Induced Thermal Stresses Research Articles

Study of the fracture propagation and the corresponding heat mining performance of multi-branch radial wells geothermal system based on the THM-D coupling model

Due to the multi-well enhanced geothermal systems can significantly improve the heat transfer efficiency and the multi-branch radial well geothermal system can reduce the well construction cost, it is necessary to investigate the fracture propagation and the heat mining performance of the multi-branch radial well geothermal system. Based on the constructed THM-D coupling model, the fracture propagation rules of multi-branch radial wells under the co-function of low-temperature induced thermal stress and radial well induced stress is explored. Then the heat mining prediction study during the heat extraction stage is conducted based on the generated fracture. Furthermore, the influence of radial well characteristic parameters on fracture propagation and the corresponding heat mining performance of multi-branch radial well geothermal system is discussed. The results show that the smaller radial well angle in multi-branch radial well system can generate a larger scope of fracture network between the included angle under the co-function of radial well induced stress and low-temperature induced thermal stress, which will correspond to a larger heat extraction scope in heat mining stage. When the radial well included angle along the direction of maximum horizontal in-situ stress is 120°, the fracture network obtained by fracturing is the most complex. Excessive branching of radial wells can lead to significant induced stress in the plane of radial wells, which will affect the propagation of the fracture network in the direction of longitudinal connection between the doublet wells, thereby affecting the corresponding heat mining performance. With the increase of radial well length, the ability to induce the formation of branching fractures raises, resulting in more complex fracture network. In the heat mining stage of 10-year development, the outlet temperature and heat mining rate respectively increased by 5.83% and 6.9% when the radial well length is 75 m compared to 50 m.

Decompression and Fracturing Caused by Magmatically Induced Thermal Stresses

AbstractStudies of host rock deformation around magmatic intrusions usually focus on the development of stresses directly related to the intrusion process. This is done either by considering an inflating region that represents the intruding body, or by considering multiphase deformation. Thermal processes, especially volume changes caused by thermal expansion are typically ignored. We show that thermal stresses around upper crustal magma bodies are likely to be significant and sufficient to create an extensive fracture network around the magma body by brittle yielding. At the same time, cooling induces decompression within the intrusion, which can promote the appearance of a volatile phase. Volatile phases and the development of a fracture network around the inclusion may thus be the processes that control magmatic‐hydrothermal alteration around intrusions. This suggests that thermal stresses likely play an important role in the development of magmatic systems. To quantify the magnitude of thermal stresses around cooling intrusions, we present a fully compressible 2D visco‐elasto‐plastic thermo‐mechanical numerical model. We utilize a finite difference staggered grid discretization and a graphics processing unit based pseudo‐transient solver. First, we present purely thermo‐elastic solutions, then we include the effects of viscous relaxation and plastic yielding. The dominant deformation mechanism in our models is determined in a self‐consistent manner, by taking into account stress, pressure, and temperature conditions. Using experimentally determined flow laws, the resulting thermal stresses can be comparable to or even exceed the confining pressure. This suggests that thermal stresses alone could result in the development of a fracture network around magmatic bodies.

Selective electron beam melting of high strength Al2024 alloy; microstructural characterization and mechanical properties

Abstract To date, the most commonly used aluminum alloys for additive manufacturing are eutectic/near-eutectic alloys. However, fabricating high strength aluminum parts has not yet been fully investigated due to solidification cracking and porosity formation, which make these alloys very hard to be processed. Electron beam selective melting (EBSM) of aluminum alloys has some advantages over selective laser melting. The process is not affected by reflectivity of aluminum powders, and parts exhibit less induced thermal stresses. In addition, oxidation is reduced due to vacuum condition. Therefore, the process provides high potential for the fabrication of aluminum alloys, specifically, Al2024 alloy which is widely used in different industries such as automotive and airline industries. Hence, these industries are highly benefitted from being able to build defect-free AM parts. This study is significant because Al2024 alloy is highly susceptible to solidification cracking and porosity formation, and crack-free samples with high relative densities have not been built by EBM process previously. The baseplate preheating temperature was set to 350 °C, and samples were fabricated by applying a proper powder bed preheating configuration for each layer. Different sets of processing parameters were used to investigate their effect on the performance of the parts. Archimedes technique was used to measure the relative density of samples, ranging from 95% to full-dense. The results showed that higher relative densities could be achieved by increasing the input energy to an optimum value; however, by further increasing the energy, the relative density decreases, which can be attributed to porosity formation. SEM and EBSD results showed equiaxed grains in a crack-free microstructure. Grain structure consisted of high angle grain boundaries having different crystallographic orientations with a few sub-grains. Additionally, AlCuMnFe, AlCuMnFeSi, and eutectic Al2Cu phases were uniformly distributed in the α phase matrix. Microhardness results showed an almost uniform change of hardness values in both horizontal and vertical sections, ranging from 100 HV to 110 HV for as-built samples. Moreover, tensile and yield strengths of as-built samples reached 314 MPa and 191 MPa, respectively, which can be further increased by a proper post-processing treatment.

A Study of Temperature Distribution and Thermal Stresses in a Hot Rock Due to Rapid Cooling

Abstract Thermal stresses may be induced in a hot dry rock when a cold fluid is injected in the well. To study this problem, we look at the thermoelastic response of a hot rock that is suddenly cooled. The cooling is assumed to be either at a constant temperature or at a constant heat flux per unit depth. Our approach is to nondimensionalize the equations and perform a parametric study and look at the temperature distribution and the induced-thermal stresses. The results indicate that depending on the extent of cooling and the cooling time, thermal stresses can be induced. Numerical simulations on sandstone, with an initial uniform temperature of 473 K, are also carried out. The results show that if the cooling is due to the surface temperature maintained at 463 K (10 °C lower than the initial temperature of the hot rock), thermal stresses that are larger than the rock tensile strength could be induced. When the cooling is due to a constant surface heat flux, this temperature can be reached after about 777 days of cooling with a minimum value of a heat flux of −20 W/m.

Dominating Driven Factors of Hydrogen Diffusion and Concentration for the Weld Joint–Coupled Analysis of Heat Transfer Induced Thermal Stress Driven Hydrogen Diffusion–

Dominating Driven Factors of Hydrogen Diffusion and Concentration for the Weld Joint–Coupled Analysis of Heat Transfer Induced Thermal Stress Driven Hydrogen Diffusion–

Development of Mirror Surface Groove Processing Technology of Glass by Laser Induced Thermal Stress

Development of Mirror Surface Groove Processing Technology of Glass by Laser Induced Thermal Stress

Influence of Multiaxiality of Thermal Field Induced Thermal Stress on Micro Crack Growth Around Cooling Holes

Influence of Multiaxiality of Thermal Field Induced Thermal Stress on Micro Crack Growth Around Cooling Holes

Induced Thermal Stresses in Core Shell Magnetic Particles

In this paper, the induced thermal stresses that appear during the cooling process from the room temperature to a lower temperature for core shell magnetic particles are analyzed. Using a finite element method for solving the Fourier heat transport equation, the thermal stresses in the system were calculated taking into account of the temperature dependence of thermal conductivity, heat capacity and different thermal expansion coefficients of the two materials (iron core + alumina shell) in contact. The thermal stresses depend on the particle's radius and the thickness of the alumina shell, having negative values due to the thermal contraction. It was estimated the influence of shell thickness on thermal stresses and on the speed of reaching the mechanical and thermal equilibrium state.

Impact of Induced Thermal Stresses During Circulation Tests in an Engineered Fractured Geothermal Reservoir: Example of the Soultz-Sous-Forêts European Hot Fractured Rock Geothermal Project, Rhine Graben, France

The wider concept of hot fractured rock geothermal energy is put forward to overcome the natural limitations of classic geothermal fields. A suite of numerical modules based on a discrete fracture network approach has been developed, specifically devoted to the understanding of flow through faulted and fractured deep rock masses. The presented application concerns the geothermal project developed at the Soultz-sous-Forets site (Alsace, France) in a graben geological setting. This area seems well suited for such a project, since most of the faults and fractures are nearly optimally-oriented for frictional slip in the present day stress field. A 3D structural model is generated from a variety of measurements collected during the 1993-1997 experimental program at depths ranging in 2850 down to 3600 m. These include induced microsismicity, geophysical logs, flow logs, hydraulic interference tests between wells 500 m apart, a four months long circulation test and two tracer tests. An interesting output of the modeling work is that rock shrinkage due to cooling at the reinjection well is likely to happen within some months of fluid circulation, and this would fit with many observations, such as a pressure decrease at the re-injection well, noticeable changes in the flow logs or a significant evolution in tracer breakthrough curves.

Continuous Curing and Induced Thermal Stresses of a Thick Filament Wound Composite Cylinder

Continuous Curing and Induced Thermal Stresses of a Thick Filament Wound Composite Cylinder

Continuous Curing and Induced Thermal Stresses of a Thick Filament Wound Composite Cylinder

A new composite manufacturing technique called continuous curing is discussed and analyzed. This method is especially suited to the manufacture of thick composite materials in which thermal spiking is a common problem. Thermal and cure fronts are propagated in the thickness direction as material is accreted on the outer surface. An experimental apparatus was designed and built for use with a filament winder to continuously cure thick composite cylinders. A demonstration experiment was carried out using IM6/3501-6 graphite/epoxy prepreg tow. A hoop-wound composite cylinder with 152 mm wall thickness was manufactured and embedded thermocouples and strain gages were monitored throughout the cure process. Results indicate that very thick and good quality composite cylinders can be fabricated without long manufacturing time, material degradation due to thermal spiking, and high level of thermally induced residual stresses.

Stress Relaxation During Diffusional Phase Transformation Under Induced Thermal Stress

ABSTRACTThermal mismatch between the expansion coefficients of a substrate and deposited thin film gives rise to extrinsic stress in the film. Different stress states are induced into the Co/Si thin film combination by depositing the multi-layers on Al and Si substrates respectively. Interdiffusion at 360°C is found to be influenced by the extrinsic stress in the films. The difference in Co2Si growth rate on different substrates is ascribed to the difference in composition (Co molar fraction) at the Co/Co2Si and Co2Si/Si interfaces due to different stress states.

Diffusional Phase Transformation under Induced Thermal Stress

AbstractWhen thin films are deposited on substrates or when compound films are formed through interdiffusion of multi-film structures, intrinsic stress develops in the various films. Thermal mismatch between the expansion coefficients of the substrate and films in multi-film structures gives rise to extrinsic stress at elevated temperaturesBy using Si<100> and rolled Al foil substrates supporting the same multi-film structure SiO2/Si/Co, the effect of extrinsic stress on interdiffusion of thin films is isolated.Silicide growth is found to be inhibited (delayed) when formed on Al substrates compared to that formed on Si substrates. The delay in silicide growth is ascribed to delamination caused by large tensile stress prior to silicide formation. The growth rate of Co2Si is found to be similar on both Al and Si substrates

Stomatal Response to Microwave Induced Thermal Stresses

ABSTRACTAttached bean leaves responded to thermal stresses, induced by microwaves in darkness, by lowering equilibrium leaf temperatures between 2 to 1O°C in still air. The lowering of equilibrium leaf temperatures of exposed water hyacinth plants in darkness were found to be even higher than 10°C in still air. The same behaviour was also observed for leaves which were placed in an air stream. The phenomenon is explained as transpirational cooling when stomates are opened in darkness in response to absorbed microwave radiation and high leaf temperatures.