High-pressure Water Flow Research Articles

Ammonia two-phase flow patterns and condensation in the inclined smooth tubes

The paper reports the experimental study of the two-phase ammonia flow patterns and condensation in the upward and downward inclined tubes. The two-phase patterns have been studied by the photography method in the transparent quartz tube of ID 7.5 mm at the inclination of −90 to 90°, saturation temperature of 35–65 °C, mass velocity of 40–160 kg m−2 s−1 and vapour quality of 0.1–0.8. The Hewitt and Roberts (1969) [19] upward pattern map in interfacial momentum flux coordinates compiled for the high-pressure steam water flows was compared with the obtained ammonia patterns, showing satisfactory qualitative correspondence. However, the transition lines quantitatively are not accurate for ammonia, especially in churn-to-slug cases. Matching the two-phase patterns and ammonia condensation HTC identified in the prior study for the smooth tubes of ID 8 and 11 mm, a so-called forced convective condensation (flow velocity dependent) domination line has been clearly shown for the upward and downward flows. This line splits the boundary conditions, providing similar condensation HTC for the horizontal and upward/downward flows independently on the expected pattern and with the essentially reduced HTC at the upward/downward configuration. The existence of the HTC maximum for the ammonia flow at the inclination of −30° was proved and quantified experimentally for the broad range of boundary conditions in the ID 8 and 11 mm tubes. Matching the identified condensation HTC and the observed flow patterns allows us to conclude that the condensation HTC maximum is mainly determined by the change of stratified-wavy pattern on a smooth stratified one.

Effects of multiple hydraulic punching for ultra-deep buried high ground stress powdered coal seam with low permeability

The high ground stress and poor gas permeability of the ultra-deep buried highland stress coal seam make it difficult for conventional unloading and permeability-increasing techniques, such as fracturing or cutting, to achieve the goal of coal seam pressure relief. This article proposes a multi-stage hydraulic punching permeability increasing scheme for the M1-7∼M1-9 gas drainage project of the powdered coal seam with highland stress (44.42 MPa) in tunnel No. 2 of Zhaotong, and studies the effect of cavity formation and gas changes caused by multiple hydraulic punching through theoretical analysis and numerical simulation methods. The gas drainage effect after multiple hydraulic punching was also monitored on-site and systematically compared with natural gas drainage and single hydraulic punching permeability-increasing techniques to determine the optimal solution for multi-stage hydraulic punching. Using the COMSOL numerical simulation software, a coal body model was established based on theoretical analysis. Boundary pressures, ideal gas pressures, and high-pressure water flow pressures were set as boundary conditions to simulate the process of hydraulic punching. The theoretical analysis and numerical simulation were then used to guide on-site experiments. The research results shows that for ultra-deep buried highland stress powdered coal seams, natural gas drainage efficiency is extremely low, and the initial effect of single hydraulic punching permeability increasing is significant, but the fast decay rate of short gas is still due to the time that the cavity formed by hydraulic punching exists. Multiple hydraulic punching effectively alleviates the gas decay rate, and the gas drainage efficiency can reach three times and 22 times that of single hydraulic punching and natural drainage techniques, respectively. When the hydraulic punching interval period is five days and the hydraulic punching frequency is three times, the gas drainage effect is optimal. Multiple hydraulic punching permeability-increasing technologies can provide reference for gas extraction in similar low permeability coal seams with highland stress. The research holds great significance in promoting efficient gas extraction and ensuring the safety construction of gas tunnels.

Fuel assemblies loading pattern optimization of pressurized water reactors using the trees social relations algorithm

Pressurized water reactors (PWR) are a type of light water nuclear reactors that constitute most nuclear power plants in the world. In PWRs, the initial coolant is water that is pumped into the reactor core with high pressure where it is heated by the energy released from nuclear fission. Then, the high-pressure hot water flows into a steam generator where its thermal energy is transferred to the water with lower pressure, and steam is generated. The steam, then, spins turbines that rotate an electrical generator to generate power. It is crucial to increase the safety of PWRs in nuclear power plants. A measure to ensure the safety of these reactors is to optimize the fuel assemblies loading (FAL) pattern. This paper presents a method to optimize the FAL pattern of PWRs by the trees social relations (TSR) optimization algorithm. The TSR algorithm is a metaheuristic algorithm inspired by the hierarchical life of trees in the jungle. The proposed method models the problem of FAL pattern optimization by the TSR algorithm. This method is practically compared with other methods. Based on the results, it outperforms similar methods in terms of the multiplication factor, power flattening, and fitness of the final solution.

Investigation of a Calibration Method of Coriolis Mass Flowmeters by Density- and Pressure-Matching Approaches for Hydrogen Refueling Stations

Hydrogen fuel cell electric vehicles are emerging as a means of transportation using renewable and carbon-free energy due to global warming and air pollution. Hydrogen fuel cell electric vehicles are typically refueled at a wide range of temperatures (−40 °C to 85 °C) in hydrogen refueling stations in accordance with globally accepted standards. Currently, there is no traceable method by which to verify and calibrate the Coriolis mass flowmeters used at hydrogen refueling stations, except for a water calibration process as a conventional method for mass flowrate calibration. To verify the hydrogen flow metering to a suitable level of accuracy under the challenging condition of high pressures and a wide range of temperatures, necessary methodologies and calibration facilities are developed in the present study. A flow measurement characteristic test of the hydrogen mass flowmeter under identical density conditions of the refueled hydrogen was conducted using the high-pressure gas flow standard system of the Korea Research Institute of Standards and Science to assess the effects on the medium and pressure of the mass flowmeter in a density-matching approach. To investigate the pressure dependence of the mass flowmeter at a hydrogen refueling station, a high-pressure water flow test was conducted in the pressure range of 2 bar to 700 bar, which is a pressure-matching approach. Finally, the KRISS Hydrogen Field Test Standard based on the gravimetric principle was developed to verify the measurement accuracy of the mass flowmeter to be used at hydrogen refueling stations for the first time in Korea.

Fabrication of robust superhydrophobic organic-inorganic hybrid coating through a novel two-step phase separation method

Artificial superhydrophobic coatings inspired by nature are expected to have extensive applications in several aspects of our daily lives once their poor mechanical and chemical durability is overcome. In this study, we developed a robust superhydrophobic organic-inorganic hybrid coating through the combination of fluorinated ethylene propylene (FEP) and aluminum dihydrogen phosphate (ADP) using a novel two-step phase separation method. An inorganic adhesive of ADP was introduced as a building block to enhance the structural robustness of the superhydrophobic coating. Carboxylated carbon nanotubes (C-CNTs) with good dispersibility in both water and ethanol were employed as emulsifiers to promote the liquid phase separation of FEP and ADP, which was beneficial for the formation of abundant microspheres in aqueous ethanol. After spraying and thermal treatment, the uniform mastoid micro-/nanostructures were formed on the coating surface due to the thermal phase separation of microspheres, which can provide excellent superhydrophobicity with a water contact angle of 162 ± 1.1° and a sliding angle of 5 ± 0.5°. The prepared coating can maintain its outstanding hydrophobicity even after 1000 abrasion cycles with sandpaper and upon jetting with high pressure water flow (200 kPa). Moreover, owing to the chemical inertness of the hybrid micro-/nanostructures, the prepared coating can provide a high level of corrosion protection against strong corrosive mediums as well as weather protection against UV radiation (300 W/m2). Therefore, it is believed that the robust organic-inorganic hybrid superhydrophobic coating prepared by facile phase separation method would present new avenues for expanding the practical applications of superhydrophobic coatings.

A comparative study on the construction methods of animal models of aortic arch dissection

Objective: To compare the effectiveness and safety of different methods to construct animal models of aortic arch dissection (AAD), and explore safe and effective methods for constructing AAD animal models. Methods: Twenty-four healthy mongrel dogs were divided into 4 groups by random number table (n=6). Group A: Venous incision needle high pressure water flow impact method; Group B: Venous incision needle non-high pressure water flow impact method; Group C: Transarterial sheath non-high pressure water flow impact method; Group D: Two-way balloon expansion combined with elastase perfusion method. Imaging examinations were performed immediately and 7 days after operation, aortic tissue biopsy and pathological staining were performed 15 days after operation to observe the formation of AAD. The operation time, aortic blood flow block time, model construction success rate, dissection tear length, postoperative survival rate and survival time of four groups of experimental dogs were collected to compare the effectiveness and safety of different construction methods. Results: There were no significant difference of the gender, age and weight between four groups of experimental dogs (all P>0.05). The operation time of four groups of experimental dogs were (111.6±8.0), (168.0±17.4), (164.4±13.9), (202.8±21.5)min, and the difference was statistically significant (F=39.973, P<0.001). The operation time of group A was significantly lower than group B, C and D (all P<0.001). The aortic blood flow block time of four groups of experimental dogs were (5.2±1.8), (19.6±3.8), (20.6±3.9), and (18.6±3.0) min, and the difference was statistically significant (all P<0.001). The aortic blood flow block time of group A was significantly lower than group B, C and D (F=27.598, P<0.001). The four groups of experimental dogs had 5, 5, 4, and 1 model were successfully constructed, respectively, and the difference was statistically significant (P=0.008). The successful rate of model construction in group A was significantly higher than that in group D (P=0.040). The dissection tear length of four groups were (14.4±3.0), (11.3±4.2), (7.0±2.3), (4.7±0.6) cm,and the difference was statistically significant (F=8.103, P=0.003). The dissection tear length of group A was significantly longer than group C, D (all P<0.05). The postoperative survival time were 15.0(10.0, 15.0), 5.0(3.0, 10.0), 3.5(1.5, 4.8), 10.0(2.8, 15.0) days, and the difference was statistically significant (χ2=7.825,P=0.036). The postoperative survival time of group A was significantly higher than group B, C (all P<0.05). There was no significant difference in the survival rate of the four groups (P=1.000). The pathological staining results showed that the elastic fiber at the tearing point of AAD was destroyed, and the elastic fiber on the outer wall of the false cavity was over-stretched, which was consistent with the pathological changes of aortic dissection. Conclusion: Transvenous incision needle high-pressure water flow impact modeling method is easy to operate. The aortic blood flow block time is short, the dissection tear length is wide, and the postoperative survival time is long, can be used as the preferred method of animal AAD model construction.

Visualization and velocity analysis of a high-speed modulated water jet generated by a hydrodynamic nozzle

• The new hydrodynamic nozzle generating self-excited water jet was tested. • The jet visualisation and determination of velocity fields was investigated. • High-pressure water flow conditions were monitored. • Knowledge of the jet velocity fields allow optimise flow numerical model. This paper deals with visualization and velocity analysis of a self-excited water jet generated by a designed prototype of hydrodynamic nozzle. The high-speed camera in combination with four high-energy pulsed LED lights and the particle image velocimetry method were tested. The influence of water pressure on the jet shape, velocity field and frequency of the self-excited jet was studied. The designed diagnostic water line consisting of pressure sensors and a turbine flowmeter was used for flow monitoring during experimental flow visualization. It was observed that the used optical equipment is suitable for velocity-frequency investigation up to 40 MPa with the maximal jet velocity 247 m/sec, 4.5 kHz oscillation frequency. The overall speed dependence of velocity on the distance downstream from the nozzle outlet (0–100 mm) decreases by 13–15% for tested pressure levels. Oscillation of self-excited jet in the 10–40 MPa pressure range is changing in range 2.5–4.5 kHz.

Graphitization damage on seamless steel tube of pressurized closed-loop of steam boiler

The pressurized closed-loop of steam boiler has been in operation for five years has experienced leakage problems at the bottom of the reducer and at the center of the tube on weldment. The metallographic analysis found that the leakage was due to the degradation of microstructure as a result of long-term overheating. The degraded microstructure of the tube boiler material dominated by graphitization. The graphitization normally applicable at 450°C, but with high-pressure water flow (90 bar) in the combination of internal stress on the tube material due to the welding process as well as the formation of the reducer, making the boiler operating temperature is sufficient to produce graphitization. The leakage occurred when the chain and accumulated graphitization happen because the cavities that covered the graphite facilitates the cracking propagation due to the presence of stresses.

Bionic optimum design of straight cone nozzle and the effectiveness evaluation of reducing fluid resistance

High-pressure water jet technology is a clean and effective approach to break, cut or clean solid materials. The nozzle’s hydraulic performance determines the efficiency and quality of the high-pressure water jet technology implementation. The fluid resistance reduction technology of bionic non-smooth surface is applied to the structural design of the straight cone nozzle successfully. The circular groove is selected as the bionic unit. The selection results in the investigation and development of a bionic straight cone nozzle with the optimum hydraulic performance. Moreover, the separated nozzle machining method is successfully implemented. A comprehensive approach that implements the orthogonal experiment, high-pressure water jets’ impact forces testing and range analysis results in the optimization of the bionic straight cone nozzle’s structure. The optimal structural parameters of the nozzle as follows: the outlet diameter is 4 mm, length-to-diameter ratio is 2.5, contraction angle is 60°, the circular groove width is 3 mm, the circular groove depth is 2 mm and the circular groove number is 2. In addition, the circular grooves are uniformly arranged on the surface of the straight cone nozzle’s internal chamber resulting in reduction of the fluid resistance effectively. Under the same experimental conditions, the impact forces of high-pressure water jets produced by the bionic straight cone nozzles are greater in comparison with the impact forces of high-pressure water jets produced by the ordinary straight cone nozzles. The average rate of fluid resistance reduction of bionic straight cone nozzles is up to 2.33%. Furthermore, the results of CFD numerical simulation show that the circular grooves at the contraction and the outlet sections can also reduce the high-pressure water flow resistance effectively. In the meantime, the opposite rotating vortexes in the circular grooves are the main reason for the reduction in fluid resistance of the bionic straight cone nozzle.

Experimental Investigation on Seepage Stability of Filling Material of Karst Collapse Pillar in Mining Engineering

In northern China, groundwater inrush of Karst collapse pillar (KCP) often affects the coal mining process. Current studies rarely consider the seepage stability of filling materials of KCP, especially through experimental investigations. This study is to quantify the impacts of variable initial porosity and cementing strength on the seepage properties of filling material. For this purpose, we designed and fabricated a test system. This system can offer high water pressure and abundant water flow rate. We tested three types of specimens which were cemented by clay, gypsum, and cement, respectively. The seepage properties were obtained under the initial porosity of 0.11, 0.13, 0.15, and 0.17, respectively. The change mechanism of seepage properties was measured through the comparison between mass loss and mass gain. The results showed the followings findings: (1) The permeability-time curves have two types: the first type is that permeability gradually increases up to the occurrence of seepage instability and the second type is that permeability gradually decreases and approaches to a stable value. No seepage instability is observed. (2) Initial porosity and cementing material significantly affect the water flow properties of filling material. In general, larger initial porosity has larger permeability. For clay as cementing material, seepage instability occurs soon and higher initial porosity has shorter time to reach seepage instability. For gypsum, seepage instability occurs after a period of time when initial porosity is large enough. For cement, the permeability decreases gradually and approaches to a stable value. The permeability-time curves have rapid decrease and slow decrease. (3) The permeability has a magnitude of 10−15–10−13 m2 and varies with initial porosity and cementing materials. The permeability is the largest for clay cementing and is the smallest for cement cementing.

Prediction of fluid flow through and jet formation from a high pressure nozzle using Smoothed Particle Hydrodynamics

This paper reports on the development and evaluation of an SPH (Smoothed Particle Hydrodynamics) model for high pressure water flow through and from a nozzle and prediction of its break up into a spray of high speed water droplets. This appears to be the first application of the SPH technique to fully model a high pressure nozzle. The model predicts the internal flow and pressure distribution and enables exploration of the role of the internal geometric insert used in this design of the nozzle. It also predicts exit velocities from the nozzle as well as the pressure distribution generated by the nozzle and droplet size distribution of the resulting spray. Three different nozzle inflow rates were simulated and for all cases the numerical simulation of nozzle and spray gave generally good agreement with experiments, but complete agreement was not achieved. For better agreement, higher resolution for the SPH solution is required. The SPH simulations also show the role that the insert in the nozzle has on the flow and the resulting jet. It produces a flat inclined high velocity liquid jet within the second half of the nozzle which will generate turbulent eddies that may enhance the nucleation of the droplets in the fragmenting jet after it exits the nozzle. Overall, SPH has been shown to have a very good capacity to model high pressure nozzles and with further refinements of the technique should be able to yield accurate, quantitative data.

Effect of inclination on frictional pressure drop of supercritical water flows in internally ribbed tubes: An experimental study

Internally ribbed tubes are highly advantageous for heat transfer enhancement in high pressure water flows. But these tubes increase the frictional pressure drop in comparison with smooth tubes. In this paper the frictional pressure drop characteristics of subcritical, near critical and supercritical water upward flows inside the inclined rifled tube with inclinations angles of 5, 20, 30, 45 and 90° with respect to the horizontal plane are studied experimentally. The test pressures were 15, 21.5, 22.5, 25 and 28MPa, the heat and mass fluxes were kept at 400kW/m2kW/m2 and 800kg/m2s. The effect of heat and mass fluxes on frictional pressure drop in inclined tubes was also investigated. The results showed the least frictional pressure drop for both subcritical and supercritical flows occurs at 5°. The effect of mass flux on frictional pressure drop in all water flow conditions was more considerable than the heat flux.

Nano-Level Surface Processing of Fine Particles by Cavitation to Improve the Photocatalytic Properties of Titanium Oxide

Titanium oxide is known as a photocatalytic material that promotes the generation of hydrogen and oxygen from water by sunlight irradiation. In the present study, titanium oxide particles were treated by water jet cavitation generated using an ejector nozzle. Sub-stream suction occurs in small-sized high-pressure ejector nozzles because of the dynamic high pressure. The water containing titanium oxide powder or a mixed powder of titanium oxide and platinum enters the high-pressure water flow as a sub-stream. In the ejector nozzle, generation, growth, and collapse of cavitation are repeated with the particles of titanium oxide and platinum. Because the cavitation has an extremely high collapse pressure, the surface of the titanium oxide particles is processed by the microjets of cavitation in a so-called reactor comprising the ejector nozzle. The titanium oxide particles subjected to ejector cavitation (EC) processing were investigated for improvements to their photocatalytic properties under ultraviolet irradiation. It was found that noted that nano-level roughness is formed by EC processing. The TiO2 particles or TiO2 particles supported by Pt particles as a cocatalyst containing water were introduced into a vacuum chamber and the gases such as hydrogen and oxygen from the particle surfaces were measured by quadrupole mass spectrometry under ultraviolet irradiation. The EC processing was found to increase the amount of gases generated, including hydrogen and oxygen. Moreover, the amount of hydrogen in particular increases remarkably when both EC processing and support of platinum as a co-catalyst are used. It was also found that the titanium TiO2 particles were supporting minute platinum particles that detached from the original Pt particles during EC processing.

Investigation of borehole stability in poorly cemented granular formations by discrete element method

Abstract Behaviour of poorly cemented formations in case of drilling a vertical exploration borehole will be studied to achieve an in-depth understanding of borehole stability problem. Analysis of the granular formation behaviour has a significant importance in identifying stability issues, designing adequate borehole supports and choosing an efficient drilling method. This paper presents numerical investigations on the behaviour of poorly cemented formations in the vicinity of an unsupported vertical cylindrical borehole. Due to poor cementation and therefore granular behaviour of these formations, Discrete Element Method (DEM) was identified as being well suited for developing realistic models. To conduct the numerical studies a cube of 8 m 3 made up of spherical particles with diameters ranging from 5 mm to 70 mm was constructed and analysed in three-dimensional Particle Flow Code ( PFC 3 D ). It is a discontinuum code used in analysis of the granular materials where the interaction of discrete grains is considered. A cylindrical opening with the diameter of 0.3 m runs along the central vertical axis of the cube simulating the presence of a borehole. The stresses applied to the cube simulate the underground conditions around an exploration borehole at the depth of 80 m. The effects of in situ stresses around the borehole, strength of particle bonding and fluid flow pressure on the stability of the formation around the borehole have been investigated. It has been shown that the development of in situ stresses in the ground due to drilling a borehole results in the formation of a plastic zone around that borehole. When there is lack of sufficient bonding between the sand grains, the interaction between them results in their movement towards the borehole opening and thus eventuates the collapse of the borehole wall. Furthermore, the presence of high pressure water flow expedites the process of the borehole collapse.

원전 배관의 반복 측정 데이터에 대한 신뢰도 분석 방법

Safety is a major concern in Nuclear Power Plants (NPPs). Piping systems in NPPs are very complex and composed of many components such as tees, elbows, expanders and straight pipes. The high pressure and high temperature water flows inside piping components. As high speed water flows inside piping, the pipe wall thinning occurs in various reasons such as FAC (Flow Accelerated Corrosion), LDIE (Liquid Droplet Impingement Erosion) and Flashing. To inspect the wall thinning phenomenon and protect the piping from damages, piping components are checked by UT measurement in every overhaul. During every overhaul, approximately 200~300 components (40,000~60,000 UT data) are examined in NPPs. There are some methods from EPRI for evaluating wear rate of components. However, only few studies have been conducted to find out the raw data reliability for the wear rate evaluation. Securing the reliable raw data is the key factor for a reasonable evaluation. This paper suggests the reliability analysis method for the repeatedly measured data for wear rate evaluation.

Glacitectonic sedimentary and hydraulic processes at an oscillating ice margin

An assemblage of subglacial, ice-terminal and proglacial landforms and sediments provides evidence for the relationship between ice-marginal glacitectonics, sedimentary processes and subglacial and proglacial hydraulic processes at a retreating late Devensian ice margin in north-central Ireland. Deltas were deposited in glacial lakes impounded between the retreating ice margin and the southern Sperrin Mountains, followed by outwash and end moraine formation as the ice margin retreated south. Sediments within the moraines show evidence for ice margin oscillation from two opposing ice margins, including subglacial bedrock rafts and breccias which are separated by glacitectonic shears with silty partings. In adjacent outwash, vertically-disturbed proglacial sands, gravels and silts located in front of moraine positions attest to high hydraulic pressure and subsurface water flow during ice oscillation. The relationship between sedimentary and hydraulic processes in the ice margin region is described by a depositional model which links glacitectonic thrusting and subsurface water flow during ice oscillation to formation of subglacial, ice-terminal and proglacial sediments. The evidence presented in this paper shows that subglacial and proglacial morphosedimentary processes and patterns of sediment deposition are mediated by the presence of proglacial permafrost, which helps direct processes and patterns of groundwater flow.

High Frequency Acoustic Signal Analysis for Internal Surface Pipe Roughness Classification

This research highlights a method of acoustic emission analysis to distinguish the internal surface roughness of pipe. Internal roughness of pipe indicates the level of corrosion occurring, where normally it is difficult to be monitored online. Acoustic Emission (AE) technique can be used as an alternative solution for corrosion monitoring in pipes, especially for complex pipelines that are difficult to achieve by other monitoring devices. This study used a hydraulic bench to provide fluid flow at two different pressures in pipes with different internal surface roughness (rough and smooth). The main source of acoustic emission was from activity in the control valve, coupled with high pressure water flow friction on the surface of the pipe. The signal from these sources was detected by using the AED-2000V instrument and assisted by the Acoustic Emission Detector (AED) software. The time domain parameter; root mean square, RMS amplitude were processed and compared at different pressures for each type of internal pipe roughness at ten different locations. It was observed that a unitless Bangi number, AB, derived from RMS values, can be used for discriminating different level of internal surface roughness. Internal surface pipe can still be considered as smooth if AB value is above 1.0.

Estimation of Heat Transfer Coefficient and Flow Characteristics on Heat Transfer Tube in Sodium-Water Reaction

In the steam generator of a sodium-cooled fast reactor, high-pressure water flows inside heat transfer tubes while liquid sodium flows on the shell side. Heat is exchanged through the tube wall. When the tube fails, water vapor leaks into the sodium stream, and a sodium-water reaction is initiated. This reaction occurs rapidly and generates a high-temperature jet. It then becomes possible for neighboring tubes to experience a secondary failure due to overheating. With regard to the secondary failure, an estimate of heat transfer from fluid to the tube is important for safety evaluation. In the present study, a numerical analysis has been carried out to determine the heat transfer coefficient from temperature data obtained in a sodium-water reaction experiment. By updating the heat transfer coefficient, an inverse problem of heat transfer has been solved in the analysis based on the result of the SWAT-1R experiment. It is found that the heat transfer coefficient fluctuates largely during the reaction. The heat transfer coefficient is affected by the flow characteristics. Hence, we characterize the flow pattern near the heat transfer tube at typical periods in the phenomenon progression.

Estimation of Heat Transfer Coefficient and Flow Characteristics on Heat Transfer Tube in Sodium-Water Reaction

In the steam generator of a sodium-cooled fast reactor, high-pressure water flows inside heat transfer tubes while liquid sodium flows on the shell side. Heat is exchanged through the tube wall. When the tube fails, water vapor leaks into the sodium stream, and a sodium-water reaction is initiated. This reaction occurs rapidly and generates a high-temperature jet. It then becomes possible for neighboring tubes to experience a secondary failure due to overheating. With regard to the secondary failure, an estimate of heat transfer from fluid to the tube is important for safety evaluation. In the present study, a numerical analysis has been carried out to determine the heat transfer coefficient from temperature data obtained in a sodium-water reaction experiment. By updating the heat transfer coefficient, an inverse problem of heat transfer has been solved in the analysis based on the result of the SWAT-1R experiment. It is found that the heat transfer coefficient fluctuates largely during the reaction. The heat transfer coefficient is affected by the flow characteristics. Hence, we characterize the flow pattern near the heat transfer tube at typical periods in the phenomenon progression.

Sonogashira C–C coupling reaction in water using tubular reactors with catalytic metal inner surface

A new reaction setup equipped with micro tubular reactor with thin catalytic metal inner surface (Pd or Pd–Cu alloy) was developed for the reactions in high-pressure and high-temperature water (HPHT-H2O) flow. To evaluate the catalytic performance of this micro tubular reactor, Sonogashira C–C coupling of iodobenzene and ethynylbenzene was investigated by using this system under alkaline aqueous medium. Under the optimized reaction conditions of 250°C and 16MPa of pressure, diphenylethyne was obtained with good yield and 100% selectivity within a very short residence time of ∼1.6s. The reaction proceeds without any additional promoters, additives or organic solvents. Leaching of catalytic metal from the reactor tube was not found under the studied reaction conditions. Alloying of Pd with Cu remarkably improved the efficiency of the reaction due to co-catalytic effect that is related to the easy electron transfer between two metals.