affected by the system configuration and operating strategy. This paper proposes an alternative operating strategy called flue gas reinjecting (FGR) for a CCHP system consisting of a small-scale gas turbine, a double-effect absorption chiller and a hot water exchanger. The FGR operating strategy elevates the compressor inlet temperature by reinjecting a portion of the flue gas into the ambient air, which seems to contradict the well-proven concept of gas turbine inlet air cooling. In contrast, improving inlet air temperature cannot obviously influence the off-design performance of the gas turbine, and more high-temperature flue gas is produced in the gas turbine, which leads to more cooling and heating output in the absorption chiller and hot water exchanger, respectively. To extend the power output range (100–20%), reducing the turbine inlet temperature (TIT) operating strategy is introduced as an auxiliary means. The off-design performance of the CCHP system is investigated under the combined FGR and TIT operating strategy and independent TIT operating strategy. It is found that improved total efficiency and energy saving performance of the CCHP system are presented with the combined operating strategy at partial load. At a load rate of 50% (876kW), the fuel energy saving ratio (FESR) increases from 20.52% to 22.96% as the temperature of the inlet air is increased from 25 to 45°C using the combined operation strategy. The exhaust gas reinjection reduces the excess air resulting in inhibition of the formation of NOX in the combustor. Moreover, using the proposed operating strategy contributes to promoting more effective utilization of low-temperature heat and the direct blending of two fluids reduces heat and pressure losses emanating from the heat exchanger. This study may provide a new operating strategy for small-scale gas turbines to improve the off-design performance of CCHP systems.

Impact of inlet coherent motions on compressor performance

Automotive engine induction systems may be characterized by significant flow angularity and total pressure distortion at the compressor inlet. The impact of the swirl on compressor performance should be quantified to guide the design of the induction systems. In diesel engines, the presence of a valve for flow reduction and control of low pressure EGR recirculation could generate coherent motion and influence the performance of the compressor. Starting from experimental map, the compressor speed-lines have been simulated using a 3D CFD commercial code imposing different concept motion at the inlet. The swirl intensity, the direction and the number of vortices have been imposed in order to taking into account some combinations. Finally, a merit function has been defined to evaluate the performance of the compressor with the defined swirl concepts.The aim of the current work is to obtain an indication on the effect of a swirling motion at the compressor inlet on the engine performance and provide a guideline to the induction system design.

A Study on the Stall Detection of an Axial Compressor through Pressure Analysis

In order to research the inherent working laws of compressors nearing stall state, a series of compressor experiments are conducted. With the help of fast Fourier transform, the amplitude–frequency characteristics of pressures at the compressor inlet, outlet and blade tip region outlet are analyzed. Meanwhile, devices imitating inlet distortion were applied in the compressor inlet distortion disturbance. The experimental results indicated that compressor blade tip region pressure showed a better performance than the compressor’s inlet and outlet pressures in regards to describing compressor characteristics. What’s more, compressor inlet distortion always disturbed the compressor pressure characteristics. Whether with inlet distortion or not, the pressure characteristics of pressure periodicity and amplitude frequency could always be maintained in compressor blade tip pressure. For the sake of compressor real-time stall detection application, a compressor stall detection algorithm is proposed to calculate the compressor pressure correlation coefficient. The algorithm also showed a good monotonicity in describing the relationship between the compressor surge margin and the pressure correlation coefficient.

Local flow measurements in a turbocharger compressor inlet

This paper describes an experimental study carried out with the objective of characterizing flow instabilities in turbocharger compressors, specially the distribution of the high-temperature compressed backflow that appears upstream of the impeller at marginal surge conditions. The inlet of a test compressor was fitted with linear and circumferential thermocouple arrays in order to measure the temperature distribution caused by this backflow, whose independence of duct wall temperature was validated through thermographic imaging. Miniaturized pressure probes at the inducer and diffuser showed how pressure spectra varied during the different operating conditions. In-duct acoustic intensity was measured in both the inlet and the outlet to investigate the correlation between a known super-synchronous broadband issue known as whoosh noise and the backflow behaviour as characterized by local pressure and temperature. Analysis of the results points to inlet whoosh noise being boosted by this reversed flow but not caused by it, the source probably being located at or downstream of the compressor impeller.

Simulation of surge in the air induction system of turbocharged internal combustion engines

A computational approach has been developed to accurately predict compression system surge instabilities within the induction system of turbocharged internal combustion engines by employing one-dimensional, nonlinear gas dynamics. This capability was first developed for a compression system installed on a turbocharger gas stand, in order to isolate the surge physics from the airborne pulsations of engine and simplify the ducting geometry. Findings fromthe turbocharger stand study were then utilized to create a new model of a twin, parallel turbocharged engine. Extensive development was carried out to accurately characterize the wave dynamics within key induction system components in terms of transmission loss and flow losses for the individual compressor inlet and outlet ducts. The engine was instrumented to obtain time-resolved measurements for model validation during surge instabilities, and simulation results agree well with the experimental data, in terms of both the amplitude and frequency. The present quasi-one-dimensional approach relaxes many of the assumptions inherent to earlier lumped parameter surge models; therefore, it provides the flexibility to model advanced boosting systems with multiple turbochargers and complex ducting geometry.

Thermo-environmental and economic analyses of combined cycle power plants with regression modelling and optimization

A 144MW combined cycle power plant (CCPP) based on simple and regenerative gas turbine units working on natural gas is investigated. By establishing mathematical model to simulate the power plants, thermo-environmental and economic analysis are conducted. The effects of five key parameters including compressor inlet temperature, compressor pressure ratio, gas turbine inlet temperature, pinch point temperature difference and main steam pressure are investigated on net power output, energy and exergy efficiencies, CO2 emissions, exergy destruction/loss and levelized cost. The multiple regression models are developed to determine the correlation amongst these variables. Moreover, a multi-dimensional optimization using Nelder-Mead method is carried out to find optimal operating parameters for maximum efficiency and minimum levelized cost. Results show significant impacts of gas turbine inlet temperature and compressor pressure ratio on the performance and costs. The optimum energy efficiency of simple and regenerative CCPP are in the range of 36.2–56.6% and 35–58.2%, respectively under varying operating parameters while the optimal levelized costs US$ 0.0398 and 0.037 per kWh, respectively are estimated. The combustion chamber and HRSG are the major contributors towards exergy destruction amongst all components, followed by exergy loss due to stack.

Impact of inlet distortion on turbocharger compressor stage performance

In a turbocharger system, curved pipes are usually used to connect compressors with other parts due to limited packaging space. It is well known that an elbow can generate flow distortion to and interact with the compressor inducer and therefore deteriorate compressor stage performance. The compressor efficiency change may vary with relative positions of inlet elbow and volute. The compressor’s stable flow range is also possible to vary due to the shift of surge and/or chock points. In this paper, eight relative circumferential positions between the inlet elbow and the volute were studied by 3D numerical simulations with experimental validations. The numerical results confirm that adjusting the inlet bend from one circumferential orientation to others does cause an obvious deviation in the compressor aerodynamic efficiency. The result also indicates that the total pressure deficit and the vortices at the compressor inlet are the main contributors to the compressor operating range. With the numerical findings in this paper which was validated by experimental measurements, it is suggested that unfavorable orientations of an elbow relative to volute should be avoided in an intake system.

Thermodynamic analysis and optimization of a supercritical CO2 regenerative recompression Brayton cycle coupled with a marine gas turbine for shipboard waste heat recovery

This communication presents the modelling and analysis of a waste-heat-recovery-system (WHRS) using supercritical carbon dioxide (SC-CO2) based regenerative recompression Brayton cycle (RRCBC) for shipboard applications following energy and exergy analyses. The influence of key operating parameters such as, the gas compositions, turbine and compressor inlet temperatures, pressure drop irreversibility, pressure ratio etc., on the overall performance of the system including the exergy destruction rate has been investigated. The results show that the proposed integration improves the overall efficiency of the system by 10% while the net power is found to be increasing up to 25% of the rated power. It is also found that the topping gas turbine exhaust gas compositions and temperatures have a significant influence on the WHRS performance. The results are also found in good agreement with those already available in the published literature.

Large eddy simulation of reacting flow in a hydrogen jet into supersonic cross-flow combustor with an inlet compression ramp

Large eddy simulation (LES) has been performed to investigate transverse hydrogen jet mixing and combustion process in a scramjet combustor model with a compression ramp at inlet to generate shock train. Partially Stirred Reactor (PaSR) sub-grid combustion model with a skeleton of 19 reactions and 9 species hydrogen/air reaction mechanism was used. The numerical solver is implemented in an Open Source Field Operation and Manipulation (OpenFOAM) and validated against experimental data in terms of mean wall pressure. Effects of a shock train induced by the inlet compression ramp on the flame stabilization process are then studied. It can be observed that the interaction of the oblique shock and the jet mixing layer enhance the combustion and stabilize the flame. Symmetrical recirculation zone, which contributes to the flame anchoring of the supersonic transverse jet combustion, is observed in the near wall region of 10 < x/D < 20. The hydrogen fuel is transported from the center of jet plume to the near wall region on both sides of the central plane (z/D = 0) and thus intense combustion near the wall is observed due to the enhanced mixing and shock compression heating. Besides, the jet penetration in the reacting field is different from that in non-reacting case with the influence of the interaction between the reflected oblique shock and the jet shear layer on the windward side.

Solution to Avoid Power Crisis in Telangana State by Implanting Non Convectional Energy

&lt;div&gt;&lt;p&gt;&lt;em&gt;Perennial Efforts to combat power crises in newly found Telangana state, compelled to use hybrid source of power which is being catered to facilitate the needs of modern trends, life style, multinational business requirements which enforced the need to explore the modern application of solar energy run household and administrative block. Air conditioning requirement, which consumes more than 30% of the state procured power from different sources, which can be save and utilize for agriculture sector and other constructive needs.&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt; In Telangana State every commercial, administrative and elite residential block is equipped with air conditioning system where the temperature ranges between 32-43&lt;sup&gt;0&lt;/sup&gt;C in summer season. Telangana State is attracting the world class business investors. This design can caters the world class needs therefore this paper explore the design and performance of solar power air-conditioning system, which is integrated with invertors, PV panels, solar charger and batteries. This design can be used in non-electrified rural arid areas to avoid the expenses of supplying electricity.&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt; This research project begins with the cooling load calculations for the selected space ideally whose dimensions are assumed to be one tone of refrigeration (3.5kW). Considering the basic parameters of cooling the photovoltaic cells has been deduced and necessary connections are arranged. &lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt; To acquire the inlet and outlet temperatures of compressor, evaporator and condenser, data logging procedure is employed. The input power for this system as well as coefficient of performance for above said climatic conditions can be deduced. The COP varies from two to four for this system and these results are compared with the convectional system performance they both match with each other considerably.&lt;/em&gt;&lt;/p&gt;&lt;/div&gt;

A high-order model of rotating stall in axial compressors with inlet distortion

In this paper, a high-order distortion model is proposed for analyzing the rotating stall inception process induced by inlet distortion in axial compressors. A distortion-generating screen in the compressor inlet is considered. By assuming a quadratic function for the local flow total pressure-drop, the existing Mansoux model is extended to include the effects of static inlet distortion, and a new high-order distortion model is derived. To illustrate the effectiveness of the distortion model, numerical simulations are performed on an eighteenth-order model. It is demonstrated that long length-scale disturbances emerge out of the distorted background flow, and further induce the onset of rotating stall in advance. In addition, the circumferential non-uniform distribution and time evolution of the axial flow are also shown to be consistent with the existing features. It is thus shown that the high-order distortion model is capable of describing the transient behavior of stall inception and will contribute further to stall detection under inlet distortion.