Supply Orifice Research Articles

Numerical evaluation and optimization of air distribution system in a small vertical farm with lateral air supply

An appropriate design for air distribution systems is crucial for achieving optimal and uniform growth conditions while reducing energy costs in vertical farms. This study employs steady computational fluid dynamics (CFD) simulations to investigate the influence of several key design parameters of air distribution systems in a small generic vertical farm with a lateral air supply. The simulation results reveal that an air supply orifice of reduced dimensions, positioned proximally to the LED lamps, coupled with an exhaust mechanism integrated into the corridor ceiling, proves most effective in removing the excess heat generated by the LED lamps. Moreover, enhanced uniformity in air distribution is attained by positioning the air supply closer to the LED lamps, utilizing larger orifices, and eliminating the corridor space. In contrast, the vertical distance between the lateral air exhaust orifices and the cultivated regions is found to have a negligible effect.

Feasibility Analysis of Adopting the Hydrogen Hydrostatic Thrust Bearing

The hydrogen hydrostatic thrust bearing (HHTB) is a key component of hydrogen liquefaction that impacts turbo-expander characteristics. To analyze the feasibility of using the HHTB in this application, characteristics of HHTBs were calculated using a CFD model. To upgrade the performance of the HHTB, the impacts of bearing structure and operating parameters on static performance were investigated. Dynamic characteristics of the HHTB were studied using the dynamic grid method. It was found that the load capacity of the HHTB is less than that of helium-lubricated bearings but higher than that of air- and methane-lubricated bearings. The turbulent kinetic energy of hydrogen is higher than that of other gases. Load capacity can be enhanced through boosting supplied pressure, expanding the diameter of supply orifices, reducing gas film clearance, increasing the orifices quantity and setting a circumferential groove. A reduction in disturbance amplitude slightly increased the bearing’s dynamic stiffness. The dynamic stability of the HHTB was improved by a small film clearance in response to disturbance.

Dynamic two-phase flow behaviors in permeable network integrated with microchannel

• Permeable network integrated with microchannel is developed. • Two-phase flow characteristics in such a structure are visually studied. • Liquid saturation increases with increasing gas flow rate. • Position for bubble generation increases with increasing gas flow rate. • Two-phase flow exhibits strong periodicity at low gas flow rates. The performance of a direct methanol fuel cell greatly depends on the two-phase flow behaviors in the anode gas diffusion layer and flow channel. However, complex and opaque nature of gas diffusion layer poses a grand challenge for deep insight into the two-phase flow behaviors. Therefore, a homogeneous permeable network integrated with a microchannel was put forward to simulate the anode gas diffusion layer and microchannel in the present study, by which the dynamic two-phase flow behaviors were visually studied with the help of adaptive image enhancement method. The influence of the position and number of the gas inlet, and the gas and liquid flow rates on the two-phase flow behavior were analyzed. The results showed that the liquid saturation decreased and the number of the position for bubble generation increased with increasing the gas flow rate in case the gas was suppled from only one gas supply orifice. When two gas supply orifices simultaneously supplied the gas, the liquid saturation was between the cases using a single one gas supply orifice. For given liquid and gas flow rates of 0.1 mL/min and 0.5 mL/min, the liquid saturation was about 84%, which was between 83% and 92% for the single-one cases. Besides, the two-phase flow exhibited strong periodicity at low gas flow rates. The obtained results provide a deep understanding of the two-phase flow behaviors in such a simulated structure, helping better design and operation of direct methanol fuel cells.

Study on Static Characteristics of Annular Array Microporous Aerostatic Bearing

In this paper, an aerostatic bearing model in the form of microorifice annular array is designed to explore the static performance of aerostatic bearing when the orifice diameter and working air film thickness are of the same order of magnitude. Firstly, the simulation model of the new bearing is established, the pressure distribution of the bearing gas film under the influence of the orifice diameter is analyzed by the CFD method, and the performance of the aerostatic bearing is compared with the traditional toroidal throttling method with the orifice diameter of 0.1 mm; at the same time, the effects of air supply pressure, orifice diameter, and orifice number on the static performance of the bearing under different air film thickness are analyzed; finally, a new bearing is developed, and the simulation results are verified by the experimental test. The results show that when the orifice diameter and the air film thickness are of the same order of magnitude, the maximum stiffness of the aerostatic bearing is significantly improved and the microporous throttled aerostatic bearing is more suitable for the field of high stiffness. The greater the air supply pressure, the greater the bearing capacity and stiffness of the bearing. The number of orifices has an effect on improving the bearing capacity of the bearing, but when the number of orifices is large, the effect will become less obvious. This study can provide a new theoretical reference for the design of aerostatic bearing.

Measurements Versus Predictions for a Hybrid (Hydrostatic Plus Hydrodynamic) Thrust Bearing for a Range of Orifice Diameters

A fixed-geometry hybrid thrust bearing is investigated with three different supply orifice diameters, (1.63, 1.80, and 1.93 mm). The test rig uses a face-to-face thrust-bearing design, with the test bearing acting as the rotor loading mechanism. A hydraulic shaker applies the static axial load, which is reacted by a second (slave) thrust bearing. The rotor is supported radially by two water-lubricated fluid-film journal bearings and is attached to a 30.6 krpm motor via a high-speed coupling with very low axial stiffness. Thrust bearings are tested for a range of supply pressures (5.17, 10.34, and 17.34 bars), fluid film thicknesses, and speeds (7.5, 12.5, and 17.5 krpm). The water-lubricated test bearings have eight pockets, with feed orifices located centrally in each pocket. Experimental results are compared to predictions from a bulk-flow model, showing generally good agreement. Thrust-bearing inlet supply and inner radius flow rates all decreased with decreasing orifice diameters and bearing axial clearances. In most cases, the bearings with larger orifice diameters exhibit higher recess pressure ratios, operating clearances, and flow rates. An optimum hybrid thrust-bearing orifice diameter will depend on the conditions of individual applications. Larger orifices generally provide larger operating clearances and higher stiffnesses, but also require higher flow rates. For most applications, a compromise of bearing performance parameters will be desired. The test results and comparisons presented will aid in sizing orifice diameters for future hybrid thrust-bearing designs and in validating and improving models and predictions.

A semianalytical method for studying the performances of aerostatic thrust bearing

The solution of Reynolds equation and computational fluid dynamics are widely employed for the lubrication performance analysis of aerostatic thrust bearing. However, the solution of Reynolds equation may be inaccurate and cannot present detailed performance near orifice, while computational fluid dynamics method has low computational efficiency with time consumption in mesh generation and solving Navier–Stokes equations. In order to overcome the drawbacks of Reynolds equation and computational fluid dynamics, based on the method of separation of variables, a semianalytical method is developed for describing the characteristics of aerostatic bearings available. The method of separation of variables considering the initial and viscous effect is more accurate than the Reynolds equation and can present detailed performance near orifice in the aerostatic thrust bearings, while method of separation of variables has great computational efficiency compared to computational fluid dynamics. Meanwhile, the pressure distribution calculated by method of separation of variables is compared to the published experimental data and the results obtained by computational fluid dynamics. The comparative results indicate validity of the method. Furthermore, the influences of flow and geometry parameters, such as supply pressure, orifice diameter, film thickness, and bearing radius, on the characteristics of aerostatic thrust bearings with single orifice are studied. The results show that there exists pressure depression phenomenon near orifice. The depression phenomenon is strengthened with increase of film thickness and supply pressure and decrease of orifice diameter and bearing radius, while the maximum speed increases with strengthening of pressure depression due to decrease of minimum local pressure near orifice. Moreover, the bearing capacity increases with increase of supply pressure, orifice diameter, and bearing radius and decreases with increase of film thickness, while mass flow rate increases with supply pressure, orifice diameter, and film thickness and it is not sensitive to bearing radius.

Optimized design of the flow network in the lubrication system for the heavy vehicle transmission

An accurate simulation model of the lubrication system is essential for early design of the heavy truck transmission. In this article, a detailed computational method for the flow network analysis of the lubrication circuit is developed based on the hydraulic theory, and the flow resistance through the oil pipes and orifices is also taken into consideration. Then, the Next Limit Technologies’ XFlow, a potential new three-dimensional computational fluid dynamics software based on lattice Boltzmann method, is adopted to obtain the relationship between the oil delivery and the lubrication effect in the low-pressure capillary lubrication network of the rear auxiliary gearbox. To achieve the best overall lubricating performance of the flow network, the optimized design of the diameter for each oil supply orifice is determined by a detailed sensitivity analysis on the contribution of each parameter to the volumetric flow rate. The bench tests for the volumetric flow rate have been performed for validating the computation model by comparing the predicted volumetric flow rate through each oil supply bore with the experimental data at various pump speeds. The endurance tests have further conducted and the test results indicate a remarkable reduction in mechanical weariness when the best solution of the flow network design for the transmission lubrication system is adopted.

Airflow characteristics generated by fabric air dispersion ventilation

The air distribution characteristics of a fabric air dispersion system (FADS) were investigated experimentally in a full-scale chamber. The jet supply velocity and outlet orientation were selected as the major factors that affect the FADS airflow field. The FADS airflow structure was described and verified in a visualization experiment and compared with the air patterns of the traditional rectangular, circular nozzle and linear slot diffusers. The induction and flow junction phenomena were analysed under different combinations of outlet orientations. Experimental results showed that this induction phenomenon can create more airflow patterns and that the FADS can meet different requirements in practical engineering. The turbulence intensity of the air supply orifices, the maximum velocity decay, and the self-similarity of the velocity profiles were examined through velocity field measurements. Our research illustrated the advantages of two-dimensional flow characteristics of the FADS model that can be treated as a plane free jet in the developed region. The phenomenon we studied should provide useful guide for the application of the FADS to heating, ventilation, and air-conditioning systems.

Discharge Coefficients in Aerostatic Bearings With Inherent Orifice-Type Restrictors

In aerostatic bearing analysis, determining film pressure by solving the Reynolds equation in a numerical model is more effective than conducting bearing experiments or performing computational fluid dynamics (CFD) simulations. However, the discharge coefficient of an orifice-type restrictor is generally a given number that dominates model accuracy. This study investigated the influence of geometry and flow parameters on this discharge coefficient. The results indicate that this discharge coefficient is sensitive to the orifice diameter and film thickness and that the effects of the supply pressure, bearing radius, supply orifice length, supply passage diameter, conicity depth, and conicity angle can be disregarded. This study also built a surrogate model of this discharge coefficient based on the orifice diameter and film thickness by using artificial neural networks (ANNs).

Resistance Coefficient Research of the Train Air Supply Orifice

High-speed train air-conditioning systems put forward higher request on the aspect of air uniformity and comfort. The use of orifice which can form a more uniform velocity and temperature field in the car can be widely applied to high-speed train air-conditioning system. The experimental study of the influence of several different factors (such as the opening rate, aperture, orifice plate thickness, etc.) in the research may provide a reference for the design choices of the orifice type.

Influence of Diameter and Number of Orifice on Static Characteristics of Radial-Thrust Aerostatic Bearing

The working performance of the spindle system is the most important factor to embody the overall performance of the machine tool. To ensure the advanced capabilities, besides the high-precision manufacturing technologies, it is mainly depending on the bearing module and the forces on the spindle. In this paper, a new strategy of the vertical spindle supporting system is presented to meet the high stiffness requirement for the aerostatic bearing. Based on the computational fluid dynamics and finite volume method, a fluid dynamic model and structure model of the large diameter incorporate radial-thrust aerostatic bearing is developed and simulated to find out the pressure distribution laws of the spindle supporting system. The grid subdivision in the direction of film thickness is paid more attentions when establishing the grid of the whole gas film. Simulation results show that this special structure of bearing module can supply enough load capacity and stiffness for the machine tool. The results also indicate that the static characteristics of the bearing are improved as the supply pressure increases and as the supply orifice diameter decreases.

Comparison between grooved and plane aerostatic thrust bearings: static performance

The demand of air bearings is increasing for those applications that require precision linear movements or high-speed rotations. In particular in this paper air pads for air motion technology are studied. The paper analyses the effect of a circumferential groove machined on the pad surface on pressure distribution, air flow consumption and stiffness. Two geometries are investigated and compared: one with three supply orifices and the other with a circumferential groove as well. The static characteristics of the pads are experimentally determined with also the pressure distributions under the pads along the radial and circumferential directions. The experimental pressure distributions are compared with the simulated ones, obtained with a numerical program at the purpose developed. The numerical model considers a general formulation of the supply holes discharge coefficient that can be used also in presence of a circumferential groove.

Influences of operational conditions and geometric parameters on the stiffness of aerostatic journal bearings

Abstract The stiffness of various geometric designs of aerostatic journal bearings for high-speed spindles was investigated under different operating conditions. First, the stiffness of the front and rear journal bearings was evaluated experimentally using the relationship of force and displacement at different supply pressures (6–9 bar). A numerical model was then developed to simulate journal-bearing stiffness under the same pressure range to validate the results. The model was extended to calculate the stiffness of the designs with various geometric parameters, including bearing length/diameter (L/D) ratios of 0.5, 1.0, and 1.5; different types of restrictor designs (e.g., pocketed orifice versus inherent orifice); supply orifice diameter; radius gap; supply pressures of 6, 7, 8, and 9 bar. These parameters are believed to be crucial to the performance of gas bearings. It was found that gas-bearing geometries had a significant effect on stiffness. The results also provide helpful design guidelines for gas-bearing spindles in high-precision machine applications.

Static Behaviour of Air Plane Pads: Comparison between Different Feeding Solutions

Air bearings are used among the others to support and guide coordinate measuring machines and instruments. There are different feeding solutions adopted to obtain the required stiffness and damping, often it is also important to minimize the air consumption. The purpose of this paper is to evaluate the effects of supply orifice number on the static characteristics of plane pad circular air bearings. Two solutions are experimentally investigated, with six and three supply inherent orifices of same dimensions. A test bench is used to obtain the static characteristics (load capacity and mass flow rate) of the pads. Then the static pressure distribution under the pads are experimentally determined in different directions. A numerical model is developed to simulate the behaviour of the pads; a comparisons between experimental and numerical results is presented.

Externally pressurized gas bearings: A comparison between two supply holes configurations

Radial vibration of a vertical rotor with externally pressurized gas bearings is analyzed. The time-dependent Reynolds equation is solved together with the journal equation of motion to obtain the response characteristics of the bearing system. The bearings are supplied with either one or two sets of supply orifices. Stiffness and flow rate are compared for both cases. Stability maps are obtained at different supply pressures and with different supply orifice diameters. The mass range from orbital stability to instability is studied as a function of supply hole downstream pressure level.

Modeling and Identification of Gas Journal Bearings: Externally Pressurized Gas Bearing Results

Static and dynamic characteristics of externally pressurized gas journal bearings with four supply orifices positioned at the central cross section for rotating shaft displacements near the bearing center are investigated. Results for transfer functions and for gas-film coefficients derived using the developed mathematical model are compared with the results derived from numerical computations of a nonlinear distributed parameter model of the gas bearings. Averaging and corrective coefficients are elaborated. The results obtained demonstrate that analytical data are in good agreement with the numerical data for the wide range of parameters and the mathematical model developed makes the simple calculation of static and dynamic characteristics of this type of externally pressurized gas bearings possible. Derived analytical relations for transfer functions and for gas-film coefficients of gas bearings provide an efficient means for designing rotor-bearing systems.

Analysis of Tangential-Against-Rotation Injection Lomakin Bearings

Abstract This work presents a thin film flow model for analyzing the static and dynamic characteristics of centered, eccentric or misaligned tangential-against-rotation injection Lomakin bearings. The Lomakin bearing is a recent device intended for use in modern turbomachinery and having characteristics similar to hybrid bearings. It can be described as an ensemble of two opposing straight annular seals separated by a circumferential feeding groove. The fluid is supplied to the groove via orifice restrictors. Their tangential inclination generates an against-rotation circumferential flow in the groove that further penetrates into the thin film. This effect, known from annular seals as the prerotation speed, improves the dynamic characteristics of the bearing. A good description of the flow in the circumferential groove and the thin film is obtained from a full Navier–Stokes calculation of the centered bearing. The zero and first order analyses are then carried out by recognizing the crucial importance of taking into account the interaction between the flow in the thin film lands, the circumferential groove and the supply orifices. Due to the high Reynolds number regime, the land flow is governed by the two-dimensional thin film inertia equations (the “bulk flow” model). A one-dimensional circumferential flow dominated by inertia forces is assumed to take place in the groove and is described by an appropriate bulk flow equation. The flows in the supply orifices, the groove and the thin film lands are linked together by the same mass flow rate balance algorithm as used for hydrostatic and hybrid bearings analysis. The algorithm is extended to Lomakin bearings by considering the groove areas surrounding each orifice as a row of intercommunicating feeding pockets. This approach enables the analysis of centered, eccentric or misaligned Lomakin bearings. Comparisons with water-lubricated test results are used to validate the present model. For the zero eccentricity case a good agreement is obtained for the cross-coupled stiffness and for the whirl frequency ratio. A parametric study shows the variation of the bearing characteristics with increasing static eccentricity or misalignment.

Pneumatic hammer in an externally pressurized orifice-compensated air journal bearing

An experimental study was made of the occurrence of pneumatic hammer in an externally pressurized air journal bearing having double plane admission. Various parameters affecting the onset of pneumatic hammer were investigated. These were:- supply recess depth, supply orifice diameter and bearing mass. In general, pneumatic hammer is relatively easily avoided in journal bearings. However, achievement of repeatable results proved difficult, because of the effects of external damping and support stiffness. These factors are not incorporated in the existing theory. There were a significant number of instances where pneumatic instability was not apparent, although existing theory gave a strong indication of its occurrence. When pneumatic hammer did occur, there was broad agreement between experimental results and predicted trends as regards supply recess volume and supply orifice diameter, but not as regards bearing mass. The effects of external damping were important.

Modeling and Identification of Gas Journal Bearings: Self-Acting Gas Bearing Results

A mathematical model is elaborated with analytical relations for transfer functions and for gas-film stiffness and damping coefficients for self-acting and externally pressurized gas journal bearings with four supply orifices positioned at the center plane for rotating shaft displacements near the bearing center. Averaging and corrective coefficients are elaborated. In this paper static and dynamic characteristics of self-acting gas bearings are investigated. Results derived using the developed mathematical model are compared with the results derived from numerical computations of a non-linear distributed parameter model of the gas bearings. The results obtained demonstrate that analytical data are in good agreement with the numerical data for wide range of parameters and the mathematical model developed makes the simple calculation of static and dynamic characteristics of self-acting gas bearings possible. Derived analytical relations for transfer functions and for gas-film coefficients of gas bearings provide an efficient means for designing rotor-bearing systems.

The Effects of a Hydrostatic Pocket Aspect Ratio, Supply Orifice Position, and Attack Angle on Steady-State Flow Patterns, Pressure, and Shear Characteristics

The flow in a hydrostatic pocket is described by a mathematical model that uses the Navier-Stokes equations written in terms of the primary variables, u, v, and p. Using the conservative formulation, a finite difference method is applied through a staggered grid. The power law scheme is applied in the treatment of the convective terms for this highly recirculating flow. The discussion pertaining to the convergence of the numerical scheme and the computational error, shows that the strict convergence criteria applied to both velocities and pressure were successfully statisfied. The numerical model is applied in a parametric mode to the study of the velocities, the pressure patterns, and shear forces that characterize the flow in a square (α = 1), deep (α>1), and shallow (α≪1) hydrostatic pocket. The effects of the variation of the location and angle of the hydrostatic jet are also investigated.