Changes In Flow Rate Research Articles

Pore-scale Simulation of Two-phase Flow in Foamed Porous Materials

This paper establishes a pore cell model of foamed silicon carbide material based on a tetradecahedron structure, and uses FLUENT software to numerically study the flow rate and pressure drop changes in the porous structure at different flow rates and the gas-liquid two-phase flow state of the channel. The research results show that the porous skeleton structure has a great influence on the velocity and pressure distribution in the calculation domain; the inlet flow velocity has a certain impact on the gas-liquid mixing zone and gas-liquid interface area in two-phase flow. The application of tetradecahedral porous media increases the thickness of the gas-liquid mixing zone and the phase interface area are increased, with a maximum increase of 11.5%, thus promoting gas-liquid heat and mass transfer.

Analytical and experimental study on shaking effects for improved stone column foundations

Stone column technology is a method used to reduce liquefaction in saturated sediments. By using materials with greater permeability than the surrounding soil, stone columns can help drain excess pore water pressure and mitigate liquefaction potential during seismic loading. In this study, analytical solutions are proposed to address the liquefaction problem in saturated soils during earthquakes, taking into account the influence of stone columns and the surrounding soil. These solutions consider the excess pore water pressure at the boundary of the zones and analyze the vertical and horizontal drainages. The study also includes centrifuge tests on sandy soils improved with stone columns, calculating the total seepage flow and converting it into settlement based on the relationship between drainage flow rate and volumetric changes in the soil. The calculated settlement aligns well with the measured value in the centrifuge test, confirming the accuracy of the analytical formula for calculating settlement in stone column foundations. The study also evaluates the combined effects of radial and vertical drainages in stone column foundations using the derived analytical solutions.

Flow Characteristics Analysis of a 1 GW Hydraulic Turbine at Rated Condition and Overload Operation Condition

Flow stability is extremely important for hydraulic turbines, especially for 1 GW hydraulic turbines, and has a strong impact on mesh stability. However, turbines often operate under non-design conditions, and current research on this aspect is still lacking. So a model of the fluid domains of a high-quality installed 1 GW Francis turbine was established to investigate the flow characteristics of the turbine and fluid domains. CFD simulations of a 1 GW Francis turbine under rated load and overload operation conditions were performed. According to simulation results, when the turbine is under the overload operation condition, the internal flow stability of the 1 GW hydraulic turbine can be obviously different from that of the rated load. In the overload condition, the flow field is more turbulent and a large number of vortices are generated in the draft tube, resulting in significant changes in pressure, flow rate, and output. In order to improve calculation accuracy, a pure clearance model containing only clearances and pressure balance pipes was established. The results of the full flow channel and pure clearance were compared. It was found that under the rated operating condition and the overload condition, compared with the pure clearance model, the axial force of the runner calculated by the full flow channel model is approximately 2–7% biased, the radial force is biased by approximately 7–8%, and the leakage flow is smaller.

Preoperative and postoperative vascular characteristics in AVF creation surgery

Background: Early postoperative vascular ultrasound can predict the maturity of arteriovenous fistulas as well as detect complications.
 Objective: To present the characteristics of upper extremity vessels on ultrasound prior to AVF surgery and to analyze the changes in vessel size and flow rate postoperatively.
 Subjects and methods: We prospectively describe 80 cases of AVF formation at Dong Nai General Hospital from April 2022 to April 2023. Vascular ultrasound evaluations were conducted preoperatively and at 1 day, 2 weeks and 6 weeks postoperatively to evaluate the diameter and the blood flow of vessels used to create AVFs.
 Results: Eighty patients underwent AVF surgery. In forearm AVFs, the median diameter of the feeding artery and the draining vein were 2.12 (1.83 – 2.5) mm and 3.38 (2.9 – 3.80) mm, respectively. In upper-arm AVFs, the median diameter of the feeding artery and the draining vein were 3.67 (3.45 – 3.99) mm and 4.0 (3.64 – 4.05) mm, respectively. The draining vein flow rate showed a strong correlation with the brachial artery flow rate (R2 = 0.94, correlation coefficient = 0.88). The diameter and flow rate of the draining vein at 6 weeks post-surgery displayed significant correlations with their respective values at 2 weeks post-surgery, with correlation coefficients of 0.92 (R2 = 0.66) and 1.04 (R2 = 0.86), respectively. After 6 weeks post-surgery, non-diabetic patients exhibited larger draining vein diameters and higher flow rates compared with diabetic patients.
 Conclusions: The study highlighted the predictive potential of vascular ultrasound at the 2-week postoperative mark for AVF maturation The brachial artery flow rate can serve as a reliable indicator of AVF flow rate. Given the tendency for diabetic patients to exhibit smaller draining vein diameter and lower AVF flow rate than non-diabetic patients, particular caution is recommended when performing preoperative ultrasound mapping in this patient population.

Effect of Change in Plant Capacity towards Controllability of Biohydrogen Production Plant from Biomass

This paper discusses the plant-wide control system of a biohydrogen plant from biomass. The plant’s control structure is designed by assessing the use of model predictive control (MPC) and proportional-integral (PI) controllers for each controlled variable. Then, the control structure design is tested by set point and disturbance change tests, and its performance is evaluated by integral square error (ISE). This plant is simulated in two different capacities to understand the effect of change in plant capacity on the plant’s controllability. Results show that the plant with capacity A has controllability of +25% and −5%, while the plant with capacity B has controllability of +100% and −5% for the dry biomass molar flow rate change test. Both plants have the same controllability of +100% and −100% for the dry biomass temperature test. Both plants result in a dry biomass conversion rate of 16.52%, where the amount of H2 produced is 382 kg/h and 2,291 kg/h, respectively.

Development and validation of transient analysis module in nodal diffusion code RAST-V with Kalinin-3 coolant transient benchmark

This study introduces a transient analysis module developed for RAST-V and validates it using the Kalinin-3 benchmark problem. For the benchmark analysis, RAST-V standalone and STREAM/RAST-V calculations were performed. STREAM supplies the few-group constants and RAST-V conducts a 3D core simulation utilizing few-group cross-sectional data. To improve accuracy, the main solver was developed based on the advanced semi-analytic nodal method. To evaluate the computational capability of the transient analysis module in RAST-V, Kalinin-3 benchmark is employed. Kalinin-3 represents a coolant transient benchmark that offers experimental data during the deactivation of the Main Circulation Pumps. Consequently, the transient calculations reflected the changes in the reactor flow rate. Benchmark comprising steady-state and transient calculations. During the steady state, the STREAM/RAST-V combination demonstrated a 30 ppm root mean square difference from 0 to 128.50 EFPD. For the transient calculations, STREAM/RAST-V showed power differences within ±7 % over a range of 0–300 s. Axial offset differences were within ±3 %, and the RMS difference in radial power ranged within 2.596 % at both 0 and 300 s. Overall, this study effectively demonstrated the newly developed transient solver in RAST-V and validated it using the Kalinin-3 benchmark problem.

A Relationship Between Preoperative Inspiratory Lung Resistance And Emphysema-Reduction Surgery Outcome

Background Surgery to reduce lung volume has recently been reintroduced to alleviate dyspnea and improve exercise tolerance in selected patients with emphysema. A reliable means of identifying patients who are likely to benefit from this surgery is needed. Methods We measured lung resistance during inspiration, static recoil pressure at total lung capacity, static lung compliance, expiratory flow rates, and lung volumes in 29 patients with chronic obstructive lung disease before lung-volume–reduction surgery. The changes in the forced expiratory volume in one second (FEV1) six months after surgery were related to the preoperatively determined physiologic measures. A response to surgery was defined as an increase in the FEV1 of at least 0.2 liters and of at least 12 percent above baseline values. Results Of the 29 patients, 23 had some improvement in FEV1 including 15 who met the criteria for a response to surgery. Among the variables considered, only preoperative lung resistance during inspiration predicted changes in expiratory flow rates after surgery. Inspiratory lung resistance correlated significantly and inversely with improvement in FEV1 after surgery (r=—0.63, P<0.001). A preoperative criterion of an inspiratory resistance of 10 cm of water per liter per second had a sensitivity of 88 percent (14 of 16 patients) and a specificity of 92 percent (12 of 13 patients) in identifying patients who were likely to have a response to surgery. Conclusions Preoperative lung resistance during inspiration appears to be a useful measure for selecting patients with emphysema for lung–volume– reduction surgery

Investigation on thermohydraulic characteristics of novel superheated steam supply system for low temperature nuclear heating reactor

In a new Chinese low temperature nuclear heating reactor (NHR) demonstration project, a novel superheated steam supply system was designed to meet new requests for the steam produced in the secondary circuit. Different from the previous version of NHR200-II, which used a vertical steam generator to produce saturated steam, this newly designed system features a preheater, a horizontal steam generator, and a superheater for generating superheated steam. Numerical simulation method was used to investigate the feasibility and thermal hydraulic characteristics of this novel superheated steam supply system. The simulation results verify the accuracy and reliability of the system design, showing that the three heat exchangers can operate in coordination under different power levels, and the superheated steam generated in the secondary circuit can meet the users’ requirements. The system also demonstrated a remarkable ability to recover from sudden disturbances within 13.64 % change of the secondary circuit mass flow rate or 2.39 % change of the secondary circuit temperature under full power condition. Besides, the system has a power adjustment ability of ±10 %, and the system can quickly return to the new steady state. RELAP5 simulation results can provide theoretical guidance for the subsequent experimental research of this novel superheated steam supply system.

On the relation between tidal and forced spirometry

Spirometry is a lung function test involving deep inhalation and forceful deep exhalation. It is widely used to obtain objective information about airflow limitation and to diagnose lung diseases. In contrast, tidal spirometry is based on normal breathing and therefore much more convenient, but it is hardly used in medical care and its relation with conventional (forced) spirometry is largely unknown. Therefore, the objective of this work is to reveal the relation between tidal and forced spirometry. Employing the strong correspondence between the forced flow-volume curves and the Tiffeneau-Pinelli (TP) index, we present a method to obtain (a) the expected tidal flow-volume curve for a given TP-index, and (b) the expected TP-index for a given tidal curve. For patients with similar values of the TP-index, the tidal curves show a larger spread than the forced curves, but their average shape varies in a characteristic way with varying index. Therefore, just as with forced curves, the TP-index provides a useful objective ranking of the average of tidal curves: upon decreasing TP-index the expiratory flow rate changes in that its peak shifts towards smaller expiratory volumes, and its post-peak part becomes dented.

Plethysmographic assessment of vasomotor response in patients with congestive heart failure before and after heart transplantation.

Sympathetic vasomotor response is the most important part of the autonomic regulation of circulation, which determines the quality of life. It is disrupted in a number of diseases, particularly in patients with congestive heart failure (CHF). However, experimental evaluation of reflex vasoconstriction is still a non-trivial task due to the limited set of available technologies. The aim of this study is to assess the dynamics of vasomotor response of forearm vessels due to both the deactivation of cardiopulmonary baroreceptors and cold stress using a newly designed imaging plethysmograph (IPG) and compare its performance with classical air plethysmograph (APG). In both vasoconstriction tests, vasomotor response was assessed as a change in the blood flow rate due to venous occlusion compared to that at rest. Both tests were carried out in 45 CHF patients both before and after heart transplantation, as well as in 11 age-matched healthy volunteers. Prior to transplantation, both APG and IPG showed a significant decrease in vasomotor response in CHF patients due to both tests as compared to the control group. After heart transplantation, an increase in vasomotor reactivity was revealed in both vasoconstriction tests. We have found that both plethysmographic techniques provide correlated assessment of changes in the vasomotor response. In addition, we have found that IPG is more resistant to artifacts than APG. The new IPG method has the advantage of measuring blood flow in a contactless manner, making it very promising for experimental evaluation of vasomotor response in clinical conditions.

Quasi-2D thermal network based heat soakage model for gas turbine transient performance modification

To overcome the limitations of traditional heat soakage analysis, a novel quasi-2D thermal network based heat soakage model is established with the consideration of component internal thermal resistance, combustor temperature profile, cooling technologies and thermal barrier coating. The method has been integrated into Turbomatch, a gas turbine performance software developed by Cranfield University, to offer a more realistic estimation of the heat soakage effect during the gas turbine transient manoeuvre. The accuracy of the heat soakage model has been validated against results obtained from GasTurb. Furthermore, a parametric analysis has been conducted to evaluate the effects of combustor temperature profile, cooling technologies, and thermal barrier coating. It is found that the combustor temperature profile will cause a significant increase in heat flow rate, which is approximately four times the conventional lumped parameter method based model. The implementation of cooling technologies and thermal barrier coating will reduce the heat flow rate by 48.97%. More importantly, the change in heat flow rate causes a further delay in engine transient response. Corrected rotational speed was decreased by 0.89%, and thrust was reduced by 2.24%. Moreover, a delay of 8s (233% increase) in the transient acceleration time was found when comparing the quasi-2D thermal network based heat soakage model with the traditional lumped parameter method based model. These highlight the significance of accurately evaluating the heat soakage effects during gas turbine transient simulation.

One-dimensional pump geometry prediction modeling for energy loss analysis of pumps working as turbines

Pumps as turbine (PAT) for small-scale hydropower, pressure relief valves, and hydro-pumping applications have recently gained popularity. In contrast to conventional turbines, pumps do not have movable guiding vanes to accommodate changes in flow rate and head. This limits their use to the single best operating point. As a result, the precise estimation of reverse mode operating parameters is critical. One of the most successful techniques in this regard is the energy loss model. However, it necessitates extremely detailed pump geometry and experimental data. Although it is claimed to be more accurate, the lack of data makes it impractical. This calls for the devising of a pump geometrical parameter prediction model from limited manufacturer information. Using 137 sets of commercial pump operating data, geometry redesign was carried out by MATLAB code. Following that, multivariate linear regression analysis was carried out, and a one-dimensional geometrical prediction model was developed. Then the result was validated with computational analysis and measurement. The model results were 99 %, 100 %, and 95 % correlated for pump inlet, volute, and throat inlet diameters, respectively, with the experimental results. Similarly, the model results were also 99 %, 71 %, and 89 % correlated for pump inlet, outlet, and volute blade width, respectively, with experimental results. The model gave a more accurate geometrical result than the analytical and numerical methods.

The Sealing Performance of Cement Sheaths under Thermal Cycles for Low-Enthalpy Geothermal Wells

The repetitive process of shut-in and production in geothermal wells promotes thermal stress on the wellbore components, including annular cement. A cement sheath at a relatively shallow depth undergoes the most significant stress change due to the high differential temperature between the geothermal gradient and the production fluid’s temperature. Understanding the impact of cyclical thermal stresses on cement is critical for assessing the barrier integrity at a shallow depth that serves as aquifer protection. A novel large-scale setup simulating a 1.5 m-long casing-cement-casing well section was built to study the changes in cement’s sealing performance of low-enthalpy geothermal wells during production. Using this setup, a cement sheath can be cured similarly to the in situ conditions, and the annular temperature can be cycled under realistic operating conditions. The change in flow rate through the cement sheath before and after cycling is quantified through leak tests. UV dye is injected at the end of the experiment to identify the location and type of damage in the cement sheath. A hydromechanically coupled finite element model was used to estimate the stress evolution in cement during the tests. The model incorporated the impact of cement hydration and strength development during curing. The numerical results were used as a guide to ensure the test design closely mimicked in situ conditions. The results show the presence of a small microannulus immediately after curing due to hydration shrinkage. Thermal cycles reduced the permeability of the microannulus. The size of the micro-annulus was observed to be sensitive to the backpressure applied to the cement sheath, indicating the need for pressure to maintain an open microannulus. Thirty-nine thermal cycles between 80 and 20 °C did not change the permeability of the cement sheath significantly. Tensile cracks in the cement sheath were not continuous and may not be a significant pathway. The new setup allows for measuring cement’s effectiveness in withstanding in situ stress conditions when exposed to thermal cycles such as geothermal and CCS wells.

Comparison of helium and argon for the production of carbon monoxide (CO) by a plasma jet for biomedical applications

Carbon monoxide (CO) has anti-inflammatory properties and its production by plasma could be a significant advantage in the field of plasma medicine. We characterized a pulsed kHz-driven plasma jet to produce CO for biomedical applications. With no target interaction, the CO2 conversion into CO, the breakdown voltage and energy delivered to the plasma were investigated for two noble carrier gases: helium and argon. The breakdown voltage and the energy delivered to the plasma in argon gas were twice as high as in helium. The breakdown voltage was barely affected by the gas flow rate and the applied voltage, while it decreased slightly with the excitation frequency because the amount of residual charges increases with the frequency. However, the energy delivered to the plasma was not particularly affected by a change in frequency or gas flow rate, while it increased linearly with the applied voltage. CO production rose from a couple of ppm to about 2000 ppm for a specific energy input from 2 to 2000 J/L (5 × 10−4 to 5200 × 10−4 eV/(atom or molecule)), making this plasma source safe in terms of CO production for biomedical applications. Unlike literature results, the nature of the noble carrier gas did not have an impact on CO production. The CO concentration produced with 0.3% CO2 admixture increased linearly with the specific energy input (SEI) until reaching a plateau at about 2100ppm. This implies that loss processes were negligible and that CO2 dissociation was mainly due to energetic particles such as electrons and excited noble atoms. The conversion decreased with the ratio of CO2. Helium and argon as carrier gases are equivalent in terms of CO production and the CO concentration can be controlled by the SEI and the ratio of CO2.

Hybrid Heat Pipe Shutdown Rod as a Novel Concept of Passive Safety System for Microreactor

Ensuring the structural integrity of the monolithic core, which houses critical components such as heat pipes and fuel rods, is crucial for the safety of a microreactor. This research introduces a hybrid heat pipe shutdown rod as a novel passive safety system to address potential temperature rises in the monolithic core during accidents. It is designed to perform a dual function under accident conditions. It simultaneously absorbs neutrons and removes heat through structural modifications to the existing shutdown rod. Specifically, this system provides a heat transfer path within the monolithic core without increasing the size of the microreactor. By selecting cesium as the working fluid, we aimed to achieve rapid operation of the heat pipe to quickly reduce the temperature gradient in the monolithic core under accident conditions. The hybrid heat pipe was fabricated and evaluated and found to develop continuous flow even at temperatures around 205.1°C. However, its unique structure causes a pronounced converging–diverging effect, resulting in a temperature drop from about 70–170°C in the evaporator region, followed by a slight recovery to below 50°C in the condenser. This effect arises from changes in the cesium vapor mass flow rate due to phase changes and variations in the flow area between the evaporator and condenser. Despite these effects, the use of liquid cesium as the working fluid enables the hybrid heat pipe to operate under natural convection, avoiding startup problems that could cause flow blockage.

APPLICATION OF AN EXACT SOLUTION OF SPECIAL TYPE OF THERMOSOLUTAL CONVECTION EQUATIONS FOR THE INVESTIGATION OF EVAPORATIVE THREE-DIMENSIONAL FLOWS

The characteristics of gas-liquid flows with evaporation at the thermocapillary interface in an infinite rectangular duct, with a linearly distributed thermal load being applied on the upper and lower walls, are studied. The theoretical research of the three-dimensional convective flows is carried out within the framework of a two-sided model of evaporative convection based on the Navier-Stokes equations in the Oberbeck-Boussinesq approximation. A solution of a special type of governing stationary equations is used for describing the heat and mass transfer in a system of two immiscible fluids. We investigate the influence of the working (equilibrium) temperature of the system and intensity of the external thermal load on the structure of the velocity and temperature fields, as well as on changes in the evaporation mass flow rate and vapor content in the gas phase. The simulations are performed for the ethanol-air system. Based on the comparison of the calculated and experimental data, an effective way of nondimensionalization is proposed that allows one to consistently take into account the impact of the gas pumping velocity being a controlled parameter in experiments. It provides correct matching of the mathematical model to the experiment conditions, as well as a better qualitative and quantitative agreement between theoretical and measured values of evaporative mass flow rate. The results of the present study can aid in developing a theoretical basis for experimental research methods of evaporative convection and also in designing equipment for thermal coating or drying.

STABILITY OF THE INTERFACE OF LIQUIDS OSCILLATING IN A VERTICAL FLAT CHANNEL

The stability of an oscillating interface between two immiscible low-viscosity fluids of different densities in a vertical flat channel with a harmonic change in the liquid flow rate is studied experimentally. The limiting case of high dimensionless oscillation frequencies when the layer width exceeds the thickness of the Stokes layer is considered. It is found that a standing wave with a length significantly exceeding the gap width develops on the oscillating interface upon reaching a critical amplitude. It is shown that the discovered oscillations are gravity-capillary waves similar to Faraday ripples oscillating with the frequency of the driving force. The wavelength is determined by the interface oscillation frequency and the gravity acceleration and agrees well with the wavelength of gravity-capillary oscillations of the interface. A description of a new phenomenon is given.

Investigation of Changes in Natural Gas Parameters along a Damaged Gas Pipeline

The paper presents a mathematical model of the stationary flow of natural gas in an inclined gas pipeline, which makes it possible to calculate the gas parameters (pressure, temperature, compressibility factor) in every cross-section of gas pipeline. An improved mathematical model is also proposed by the authors, which considers the change in the gas flowrate along the gas pipeline. Complex 1 characterizing the effect of frictional forces and pressure losses and Complex 2 determining the effect of flow velocity were proposed to confirm the need to use an improved mathematical model. Based on the ratio of these complexes, a quantitative criterion was formed for the application of the improved mathematical model. An example of a comparison of complexes for a long pipeline and a short pipeline with a large gas flowrate is presented. Provided that the complexes are of the same order, the relative deviation of the pressures at the end of the gas pipeline obtained by the known and improved model can differ by 8 – 10%. Therefore, in such a case, it is necessary to apply the mathematical model improved by the authors. An example of the application of mathematical models is presented for the analysis of gas pressure and temperature distribution along a gas pipeline with significant damage. The pressure profile along this gas pipeline was obtained for its operating mode with gas flowrate limitation at the inlet and without limitation. It is shown that when the area of damage increases, the change in the pressure profile for these operating modes has features that can be used during the development of a system for determining the volume of gas lost because of sudden damage to gas pipelines.

토출유량변화에 따른 배수용 수중펌프 성능 특성에 대한 해석적 연구

Abnormal weather owing to climate change has become commonplace. Large and small floods have steadily occurred annually, increasing damage owing to flooding of agricultural land. Recently, owing to torrential rain, three of four rainwater pumping stations installed in Cheongyang-gun, Chungcheongnam-do, had failed to operate properly, thereby flooding several buildings and facility houses. In this study, an analytical study was conducted on the performance characteristics of centrifugal submersible pumps according to changes in the discharge flow rate. The results confirmed that the efficiency of the submersible pump for the experiment and analysis was within ±3.4% with the discharge flow rate.

LNG 기화열을 이용한 수조 수온 냉각성능에 관한 실험적 연구

In this study, a heat transfer performance experiment was conducted by experimentally testing the vaporization process of liquefied natural gas (LNG) using a seawater vaporizer and the process of supplying cooled seawater to the aquaculture tank. By using liquid nitrogen instead of LNG, we experimentally analyzed changes in tank water temperature according to changes in liquid nitrogen supply mass flow rate, water supply mass flow rate, and injection angle of the aquaculture tank nozzle. When testing was conducted by fixing the water mass flow rate at 0.05 kg/s and changing the liquid nitrogen mass flow rate to 0.0058 kg/s, 0.0075 kg/s, and 0.0092 kg/s, the target temperature of 17°C was reached under the experimental condition of 0.0092 kg/s.
 When the water supply mass flow rate was set to 0.05 kg/s, 0.07 kg/s, 0.08 kg/s, and 0.10 kg/s at the constant mass flow rate of liquid nitrogen of 0.0092 kg/s, the target temperature of 17°C was reached under the experimental condition of 0.07 kg/s. When the angle of the water nozzle was adjusted to 0°, 30°, and 60°, the fastest way to reach the target temperature of 17°C was the 0° experimental condition in which water was injected tangentially to the water tank.