Quick-closing Valve Method Research Articles

Ammonia void fraction in smooth tubes at different gravity orientation

Ammonia is an environment-friendly natural refrigerant and working fluid with negligible global warming and ozone depletion. Nowadays, ammonia is widely used in industrial refrigeration systems, heat pumps and thermal control systems, including heat pipes, loop heat pipes and two-phase mechanically pumped loops. In perspective, “green” ammonia is considered an energy carrier and carbon-free fuel. In two-phase systems, the void fraction is one of the critical factors determining the frictional and local pressure losses, boiling and condensation heat transfer and phase separation. The experimental study of ammonia void fraction in tubes with inner diameters of 8.5 mm and 15 mm is proposed in this paper. The quick-closing valve method has been chosen. Three flow configurations are considered: vertical downward, vertical upward and horizontal. The tests were provided for the two-phase ammonia at a mass velocity of 50…500 kg·m−2s−1, saturation pressure of 15…30 bar, and vapour quality of 0.05…0.30. One hundred and five points have been tested. No existing single correlation predicts the ammonia void fraction well at the considered boundary conditions for at least two orientations in the gravity field. A new single correlation has been proposed based on the Rouhani drift model with the tube inclination angle-dependent distribution parameter allowing the adequate prediction of void fraction in a tube with ammonia flow at horizontal, upward and downward orientations.

Study on improvement for the prediction accuracy of natural circulation flow rate by investigating void fraction correlation

Natural circulation is a key technology for developing the molten core cooling system without an external power source from the lessons of the severe accident at Fukushima-Daiichi Nuclear Power Station. This study is devoted to quantify the void fraction which is an important parameter for the driving force of natural circulation flow, and to evaluate the effect of the void fraction correlation on the prediction accuracy of the natural circulation flow rate. Test was conducted at atmospheric pressure and room temperature, using the upward air–water two phase flow. Vertical tubes with an inner diameter of 36 and 25 mm were used as the test section. The void fraction was measured by three different methods: quick-closing valve method, pressure drop method, and conductive void-probe method. The following conclusions are obtained from this study: (1) The data of the natural circulation flow rate, void fraction and pressure drop for the upward air–water two phase flow at atmospheric pressure and room temperature were obtained to develop and verify the new model. (2) By improving the void correlation, it was found that the prediction accuracy of the natural circulation flow rate could be improved by about 10% to 5%, that is, the prediction error can be halved in the range of this study. (3) The natural circulation flow rate for 25 mm test section was saturated with increasing the air flow rate at higher air flow condition. The model cannot predict this tendency. From the point of design of the actual molten core cooling system, the model improvements in this region are necessary in the future.

Flow Characteristics of Air-Water Two-Phase Flows in a Serpentine Tube

Experiments on air-water two-phase flows in a serpentine tube consisting of vertical U-bends and circular straight pipes were carried out to discuss the flow characteristics based on the high-speed video images of the flows at various gas and liquid superficial velocities. The pipe diameter, D, and the bend radius of curvature, R, were 20 mm, i.e. the bend ratio, R/D, was unity, and the length of the straight pipe was 1500 mm. The void fraction in each section was measured by using a quick-closing valve method. As a result, the following conclusions were obtained: (1) the top and bottom U-bends cause coalescence of large bubbles and liquid slug formation, respectively, which results in enhancement of flow pattern transition between the slug and annular flows, (2) the void fraction in the downward flow is larger than that in the upward flow due to acceleration of the liquid phase and the buoyancy acting on bubbles in the downward flow, and (3) void correlations based on the drift-flux model for fully-developed flows are applicable to the void fractions in the straight pipe sections under the present experimental conditions.

Experimental investigation and new void-fraction calculation method for gas–liquid two-phase flows in vertical downward pipe

The void fraction is a key parameter of the two-phase flow in vertical downward pipes, particularly for calculating the mixture density, mixture velocity, mixture viscosity, heat transfer coefficient, and pressure gradient of the flow. Studies on two-phase flows have focused primarily on vertical upward and horizontal pipe flows, while vertical downward pipe flows have been largely neglected. Compared with the flow characteristics of the gas–liquid two-phase flow in upward pipes, those of a downward pipe flow are more complex under the interaction of the gravity, buoyancy, and inertial forces. In this study, a detailed experimental analysis of the void fraction of the gas–liquid two-phase flow in a vertical downward pipe was conducted with a pipe having an inner diameter of 20 mm. A total of 171 void-fraction data points were measured using the quick-closing valve method, and the performances of 12 commonly used correlations that do not take into consideration the flow pattern were assessed based on experimental data points. Errors were obtained on using some of the correlations for calculating the void fraction of the gas–liquid two-phase.flow in a vertical downward pipe at a low liquid superficial velocity. These models will regularly produce errors in the calculation of the void fraction, mainly because this problem is outside the scope of their application. In addition, a new model that takes into consideration the flow pattern was established based on the drift flux model; this new model overcomes the deficiencies of the conventional correlations in the calculation of the void fraction of the gas–liquid two-phase flow in vertical downward pipes at a low liquid superficial velocity. The reliability of the new method and 12 conventional correlations was assessed using 243 published data points. The mean relative errors of these correlations ranged from −21.65% to 8.65%, and the average absolute errors ranged from 8.57% to 23.17%. The results of the proposed method fit the experimental data in the literature better than those of the 12 existing correlations; the average relative error was −2.80%, and the average absolute error was 6.49%. The proposed model thus improves the prediction of void fractions of the gas–liquid two-phase flow in downward pipes.

Investigation into atomization spray blending property in heavy crude oil extraction under laboratory conditions

Abstracts In this study, the atomization blending property for heavy crude oil extraction was systematically investigated both numerically and experimentally. In the experiment conducted, the blending behavior was simulated using hydraulic oil and spray with 1:10 light phase-gas atomize volume flow rate ratio in an equipment sharing the same scale as the on-site production. A Malvern Insitec droplet size analyzer was applied for the droplet size measurement, and a quick closing valve method was applied for the phase fraction measurement. A numerical simulation combined with a population balance model and the RNG k-e model was performed under both the corresponding operating conditions and a high-pressure drop environment to further investigate the blending procedure. The results show that the atomization spray blending performs better than the equivalent pure gas lifting method with more crude oil carried at the exit. Under 0.6 m3/h light phase inlet conditions, spray blending brings 8% more heavy crude than gas lifting, and the improvement rises as inlet flow rate increases. Both a droplet and liquid film are present in the casing space before blending for the spray liquid phase. In addition, the light phase droplet diameter decreases with an increase in the inlet flow rates in the lifting pipe after blending. Moreover, the blending behavior differs under various light phase inlet flow rates, while the mixture viscosity is reduced by 50% for the atomization spray method. Each of these factors was shown to be beneficial for refining the blending used in a heavy crude oil extraction technique.

Void fraction measurement and flow regimes visualization of R134a in horizontal and vertical ID 7 mm circular tubes

Flow regimes and void fraction in horizontal and vertical round smooth tubes ID 7 mm with R134a in the adiabatic conditions (saturation temperature at 33 °C) and low mass flux (40–150 kg/m2 s for horizontal tubes and 65–115 kg/m2 s for vertical tubes) are presented in this paper. Flow regimes are captured by a high-speed camera while void fraction is measured by quick-closing valve method. The horizontal flow patterns are compared to Wojtan et al. (2005a) flow-regime map and some modifications based on visualization results are proposed. Void fraction results for both horizontal and vertical flows are compared to some widely used correlations. Influences of tube orientation and mass flux on void fraction are discussed. When the vapor quality keeps constant, void fraction of horizontal tubes is larger than that of vertical tubes. Higher mass flux also results in larger void fraction compared that of lower mass flux.

Effects of flow patterns and salinity on water holdup measurement of oil-water two-phase flow using a conductance method

Abstract This research investigates the effects of flow pattern and salinity of oil-water two-phase flow on water holdup measurement using a conductance method. Firstly, vertical upward oil-water two-phase flow experiment is conducted in a 20 mm inner diameter (ID) pipe, in which the salinities of aqueous solutions are set as 151 ppm, 1003 ppm, 2494 ppm and 4991 ppm respectively. Experimental water-cut and mixture velocity are set as 80–100% and 0.0184–0.2576 m/s. In the experiment, three different flow patterns, i.e., dispersed oil-in-water slug flow (D OS/W), dispersed oil-in-water flow (D O/W) and very fine dispersed oil-in-water flow (VFD O/W) are observed and recorded by a high speed camera. Meanwhile, we collect the response of Vertical Multiple Electrode Array (VMEA) conductance sensor excited by a sine voltage signal. The result shows that, for VFD O/W, the water holdup from VMEA sensor shows a satisfied agreement with that of quick closing valve (QCV) method under certain salinities, i.e., 1003 ppm as well as 2494 ppm. For D OS/W flow and D O/W flow characterized by dispersed oil droplets with various sizes, considerable deviations of water holdup between VMEA sensor and QCV method under four kinds of salinity aforementioned are presented. Afterward, according to experimental analysis along with theoretical deviation, it is concluded that the deviation of the measurement system reaches its minimum when reference resistance in the measurement circuit and salinity of the aqueous solution satisfy constraint conditions, and the accuracy of water holdup using the conductance method can be improved through adjusting reference resistance to match the salinity of water phase. Finally, the recurrence plot algorithm is utilized to identify typical flow patterns mentioned above and it shows satisfied results on comprehending the discrepancies among different flow patterns, demonstrating that the recurrence plot algorithm can be effectively applied in flow pattern identification regarding oil-water flows.

Investigation on the void fraction of gas–liquid two-phase flows in vertically-downward pipes

A special experimental loop is designed and constructed to study the characteristics of the void fraction of gas–liquid two-phase flow in vertically-downward pipes. The test section is made of transparent pipe with a length of 6m and an internal diameter of 25mm. The void fraction ranging from 0.1 to 0.98 widely is measured using quick-closing valve method. It is found that the range of the void fraction could be divided into three regions with different flow patterns and different relationships between the void fraction and the gas–liquid volumetric flow rate ratio. Moreover, 39 correlations for calculating the void fraction collected from present literature, are classified, and evaluated using the experimental data obtained in this study. The prediction of correlations in the literature needs to be improved when the void fraction is small.

Helical Capacitance Sensor-Based Gas Fraction Measurement of Gas–Liquid Two-Phase Flow in Vertical Tube With Small Diameter

A helical capacitance sensor for gas fraction including void fraction and volumetric void fraction measurement of gas-liquid two-phase flow in a vertical tube of 5 mm in diameter is presented in this paper. The structure of the helical capacitance sensor is optimized using a finite element method to achieve a homogeneous sensitivity field distribution. A calibration device using the quick closing valve method is designed and used to calibrate the void fraction measurement. Experiment results show that the relative error of gas fraction is less than 10%. The reason for the nonlinearity between the sensor output and gas fraction to be measured is discussed. The linear model describing the relationship between capacitance and gas fraction is obtained by removing the wall capacitance.

An investigation on void fraction of vapor–liquid two-phase flow for smooth and microfin tubes with R134a at adiabatic condition

The present paper deals with experiments and a prediction method for the void fraction of R134a vapor–liquid two-phase flow in horizontal smooth and microfin tubes in adiabatic condition. The void fraction is measured by the quick closing valve method. The smooth tube tested is 1024 mm in length and 7.52 mm in inside diameter. The microfin tube tested is 1015 mm in length and 8.86 mm in mean inside diameter; the fin height is 0.18 mm, the helix angle of fins is 25° and the total number of fins are 70. The experiments were carried out in the range of vapor quality from 1% to 96%, where the pressure was kept at 1.2 and 0.8 MPa and the mass flow rate was kept at 20 and 40 kg h −1. It is confirmed that the void fraction for smooth tube is well correlated by the Smith or the Baroczy correlations. It is also shown that the void fraction in the microfin tube is lower than that of smooth tube in any quality and the prediction results using previous correlations for smooth tube are higher than the present experimental data of microfin tube. The void fraction prediction method consisting of a stratified-annular flow model and an annular flow model is proposed. In the stratified-annular flow model, it is assumed that most of liquid flows at the bottom of the tube and all grooves are filled with additional liquid. The momentum equations are constructed for regions of vapor, main liquid flow at the bottom and additional liquid flow in grooves, respectively. These coupled equations are solved numerically. In the case of annular flow model, it is assumed that all grooves are filled with liquid uniformly. The momentum equations in the vapor and liquid flows in grooves are also solved numerically. The values of the predicted void fraction are in good agreement with experimental data in high vapor quality region, while the predicted values are slightly smaller than experimental ones in low vapor quality region.

Flow pattern and flow characteristics for counter-current two-phase flow in a vertical round tube with wire-coil inserts

Flow pattern, void fraction and slug rise velocity on counter-current two-phase flow in a vertical round tube with wire-coil inserts are experimentally studied. Flow pattern and slug rise velocity are measured visually with a video camera. The void fraction is measured by the quick-closing valve method. Four kinds of coils with different coil pitches and coil diameters are used as inserts. The presence of wire-coil inserts induces disturbance into gas and liquid flows so that the shape and motion of gas slug or bubbles in a wire-coil inserted tube are quite different from those observed in a smooth tube without insert. The bubbly flow occurs in the low gas superficial velocity region in the wire-coil inserted tube, while the slug or churn/annular flow only appears in the smooth tube without insert over the all test range. The measured slug rise velocity in the wire-coil inserted tube is higher than that in the smooth tube. With modified mean flow velocity calculated with core area, the slug rise velocity in wire-coil tube inserted is in good agreement with Nicklin's correlation. The void fraction in a wire-coil inserted tube is lower than that in a smooth tube in the range of high gas superficial velocities. By introducing a simple assumption on considering the effective flowing area, the measured void fractions in a wire-coil inserted tube are in relatively good agreement with the predicted result based on the drift flux model proposed by others with the correlation for slug rise velocity given by others when the coil pitch is dense.