Small Flow Rate Research Articles

Study on flow and heat transfer characteristics of supercritical CO2 inside horizontal tube under ocean rolling condition

The flow and heat transfer characteristics of supercritical CO2 in a horizontal tube are studied numerically under the condition of ocean rolling. It is found that the rolling motion is beneficial to alleviate the deterioration of heat transfer at the top of the tube. However, the heat transfer deterioration is performed periodically with the rolling motion, which can cause periodic fluctuations in temperature and thermal stress of tube wall. This will affect the service-life. At a relatively small mass flow rate or large heat flux, the effect of rolling motion on the heat transfer performance increases since the density difference and buoyancy is relatively large. With the increase of inlet temperature and the decrease of buoyancy effect, the influence of rocking motion on heat transfer gradually decreases. The influence of rolling motion on the heat transfer for the floating nuclear power plant should be taken into consideration in the design.

A High-Performance Vortex Adjustment Design for an Air-Cooling Battery Thermal Management System in Electric Vehicles

To boost the performance of the air-cooling battery thermal management system, this study designed a novel vortex adjustment structure for the conventional air-cooling battery pack used in electric vehicles. T-shape vortex generating columns were proposed to be added between the battery cells in the battery pack. This structure could effectively change the aerodynamic patterns and thermodynamic properties of the battery pack, including turbulent eddy frequency, turbulent kinetic energy, and average Reynolds number, etc. The modified aerodynamic patterns and thermodynamic properties increased the heat transfer coefficient with little increase in energy consumption and almost no additional cost. Different designs were also evaluated and optimized under different working conditions. The results showed that the cooling performance of the Design 1 improved at both low and high air flow rates. At a small flow rate of 11.88 L/s, the Tmax and ΔT of Design 1 are 0.85 K and 0.49 K lower than the conventional design with an increase in pressure drop of 0.78 Pa. At a relative high flow rate of 47.52 L/s, the Tmax and ΔT of the Design 1 are also 0.46 K and 0.13 K lower than the conventional design with a slight increase in pressure drop of 17.88 Pa. These results demonstrated that the proposed vortex generating design can improve the cooling performance of the battery pack, which provides a guideline for the design and optimization of the high-performance air-cooling battery thermal management systems in electric vehicles.

Theoretical and Experimental Study on the Performance of Photovoltaic using Porous Media Cooling under Indoor Condition

This paper presents the theoretical and experimental investigation on performance of a photovoltaic (PV) panel cooled by porous media under indoor condition. Porous media offer a large exterior surface area and a high fluid permeability, making them ideal for PV cells cooling. The photovoltaic panel was cooled using 5 cm thick cooling channel filled with porous media (gravel). Several sizes of porosity (0.35, 0.4, 0.48, and 0.5) at different volume flow rates (1, 1.5, 2, 3, and 4 L/min) were tested to obtain the best cooling process. The theoretical analysis was performed at the optimum case found experimentally, which has a porosity of 0.35 and a volume flow rate of 2 L/min, to test various experimental results of the PV hot surface temperature, related power output, efficiency and I-V characteristic curve. The enhancement obtained in PV power output and efficiency is compared against the case without cooling and the case using water alone without porous media. Results showed that cooling using small size porous media and moderate flow rate is more efficient which reduces the average PV hot surface temperature of about 55.87% and increases the efficiency by 2.13% than uncooled PV. The optimum case reduced the PV hot surface temperature to 38.7°C, and increased the power output to 19 W, efficiency to 6.26%, and the open voltage to 22.77 V. The results showed that the presence of small porous media of 0.35 in the PV cooling process displayed the maximum effectiveness compared to the other two scenarios, because the heat loss from PV surface through porous media layer have developed a homogenous heat diffusion removed much quicker at high flow rate (2 L/min). A good agreement was obtained between experimental and theoretical results for different cases with a standard deviation from 3.2% to 5.6%.

Time–frequency signal analysis of flow pulsation in siphon outlet conduit based on HHT considering the pump‐conduit interaction

AbstractThe unsteady three‐dimensional numerical simulation calculation of the vertical axial flow pump device is performed based on CFD to examine the pressure pulsation and energy distribution features of the water flow within the siphon outlet conduit (SOC) under the hydraulic coupling of the pump and the flow conduit. The pressure pulsation signals (PPS) of monitoring points are decomposed using the Hilbert–Huang approach via empirical mode decomposition (EMD) and Hilbert spectrum analysis. The results show that the PPS of monitoring points of the SOC has no obvious periodicity. The low‐frequency range below 20 Hz serves as the primary frequency, and the energy ratio of the high‐frequency signal above 700 Hz is less than 1%. Under the condition of a small flow rate 0.3Qbep, there is obvious high‐frequency pulsation above 500 Hz at the inlet of the upstream section of the SOC, and there are periodic components distributed around 200 Hz. The energy of the pressure pulsation is primarily focused in the low‐frequency range below 40 Hz at the SOC outlet section. The PPS at the top and bottom monitoring points of the hump section are consistent, and the pressure pulsation energy (PPE) is mainly concentrated in the low frequency below 40 Hz. In both the big flow condition (1.2Qbep) and the optimal flow condition (1.0Qbep), the PPE of the monitoring points at the top of the hump section is distributed in the middle and low‐frequency band below 40 Hz, and the energy of monitoring points at the bottom of the hump section is concentrated in the low‐frequency band below 20 Hz, accounting for more than 70%. When the flow rate increases from 0.3Qbep to 1.2Qbep, the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the top of the hump section changes little, and the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the bottom increases first and then decreases. From the upstream section to the hump section of the SOC, the average frequency of each intrinsic mode function (IMF) of the PPS under different flow conditions shows an overall increasing trend. From the hump section of the SOC to its outlet, the average frequency of each IMF of the PPS decreases under the conditions of 1.0Qbep and 1.2Qbep, and there is no obvious change under the condition of 0.3Qbep.

Toward the Utilization of 3D Blading in the Cantilevered Stator from Highly Loaded Compressors

Three-dimensional blading is an efficient technique in compressor aerodynamic design, and its function mechanism in the cantilevered stator needs to be addressed. This paper focuses on the sweep and dihedral in the cantilevered stator and seeks to expose their effects through detailed flow field analysis. Results show that the forward sweep could alleviate the corner flow separation by preventing the accumulation of the secondary flow toward the corner region, resulting in stronger flow separation at the blade trailing edge; in summary, forward sweep with appropriate parameters could increase static pressure rise by 14.3%. The positive dihedral will carry the endwall flow to the upper-span sections, thereby reducing blade corner separation; hence, as much as 23.5% improvement in static pressure rise could be obtained with the appropriate dihedral. Moreover, the combination of a relatively large sweep height and a moderate sweep angle with a low dihedral height and a moderate sweep angle provides optimum aerodynamic performance; the static pressure rise coefficient sees an increment of 25.5% at the near stall point. An experiment is then performed to further validate the theory, which shows a 2% improvement in efficiency of 3D blading at small mass flow rates. However, the secondary leakage should be given attention at high mass flow coefficients, while the corner separation needs further elimination at small mass flow rates.

Passive Wireless Pressure Gradient Measurement System for Fluid Flow Analysis

Using distributed MEMS pressure sensors to measure small flow rates in high resistance fluidic channels is fraught with challenges far beyond the performance of the pressure sensing element. In a typical core-flood experiment, which may last several months, flow-induced pressure gradients are generated in porous rock core samples wrapped in a polymer sheath. Measuring these pressure gradients along the flow path requires high resolution pressure measurement while contending with difficult test conditions such as large bias pressures (up to 20 bar) and temperatures (up to 125 °C), as well as the presence of corrosive fluids. This work is directed at a system for using passive wireless inductive-capacitive (LC) pressure sensors that are distributed along the flow path to measure the pressure gradient. The sensors are wirelessly interrogated with readout electronics placed exterior to the polymer sheath for continuous monitoring of experiments. Using microfabricated pressure sensors that are smaller than ø15 × 3.0 mm3, an LC sensor design model for minimizing pressure resolution, accounting for sensor packaging and environmental artifacts is investigated and experimentally validated. A test setup, built to provide fluid-flow pressure differentials to LC sensors with conditions that mimic placement of the sensors within the wall of the sheath, is used to test the system. Experimental results show the microsystem operating over full-scale pressure range of 20,700 mbar and temperatures up to 125 °C, while achieving pressure resolution of <1 mbar, and resolving gradients of 10-30 mL/min, which are typical in core-flood experiments.

Simulation of hydraulic fracture initiation and propagation for glutenite formations based on discrete element method

The existence of gravels in the glutenite formations leads to the complex geometries of hydraulic fracturing propagation and difficult construction in fracturing engineering. To study the hydraulic fracturing propagation law of glutenite formations, this paper establishes a fracture propagation model for the heterogeneous glutenite formations based on discrete element method, and analyzes the effects of gravel content, particle size, distribution, horizontal stress difference, fracturing fluid viscosity and flow rate on hydraulic fracturing propagation behavior. Results show that the complex geometries of hydraulic fractures in glutenite formations can lead to the generation of branched fractures and fracture bifurcation. Small-sized gravels have little effect on the fracture propagation shape which leads to a single main fracture with a flat fracture surface, on the contrary, large-sized gravels may induce hydraulic fractures to deflect along the gravel interface and form branched fractures with distorted fracture surfaces. Hydraulic fractures can propagate around gravels under the condition of high stress difference, high viscosity and medium flow rate. Gravels can prevent the propagation of hydraulic fractures under low stress difference, low viscosity and small flow rate. Hydraulic fracture bifurcation can occur when encountering gravels under high stress difference and large displacement. Properly increasing the high viscosity of fracturing fluids can effectively promote the main hydraulic fracture propagation and reduce the fracture tortuosity, thereby avoiding sand up.

Analysis of spray characteristics of a jet-film injection element based on Voronoi tessellation

The present paper presents a computational study based on a validated Volume-of-Fluid method on the effects of film thickness and film width on spray characteristics for the simplified jet-film injection element with varying mass flow rate conditions. First, the spray characteristics of a typical jet-film collision were analyzed in terms of the spatial distribution of Sauter Mean Diameter and Voronoi tessellation. Both the Voronoi diagram and the Sauter Mean Diameter contour are useful to evaluate the spray characteristics because they show two different aspects of the sprays. Second, the jet-film spray characteristics were analyzed by decreasing either film thickness or film width to change the mass flow rate. The results show that decreasing film width results in approximately insensitive spray angle and improved uniformity of droplet distribution for different throttleable levels. The present computational results verified our design concept that adopting traditional jet-film injection at a large mass flow rate and modified jet-jet injection at a small mass flow rate to maintain good spray performance during the entire throttleable levels.

Experimental study of gas–liquid two-phase operating characteristics and bubble evolution law of a semi-open mixed-flow pump

This work experimentally studied the influence of gas and liquid distribution on a semi-open mixed-flow pump performance. High speed photography technology was contributed to obtain the evolution law of bubbles in the impeller. The results show that the inlet gas volume fraction (IGVF) and liquid flow rate are the main factors affecting the performance of the pump. The pressurization capacity linearly decreases with the increase in IGVF when the liquid flow rate is close the best efficiency point. However, this factor suddenly drops when the IGVF reaches a certain critical value under the condition of a low liquid flow rate. The spatiotemporal evolution characteristics of the isolated bubbles and gas column in the segregated flow were investigated. In addition, the bubbles are evenly distributed, and the flow pattern is mainly bubbly flow (BF) or aggregated BF (ABF) in the impeller inlet area without blades. Under small liquid flow rate conditions, the bubbles tend to coalesce into larger-sized gas-pocket with an increase in IGVF. The tip leakage vortex increases the turbulence intensity of the flow field. The results show that the bubbles downstream of the tip leakage vortex in the impeller channels are more easily broken into smaller bubbles and form a BF or ABF.

Study of a novel hydro turbine with ultra-small unit discharge in theoretical calculation and numerical simulation

A novel hydro turbine with the ultra-small unit discharge was suggested and studied for the first time. It was specially developed for hydraulic energy recovery with a smaller flow rate and medium available head, its highlight feature is straight blades in the radial direction. In this paper, the theoretical and numerical simulation of a novel hydro turbine was studied. First, with the working process and principles introduced, the theoretical models were established for the prediction of optimal unit speed, optimal unit discharge, and performance curves. Second, numerical simulation was carried out to study the performance of the novel turbine and verify the theoretical models. Different mesh quantity cases were investigated to select an accurate configuration. The numerical simulation predicted that optimal unit speed was 57.07 r/min, and optimal unit discharge was 0.0705 [Formula: see text]/s, while the specific speed was 42.3 m kW. Comparisons between theoretical calculation and numerical simulation show the accuracy of the theoretical models. Finally, a tail energy recovery runner was proposed to improve the performance of the novel turbine, and maximum efficiency was improved from 79.6% to 84.5%. The novel hydro turbine fills the blank working area between Pelton turbine and Francis turbine, and could be easily applied to engineering with low cost and simple manufacture.

Flow Regulation of Low Head Hydraulic Propeller Turbines by Means of Variable Rotational Speed: Aerodynamic Motivations

To date, hydraulic energy is still, among the renewable ones, the most widespread and most exploited to produce electricity. With the current trend to exploit any renewable source available, the limits for the economic convenience of hydroelectric power plants have significantly changed, making it interesting and convenient to use even small heads and low flow rates. In the specific applications of hydraulic turbines operating with low heads, the Kaplan turbine plays the predominant role among the available machines, also given the possibility of carrying out an “on cam” regulation, acting simultaneously on the geometry of the rotor and distributor rows, thus allowing a wide flow rate adjustment range. However, for applications characterized by very low heads and low available powers, it may not be convenient to use complex regulating devices. For this reason, these plants usually use axial machines characterized by a partial regulation (of the distributor or of the rotor), significantly reducing the operating range of the machine compared to the case of double regulation. In the last decade, the development of reliable and less expensive permanent magnet generators and power electronic converters and related new control strategies has paved the way for the concept of regulating hydraulic turbines by means of variable rotational speed. This regulation principle is based on the possibility of acting in the case of using synchronous permanent magnets electric generators and electronic power converters and on the variation of the rotational speed of the machine while keeping the grid frequency constant. The concept can be applied both to pure propellers with fixed a rotor and fixed distributor and to hydraulic axial turbines with regulation based on the modification of the variable guide vane opening angle. Although this new regulation approach, even in the case of the combined guide vane and rotational speed regulation, does not allow to recover most of the energy losses due to the variation of the operating conditions as effectively as the Kaplan double regulation does, the variation of the rotation speed, coupled with the variation of the opening of the distributor row, allows to reduce the tangential kinetic energy losses generated at the turbine exit during the off-design operations of a fixed blade opening angle rotor. At the same time, this type of regulation offers a simple and thus low-cost solution. The present study develops the theory underlying this regulation concept, based on the use of the turbomachinery fundamental equations, and reports the results of the off-design CFD analysis carried out for different combinations of rotation speeds and openings of the distributor, showing the improvement of the hydraulic efficiency over a large range of operating conditions with respect to the single regulation approach.

On the cone-to-jet transition region and its significance in electrospray propulsion

A novel method for identifying the cone-to-jet transition region is proposed to characterize the electrospray dynamics, and thus the Taylor cone, a fundamental principle of ion extraction from the tip of the Taylor cone in an electric field to produce μN thrust for nanosatellites' application. A numerical model is developed and validated against the droplet's diameter with a proper characterization of the cone-to-jet transition region based on the hydrodynamic pressure gradient at the cone-jet axis. The results show that the cone-to-jet transition region is reduced when the electric potential increases and the flow rate decreases. Moreover, the current density is found to be higher for the lower flow rate and large electric potential. Interestingly, the current density at the jet axis increases significantly at the flow rate of 1 cc/hr. This implies that below a certain droplet diameter, the current density carried by the jet interface is completely migrated into the jet, and the substantial change in the current density occurs within the cone-to-jet transition region. When comparing the current density along the jet axis, the small flow rate and large electric potential carry the maximum current density at the jet interface. The identification of cone-to-jet transition region is central in modeling the ion beam trajectory via initial current density profile required for particle-in-cell calculation for assuring the performance of a field emission electric propulsion thruster.

Mechanism Affecting the Performance and Stability of a Centrifugal Impeller by Changing Bleeding Positions of Self-Recirculating Casing Treatment

This study aimed to investigate the influence of the bleeding position of a self-circulating casing on the aerodynamic performance of a transonic centrifugal compressor. Three types of self-circulating structures with the bleeding positions of 11% Ca (the axial chord length of the blade tip), 14% Ca and 20% Ca from the leading edge of the blade were studied by using the numerical simulation method, with the Krain impeller taken as the research object. It was found that all three types of self-recirculating casing treatments can expand the stable operating range of the impeller, and that at medium and small flow rates, the total pressure ratio and efficiency of the impeller increase gradually with the backward movement of the bleeding position. The self-circulating casing treatment can restrain the development of tip leakage vortex, reduce the blockage area, and improve the stability of the impeller by sucking low-energy fluid. The farther back the bleeding position is, the greater the bleeding mass flow rate of the self-circulating casing for the low-energy fluid in the blade-tip passage becomes. Additionally, a greater inhibition effect on the tip leakage vortex, and a better effect of improving the performance and stability of the impeller, can be obtained. The best air bleeding position is 20% Ca, but it is not directly above the blade-tip blockage center of the solid wall casing passage. Instead, it is downstream of the blockage area.

Effect of a Reduced Oil Flow Rate on the Static and Dynamic Performance of a Tilting Pad Journal Bearing Running in Both the Flooded and Evacuated Conditions

Abstract The mechanical efficiency of rotating machinery improves as drag power losses in bearings reduce; hence, an operation mode that reduces the supplied flow brings immediate benefits. The paper presents measurements of the static and dynamic load performance conducted with a tilting pad journal bearing configured as flooded and evacuated, and supplied with flow rates from 150% to ∼25% (or lesser) of a nominal magnitude, proportional to shaft speed. The lubricant is ISO VG 46 oil supplied at 60 °C. The four pads bearing has center pivots with single orifice feeds for the flooded condition and spray bar injection for the evacuated condition. The shaft, 102 mm in diameter, operates at two speeds, 6 and 12 krpm (= 64 m/s surface speed), while a static load is applied between pads (LBP). The specific loads equal 345, 1034, and 2068 kPa. A reduction in flowrate makes both bearings operate more eccentrically. The evacuated bearing operates at a larger eccentricity, which for the lowest flowrate does not align with the direction of the applied load, hence displaying a sizable attitude angle. Pad subsurface temperatures are similar for both bearing configurations, although the evacuated bearing is colder by a few degrees Celsius. Drag power losses derived from the oil exit temperatures show the evacuated bearing produces up to ∼40% lesser power loss than the flooded bearing for a nominal oil flowrate. The bearings direct stiffnesses, Kxx and Kyy, increase with applied load and show little dependency on shaft speed. The evacuated bearing has lower magnitude stiffnesses, 20% or so lesser, than the flooded bearing. Damping coefficients, Cxx ∼ Cyy, reduce in magnitude as the flowrate decreases. In particular for low flow rates, 35% or lower, the evacuated bearing shows rather small (though highly uncertain) damping coefficients. For sufficiently small flow rates, operation at 6 krpm shaft speed and under the smallest applied unit load (345 kPa) produced subsynchronous shaft vibrations with a broad band spectrum (subsynchronous shaft vibrations (SSV) hash). The evacuated bearing produced SSV hash at flow rates equal to 30% or so of nominal, while the flooded bearing demanded very low flow rates (∼15% and lesser of nominal) to produce SSV hash. For both bearings, the SSV amplitude motions were rather small in amplitude. The experimental campaign demonstrates that tilting pad bearings (flooded and evacuated) can safely operate with a reduced flowrate (50% or so of nominal) to produce significant savings in drag power losses and without significant effect on the pads' metal temperatures that could affect the bearing long-term operation.

Assessment of a Smartphone App for Open Channel Flow Measurement in Data Scarce Irrigation Schemes

Accurate water flow measurement ensures proper irrigation water management by allocating the desired amount of water to the irrigation fields. The present study evaluated whether the non-intrusive smartphone application “DischargeApp” could be applicable and precise to measure small canal flow rates in the Koga irrigation Scheme. The app was tested in unlined canals with flow rates ranging from 15 to 65 l/s using a 90° V-notch weir. The app is found to overestimate high flow rates. Another source of uncertainty is that the app employed a constant surface velocity conversion factor (C = 0.8) to compute discharge. The accuracy was enhanced by recalculating the measured discharge using a new surface velocity conversion factor that depends on depths. The new conversion factor decreased the errors of MAE and RMSE by 47% and 52%, respectively. Where channel and other optional measuring techniques are not available without interfering with the flow operation conditions in place, the DischargeApp devices can be used to measure flows. The DischargeApp could be used to collect data using local citizens in data-scarce areas. This study suggested reconfiguring the DischargeApp with a new surface velocity conversion coefficient based on flow depths in field conditions for better performance.

Experimental footprints of a water-rich depletion layer in the Herschel–Bulkley pipe flow of solidifying polyelectrolytes

A fundamental understanding of the transition from fluid-like to gel-like behavior is critical for a range of applications including personal care, pharmaceuticals, food products, batteries, painting, biomaterials, and concrete. The pipe flow behavior of a Herschel–Bulkley fluid is examined by a combination of rheology, ultrasound imaging velocimetry, and pressure measurements together with modeling. The system is a solution of 0.50 wt. % polyelectrolytes of sulfated polysaccharides in water that solidifies on cooling. Fluids with different ionic strengths were pumped at various rates from a reservoir at 80 °C into a pipe submerged in a bath maintained at 20 °C. The fluid velocity, pressure drop ΔP, and temperature were monitored. The same quantities were extracted by solving continuity, energy, and momentum equations. Moreover, the modeling results demonstrate that the local pressure gradient along the pipe dPdx|x is related to the local yield stress near the pipe wall τywall|x, which explains the variations of dPdx|x along the pipe. Experimental results show much lower values for ΔP compared to those from modeling. This discrepancy is exacerbated at higher ionic strengths and smaller flow rates, where fluid shows a higher degree of solidification. The tabulated experimental ΔP data against the solidification onset length Lonset (where the fluid is cool enough to solidify) along with the ultrasound imaging velocimetry associate these discrepancies between experiments and models to a depletion layer of ∼1 μm, reflecting the lubrication effects caused by the water layer at the wall.

Research on precise and stable seed flow delivery control for plasma MHD power generation

In this paper, a technique for precise and stable delivery control of alkali metal seed flow is proposed and experimentally verified. A high-pressure syringe driven by a stepping motor delivers liquid alkali metal seeds through a pneumatic atomizing spray gun. The seed jet is uniformly mixed, heated, vaporized and ionized by the high-temperature main flow in the plasma generator to produce a plasma with high conductivity. Based on the high-temperature arc wind tunnel test platform, an experimental study of the alkali metal cesium seed flow measure and plasma ionization characteristics was carried out. The results show that the fluctuation range of the measured seed flow was 5.93-10.39% at a small flow rate of 19 mL/min. For the back pressure of 6 atm, the fluctuation range of the measured seed flow is 6.04-11.55%, which proves that the back pressure of the plasma generator has insignificant effect on the seed flow. The plasma ionization characteristics test shows that the conductivity of the argon cesium equilibrium plasma is between 26.93-31.69 S/m, indicating that the ionization characteristics of the plasma are relatively stable, which can indirectly prove that the seed system has a precise and stable flow rate during the actual power generation. Key words: MHD power generation, alkali metal seed, seed fraction, precise and stable injection. Tables 1, Figs 9, Refs 11.

Experimental Device for the Measurement of Small Gas Flows Utiliying the Principle of Lamilar Flow Elements

In this paper, the authors proposed an experimental device for measuring small flow rates of gaseous media. The device is based on the measurement of the pressure gradient upstream and downstream of the measuring element. The materials used in the design and construction of the device provide local pressure resistance, which enables accurate measurement. The proposed device can serve as an alternative to actual measuring devices for detecting the instantaneous quantity flowing in the measurement assembly. The results of the experimental measurements will be used to determine the characteristics of the measuring elements of the device.

Effects of Duct Height and Fire Location on Fire Phenomena of Enclosure with Two Horizontal Vents Installed on Ceiling

The effects of duct height (DH) and fire location (FL) in an enclosure on the mass flow rate and flow pattern of horizontal vent (HV) flow and temperature distribution in the enclosure were investigated through numerical simulations under the condition that two HVs were installed on the ceiling of the enclosure. To evaluate the effect of DH, DHs of HV1 were set to 0.19 m (HV1_DH0.19) and 0.05 m (HV1_DH0.05) under the condition that DH of HV2 was 0.05 m (HV2_DH0.05). The effect of FL was evaluated in three cases where the fire sources were located in the center of the floor (F LC), below HV1 (F L1), and below HV2 (F L2). With respect to the DH effect, the total mass flow rate of the vent flow was slightly higher and temperature was slightly lower in the case of HV1_DH0.19 than that in the case of HV1_DH0.05. However, considering the error bars, the effect of DH in this numerical simulation condition was considered to be insignificant. Furthermore, bidirectional flow patterns appeared in HV1 and HV2 in both DH conditions. Meanwhile, with respect to the FL effect, a bidirectional flow dominated by the mass flow rate of outflow occurred in the HV where the fire source was located, and a unidirectional inflow dominated by the mass flow rate of inflow occurred in the HV where the fire source was not located. The total mass flow rates of FL1 and FL2 conditions were similar, which were higher than those of FLC condition. The temperature was higher in FLC than those in FL1 and FL2. This was due to the small mass flow rate through the HV in the FLC. Meanwhile, an increasing trend of the temperature with the rising measurement height from the floor was observed at most of the temperature measurement points. However, when the fire source was located below HV1 and HV2, as the height from the floor increased, the temperature decreased and the overall temperature was low at the temperature measurement points below the vent where the fire source was not located. This trend was attributed to the occurrence of a strong unidirectional inflow wherein a large volume of low-temperature air flowed into the enclosure from the HV where the fire source was not located.

Application of GA-BPNN on estimating the flow rate of a centrifugal pump

Pumps consume nearly 8% of global electricity as the essential equipment for liquid transportation. A practical method for improving centrifugal pump energy efficiency is accurately predicting and controlling the pump operation status. However, current estimation methods for sensorless flow rate prediction have a significant error at low flow rate conditions. This study adds valve opening as the estimation model input variable, including motor shaft power and speed, to form a back-propagation neural network (BPNN) on an asynchronous motor-driven multistage centrifugal pump. By optimizing the initial weights and thresholds of BPNN, a GA-BPNN model was proposed to improve the prediction accuracy by using a genetic algorithm (GA). The results indicate that, with the addition of the valve opening as an input variable, the accuracy of BPNN-VO and GA-BPNN prediction improves significantly more than BPNN-NVO. Furthermore, the GA-BPNN model produces a significantly lower mean square error (MSE) and root mean square error (RMSE) than the original BPNN model. According to the experimental comparison and analysis, the absolute error of GA-BPNN between predicted flow rate and measured flow rate is less than 0.3 m3/h, the average relative error is less than 2%, and the relative error of low flow rate is less than 5%. This GA-BPNN estimation model significantly improves the accuracy of flow rate prediction, especially at small flow rates, and extends the scope of centrifugal pumps’ monitoring and control technology without flow sensors.