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"thermal-hydraulic"
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Investigating the effect of the shale bedding structure on hydraulic fracture propagation behavior on the basis of a coupled thermal–hydraulic–mechanical numerical model
The interaction process among hydraulic fractures and natural fractures, bedding planes, and other discontinuities during shale fracturing determines the complexity of the fracture network that is formed. However, the current conclusions and understanding of the mechanisms underlying the interaction between hydraulic and natural fractures, as well as their primary controlling factors, fail to meet the requirements of hydraulic fracturing operations, thereby restricting the efficient development of shale gas resources. Therefore, in this study, a coupled thermal‒hydraulic‒mechanical finite element numerical model that is based on the maximum tensile stress and the Mohr‒Coulomb criterion is established, thereby considering rock deformation, fluid flow, and heat transfer. The reliability of this model is validated on the basis of previous research. This model is subsequently employed to simulate the propagation behavior of hydraulic fractures in shale with well-developed bedding. The results indicate that when hydraulic fractures propagate to the bedding, five propagation modes may occur: arrest, diversion, diversion and crossing, crossing and diversion, and direct crossing. These modes are controlled by factors such as the mechanical properties of the shale matrix and bedding, geostress, bedding dip angle, temperature, and fracturing fluid injection rate. During fracture propagation, increases in the elastic modulus ratio between the rock matrix and the bedding, the bedding dip angle, and the temperature are favorable for hydraulic fractures turning along the bedding, whereas increases in the difference in vertical stress and the injection rate are favorable for hydraulic fractures directly crossing the bedding. Second, on the basis of four influencing factors, namely, the shale matrix and bedding elastic modulus ratio, bedding dip angle, difference in vertical stress, and temperature, propagation criteria for hydraulic fractures along the bedding under various combinations of influencing factors are established. The results provide theoretical reference data for the design and optimization of fracturing in shale with well-developed bedding.
Journal Article
PBMR-400 BENCHMARK SOLUTION OF EXERCISE 1 AND 2 USING THE MOOSE BASED APPLICATIONS: MAMMOTH, PRONGHORN
High temperature gas cooled reactors (HTGR) are a candidate for timely Gen-IV reactor technology deployment because of high technology readiness and walk-away safety. Among HTGRs, pebble bed reactors (PBRs) have attractive features such as low excess reactivity and online refueling. Pebble bed reactors pose unique challenges to analysts and reactor designers such as continuous burnup distribution depending on pebble motion and recirculation, radiative heat transfer across a variety of gas-filled gaps, and long design basis transients such as pressurized and depressurized loss of forced circulation. Modeling and simulation is essential for both the PBR’s safety case and design process. In order to verify and validate the new generation codes the Nuclear Energy Agency (NEA) Data bank provide a set of benchmarks data together with solutions calculated by the participants using the state of the art codes of that time. An important milestone to test the new PBR simulation codes is the OECD NEA PBMR-400 benchmark which includes thermal hydraulic and neutron kinetic standalone exercises as well as coupled exercises and transients scenarios. In this work, the reactor multiphysics code MAMMOTH and the thermal hydraulics code Pronghorn, both developed by the Idaho National Laboratory (INL) within the multiphysics object-oriented simulation environment (MOOSE), have been used to solve Phase 1 exercises 1 and 2 of the PBMR-400 benchmark. The steady state results are in agreement with the other participants’ solutions demonstrating the adequacy of MAMMOTH and Pronghorn for simulating PBRs.
Journal Article
Numerical Simulation of the Effect of Injected CO2 Temperature and Pressure on CO2-Enhanced Coalbed Methane
The injection of CO2 to displace CH4 in coal seams is an effective method to exploit coalbed methane (CBM), for which the CO2 injection temperature and pressure are important influential factors. We performed simulations, using COMSOL Multiphysics to determine the effect of CO2 injection temperature and pressure on CO2-enhanced coalbed methane (CO2-ECBM) recovery, according to adsorption/desorption, seepage, and diffusion of binary gas (CO2 and CH4) in the coal seam, and deriver a thermal–hydraulic–mechanical coupling equation of CO2-ECBM. The simulation results show that, as CO2 injection pressure in CO2-ECBM increases, the molar concentration and displacement time of CH4 in the coal seam significantly decrease. With increasing injection temperature, the binary gas adsorption capacity in the coal seam decreases, and CO2 reserves and CH4 production decrease. High temperatures are therefore not conducive for CH4 production.
Journal Article
A Freezing-Thawing Damage Characterization Method for Highway Subgrade in Seasonally Frozen Regions Based on Thermal-Hydraulic-Mechanical Coupling Model
Seasonally frozen soil where uneven freeze–thaw damage is a major cause of highway deterioration has attracted increased attention in China with the rapid development of infrastructure projects. Based on Darcy’s law of unsaturated soil seepage and heat conduction, the thermal–hydraulic–mechanical (THM) coupling model is established considering a variety of effects (i.e., ice–water phase transition, convective heat transfer, and ice blocking effect), and then the numerical solution of thermal–hydraulic fields of subgrade can be obtained. Then, a new concept, namely degree of freeze–thaw damage, is proposed by using the standard deviation of the ice content of subgrade during the annual freeze–thaw cycle. To analyze the freeze–thaw characteristics of highway subgrade, the model is applied in the monitored section of the Golmud to Nagqu portion of China National Highway G109. The results show that: (1) The hydrothermal field of subgrade has an obvious sunny–shady slopes effect, and its transverse distribution is not symmetrical; (2) the freeze–thaw damage area of subgrade obviously decreased under the insulation board measure; (3) under the combined anti-frost measures, the maximum frost heave amount of subgrade is significantly reduced. This study will provide references for the design of highway subgrades in seasonally frozen soil areas.
Journal Article
Numerical Investigations of the Thermal-Hydraulic Characteristics of Microchannel Heat Sinks Inspired by Leaf Veins
A microchannel heat sink (MCHS) is a potential solution for chip and battery thermal management. The new microchannel structure is beneficial for further improving the thermal-hydraulic performance of MCHSs. Inspired by leaf veins, six new channel structures were designed, and the effects of the channel structures (three parallel structures named PAR I, II, and III and three pinnate structures named PIN I, II, and III), channel depths (0.4, 0.8, and 1.6 mm), and heat fluxes (20, 50, and 80 kW/m2) were investigated via numerical simulation. The cooling medium was water, and the heating area was 40 × 40 mm2. Both PAR II and PIN III exhibit superior overall performance, characterized by the highest Nusselt number and the lowest heating wall temperature. Moreover, PIN III demonstrates the lowest standard deviation in heating wall temperature, while PAR II exhibits the lowest friction factor. The greater the channel depth is, the larger the solid–liquid contact area is, leading to a reduced wall temperature at the interface under identical conditions of inlet Reynolds number and heating wall heat flux. Consequently, an increase in the Nusselt number corresponds to an increase in the friction factor. The maximum value and standard deviation of the heating wall temperature increase with increasing heat flux, while the Nusselt number and friction factor remain unaffected. The overheating near the two right angles of the outlet should be carefully considered for an MCHS with a single inlet–outlet configuration.
Journal Article
Numerical study of coal reservoir and borehole parameters evaluation considering temperature and multi-borehole superposition effects
To reveal the effects of temperature on the effective extraction radius and coal reservoir parameters during gas extraction in bedding boreholes, a hydraulic-mechanical coupling model (HM) and a thermal–hydraulic-mechanical coupling model (THM) for borehole gas extraction are established. The impact of temperature effects on the effective extraction radius, coal seam permeability, and gas pressure under single-borehole conditions are analyzed. Based on the mechanism of extraction superposition effect in multi-borehole extraction, the variation patterns of extraction superposition effect with key borehole parameters under borehole group conditions is explored. The results show that the model considering temperature effect shows a gradual increase in coal seam permeability, while ignoring temperature effect will overestimate the gas pressure drop and underestimate the permeability of the coal seam. Using the extraction superposition effect as the criterion for evaluating extraction effectiveness, the smaller borehole spacing and the larger diameter, the more obvious the extraction superposition effect between adjacent boreholes. The impact of extraction negative pressure on the borehole superposition effect is minimal. Under the premise of determining the effective extraction radius
R
for a single borehole, the superposition effect
k
is exactly 1.01 when the borehole spacing is 2.2
R
and the diameter is 95 mm in this model.
Journal Article
Review of Experimental and Numerical Studies on Critical Heat Flux in China
This article presents an exhaustive and comprehensive review of research endeavors conducted in China over the past three decades focusing on critical heat flux—a thermal–hydraulic phenomenon of paramount importance in nuclear engineering. CHF represents the ultimate threshold of heat transfer capability, governed by fundamental physical principles, and serves as a cornerstone in the design of reactor cores, fundamentally delineating the reactor’s capacity for safe heat dissipation. In this study, we undertake a meticulous analysis of 60+ research papers published in Chinese by a diverse array of Chinese research institutions spanning the last three decades, encompassing both experimental and numerical simulation investigations. The experimental research is systematically reviewed. The experimental setups and test sections are examined in detail. Then, the experimental parameters and conclusions are analyzed comprehensively. This examination elucidates the achievements attained and the challenges encountered in the experimental domain. In the realm of numerical simulation research, this review consolidates the prevailing hypotheses regarding inherent mechanisms, modeling methodologies, and their validations against experimental data. Building upon the existing research accomplishments and acknowledging the emerging trends in fluid mechanics research, particularly the integration of next-generation measurement technologies and artificial intelligence, a strategic and forward-looking research trajectory is proposed. This trajectory aims to guide and inspire future endeavors in this crucial and intricate field, fostering a deeper understanding and enhanced performance of nuclear reactors through innovative and rigorous research.
Journal Article
A Review of Molten Salt Reactor Multi-Physics Coupling Models and Development Prospects
Molten salt reactors (MSRs) are one type of GEN-IV advanced reactors that adopt melt mixtures of heavy metal elements and molten salt as both fuel and coolant. The liquid fuel allows MSRs to perform online refueling, reprocessing, and helium bubbling. The fuel utilization, safety, and economics can be enhanced, while some new physical mechanisms and phenomena emerge simultaneously, which would significantly complicate the numerical simulation of MSRs. The dual roles of molten fuel salt in the core lead to a tighter coupling of physical mechanisms since the released fission energy will be absorbed immediately by the molten salt itself and then transferred to the primary heat exchanger. The modeling of multi-physics coupling is regarded as one important aspect of MSR study, attracting growing attention worldwide. Up to now, great efforts have been made in the development of MSR multi-physics coupling models over the past 60 years, especially after 2000, when MSR was selected for one of the GEN-IV advanced reactors. In this paper, the development status of the MSR multi-physics coupling model is extensively reviewed in the light of coupling models of N-TH (neutronics and thermal hydraulics), N-TH-BN (neutronics, thermal hydraulics, and burnup) and N-TH-BN-G (neutronics, thermal hydraulics, burnup, and graphite deformation). The problems, challenges, and development trends are outlined to provide a basis for the future development of MSR multi-physics coupling models.
Journal Article
Proof of the Concept of Detailed Dynamic Thermal-Hydraulic Network Model of Liquid Immersed Power Transformers
The paper presents a physics-based method to calculate in real time the distribution of temperature in the active part of liquid immersed power transformers (LIPT) in a transient thermal processes during grid operation. The method is based on the detailed dynamic thermal-hydraulic network model (THNM). Commonly, up to now, lumped models have been used, whereby the temperatures are calculated at a few points (top-oil and hot-spot), and the parameters are determined from basic or extended temperature-rise tests and/or field operation. Numerous simplifications are made in such models and the accuracy of calculation decreases when the transformer operates outside the range of tested values (cooling stage, loading). The dynamic THNM reaches the optimum of accuracy and simplicity, being feasible for on-line application. The paper presents fundamental equations of dynamic THNM, which are structurally different from static THNM equations. The paper offers the numerical solver for the case of a closed-loop thermosyphon. To apply the method for real transformer grid operation, there is a need to develop details as in static THNM, which has been used to calculate the distribution of the temperatures in LIPT thermal design. The paper proves the concept of dynamic THNM using the experimental results of a closed-loop thermosyphon small-scale model, previously published by authors from McGill University in 2017. The comparison of dynamic THNM with measurements on that model are presented in the paper.
Journal Article