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Based on Recursive Radial Basis Function (RRBF) neural network, the Reduced Order Model (ROM) of compressor cascade was established to meet the urgent demand of highly efficient prediction of unsteady aerodynamics performance of turbomachinery. One novel ROM called ASA-RRBF model based on Adaptive Simulated Annealing (ASA) algorithm was developed to enhance the generalization ability of the unsteady ROM. The ROM was verified by predicting the unsteady aerodynamics performance of a highly-loaded compressor cascade. The results show that the RRBF model has higher accuracy in identification of the dimensionless total pressure and dimensionless static pressure of compressor cascade under nonlinear and unsteady conditions, and the model behaves higher stability and computational efficiency. However, for the strong nonlinear characteristics of aerodynamic parameters, the RRBF model presents lower accuracy. Additionally, the RRBF model predicts with a large error in the identification of aerodynamic parameters under linear and unsteady conditions. For ASA-RRBF, by introducing a small-amplitude and high-frequency sinusoidal signal as validation sample, the width of the basis function of the RRBF model is optimized to improve the generalization ability of the ROM under linear unsteady conditions. Besides, this model improves the predicting accuracy of dimensionless static pressure which has strong nonlinear characteristics. The ASA-RRBF model has higher prediction accuracy than RRBF model without significantly increasing the total time consumption. This novel model can predict the linear hysteresis of dimensionless static pressure happened in the harmonic condition, but it cannot accurately predict the beat frequency of dimensionless total pressure.

Liquid Droplet Radiator (LDR) system is regarded as a quite promising waste heat rejection system for aerospace engineering. A comprehensive review on the state-of-the-art of LDR system was carried out. The thermal design considerations of crucial components such as working fluid, droplet generator and collector, intermediate heat exchanger, circulating pump and return pipe were reviewed. The state-of-the-art of existing mathematical models of radiation and evaporation characteristics of droplet layer from literatures were summarized. Furthermore, thermal designs of three LDR systems were completed. The weight and required planform area between the rectangular and triangular LDR systems were respectively compared and the evaporation models for calculating the mass loss were evaluated. Based on the review, some prospective studies of LDR system were put forward in this paper.

Soft pneumatic actuators (SPAs) that can twist dominantly provide a promising solution for the design of soft robots due to their flexibility, compliance, and easy fabrication. However, the torsional SPAs also face challenges such as overpressure risk and small torsion angle. To tackle those challenges, a new type of torsional SPAs is designed based on the reversible, cooperative buckling of elastomer, which yields a torsion angle of 1.94 deg/mm and an output torque of 26 N .mm with a secure operation pressure. Moreover, this actuator can achieve a wide range of torsional motion by varying the structure parameters, including the height of actuators and the pitch of helical chambers. The relationship between structure parameters and actuator performance is investigated experimentally, and experimental results show that the torsion angle and output torque increase with the height growing from 20 to 44 mm, while decrease with the pitch rising from 75 to 150 mm. The effect of different materials used for constructing the actuator is also studied numerically, and results show that the output torque can be improved by changing the materials. Additionally, several soft machines constructed by utilizing the actuators as a torsional joint are able to perform different manipulating tasks, such as screwing the light bulb, grasping and rotating objects. The actuator developed in this paper is capable of extending the researches on SPAs and offering an alternative for the actuation of soft machines.

Free surface vortex, especially in a pattern of full air core vortex, causes serious security problems in the residual heat removal system. Vortex in a T-junction pipe system was numerically investigated under the premise that the simulation results are in agreement with the experimental results. First, four typical states were obtained in the formation and evolution process of vortex, namely, surface dimple, critical submergence state, air entrainment vortex state, and large air entrainment state. With increasing Froude (Fr) number, the time from an initiate flow field to the critical submergence state decreased, and the time interval between critical submergence state and large air entrainment state increased. Finally, the variation law of vortex intensity was analyzed during the evolution process. The vortex intensity initially increased with time and reached its maximum value and then decreased until it reached a minimum value before the large air entrainment state. With the increase of Fr, the maximum values of vortex intensity gradually increased.

The condensation induced water hammer (CIWH) phenomenon may cause serious damage to the pipes and related system, which often occurs during the steam-water direct contact condensation process. In this paper, an experimental investigation was performed to study CIWH phenomenon caused by steam-water direct contact condensation in a horizontal pipe. The entire CIWH process was captured by a high speed video camera and its pressure fluctuation was synchronously measured. Four typical flow patterns were observed during CIWH process: stratification flow, wave flow, slug flow and bubble collapse. Bubble collapse would generate a high pressure peak. Based on different variations of steam-water phase interface and pressure fluctuation signals, three types of CIWH were defined: non-periodic CIWH, periodic CIWH and no CIWH. A CIWH region map was given considering the effect of steam mass flux and water temperature. In periodic CIWH region, the generation frequency of CIWH was found to range from 0.19 Hz to 0.39 Hz, which decreased with the rise of steam mass flux and water temperature. A dimensionless correlation was obtained to predict Strouhal number of CIWH generation frequency. Predicted values corresponded well to the experimental data with the deviation in the range of −16% to +23%.

Transient numerical study was performed to investigate the characteristics of interphase heat transfer in unstable steam jet under different operating conditions. Bubble radius change rate, interfacial heat transfer coefficient and overall condensation mass flux reached their maximum values during the bubble necking stage. The maximum peak value of interfacial heat transfer coefficient and bubble radius change rate decreased with the decrease of inlet pressure differential and water subcooling. The peak values of interfacial heat transfer coefficient and internal velocity were found in the bubble neck region. The effect of interphase heat transfer on bubble growth and necking stages was analyzed on the basis of overall force balance. Momentum force played a major role during the bubble growth stage, and the condensation force had a dominant effect on bubble necking stage. Condensation force first decreased and reached its minimum value during bubble rapid necking stage. Subsequently, the condensation force rapidly increased and promoted the movement of bubble necking. Moreover, the condensation force curves under different conditions had the same change law.

Submerged steam jet condensation is widely applied in various fields because of its high heat transfer efficiency. In this paper, sonic steam jet condensation through a double-hole nozzle was numerically researched. First, the effect of L/D (pitch to diameter) on steam plumes was investigated. When L/D increased from 1.2 to 2.5, two steam plumes transformed from merging into one steam plume to being independent. Besides, thermal hydraulic parameters along radial directions were analyzed, revealing the existence of expansion and compression waves. Radial distributions of steam volume fraction, temperature and velocity were all largely symmetric about nozzle centerline and there all existed minimum values at nozzle centerline position. Finally, the effect of L/D on thermal hydraulic parameters of nozzle centerline was obtained. There existed peak values for steam volume fraction, temperature and velocity of nozzle centerline at one position. As L/D increased, the peak value decreased and its position moved downstream.

Nuclear safety has attracted increasing global attention. Passive Containment Cooling System (PCCS) is one of the several passive safety systems designed to ensure the safety of nuclear power plants (NPPs). A large-scale test facility was built to simulate the PCCS for understanding the thermal–hydraulic characteristics with operating conditions in the start-up process. Parameter analysis is carried out to reveal the influences of various parameters on the thermal–hydraulic characteristics. Results show that the transient-state performance of the PCCS strongly depends on the initial containment pressure and air mass fraction. The air mass fraction has a greater effect on the transient heat transfer process. Meanwhile, the effect of cooling water temperature on the transient characteristics can be ignored. The response time, which is defined to characteristic the heat transfer ability of PCCS, is proposed. In addition, a non-dimensional empirical correlation for response time is developed to reveal the relationship between the heat transfer capacity of the natural circulation and forced circulation, while the deviation mostly within ± 20%. Studies on the relevant physical processes or phenomena are helpful for the safety analysis or accident study related with PCCS.

The operational flexibility of combined heat and power (CHP) units is highly required owing to the high penetration level of intermittent renewable power. Traditional CHP units should run in heat-controlled mode, which limits their operational flexibility. Therefore, the heat–power decoupling of CHP units is necessary. In this study, steam ejectors are used in designing low-cost and highly efficient heat–power decoupling systems with simple structures. Three new CHP systems integrated with ejectors are proposed, and multiple system parameters are optimized. The heat–power decoupling performances and energy consumption characteristics of the three reformed systems are also compared. Results show that all three reformed systems can achieve heat–power decoupling, and System II (coupled with two ejectors in series) has the largest peak-load regulating capacity (ΔPe) of 94.8 MW. System III (coupled with two ejectors in parallel) shows the best energy and exergy efficiencies. Compared with the Basic System, System III can enhance energy efficiency by 13.47% and the exergy efficiency by 13.46% at ΔPe of 40 MW. This study provides a promising approach for utilizing steam ejectors in enhancing flexibility for CHP plants.

Supersonic ejectors involve very complex phenomena such as interaction between supersonic and subsonic flows, shock trains, instabilities, which strongly influences the performance of super...

Computational fluid dynamics (CFD) technique is employed to investigate the effect of primary nozzle structures on the supersonic ejector performance. The performance of the supersonic ejectors with three different nozzle structures, including conical nozzle, petalage nozzle and crenation nozzle, have been compared under the same conditions. Compared with the ejector equipped with the conical nozzle, the entrainment ratio of petalage nozzle is slightly smaller, while the critical back pressure increases by 5.2%. Just the opposite, the entrainment ratio of crenation nozzle is slightly higher, and the critical back pressure would decrease by 2.1%. In addition, the effects of primary/induced fluid pressure on the flow field (pressure and Mach number along the ejector centerline) are observed and analyzed to explain the mixing process occurring inside the ejector. It finds out that the shape of the mixing layer in the supersonic ejector with different nozzles is different.

Three-dimensional steady method was employed to simulate the process of stable supersonic steam jet condensed into a water pool. A thermal equilibrium phase change model was inserted into Ansys as a user defined function to simulate the condensation process. To testify the correctness of simulation model, steam plume and radial temperature distribution were compared between experiment and simulation. Then four kinds of steam plume shapes, including contraction, expansion-contraction, double-expansion-contraction, and contraction-expansion-contraction shapes, were observed from numerical results as experimental results indicated. Combined with the corresponding contours of steam void fraction, the distribution of axial thermodynamic parameters, such as pressure, temperature and velocity were analyzed for each kind of steam plume. The theory of expansion and compression wave was employed to explain the flow mechanism in each kind of steam plume.

The ejector refrigeration integrated in the air-conditioning system is a promising technology, because it could be driven by the low grade energy. In the present study, a theoretical calculation based on the real gas property is put forward to estimate the ejector refrigeration system performance under overall modes (critical/sub-critical modes). The experimental data from literature are applied to validate the proposed model. The findings show that the proposed model has higher accuracy compared to the model using the ideal gas law, especially when the ejector operates at sub-critical mode. Then, the performances of the ejector refrigeration circle using different refrigerants are analyzed. R290 and R134a are selected as typical refrigerants by considering the aspects of COP, environmental impact, safety and economy. Finally, the ejector refrigeration performance is investigated under variable operation conditions with R290 and R134a as refrigerants. The results show that the R290 ejector circle has higher COP under critical mode and could operate at low evaporator temperature. However, the performance would decrease rapidly at high condenser temperature. The performance of R134a ejector circle is the opposite, with relatively lower COP, and higher COP at high condenser temperature compared to R290.

Melt drop collision is an important phenomenon in the circumstance of pressure wave propagation during fuel–coolant interaction (FCI). The deformation and fragmentation of melt drops can increase the contact area with coolant, and as a result will affect the heat transfer and melt oxidation. In this study, a numerical model was established by considering surface tension and validated with the experimental results that were obtained from water droplet collision in gaseous environment. Then, the head-on collision of two UO2 melt drops in water pool was investigated at different Weber numbers, and the melt morphology, contact area, and the number and size distribution of children droplets were analyzed. The results show that interfacial waves and wrinkles could be clearly observed on the melt film, and the finger structures presented at the rim of melt film and finally separated into children melt droplets. The increase of fuel–coolant contact area could be divided into the inducements by deformation and fragmentation. The melt deformation only had influence to the area increase at intermediate process but no effect to that at steady state. By contrast, the final fuel–coolant contact area was determined by the intensity of melt fragmentation. The size distribution of melt children droplets was like an off-centered normal distribution, where the maximum number of children droplets existed in the size range of 0.03

Submerged steam jet condensation is widely applied in various fields because of its high heat transfer efficiency. Condensation oscillation is a major character of submerged steam turbulent jet, and it significantly affects the design and safe operation of industrial equipment. This study is designed to reveal the mechanism of the low-frequency pressure oscillation of steam turbulent jet condensation and determine its affected region. First, pressure oscillation signals with low frequency are discovered in the downstream flow field through oscillation frequency spectrogram and power analysis. The oscillation frequency is even lower than the first dominant frequency. Moreover, the critical positions, where the low-frequency pressure oscillation signals appear, move downstream gradually with radial distance and water temperature. However, these signals are little affected by the steam mass flux. Then, the regions with low-frequency pressure oscillation occurring are identified experimentally. The affected width of the low-frequency pressure oscillation is similar to the turbulent jet width. Turbulent jet theory and the experiment results collectively indicate that the low-frequency pressure oscillation is generated by turbulent jet vortexes in the jet wake region. Finally, the angular coefficients of the low-frequency affected width are obtained under different water temperatures. Angular coefficients, ranging from 0.2268 to 0.2887, decrease with water temperature under test conditions.

Increasing production and recovery from low-pressure natural gas fields in China is highly desirable. A two-stage ejector (TSE) is proposed to deal with this situation. The effect of the second stage geometrical factors (area and length to diameter ratios) on the TSE performance is analyzed through the numerical technique, as well as the operational factors. Results show that the improvement effect becomes larger under relatively larger induced pressure and area ratio. However, choosing a lower area ratio is more suitable because its performance is superior at low induced pressure. An optimal length to diameter ratio exists for the maximum entrainment ratio, and it varies with operational factors. In the present study, it's a good choice when the length to diameter ratio equals to 5. TSE has better entrained capacity compared than single stage ejector, when the primary or induced pressure is higher than the design value. Meanwhile, TSE has better entrained capacity when the pressure of the first stage induced inlet is higher than that of second stage induced inlet.

The effect of air with low mass fraction on the oscillation intensity and oscillation frequency of a submerged steam jet condensation is investigated under stable condensation region. With air mixing in steam, an obvious dynamic pressure peak appears along the jet direction. The intensity peak increases monotonously with the rise of steam mass flux and water temperature. Peak position moves downstream with the rise of air mass fraction. Moreover, when compared with that of pure steam jet, the oscillation intensity clearly decreases as air is mixed. However, when water temperature is lower than approximately 45 °C, oscillation intensity increases slightly with the rise of air mass fraction, and when water temperature is higher than 55 °C, the oscillation intensity decreases greatly with the rise of air mass fraction. Both the first and second dominant frequencies decrease with rise of air mass fraction. Finally, effect of air mass fractions on the oscillation power of the first and second dominant frequency bands shows similar trends. Under low water temperature, the mixed air has little effect on the oscillation power of both first and second frequency bands. However, when water temperature is high, the oscillation power of both first and second frequency bands appears an obvious peak when air mass fraction is about 1%. With further rise of air mass fraction, the oscillation power decreases gradually.

The condensation oscillation of submerged steam was investigated theoretically and experimentally at the condensation oscillation regime. It was found that pressure oscillation frequency was consistent with the bubble oscillating frequency and there was a quasi-steady stage when bubble diameters remained constant. A thermal-hydraulic model for the condensation oscillation regime was proposed based on potential flow theory, taking into account the effects of interface condensation and translatory flow. Theoretical derivations indicated that oscillation frequencies were mainly determined by bubble diameters and translatory velocity. A force balance model was applied to the calculation of bubble diameters at quasi-steady stage, and the oscillation frequencies were predicted with the calculated diameters. Theoretical analysis and experimental results turned out that oscillation frequencies at the condensation oscillation regime decreased with the increasing steam mass flux and pool temperature. The predicted frequencies corresponded to the experimental data well with the discrepancies of ±21.7%.

This paper deals with an exergetic analysis of the flue gas pre-dried lignite-fired power system (FPLPS) based on the boiler with open pulverizing system (OPSB) to explore the energy-saving potential of the FPLPS. A steady-state simulation was performed to obtain thermodynamic properties of process streams in a 600 MW unit. Results indicated that the plant efficiency of the FPLPS was relatively 3.42% higher than that of the conventional lignite-fired power system (CLPS). The improvement benefited from the integration of the flue gas dryer with the OPS, in which the dryer exhaust gas was separated from coal powders and prevented from recycling in the furnace. Consequently, the exergy destruction in the combustion process was reduced by 2.32%-pts for increased flame temperature, and the exergy loss of the boiler exhaust gas was reduced by 0.68%-pts for decreased temperature. Moreover, the dryer exergy efficiency was only 20.20% due to considerable exergy destructions in the moisture evaporation and the mixing of drying agents. The proposed retrofitting option by extracting cold flue gas from the economizer outlet could increase the plant efficiency by 0.33% relatively. Finally, attempts were made to examine the influence of varying pre-drying parameters on system performances.

An experimental study was conducted to investigate the condensation regime and pressure oscillation characteristics of vertical upward steam jet condensation with low mass flux. Steam mass flux and water temperature were 8.34–16.71 kg/(m2·s) and 40–85 °C, respectively. Steam bubble behavior, pressure oscillation amplitude and frequency were recorded and analyzed. Four typical regimes were found, namely, chugging, detached oscillatory, detached cracked and secondary bubble impinged regimes. A bubble condensation region map was developed by considering the effects of steam mass flux and water temperature. The average amplitude of pressure oscillation initially increased, and then decreased as water temperature increased. It reached its maximum value when water temperature was approximately 60–65 °C, which was the transition temperature range from the chugging regime to the detached oscillatory regime. Meanwhile, the frequency of pressure oscillation was within the range of 12–28 Hz. These values were higher than those for a vertical downward steam jet with the same steam mass flux and water temperature. A dimensionless correlation was obtained to predict the Strouhal number of pressure oscillation frequency. The predicted values corresponded well with the experimental data. The deviation was within the range of –9.12% to +8.30%.

Condensation oscillation of steam jet is of high importance for industrial facility. In this study, the mechanism and propagation characteristic of the second dominant frequency is investigated. Firstly, the second dominant frequency is found under all the test conditions based on frequency spectrum. The second dominant frequency decreases with the rise of water temperature and steam mass flux. Then, the second dominant frequency is proved to be generated by the separated steam bubbles oscillation based on the bubble oscillation theory. And the theoretical oscillation frequency equation of separated steam bubble is used to predict the second dominant frequency, the predicted deviation ranges from −17% to 6%. Furthermore, the propagation characteristic of the second dominant frequency is investigated, and a theoretical propagation equation for the second dominant frequency is derived. Then, the axial and radial distribution characteristic of oscillation amplitude and energy of the second dominant frequency are analyzed and researched. In the downstream flow field and the radial direction, the propagation characteristic of steam bubble oscillation wave is well corresponding to the predicted results. However, in the upstream flow field, due to the effect of steam plume, the oscillation amplitude and energy of the second dominant frequency attenuate rapidly and the experimental data are much smaller than the predicted value.

In order to improve the energy utilization efficiency of thermal power plants and to solve the heating shortage problem in China, the absorption heat pump is usually employed to recover the heat of turbine exhaust steam for heating supply. In the existing references, few researchers considered the heating load characteristics when designing the recovery system. In this paper, the design thought of heat recovery system of turbine exhaust steam using absorption heat pump for heating supply based on heating load characteristics was presented. With an engineering case, the heat recovery system was designed and its economic efficiency was calculated.

The effect of nozzle structure on the steam jet lengths of submerged condensation in quiescent water is investigated theoretically and experimentally. Two typical nozzles are analyzed and tested. Theoretical analysis shows that nozzle structure has a great influence on the steam jet length but was paid little attention before. Then a theoretical model for steam jet length with different nozzle structures is proposed based on the expansion and compression wave theory. Theoretical model indicates that steam jet length is greatly affected by nozzle structure. The steam jet length of straight pipe nozzle is longer than that of orifice nozzle under the same pool water temperature and steam mass flux, and the steam jet length is inverse proportion to the maximum expansion ratio, approximately. Then the theoretical model is verified by the experimental results. Finally, a universal semi-empirical correlation considering the nozzle structure is proposed. The prediction length corresponds to the experimental data very well and the discrepancy is within ±25% for different nozzle structures for the steam mass flux 400–800 kg·m−2·s−1 and water temperature 10–70 °C.

Based on the preliminary validation of the numerical results with an experiment, the steady results of different tip clearance size effects on the performance and tip leakage vortex of counter-rotating compressor were discussed. The predicted results showed that the stable margin and isentropic efficiency of the counter-rotating compressor decreased with increasing of the tip clearance size. Furthermore, increasing the tip clearance size had a greater negative effect on the performance of the upstream rotor than the downstream rotor. Detailed flow field analyses further demonstrated that the unstable flow occurred in the two counter-rotating rotors with greater tip clearance size. The rotor downstream was the main unstable factor which caused the counter-rotating compressor to breakdown when a smaller tip clearance size was used.

highlights � The performance and flow field inside ejectors are studied numerically and experimentally. � The pressures before the second shock position remain constant during the critical mode. � NXP has an optimal value for entrainment ratio, but no effect on the critical discharged pressure. abstract The present paper performs experimental and numerical investigations on the global performance and internal flow of a supersonic air ejector. The effects of operation parameters and geometrical factor on the air ejector performance have been analyzed. The results show that: the static wall pressure and axisymmetric line static pressure remain constant in critical mode under different discharged pressures, but they both increase in sub-critical mode with the increase of the discharged pressure. The shock position of the mixed fluid moves upstream in critical mode. The second shock position disappears in sub-critical mode. The experimental and numerical results indicate that there exists an optimal nozzle exit position (NXP) corresponding to maximum entrainment ratio, but the critical value of discharged pressure is almost independent of NXP.

Characteristics of NVH (Noise, vibration and harshness) in twin screw refrigeration compressors, mainly caused by mechanical vibration and turbulent gas flow, are discussed in detail. According to the different generation mechanism, suppression methods of mechanical NVH and hydrodynamic NVH are proposed, respectively. Mechanical NVH is related to rotor profile, bearings, lubricating conditions and maching precision, while hydrodynamic NVH is inevitable and severe for all positive displacement compressors due to gas compression and turbulent flow. Concluded from three cases of NVH suppression for semi-hermetic twin screw refrigeration compressors, half-wave method based on acoustic interference theory, pulsation damper evolving from Helmholtz resonator and broadband perforated tube silencer are effective paths to alleviate hydrodynamic NVH in twin screw refrigeration compressors without bringing in extra energy losses.

Increasing production and recovery from the mature oil and gas fields often requires a boosting system when the gas pressure is lower than that demanded by the transportation or process system. The supersonic ejector, considered to be a cost-effective way to boost the production of a low-pressure gas well, was introduced into the industrial field. However, the exploitation of natural gas often accompanies with water. The computational fluid dynamics (CFD) technique was employed to investigate the two-phase effect (water droplets) on the performance of natural gas ejector for the motive pressure ranging from 11.0 MPa to 13.0 MPa, induced pressure from 3.0 MPa to 5.0 MPa, and backpressure from 5.1 MPa to 5.6 MPa, while the injected water flow rate was less than 0.03 kg s−1. The numerical results show that the entrainment ratio of the two-phase operation was higher than that of the single-phase operation with the variation of backpressure. Meanwhile, the entrainment ratio increased with the increase of injec...

Supersonic ejectors are applied to increase production and recovery from mature oil and gas fields.Compared to compressors, natural gas ejectors are a cost-effective way to boost the production of lowpressure natural gas wells. In this study, two main ejector geometrical factors, the primary nozzle exitposition (NXP) and the mixing tube length to diameter ratio (R), are investigated based on the CFDtechnique. Additionally, these two geometrical factors are proved to be influential factors with respect toejector performance, including not only the entrainment ratio but also the pressure ratio. The numericalresults show that the optimum NXP for the entrainment ratio varies from 3.6 to 7.2 mm, but for thepressure ratio, it is in the range of 1.2e7.2 mm. The optimum value R decreases with increasing primaryflow pressure, and the optimum R for the entrainment ratio varies from 2 to 8, but for the pressure ratio,it is in the range of 3e7. The CFD technique is found to be an effective performance predictor and alsoprovides an insightful understanding of the flow and mixing process within the ejector. This study mayprovide a beneficial reference for the design of supersonic ejectors and may be helpful for further ap-plications in boosting natural gas production. 2013 Elsevier Ltd. All rights reserved.

This paper proposes a new 1D model to predict ejector performance at critical and sub-critical operational modes, while most previous 1D models have only predicted ejector performance at critical mode operation. Constant pressure mixing is assumed to occur inside the constant area section of the ejector at critical and sub-critical mode operation, and the effectiveness of the model is verified against four sets of experimental data that include different working fluids and geometries. The results show that the proposed model accurately predicts ejector performance over all ranges of operation, and is a useful tool for predicting ejector performance within larger refrigeration cycle models.

Steam discharged into subcooled water is investigated experimentally to demonstrate the direct contact condensation phenomena in nuclear reactor safety system and underwater propulsion apparatus. The steam jet condenses to various shapes at different thermal hydraulic conditions. A condensation regime diagram is drawn to classify the regime for different flow patterns, among which there are three typical shapes of steam plume characterizing the chugging, condensation oscillation, stable condensation regime (Figure 1). The flow region can be separated into three parts—vapor, water and two-phase regions, and the white patch in the image indicating the two-phase region is a mixture of condensed vapor and subcooled water. Three typical stages of bubble motions—growth (subimage 1 to 6, Figure 2), necking (subimage 7 to 10, Figure 2), and detachment (subimage 11 to 13, Figure 2)—are demonstrated. The bubble diameter reaches the maximum at the necking stage and remains approximately invariant with the connecting neck prolonging for a period. A series of sequent photos exhibits shape transformations at the stable condensation regime, implying that the steam plume grows and shortens periodically due to comprehensive effects of injection, viscosity damping and condensation (Figure 3). The dimensionless penetration length, defined as the ratio of penetration length to nozzle diameter, is in the range of 8.23–11.67 in the Figure 3. The majority of previous literatures present the average dimensionless penetration length which is closely related with time-averaged heat transfer characteristic. However, variations of steam plume are proven to account for pressure oscillation phenomena by the transient visualization investigations, in which the first dominant frequency acquired from the FFT domain graph of pressure signal is consistent with the period of steam plume variations. The second dominant frequency is verified to be caused by oscillations of detached bubbles (subimage 8 and 9, Figure 3) in the research.

When the ejector was applied in the natural gas exploitation and sea water desalination industries, the ejector always operated on the two phase operation, because of the primary fluid or the induced fluid usually companying some water inside. The water inside the primary and induced gas will affect the ejector performance. In the present study, the experimental and CFD methods were used to investigate the two phase flow inside the ejector, when the water was injected into the induced flow. The results show that: when the water was injected into the induced flow, the experimental results decreased, as well as numerical results. The numerical results agreed with the experimental data, with the maximum deviations less than 20% for critical mode and less than 40% for sub-critical mode.