Compression Chamber Research Articles

Numerical investigation on scroll compressor with intermediate discharge valve for VRF annual performance promotion

Over-compression of scroll compressor in variable refrigerant flow (VRF) system is a common problem in improving system efficiency because it operates in part load conditions for most of the year. By introducing intermediate discharge valves (IDVs) to allow gas bypass from compression chamber to discharge side during compression process, the over-compression loss can be eliminated. In this study, the characteristics of compression process in IDV compressor are analysed and the effects of IDV port location and port size on compressor efficiency are discussed based on the validated high fidelity scroll compressor model. It is found that the IDVs could be able to adjust gas bypass process in different compression ratio conditions and maintain high efficiency over wider compression ratio range than that of non-IDV compressor. In addition, the VRF system model is integrated to verify the system performance improvement by IDV compressor. It is found that VRF system performance is significantly improved in cooling conditions with the IEER enhanced by 23.9 %, while limited improvement is obtained in heating conditions as the operating compression ratios are relatively higher.

A robust and fail-safe semi-active vertical damper to improve ride comfort

In recent years, the technical progress in railway engineering has led to the integration of electronic elements in suspension components that once were purely mechanical. Many studies have been carried out, developing active and semi-active suspensions. Among these, semi-active suspensions are particularly attractive due to their simpler design compared to fully active ones. In this context, this paper proposes a semi-active vertical damper to be implemented on the secondary suspension stage of rail vehicles. A prototype is developed by modifying a pre-existing passive damper through the addition of an external servo-valve which manages an additional by-pass channel between the compression and rebound chambers. The prototype is characterised on a dedicated test rig. A reduced vehicle model is then developed as the starting point in developing a sliding mode controller to manage the semi-active feature of the damper. A time-varying sliding surface containing the state of the system and car body accelerations is proposed. Finally, the damper prototype is tested on a hardware-in-the-loop test rig, focusing the experimental campaign on quantifying the damper performance, the evaluation of the controller robustness and a failure analysis to study the behaviour of the proposed solution even in the case of unexpected failures.

Numerical analysis of scroll compressor performance with pre-discharge valve for low-temperature heat pumps

Scroll compressors are a crucial component of automotive air conditioning systems. When operating at off-designed working conditions, over-compression can occur in the scroll compressor. A pre-discharge valve (PDV) is proposed to enhance the performance of the scroll compressor under off-design working conditions. The performance of the scroll compressor with a PDV for a low-temperature heat pump system is simulated. The results show that the scroll compressor with the PDV structure has lower pressure in the compression chambers and improved over-compression compared to conventional scroll compressors. The use of the PDV also leads to a reduction in the temperature of the refrigerant gas in the compression chambers and a decrease in the leakage between the compression chambers. As the evaporating temperature increases from −25 °C to −5 °C, the mass flow rate and volumetric efficiency increase, and the discharge temperature decreases. At an evaporating temperature of −5 °C, the discharge temperature at the center discharge port of the scroll compressor with the PDV is reduced by 2.4 °C compared to the conventional scroll compressor. The input power of the scroll compressor is reduced by 165.4 W–897.7 W. The volumetric efficiency and the isentropic efficiency are improved by 0.13 % and 6.63 % respectively.

Impact of hydrogen-assisted combustion in a toroidal re-entrant combustion chamber powered by rapeseed oil/waste cooking oil biodiesel

This study investigates the performance and emission characteristics of biodiesel blends of rapeseed oil and waste cooking oil in a toroidal re-entrant combustion chamber (TCC) compression ignition engine. Hydrogen was allowed into the engine in dual fuel mode to enhance the engine performance. The presence of oxygen in the biodiesel and hydrogen induction increased the peak pressure and heat release rate significantly for all the engine loads. At a peak load of 4.88 kW, the maximum brake thermal efficiency (BTE) of 31.77% was recorded for the D70R20W10 (diesel 70%, rapeseed oil 20%, waste cooking oil 10%) biodiesel blend. Furthermore, hydrogen induction enhanced the BTE by around 3%. The biodiesel blending substantially lowered the emissions of unburnt hydrocarbons, carbon monoxide, and smoke opacity. Additionally, hydrogen supplementation facilitated 5–10% carbon monoxide reduction over biodiesel blends by enabling more complete oxidation. However, higher temperatures generated due to complete combustion resulted in more NOx formation. Thus, the authors propose that biodiesel blends of rapeseed oil, waste cooking oil, and diesel with hydrogen induction improve engine performance and reduce regulated emissions.

Visualization of vane chattering in rotary compressor

In this study, the impacts of various factors on the chattering phenomenon in sliding vane compressors, which is a crucial aspect that influences their performance and efficiency were explored. The analysis focused on the compressor rotational speed, pressure ratio, and operating temperature, considering both ambient and heated conditions. The aim was to provide a comprehensive understanding of the relationship between these factors and the occurrence of chattering at different operational intervals, as well as the vane sealing performance and adherence to the chamber wall.The methodology involved examining vane behavior and the chattering occurrence across three intervals under various conditions, specifically looking at oil films formation and sealing performance degradation. The experimental results provided notable insights into the chattering phenomenon. It was shown that as the pressure ratio increased and the compressor rotational speed decreased, the sealing performance deteriorated. Moreover, when operating under heated conditions, a decrease in oil viscosity leads to reduced friction between the vane and bearing, improving vane adherence compared to ambient conditions.The methodology and findings of this study provide insights into the chattering phenomenon in vane compressors by considering the interplay between various factors. The results emphasize the importance of optimizing the compressor oil refueling flow, rotational speed, pressure ratio, and operating temperature, to ensure proper lubrication and efficient interaction between the vanes and compression chamber walls for improved compressor performance and reduced operational challenges.

Investigation of the minimum filling amount of ionic liquid in the multi-stage ionic liquid compressor

Ionic liquid compressors are the ideal solution for hydrogen refueling stations, and multi-stage compression is an inevitable choice for achieving high-pressure refueling, such as 90 MPa level. However, the initial filling amount of the ionic liquid in the compression chamber is lacking basis as the characteristics of gas-liquid two-phase flow during the reciprocating movement of the liquid piston are not understood. This study numerically investigates the variation characteristics of the gas-liquid interface in the compression chambers under different structural and operating parameters of a five-stage ionic liquid compressor. Based on the fluctuation feature of the phase interface, the minimum liquid piston heights in each stage that ensure effective sealing for the compression chamber with different stroke-to-diameter ratios (r) are determined. Finally, the mathematical relationship for calculating the minimum ionic liquid filling amount related to structural parameter r and suction pressure is established, which provides guidance for the design of the ionic liquid compressor.

Energy and exergo-environmental performance analysis of a Stirling micro-fridge with imperfect regenerator

In search of very small and ecological refrigeration machines, Stirling chillers are studied on a micro-scale. This article analyzes the performance of a Stirling microcooler using a new modeling approach. This micro-cooler consists of a pillar network as regenerator, a compression and expansion chamber suitable for batch manufacturing, Alpha configuration with helium as working fluid. The Schmidt model with imperfect regeneration is used with consideration of work losses due to gas spring hysteresis. The equations solved analytically using the laws of thermodynamics are used to evaluate the energy and exergy performance of the microcooler. The parameters like height and internal width of the regenerator, phase angle, temperature ratio, swept volume ratio, cooling pressure, dead volume ratio are studied. A numerical code is developed in Matlab. Results show that optimal parameters develop a cooling capacity of 18.99 mW at a phase angle of 45°, a coefficient of performance of 1.104 at an internal height of the regenerator of 0.85 mm, an ecological coefficient of performance of 10.9 mW, an exergy yield of 6.13%, a destroyed exergy of 0.66 mW. The comparison between the present work and those in the literature shows that the current micro-cooler explores a COP improvement of 35%.

Development of Improved Confined Compression Testing Setups for Use in Stress Relaxation Testing of Viscoelastic Biomaterials.

The development of cell-based biomaterial alternatives holds significant promise in tissue engineering applications, but it requires accurate mechanical assessment. Herein, we present the development of a novel 3D-printed confined compression apparatus, fabricated using clear resin, designed to cater to the unique demands of biomaterial developers. Our objective was to enhance the precision of force measurements and improve sample visibility during compression testing. We compared the performance of our innovative 3D-printed confined compression setup to a conventional setup by performing stress relaxation testing on hydrogels with variable degrees of crosslinking. We assessed equilibrium force, aggregate modulus, and peak force. This study demonstrates that our revised setup can capture a larger range of force values while simultaneously improving accuracy. We were able to detect significant differences in force and aggregate modulus measurements of hydrogels with variable degrees of crosslinking using our revised setup, whereas these were indistinguishable with the convectional apparatus. Further, by incorporating a clear resin in the fabrication of the compression chamber, we improved sample visibility, thus enabling real-time monitoring and informed assessment of biomaterial behavior under compressive testing.

Experimental and numerical analysis of heat transfer mechanisms for two-phase oil-refrigerant flow process in the cylinder of rotary compressor

Investigating the heat transfer mechanisms in rolling piston type rotary compressors is crucial for improving their operational efficiency. A thermal test platform was established and steady-state temperature fields of key components were measured under various conditions, revealing a correlation between these temperatures and crank angles, except near the angle of 54° for the cylinder head-up. It provided important boundary conditions for simulation research. A novel three-dimensional fluid–solid-heat coupled simulation method was proposed, calculating heat transfer coefficients at fluid–solid interfaces. The two-phase heat transfer characteristics post oil–gas miscibility was studied, arising from the injection of lubricating oil into the working chamber. Two-phase oil-refrigerant mixtures, compared to single-phase refrigerant, increased heat transfer coefficients by 2.35 % in the suction channel and 2.99 % in the cylinder head-up, but decreased by 5.85 % in the cylinder head-down, 17.42 % in the piston, and 5.63 % in the cylinder. Oil injection was found to significantly enhance convective heat transfer in the suction chamber, increasing suction superheat in the cylinder by up to 29 K and reducing temperature of the compression chamber by up to 17 K. These results provide novel insights into the complex heat transfer in rotary compressors.

The Stability of Compressed Air Storage Underground Gas Storage Chamber and Steel Lining Structure Analysis

According to the address characteristics and structural characteristics of an underground artificial chamber gas storage, a structural model of an underground chamber including steel lining, flexible concrete, concrete lining, and surrounding rock is established, and two limit states of large slip and no contact between steel lining and flexible concrete are simulated respectively. The stability of the surrounding rock and lining structure are calculated and analyzed by using large finite element software FLAC3D and ANSYS respectively. The results show that the maximum deformation of the surrounding rock is 1.57cm, the maximum stress of steel lining is 262.08MPa, and the changes of plastic zone, displacement, and steel lining stress of surrounding rock can meet the design requirements of this project.

Numerical analysis of stress and deformation characteristics of compressed air energy storage chambers developed from a modified coal mine tunnel

The use of abandoned coal mine tunnels as underground compressed air energy storage (CAES) facilities has garnered significant attention given that it effectively repurposes unused underground space and enhances the efficiency of renewable energy utilization. However, existing coal mine tunnels, without optimization and retrofitting, may not meet the stability requirements of compressed air energy storage repositories. Sectional transformation is a retrofitting method with excellent optimization effects. In this study, numerical simulation based on Midas software was employed to create a three-dimensional model of straight-wall arched mine tunnels. The stress and displacement deformation of the tunnel sections were simulated under internal pressure of 10 MPa, and scenarios with no modification and circular-section backfilling were compared. The outcomes of the study are (1) For deeply buried soft rock mines, the existing structure without modification may not meet the stability requirements of compressed air storage facility due to low rock strength. (2) In the unmodified scenario, stress concentration effects and excessive floor tensile stress occur near the tunnel closure. (3) Backfilling straight-wall arched tunnels into circular shapes effectively reduces stress and displacement along the tunnel walls, preventing stress concentration near the tunnel closure. This study provides a retrofitting approach for repurposing abandoned mines into compressed air energy storage facilities, providing guidance for future projects facing complex geological conditions.

Optimisation of design parameters for a novel two-piston ionic compressor applied in hydrogen storage

The ionic compressor is an advanced and prospective compression technology for hydrogen storage. However, a complex wave phenomenon was observed inside the compression chamber due to the fluid flow vortex. This complex gas-fluid interaction can be intervened by a new mechanical design of the motion piston. In this paper, the thermodynamic performance of a novel homocentric two-piston ionic compressor was carried out by mathematical modelling of one compression cycle. The optimisation of the design parameters of the compressor proposed was conducted by the Taguchi method. This study found that the piston diameter ratio was the dominating factor accounting for more than 80 % of the contribution to the mass delivered, power consumption and specific energy consumption. The optimal design parameters were obtained as 0.7 for the piston diameter ratio, 0.5 for the stroke diameter ratio of Piston A and 0.1 for the trajectory parameter. Under the optimal design parameters, the specific energy consumption was obtained as 1563.38 kJ/kg.

Towards the Isothermal Gas Compression—A Novel Finned Piston-Cylinder with Increased Efficiency

In this paper, a novel concept of a finned piston system is presented and analyzed in which the compression heat is continuously extracted from the compression chamber. The resulting compression characteristic moves in the direction of an isothermal process, reducing the temperature of the compressed fluid in the compression chamber and reducing the necessary mechanical work required to carry out the process. The finned piston concept consists in an integrated heat exchanger inside of the chamber that is constituted of imbricated flat fins placed on the stator part and on the mobile piston. The internal heat exchange on the surface is strongly increased in comparison with a classical piston/cylinder. The energetic performance of the new system is evaluated with the help of simulation. The pressures, forces, and temperature of the compressed gas are simulated as well as the mechanical work needed. The different curves are compared with the system’s adiabatic and isothermal characteristics.

Simulation on two-phase refrigerant compression in the cylinder of rotary compressors using CFD method

The two-phase compression process in the rotary compressor often occurs, such as defrosting and startup processes, which has a significant impact on the performance and reliability of air conditioning systems. In this paper, the CFD simulations predicting the two-phase refrigerant compression process in the compressor cylinder are conducted using the commercial software ANSYS Fluent. The dynamic mesh for the fluid domain and phase change model for the refrigerant are considered in the simulation. Effects of initial liquid volume fraction, refrigerant type and compressor type on the two-phase compression characteristics using R290 as refrigerant are carried out. Variations of the pressure, temperature, gas fraction distribution and evaporation rate in the cylinder are discussed. The results show that most liquid accumulates near the leakage gap and the bottom of the compression chamber during the two-phase compression process. The peak pressure during the two-phase compression decreases with the increase of the liquid volume fraction. The evaporation rate of R32 in the cylinder is much higher than that of R290. The maximum pressure of the reciprocating compressor is 2.26 times higher than that of the rotary compressor.

Decompression sickness of the inner ear and relationship with a patent oval foramen: a study of 61 cases.

To discuss the link between inner ear decompression sickness and patent foramen ovale. Monocentric and retrospective study on decompression sickness of the inner ear requiring hyperbaric chamber treatment, from 2014 to 2021. Sixty-one patients of inner ear decompression sickness were included in this study. Twenty-four patients had vestibular injuries, 28 cochlear injuries and 9 cochleo-vestibular injuries. Compression chamber treatment was given, using an oxygen-helium mixture with oxygen partial pressure (PIO2) limited to 2.8 atmosphere absolute (ATA). All vestibular accidents completely recovered without clinical sequelae. For cochlear accident only 10 out of 37 patients (27%) recovered completely. A right-left shunt (patent foramen oval or intra-pulmonary shunt) was found in 31.1% of patients with inner ear decompression sickness (p > 0.05). The presence of patent foramen oval in patients with inner ear decompression was not statistically significant in our study. Understanding of the pathophysiology of decompression illness and the physiology and anatomy of the labyrinth would suggest a mechanism of supersaturation with degassing in intra-labyrinthine liquids.

Study on pressurization characteristics of single-screw steam compressor with water spray cooling under fluctuating heat source operating conditions

For a water-injected single-screw steam compressor (SSSC), the performance of the compressor is significantly affected by the water spray rate. However, the precise relationship between the water injection parameters and the operating parameters of the heat source under fluctuating heat source operating conditions (FHSOC) has not been elucidated. This paper introduces a constructed thermodynamic analysis model for the wet compression process under FHSOC aiming to explore the impact of fluctuating heat source parameters such as inlet steam temperature (IST) and inlet steam dryness (ISD) on the thermodynamic performance parameters of the compressor. The operational performance of the SSSC is then analyzed and compared under two distinct conditions: optimal water spray rate (OWSR) and fixed water spray rate (FWSR). The results demonstrate that when the IST of the SSSC increases within the range of 375 K–400 K, there is an initial decline followed by an increase in both the leakage rate and volumetric efficiency. Simultaneously, displacement and power consumption decrease, while adiabatic indicated efficiency and OWSR increase. Within this range, an optimal synergy is observed between IST and water spray parameters enabling the compressor to exhibit superior lubrication, sealing, and pressurization performance. On the other hand, when the ISD increases within the range of 0.92–1, the total heat transfer in the compression chamber decreases, and the leakage, OWSR, displacement, power consumption, adiabatic indicated efficiency, and volumetric efficiency all show varying degrees of increase. Regarding the volumetric efficiency corresponding to the OWSR, the impact of ISD on volumetric efficiency surpasses that of IST to a significant degree.

A model of the steam compression process in a piston reactor

The paper discusses the possible determination of steam parameters in a new type of piston machine for steam compression to generate supercritical water parameters. It presents a calculation model that allows one to simulate the process of steam compression in a cylinder with volume regulated by the piston position. In each calculation step, the steam parameters were determined on the basis of fast adiabatic changes which were corrected by the effect of leakage and heat transfer occurrence. The seal of the reactor was assumed to be a compression ring. Depending on the pressure drop on the seal, subcritical and supercritical flow was taken into account. The leak was corrected by the coefficient of flow contraction. Heat transfer was determined by equations for the Nusselt number for water and steam from the homogenous area. The programmed model allows one to simulate changes in the thermodynamic parameters of steam during the process of steam compression with any calculation step. The results presented in this paper show that the application of one compression ring allows us to obtain supercritical steam parameters. Various degrees of sealing leak tightness and their impact on the changeability of steam parameters were analyzed. Heat transfer was shown to have an impact not only on changes in steam temperature, but also on pressure. This paper analyzes the impact of the temperature of the walls of the compression chamber on the value and direction of heat transfer.

A Study on the Transient Response of Compressed Air Energy Storage in the Interaction between Gas Storage Chambers and Horseshoe-Shaped Tunnels in an Abandoned Coal Mine

This study focuses on the renovation and construction of compressed air energy storage chambers within abandoned coal mine roadways. The transient mechanical responses of underground gas storage chambers under a cycle are analyzed through thermal-solid coupling simulations. These simulations highlight changes in key parameters such as displacement, stress, and temperature within the chamber group during the loading and unloading processes of compressed air energy storage. It is found that within a cycle, the small circular chamber experiences the most significant deformation, with an average peak displacement of 0.24 mm, followed by the large circular chamber and horseshoe-shaped tunnels. The small circular chamber exhibits maximum tensile and compressive stresses. Therefore, special attention in engineering practice should be paid to the long-term safety and stability of small circular tunnels, and the stability of horseshoe-shaped tunnels should be also carefully considered. The findings from this study offer some insights for theoretical support and practical implementation in the planning, design, construction, and operation of high-pressure underground gas storage chambers for compressed air energy storage.

Evaluation of the mechanical properties of porcine kidney.

With the development of medical diagnosis and treatment, knowing the mechanical properties of living tissues becomes critical. The aim of this study was to investigation material properties of the fresh porcine kidney and the parametric characterization of its viscoelastic material behavior. The material investigation included uniaxial tension tests in different strain rates, relaxation tests, as well as hydrostatic compression tests on the samples extracted from the fresh porcine kidney cortex. Tension tests and relaxation tests were performed by a planar dog-bone specimen with a micron loading testing machine. Hydrostatic compression tests were performed on the kidney cylinder sample which was placed in a compression chamber. Furthermore, a nonlinear viscoelastic model recently proposed by us was employed to characterize the tension data at different strain rates and relaxation test data. The the experimental and numerical results show that the stress-strain relations of the porcine kidney cortex at different strain rates in tension are presented for the first time and a higher strain rate results in higher ultimate strength and initial Young modulus but a lower rupture strain. A damage-dependent visco-elastic model is employed to model the tension data at different strain rates and relaxation data and exhibits a good agreement with the experimental data, which also demonstrates that the damage has an obvious influence on the stress-strain relation. Through comparison with the existing reference covering the uniaxial compression data, it seems that the mechanical behavior of the porcine kidney cortex manifests a stress state-dependent mechanical behavior. The ultimate strength and rupture strain are larger in compression than that in tension.

Experimental investigation on the performance of compressed air energy storage using spray-based heat transfer

Near-isothermal compression and expansion may be accomplished by injecting water droplets into the air during the process to increase the overall efficiency. However, little is known about the relationship between spray system parameters and compressed air energy storage (CAES). Furthermore, the experiments about compressed air energy storage using spray-based heat transfer have not been investigated. The aim of this paper is to study the relationship between the performance of CAES and the spray system parameters by experimentally. The parameters including the spray closing time, the spray opening time, and the nozzle diameter are discussed. Results show that under the same operating conditions, the maximum air pressure in compression chamber reach to constant value when the spray closing time is 0.6 s; and spraying water mist within 0.6-1.2 s has no heat exchange effect on the air in the cylinder. During the compression process, the smaller the nozzle diameter is, the higher maximum pressure in compression chamber is. During the expansion process, if we ignore the energy consumption of spray system, the larger the nozzle diameter is, the more the expansion output is. Further investigation is recommended to optimize spray parameters based on different CAES systems.