Decrease Of Mass Flow Rate Research Articles

A numerical study on the lubrication system for a hermetic reciprocating compressor used in household refrigerators

This study presents a numerical investigation of an oil supply system for a hermetic reciprocating compressor used in household refrigerators. It is aimed to investigate the geometric parameters of the crankshaft affecting the mass flow rate of the lubricant released from the outlet of the crankshaft. The change of the mass flow rate from the outlet of the crankshaft associated with helix-screw indicates that with reducing the screw pitch, the mass flow rate decreases. An important finding is that increasing the depth of the helical channel plays a more significant role than increasing the width of the helical channel. The mass flow rate increases when the distance between the suction hole of the crankshaft and the oil sump bottom increases. The wall thickness of the crankshaft does not significantly affect the mass flow rate whereas it plays a crucial role in formation of the vortices around the crankshaft.

Three-dimensional CFD modeling of a planar membrane humidifier for PEM fuel cell systems

A three-dimensional numerical model is developed to investigate and compare the performance of humidifiers with counter-flow and parallel-flow configurations. This model has a set of coupled equations including conservations of mass, momentum, species and energy. The results indicate that in counter-flow humidifier, water and heat transfer is more than that of the parallel-flow that leads to a higher dew point at dry side outlet, consequently, a better humidifier performance. An increase in temperature and a decrease in mass flow rate at dry side inlet lead to a better humidifier performance. However at the low flow rates the humidifier performance does not change a lot by preheating the inlet dry gas. An increase in relative humidity at dry side inlet does not offer any advantage.

Coronal accretion: the power of X-ray emission in AGN

AbstractThe optical/UV and X-ray emissions in luminous AGN are commonly believed to be produced in an accretion disk and an embedded hot corona respectively. We explore the possibility that a geometrically thick coronal gas flow, which is supplied by gravitational capture of interstellar medium or stellar wind, condenses partially to a geometrically thin cold disk and accretes via a thin disk and a corona onto the supermassive black hole. We found that for mass supply rates less than about 0.01 (expressed in Eddington units), condensation does not occur and the accretion flow takes the form of a corona/ADAF. For higher mass supply rates, corona gas condenses to the disk. As a consequence, the coronal mass flow rate decreases and the cool mass flow rate increases towards the black hole. Here the thin disk is characterized by the condensation rate of hot gas as it flows towards the black hole. With increase of mass supply rate, condensation becomes more efficient, while the mass flow rate of the coronal gas attains values of order 0.02 in the innermost regions of the disk, which can help to elucidate the production of strong X-ray with respect to the optical and ultraviolet radiation in high luminosity AGN.

Extreme fuel-rich combustion characteristics of RBCC embedded rocket engine with gas-liquid shear coaxial injectors in continuously varying mixture ratios

In order to achieve stable and effective transition between the operation modes in a rocket-based-combined-cycle engine (RBCC), the embedded rocket engine should be capable of throttling continuously in a wide range of operation conditions. A kerosene/GO2 RBCC embedded rocket engine with gas–liquid shear coaxial injectors was designed to investigate the combustion characteristics under varying operation conditions. Throttling cold test, static hot test, and throttling hot tests in varying mixture ratios (0.102–0.221) were conducted with a throttleable venturi and a throttleable sonic nozzle. In these tests, the mixture ratio was adjusted in two ways: one is to linearly decrease the fuel mass flow rate with a constant oxygen mass flow rate, and the other is to increase the oxygen mass flow rate with a constant fuel mass flow rate. Results indicate that the combustion efficiency and the characteristic velocity increase along with the mixture ratio, but show a different growth rate depending on the mixture ratio adjustment method. To specify, characteristic velocity and combustion efficiency of hot test throttled by increasing oxygen mass flow rate grow faster. And in the range of mixture ratios ( Φ<0.25), the combustion efficiency obtained by both adjustment methods is lower than 55%. The flame behaviors are influenced significantly by the oxygen mass flow rate, and a reasonable explanation is that increasing oxygen mass flow rate can significantly increase the spray angle and decrease the mean diameter. And the flame behaviors can influence the discharge coefficient of the kerosene injector. Furthermore, the discharge coefficient decreases along with the decrease of kerosene mass flow rate in both hot and cold tests.

Computational Study on Hysteretic Inlet Buzz Characteristics Under Varying Mass Flow Conditions

This paper presents a computational investigation of the hysteretic buzz characteristics of a supersonic inlet under a complete historic path of a mass flow change. It is observed that the amplitude and frequency of inlet buzz suddenly change in spite of the gradual variation in the mass flow rate. Furthermore, inlet buzz is found to exhibit quite different behavior depending on the historic path of the mass flow rate change, which leads to the hysteretic inlet buzz phenomenon. To investigate the hysteretic characteristics of inlet buzz and to provide a physical explanation of such a phenomenon, a series of numerical simulations are performed with the following three stages. First, an inlet without a center body is calculated to validate the flow solver and basic resonance mode results. Second, an inlet under a decreasing mass flow rate condition is simulated. Last, the effect of an increasing mass flow rate on inlet buzz is examined. Through computations, multiple inlet buzz transitions from fundamental to higher buzz modes are obtained, in accordance with previous experimental observations. The three sets of the computed results are compared and discussed from the viewpoint of acoustics to explain the physical mechanism of the hysteretic buzz characteristics and the buzz transition phenomenon.

Experimental investigation of fluid flow in horizontal pipes system of various cross-section geometries

The current research work presents experiments of an essentially incompressible fluid flow in pipes. The experimental equipment consists of a horizontal pipe including a gate valve, a Venturi meter, a wide angle diffuser, an orifice plate, a 90-degree elbow and pressure tappings. An elbow connects the pipe to a rotameter with further pressure tappings. All pressure tappings connected to manometers held on a vertical panel behind the pipe work and show pressure at various points. The effect of the pipe geometry in the flow pattern is presented. Furthermore head losses are estimated, at specific stream-wise cross-sections, for mass flow rate numbered from 0.056 to 0.411 l/s. The manometers measure and clearly show pressure distribution against a calibrated scale. The diagrams of mass flow rate and head losses are presented in specific cross- sections, where geometry changes. All measurements were calibrated and validated in a maximum standard deviation difference of 5%. The head losses decrease as the mass flow rate decreases, for all pipe geometries. In the future the experimental results can be used to verify numerical simulation results.

COMPARISON OF THE EFFECTS OF DIFFERENT TYPES OF TUBE INSERTS ON TWO-PHASE FLOW INSTABILITIES

Turbulence promoting inner elements such as rings, wings or winglets, twisted tapes, etc., is widely used in single- and two-phase flows. In this experimental work, the two-phase flow instabilities of forced convection boiling in a horizontal tube with ring- and twisted-tape-type inner elements inside are investigated. In order to analyze the two-phase flow of water, the experiments were conducted under a constant system pressure of 7.5 bar, and a constant heat input of 24 kW was applied to the outer surface of the circular test pipe with constant exit restriction. Three different inlet temperatures (Ti = 15, 25, and 35°C) were used to see the effect of inlet sub-cooling, and the mass flow rate was decreased from 110 to 20 g/s to obtain the characteristic curve. Two different pitch ratios for both the ring and twisted tape were evaluated in terms of stability. The results were evaluated in terms of appropriate variables for both the tube with insertions and the smooth tube. The analysis shows that the pressure drop increases with decreasing mass flow rate for all cases. The presence of the inner elements in the test pipe causes the boundaries of the oscillations to narrow in comparison with smooth tube. On the other hand, with the increase in the effective diameter of the test pipe the boundaries of the oscillations broaden. For each type of insertion, the increase of the pitch ratio makes the system less stable.

Thermoelectrically controlled micronozzle — A novel application for thermoelements

This paper introduces and assesses the concept of the recently invented thermoelectrically controlled micronozzle (TECMN). A generalized quasi-one-dimensional model for gas flow, which is influenced by area variation and by wall heat transfer, is considered. In order to assess the merits of wall temperature control in micronozzles, the flow in the micronozzle is solved numerically for cases of convergent wall heating, divergent wall cooling, and a combination of both. Thermal efficiency and specific impulse are affected by heat exchange through the side wall of the micronozzle. By cooling the divergent section, kinetic energy increases, thus improving thermal efficiency. The mass flow rate is decreased in all cases that include convergent section heating, thereby enhancing specific impulse. The combination of convergent section heating with divergent part cooling results in significant performance enhancement in terms of thermal efficiency and specific impulse. To determine the TECMN wall temperature profile, we developed a one-dimensional general energy model for a thermoelement (TE) subject to an electric field as well as for heat convection on the lateral surface. The energy equation is analytically solved for constant properties and for Joule heating equivalent to heat convection. The temperature profile is then imposed on the quasi-one-dimensional flow model, which is solved numerically for various mass flow rates and exit wall temperature (cold junction). As the exit section wall temperature and mass flow rate decrease, the utilization of TEs to control the temperature of micronozzle walls considerably increases the Mach number at exit.

스프링클러 분무가 화재유동특성에 미치는 영향에 관한 수치해석 연구

The present study investigates the effects of sprinkler spray on fire driven flow characteristics in a compartment based on numerical approach. The FDS (Fire Dynamics Simulator), a widely used fire field model, was used to simulate the fire induced flow and sprinkler spray and a series of grid independence tests have been performed to obtain the optimal grid size. In order to validate the result predicted by FDS model, the calculated results were compared with experimental results of Magnone et al.. The FDS model matches quite well to experiments in temperature profile and mass flux through doorway, however, the discrepancy between the FDS model and experiments increases with increasing water discharge rate. As with previous study, the FDS calculation also shows a decrease of mass flow rate of combustion products through doorway due to the sprinkler spray. This study can contribute to optimize the sprinkler system design and verify the validity of the fire field model with sprinkler spray.

Development and evaluation of garlic incorporated ready-to-eat extruded snacks.

The present study was carried out to develop and evaluate ready to eat extruded snacks incorporated with garlic powder at various levels (5%, 10%, 15%, 20%). The organoleptic evaluation was conducted for the developed products and the well accepted products were selected for further studies like physical properties and shelf life (stored at room temperature for 2months). The organoleptic evaluation of the developed snacks revealed that 15% and 20% garlic incorporated snacks were not acceptable due to strong garlic flavor, therefore T1 (control), T2 (5% garlic) and T3 ( 10% garlic) were selected for further studies. The physical properties showed significant changes with incorporation of garlic powder at 0%-10% level. There was an increase in mass flow rate, tap density and bulk density but decrease in the water holding capacity, oil absorption capacity and expansion ratio. The water soluble index and moisture retention of the products showed the same values for all the three selected treatments. The products were packed by ordinary, nitrogen and vacuum packing and stored for 2months. It was found that there was an increase in moisture content and microbial load, however the increase was within limits. The increase in the moisture content was low in nitrogen packed products where as the microbial load decreased with increase in the percentage of garlic incorporation. The nitrogen and vacuum packed products showed less microbial load than the ordinary packed products. Garlic powder can be incorporated at 5 and 10% levels in ready-to-eat extruded snacks with well acceptability and can be stored for a period of 2months with nitrogen packing as an effective packaging.

An investigation of the effects of fuel injection pressure, ambient gas density and nozzle hole diameter on surrounding gas flow of a single diesel spray by the laser-induced fluorescence–particle image velocimetry technique

The characteristics of ambient gas motion induced by a single diesel spray were measured quantitatively by using a laser-induced fluorescence–particle image velocimetry technique under non-evaporating quiescent conditions. The effects of fuel injection pressure, ambient gas density and nozzle hole diameter on the ambient gas mass flow rate into the spray through the whole spray periphery (spray side periphery and tip periphery) were investigated quantitatively according to the gas flow velocity measurements. The results show that the captured gas mass flow rate through the spray tip periphery is prominent in the whole periphery and the proportion of the gas entrainment through the spray side periphery increases with spray development. The higher injection pressure significantly enhances the total gas mass flow rate through the whole periphery; however, the increase in the ratio of ambient gas and fuel mass flow rate becomes moderate gradually with the increase in the injection pressure. The higher ambient gas density results in a slight increase in ambient gas flow velocity along the spray side periphery and the tip periphery and a reduction of the spray volume; however, the ambient gas mass flow rate was apparently enhanced. The smaller nozzle hole diameter results in a significant decrease in the ambient gas mass flow rate and an increase in the ratio of the gas and fuel mass flow rate. Numerical simulation results provide more understanding of the spray-induced gas flow field and validate the measurement accuracy of the laser-induced fluorescence–particle image velocimetry results.

+Transient characteristics of a liquid-to-air membrane energy exchanger (LAMEE) experimental data with correlations

In this paper, the transient and steady-state performance of a liquid to air membrane energy exchanger (LAMEE) is investigated experimentally. The transient sensible, latent and total effectiveness are each presented for particular air and desiccant mass flow rate for both summer and winter supply air test conditions. After a step change in inlet conditions the effectiveness increases with time. Also, the transient effectiveness is assessed for various air and desiccant mass flow rates under summer test conditions and the LAMEE’s time constant is investigated as an important variable that depends primarily on the thermal capacity of the exchanger and liquid content. The calculated effectiveness shows considerable dependency on the air and desiccant mass flow rate. Finally, steady-state results reveal that as the desiccant mass flow rate increases or air mass flow rate decreases, the effectiveness increases.

Effects of geometry and inconstant mass flow rate on temperatures within a pressurized hydrogen cylinder during refueling

Higher refueling rate leads to higher temperature rise within the cylinder. Excessive temperature should be avoided during the refueling progress. In this paper, we studied the effective methods to control the temperature rise by simulations based on the Computational Fluid Dynamics (CFD). Cylinders of different length to diameter ratios and different inlet diameters were simulated. We found that smaller radio of length to diameter can boost for temperature control and temperature distribution. Larger inlet diameter can restrain temperature rise. Comparing the simulation results with constant, increasing and decreasing mass flow rate, the refueling with increasing flow rate obtains the lowest temperature rise.

Single and two-phase flow modeling and analysis of a coaxial vacuum tube solar collector

In this paper, an analytical steady state model is developed to study the thermal performance of an individual vacuum tube solar collector with coaxial piping (direct flow type) incorporating both single and two-phase flows. A system of equations which describe the different heat transfer mechanisms and flow conditions was established, discretised, and solved in an iterative manner. For the case of good vacuum condition (10−5 mb) the calculated efficiency curve for single phase flow deviates significantly from the experiments with increasing collector temperature, but agrees well for the case of gas conduction inside the glass envelope at very low pressure (≪1 mb) due to the corresponding increase in overall heat loss coefficient (U-value). For two-phase flow, the occurrence and propagation of flow boiling and condensation inside the collector piping under saturated condition is hypothesized. The modeling results indicate that for all-liquid-single-phase fluid flow, the collector efficiency decreases with decreasing mass flow rate. Once the fluid reaches the boiling point at a certain mass flow rate, no significant reduction in efficiency is observed anymore, which is in accordance with the experimental study.

자동차용 진공펌프 멀티 베인의 최적 설계를 위한 유동장 수치해석

진공 펌프의 최적설계를 위해 수치해석을 수행하였다. 진공 베인 펌프 설계인자인 베인 각도 변화, 입출구 파이프의 위치와 각도 변화, 베인 개수 변화와 회전속도에 따른 진공도의 영향을 평가하였다. 베인 각도 변화는 동일한 체적의 유지로 최대 진공도 값에 큰 영향을 미치지 않았으나, 토출부의 각도 변화는 유동흐름의 간섭을 줄일 수 있고 이것으로 인한 펌프의 손실을 줄일 수 있다. 회전속도가 증가할수록 질량유량은 증가하였으나 고속 회전속도에서 최대 진공도 값을 나타내지는 않았다. 또한 베인의 개수가 증가할수록 질량유량의 변화폭은 감소하였고, 압력강하는 완화됨을 확인하였다.

Direct Measurement of the Gas Entrainment Into a Turbulent Thermal Plasma Jet

An experimental study is conducted to investigate the entrainment characteristics of a turbulent thermal plasma jet issuing from a DC arc plasma torch operating at atmospheric pressure. The mass flow rate of the ambient gas entrained into the turbulent plasma jet is directly measured by use of the so-called “porous-wall chamber” technique. It is shown that a large amount of ambient gas is entrained into the turbulent plasma jet. With the increase of the gas mass flow rate at the plasma jet inlet or the plasma torch exit, the mass flow rate of entrained ambient gas almost linearly increases but its ratio to the jet-inlet mass flow rate decreases. The mass flow rate of the entrained gas increases with the increase of the arc current or jet length. It is also found that using different ways to inject the plasma-forming gas into the plasma torch affects the entrainment rate of the turbulent plasma jet. The entrainment rate expression established previously by Ricou and Spalding (J. Fluid Mech. 11: 21, 1961) for the turbulent isothermal jets has been used to correlate the experimental data of the entrainment rates of the turbulent thermal plasma jet, and the entrainment coefficient in the entrainment rate expression is found to be in range from 0.40 to 0.47 for the turbulent thermal plasma jet under study.

Numerical simulation of gas-contaminated refrigerant two-phase flow through adiabatic capillary tubes

An unfavorable effect of gas impurities on the throttling process inside a small-diameter tube, i.e. a capillary tube, has been studied in detail. A special testing capillary tube equipped with precise temperature and pressure sensors has been used for an experimental investigation of the capillary flow of a saturated fluorocarbon refrigerant, R218, contaminated by dissolved nitrogen. The gas impurities significantly affected the throttling process, since the two-phase flow started notably earlier than in the case of pure refrigerant flow. Moreover, the gas contamination resulted in a decreased mass flow rate of refrigerant delivered through the capillary tube. A comprehensive numerical model has been developed to simulate the capillary flow of gas-contaminated refrigerant. The model takes into account two coincident thermodynamic events: the throttling process of the refrigerant (solvent) and the gradual release of the dissolved gas impurities (solute) from the refrigerant liquid phase. The gas release is in principle described by using the temperature correlation of the Henry’s law constant. The model considers adiabatic, thermodynamically equilibrated capillary flow with homogeneous two-phase flow. The numerical simulation is in good agreement with our experimental data measured for R218 contaminated by nitrogen.

Using Direct Simulation Monte Carlo With Improved Boundary Conditions for Heat and Mass Transfer in Microchannels

Micro-electromechanical systems and nano-electromechanical systems have attracted a great deal of attention in recent years. The flow and heat transfer behaviors of micromachines for separation applications are usually different from that of macro counterparts. In this paper, heat and mass transfer characteristics of rarefied nitrogen gas flows in microchannels are investigated using direct simulation Monte Carlo with improved pressure boundary conditions. The influence of aspect ratio and wall temperature on mass flowrate and wall heat flux in microchannels are studied parametrically. In order to examine the aspect ratio effect on heat and mass transfer behaviors, the wall temperature is set constant at 350 K and the aspect ratio of the microchannel varies from 5 to 20. The results show that as the aspect ratio increases, the velocity of the flow decreases, so does the mass flowrate. In a small aspect ratio channel, the heat transfer occurs throughout the microchannel; as the aspect ratio of the microchannel increases, the region of thermal equilibrium extends. To investigate the effects of wall temperature (Tw) on the mass flowrate and wall heat flux in a microchannel, the temperature of the incoming gas flow (Tin) is set constant at 300 K and the wall temperature varies from 200 K to 800 K while the aspect ratio is remained unchanged. Results show that majority of the wall heat flux stays within the channel entrance region and drops to nearly zero at the halfway in the channel. When Tw<Tin, under the restriction of pressure-driven condition and continuity of pressure, the molecular number density of the flow decreases along the flow direction after a short increase at the entrance region. When Tw>Tin, the molecular number density of the flow drops rapidly near the inlet and the temperature of the gas flow increases along the channel. As Tw increases, the flow becomes more rarefied, the mass flowrate decreases, and the resistance at the entrance region increases. Furthermore, when Tw>Tin, a sudden jump of heat transfer flux and temperature are observed at the exit region of the channel.

CO2 가스쿨러용 콤팩트열교환기 개발에 관한 연구(1) -다중관식 헬리컬 코일형 가스냉각기내 CO2의 열유량과 압력강하-

The heat flowrate and pressure drop of in a multi-tube-in-tube helical coil type gas cooler were investigated experimentally. The mass flowrate of and coolant were varied from 0.06 to 0.075 [kg/s], respectively and the cooling pressure of gas cooler were from 8 to 10 [MPa]. The heat flowrate of in the test section is increased with the increase in mass flowrate of coolant, the cooling pressure and mass flowrate of . The pressure drop of is decreased with the decrease in mass flowrate of coolant and , but decreased with increase in cooling pressure of . The heat flowrate of in the multi-tube-in-tube helical coil type gas cooler is greatly higher than that of in the double pipe type gas cooler, while the pressure drop of in the multi-tube-in-tube helical coil type gas cooler is greatly lower than that of in the double pipe type gas cooler. Therefore, in case of the application of at the multi-tube-in-tube helical coil type gas cooler, it is expected to carry out the high-efficiency, high-performance and compactness of gas cooler.

핀틀 형상이 추력 크기에 미치는 영향에 대한 수치해석적 연구

본 논문에서는 Fluent의 Spalart-Allmaras 난류모델을 적용하여 연소실 내부에 설치된 핀틀 형상이 핀틀 추진기관 추력 크기에 미치는 영향을 수치해석으로 분석하였다. 핀틀이 존재하면 노즐목을 지나는 질량 유량율은 이론적으로 예측된 값 보다 항상 작았으며, 핀틀 직경이 커질수록 노즐목에서 경계층 두께가 차지하는 비율이 증가되어 노즐목의 질량 유량율이 더욱 감소하였다. 핀틀 직경이 커질수록 핀틀 팁에 나타나는 재순환 영역의 압력에 의한 추력은 증가하지만 노즐 및 연소실 압력에 의한 추력은 감소하여 총 추력은 핀틀 직경이 작은 것 보다 감소하였다. 핀틀 추진기관의 비추력은 큰 차이가 없었다. The effect of pintle shape on the thrust level of pintle-nozzle Solid Rocket Motor(PNSRM) was studied numerically using the Spalart-Allmaras turbulent model of Fluent. Mass flow rate of PNSRM was always less than theoretical value and the extent of decrease in mass flow rate grew in the large pintle because of increase in the relative boundary layer thickness between pintle body and nozzle wall. The bigger pintle size was, the more thrust of pintle tip pressure was obtained. Meanwhile the more thrust of nozzle and chamber pressure decreased. Hence, total thrust of big pintle was less than a small pintle under same throat area condition. Specific impulse was relatively flat for all pintle shape.