Bypass Air Research Articles

The study of cascading effect in the integration of intake with gas turbine engine bay in subsonic cruise vehicle

Abstract Submerged air intake is often acquainted with the merit of reducing the drag and fitting well within the frame of weight constraints imposed on subsonic cruise vehicle. A novel method for designing an Intake was developed by GTRE, which has been successful with the validation against wind tunnel testing. The designed intake has been integrated with engine bay area of subsonic cruise vehicle. In this study, a provision of bleed from the ramp surface of the intake into the bay through splitter is used for cooling the engine frame, mechanical fixtures, oil tank and other electronic instruments mounted around the engine frame. Different sets of cowl ventilation slots provided on the bay wall will effuse this by-pass air from the intake into the atmosphere there by influencing the heat distribution within the bay area. The cascading effect of the intake with the bay area is extensively studied in this paper.

Experimental investigation and performance analysis of a spray-type ionic liquid desiccant dehumidifier

Ionic liquid desiccants (ILDs) have vapor pressures similar to lithium chloride and no corrosion and crystallization problems, so they are considered a promising alternative to halide salt desiccant solutions. However, the cost of ILDs is more expensive than conventional halide salts, which limits their practical application. Thus, this study developed a spray-type dehumidifier using an ionic liquid desiccant to increase dehumidification performance and reduce the required amount of ILDs. The presented dehumidifier was tested at various operating conditions. Also, a theoretical model was established to analyze heat and mass transfer coefficients of the dehumidifier. Results indicate that the increase in the flow rate ratio of solution to air benefits absorption performance, and the mass flux of solution is suggested to exceed 170 mL s−1 to avoid the occurrence of air bypass. Moreover, compared with the packed bed type, the spray type can reduce the required solution flow rate by 35 % and save power consumption by 19 % under the same moisture removal rates. The dehumidification effectiveness of the presented dehumidifier was up to 0.64 and comparable to the conventional packed bed dehumidifier using lithium chloride solutions.

Theoretical model and control-parameter classification analysis for solid oxide fuel cell systems with cooling air bypass into burner

The burner is central to the thermal management of solid oxide fuel cell (SOFC) system. Using cooling air bypass (CA) into burner is simple and effective to control the excessive temperature. A novel theoretical model for SOFC systems equipped with CA into burner is developed and verified with multiple experimental data. A comprehensive control-parameter classification analysis is carried out with the model, revealing quantitatively the impacts of the fuel utilization (Uf), air flow rate (Vair), and maximum burner temperature (TBM), on the system performance. The results confirm CA can minimize thermal shock to the stack. Favorable combinations of (Uf, Vair, TBM) satisfying the thermal constrains of maximum cell temperature and temperature difference are identified, and capable of achieving a system alternating current efficiency of 55 % or more. The theoretical model can help the system design optimization targeting the specifics of the stack.

Combustion stage configurations for intercooled regenerative reheat gas turbine systems

Low-power gas turbines have been widely used for decades as combined heat and power. In the recent years, they received increasing interest with respect to applications such as range extenders in the automotive sector and for alternative fuels use.In this framework, the present work analyzes the combustion stages optimization of an intercooled regenerative reheat gas-turbine system, for a low power gas turbine. In particular, a thorough analysis was carried out to identify the optimal combustion system configuration in order to ensure suitable turbine inlet temperature and global efficiency of the thermodynamic cycle higher than 40%. Starting from the typical intercooled regenerative reheat gas turbine system, several configurations were analyzed. In particular, air bypass systems were introduced as suitable strategy able to tune the combustion chamber working temperatures and turbine inlet ones, according to operating requirements and combustion unit specifications. Furthermore, different bypass ratios were considered, analyzing the effectiveness of air bypass systems in terms of efficient combustion and reduced pollutant emissions (CO and NOx).An innovative cyclonic flow burner, assumed to operate under MILD (Moderate or Intense Low oxygen Dilution) combustion conditions, was considered as main combustion unit and in the reheat process. In this respect, the choice was motivated by the well-established high fuel flexibility and very low pollutants emission typical of such a combustion unit and the MILD process.Analyses were performed considering methane as fuel, which is currently the most used fuel in land-based applications. However, results here reported have general validity and may be directly applied with respect to the use of innovative energy vectors.

Turn-Down Capability of Ansaldo Energia's AE94.3A

Abstract At an ever-faster pace, market's requirements for operational flexibility and turn-down capabilities are fundamental for heavy-duty gas turbines. Gas turbine energy plants require the lowest minimum environmental load (MEL) for times when the power request is mainly covered by renewable sources and, however, need to promptly respond to green energy shortages. Ansaldo Energia has addressed such requirements overall its gas turbine portfolio, recently including GT26, as discussed in GT2021-59457. This paper addresses the MEL reduction for AE94.3A via a modular upgrade package intended for the 110+ units Service fleet. To accomplish that, several features were designed and tested including variable inlet guide vanes (VIGV) extra-closure, air bypass through compressor blow-off lines, and extended use of anti-ice air recirculation. None of these require major hardware changes but only upgrades within a normal service outage, together with minor control system adaptations. The wide-ranging technical challenges attached to the MEL reduction features are discussed. Validation on field via special instrumentation focused on compressor, secondary air system (SAS), and turbine for several engines is also presented. The achieved minimum environmental load reduction is shown and its potential discussed together with some features already in place, such as the use of CO catalyzer or the regulation of control valves put on external cooling lines. The readiness and performance level of this MEL upgrade package, already in operation on several power plants, is here demonstrated. This makes the AE94.3A gas turbine more flexible toward current and future market requirements.

Experimental investigation on the drying characteristics in a solar assisted ejector enhanced heat pump dryer system

A new designed solar assisted ejector enhanced heat pump dryer system (SE-HPD) with closed-loop drying chamber using the R134A refrigerant has been experimentally investigated. In the SE-HPD, a hot water cycle system has been designed to simulate the solar collector. The dynamic drying characteristic of SE-HPD and the conventional heat pump dryer system (CHPD) were compared. Further, various drying characteristic parameters and the ejector performances of the new system under different solar radiation intensities, valve opening (OP) of electronic expansion valves and by-pass return air ratios (BR) were studied. The experimental results revealed that the exergy efficiency and moisture extraction rate (MER) of SE-HPD were always better than those of the CHPD. The exergy efficiency and MER of SE-HPD were improved by 28.7% and 54.3% compared with those of CHPD under the given operating condition. It was found that higher solar radiation intensity could significantly improve the pressure lift ratio of the ejector and contributed to the higher heating performance of SE-HPD. The optimum OP and BR to obtain the maximum MER for SE-HPD were also found to be 50 % and 70 %, respectively. The performance advantages of the proposed system have been verified through this experimental research.

On-site measurement and optimization of energy efficiency of the cascading desiccant wheel deep dehumidification systems in the lithium-ion battery manufacturing factory

The desiccant wheel deep dehumidification system in the lithium-ion battery manufacturing factory is significantly energy intensive, which substantially treats the process air from the ambient to the supply air state with a dew point temperature below −20 °C. On-site measurements were conducted in this study to investigate the actual performance of the deep dehumidification systems. The air treatment process and energy consumption during the operation were continuously monitored. The results reveal that the coefficient of performance of the dehumidification process of the systems ranges from 0.54 to 0.63 under basic winter conditions and ranges from 1.15 to 1.25 under basic summer conditions. The deep dehumidification processes of the systems are divided into multiple stages, and with the deepening of the process air humidity ratio from above 6 g/kg to below 0.3 g/kg, the partial energy efficiency of the treatment stages decreases. The efficient operational strategies are further elaborated for the improvement of the deep dehumidification system, including the proper match between the dehumidification gradient and the dehumidification stages, and the appropriate use of outlet process air with low humidity ratio as the regeneration air. The energy consumption of the cascading desiccant wheel dehumidification system can be reduced by lowering the cooling temperature of the cooling coil to undertake more latent load in the preliminary dehumidification stage. The effect of the bypass air state as the regeneration air is revealed, and the energy efficiency of the system is enhanced by up to 32 % by applying appropriate bypass air. This study offers guidance for the future design of the cascading desiccant wheel deep dehumidification system in similar applications.

Innovative Air Bypass System for Low-Emission Multi-Can Combustors

Abstract Gas turbines that are used as compressor drives are often operated in the part load regime because compressor stations are usually designed for operation with full power at extreme weather conditions. Consequently, these gas turbines must comply with strict emission regulations at unfavorably low turbine inlet temperatures. To extend the low-emission operation range of the premixed combustion systems, many gas turbines bypass a part of the compressed air upstream of the combustor and either blow it off into the exhaust stack or reinject it into the secondary combustion zone. This study presents a new approach that overcomes shortcomings by injecting the compressed air in the burner head in the vicinity of the primary combustion zone. This is particularly attractive for multi-can combustors. Atmospheric combustion tests are conducted for two different air injection designs. The first design features lower air injection velocity and the second features higher injection velocities. Both injection strategies are tested with the industrial MGT gas turbine can combustor. The full size burner is tested at atmospheric conditions in a burner test rig with a quartz flame tube and natural gas as fuel. The performance of the air bypass system is assessed by means of CO and NOx emission measurements for different air bypass ratios. Additionally, OH* chemiluminescence camera pictures are presented and compared to numerical calculations. It is found that the air injection in the annular vicinity of the swirl flame does not cause increased CO emissions by quenching or other effects.

Limiting the available pneumatic power in a U-OWC

A fixed oscillating water column is a hollow structure open to the sea at its submerged part. The water column motion alternately compresses and decompresses the enclosed air above the inner free surface, which drives a self-rectifying air turbine. In 2003, Boccotti proposed the so-called U-OWC having in view the integration into breakwaters. In this configuration, the inner water is connected to the sea by a U-shaped duct whose opening faces upwards rather than sideways or downwards. This allows the OWC length to be extended (and the resonance frequency reduced) without placing the opening too deeply submerged where wave energy is attenuated by distance to the free-surface. An advantage of OWC converters is the capability to control or dissipate the excess energy available to the power take-off system in excessively energetic sea states. This is in general done by limiting the air turbine torque by controlling a by-pass air valve or a valve in series with the turbine. What is proposed here is to take advantage of the water column configuration to limit the energy absorbed from the waves in the more energetic sea states. This requires the tidal amplitude to be small as occurs in coastal areas like the Mediterranean Sea. The distance of the OWC opening to the mid-sea-level should be chosen such that, in the more energetic sea states, that opening is left uncovered by the troughs of the higher waves. This introduces a limitation to the energy absorbed in the more energetic sea states. This paper reports experiments with a 1:40th-scale U-OWC in a wave flume. The results show that limitations to the capture width ratio occurs in the more energetic wave systems.

Research on Solid Oxide Fuel Cell System Model Building and 3D Testing Based on the Nodal Idea

The Solid Oxide Fuel Cell (SOFC) system is a highly intricate system characterized by multiple variables and couplings. Developing an accurate model for the SOFC independent power generation system is of paramount importance. Conducting experimental studies on the SOFC system is costly, and it carries certain risks due to the requirements for pure hydrogen, high-temperature environments, and other factors. To address these challenges, a high-performing model that precisely reflects the inherent characteristics of the SOFC is essential for dynamic static analysis and the identification of optimal operating points. This paper presents a SOFC system model based on current controls, which was implemented in the MATLAB/Simulink environment, and it utilized a nodal approach for modeling. The model incorporated a cold air bypass, which enabled the more precise control of the SOFC reactor’s inlet and outlet temperatures. Furthermore, a 3D test and verification method are proposed in order to focus on the influence of input parameters on the four electrical characteristics, and four thermal characteristics, of output parameters. By conducting one-dimensional, two-dimensional, and three-dimensional studies of these output parameters, a more intuitive understanding of the system’s response to changes in input parameters was obtained. Under conditions wherein all other variables were kept constant, the entire system attained its maximum efficiency at approximately FU = 0.8, BP = 0, and AR = 6. The outcomes of this study have significant implications for exploring the optimal operating point in the SOFC independent power generation system in an in-depth manner. It provides valuable insights for enhancing the system’s efficiency and performance.

A time-varying state-space model for real-time temperature predictions in rack-based cooling data centers

Fast-growing data centers (DCs) require efficient cooling systems (such as rack-based cooling architectures) and control strategies to reduce operating costs and guarantee desired indoor conditions. Thus, this study proposed a novel real-time temperature prediction model for rack-based cooling DCs, in order to facilitate advanced control regarding cooling management and workload assignment. Specifically, a data-driven technology was introduced to estimate time-invariant model parameters, in order to avoid the time-consuming physics-based parameters extracting process. The mass conservation relationships were employed to update time-varying flow parameters in real-time to capture the nonlinear behaviors in DCs. Moreover, the proposed control-oriented thermal modeling method can model hot air recirculation and cold air bypass occurring simultaneously for the first time. The performance of the developed time-varying state-space model was validated by CFD simulation data. Additionally, the timeliness of modeling and temperature prediction was also investigated. The results show that the developed model achieves sufficient accuracy with a mean absolute error (MAE) equal to 0.28 °C, even for long prediction horizons and dynamic IT workloads. Also, the developed model has outstanding timeliness for advanced control techniques, in terms of less than 30 min for parameter identification and less than 10 s for temperature prediction.

Study on particle filtration performance of high volume air purifier: Experimental results

With the spread of SARS-CoV-2 virus all over the world, the indoor air quality of commercial buildings has received intense attention. The evaluation of high-volume air purifiers (HAP, CADR≥800m3/h) is of unprecedented importance. According to the national standard GB/T 18801-2015, the purification performance of HAP and its three different replacement elements was tested by the environmental chamber method. The results show that the particulate matter purification of single effect filter is better than that of composite filter. The presence of particulate matter generated by activated carbon layer and bypass air flow leads to a difference of about 10% between the clean air delivery rate (CADR) value for the count and weight of composite filter. In the durability test, the CADR value decreases greatly when the smoke volume is 1000 pieces due to the increase of resistance and the electrostatic elimination effect of incense smoke. The CADR test standards of air purifiers in 5 countries were compared. Only Korea mentioned that when the air volume of the air purifier is greater than 960m3/h, 50m3 test chamber is used. However, due to the different sources of experimental dust and sampling methods, this standard does not conform to China's national conditions. The analysis results will provide reference for the formulation of relevant test methods and standards

Performance of a Solid-Fuel Ramjet Combustor with Bypass Air Addition

The influence of bypass air addition on the performance of a solid-fuel ramjet combustor was investigated. Experiments were performed with cylindrical center-perforated hydroxyl-terminated polybutadiene fuel grains and unvitiated heated air at flight-relevant pre-ignition combustor inlet total temperatures. The core air mass flow rate was kept constant, whereas the bypass ratio was varied from 0 to 30% with consistent pre-combustion chamber pressures. The average regression rate and mass flow rate of the fuel were greatest for the 0% bypass ratio case. The regression rate decreased for the 30% bypass ratio and for cases in which carbon black was not added to the fuel grain. Increasing the mass flow rate of air bypassed to the secondary combustion zone reduced the overall chamber pressure. The thrust increased with the increasing bypass ratio. The effect of bypass air on the chamber pressure yielded lower characteristic velocities at the 30% bypass ratio than at the 0 and 15% bypass ratios. The combustion efficiency of the device was maximized for the 15% bypass ratio. The key outcomes of the bypass air addition are to lower the global equivalence ratio and to reduce the combustion chamber pressure such that there is a nonzero bypass ratio for which the combustion efficiency is maximized.

Evaluation of heat pump dryers from the perspective of energy efficiency and operational robustness

Vapor compression heat pump dryers (HPDs) are widely applied in food and industrial drying. Many efforts have been devoted to evaluating the HPD performance from the perspectives of energy, exergy, economy, etc. The current work offers a perspective of both energy efficiency and operational robustness to evaluate HPDs, intending to measure their design and off-design performance for various drying applications. Based on the proposed method, a case study on conveyor seaweed drying is presented. The preferable system(s) are found out among three candidates in general use, i.e., the basic heat pump dryer HPDbasic, the HPD with air bypass HPDbypass, and the HPD with air bypass and subcooler HPDsubcooler. The results show that, HPDbasic is not applicable for seaweed drying due to the required huge circulating air flow rate. HPDbypass and HPDsubcooler are more preferred with better energy performance and operational robustness. Moisture extraction rate (MER) of 30.4 kg/h and specific moisture extraction rate (SMER) of 2.20 kg/kWh are reached in HPDbypass at the design condition (Tdb = 45 °C, RH = 0.4), and are further increased to 35.8 kg/h and 2.58 kg/kWh in HPDsubcooler. Meanwhile the off-design robustness indices are 0.14 and 0.22 for HPDbypass and HPDsubcooler, and can be enlarged to 0.19 and 0.33 after reselecting a compressor withstanding condensing temperature up to 58 °C (2 °C higher). Besides, HPDbypass and HPDsubcooler can bear at least 30% air leakage in operation. Finally, operational robustness on other applications is also discussed for conveyor and batch dryers.

Novel modulation approach of flat force–displacement characteristic of linear electro-mechanical converter for electro-hydraulic servo-proportional valve

Flat force–displacement characteristic has crucial influence on the performance of linear electro-mechanical converter of electro-hydraulic servo-proportional valves. The commercial proportional solenoids obtain such features by welding a non-magnetic separator ring, which is complicated and time-consuming. This article presents a novel modulation approach to obtain the flat force–displacement characteristic of linear electro-mechanical converter by constructing a by-pass air gap. Taking an existing linear force motor as an example, the force–displacement characteristic curves of the linear force motor with by-pass air gap and without by-pass air gap are both studied using magnetic circuit analysis and finite element method under different excitation currents. Based on the finite element method simulated data, the response surface method is used to perform the experiment design for structure parameters of linear force motor with by-pass air gap, and the quadratic fitting equations are obtained for further optimization. To balance conflicted design objectives such as linearity, mean value of output force and power-to-weight ratio, the structural parameters of the linear force motor with by-pass air gap are optimized using a multi-objective optimization algorithm based on particle swarm. Prototypes of linear force motor with by-pass air gap and without by-pass air gap are both manufactured, and a special test rig is built. The static and dynamic experimental results are consistent with the theoretical analysis. The former proves that the linear force motor with by-pass air gap can obtain a nearly flat force–displacement curve with reasonable parameter optimization and also improve output force, and the latter reveals that a linear electro-mechanical converter with flat–displacement characteristic has better working stability over common ones. The proposed modulation approach provides a new approach for the design of flat force–displacement characteristic of linear electro-mechanical converter.

Parametric Research and Aerodynamic Characteristic of a Two-Stage Transonic Compressor for a Turbine Based Combined Cycle Engine

This paper researches the parametric optimization of a two-stage transonic compressor having a large air bypass at partial rotating speed according to flow analysis for a turbine-based combined cycle engine (TBCC). To obtain adequate thrust, the inlet transonic compressor of the turbofan part of the TBCC is required to have a wider frequently used corrected rotating speed range and a larger mass-flow rate at low rotating speed, which is different from a typical transonic compressor. The one-dimensional blade design parameters and flow path of the baseline two-stage transonic compressor are introduced. With the widely used CFD software Numeca, the three-dimensional flow fields of the baseline transonic compressor and effects of the flow path between Stage 1 and Stage 2 on the inlet mass flow rate are analyzed for indicating the further improvement direction. For design speed (NC = 1.0), to improve the efficiency at the design point, parametric research is carried out on Rotor 2 to optimize the shock structure and strength, resulting in enhanced efficiency at the design point due to reduced shock loss of Rotor 2. For partial speed (NC = 0.8 and 0.7), since the flow field analysis indicates that the flow blockage in S1 limits the entire mass flow rate, the parametric redesign of stator S1 aims at obtaining an increased blade throat width to enhance the flow capacity of S1. Simulation confirms the increase in the mass-flow rate and efficiency at partial speed due to the reduction in flow blockage and related viscous losses. Aerodynamic analysis at representative operation points indicates that the modifications of R2 and S1 lead to obvious aerodynamic improvement at all rotating speeds (NC = 1.0 to 0.7), while maintaining sufficient stall margin.

Performance Investigation of a Constant Temperature Heat Pump Dryer

Abstract Heat pump drying systems (HPDS) are systems composed of a heat pump (HP) that carries out a drying process which is energy efficient and environmentally friendly. However, in the HPDS, HP technology is used in the drying process, which makes it a very complex system coupling a hot air cycle and compressed refrigeration cycle. The control strategy of the drying process is important when developing heat pump dryers (HPDs) with high efficiency and reliability. An auxiliary condenser can be used to release excess heat from the system and maintain a constant temperature drying process, while equipping an evaporator bypass is a simple method for controlling the heat pump dehumidification rate. In this study, a novel enclosed drying system that incorporates a commercial 2.65 kW HP dehumidifier with an evaporator bypass was designed and constructed. The drying performance, such as the drying time and drying degree, and the HP performance, such as the coefficient of performance of an enclosed system with an air bypass, were experimentally investigated. According to the results of the investigation, increasing the circulating air bypass ratio can greatly reduce the drying time and improve the drying degree and the drying performance of the drying system. However, the air bypass reduces the performance of the HP, especially at a higher air bypass ratio, which should be taken into account in research and design of HPDS in the future. Besides, an attempt has been made to investigate the feasibility of using this novel HPD to preheat the drying room before drying process and refrigeration storage in drying room after drying process. Contribution of this research can diversify the function of the HPD.

Development and validation of an open-source CFD model for the efficiency assessment of data centers

In this study, an open-source computational fluid dynamics (CFD) model was developed based on OpenFOAM libraries for the accurate and robust simulation of thermal distribution in a data center. Two boundary conditions were developed for the temperature field in the black-box modeling of server components. The numerical model was first validated by comparing numerical results with the experimental measurements for three benchmark problems in the field of thermal engineering. Then, thermal distribution in an open-aisle data center was simulated using the proposed numerical model and results were compared with the experimental measurements. The consistency between numerical results and previous experimental measurements indicates that the present numerical model can be reliably used for the efficiency assessment of air-cooled data centers. Efficiency of the data center can be evaluated with respect to four metrics in the proposed numerical model. In addition to the determination of the overall efficiency, distribution of the efficiency can be monitored over the racks to capture thermal zones where the efficiency decreases due to the recirculation effects and cold air by-pass.

Experimental and simulation performance optimization of an exhaust air heat recovery heat pump unit

Abstract In order to optimize the performance of exhaust air heat recovery heat pump unit (EAHRHPU), Simulink system simulation and Simulink-M file optimization model were established in this paper to study the performance of the unit in variable outdoor air conditions by combining experiment. Finally, the optimal performance of coefficient and the corresponding optimal bypass fresh air flow rate of the unit in different outdoor temperature was obtained. The results showed that the change trend of the simulation value and the test value of the unit’s performance parameters is consistent, and the maximum deviation is controlled within ±7.00% in the standard cooling condition and variable bypass fresh air. The simulation model can correctly reflect the performance changes of the unit during the operation. The operation performance of the unit was affected by the temperature and air flow rate of the bypass fresh air in variable outdoor conditions. The Simulink-M file optimization model can obtain the specific value of the optimal bypass air flow rate in different outdoor temperatures. As the outdoor temperature increases, the optimal bypass fresh air flow rate increases first and then decreases. With the use of variable frequency fans, the unit can achieve better energy utility effect. The research could be considered as the useful reference for improving the operation performance of the EAHRHPU.

Influence of the Middle Air Shaft and Bypass Duct on Aerodynamic Pressure of Platform Screen Doors in The High-Speed Subway Station

Influence of the Middle Air Shaft and Bypass Duct on Aerodynamic Pressure of Platform Screen Doors in The High-Speed Subway Station