Liquid Zone Research Articles

Controller design for operation of a 700 MWe PHWR with limited voiding

Enhancement of available power output from a 540 MWe Pressurized Heavy Water Reactor (PHWR) with limited coolant voiding has been attempted in the recent past. Coolant voiding in such a core usually occurs in the high power regime and introduce positive reactivity in the core which makes a reactor increasingly unstable. This paper presents a scheme for a 700 MWe PHWR, which is capable of controlling the reactor from 60% to 92% of its Full Power (FP) using the Liquid Zone Control System (LZCS) and again from 92% to 100%FP in conjunction with a pressurizer which is activated to change the pressure in the coolant channel by a small amount, thus keeping the void fraction constraint. This paper presents a dynamic model for estimation of void fraction in the PHWR core as a function of reactor power and then proposes an optimal controller for pressurizer control using Genetic Algorithm (GA) to keep void fraction limited. The controller performance has been evaluated using credible Hardware-in-Loop (HiL) simulation.

R290(Propan) ve R600(N-Bütan) Soğutucu Akışkanlarının Kullanıldığı Ardışık İki Kademeli (Kaskad) Bir Soğutma Sisteminin Optimum Çalışma Parametrelerinin Belirlenmesi

Ardışık iki kademeli soğutma sistemleri özellikle buhar sıkıştırmalı soğutma çevrimlerinin düşük sıcaklık uygulamaları için yaygın bir şekilde kullanılmaktadır. Bu tarz sistemlerin daha verimli çalışabilmesi için izlenecek önemli adımlardan biri sistemde kullanılacak soğutucu akışkanın seçimidir. Çünkü bir soğutma çevriminde en yüksek COP değerini elde etmek özellikle soğutucu akışkan seçimine ve çalışma parametrelerinin en iyi şekilde belirlenmesine bağlıdır. Hidrokarbonlar topraktaki madde döngüsünden ortaya çıktıkları için doğal soğutucu akışkan olarak adlandırılırlar. Özellikle propan (R290) ve bütan (R600) sağladığı avantajlardan dolayı son yıllarda soğutucu akışkan olarak tercih edilen doğal hidrokarbonlardır. Bu çalışmada, örnek olarak, R290 ve R600 soğutucu akışkanının kullanıldığı iki kademeli bir soğutma çevrimi modeli geliştirilerek sistemin optimum çalışma şartları belirlenmiştir. Bu amaç doğrultusunda Java programlama dili kullanılarak örnek bir simülasyon modeli geliştirilmiştir. Bu modelde, olası hataları önlemek için stokastik (istatistiksel) optimizasyon yöntemleri kullanılmıştır. Ayrıca, soğutucu akışkanın bütün fazlarına ait termodinamik özellikler için Java dilinde ayrı bir simülasyon modeli geliştirilmiştir. Termodinamik özelliklerin belirlenmesi için geliştirilen simülasyon çalışmasında sıvı ve kızgın buhar bölgesi için özellikler Helmholtz gerçek gaz hal denklemi kullanılarak belirlenmiştir. Soğutucu akışkanların doyma bölgesi özellikleri de kübik şerit polinom denklemleri kullanılarak hesaplanmıştır. Geliştirilen bu simülasyon çalışmasından elde edilen sonuçların gerçek bir soğutma çevrimi önemli ölçüde uyum gösterdiği ve bu çalışma kapsamında geliştirilen bu modelin endüstriyel soğutma uygulamalarında özellikle sistem tasarımı ve analizi aşamasında önemli avantajlar sağlayacağı gözlemlenmiştir.

Tritium tracer Injection test at Wayang Windu Geothermal Field, West Java, Indonesia

Abstact The Wayang Windu Geothermal Field (WWGF), with an installed capacity of 227 MWe (Units 1 & 2), has been in production for eighteen (18) years. Currently, there are twenty-nine (29) active production wells, located mainly in the northern and central areas of the field (Gambung-Wayang). About 100 kg/s of condensate and 60 kg/s of brine are disposed of (by gravity) to three (3) injection wells in the southern (Windu) area, with less than 5% recharge to the reservoir (NDSA tracer test). A tracer injection test was conducted in 2014 and 2016 to better understand the vertical connectivity between the deep brine and the steam cap reservoir in the northern Gambung area. The tracer used was tritium in water or tritiated water (HTO). Around 20 ml (equal to 20–23 Ci) of tritium was injected using capillary tubing to the depth of deep liquid feed zones in two wells, MBE-5 and WWS-1, located in the central area of the field. Tracer returns were monitored mostly in dry steam wells in the northern Gambung area. Interpretation of the tracer return profiles included 1) the tracer breakthrough time; 2) time of maximum concentration, which reflects the average fluid velocity; 3) the width of the tracer ‘pulse’, which reflects the flow path dispersion; and 4) tracer recovery as a function of time. Three typical tracers return profiles were observed (fast, intermediate, and slow); the shape of the tracer ‘pulse’ was consistent with a single flow-path. Monitoring wells WWQ-5 and WWT-2 showed the highest mass recovery and the fastest breakthrough times. Total mass breakthrough calculated from the tritium tracer (using TRINV calculation) was about 5%, which is similar to results from earlier liquid tracer tests (NDSA), albeit for a different area of the field (laterally and vertically). Despite the low percentage of mass breakthrough, the data may provide some insight for assessing possible future central-deep infield-injection strategy. The different tracer returns profiles observed in the monitoring wells may contribute to refining the structural interpretation and identifying preferred fluid pathways. Overall, the results of the tritium tracer test provide some insight about the heterogeneity of the fracture network that controls how the tracers are dispersed.

Liquid jet impact on a wet wall

Abstract The impact of an axisymmetric liquid jet on a flat rigid wall wet with a thin film of the same liquid is numerically studied, using the two-dimensional Euler equations with axial symmetry solved by CIP-CUP method. The main attention is paid to the film effect on the liquid pressure field and the wall pressure load for the impact velocities 150 − 350 m/s. Such a velocity range is important for applications related to liquid and cavitation damage and erosion. Small film thicknesses up to 1/5 of the jet radius are considered because they may result in high pressure load on the wall, comparable to that in the dry wall case. The initial most intense period of the impact is investigated. The results show that for the film thickness up to about 1/10 of the jet radius throughout the impact-velocity range considered, a pressure peak appears at the periphery of the loaded zone on the wall, which is similar to the dry wall case. For sufficiently thin films and large impact velocities, the peripheral pressure peak may exceed the water hammer pressure. With increasing the film thickness, the wall-pressure distribution becomes more uniform, the maxima of the wall pressure in the center and at the periphery of the loaded area decrease. Unlike the dry wall case, the level of the wall pressure in terms of its ratio to the water hammer pressure lowers with decreasing the impact velocity because of an increase in the curvature of the shock wave incident on the wall. Rather large negative pressures arise in a small liquid zone near the wall as the expansion wave, generated by interaction between the shock wave and the film surface, reflects from the wall. With increasing the film thickness or lowering the impact velocity, their magnitude decreases. The dependences of the maximum average and maximum local wall pressure on the film thickness and the impact velocity have been determined. The impact of the jet without allowing for its axial symmetry has also been considered. It is found that the neglect of the axial symmetry may significantly reduce the damping effect of the film. With decreasing the film thickness and increasing the impact velocity, the reduction gradually vanishes.

Growth and property analysis of large-area epitaxial Tl-2212 high temperature superconducting films

The extensive use of large-area high temperature superconducting (HTS) thin films has emerged in superconducting microwave devices. The interest in Tl-based HTS films arises from their high critical temperature (Tc), allowing the microwave device made on Tl films to work above the liquid nitrogen temperature zone. Here, we introduce a simplified two-step method to fabricate high-quality Tl2Ba2CaCu2O8 (Tl-2212) films on 2-inch LaAlO3 substrates. This method enables the preparation of Tl-2212 films to be easy and repeatable, promoting the theoretical research and practical applications of Tl-based films. Based on the high reproducibility of this fabricating process, we studied the superconducting properties of Tc, the critical current density Jc (77 K, zero field) and surface resistance (Rs) of 2-inch Tl-2212 films. Results show that the Tc values of the sample films prepared at different conditions vary from 99 K to 103 K, depending on the oxygen content; the Jc of the films ranges from 0.7 to 1.8 MA/cm2, relying on the surface roughness. On the basis of the two-fluid model, the influence of Jc on Rs of the Tl-2212 films is incorporated to explain the variation of Rs in different samples.

Thermodynamic analysis and prediction of reservoir temperature distribution for steam stimulation

During steam stimulation of horizontal wells in heavy oil reservoir, it is necessary to estimate the reservoir temperature distribution, which has a huge impact on oil production and ultimate oil recovery. Most of previous models were derived based on infinite boundary condition and constant fluid velocity, which were not consistent with real situation of reservoir. In this paper, new energy balance equations combined with mobile boundary conditions were developed for increasing the accuracy of predicted results. Based on dimensionless conversion and numerical analysis, the optimum solution of equation system could be easily obtained, and its good performance in predicting temperature distribution was also validated. Moreover, thermodynamic mechanism of hot fluid, latent heat and sensible heat of steam, and their contributions to heating reservoir were also discussed to investigate the heat transfer pattern in reservoir. Finally, factors that could influence the reservoir temperature distribution were analyzed. It is found that: (a) both the heat conduction and the heat convection contribute to the heat transfer in hot liquid zone, and the heat convection predominates; (b) both the condensation front and heat front move outward with the injection of steam, but their expanding rates gradually drop with time; (c) as the radius increases, the radial fluid velocity will go down, leading the heat convection effect to be weakened and the heat conduction effect to become obvious; (d) there are some factors that can influence the reservoir temperature distribution including steam injection duration, fluid velocity, volumetric heat capacity of fluid, steam quality and thermal conductivity of reservoir.

Atmospheric Evolution on Low-gravity Waterworlds

Low-gravity waterworlds ($M\lesssim 0.1 M_{\oplus}$) are of interest for their potential habitability. The weakly bound atmospheres of such worlds have proportionally larger radiative surfaces and are more susceptible to escape. We conduct a unified investigation into these phenomena, combining analytical energy balance and hydrodynamic escape with line-by-line radiative transfer calculations. Because outgoing radiation is forced to increase with surface temperature by the expansion of the radiative surface, we find that these worlds do not experience a runaway greenhouse. Furthermore, we show that a long-lived liquid water habitable zone is possible for low-gravity waterworlds of sufficient mass. Its inner edge is set by the rate of atmospheric escape, because a short-lived atmosphere limits the time available for life to evolve. In describing the physics of the parameter space transition from "planet-like" to "comet-like", our model produces a lower bound for habitability in terms of gravity. These results provide valuable insights in the context of the ongoing hunt for habitable exoplanets and exomoons.

Contactless conductivity detector from printed circuit board for paper-based analytical systems

This work presents a capacitively coupled contactless conductivity detector (C4D) etched out from a printed circuit board (PCB) as potential sensor for paper-based analytical systems. Two lines of any desirable pattern forming 35-μm thick planar copper electrodes were produced on a PCB plate (40 mm × 60 mm) by photolithography. The final PCB plate was covered with polypropylene film to serve as the insulating layer for the C4D detector. The film also protected the copper electrodes from corrosion. Electrodes made in this planar geometry make the PCB-C4D suitable as sensor for flat devices such as paper-based analytical devices. For this work, plain paper strips were employed as sample reservoir and as fluidic channel without hydrophobic pattern. A dried paper strip was first placed over the sensor, followed by dispensing a fixed volume of the liquid sample onto the paper. Entrapment of the liquid sample in the paper strip leads to reproducible size and position of the detection zone of the sample liquid for the capacitive coupling effect. High precision was obtained with %RSD ≤1% (n = 18) for standard solutions of KCl. Soil suspensions could be analyzed without prior filtration by placing a drop onto the paper strip extending away from the detector zone. The paper strip filtered out soil particles at the surface of the paper. Therefore, only soil filtrate moved towards the detection zone by lateral flow. The C4D detection using paper strip showed high tolerance to soil suspension with turbidity up to 6657 NTU, offering direct analysis of soil salinity. Cleaning with moist tissue paper between samples is adequate even for dirty samples such as soil suspension. We also monitored conductivity of acid-base reaction in the microfluidic paper channels, which was later applied to the quantification of bicarbonate in water and in antacid tablet (“Soda Mint Tablet”).

Effective Self-Healing Behavior of Amorphous-Nanocrystalline Alloy Under Neutron Irradiation

The issue, structural response of the amorphous-nanocrystalline alloys (ANA) under neutron irradiation, has been investigated by a series of simulations and calculation. It is found that the irradiation-induced vacancies are fully annihilated by the migration of the phase boundary between the nanocrystal and amorphous or liquid zones. In addition, there is an effective self-recovery in the nanocrystal zone, because the nanocrystal phase is more competitive than the amorphous phase during the quench. This work reveals the effective structural self-healing mechanism in the ANA materials, and will shed light on the development of new materials with high irradiation resistance.

Experimental Research on Water Level Measurement Characteristics of Pressurizer in Transient Condition

Pressurizer is the main equipment of the pressure safety system of PWR nuclear power plants. Its water level reflects the water volume of the primary loop, which is one of the key parameters for the operation and control of the pressurizer. Based on the two-zone unbalanced model, this paper simulates the water level change under the condition of steam leakage and tests the characteristics of water level measurement for the steam leakage condition of the pressurizer, and the pressure drop of the water level under the pressure drop rate of 2.6~7.8 kPa/s in the pressurizer was investigated. It is found that the water level calculated by the pressure difference correction liquid zone density has a good follow-ability in the case of pressure transient, which can better reflect the water level characteristics. Pressure drop characterizing the change of the density in the liquid region of the pressurizer during the pressure reduction, the transition time is less than 40s and there is no strong correlation between the transition time and the single factor of the pressure drop rate. This provides basic research data for the safe operation of the pressurizer.

Low working temperature near liquid helium boiling point of RNiAl2 (R = Tm, Tb and Gd) compounds with large magnetocaloric effect

A polycrystalline TmNiAl2 compound with transition temperature near the liquid helium boiling point was successfully synthesized. Magnetic measurements show that FM (ferromagnetic) to FM and FM to PM (paramagnetic) transitions take place at 2.4 K and 4.0 K, respectively. Magnetic entropy change (–ΔSM) is calculated, and its maximal value [(–ΔSM)max] reaches as high as 20.7 J/kg K with the field change of 0–5 T. The low transition temperature together with large (–ΔSM)max at the liquid helium temperature zone originates from the weak spin-spin exchange interaction between Tm atoms. For a clear comparison, the magnetocaloric effect (MCE) of polycrystalline RNiAl2 (R = Tb and Gd) samples was also prepared and investigated. For the TbNiAl2 compound, FIM (ferrimagnetic) to AFM (antiferromagnetic) and AFM to PM transitions occur at 11.0 K and 21.5 K, respectively. As for the GdNiAl2 compound, an FM to PM transition occurs at 30.5 K. The value of (–ΔSM)max under the field change of 0–5 T is calculated to be 11.8 J/kg K and 17.3 J/kg K for TbNiAl2 and GdNiAl2, respectively. Compared with other RNiAl2-series MCE materials, TmNiAl2 exhibits the lowest working temperature and relatively larger (–ΔSM)max. The large MCE at low temperature indicates that TmNiAl2 is competitive among the MCE materials working at a liquid helium temperature zone.

Effect of Final Electromagnetic Stirring Parameters on Central Cross-Sectional Carbon Concentration Distribution of High-Carbon Square Billet

The effect of final electromagnetic stirring parameters, with current intensity increasing from 300 A to 400 A and frequency increasing from 4 Hz to 12 Hz, on the electromagnetic forces and carbon concentration distribution of the central cross section of a 70 steel square billet have been studied. Along the center line of the liquid core zone, current intensity of 400 A and frequency of 8 Hz achieve the maximum electromagnetic force at the position 48 mm away from the billet edge among the 10 groups of stirring parameters. Nevertheless, along diagonal of the liquid core zone, the electromagnetic force near the diagonal center is the greatest and the current intensity of 280 A and frequency of 12 Hz obtain the maximum electromagnetic force. The optimal final electromagnetic stirring (F-EMS) parameter to uniform the central cross-sectional carbon concentration and minimize the center carbon segregation of 70 steel billet was obtained with a current intensity of 280 A and frequency of 12 Hz. Under this stirring parameter, the area ratios of carbon concentrations of 0.66 wt%, 0.70 wt% and 0.74 wt% in the middle of the billet cross section reached 28.5%, 56.9% and 10.9%, respectively. Moreover, the carbon segregation indexes for all sampling points were in the range of 0.92–1.05.

Design of a Test Section to Analyze Magneto-Convection Effects in WCLL Blankets

The water-cooled lead lithium (WCLL) blanket is one of the European concepts for a Demonstration nuclear fusion reactor (DEMO). The spatial distribution of the water-cooling pipes inside the liquid metal blanket breeder zone is a critical issue since efficient heat removal from the liquid metal has to be ensured, avoiding local hot spots in the fluid or in blanket walls. Convective motion, driven by density gradients due to volumetric heat sources in the liquid breeder and heat removal by cooling pipes, is affected by magnetohydrodynamic interactions of the electrically conducting lead lithium with the external magnetic field. For the recent complex design of the DEMO WCLL blanket, prediction of the liquid metal flow is quite difficult. Preliminary numerical and experimental studies are necessary to determine the flow distribution resulting from the combined interaction of electromagnetic forces, buoyancy, and pressure. A test section based on a simplified model geometry supported by preliminary numerical simulations has been designed for experiments in the MEKKA laboratory at the Karlsruhe Institute of Technology and is presented in this paper.

Validation of a melting fraction-based effective thermal conductivity correlation for prediction of melting phase change inside a sphere

It is complicated and costly to directly simulate the natural convection influenced melting processes involving multiple PCM units in packed bed phase change system. An effective method to simulate such melting process is using an equivalent conduction model, in which the effective thermal conductivity (ETC) of PCM considering the natural convection effects is an important thermal parameter needing to be determined. In this paper, the ETC of PCM is investigated and determined by comparing numerical results based on models considering natural convection and pure conduction, respectively. Parameters of interest include melting fraction (α), Rayleigh number (Ra, 1.5 × 104 ≤ Ra ≤ 6.3 × 107), Prandtl number (Pr, 17 ≤ Pr ≤ 550) and Stefan number (Ste, 0.011 ≤ Ste ≤ 0.276.). Results show that the ETC of PCM has a strong relation to α and Ra, while it has little relation to Pr and Ste. Hence, an ETC correlation is developed as a function of Ra and α. Validation and application of the ETC correlation are further carried out, and it is found that the melting fraction predicted based on the present ETC correlation can better reflect the effect of liquid zone geometry on the melting heat transfer with natural convection than that predicted based on the previously reported correlations using a liquid gap parameter.

Consequences of Tidal Dissipation in a Putative Venusian Ocean

Abstract The solar tide in an ancient Venusian ocean is simulated using a dedicated numerical tidal model. Simulations with varying ocean depth and rotational periods ranging from −243 to 64 sidereal Earth days are used to calculate the tidal dissipation rates and associated tidal torque. The results show that the tidal dissipation could have varied by more than 5 orders of magnitude, from 0.001 to 780 GW, depending on rotational period and ocean depth. The associated tidal torque is about 2 orders of magnitude below the present day Venusian atmospheric torque, and could change the Venusian daylength by up to 72 days per million years depending on rotation rate. Consequently, an ocean tide on ancient Venus could have had significant effects on the rotational history of the planet. These calculations have implications for the rotational periods of similarly close-in exoplanetary worlds and the location of the inner edge of the liquid water habitable zone.

Influence of the Solid Phase's Fractional Composition on the Filtration Characteristics of the Drilling Mud

Filtration of the drilling mud is one of it's most important parameters, especially when drilling-in producing formation. Decrease of filtration characteristics allows reducing both solid and liquid phases's penetration zone into the formation. The study of the effect of the weighting-bridging agent's fractional composition on the filtration rate allows selecting of optimal composition of the solid phase in the the drilling mud. This paper presents studies of the static filtration rate of drilling mud with addition of various weighting-bridging agents. The obtained result indicates that an intensive decrease in the filtration rate is observed at calcium carbonate's introduction into the solution with an average particle size of up to 50 μm. Further studies should be directed to investigate the dynamic filtration rate, the possibility of mixing of various fractions in the composition of one solution and the evaluation of their influence on the filtration rate.

Finite volume simulation framework for die casting with uncertainty quantification

The present paper describes the development of a novel and comprehensive computational framework to simulate solidification problems in materials processing, specifically casting processes. Heat transfer, solidification and fluid flow due to natural convection are modeled. Empirical relations are used to estimate the microstructure parameters and mechanical properties. The fractional step algorithm is modified to deal with the numerical aspects of solidification by suitably altering the coefficients in the discretized equation to simulate selectively only in the liquid and mushy zones. This brings significant computational speed up as the simulation proceeds. Complex domains are represented by unstructured hexahedral elements. The algebraic multigrid method, blended with a Krylov subspace solver is used to accelerate convergence. State of the art uncertainty quantification technique is included in the framework to incorporate the effects of stochastic variations in the input parameters. Rigorous validation is presented using published experimental results of a solidification problem.

A special single variant zone in directionally solidified Ni-Mn-Ga alloy

Three distinct structures comprising self-accommodated solid zone, (110)M preferred oriented liquid zone and (001)M oriented single variant zone were discovered in directionally solidified Ni-Mn-Ga alloy rod. The preferred (110)M orientation in liquid zone directly causes a special single variant zone to form around quenching interface. It is attributed to a longitudinal, suddenly-shrinking lattice, produced in the liquid zone after martensitic transformation, which induces a tension force at the joint. A tensile test simulates and validates the formation of single variant induced by inner force. A mechanism of variant formation is described in the present study, too.

Diurnal thermal performance characterization of a solar air heater at local and global scales integrated with thermal battery

The diurnal thermal performance of a Solar Air Heater (SAH) integrated with Phase Change Material (PCM) based thermal battery is numerically studied. A control volume based advection-diffusion model is coupled with Discrete Ordinate Model (DOM) for considering the effects of solar radiation. Enthalpy-porosity technique is employed to consider various phases of the PCM (solid, liquid and mushy zone). At first, the model is validated with the available experimental result of outlet air temperature for a solar air heater. Thereafter, solar air heaters with and without thermal battery are compared to evaluate the effect of PCM on the thermal performance of the SAH. The local and global heat transfer, the phase change characteristics and their effect on the charging/discharging operation are described. Various numerical simulations are performed to propose optimized operational and design parameters. The integration of the thermal battery enables the SAH to work as diurnal (both day and night) which was not possible with the conventional SAH. The operating time of SAH integrated with thermal battery increases notably by 6 h. To evaluate the enactment of the system, thermal performance indicators are discussed.

Numerical study on action of HMF, PMF, DHMF, and DPMF on molten metal during electromagnetic casting

The effect of harmonic magnetic field (HMF), pulse magnetic field (PMF), differential phase harmonic magnetic field (DHMF), and differential phase pulse magnetic field (DPMF) on liquid and mushy zones of crystallizing metal was investigated by numerical simulation referring to electromagnetic DC (direct chill) casting process. Firstly, the experimental pulse current for electromagnetic casting was obtained by a digital oscilloscope. The physical and finite element models of Φ300-mm cylindrical crystallization for the electromagnetic field simulation were established. Then, the distribution of magnetic flux density (B) and electromagnetic forces (FMAG) generated by the four types of magnetic fields were obtained in a period (T). Actions of HMF, PMF, DHMF, and DPMF on molten melt were discussed based on radial and axial electromagnetic forces. Finally, the effects of electromagnetic parameters (current intensity, frequency, and duty cycle) on electromagnetic forces under PMF and DPMF were studied. The effect of electromagnetic forces on metal flow has been discussed. The results indicate that compared with harmonic current, the pulse current can generate a stronger magnetic field with the same conditions. Single-coil magnetic field can easily cause the molten metal radial vibration. The differential phase magnetic field can not only cause radial vibration but also produce axial convection, while the vibration effect is weaker. The electromagnetic forces increase with the increase of current intensity and duty cycle under PMF and DPMF. Moreover, the electromagnetic force has low sensitivity to frequency under DPMF.