Average Mass Flow Research Articles

Experimental investigation of droplet entrainment and deposition in horizontal stratified wavy flow

An experimental study of the local droplet parameters for an atmospheric horizontal stratified wavy flow was conducted in a horizontal circular pipe with an inner diameter of 40 mm and a length of 5.5 m. The local distributions of the droplet fraction, droplet velocity, droplet diameter, and droplet mass flux in the cross section of the pipe were measured using single optical fiber probes at four locations with length-to-diameter ratios of 17.5, 55.0, 80.0, and 105.0 from the inlet of the test section. The average droplet mass flow rate along the axial direction of the flow channel was also obtained from the droplet parameters. The combination of the droplet entrainment and deposition rate models of Schimpf et al. was evaluated for droplet mass flow rates obtained from five different experiments including the present experiment in the horizontal stratified flow. However, its prediction accuracy was not good for the present and REGARD data. Finally, new droplet entrainment and deposition rate models for the horizontal stratified flow were proposed based on those five experiments. The applicable ranges of the proposed models are 65,500–571,400 and 170–11,000 for the gas (Reg) and liquid (Rel) Reynolds numbers, respectively.

Experimental and numerical investigation of lubrication system for reciprocating compressor

Sufficient lubrication of the moving parts in a variable capacity inverter compressor is vital since it can directly affect the performance and expected lifetime. In this study, the lubrication system of a compact inverter compressor (CIC) is numerically and experimentally investigated. In the numerical modeling, a finite volume-based algorithm is used to model two-phase (air–oil) flow inside the compressor using Volume of Fluid Method (VoF) method. Transient behavior of the oil flow under laminar flow conditions is both simulated by imposing Sliding Mesh (SM) and the Moving Reference Frame (MRF) methods at various crankshaft speeds varying between 1200 and 4500 rpm. The measurements are taken using an experimental setup to compare/validate CFD results obtained from SM and MRF methods. Flow visualizations are performed with a high-speed camera to determine the oil climbing and required time for sufficient lubrication precisely. Moreover, the acceleration of the crankshaft is determined via high-speed camera and employed as a user-defined function to model the start-up period of the compressor. It is shown that with increasing crankshaft speeds, the average oil mass flow rate released from the upper part of the crankshaft is increasing almost linearly. It is also shown numerically that with increasing oil viscosity, the mass flow rate decreases. The comparison of experimental and CFD results reveals that the MRF solutions are in a better agreement with the measurements up to 2800 rpm. The SM method became favorable as a CFD method due to better agreement with measurements between 3000 and 4500 rpm.

Optimization of Suction Chamber Structure in a Scroll Refrigeration Compressor

In order to improve the suction performance of the scroll compressors, five modification models are proposed by reducing or enlarging the area of the suction flow passage based on a scroll refrigeration compressor. The three-dimensional numerical simulation model is established using the commercial software PumpLinx to calculate the flow field and the performance of every modified model. The comparison and analyses has been done based on the simulation results. The results indicated that the enlargement of the suction passage only improve the volumetric efficiency a little while the shrink of the suction passage can improve it effectively. The mass flow rate pulsation when the modification angle is 270° is much higher than that of the original model, but it decreases with the modification angle. As the modification angle increases, the volume of inner suction passage and the back flow rate from the inner suction passage decrease and less fluid from suction chamber 2 flows back to the suction port, so the average mass flow rate increases and the mass flow rate pulsation decreases. The Model 5 has the maximum volumetric efficiency and lower mass flow pulsation, but the tangential and radial forces on the orbiting scroll are the highest.

Linear stability of horizontal throughflow in a Brinkman porous medium with mixed thermal boundary conditions

The onset of convective instability in a horizontal throughflow due to external heating and viscous dissipation is investigated. The flow is considered along a porous layer with high permeability, bounded by two impermeable surfaces subjected to external heating. Hence, the third kind of thermal boundary conditions are used at the two boundaries. The Brinkman extended Darcy's law is adopted for the equations governing flow through the layer. The base flow is assumed to be inclined to the horizontal axis at an angle γ. An average mass flow along the horizontal direction is considered, the magnitude of which is given by Pe (Péclet number). The disturbances in the flow are assumed in the form of two-dimensional oblique rolls inclined to the base flow at an angle γ(0≤γ≤π2). The four limiting cases with different combinations of B0,B1→0,∞, are also discussed. The effect of viscous dissipation and external heating at the two boundaries, on the instability of the flow is discussed. The instability remains unaffected by the direction of the throughflow. However, the instability is affected by the magnitude of the throughflow. Viscous dissipation has a stabilizing effect on the flow, as long as the external heating at the bottom boundary is higher than that at the upper boundary. The longitudinal rolls (at γ=π2) are the preferred mode of instabilities.

Air Flow and Camshaft Stress Analysis of Variable Valve Lift Gas Engine

The use of variable valve lift technology on diesel gas engine has been able to increase power without having to change the dimensions of the engine. However, in-depth analysis of how the flows that occur when air enters and stress that occurs in camshaft of the gas engine needs to be studied more deeply. Simulation Analysis incoming airflow and stress on the gas engine camshaft variable valve lift types expected to describe the effect of the use of valve lift on the gas engine. In this simulation experiments using Computational Fluid Dynamics (CFD) approach and structural stress with variable valve opening on the condition of default by 11.1 mm, openings increased by 16.65 mm or 1.5 times, 2 times by 22.205 mm, and 2.5 times by 27.7 mm. Where the results of the simulation showed that the condition of the valve from 11.1 mm to 22.205 mm increased the average air velocity and mass flow rate, while at the opening valve 27.7 mm decreased average speed. The resulting stress value of the valve 11.1 mm to 27.7 mm continues to increase due to the force created in the spring getting into the valve then increasing the force on the spring.

The effect of jet pulsation on the flow field of a round impinging jet and the radially expanding wall jet

A pulsating round jet having a constant average mass flow rate may increase heat transfer in comparison to a steady jet impinging on a surface. However, while several studies have focused on the heat transfer, flow field characteristics remain poorly understood. Here, the mean and turbulent flow characteristics of a pulsating, round jet impinging on a flat plate were measured using planar, phase-locked particle image velocimetry (PIV) and compared to those of a steady jet. The surface to jet nozzle stand-off distance equaled two nozzle diameters and Reynolds numbers based on the average steady jet exit velocity were Re = 4606, 8024 and 13,513. Jet exit velocities varied nearly sinusoidal and Strouhal numbers ranged between 2×10-3≤Sr≤15.6×10-3. The results indicate that jet pulsation did not affect the normalized, phase-averaged radial and axial velocity distributions in the impingement region and these could be predicted based on a quasi-steady assumption. However, at the center of the jet, rms values of radial and axial velocity fluctuations were enhanced at pulsation phases for which the jet exit velocity was lowest. In contrast, profiles of radial and axial velocity fluctuations and the Reynolds shear stress in the wall jet were significantly affected by jet pulsation. For the here investigated range of parameters, our results indicate that outer layer self-similarity in the wall jet is not attained when the jet is pulsating, and the wall jet cannot be treated as quasi-steady.

Impact of dissolved salts on two-phase flow and boiling heat transfer in a natural circulation loop

Two-phase natural circulation and boiling experiments are conducted in this study with artificial seawater as a heat transfer fluid or process coolant. This experimental work is focused on understanding the role of dissolved salts in water on the steady state two-phase natural circulation flow rates. Mass flow rates were measured at different heat flux levels with artificial seawater, deionized water and tap water in the experimental loop. It was found that the average quasi-steady state mass flow rates were the same at any particular heat flux level regardless of the fluid being used. Artificial seawater coolant exhibited more stable natural circulation at higher heat flux as compared to the other two coolants. Mass flow measurements recorded at 2 s intervals show that magnitude of flow oscillations are much higher in case of tap water and deionized water. Also, high speed camera images revealed that the bubble departure diameters are smaller in seawater compared to tap or deionized water. This can be attributed to the increased local wettability due to the presence of dissolved salts in the fluid. Visual observations of the riser section showed that bubble coalescence and formation of slugs is inhibited in the seawater. These observations also explain the reduced pressure drop across test section when seawater was used as a coolant.

Investigations of powder flow patterns in hopper model through discrete element method

In this paper, a comparative study was conducted to observe the flow patterns of bulk powder materials through a conical shaped hopper. Hoppers were designed based on Jenike charts and further analyzed using discrete element method. The paper focuses on the flow of micro-sized powder materials and how their area flow pattern changes along with velocity distribution variation with a change in hopper angle. Discrete element method was used to predict the flow patterns for different hopper angles and to study the transition of flow from funnel flow to mass flow. A comparison was made among these hoppers based on their average velocity and average mass flow rate to have an optimum design for mass flow. It was observed that a decrease in hopper angle resulted in an increase in both the mass flow rate and average velocity.

Flow Mixing Optimisation inside a Manifold using Computational Fluid Dynamics

This paper presents an analysis of fluid flow in a typical manifold. A commerciallyavailable Computational Fluid Dynamics (CFD) package has been used to analyze the flow pattern inside the manifold. Temperatureand velocity in whole fluid domain and mass flow rate in all the outlets in the manifold have been computed. Based on the preliminary results, a simple modification to inside of the main pipe of the manifold has been incorporated. The performance of the modified design has been compared with the original design from the point of view of average temperature and mass flow rate at the outlets. This simple modification has been shown to improve the uniformity of temperature and mass flow at the outlets, thus enhancing the efficiency of the mixing manifold.

Ventilation potential of an absorber-partitioned air channel solar chimney for diurnal use under Mexican climate conditions

This research presents a thermal evaluation of an absorber-partitioned air channel solar chimney (SC-AP) to determine its feasibility as a building ventilation system in a warm-humid weather. Hourly climatic data from the coldest and the warmest days of each month of 2014 were used to assess the behavior of the SC-AP in Mérida, México. A numerical code based on the Finite Volume Method was developed to evaluate the ventilation potential of the SC-AP. The results indicate that the average mass flow rate of the coldest day is greater than the one corresponding to the warmest day in most of the months; therefore, even under the worst conditions of the year, the SC-AP extracted an average mass flow rate of 0.0832 kg/s. In addition, when the SC-AP is attached to a building, it is able to generate between 7.9 and 11.4 ACH for a residential bedroom of 27 m3 and more than 3.5 ACH for a classroom of 54 m3 during the hours with solar irradiance along the year, those values comply with the requirements recommended by ASHRAE.

LES of primary breakup of pulsed liquid jet in supersonic crossflow

The injection of a pulsed liquid jet into supersonic air flow is a promising approach to improving the fuel atomization performance in a Scramjet engine. Therefore, the primary breakup of a pulsed liquid jet in supersonic crossflow is numerically investigated in the present paper. A two-phase flow Large Eddy Simulation (LES) algorithm is developed for simulations of liquid jet atomization in supersonic gas flow. A coupled Level Set and Volume of Fluid (VOF) method is used to track the interface deformation and disintegration. The supersonic gas flow is solved using a compressible flow solver while the liquid phase is solved by an incompressible flow solver. Appropriate boundary conditions are specified at the interface for both solvers to correctly capture the interaction between the gas and liquid phases. The primary atomization of a steady liquid jet with the same average mass flow rate as the pulsed jet is also simulated as a benchmark test case. The liquid velocity pulsation produces a very different primary atomization morphology in comparison with the steady liquid jet, which significantly enhances the primary breakup process. It is observed that Rayleigh-Taylor instability dominates the development of surface waves for the steady liquid jet. For the pulsed liquid jet, the liquid column deformation induced by the liquid velocity pulsation determines the wavelength of the surface waves and thus the liquid jet breakup location. In comparison with the steady liquid jet, the penetration of the pulsed liquid jet increases by 20%, and the width of the wake zone expands by 25%, resulting in improved atomization and mixing performance.

Reciprocating liquid‐assisted system for electronic cooling applications

AbstractIncreasing the power density and heat dissipation in electronic equipment and their need for an efficient thermal management system have made the liquid cooling techniques inevitable in recent years. In most applications, liquid cooling systems work in conjunction with more traditional cooling methods, such as conduction and convection heat transfer, using air cooling systems. In this study, the performance of Reciprocating Mechanism‐Driven Heat Loop (RMDHL) for electronic and power electronic cooling applications has been studied and compared with that of a conventional Dynamic Pump‐Driven Heat Loop (DPDHL). A numerical model using moving boundaries in Ansys Fluent commercial code has been developed to generate the reciprocating motion of working fluid with desired frequency and amplitude. The temperature distribution contours and Nusselt numbers show the superior performance of the RMDHL system in terms of heat transfer and temperature uniformity of the heated surface. The results show that, for the same average mass flow rate in the cooling loops the average surface temperature in the RMDHL loop is considerably lower than that of DPDHL especially at higher reciprocating frequency. The results also indicate that similar to the effect of the oscillatory frequency, increasing the amplitude also increases the heat transfer rate in the RMDHL loop. In addition, the Nusselt number shows a linear increment with the increase of both oscillatory amplitude and frequency. Uniform temperature distribution and efficiency of thermal management systems based on RMDHL loop could decrease the resultant thermal stress in electronic devices and increase the reliability of them.

Investigation on optimization of the thermal performance for compressible laminar natural convection flow in open-ended vertical channel

The present paper focuses on the optimization of the thermal performance for compressible laminar natural convection flow induced under high-temperature difference in an open-ended vertical channel by optimizing the channel inter-plate spacing using numerical simulation. The present investigation is conducted for a wide range of Rayleigh number (Ra) 104 to 107 in channel heated asymmetrically by uniform surface temperature with air (Pr0.72) as working fluid. Several values of channel gap between plates, new modified preconditioned all-speed Roe scheme along with dual time stepping technique and modified Local One-dimensional Inviscid (LODI) relations as channel inlet and outlet boundary conditions suitable for compressible laminar natural convection is employed for the current simulation. Heat transfer rate in terms of average Nusselt number is obtained for all Rayleigh number and channel aspect ratio is obtained. Variation of thermal and velocity profiles, the variation of average Nusselt number and mass flow rate into the channel for the combination of each Rayleigh number and channel aspect ratio is reported. From the results obtained, a correlation for optimum aspect ratio with Rayleigh number which maximizes the heat transfer within the channel is presented.

Modeling a dry running twin-screw expander using a coupled thermal-fluid solver with automatic mesh generation

Understanding the details of the internal flow processes in screw compressors and expanders is very important for their efficient and robust design. Computational fluid dynamics (CFD) provides full access to a modeled three dimensional flow field and its variation in time. However, the application of CFD to screw compressors and expanders can be difficult because of the complicated geometries involved and the need to supply the computational grid on which the modeled equations are solved over a large number of time steps. While the majority of previous research on CFD applications to screw machines features inventive techniques for generating meshes that adequately resolve the flows in the small clearances, an alternate approach is demonstrated in this work. The screw expander SE 51.2 from TU Dortmund University is analyzed here through a CFD model which generates the grid automatically based on a modified Cartesian cut-cell approach. The grid is then adaptively refined based on local gradients of velocity and temperature. At each time step, the grid is regenerated based on the geometry motion. As opposed to resolving the flow in the clearances, a model is applied so that the cells in the clearance can remain relatively large. The detailed measurements of the screw expander are used to validate the model. The operating conditions investigated include the expansion of dry air at a four-to-one pressure ratio for four different rotational speeds. The measured internal chamber pressures are compared to the results from the model, as are the average mass flow rate, indicated power, and outlet temperature. A coupled thermal-fluid approach is used to model the rotor temperatures and corresponding thermal deformation of the rotors and housing. In this approach, the fluid and solid temperatures are solved together; to deal with the problem of the disparate time scales between the fluid and solid heat transfer, the solids are periodically solved to steady state using heat transfer coefficients and near-wall temperatures computed from an energy conserving averaging over several cycles. The effects of the various leakage flow paths in the model, including the rotor-to-rotor, rotor-tip-to-housing, and bearing leakage are demonstrated and quantified. Finally, simulation and experimental results are compared in terms of different rotor-tip-to-housing clearance heights. The model considering the appropriate thermal deformation of the rotors is shown to yield the best agreement with the measurements, however there is work remaining to reduce the model calculation time, especially at low rotational speeds.

Dynamic vacuum pressure tracking control with high-speed on-off valves

A vacuum pressure tracking system with high-speed on-off valves is a discontinuous system due to the discrete nature of high-speed on-off valves. Chamber pressure changes in the system are determined by the mass flow rates during the processes of charging and discharging. Here, a sliding mode controller with an asymmetric compensator based on average mass flow rate is designed for accurate vacuum pressure tracking. The controller output signal is converted into the duty cycles of the high-speed on-off valves via a pulse width modulation pulsing scheme. Owing to the extreme asymmetry of the processes, an asymmetric structure comprising one high-speed on-off valve in the charging unit and three high-speed on-off valves in the discharging unit is applied to weaken the impact of asymmetry. In addition, an asymmetric compensator is also designed to modify the pulse width modulation pulsing scheme to further eliminate the asymmetry. Experimental results indicate that the proposed controller achieves better performance in pressure tracking with the asymmetric compensator overcoming process asymmetry and enhancing system robustness.

Experimental research on the heating performance of a single cylinder refrigerant injection rotary compressor heat pump with flash tank

A single cylinder rotary compressor was applied in the refrigerant injection air-source heat pump to improve the heating performance in cold regions. In this study, the performance of an R410A single cylinder rotary compressor vapor injection (SCRCVI) system was measured and analyzed by varying the compressor frequency f and injection pressure Pinj at the ambient temperature Tod=–10°C.The experimental results indicated that an optimum injection pressure to gain the maximum COPh (coefficient of performance) existed in the SCRCVI cycle. However, the maximum COPh of the SCRCVI system decreased as the increase of the frequency, and the maximum COPh was even lower than that of the CSVC system at high compressor frequency. Therefore, in view of the energy saving and emission reduction, the SCRCVI system should be switched to single stage compression system when the heating capacity demand could be satisfied at high compressor frequency f. Compared to the conventional single-stage vapor compression (CSVC) system, refrigerant injection could enhance the heating capacities and COPh by 28.2% and 7.91%, respectively. The average total mass flow rate of the SCRCVI system was 24.68% higher than that of the CSVC system. As the SCRCVI system worked at the optimum injection pressure, the variation trends of the different system parameters were investigated in detail. These trends were reliably used to optimize the refrigerant injection system design and the control strategy. The parameter of (Pinj–Ps) could be adopted as the signals to control the opening of the upper stage electronic expansion valve EEV1.

Combustion Characteristics of Ramjet Fuel Grains with Boron and Aluminum Additives

An experimental investigation of the effect of boron (B) and aluminum (Al) additives to fuel-rich propellant for a solid fuel ramjet application was performed. In this research, depending on the composition of metal particles, three types of fuel grains with 15 wt % ammonium perchlorate particles were prepared and tested. To provide a short ignition delay, an ignition support material consisting of and a composite propellant were coated on the fuel grain. For the test, an oxidant gas having a controlled temperature and pressure and an oxygen composition close to that of the air in a ramjet combustor was supplied using an ethanol-blended hydrogen peroxide () gas generator. Air simulant gas was supplied with an average mass flow rate near and a Mach number of 0.21 in the fuel grain port. Through the test, the noticeable effect of B particles on combustion was confirmed by a high regression rate over and combustion efficiency over 80%. Al particles were not effective additives individually; however, Al particles contributed to the ignition of B. In addition, metal oxide particle deposits on the nozzle confirmed the existence of a two-phase flow.

Experimental investigation of solar chimney with phase change material (PCM)

Abstract The effect of latent heat storage (LHS) on a solar chimney pilot was studied experimentally. Two kinds of experiments including with and without phase change material (PCM) were carried out, and the parameters including temperature and velocity were measured to investigate the solar chimney (SC) performance. Paraffin wax was used as a PCM in the constructed SC with 3 m chimney height and 3 m collector diameter in the campus of University of Tehran. The results show that the maximum absorber surface temperature for the SC with PCM and the conventional solar chimney (CSC) are 72 °C and 69 °C, respectively. Also, the maximum air velocity for the CSC is 1.9 m/s, while it is 2 m/s for the system equipped with PCM thermal storage. So, the LHS system causes increasing the average mass flow rate of the pilot around 8.33%. As a result, using LHS system in SC leads to improve the solar chimney performance.

Simulation Analysis on Water’s Micro Seepage Laws under Different Pressure Gradients Using Computed Tomography Method

The aim of this paper was to develop a model that can characterize the actual micropore structures in coal and gain an in‐depth insight into water’s seepage rules in coal pores under different pressure gradients from a microscopic perspective. To achieve this goal, long‐flame coals were first scanned by an X‐ray 3D microscope; then, through a representative elementary volume (REV) analysis, the optimal side length was determined to be 60 μm; subsequently, by using Avizo software, the coal’s micropore structures were acquired. Considering that the porosity varies in the same coal sample, this study selected four regions in the sample for an in‐depth analysis. Moreover, numerical simulations on water’s seepage behaviors in coal under 30 different pressure gradients were performed. The results show that (1) the variation of the simulated seepage velocity and pressure gradient accorded with Forchheimer’s high‐velocity nonlinear seepage rules; (2) the permeability did not necessarily increase with the increase of the effective porosity; (3) in the same model, under different pressure gradients, the average seepage pressure decreased gradually, while the average seepage velocity and average mass flow varied greatly with the increase of the seepage length; and (4) under the same pressure gradient, the increase of the average mass flow from the inlet to the outlet became more significant under a higher inlet pressure.

Effect of Injection Pressure, Injection Duration, and Injection Frequency on Direct Injector’s Mass Flow Rate for Compressed Natural Gas Fuel

A conventional gasoline direct injector is converted for gaseous fuel application. The conversion alters the injector characteristic which further affect the mixture formation and combustion processes. The purpose of this study is to investigate the effects of injection pressure (case 1), injection duration (case 2), and injection frequency (case 3) on the injector’s mass flow rate. An injector was independently tested by using an injector test bench. In Case 1, the injection pressure was tested from 20 bar to 60 bar at 24 ms of injection duration for 1000 injection counts. In Case 2, the injection duration was set from 2 to 24 ms at a constant 50 bar injection pressure for different engine speed. Whereas in Case 3, the averaged mass flow rate are plotted at different injection frequency. Theoretical calculations were carried out to compare the experimental and theoretical result. The experiment results shown that the injection pressure affected the injector mass flow rate linearly. At short injection duration, the mass flow rate inconsistent and highly fluctuated. At higher injection frequency, the mass flow rate is becoming higher. The theoretical results able to predict the mass flow rate trend but were unable to spot the fluctuating effects.