Second law analysis on performance of double stage reciprocating air compressor with inter cooler

Thermodynamic modeling, CFD analysis and parametric study of a near-isothermal reciprocating compressor

There is a growing demand for compressed air in the industry for various applications. Majority of industrial requirements is in line with screw compressor operating range. Design and construction of screw compressors are demanding tasks that require advanced calculations and theoretical knowledge. Clearances play a major role in the performance and reliability aspects of a screw compressor. Seals are provided in compressors to fit around rotor shafts in order to prevent the leakage of lubricating oil and working medium. However there is a small clearance between the seal and rotor shaft, which can cause potential leakage of the working medium. The performance of the compressor is directly related to the leakage rate through the seals. The labyrinth seal is a special type of seal, used in screw compressors and turbo-machinery for sealing purpose. Labyrinth seal is a non-contacting type seal that uses a tortuous path to minimize the gas leakage. The pressure drop occurs at each labyrinth tooth as the medium is squeezed between the labyrinth tooth and the rotor. The leakage through the seal is directly related to the labyrinth profile and also the clearance between the rotor and the labyrinth tooth. The present work is carried out to reduce the leakage through the labyrinth seal by optimising the tooth profile and operating clearances. Heat transfer analysis is carried out on the housing of the labyrinth seal to find out the boundary temperature of the seal. Also the heat transfer analysis on the labyrinth seal followed by Thermo-structural analysis is carried out to find out the accurate operating clearance of the seal. By using CFD as a tool, the optimisation is carried out on different design configurations of labyrinth seal by comparing the deviation in leakage rates. Effect of rotor speed, width of seal and pressure ratio on air leakage rate is also investigated. A set of labyrinth seals has been designed based on the above optimisation and tested in the compressor. The results have been compared with the CFD prediction.

The objective of the current experimental study is to build a system that can provide a steady state mass flow rate of air and constant temperature which will be used for cooling system of gas turbine blade. The compressed air is used as air supply for jet impingement in a rotating test model. The system is capable to provide 200 l/min of compressed air at constant temperature for a period of 50 minutes at 4 bar pressure. Three different designs have been tested with different tanks arrangements. Three tanks with total volume of 2 m2 where used to produce the compressed air conditions.

An air compressor is the core component of the air supply system of a hydrogen fuel cell, which demands high efficiency and reliable stability in a wide operation region. In this work, a centrifugal air compressor for a hydrogen fuel cell is first designed and then measured experimentally. Furthermore, a test rig for assessing the aerodynamic performance of the centrifugal air compressor is established, which includes a pipeline, gas flowmeter, flow regulating valve, pressure transmitter, centrifugal compressor, controller, DC power supply and computer. Then, the orthogonal method is employed to conduct the aerodynamic performance optimization. Four optimization parameters—including blade number, blade angle at the inlet, blade angle at the outlet and wrap angle—are set with three levels. Nine compressor individuals are designed according to the orthogonal method, and then numerical simulation is implemented to confirm the aerodynamic performance and flow pattern. Results show that the blade number has the greatest influence on the compressor’s performance, and the blade angle at inlet is also very important. The optimal performance of the compressor improves compared to that of the baseline compressor; the efficiencies of the baseline compressor and optimal compressor are 81.3% and 83.8%, respectively, improving by 2.5%. The frequency domain of pressure fluctuation in the centrifugal compressor is related to the stator-rotor interaction. The peak value of pressure fluctuation amplitude occurs at the rotation frequency of 833 Hz and its harmonic frequency. In comparison with the baseline compressor, the pressure fluctuation amplitude of the optimal compressor is obviously reduced, especially near the volute tongue.

Analysis of air compression, progress of compressor and control for optimal energy efficiency in proton exchange membrane fuel cell

Maintaining required performance and rated power output of proton exchange membrane fuel cells while reducing fuel consumption demands and improving efficiencies at the largest parasitic work loss contributor, namely the air compressor. In this paper, we built a high-efficiency one-dimensional match model of centrifugal compressor for proton exchange membrane fuel cells first, which was based on the fuel cell air supply system and the optimal trim factor. And then a variable map width enhancement slot design adjusted by a closed ring was first introduced to extend the surge margin and keep high efficiency. Finally, the compressor with a variable map width enhancement slot was validated at a compressor performance rig and a fuel cell simulation system. The results from compressor performance test rig indicate that the compressor peak efficiency is as high as 77% and the surge margin is enhanced by about 28.1∼ 42.7 %. The simulation results of the fuel cell system indicate the maximum power consumption of the compressor and the H2 consumption of comprehensive adapted world transient vehicle cycle are reduced by nearly 1.6 kW and 4.86%, respectively, in comparison with the baseline screw compressor.

Design and development of an oil-free double-scroll air compressor used in a PEM fuel cell system

Piston rings of oil free reciprocating air compressors operate under completely dry sliding conditions. The life of these piston rings is almost half, when compared to the metallic piston rings of oil lubricated reciprocating air compressors as the latter operates with a continuous layer of oil film at the asperity. Self-lubricating materials like PTFE and its composites when used for these piston rings confront challenges in meeting the desired durability in terms of their useful lifetime. In this paper, the performance of existing ring material of an oil free compressor is studied, followed by understanding the behaviour of PTFE-based composites at compressor operating conditions through literature survey. Benchmarking was also done against the materials used by market competitors. New material compositions are formulated and validated using a QFD-based House of Quality (HoQ) model. The formulated materials are then subject to wear simulation based out of Archard’s wear model to identify the optimal material composition for manufacturing the piston rings of oil free reciprocating compressors. Behaviour of the identified material under varying loads and mean sliding velocities are evaluated, and a model is formulated for wear rate. Based on the simulation results, it is identified that PTFE filled with carbon as the primary reinforcement and copper and molybdenum disulphide as secondary fillers is the most optimal material composition for the oil free piston rings.KeywordsPTFE compositesWearOil free reciprocating air compressorArchard’s modelPiston rings

Numerical investigation of underground reservoirs in compressed air energy storage systems considering different operating conditions: Influence of thermodynamic performance on the energy balance and round-trip efficiency

The single screw compressor (SSC) is widely used in air compression and refrigeration systems due to its many advantages. The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance. In this paper, mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights. The refrigerating capacity, volume efficiency and adiabatic efficiency of the SSC are calculated and discussed. Three prototypes, with different meshing clearance heights, were manufactured to study the internal influence mechanisms. The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results. Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%–7.98% and 5.92%–9.4%, respectively. Based on the models, analysis under varying meshing clearance heights and working conditions was performed. Taking into account working performance, actual manufacturing conditions and manufacturing cost limitations, a meshing clearance height range from 0.01 mm to 0.08 mm is suggested. This study can provide important theoretical data and experimental support for the design, manufacturing and optimization of single screw compressors.

Energy and exergy analysis and multi-objective optimization of an air based building integrated photovoltaic/thermal (BIPV/T) system

As fuel cell vehicles have broad development prospects, improving the performance of their air compressors is crucial for the normal and efficient operation of onboard fuel cells. To improve the performance of the air compressor and solve the contradictory relationship between the pressurization capability and efficiency of the impeller, this study proposes a method combining an approximation model and a multi-objective whale optimization algorithm. First, three-dimensional numerical models of the single-flow passage and the full compressor flow passage in the impeller were established, and the accuracy of the numerical calculations was verified using open-test-case compressors. Then, choosing the pressure ratio and isentropic efficiency as the optimization objectives, sensitivity analysis of the structural parameters of the impeller was conducted via Latin hypercube sampling, and surrogate optimization models were constructed using the least squares method for designing and setting the typical operating conditions for the impeller. Finally, the whale optimization algorithm, which is superior in impeller optimization compared to genetic algorithms, was employed to derive the Pareto solution set. Compared to the original impeller, the optimized impeller exhibited improvements in the pressure ratio as well as isentropic efficiency for the single-flow passage as well as full-model configurations. Under design conditions, the pressure ratio and isentropic efficiency increased by 5.5 % and 1.4 %, respectively, whereas under typical operating conditions, they improved by 3.6 % and 4.1 %, respectively. In addition, the three-dimensional flow characteristic analysis revealed reductions in the internal losses and recirculation within the optimized impeller. Thus, we can conclude that the proposed optimization method effectively enhances the overall performance of the fuel cell vehicle compressors.

The power and the efficiency of a triple-shaft open intercooled, recuperated gas turbine cycle are analyzed and optimized based on the model established using thermodynamic optimization theory in Part 1 of this paper by adjusting the low-pressure compressor inlet relative pressure drop, the mass flow rate and the distribution of pressure losses along the flow path. First, the power output is optimized by adjusting the intercooling pressure ratio, the air mass flow rate or the distribution of pressure losses along the flow path. Second, the thermodynamic first-law efficiency is optimized subject to a fixed fuel flow rate and a fixed overall size by seeking the optimal intercooling pressure ratio, the compressor inlet pressure drop and optimal flow area allocation ratio between the low-pressure compressor inlet and the power turbine outlet. The numerical examples show that increase in effectiveness of intercooler increases power output and its corresponding efficiency and increase in effectiveness of recuperator decreases power output appreciably but increases its corresponding efficiency; there exist an optimal low-pressure compressor inlet relative pressure drop and an optimal intercooling pressure ratio, which lead to a maximum power. For a fixed fuel mass rate and a fixed overall area of low-pressure compressor inlet and power turbine outlet, maximum thermodynamic first-law efficiency is obtained by optimizing low-pressure compressor inlet relative pressure drop and intercooling pressure ratio. The double-maximum thermodynamic first- law efficiency is obtained by searching optimal flow area allocation between low-pressure compressor inlet and power turbine outlet.

Numerical and Experimental Analysis of the Intake and Exhaust Valves of a Rotary Expansion Device for Micro generation

The study presents the dynamics of specific energy consumption in various countries, as well as the calculation of the specific useful energy consumption in industry and residential sectors, considering the efficiency of the final use of energy resources. Groups of countries with different dynamics of energy intensity over the past 30 years were distinguished: some countries have a growing trend of energy consumption, others have a stable trend, and the last have a decline. The article identified countries for which the specific useful energy consumption in industry and residential sectors should not decrease even if the current dynamics of indicators are maintained. This study can be useful for understanding energy consumption trends of different countries and developing effective resource management strategies. The results may be relevant when analysing development problems of territorial socio-economic systems, since energy efficiency is a key factor in achieving sustainable development.