Range Of Pressure Differences Research Articles

Semi-theoretical compression model of wet fiber web for the prediction of airflow rate in vacuum dewatering process of papermaking

This study expands the investigation of a mathematical method for predicting the airflow rate during the vacuum dewatering process of papermaking based on our previous research. By integrating poroelastic theory and initial saturation thickness, based on experimental data with a range of 20–60 kPa pressure difference and 20-200 g · m − 2 basis weight, a mathematical method with a semi-theoretical model for compression characteristics of the wet fiber web, the poroelastic porosity model (PEPM), was developed to support and expand on our previously established empirical model for porosity variations in wet fiber web, the variable porosity model (VPM). The accuracy of the mathematical method with the PEPM in predicting the airflow mass flux passing through the wet fiber web was validated using experimental data with a range of 0–60 kPa pressure difference and 20-200 g · m − 2 basis weight. The mean relative errors with the PEPM within the pressure difference range of 0-20 kPa and 0-60 kPa were 7.68% and 8.80%, respectively, compared to 17.44% and 11.67% for those with the VPM, demonstrating the improved applicability and generalization of the mathematical method, particularly in the zone of low pressure difference exceeding the range of the modeling experimental data. The PEPM effectively revealed the strain hardening behavior during the compression process and the diminishing returns of energy in the vacuum dewatering process with an increasing pressure difference. The developed mathematical method with the PEPM for the compression characteristics of the wet fiber web provides an effective and accurate way to predict the airflow rate during the vacuum dewatering process of papermaking.

Fabrication and Characterization of Novel Pebax2533/POSS-FS Nanocomposite Membranes for CO2 Removal

In this work, novel mixed matrix membranes (MMMs) were fabricated by incorporation of octatrimethylsiloxy polyhedral oligomeric silsesquioxane (POSS) and fumed silica (FS) as nanoparticle fillers into poly(ether-block-amides) (Pebax2533) as polymer matrix in order to carbon capture and remove acid gas from natural gas. Fourier transforms infrared (FTIR) spectroscopy proved the chemical structure of the nanocomposites and field-emission scanning electron microscopy (FESEM) unveiled the appropriate filler dispersion and adhesion between fillers and polymer. Thermogravimetric analysis (TGA) showed that all the samples have reasonable thermal stability which is enhanced by nanoparticles. The permeability and selectivity of pure CO2, CH4, and N2 gases were measured in the 4-10bar pressure difference range. The incorporation of studied nanoparticles caused improve performance including the permeability and selectivity relative to the neat Pebax. In 4bar and 0.1wt% POSS, CO2 permeability raised by 87%, while the highest increase in CO2/CH4 selectivity is at 2wt% POSS. The gas transport and free volume were also interpreted by densitometry showing that the addition of the fillers had a positive effect on the free volume and chain packing of the polymeric membranes.

Numerical investigation on the radiation performance of a crisscross liquid droplet radiator in space under different operating conditions

Crisscross liquid droplet radiator (LDR) is a promising solution for the heat dissipation of large-power spacecraft. In this study, a three-dimensional steady numerical simulation of the radiation performance of crisscross LDR in space under different operating conditions was conducted. Significantly, the radiation interaction between adjacent droplet planes was introduced into the radiation model to accurately compute the radiative heat transfer in the crisscross droplet sheet. Simulation results indicated the radiation performance of crisscross droplet sheets deteriorated with an increase in the nonuniformity of droplet plane arrangement and the radiation power of uniform crisscross LDR was 17.7% higher than that of the most nonuniform. Moreover, there existed a critical droplet sheet angle of 72° where the pressure disturbance frequency almost did not influence the radiation performance of crisscross LDR. For a certain pressure disturbance frequency, decreasing the droplet sheet angle can expand the available operational pressure difference range. The radiation performance of high-temperature crisscross LDR was more sensitive to the variation of droplet sheet angle than that of the low-temperature crisscross LDR. Furthermore, the optimal working medium collocation scheme and droplet sheet structure for liquid metal crisscross LDR were proposed. Given the lightweight and efficiency of liquid metal crisscross LDR, the collocation scheme of working medium including liquid tin and lithium can be adopted and the droplet sheet angle should be designed as 15°. The present work can provide significant guidance for selecting suitable operating conditions for droplet generators to optimize the thermal design of a crisscross LDR.

Numerical Comparative Study of Fuel Cavitation in Microchannels under Different Turbulence Models

The fuel injector is a critical component of the internal combustion engine. The diameters of the injector nozzle and the control chamber’s oil inlet and outlet are generally between 0.2 and 0.5 mm, which are typical microchannel structures. During high-pressure injection, the cavitation phenomenon in the channel seriously affects the reliability of the internal combustion engine. The choice of turbulence and cavitation models is the key to investigate the cavitation in the microchannel by using numerical methods. Based on the Winklhofer microchannel fuel experiment, five representative turbulence models were used to construct a microchannel model, and the results were compared and analyzed with the experiment. The results show that the pressure gradient values obtained from the combination of RNG k-ε and ZGB models were similar to the experimental data, with an error of less than 6%. The cavitation distribution calculated from the combination of LES and ZGB models was most consistent with the experimental observation data. The outlet mass flow rate obtained from the LES and ZGB models matched the trend of the experimental data in the pressure difference range of 19 bar to 85 bar, with an error of less than 2%. For the cross-sectional flow rate calculation, the RNG k-ε and ZGB models had the smallest calculation errors, with errors below 11%.

Improving Water Pressure Measurement Using Temperature-Compensated Wireless Passive SAW Bidirectional RDL Pressure Sensor

Currently pressure sensors utilized for water pressure measurement need batteries for direct power supply. However, batteries are lifespan-limited and not so reliable in the buried water pipe environment. The maintenance work due to battery failures leads to high cost to utility owners. Wireless passive surface acoustic wave (WP-SAW) sensors do not need direct power supply from batteries and can work in harsh environment. They are low-cost and compatible with micro-electromechanical systems (MEMS) technologies. This study investigates a temperature-compensated WP-SAW bidirectional reflective delay line (RDL) pressure sensor and its feasibility in improving water pressure measurement. The linear temperature-compensated pressure sensing functional model between the output phase shifts and the pressure change is established theoretically and verified by experiments. An experimental framework for testing the sensor node is built. The water pressure sensing adaptor is proposed. Experimental results: the experimental data show good linearities, which fits the established functional relationship; the numerical functional relationship has been derived and expressed; the sensor node has a good performance in the range of pressure difference from 0 to 0.5 MPa, which meets the normal 28-meter water pressure sensing requirements; the accuracy of this sensor is 7.22 kPa, which can be utilized for the water pressure sensing tasks in water distribution systems.

Experimental investigation of cavitation-induced erosion around a surface-mounted bluff body

The objective of this study is to investigate the collapsing behavior of cavitation, which leads to the erosion of material. An experimental examination was conducted in a channel with a semi-circular cylinder obstacle, which serves as a “vortex cavity” generator. Cavitation was achieved by employing a range of pressure differences over the test section and a high-speed camera was used to observe the cavitation behavior. The flow field behind the semi-circular cylinder was investigated as a characteristic example of bluff bodies that exhibit a distinct, separated vortex flow in their wake. The cases with the bluff body were also compared to the ones without the bluff body. Erosion tests were performed using paint (stencil ink). The intensity of cavitation is characterized by the cavitation number (σ); the lower the cavitation number, the higher the cavitation intensity. The erosion (removal of paint) after 40 min of operation revealed distinct and repeatable results. For a high cavitation number, a large number of von Karman-vortex-like cavities are shed downstream of the obstacle. This results in a higher number of collapse events and, ultimately, more erosion. On the other hand, at lower cavitation numbers, the erosion took place at the cavity's closure line. It was seen that with the increase in cavitation intensity, the erosion area increases. Moreover, the bluff body obstacle promotes and localizes cavitation-induced erosion on the sample plate compared to the cases without the bluff body. This ultimately means that in the cases with the bluff body, less power is required in the system to cause erosion. The erosion patterns caused by the bluff body cavitation are more repeatable compared to the cases without the bluff body due to the localized cavitation load. The erosion pattern from the paint test is also compared with a material loss test (30 h of operation). A very good qualitative agreement is found between the two tests, with the paint test requiring approximately two orders of magnitude less running time of the facility. We demonstrate that paint tests, combined with this geometry, provide an efficient and economical way to investigate erosion patterns compared to expensive material loss tests.

Experimental investigation of a prototype semi-dry revolving vane expander: Design challenges and performance criteria

The current study focuses on the design and use of a modified revolving vane expander (M-RVE). It was designed to overcome the limitations of a previous Revolving Vane expander design (RV-I) with the eventual aim of its use in an Organic Rankine Cycle (ORC). The M-RVE is a semi-dry prototype with no active lubrication system. The prototype functioned well for a range of pressure differences of up to 6.5 bar(g) and speeds of up to 600 rpm, in test that used compressed air as the working fluid. Compared to the RV-I, the M-RVE prototype generated higher torque (as much as 3 times that of the RV-I), exhibited higher isentropic efficiencies of up to 41%, but with lower volumetric efficiencies of less than 3%. The low volumetric efficiency was mainly due to the lack of an active lubrication system. Analysis of the internal leakages demonstrated severe leakages at the suction valve (blocker) and vane endface clearance gaps. The ratio between the ideal and the total leakage mass flow rates was between 1.2% and 7.3% at a suction pressure of 6.5 bar(g).

Investigation of Hydrodynamically Dominated Membrane Rupture, Using Smoothed Particle Hydrodynamics–Finite Element Method

The rupturing process of a membrane, located between two fluids at the center of a three-dimensional channel, is numerically investigated. The smoothed particle hydrodynamics (SPH) and the finite element method (FEM) are used, respectively, for modeling the fluid and solid phases. A range of pressure differences and membrane thicknesses are studied and two different rupturing processes are identified. These processes differ in the time scale of the rupture, the location of the rupture initiation, the level of destruction and the driving mechanism.

Numerical study of liquid nitrogen cavitating flow through nozzles of various shapes

The cavitating flow of cryogenic liquid through a spray nozzle is influenced by many factors, such as unique thermophysical properties of cryogenic liquid, the inflow temperature and the complicated geometrical structure of the spray nozzle. The geometrical parameters of liquid nitrogen spray nozzles have a profound impact on cavitating flow which in turn affects spray atomization characteristics and cooling performance. In present study, CFD simulations are performed to investigate influence of the nozzle geometry on the liquid nitrogen cavitating flow. The mixture model is used to describe the liquid-vapor two phase flow, and both the cavitation and evaporation are considered for the phase change. The predictions of mass flow of liquid nitrogen spray are validated against experimental results. The effects of geometric parameters, including the outlet orifice diameter and the length of nozzle, the inlet edge angle of orifice, the inlet corner radius of orifice, the orifice shape and different positions of swirl vanes, are investigated under a wide range of pressure difference and inflow temperature. The results show that the effects of geometric parameters on cavitating flow show different trends under subcooled conditions compared with saturated temperature conditions. The flow characteristics are more affected by the changes of the inlet edge angle, the inlet corner radius, and the orifice shape. The insert of swirl vanes has an effect on the distribution of the cavitated vapor within the orifice, but it has little influence on flow characteristics. The results could enrich our knowledge of liquid nitrogen cavitating flow in spray nozzles of various shapes.

Dielectric Elastomer Fluid Pump of High Pressure and Large Volume Via Synergistic Snap-Through

Harnessing reversible snap-through of a dielectric elastomer (DE), which is a mechanism for large deformation provided by an electromechanical instability, for large-volume pumping has proven to be feasible. However, the output volume of snap-through pumping is drastically reduced by adverse pressure gradient, and large-volume pumping under high adverse pressure gradient by a DE pump has not been realized. In this paper, we propose a new mechanism of DE fluid pumping that can address this shortcoming by connecting DE pumps of different membrane stiffnesses serially in a pumping circuit and by harnessing synergistic interactions between neighboring pump units. We build a simple serial DE pump to verify the concept, which consists of two DE membranes. By adjusting the membrane stiffness appropriately, a synergistic effect is observed, where the snap-through of membrane 1 triggers the snap-through of membrane 2, ensuring that a large volume (over 70 ml/cycle) can be achieved over a wide range of large adverse pressure gradients. In comparison, the conventional single DE pump's pumping volume rapidly decreased beyond a low adverse pressure gradient of 0.196 kPa. At the pressure difference of 0.98 kPa, the serial DE pump's pumping volume is 4185.1% larger than that of the conventional DE pump. This pumping mechanism is customizable for various pressure ranges and enables a new approach to design DE-based soft pumping devices such as a DE total artificial heart, which requires large-volume pumping over a wide range of pressure difference.

Cavitation behind a circular micro pillar

An experimental study of hydrodynamic cavitation was conducted in a rectangular microchannel with a pillar. Distilled water was used as working fluid in an open fluid loop, and cavitation was obtained by applying a range of pressure differences between inlet and outlet tanks. High speed camera captured the flow patterns from inception to fully developed cavitating flow. A minimum delay of 10 min in the formation of cavitation was recorded in all experiments, which is due to the stochastic nature of phenomenon. Cavitation inception conditions were obtained in terms of the cavitation numbers, and a flow map was developed for subsequent cavitation flow. By analyzing time series of gray scale intensity of pixels inside the cavity, dominant frequencies were identified. Transient single phase numerical simulations were performed to gain a better understanding of the flow field in the microchannel, verify pressure measurements, and to relate the separation angle to the attached cavitation angle around the pillar. Emphasis was placed on characterizing the wake region downstream the pillar as it is closely related to the occurrence of the cavitation phenomena.

The influence of cavitation on the flow characteristics of liquid nitrogen through spray nozzles: A CFD study

Spray cooling with cryogen could achieve lower temperature level than refrigerant spray. The internal flow conditions within spray nozzles have crucial impacts on the mass flow rate, particle size, spray angle and spray penetration, thereby influencing the cooling performance. In this paper, CFD simulations based on mixture model are performed to study the cavitating flow of liquid nitrogen in spray nozzles. The cavitation model is verified using the experimental results of liquid nitrogen flow over hydrofoil. The numerical models of spray nozzle are validated against the experimental data of the mass flow rate of liquid nitrogen flow through different types of nozzles including the pressure swirl nozzle and the simple convergent nozzle. The numerical studies are performed under a wide range of pressure difference and inflow temperature, and the vapor volume fraction distribution, outlet vapor quality, mass flow rate and discharge coefficient are obtained. The results show that the outlet diameter, the pressure difference, and the inflow temperature significantly influence the mass flow rate of spray nozzles. The increase of the inflow temperature leads to higher saturation pressure, higher cavitation intensity, and more vapor at nozzle outlet, which can significantly reduce mass flow rate. While the discharge coefficient is mainly determined by the inflow temperature and has little dependence on the pressure difference and outlet diameter. Based on the numerical results, correlations of discharge coefficient are proposed for pressure swirl nozzle and simple convergent nozzles, respectively, and the deviation is less than 20% for 93% of data.

CFD analysis of roof tile coverings

In hot climates tiled pitched roofs significantly reduce the heat transfer across the roof structure, due to the ventilated air layer between tiles and roofing underlay formed by the arrangement of battens and counter-battens supporting the tiles. This so-called Above Sheathing Ventilation (ASV) depends on the air entering and leaving at the eaves, ridge and the gaps between the tiles. With a view towards higher energy savings in space cooling, the natural and forced convection occurring in ASV could be enhanced by increasing the roof air permeability by means of novel tile shapes, as here analysed in two stages.The first stage of designing the new tile shapes was to measure the air permeability for a type of existing tile (Marseillaise style) using an experimental test rig, by monitoring the volumetric flow rate through the tiles over a range of pressure differences across the tiles. Then, a three-dimensional CFD model was implemented to replicate the full test rig geometry, and this was calibrated against the experimental data. In the next stage, the calibration was used to support the design of novel Marseillaise tile shapes, and to compare their performance against existing tiles. Finally, in order to analyse the variation in air flow under typical wind conditions for a pitched roof, a parametric study was undertaken, consisting of 72 scenarios varying wind speed, direction and angle of incidence.An increase in volumetric flow rate through the tiles was found to be related not only to an increase in the open area between tiles, but also to the design of the tile locks. By redesigning the geometry of these locks, whilst still giving consideration to their primary purpose of preventing the ingress of driving rain, it was possible to yield an improvement in air permeability of up to 100% in comparison with the original designs. Additionally, these novel designs were shown to increase the air flow rate as the wind angle moved from being directly up the roof slope around to the side, in contrast to the decrease seen with existing tile shapes.

Methane steam reforming in a membrane reactor using high-permeable and low-selective Pd-Ru membrane

We performed a methane steam reforming (MSR) reaction through a membrane reactor packed with commercial Ni/Al2O3 catalyst and a tubular Pd-Ru membrane deposited on a YSZ modified porous stainless steel support under mild operating conditions: 773 K and a pressure difference range of 100-250 kPa. We prepared the Pd-Ru membrane with thickness of ~6 μm on a tubular stainless steel support (diameter 12.7mm, length 25 cm) using electroless plating, which was observed for the membrane performance using hydrogen and nitrogen. Gas permeation test carried out at 773 K and 31.4 kPa of pressure difference between retentate and permeate sides showed that the hydrogen permeation rate and nitrogen leakage were ~0.1050mol s−1 m−2 and ~0.0018 mol s−1 m−2, respectively. The MSR reaction was under the following conditions: temperature 773 K, pressure 100-250 kPa, gas hourly space velocity (GHSV) 837 h−1, and steam-to-carbon feed ratio (S/C) 3. The MSR reaction result showed that methane conversion was increased with increasing pressure difference and reached ~77.5% at 250 kPa. In this condition, the composition of carbon monoxide was ~2%, meaning that no two series of water gas shift reactors were needed in our membrane reactor system. Longterm stability test carried out for ~100 h showed that methane conversion and the hydrogen yield remained constant.

Experimental study on the flow characteristics of air curtains at building entrances

Air infiltration through building entrances is one of the main sources of energy loss in modern buildings. Previous studies have shown that air curtains, when used at building entrances, can reduce infiltration-related energy loss significantly. A recent computational fluid dynamics (CFD) study proposed a new empirical model to capture air curtain door infiltration/exfiltration characteristics under varying operation conditions and pressure differences. Extending the recent CFD study, this paper presents an experimental study to verify and further investigate the flow characteristics of building entrances equipped with air curtains. A small scale chamber of 2.44 m × 2.44 m × 1.3 m (L × W × H) was constructed and used for the measurements of infiltration/exfiltration and pressure differentials, which were then used for developing the empirical model across the operating air curtain. A 2-D particle image velocimetry (PIV) system with helium filled soap bubbles as seeds was used to visualize the airflow fields captured at the doorway. Both the PIV and the measurement-based correlations were also compared to CFD simulations. The flow/pressure measurements confirmed that, for the tested pressure difference range, air curtains can significantly reduce infiltration. The PIV results confirmed the existence of multiple flow characteristics subject to pressure differences across the air curtain. The experimental results also validated the CFD modeling methods for air curtain, and verified that the empirical model of air curtain from the literature is valid in estimating infiltration through building entrances equipped with air curtains.

Estimation of the Pressure Drop Required for Lymph Flow through Initial Lymphatic Networks

Lymphatic function is critical for maintaining interstitial fluid balance and is linked to multiple pathological conditions. While smooth muscle contractile mechanisms responsible for fluid flow through collecting lymphatic vessels are well studied, how fluid flows into and through initial lymphatic networks remains poorly understood. The objective of this study was to estimate the pressure difference needed for flow through an intact initial lymphatic network. Pressure drops were computed for real and theoretical networks with varying branch orders using a segmental Poiseuille flow model. Vessel geometries per branch order were based on measurements from adult Wistar rat mesenteric initial lymphatic networks. For computational predications based on real network geometries and combinations of low or high output velocities (2 mm/s, 4 mm/s) and viscosities (1 cp, 1.5 cp), pressure drops were estimated to range 0.31-2.57 mmHg. The anatomical data for the real networks were also used to create a set of theoretical networks in order to identify possible minimum and maximum pressure drops. The pressure difference range for the theoretical networks was 0.16-3.16 mmHg. The results support the possibility for suction pressures generated from cyclic smooth muscle contractions of upstream collecting lymphatics being sufficient for fluid flow through an initial lymphatic network.

Experimental Investigation of Microscale Effects in Perforated Plate Aerodynamics

This paper contains an extensive analysis of the flow in microholes based on an experimental investigation. Experiments of the gas flow past a perforated plate with microholes (110μm) were carried out. A wide range of pressure differences between the inlet and the outlet were investigated for that purpose. Two distinguishable flow regimes were obtained: the laminar flow with the slip effects and the turbulence transition regime for a very low Reynolds number. The results are in good agreement with the theory, simulations, experiments for large scale perforated plates, and compressible flows in microtubes. The relation between the mass flow rate and the Knudsen, Reynolds, and Mach numbers for the laminar and transitional regime was obtained. It is a quadratic function of the Reynolds and Knudsen numbers (ReKn) based on the hole's diameter. The value of the first order tangential momentum accommodation coefficient was estimated. It shows a strong relation to the inlet Knudsen number.

Numerical simulation of TBM construction ventilation in a long diversion tunnel

A three-dimensional Renormalization-group ( RNG) k– ε model has been performed for forced ventilation to the working face of a long diversion tunnel, taking into account the effects of air leakage and the frictional resistance along the tunnel. The case study involves the working face during TBM construction of the Xinjiang 81 Daban long diversion tunnel, China. Analysis of the flow-field distribution and the pressure distribution near the working face and tunnel outlet revealed the relationships among the air leakage rate per 100 m, pressure difference at the air leakage port, and quantity of air in the air duct. The simulation results show that the air flux, velocity, and leakage rate gradually decrease along the tunnel. The air leakage rate per 100 m increases logarithmically along with pressure growth when the latter is limited within a certain pressure difference range. A low-pressure area can be found on the duct wall near the air leakage port, and the pressure inside the tunnel gradually decreases from the working face to the tunnel outlet; the velocity is relatively high near the leakage port, and is low in the tunnel. The simulated results were in good agreement with the experimental work by Cigdem Aydin and Hui-min Wang, and the simulated axial velocities of the tunnel were validated with the empirical value.

Shape of hexagonal hydrostatic menisci

A numerical method is implemented for computing the shape of an infinite, hexagonal, doubly periodic, hydrostatic meniscus originating from contact lines whose projections in the horizontal plane are circles. The contact lines themselves may lie on vertical cylinders or spherical objects. The Laplace–Young equation determining the meniscus shape is solved by a finite-difference method in orthogonal curvilinear coordinates generated by conformal mapping. The elevation of the contact lines is either prescribed or computed as part of the solution to ensure a specified contact angle. The results illustrate that the contact line spacing has an important effect on the contact angle or contact line distribution. Meniscus shapes exist only for a limited range of pressure differences between the upper and lower fluid that depend on the capillary length. Copyright © 2009 John Wiley & Sons, Ltd.

Hysteresis phenomena in a plane rotatable nozzle

The flow in a rotatable nozzle is calculated within the framework of the Reynolds equations and the Spalart-Allmaras turbulence model on the pressure difference range 1.1 < π < 5 for four configurations of the nozzle with the area ratio e = 1.52 and two angles of the nozzle axis rotation. The flow structure is determined and the thrust characteristics and the angles of the thrust vector rotation are obtained. It was found that in the overexpansion regime the flows in plane symmetric and rotatable nozzles involve hysteresis phenomena due the Coanda effect and the interaction between the boundary layer and a shock generated within the nozzle on its supersonic walls. The hysteresis phenomena detected provide an up-to-4% divergence in the thrust coefficient for the same problem parameters. The results of the numerical modeling are compared with the experimental data and the results of calculations in accordance with Sekundov’s model.