Plunger lift is an economical method to solve the liquid loading problem in wells. Following our previous research (Zhao a al., 2018), which focused on the steady-state process of liquid leakage during lifting, the tr...
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Plunger lift is an economical method to solve the liquid loading problem in wells. Following our previous research (Zhao a al., 2018), which focused on the steady-state process of liquid leakage during lifting, the transient variations of plunger velocity, liquid leakage and stress conditions during plunger lifting process are investigated theoretically and experimentally in this paper. Based on the force analysis and finite difference method, the transient physical model for the mass and gas volume fraction of gas-liquid column above plunger is proposed. Combining the similarity experiments and infrared measuring technology, the proposed transient model is verified quantitatively with the relative deviation less than +/- 10%. The results show that both the liquid leakage and the gas volume fraction of gas-liquid column above plunger cannot be neglected during plunger lifting. The transient change rules of lifting differential pressure, plunger velocity, gas volume fraction of gas-liquid column and liquid leakage flow rate during lifting process are obtained. The influences of liquid loading condition and gas production rate on transient plunger lifting process are discussed. Through the dimensionless analysis, a dimensionless correlation for transient gas volume fraction of gas-liquid column is developed.
Density is one of the most important thermophysical properties of aviation fuel for the advanced fuel-cooled thermal management. The density of a hydrocarbon fuel JP-10 was measured using a gamma-ray radial method cal...
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Density is one of the most important thermophysical properties of aviation fuel for the advanced fuel-cooled thermal management. The density of a hydrocarbon fuel JP-10 was measured using a gamma-ray radial method calibrated with deionized water, cyclohexane, and a mixture of n-heptane and n-octane. The average absolute deviation (AAD) of deionized water is 0.22% under 3.0 MPa and 0.43% under 5.0 MPa, that of cyclohexane is 0.80% under 5.0 MPa, and that of the mixture of n-heptane and n-octane is 0.33% under 5.1 MPa. The experimental density of JP-10 was reported at 267 to 873 K under the pressure of 0.70 to 6.00 MPa. Two empirical correlations were used to fit the liquid and gas density data separately. The results are that the AAD for all the liquid data is 0.46%, and that for all the gas data is 6.12%. Finally, the isobaric thermal expansion was calculated.
An improved model is developed to calculate flow distributions of supercritical pressure water in parallel pipes with non-uniformly distributed heat load. On the basis of the limitation of the previous models, two mai...
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An improved model is developed to calculate flow distributions of supercritical pressure water in parallel pipes with non-uniformly distributed heat load. On the basis of the limitation of the previous models, two main improvements have been proposed. Firstly, the effects of both the manifold and heat load on flow distribution are simultaneously taken into account by the present model, which is better suitable for engineering practices. Secondly, the prediction of flow distribution under both supercritical and subcritical pressure conditions has been integrated into our code. By using the experimental data from the existing literature, the present model is verified, and then is employed to investigate the flow distribution in parallel vertical upward pipes affected by both the manifolds and the heat load. It is found that a critical mass velocity (G_cr) exists under supercritical pressure conditions, which is much similar to the cases at subcritical pressure conditions. The value of G_cr increases with the pressure under both subcritical and supercritical pressure conditions. The average of G_cr at supercritical pressure conditions is about 1.5-2 times that at subcritical pressure conditions in the range of pressure from 13 MPa to 31 MPa. (C) 2017 Elsevier Ltd. All rights reserved.
The thermo-acoustic instability and heat transfer coefficients of a kerosene kind endothermic hydrocarbon fuel were experimentally investigated in a horizontal mini tube at supercritical pressure. The test section was...
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The thermo-acoustic instability and heat transfer coefficients of a kerosene kind endothermic hydrocarbon fuel were experimentally investigated in a horizontal mini tube at supercritical pressure. The test section was a 316 stainless steel tube with a length of 240 mm and an inner diameter of 1.60 mm. Experiments were conducted at pressures of 2.5-4.0 MPa, mass fluxes of 800-1200 kg/m(2)-s, and heat fluxes of 665-950 kW/m(2). The relative standard deviation (RSD) of pressure drop was used to evaluate the intensity of thermo-acoustic instability. The correlation between heat transfer coefficient and the oscillation intensity was discussed. The results indicate that the periodic decrease in wall temperature is accompanied by synchronous increases in the outlet bulk temperature and pressure drop during oscillation. Thermo-acoustic oscillation is more pronounced at lower mass flux, lower pressure, or higher heat flux. The instability disappears when the inlet bulk temperature exceeds a threshold value. In the oscillation region, the heat transfer coefficient is positively correlated with the oscillation intensity. Heat transfer deterioration will occur at the stable boundary between the oscillation region and the stable region. A dimensionless criterion is obtained to evaluate the stable boundary of thermal-acoustic oscillation.
In this work, a series of experiments on circulatory flash vaporization of 10% and 20% NaCl solution was performed. The heat transfer characteristics in circulatory flash vaporization under different experimental cond...
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In this work, a series of experiments on circulatory flash vaporization of 10% and 20% NaCl solution was performed. The heat transfer characteristics in circulatory flash vaporization under different experimental conditions were presented. The non-equilibrium fraction of circulatory flash vaporization (NEF) was adopted to describe the extent of flash vaporization process completion. A volumetric heat transfer coefficient of circulatory flash vaporization (h(v)) was introduced in the present study to evaluate the heat flux evolution from per unit volume of liquid pool under unit superheat degree. Moreover, the influences of superheat degree, pressure of flash evaporator, initial liquid level, circulating flow rate and concentration of NaCl solution on the volumetric heat transfer coefficient were also analyzed. Results suggested that the volumetric heat transfer coefficient increased with the superheat degree and flash chamber pressure. Lowering the initial liquid level and brine concentration promoted the heat transfer intensity. And Nusselt number of circulatory flash vaporization Nu(A) was proposed to describe the heat transfer performance of circulatory flash vaporization according to the definition of volumetric heat transfer coefficient. Moreover, a correlation between Nusselt number of circulatory flash vaporization and dimensionless parameters was obtained with the relative error between -31.1% and 32.8% for 1.5 <= Delta T <= 20 K, 400 <= Q <= 1200 L h(-1), 7.4 <= P-f <= 31.2 kPa and 0.05 <= f(m) <= 0.2.
A steam-water injector (SI), which is a passive jet pump, has been widely used in various industries. In the present work, exergy analysis models of a centered water nozzle SI were developed based on experiments to ev...
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A steam-water injector (SI), which is a passive jet pump, has been widely used in various industries. In the present work, exergy analysis models of a centered water nozzle SI were developed based on experiments to evaluate the performance of SI. The thermodynamic perfect degree of SI was found to be not so bad, and exergy efficiency was within the range of 18%-45%. In general, SI is used to work as a pump. However, exergy analysis can only evaluate the thermodynamic perfect degree of SI, but cannot evaluate its lifting-pressure performance. Therefore, thermo-mechanical exergy was divided into temperature-based exergy and pressure-based exergy in the present work, and the pressure-based exergy analysis was introduced. Such analysis was determined to be more reasonable than exergy analysis for a passive jet pump and helpful for achieving optimal SI design. Moreover, the effects of physical and geometric parameters on exergy efficiency and pressure-based exergy efficiency were investigated experimentally, and several optimal values for these geometric parameters were found. Finally, the distributions of exergy losses in separate parts of SI, particularly inevitable exergy losses, were evaluated. These analyses will be helpful in eliminating the effects of inevitable factors and in identifying the key factor, thereby considerably improving SI performance.
Entropy generation analyses on the transient processes of heat exchangers can guide their designs and operations. A dynamic model of a typical recuperative heater is developed based on mass, energy, and momentum conse...
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Entropy generation analyses on the transient processes of heat exchangers can guide their designs and operations. A dynamic model of a typical recuperative heater is developed based on mass, energy, and momentum conservation equations. Dynamic behaviors of the heater during transient processes are analyzed based on the second law of thermodynamics. The real-time entropy generation rate due to the heat transfer between the work medium and metal surfaces, and the heat conduction in metals are presented and discussed. A cold fluid flow rate with 20% step increase is adopted as the boundary disturbance, and dynamic performances are obtained. Additional entropy is generated in the heater during the transient processes compared with stationary work conditions. Several design and operation factors of the heater are discussed. Calculation results show that the additional total entropy generation diminishes during the transient processes with the increase in the thermal diffusivity of metal. This rule is also suitable for the influence of thermal transfer resistance between the fluid and metal. By contrast, the metal thickness and specific heat capacity of hot work fluid have opposite influences on the total additional entropy generation of the heater during the transient processes. (C) 2018 Elsevier Ltd. All rights reserved.
Surfactants are widely used in the manipulation of drop motion in microchannels, which is commonly involved in many applications, e.g., surfactant assisted oil recovery and droplet microfluidics. This study is dedicat...
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Surfactants are widely used in the manipulation of drop motion in microchannels, which is commonly involved in many applications, e.g., surfactant assisted oil recovery and droplet microfluidics. This study is dedicated to a crucial fundamental problem, i.e., the effects of a soluble surfactant on drop motion and their underlying mechanisms, which is an extension of our previous work of an insoluble-surfactant-covered droplet in a square microchannel [Z. Y. Luo, X. L. Shang, and B. F. Bai, "Marangoni effect on the motion of a droplet covered with insoluble surfactant in a square microchannel," Phys. Fluids 30, 077101 (2018)]. We make essential improvements to our own three-dimensional front-tracking finite-difference model, i.e., by further integrating the equation governing surfactant transport in the bulk fluid and surfactant mass exchange between the drop surface and bulk fluid. We find that the soluble surfactant generally enlarges the droplet-induced extra pressure loss compared to the clean droplet, and enhancing surfactant adsorption tends to intensify such an effect. We focus specifically on the influences of four soluble-surfactant-relevant dimensionless parameters, including the Biot number, the dimensionless adsorption depth, the Damkohler number, and the bulk Peclet number. Most importantly, we discuss the mechanisms underlying the soluble surfactant effect, which consists of two aspects similar to the insoluble case, i.e., the reduced surface tension to decrease droplet-induced extra pressure loss and the enlarged Marangoni stress playing the opposite role. Surprisingly, we find that the enlarged Marangoni stress always makes the predominant contribution over the reduced surface tension in the effects of above-mentioned four soluble-surfactant-relevant dimensionless parameters on drop motion. This finding explains why the droplet-induced extra pressure loss increases with the film thickness, which is opposite to that observed for clean droplets. Publish
Heat transfer in gas-solid flows has been numerically investigated via an immersed boundary-thermal lattice Boltzmann method. Stationary random assemblies of spheres are adopted in the simulations. The effect of parti...
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Heat transfer in gas-solid flows has been numerically investigated via an immersed boundary-thermal lattice Boltzmann method. Stationary random assemblies of spheres are adopted in the simulations. The effect of particle velocity fluctuations whose magnitude is represented by the so-called granular temperature is accounted for by implementing velocity fluctuations obeying the isotropic Maxwellian distribution on spheres. It is found that particle fluctuations enhance the heat transfer between the gas and solid phases. This enhancement increases with increasing granular temperature-based Reynolds number and becomes less significant as the particle Reynolds number and the solid volume fraction increase. It is also found that the Nusselt numbers on individual particles follow the Log-Normal distribution at both zero and finite granular temperature conditions. The long tail of this distribution is caused by the existence of a non-negligible portion of the domain with fast local gas velocities that could significantly promote heat transfer. (C) 2019 Elsevier Ltd. All rights reserved.
Steam jet condensation through multi-hole nozzles in a pressure relief pool is important for the design and safe operation of a nuclear reactor system. In this study, stable steam jet condensation through a double-hol...
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Steam jet condensation through multi-hole nozzles in a pressure relief pool is important for the design and safe operation of a nuclear reactor system. In this study, stable steam jet condensation through a double-hole nozzle was investigated at different water temperatures and steam pressures by CFD method. Simulation results indicated that the shape of steam cavity changed from conical to ellipsoidal with an increase in water temperature and steam pressure, and steam jet length gradually increased. Meanwhile, the interaction between two steam cavities was enhanced and they even merged under certain conditions. Expansion and compression waves were found by analyzing the thermal hydraulic parameters along the hole centerline. Water temperature and steam pressure exerted different effects on the intensity of expansion/compression waves and the positions of maximum expansion/compression. Finally, thermal hydraulic parameters along the nozzle centerline were analyzed. Steam volume fraction, temperature, and velocity initially increased and then decreased as axial distance increased, which appeared as evident peaks under the present conditions. When water temperature and steam pressure increased, the peak values of steam volume fraction, temperature, and velocity gradually increased and their positions moved downstream. (C) 2018 Elsevier Ltd. All rights reserved.
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