Adiabatic Efficiency Research Articles

Operation Characteristic of a Mechanical Vapor Recompression Heat Pump Driven by a Centrifugal Fan

A mechanical vapor recompression heat pump driven by a centrifugal fan is designed together with falling-film evaporation. Based on theoretical analysis, experimental research is applied to study the fan type of MVR. Choosing water as the experimental medium, the operation characteristic of MVR applied to low evaporation is examined. Practically, the pressure difference of the unit is likely to keep stable while its evaporation pressure goes up. After the system performance is tested and analyzed, it shows that the total evaporation water and total input energy increase as its evaporation pressure grows. Further, some calculation is done and the result indicates that its SMER and COP decrease while the evaporation pressure rises. The reason of this phenomenon is: the leakage loss of the fan inside goes up and its displacement efficiency reduces as the evaporation temperature and pressure is high; finally, it brings forth the drop of the systems adiabatic efficiency. Finally, the trend of average input work for compressed vapor is compared in three different terms. The trend of average input work by calculation is the same as that in theory; that is to say, both of them descend when the evaporation pressure ascends. Because of displacement efficiency, the trend of average input work by measure is different from that in theory; that is to say, the average input work by measure grows slightly when the evaporation pressure goes up.

Studies on the performance of a small reciprocating compressor with different nitrogen–hydrocarbon mixtures

The performance of Joule–Thomson refrigerators operating with mixed refrigerants depends on the composition of mixtures as well as the hardware employed. The role of mixture composition on the overall performance of the system has been well addressed in the open literature. What is not well known is the role of mixture composition on the performance of individual components such as the compressor, heat exchanger, etc. The adiabatic efficiency of a single stage Joule–Thomson refrigerator compressor was measured with thirty different nitrogen–hydrocarbon and neon–nitrogen–hydrocarbon mixtures. Our results show that the adiabatic efficiency of the compressor is independent of the mixture composition in the range of pressure ratios tested.

Clearance seal compressors with linear motor drives. Part 2: Experimental evaluation of an oil-free compressor

Oil-free compressors are required for various applications, including cryocoolers and refrigeration systems that use compact evaporators. A novel low-cost moving magnet oil-free linear compressor is described here, and follows a companion paper on the linear motor system. The experimental apparatus to evaluate the thermodynamic performance of the linear compressor is comparatively straightforward, but the data analysis is involved, since key measurements have to be corrected for the phase response of the transducers. Harmonic fitting, using fast Fourier transform with zero-padding and minimisation algorithms, have been used for the voltage, current and displacement signals. This enables corrections to be made for the phase lag in the voltage, current and displacement measurements. The experiments using nitrogen, with a constant pressure ratio, show that the linear motor system under resonance achieves a high overall efficiency. For the design point, the motor efficiency is 74%, while for a pressure ratio of 3.0, the average overall adiabatic efficiency is 54% and the isothermal efficiency is 46%, all of which are within a reasonable range for a small compressor.

Analysis and Judgment of the Local Loss Based on the Entropy Gradient

Analysis of the flow loss is important in the turbomachinery, the current analysis methods based on the cumulative loss such as the total pressure loss coefficient and the adiabatic efficiency, and the local loss method reflect the loss, can’ t quickly reflect the physical principles that leads the loss and its’ development. To solve this problem, the paper based on the first and second laws of thermodynamics, a local losses model about the compressor internal flow was estimated using the entropy gradient, give a dimensionless loss function parameter I , and was verified in a three-dimensional numerical simulation about Rotor67. The numerical results show that: the model can quickly capture the magnitude and location of loss, it also can reflect the loss source, when the dimensionless parameter , the area is considered as an high loss area, the local loss is expressed as I. If the parameter near the wall for negative value indicates that reflux occurred.

Performance study on compressed air refrigeration system based on single screw expander

A new kind of expanders, called as single screw expander, has been developed by our team and applied to refrigeration systems. The present paper is to determine experimentally the refrigeration performance of a compressed air refrigeration system which is based on a single screw expander with 175 mm diameter rotor. Results indicate that the single screw expander has good refrigeration performances with a 70 °C odd temperature drop and an adiabatic efficiency above 65%. A high refrigerating output can be obtained at high intake pressure and high rotational speed. The coefficient of performance (COP) varies a little with increasing intake pressure at low rotational speed, but has an obvious increase with increasing intake pressure at high rotational speed; and the higher the rotational speed, the higher the COP. The maximum COP of 0.9 can be achieved. This preliminary study shows that the compressed air refrigeration system based on single screw expanders exhibits good refrigeration performances.

A novel exergy recuperative drying module and its application for energy-saving drying with superheated steam

A novel exergy recuperative drying module with superheated steam as the drying medium was developed. The process is based on self-heat recuperation technology which can recirculate both the sensible and latent heats without heat addition. This drying module was applied as an exergy recuperative process for the drying of wet solids. The energy consumption for the exergy recuperative drying system could be reduced to 1/7–1/12 that required for a conventional heat-recovery drying system in the case of drying wet solids from 65 to 10wt% (wet basis, wb) of water content. The effects of adiabatic efficiency of the compressor and the final water content of the dried samples on the energy consumption of the proposed drying system were calculated by the process simulator PRO/II.

Parametric Study on Aerodynamic Performance of a Transonic Axial Compressor with a Casing Groove and Tip Injection

This paper presents a parametric study on aerodynamic performance of a transonic axial compressor combined with a casing groove and tip injection using three-dimensional Reynolds-average Navier-Stokes equations. The front and rear lengths and height of the groove are selected as the geometric parameters to investigate their effects on the stall margin and peak adiabatic efficiency. These parameters are changed with constant injection. The validation of the numerical results is performed in comparison with experimental data for the total pressure ratio and adiabatic efficiency. As the results of the parametric study, the maximum stall margin and peak adiabatic efficiency are obtained in the axial compressor having 70% groove height of the reference groove. The stall margin and peak adiabatic efficiency in other cases are also improved in comparison with the axial compressors with the smooth casing and reference groove. The results show that both the stall margin and the peak adiabatic efficiency are considerably improved by the application of the casing groove combined with tip injection in an axial compressor.

Effects of Number of Circumferential Casing Grooves on Stall Flow Characteristics of a Transonic Axial Compressor

This work investigates the effects of circumferential casing grooves on stall flow characteristics of a transonic axial compressor. Numerical analysis is conducted by solving three-dimensional steady Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. The results of flow analysis for an axial compressor with smooth casing are validated in comparison with experimental data for the pressure ratio and adiabatic efficiency. The numerical stall inception point is identified from the last converged point by convergence criteria, and the stall margin is predicted numerically. The peak adiabatic efficiency point is also obtained by reducing the normalized mass flow in the high mass flow region. In order to explore the influence of number of the circumferential casing grooves on the performance of the compressor, the stall margins and peak adiabatic efficiencies are evaluated compared to the case smooth casing. The stability of the axial compressor with circumferential casing grooves is found to be sensitively influenced by the number of grooves.

431 ビル用マルチ空調システムの数値シミュレーションンによる性能分析 : インバータ駆動圧縮機のモデル化と性能分析(省エネルギー(1))

Multi-split type air-conditioning systems for buildings that have multiple indoor units require a system performance analysis under various operating conditions in order to optimize their design and operation. Based on the background that inverter-driven compressors have been widely applied due to their high efficiencies under partial-load conditions, this study focuses on modeling an inverter-driven compressor. In the developed model, the adiabatic efficiency, volumetric efficiency and motor efficiency of an inverter-driven compressor are identified from a wide range of experimental data. Moreover, the influence of outside and inside air temperatures on a system performance is analyzed by using the simulation model modified with the inverter-driven compressor model. The results show that the input power and COP are influenced more by the outside air temperature than by the inside air temperature. The relationship between the refrigerant flow rate and the inverter frequency, which is a useful information for optimal operation, can al so be revealed.

A Study on High Efficiency and Low Noise of a Diffuser Vanes with Slits for a Centrifugal Blower

In order to improve the efficiency and decrease the noise level of centrifugal blowers at the same time, we have developed a “slit diffuser” which has a slit structure that connects the flow passages of neighboring diffuser vanes. We investigated the influence of slit structure in terms of performance, internal flow field, as well as noise level. We obtained the following conclusions. Compared with non-slitted diffusers, for the diffusers with slits, the stagnation area generated from the diffusers decreases near the slits and there is less diversion of the mainstream flow. Owing to the flow that goes through the slits from the pressure side to the suction side, the stagnation inside the diffuser is improved and the adiabatic efficiency increases by 0.8%. Compared with non-slitted diffusers, it is possible with slit diffusers to reduce the blade-passing frequency noise and to suppress the acoustic resonance.

The Effect of Ultrapolish on a Transonic Axial Rotor

Back-to-back testing was done using NASA fan rotor 67 in the Glenn Research Center W8 Axial Compressor Test Facility. The rotor was baseline tested with a normal industrial root-mean-square (RMS) surface finish of 0.5 μm to 0.6 μm (20 microinches to 24 microinches) at 60, 80, and 100% of design speed. At design speed the tip relative Mach number was 1.38. The blades were then removed from the facility and ultrapolished to a surface finish of 0.125 μm (5 microinch) or less and retested. At 100% speed near the design point, the ultrapolished blades showed approximately 0.3% to 0.5% increase in adiabatic efficiency. The difference was greater near maximum flow. Due to increased relative measurement error at 60 and 80% speed, the performance difference between the normal and ultrapolished blades was indeterminate at these speeds.

Comprehensive Application of a First Principles Based Methodology for Design of Axial Compressor Configurations

Axial compressors are widely used in many aerodynamic applications. The design of an axial compressor configuration presents many challenges. It is necessary to retool the design methodologies to take advantage of the improved accuracy and physical fidelity of these advanced methods. Here, a first-principles based multiobjective technique for designing single stage compressors is described. The study accounts for stage aerodynamic characteristics and rotor-stator interactions. The proposed methodology provides a way to systematically screen through the plethora of design variables. This method has been applied to a rotor-stator stage similar to NASA Stage 35. By selecting the most influential design parameters and by optimizing the blade leading edge and trailing edge mean camber line angles, phenomena such as tip blockages, blade-to-blade shock structures and other loss mechanisms can be weakened or alleviated. It is found that these changes to the configuration can have a beneficial effect on total pressure ratio and stage adiabatic efficiency, thereby improving the performance of the axial compression system.

Experimental investigation of a Lysholm Turbine operating with superheated, saturated and 2-phase inlet conditions

Low temperature power cycles can benefit from the use of multi-phase flow expansion devices from a thermodynamic cycle efficiency point of view. Particularly power cycles such as ORC, Kalina and Trilateral Flash Cycles can be improved by multi-phase expansion. This article presents the experimental findings in a series of laboratory tests on a semihermetic Lysholm Turbine operating with R134a with superheated, saturated and wet inlet gas conditions. The test arrangements are described as well as discussion on the relevance of such test data.Finally comparison is made with findings from other investigations and recommendations for further studies are made. A correlation between peak efficiency and sensitivity to inlet vapour fraction was discovered which allows for estimations of adiabatic efficiencies with 2-phase inlet conditions even when only test data, or simulations, from single phase inlet conditions exist.The conclusions made are that Lysholm Turbines are well suited for low temperature power generation and that further understanding of the performance during 2-phase conditions is required.

Turbine Aerodynamic Performance Measurement Under Nonadiabatic Conditions

The practical performance, both the efficiency and durability, of a high-pressure (HP) turbine depends on many interrelated factors, including both the steady and unsteady aerodynamics and the heat transfer characteristics. The aerodynamic performance of new turbine designs has traditionally been tested in large scale steady flow rigs, but the testing is adiabatic, and the measurement of heat transfer is very difficult. Transient facilities allow fully scaled testing with simultaneous heat transfer and aerodynamic performance measurements. The engine matched gas-to-wall temperature ratio simulates more closely the boundary layer and secondary flow development of the engine case. The short duration of the testing means that the blades are effectively isothermal with a rise of only a few degrees during a test. To isolate the aerodynamic losses, and thus the entropy generation due to the viscous losses, the entropy reduction due to heat transfer during the expansion needs to be determined. This entropy reduction is path dependent and requires knowledge of the full temperature and heat flux fields. This paper demonstrates a simple methodology for estimation of this entropy reduction, which allows the calculation of the adiabatic efficiency from the results of engine representative nonadiabatic testing. The methodology is demonstrated using a computational fluid dynamics (CFD) prediction which is validated against experimental heat flux data. Details of the other corrections required for transient test techniques such as unsteady leakage flows are also discussed.

The Effects of Wet Compression and Blade Tip Water Injection on the Stability of a Transonic Compressor Rotor

The rotor blade tip leakage flow and associated formation of the tip leakage vortex and interaction of the tip leakage vortex with the shockwave, particularly in the case of a transonic compressor rotor have significant impact on the compressor performance and its stability. Air injection upstream of the compressor rotor tip has been shown to improve compressor performance and enhance its stability. The air required for rotor blade tip injection is generally taken from the later stages of the compressor thus causing penalty on the gas turbine performance. In this study, effects of water injection at the rotor tip with and without the wet compression on the compressor performance and its stability have been examined. To achieve the stated objectives, the well tested transonic compressor rotor stage, NASA rotor stage 37, has been numerically simulated. The evaluation of results on various performance parameters, such as total pressure ratio, inlet flow capacity, and adiabatic efficiency combined with contours of total pressure losses, entropy, Mach number, and temperature including limiting streamlines, shows that the blade tip water injection could help in reducing low energy region downstream of the shockwave and strength of the tip leakage vortex with the compressor operating at its rotating stall boundary condition. The extent of reduction depends on the droplet size, injection flow rate, and its velocity. Furthermore, results show that combined case of the blade tip water injection and the wet compression could provide better stall margin enhancement than the blade tip water injection case.

Positron source investigation by using CLIC drive beam for Linac-LHC based [formula omitted] collider

Three different methods which are alternately conventional, Compton backscattering and Undulator based methods employed for the production of positrons. The positrons to be used for e+p collisions in a Linac-LHC (Large Hadron Collider) based collider have been studied. The number of produced positrons as a function of drive beam energy and optimum target thickness has been determined. Three different targets have been used as a source investigation which are W75–Ir25, W75–Ta25, and W75–Re25 for three methods. Estimated number of the positrons has been performed with FLUKA simulation code. Then, these produced positrons are used for following Adiabatic matching device (AMD) and capture efficiency is determined. Then e+p collider luminosity corresponding to the methods mentioned above have been calculated by CAIN code.

The Expansion-Cycle Evaporation Turbine

This paper investigates a continuous-flow heat engine based on evaporative cooling of hot air at reduced pressure. In this device, hot air is expanded in an expansion turbine, spray-cooled to saturation and re-compressed to ambient pressure in several stages with evaporative cooling between each stage. More work is available in expansion than is required during re-compression, so the device is a heat engine. The device provides a relatively cheap way to boost the power output of open-cycle gas turbines. The principal assumptions for the theoretical model developed herein are that air and water vapor are regarded as ideal gases with constant specific heat capacities. In the absence of losses associated with expansion and compression, the engine produces more power as the inlet temperature and the pressure ratio increase. The effects of irreversibilities are subsequently included in the expansion and compression stages, with realistic values used for the adiabatic efficiencies of turbine and fans. Purification and injection of water are also considered in the overall energy budget. As a typical result for the new engine, if the inlet air is the exhaust of a 56 MW open-cycle gas turbine, the adiabatic efficiencies of turbine and fan are 0.9, the pressure ratio is 6.5 and there is four-stage re-compression, then the power output is 20.5% that of the gas turbine. The power output is sensitive to the adiabatic efficiencies of turbine and fans.

J051031 曲線要素羽根を用いた遠心圧縮機の最適設計と性能試験

This paper describes the numerical design optimization and experimental study of centrifugal compressors with leaned curvilinear element blades. The design targets were a fully shrouded centrifugal impeller and a low-solidity vaned diffiiser. A new method of defining the curvilinear element blade was developed for centrifugal turbomachinery using coordinate transformations between a revolutionary flow-surface coordinate system and a cylindrical coordinate system. Geometries of model compressors with curvilinear element blades were then numerically optimized at a suction flow coefficient of 0.073, using a multi-objective genetic algorithm, Kriging surrogate model, and steady Reynolds-averaged Navier Stokes simulations. The optimal impeller had a concave blade suction surface and a concave leading edge. Although clear patterns in geometrical features for optimal diffiiser vanes could not be captured, we found that the dihedral profile had a predominant effect on aerodynamic performance. The performance of model compressors was experimentally measured and compared with traditional compressors as to their aerodynamic performance. The results demonstrated that the models' adiabatic efficiency was higher by 1.4% at the design point. The stall margin stayed unchanged and the surge margin expanded by 6.7%.

Aerodynamic Characteristics of a Centrifugal Compressor Working in Supercritical Carbon Dioxide

Development of a closed cycle gas turbine with supercritical carbon dioxide as a working fluid is underway to generate power from low-range or intermediate-range waste heat sources. A demonstration test using a reduced scale turbomachine was conducted and the aerodynamic characteristics of a compressor were examined. A compressor was selected as centrifugal with 30mm outer diameter and rated rotational speed of 1.7kHz and mass flow rate of 1.2kg/s. To reduce compression work, the operating condition at the inlet to compressor was chosen in a supercritical state close to the critical point of 7.38MPa, 304K where the compressibility coefficient z becomes markedly small and real gas effect dominant. The experimental range in terms of z is 0.16<z<0.6. The measured pressure ratio and adiabatic efficiency of the compressor are compared with calculations conducted using the Meanline method. The compressor performance in the supercritical liquid-like phase becomes highest in the experiment, which is well simulated by the method. The calculated pressure ratio shows excellent matching with experimental data in the supercritical liquid-like phase. However overestimation is recognized at the off-design point in the supercritical gaslike or subcritical region. Experiments also show that the compressor performance improves with reduction of the compressibility coefficient, which the Meanline method has well predicted.

F121 超臨界CO_2ガスタービン発電システムのベンチスケール実証試験(OS10 外燃機関・廃熱利用技術)

Power generation with supercritical CO_2 closed cycle gas turbine was successfully demonstrated using a bench scale plant. 60 minutes self-sustaining operation including 40 minutes of continuous power generation was realized. Compressor work reduction derived from decrease in compressibility coefficient at the compressor inlet was experimentally confirmed. The typical continuous power output was 200W, which was much smaller than the designed specification of the test plant. The main reason of small generated power was estimated to be low adiabatic efficiency of the turbo machineries, windage around the generator rotor, and the presence of leak flow from the compressor outlet to the turbine inlet through the inside of generator. The effects of these causes for power decrease were quantitatively analyzed.