Back Pressure Chamber Research Articles

Analysis of the oil temperature in a scroll compressor with oil carter at discharge pressure using propane as refrigerant: Performance analysis for abnormally low oil volume

Scroll compressors are widely utilized in refrigeration systems and heat pumps, operating through the interaction of two spiral-shaped elements, one stationary and the other orbital. These elements fit together and continuously oscillate, compressing the fluid into diminishing volumes. They offer significant advantages such as high volumetric and compressor efficiencies, low vibrations, and reduced leaks. In direct suction scroll compressors, the oil sump is at discharge pressure, resulting in a wide pressure difference between the housing and the backpressure chamber; also, the oil temperature is higher than in the most common suction-side oil crankcase design. Knowing the oil temperature is crucial in determining the properties of the oil/refrigerant mixture that affect the system's performance. It also allows us to estimate the amount of refrigerant dissolved in the oil. In the current study, a series of tests are conducted under various operating conditions to measure the oil sump temperature in a direct suction scroll compressor. This experimental campaign was conducted using a compressor with an unusually low oil level, and an analysis of the system's performance was performed until a failure occurred.

Numerical Prediction of Refrigerant Oil Two-Phase Flow from Scroll Compressor Discharge to the Suction Side via Back Pressure Chamber

Oil lubricates the contact between the orbiting and stationary scroll in the refrigerant scroll compressor, while the sealing between the scrolls is achieved through the refrigerant vapour pressure in the sealed back pressure chamber. The back pressure should be adjusted using the refrigerant oil two-phase flow from the oil separator at the compressor discharge to the back pressure chamber and the refrigerant oil flow from the back pressure chamber to the compressor suction side. Both of the flows are conducted through connecting tubes with corresponding high-pressure and low-pressure nozzles with small diameters. Models for predicting the refrigerant oil critical and subcritical flows through the nozzles were developed and applied in enable the prediction of the back pressure. The models are original, because the slip between the oil and the refrigerant as well as the refrigerant solubility in the oil are taken into account. The critical flow model is validated against the experimental data that are available in the literature. The back pressure is predicted by equating the mass flow rates of refrigerant and oil two-phase mixtures through the high- and low-pressure nozzles. The results show that the critical flow takes place through the high-pressure nozzle, while the subcritical flow through the low-pressure nozzle can also exist in cases with a small pressure difference between the back pressure chamber and the compressor suction side. The refrigerant solubility in the oil has a small influence on the critical and subcritical refrigerant oil mixture mass flow rates, while the influence on the back pressure is more pronounced.

The Effect of Ignition Procedure on Flashback of Hydrogen-Enriched Flames

Abstract The impact of different ignition sequences on the ignition dynamics of CH4-H2 flames in a bluff body burner is investigated at atmospheric conditions. Experiments are performed over a wide range of operating conditions covering pure methane injection (PH0) to pure hydrogen injection (PH100). A perforated plate of total porosity σ=0.17 is positioned at the outlet of the combustion chamber to increase the chamber back pressure and trigger transient flashback during ignition. Time-series of pressure, OH* chemiluminescence and OH-PLIF images of the propagating flame branch are recorded simultaneously to characterize the ignition process. Two ignition procedures are investigated. For ignition procedure A, designated as an early ignition procedure, the spark is initiated before fuel injection. For ignition procedure B, designated as a late ignition, the spark is only activated after the fuel injection. The impact of the fuel air mixing on the final stabilization state is investigated by changing the fuel delivery time (dt) before the initial spark. Three different time delays are considered dt = 1, 3, and 5 s. The final state of the flame is found to be highly sensitive to the selected ignition procedure and increasing dt favors the occurrence of flashback. At constant power, the magnitude of the pressure peak is driven by a competition between the fuel mass flowrate at the moment of ignition and the high reactivity of hydrogen, which shifts the flammability limit toward lower equivalence ratios, hence generating a lower reaction rate. For procedure A, the peak of the chamber over pressure shows a nonmonotonic growth for increasing levels of H2 in the fuel blend, while it linearly increases for procedure B. Experiments are then conducted at a fixed injection flow velocity Ub = 5 m s–1 and fixed laminar burning velocity Sl0=0.25 m s–1 by varying the level of hydrogen enrichment. For procedure A, the over pressure amplitude decreases with increasing the hydrogen enrichment leading to a soft ignition for all CH4-H2 blends. Under ignition procedure B, the amplitude of the over pressure reached during ignition is found to be relatively unaffected by the hydrogen concentration, but the flame stabilization mode shows a strong dependence to both the level of H2-enrichment and fuel delivery time dt. OH* as well as OH-PLIF images reveal that the trajectory of the flame leading point changes as dt increases. The different dynamics of the flame leading points is likely to be the cause the different types of stabilization modes observed.

Research on the performance characteristics of an oil-free scroll expander that is applied to a micro-scale compressed air energy storage system

The oil-free scroll expander, which is the power component of the micro-scale compressed air energy storage (CAES) system, exhibits a satisfactory application prospect. The expander's performance directly influences the efficiency of the expansion power generation system. To enhance the work efficiency of the power generation system, we built a thermodynamic model that facilitates the oil-free scroll expansion mechanism by considering heat transfer and leakage; furthermore, for the micro-scale CAES, we constructed an experiment bench that utilizes air as the working fluid. Based on computational fluid dynamics (CFD), we conducted a three-dimensional unsteady numerical simulation of the fluid flow that occurs in the working chamber of the scroll expander. We observed that the suction pressure loss that occurs during the suction process, which is initiated by the scroll expander, leads to inlet pressure drop, and we noted that the suction pressure directly influences the work efficiency of the power generation system. When the setup is subjected to rotational speeds of 1200–3200 r/min, the difference between the theoretical and measured values of volumetric flow decreases from 0.0226 to 0.000527 m3/min. The pressure, velocity, and temperature distribution of the fluid that exists in the working chamber of the expander are not uniform, and the mass exchange that occurs between adjacent working chambers considerably impacts the distribution of velocity and temperature. As gas flows from the back-pressure chamber to the outlet pipe, most of it flows through the non-deforming domain before flowing into the outlet pipe. The fluid flow in the deforming domain is highly complicated, and even secondary flow can occur.

Experimental Study on the Dynamic Characteristics of Gas-Centered Swirl Coaxial Injector under Varying Ambient Pressure

To determine the dynamic characteristics of a gas-centered swirl coaxial injector under backpressure, an experimental system of dynamic injection in a backpressure chamber was constructed. Filtered water and nitrogen were used as simulant media for rocket propellants, which are typically used with this kind of injector. An inertial flow pulsator was manufactured to generate the pulsation of the flows that feed to the liquid injector. The electric conductance method was adopted to measure liquid film thickness. After the pulsation of incoming flow in the feedline was tested, and the operating conditions for the injector to start pulsating were validated, the effects of the chamber backpressure and the recess length of the injector on the dynamic characteristics of spray, such as liquid film thickness, breakup length, and amplitude of pulsation, have been investigated in detail. Experimental results demonstrated that the increase in chamber backpressure prompts the liquid sheet to rupture earlier with a shorter breakup length, which results from the increased density of the ambient gas. Chamber backpressure suppresses the pulsation of the outlet flow, especially for a longer recess length. Moreover, a decrease in the recess length results in a reduction in breakup length due to an intense gas–liquid shearing in a narrower recess section. For a lower backpressure, the amplitude of outlet flow generally increases when the recess length increases. However, this phenomenon is not obvious for the conditions of higher backpressure and lower pulsation frequency.

Impact of chamber back pressure on the ignition dynamics of hydrogen enriched premixed flames

The impact of chamber back pressure and H2-enrichment on flashback of premixed CH4−H2-Air flames triggered by ignition dynamics is investigated. Different back pressures are imposed by varying the exhaust flow blockage with perforated plates of different porosities. Experiments measuring the ignition transient, from kernel formation to stable flames and flashback, with increasing levels of H2-enrichment covering a wide range of operating conditions are conducted. Time-series of pressure, velocity and heat release rate are examined to characterise the ignition process. It is shown that the final state of the flame is highly modified by the over pressure caused by the volumetric expansion of the hot gases. Three different scenarios are identified: Soft ignition with direct stabilisation, transient flashback and permanent flashback. The magnitude of the over pressure generated at ignition is significantly amplified by small increases in mean back pressure which, in turn, modifies the flowrate through the injector thereby promoting flashback. In addition to its role as a pressure amplifier, increasing the combustor back pressure also affects the time lag between the over pressure and the peak in heat release rate just after ignition. The impact of H2-enrichment on flashback is investigated by keeping both the bulk injection velocity Ub and laminar burning velocity Sl0 constant for flames with 0% to 100%H2-content. It is shown that the magnitude of the over pressure approximately scales with Ub/Sl0 and is independent of the total thermal power and H2 enrichment. Although the mean flow conditions and over pressures are kept constant, the stabilisation mode directly depends on H2-content. This shows that flashback triggered by the ignition dynamics cannot be fully described by classical kinematic arguments and a new mechanism is presented.

Analysis on influence factors of back pressure in an asymmetrical algebraic scroll compressor

The back-pressure mechanism plays an important role in the performance and efficiency of the scroll compressor. In this work, the level of back pressure of an asymmetrical algebraic scroll compressor is experimentally measured and it is shown that the back pressure decreases with the increase of compressor frequency under all tested operating conditions. The mathematical model of the scroll compressor is also developed in order to further investigate other influence factors of back pressure. The predicted back pressure is compared with experiment result, showing a similar trend to them. The pressures in each working chamber and back-pressure chamber are studied to identify the effect of leakage through flank and radial leakage gaps. The influences of compressor frequency, leakage gap size, back-pressure volume on back pressure are discussed in detail based on developed model. The axial forces and stability of the orbiting scroll are also evaluated under these operating conditions by using interpolation method to calculate the pressure distribution on tips.

A study of an industrial counter pressure casting process for automotive parts

Counter pressure casting (CPC) is emerging in the automotive manufacturing industry as an alternative to low-pressure die casting (LPDC) due to its reported superior capabilities in aluminum parts production. This study presents the first comprehensive investigation of how CPC's characteristic feature (applied chamber pressure) influences the fluid flow and heat transport occurring in the process and its effect on casting quality. A large amount of high-quality data was acquired from a commercial CPC process for the production of automotive suspension control arms with two process conditions (standard production and low back-pressure condition). Analysis of the data shows that there are no significant differences between the two process pressure conditions with respect to heat transfer during solidification, as-cast microstructure nor mechanical properties. Generally, in-die measured temperatures exhibited a difference within 10 °C for the two process conditions examined and the ultimate tensile strengths (UTSs) of the samples obtained from castings were within 7% for the two process conditions. Furthermore, there was no measurable difference observed in the Secondary Dendrite Arm Spacings (SDASs) obtained under the two process conditions. However, the implementation of chamber back pressure noticeably reduces the venting rate during the filling stage, leading to 12 s delay in the filling time relative to the low back-pressure condition. A computational modelling methodology, originally developed for LPDC, was applied to simulate the CPC process. The model required only an adjustment to pressure curve to account for the delay of filling owing to the reduced venting rate observed for the higher back-pressure condition. The predicted results were found to correlate well with the measured data, demonstrating that the modelling methodology is broadly applicable to permanent die casting processes.

Prediction of blowdown of a pressure relief valve using response surface methodology and CFD techniques

In this study, parametric assessment of the main geometric design features of a pressure relief valve (PRV) with a backpressure chamber and two adjusting rings was conducted using response surface methodology. This design approach was established by using computational fluid dynamics (CFD) to model the dynamic performance of the opening and closing of a nuclear power main steam pressure relief valve (NPMS PRV). An experimental facility was established to test the NPMS PRV in accordance with the standard ASME PTC 25, and to validate the CFD model. It was found that the model can accurately simulate the dynamic performance of the NPMS PRV; the difference in blowdown between the simulation and experiment results is found to be below 0.6%. Thus, the model can be used as part of a design analysis tool. The backpressure chamber assisted in the reseating and decreased the blowdown of the NPMS PRV from 18.13% to 5.50%. The sensitivity to valve geometry was investigated, and an explicit relationship between blowdown and valve geometry was established (with a relative error less than 1%) using the response surface methodology; this will allow designers to assess the valve settings without the need for a CFD model.

Investigations on gas-air mixture formation in the ignition chamber of two-stage combustion chamber using high-speed Schlieren imaging

Combustion of the lean mixtures in the spark ignition engines provides higher thermal efficiency compared to the combustion of the stoichiometric mixture but is more restrictive to the ignition systems. Due to the limitations of conventional ignition systems, advanced concepts are being used, e. g. spark-jet ignition. Presented research has been carried to determine: 1. The impact of fuel injection pressure on the velocity of mixture formation, 2. Fuel distribution inside ignition chamber in defined phases of chamber filling, 3. Influence of chamber back-pressure on gas jet development. Investigations have been carried using the ignition chamber providing optical access. The visualization has been done with Schlieren-method with “Z”-setup basing on two ϕ = 150 mm parabolic mirrors. Images have been recorded with LaVision HSS5 camera with CMOS transducer. The paper contains a comparison of gas penetration parameters for a different injection pressures and chamber backpressures. The injection into the quasi-static air has been compared to the injection in dynamic conditions. It is stated, that both injection pressure and chamber back-pressure influence gas jet-development in the ignition chamber. The regions of the chamber with increased swirling and therefore providing more efficient micromixing have been identified.

Inductively-coupled plasma-enhanced chemical vapour deposition of hydrogenated amorphous silicon carbide thin films for MEMS

In this study, the impact of various deposition parameters such as the reactive gas flow ratio, plasma power, substrate temperature and chamber back pressure of ICP-CVD deposited a-SiC:H thin films is investigated and the influence on important MEMS-related properties like residual stress, Young’s modulus, hardness, mass density and refractive index is evaluated. Basically, tailoring of the as-deposited a-SiC:H characteristics is possible to a great extent with residual stress values ranging from −16 up to −808MPa, Young’s modulus values between 36 and 209GPa or deposition of layers with hardness values ranging from 5.3 to 27.2GPa is feasible. Especially the mechanical parameters are strongly linked to both the SiC bond density and the amount of incorporated hydrogen obtained from Fourier transform infrared spectroscopy analyses.

Numerical investigation of the effects of chamber backpressure on HFO spray characteristics

In the current study, effect of chamber ambient backpressures and temperatures on non-reacting fuel spray characteristics of heavy fuel oil (HFO) under high pressure injection is numerically studied. Four different chamber backpressures ranging from 0.05 up to 2.8 MPa at two different ambient temperatures have been considered in a medium speed engine. An Eulerian-Lagrangian multiphase scheme is implemented to model HFO interaction with air continuous phase by using Open source CFD toolbox of OpenFOAM. Numerical results of fuel spray are validated with good accordance against existing experimental data. Based on the computational findings, enhancement of chamber backpressure results in reduction of temporal spray penetration and increase of spray cone angle at both ambient temperatures. Furthermore, the SMD is found to decrease due to enhancement of chamber backpressures up to 1.4 MPa. Finally, it was found that higher ambient temperature increases the spray penetration length at all chamber backpressures.

Study on Mathematical Model in Working Process of Automotive Air Conditioning Scroll Compressor

In order to study the working features of automotive air conditioning scroll compressor, this paper uses mathematical model of working process to analyze it. After studying working process, a equation of suction volume is given. The thermodynamic model of compression chamber and back pressure chamber includes mass conservation and energy conservation. Based on Hydromechanics, leakage models of radial leakage and tangential leakage are discussed. The model lays a foundation of automotive air conditioning scroll compressor performance simulation.

Press for hydrostatic extrusion with back-pressure and the properties of thus extruded materials

A press for hydrostatic extrusion within the extrusion pressure range up to 2GPa with back-pressure up to 0.7GPa was designed and constructed. The press is equipped with an integrated pressure intensifier, and a control and recording system which permits recording the process parameters, such as extrusion pressure, back-pressure and its stability, time and speed of the extrusion, and enables monitoring the process on-line. The double-layer high-pressure chamber and the monobloc back-pressure chamber were analyzed using the finite element method with allowance made for the self-strain-hardening effect known as autofrettage. The maximum permissible load imposed on chambers and the resulting balance pressure established in the case of the two chambers being accidentally connected were also evaluated. Several cold extrusion processes assisted with back-pressure from 400MPa to 700MPa were conducted, experimenting with low or non-ductile materials, such as the ZW3 magnesium alloy, GJL250 grey cast iron, GJS500 nodular cast iron, bismuth of 99.999% purity, and molybdenum of 99.9% purity. The bulk, non-defected products with diameters ranging from 4 to 7mm were obtained. The use of back-pressure permitted the materials to be plastically deformed during a single cold operation with the percent deformation from 36% in grey cast iron to more than 80% in Bi. Thanks to the strain-hardening due to the severe plastic deformation, the materials acquired excellent properties (YS=392MPa in the magnesium alloy, σd0.2=709MPa in molybdenum, σdM=1140MPa in grey cast iron, and σd0.2=643MPa in nodular cast iron) impossible to achieve by classical plastic deformation processes. The hardness of the materials was also increased adequately, and the refinement of their microstructure resulted in an increase of ductility. These advantageous results obtained by using the press indicate that hydrostatic extrusion with back-pressure has a great applicative potential.

바이오매스를 에너지원으로 하는 유기냉매 사이클 스크롤 팽창기 발전 장치 설계

A scroll expander has been designed to produce a shaft power from a R134a Rankine cycle for electricity generation. Heat was supplied to the Rankine cycle through a heat exchanger, which received heat from another cycle of water. In the water cycle, water was heated up in a boiler using biogenic solid fuel. The designed scroll expander was a horizontal type, and a trochoidal oil pump was employed for oil supply to bearings and Oldham-ring keys. For axial compliance, a back pressure chamber was created on the backside of the orbiting scroll base plate. Numerical study has been carried out to estimate the performance of the designed scroll expander. The expander was estimated to produce the shaft power of about 2.9 kW from a heat supply of 36 kW, when the temperature of R134a was <TEX>$80^{\circ}C$</TEX> and <TEX>$35^{\circ}C$</TEX> at the evaporator and condenser of the Rankine cycle, respectively. The expander efficiency was about 70.5%. When the amount of heat supply varied in the ranges of 7.5~55 kW, the expander efficiency changed in the range of 45.6~70.5%, showing a peak efficiency of 70.5% at the design shaft speed.

엔진 냉각수 폐열 회수용 스크롤 팽창기 설계

A scroll expander was designed for an energy converter from waste heat of IC engine coolant to useful shaft work. The scroll expander is to run in a Rankine cycle which receives heat energy transferred from engine coolant circulation cycle. The working fluid was Ethanol. For axial compliance, a back pressure chamber was provided on the rear side of the orbiting scroll. Lubrication oil was delivered by a positive displacement type oil pump driven by the shaft rotation. Performance analysis on the scroll expander showed that the expander efficiency was 63.4%. It extracts shaft power of 0.6 kW out of engine coolant waste heat of 17.5 kW, resulting in the Rankine cycle efficiency of 3.43%.

Applicability of scroll expander and compressor to an external power engine: Conceptual design and performance analysis

A scroll expander and scroll compressor for a 10-kW class Ericsson engine utilizing solar energy as heat source has been suggested. Orbiting scroll members of the expander and compressor were designed to have a base plate with double-sided wrap structure for compact size and axial gas force cancellation. For axial compliance of the scroll machines, a back pressure chamber was created on each fixed scroll. In order to compensate for the thermal expansion, flexible coupling between the orbiting scroll base plate and the scroll plate holders and sliding keys between the fixed scroll and the supporting frame were designed. Common shafts were shared by the expander and compressor for direct power transmission. For high- and low-side pressures of 6 and 2.5 MPa, respectively, and expander inlet temperature of 700°C, the proposed engine efficiency was estimated to be 7.3%. The engine efficiency strongly depends on the expander and compressor efficiencies as well as on the regenerator efficiency. The shaft output of the designed scroll expander was calculated to be 38.84 kW, while the input power for the scroll compressor was 27.97 kW, yielding 10.87 kW for the engine output. Copyright © 2011 John Wiley & Sons, Ltd.

The qualitative spray analysis of liquid fuel in high-pressure piezoelectric injection system

The paper presents the methodology and tests results of the influence of the fuel injection pressure and combustion chamber back pressure on the changes of the fuel spray geometrical parameters injection uniformity and its quality during the injection. While evaluating the geometrical fuel spray parameters the spray penetration, speed of propagation were taken into account and while evaluating the quality of the fuel atomization the outflow of the fuel from the injector were considered. The tests reported here were performed for one value of the air back pressure at the various injection pressures. The fuel doses were changed by modifying the duration of the injection. A significant influence of theses parameters on the values of the operating indexes of the injection and atomization processes has been noted.

Effect of Chamber Backpressure on Swirl Injector Fluid Mechanics

Fluid mechanics of a liquid swirl injector element at various chamber backpressures were investigated. The center-jet swirling element was designed using typical liquid propellant rocket engine parameters, then manufactured and tested in a high-pressure, optically accessible, cold flow facility. Water was injected into a chamber pressurized with gaseous nitrogen at a constant swirl injector flow rate of 0.09 kg/s. The chamber backpressure ranged from 0.10 to 4.81 MPa. The film thickness and spray angle near the nozzle exit were measured by shadowgraphy. The film thickness was also measured within the injector upstream of the exit through a transparent nozzle tube section. Increasing the chamber backpressure for this fixed mass flow rate increased the film thickness from predicted design values. Measured discharge coefficient values increased with increasing chamber backpressure, reflecting the observed increase in internal nozzle film thickness. The spray angle decreased for increasing chamber backpressure.

Pressure-affected flow properties of powder injection moulding compounds

The effect of pressure and temperature on the flow properties of the materials intended for Powder Injection Moulding (PIM) technology was studied using a single-piston capillary rheometer modified by additional backpressure chamber. The influence of pressure and temperature on shear viscosity has been quantified through pressure and temperature sensitivity coefficients derived from Carreau-Yasuda model. The temperature sensitivity of the 50 vol.% compound based on cemented carbide powder is lower than that of pure polymeric binder, and it varies only slightly with pressure. In contrast, the pressure sensitivity of compounds was found to be higher than that of pure polyolefin binder, and it is decreasing function of temperature. In addition, it is shown that temperature sensitivity of binder, which is considerably enhanced by pressure (in contrast to the PIM demands), cannot be determined as being equal to the properties of particular binder components.