Injection Temperature Research Articles

Experimental research of direct water injection characteristics over wide range of injection temperature and ambient pressure

Direct water injection (DWI) within internal combustion engine has become a promising technology due to its potential for suppressing knock, reducing emissions and lowering fuel consumption. The spray morphology shows a significant impact on the effectiveness of DWI, which makes it of great research significance. In this research, the spray characteristics of water jet under different conditions were investigated based on a constant volume vessel. The water injection temperature ranged from 30 °C to 240 °C, and the ambient pressure varied from 0.2 bar to 10 bar. The results showed that the spray width at near-field increases with water temperature. However, at ambient pressures of 0.8 bar–2.5 bar, higher superheat level resulted in severe spray collapse, manifested as significantly reduced spray width. It was identified that the collapse under flash boiling occurs as a result of the presence of the low-pressure zone at the center of the spray, and higher superheat level migrate the low-pressure zone closer to the nozzle exit, resulting in enhanced spray collapse. This could lead to excessive water mist concentration in partial region, negatively affecting combustion process and potentially causing oil emulsion in actual engine operation. This work also suggests a strong correlation between spray collapse and water injection pressure, in addition to superheat level and ambient pressure. The findings of this work have the potential to provide effective reference for high-temperature water injection strategies in internal combustion engines.

In-cylinder spray evolution in a motored central-injection gasoline engine: Imaging and simulating the effects of flash-boiling and intake crossflow

Accurate predictions of fuel spray behavior and mixture formation in simulations of direct-injection spark-ignition (DISI) engines are fundamental to ensure proper description of all subsequent processes including ignition, combustion, and emissions. In this work, the spray evolution in a single-cylinder optical DISI engine was studied experimentally and numerically with the goal of enabling predictive computational fluid dynamics (CFD) modeling of in-cylinder sprays. The authors explored a wide range of operating conditions characterized by several fuel injection temperatures and engine speeds, using a well-characterized nine-component gasoline surrogate known as PACE-20. The effect of flash boiling and intake crossflow on the spray is discussed, with a focus on evaluating the ability of the spray models to capture highly transient spray behavior. In the experiments, the fuel temperature was varied between 20°C and 80°C, allowing for non-flash- to flash-boiling transition to emerge with enhanced flashing intensity at the highest temperatures. Spray collapse resulted in vapor-rich regions, owing to the locally lower inertia of the fluid. Varying the engine speed from 650 to 1950 rpm promoted increasingly more turbulent in-cylinder crossflow which interacted with the spray during the injection event and resulted in enhanced spray dispersion. The CFD model was able to capture the spray morphology transition at different fuel temperatures and engine speeds adequately. It is shown that the spray breakup model could capture the transitional spray behavior induced by flash boiling atomization and intake flow via proper initialization of the spray cone angle and calibration of the spray models’ constants.

PLA-Sago Starch Implants: The Optimization of Injection Molding Parameter and Plasticizer Material Compositions

Previous research extensively characterized PLA blends for various biomedical applications, especially in polymer-based biodegradable implant fixations, offering advantages over metallic counterparts. Nevertheless, achieving an optimal PLA mixture with both mechanical resistance and fast biodegradability remains a challenge. Currently, literature still lacks insights into the manufacturing parameter impact on sago starch/PLA in combination with PEG plasticizer. The objective of this study is to assess variations in injection molding temperatures and sago/PLA/PEG weight compositions to identify the optimal combination enhancing miniplate mechanical properties and biodegradation behavior. Mechanical tests reveal that incorporating PEG into pure PLA yields high mechanical performance, correlating linearly with increasing injection temperature. However, the interaction once the three materials are mixed decreases mechanical performance across tested temperatures. Higher biodegradation rates are observed with a larger weight composition of the hydrophilic behavior attributed to sago starch presence. The observed novelty in PLA mixed with 20% sago starch and 10% PEG at 170 °C indicates a better performance in elastic modulus and elongation at break also the degradation rate, emphasizing the role of injection temperature in molding miniplate implants. In conclusion, the interplay of injection molding parameters and material compositions is crucial for optimizing PLA-based miniplate implants, with potential contributions to tissue implants rather than bone implants due to their mechanical limitation.

Numerical simulation study of the injection characteristics affecting trans-/supercritical sprays based on orthogonal experiment design

A mixture of numerical models and orthogonal experiments was used to better understand the mixing behavior and heat/mass transfer in jets operating under supercritical conditions. The goal is to investigate the effects of injector diameter (Dinj), ambient pressure (Pamb), injection temperature (Tinj), injection velocity (Vinj), and ambient temperature (Tamb) on jet evolution. The findings highlight that, among these parameters, Tinj and Dinj exert the most substantial impact on jet mixing characteristics. Higher Tinj and Dinj enhance the jet spreading angle (θhsa) and mixing layer thickness (δ) for improved mixing efficiency. Increasing Tinj and reducing Dinj effectively shorten the potential core length (Lp). Moreover, higher Tinj enhances the temperature rise rate (Tr), effectively raising fuel temperature over a shorter distance. The velocity decay rate (Vd) increases with Vinj and Tinj. Furthermore, this study explores the effects of injection density ratio on evaluation indexes (θhsa, Lp, Vd, Tr and δ) for jet mixing efficiency and trends of jet structural development (Lp, turbulent chaos length (CL) and self-similarity length (SL)). These findings are important for understanding supercritical spray development, guiding engine chamber design and setting operational conditions based on spray behavior.

Advancing injection force modeling and viscosity-dependent injectability evaluation for prefilled syringes

The development of PFS requires a detailed understanding of the forces occurring during the drug administration process and patient’s capability. This research describes an advanced mathematic injection force model that consisting hydrodynamic force and friction force. The hydrodynamic force follows the basic law of Hagen-Poiseuille but refines the modeling approach by delving into specific properties of drug viscosity (Newtonian and Shear-thinning) and syringe shape constant, while the friction force was accounted from empty barrel injection force. Additionally, we take actual temperature of injection into consideration, providing more accurate predication. The results show that the derivation of the needle dimension constant and the rheological behavior of the protein solutions are critical parameters. Also, the counter pressure generated by the tissue has been considered in actual administration to address the issue of the inaccuracies of current injection force evaluation preformed in air, especially when the viscosity of the injected drug solution is below 9.0 cP (injecting with 1 mL L PFS staked with 29G ½ inch needle). Human factor studies on patients’ capability against medication viscosity filled the gap in design space of PFS drug product and available viscosity data in very early phase.

Preparation, shape memory properties and application research of PLA/PCL‐based shape memory polymers doped with Al2O3 and lignin

AbstractIn this paper, the influence of different material trademarks, mass ratios, the melt mass‐flow rate (MMFR) and molecular weights (MW), mold and injection temperatures, Al2O3 powder and lignin on the shape memory properties of PLA/PCL SMP material (PPSM) were then analyzed in detail by different characteristic methods. Besides, three promising applications (Origami metamaterials and variable‐stiffness grippers) are provided utilizing the PPSM doped with Al2O3/lignin. Eventually, a compensating strategy was discussed to improve the final configuration of the SMP after multi‐cycles. The shape memory recovery ratios could be improved by increasing the MMFR of PLA and the MW of PCL. The addition of 2 g‐Al2O3 could shorten the recovery time, while the addition of 2 g‐lignin could increase the thermal‐recovery force and mechanical performance. The shape memory rate under 20 g weights, initial peak forces at room and high temperatures of the origami metamaterials could reach 57%, 2027.29 N and 17.49 N, respectively. The tensile force of banding rebars could reach 150.29 N, which is promising to apply into the construction field.

Analysis of heat transfer performance and system energy efficiency of catalytic combustion heaters for low calorific value waste gas application to oil shale in-situ conversion

In this study, we explore the utilization of low calorific value waste gas for in-situ conversion mining of oil shale. Through simulation, we analyze the effects of variations in the parameters of the catalytic combustion heater's independent variables on the exhaust gas temperature, methane conversion rate, and system energy efficiency (dependent variables). The results demonstrate that larger values of the pore radius, gas injection flow rate, and pulsation flow rate parameters lead to reductions in the corresponding dependent variables. The system's energy efficiency remains stable between 21.94% and 22.46% with increasing gas injection temperature. Furthermore, an increase in the oxygen molar fraction results in elevated methane conversion rates from 0.64% to 58.2% and system energy efficiency from 0.4% to 21.51%. Conversely, an increase in the methane molar fraction causes a decrease in methane conversion from 76.17% to 7.18% and a decline in system energy efficiency from 32.83% to 7.18%. Notably, gas flowback occurs at downhole pressure conditions of 2 MPa. The variation in pressure stabilizes the system's energy efficiency between 21% and 22.10%. The simulation and analysis findings of this study provide significant reference value for subsequent practical testing efforts.

Injection Temperature Impacts on Reservoir Response during CO2 Storage

SummarySustained injection of industrial-scale volumes of cold CO2 into warmer subsurface rock will result in extensive cooling which can alter rock mass mechanical behavior and fluid migration characteristics. Advanced simulation tools are available to assess and characterize such phenomena; however, the effective use of these tools requires appropriate injection temperatures and rock thermophysical parameters (in addition to geomechanical and hydraulic properties). The primary objective of this study was to demonstrate the sensitivity of injection-induced tensile fracturing and fault reactivation to injection temperature and reservoir thermophysical properties during CO2 injection operations. This was achieved by (1) compiling and reviewing thermophysical parameter data available for formations in the province of Alberta, Canada, and CO2 injection temperature records for CO2 injection projects in western Canada and (2) using a 3D, physics-based, fully integrated hydraulic fracturing and reservoir simulation numerical model to examine the geomechanical response of several potential CO2 reservoirs in the Alberta Basin as a function of injection temperature, thermal conductivity (TC), and coefficient of linear thermal expansion (CLTE) values. The simulation results indicate that reducing the fluid injection temperature from 15°C (assumed in previous work) to 2°C (conservative value selected based on temperature data reviewed in this work) could trigger extensive vertical (20–130 m high, 100–600 m long) tensile fractures with rapid fracture initiation and full vertical growth within short periods (weeks to months) and continued horizontal length increase. When low values for thermophysical properties are used, the results show that thermally-induced tensile fracturing is unlikely, whereas the use of high values results in extensive tensile fracturing in all simulations. A similar conclusion was reached for the thermally-induced reactivation (unclamping) of proximal, critically-stressed faults. Notably, slip is predicted for all simulations where high thermophysical property values are used. This confirms that accurate determination of minimum fluid injection temperature and thermophysical parameters is important for containment risk assessment for commercial-scale CO2 storage projects. Another significant outcome of this work is the observation that most thermophysical parameters in the available data were measured using experimental conditions and/or temperature paths that are not representative of CO2 injection projects. As such, the development and validation of best practice approaches for accurate assessment of these parameters seem necessary.

Coupled thermo-hydro-mechanical modeling on geothermal doublet subject to seasonal exploitation and storage

Combining the conventional high-temperature aquifer thermal energy storage system with the common geothermal reservoir development system is a potential alternative to increase energy access, but effects of natural parameters like fracture aperture and reservoir permeability and development parameters like flow rate and injection temperature on the efficiency of energy exploitation and storage have seldomly been investigated. In this study, three assessment parameters and three evaluation criteria were defined to evaluate the sustainability and efficiency of deep geothermal reservoirs with seasonal energy exploitation and storage, and a robust approach of optimizing the development parameters was proposed by combining numerical reservoir model, experimental design and surrogate model, and multiple response optimization method. Based on a case study of the geothermal doublet in Tsinghua University, China, the robustness and reasonability of the developed optimization method were demonstrated. The results show that the optimal development parameters can not only maximize the total recoverable energy and effective recovery efficiency, but also satisfy the requirements of sustainably developing deep geothermal reservoirs. The recoverable heat energy can increase about 20% by adding artificial thermal storage into geothermal reservoir development. Therefore, it is strongly recommended to add energy storage into the future geothermal reservoir development system.

Comparing the properties and growth of graphene on electrolytic and rolled Cu foils by chemical vapor deposition

In this work, we use electrolytic copper foils as substrates for the deposition of graphene by chemical vapor deposition. We investigate the effects of preannealing conditions, methane injection time, and temperature to synthesize graphene with a similar quality as when grown on cold-rolled copper. We find that the electrolytic copper foil’s annealing conditions and CH4 injection temperature determine the quality of graphene.

Using Particle Swarm Optimization with Backpropagation Neural Networks and Analytic Hierarchy Process to Optimize the Power Generation Performance of Enhanced Geothermal System (EGS)

The optimization of the production scheme for enhanced geothermal systems (EGS) in geothermal fields is crucial for enhancing heat production efficiency and prolonging the lifespan of thermal reservoirs. In this study, the 4100–4300 m granite diorite stratum in the Zhacang geothermal field was taken as the target stratum to establish a numerical model of water-heat coupling of three vertical wells. However, relying solely on numerical simulation for optimization is time-consuming and challenging for the determination of the globally optimal production plan. The present study proposes a comprehensive evaluation method for optimizing the performance of EGS power generation based on the integration of particle swarm optimization with backpropagation neural network (PSO-BPNN) and analytic hierarchy process (AHP). Five different PSO-BPNN models were constructed based on the numerical simulation data to predict different EGS power generation performance indexes, including the production temperature, the injection pressure, the total electricity generation, the electric energy efficiency and the levelized cost of electricity. Based on these PSO-BPNN models, the weights of various thermal development evaluation indexes were calculated by AHP to conduct a comprehensive evaluation of the power generation performance of the three vertical wells EGS. The results show that the PSO-BPNN model has good prediction accuracy for EGS prediction of various performance indicators, with a coefficient of determination (R2) exceeding 0.999. The AHP evaluation of all production schemes reveals that the optimal power generation scheme entails a well spacing of 580 m, water injection rate of 56 kg/s, injection temperature of 38 °C and fracture permeability of 2.0 × 10−10 m2. Over a span of 30 years, this scheme can provide a total power generation capacity amounting to 1775 GWh, with an associated LCOE value of 0.03837 USD/kWh. This not only provides a reference for the development and optimization of geothermal systems in the Zhacang geothermal field but also provides a new idea for the optimization design of other geothermal projects.

Heat transfer effect on the modeling of jets under supercritical and transcritical conditions

The injection of nitrogen under supercritical and transcritical conditions, where the injection temperature is below nitrogen’s critical point, but the pressure is above it, is considered in this paper. While the scientific community recognizes that the sharp gradients of the different thermophysical parameters make it inappropriate to employ a two-phase flow modeling at conditions above the critical point, the issue is not restrained to the mere representation of turbulence for a mono-phase flow. Instead, a quantitative similarity with gas-jet-like behavior led to proposing an incompressible but variable density hypothesis suitable for describing supercritical and sub/near-critical conditions. Presently, such an approach is extended and assessed for a configuration including injector heat transfer. As such, axial density and temperature decay rates and jet spreading rates of density and temperature are evaluated, indicating a higher mixing efficiency in the supercritical regime and an overall dominance of heat propagation over momentum transport, with a greater preponderance in the supercritical regime.

Computational Fluid Dynamics Modeling and Analysis of Axial and Radial Temperature of Wellbore during Injection and Production Process

Summary To solve problems such as additional tubing/casing load, casing deformation, and packer failure caused by changes in annular temperature during oil and gas reservoir fracturing and production, based on the well structure of oil and gas reservoirs and transition transient heat transfer mechanism, a four-field coupling simulation model of the temperature field in the main fluid domain of the tubing, the temperature field in the solid domain of the tubing, the temperature field in the annular fluid domain, and the temperature field in the solid domain of the casing is proposed. Considering the coupling of fluid temperature, pressure, and physical parameters, boundary conditions are established based on reservoir characteristics, wellbore heat transfer characteristics, and fracturing and production conditions, and are compiled into Fluent software for simulation through the user-defined function (UDF) method. The effects of the temperature and flow rate of injected fracturing fluid and produced oil and gas on the distribution of the wellbore temperature field and temperature gradient are studied. The research results show that by applying D14-1 and D5-5 gas wells to the model, the simulated temperature is in good agreement with the measured wellbore temperature, and the maximum errors of the simulated values of the two different wells are 6.4% and 4.3%, respectively. As the injection and production operation time increase, the heat transfer between the wellbore and the formation gradually stabilizes. At this time, the injection and production flow rate have little impact on the wellbore temperature field, while the injection and production temperature have a greater impact on the wellbore temperature field. The injection and production temperature will cause changes in annular temperature and temperature gradient, leading to an increase or decrease in pressure within a limited annular volume, resulting in local stress on the tubing and casing. The research results can provide a theoretical basis for the analysis of the temperature field and pressure field of the wellbore during fracturing and oil and gas production, ensuring the safety and stability of fracturing and production.

Risk of surface movements and reservoir deformation for high-temperature aquifer thermal energy storage (HT-ATES)

High-temperature aquifer thermal energy storage (HT-ATES) systems are designed for seasonal storage of large amounts of thermal energy to meet the demand of industrial processes or district heating systems at high temperatures (> 100 °C). The resulting high injection temperatures or pressures induce thermo- and poroelastic stress changes around the injection well. This study estimates the impact of stress changes in the reservoir on ground surface deformation and evaluates the corresponding risk. Using a simplified coupled thermo-hydraulic-mechanical (THM) model of the planned DeepStor demonstrator in the depleted Leopoldshafen oil field (Upper Rhine Graben, Germany), we show that reservoir heating is associated with stress changes of up to 6 MPa, which can cause vertical displacements at reservoir depth in the order of 10–3 m in the immediate vicinity of the hot injection well. Both the stress changes and the resulting displacements in the reservoir are dominated by thermoelasticity, which is responsible for up to 90% of the latter. Uplift at the surface, on the contrary, is primarily controlled by poroelasticity with by two orders of magnitude attenuated displacements of << 10–3 m. Our calculations further show that the reservoir depth, elastic modulus, and injection/production rates are the dominant controlling parameters for the uplift, showing variations of up to two order of magnitudes between shallower reservoirs with low elastic moduli and deeper and more competent reservoirs. In addition, our findings demonstrate that the cyclic operation of HT-ATES systems reduces the potential for uplift compared to the continuous injection and production of conventional geothermal doublets, hydrocarbon production, or CO2 storage. Consequently, at realistic production and injection rates and targeting reservoirs at depths of at least several hundred meters, the risk of ground surface movement associated with HT-ATES operations in depleted oil fields in, e.g., the Upper Rhine Graben is negligible.

Thermo-hydro-chemical modeling and analysis of methane extraction from fractured gas hydrate-bearing sediments

Hydraulic fracturing is widely used in enhancing hydrocarbon recovery efficiency of unconventional reservoirs including gas hydrate-bearing sediment (GHBS). However, the underlying mechanisms governing the influences of fractures on the intricate multi-field coupled processes during methane extraction remain poorly understood. This study develops a fully coupled thermo-hydro-chemical (THC) model for methane extraction from fractured GHBS under combined heat injection and depressurization operations. Novel dimensionless numbers are proposed to characterize the underlying heat transfer, fluid flow, and hydrate decomposition processes. The results reveal that depressurization induced fluid flow dominates methane extraction in the early stages, while heat injection induced thermal processes become the primary controlling factor in the intermediate and long-term stages. The flow field primarily governs the global-scale hydrate decomposition process, whereas the thermal field dictates the local-scale evolution of the pre-decomposition front. We find that increasing injection temperature and decreasing production pressure could improve gas recovery efficiency, although economic consideration may constrain these production strategies. Particularly, increasing injection temperature expands local hydrate decomposition zone and boosts gas production, while depressurization at the production well reduces the overall gas hydrate saturation and leads to extra gas production. Variation in well spacing show little effect on the gas recovery efficiency, but the total gas production changes for the change of reservoir scale. This study provides insights into the mechanisms of coupled thermo-hydro-chemical behaviors during methane extraction from fractured GHBS, and offers a fundamental model for the optimization of both extraction efficiency and economic viability of gas hydrate recovery.

Increasing the efficiency of the bactericide use at PS-4 of "Ozenmunaigas" JSC

Background: The study is devoted to increasing the efficiency of bactericidal treatment of sediments at the oil fields of Ozenmunaigas JSC. Calculations were carried out to assess the capability of heating the formation and the pipeline, hydraulic heat loss when injecting a bactericide, and the efficiency of mixing the reagent with water. The analysis revealed the ineffectiveness of mixing the bactericide with water at low temperatures and rates of inhibitor introduction.&#x0D; Aim: The purpose of the study was to identify solutions to overcome the problems caused by the increased content of hydrogen sulfide in the fields of Ozenmunaigas JSC. This included addressing the temperature issues during bactericide delivery and increasing the rate of inhibitor injection.&#x0D; Materials and methods: Heat loss calculations were carried out using the UniSim program for both tank heating and input lines, as well as an analysis of bactericide mixing inside the pipeline using the ANSYS program.&#x0D; Results: The results of the study led to specific recommendations and measures that could mitigate the problems associated with temperature and rate of injection. These included measures such as heating and insulation, temperature control, regular inspection of thermal insulation, and selection of a new reagent with improved mixing properties at lower temperatures. It is also recommended to install reagent flow and temperature sensors along with power supply control.&#x0D; Conclusion: The implementation of the proposed measures will effectively solve the problems associated with high levels of hydrogen sulfide. This approach will ensure a smooth and safe flow of bactericide and help maintain the operating efficiency of the affected facilities.

A Numerical Simulation Approach for Superheated Steam Flow during Multipoint Steam Injection in Horizontal Well

Superheated steam flow during multipoint steam injection technology has a good effect on improving the steam absorption profile of heavy oil thermal recovery wells, enhancing the production degree of horizontal section of thermal recovery wells, and enhancing oil recovery. Based on the structure of multipoint steam injection horizontal string, considering the characteristics of variable mass flow, pressure drop of steam-liquid two-phase flow, and throttling pressure difference of steam injection valve in the process of steam injection, this paper establishes the calculation model of various parameters of multipoint steam injection horizontal wellbore and calculates the distribution of steam injection rate, temperature, pressure gradient, and dryness along the section of multipoint steam injection in horizontal wellbore. The results show that the temperature and pressure decrease gradually from heel to toe, and the steam dryness decreases gradually. Considering the influence of throttle pressure difference of steam injection valve and pressure drop of gas-liquid two-phase flow in the wellbore, the traditional calculation model of steam injection thermodynamic parameters is optimized, and the optimization of wellbore structure and steam injection parameters is an effective method to achieve uniform steam injection in horizontal wells. The steam injection uniformity of horizontal wells can be effectively improved by adjusting the steam injection valve spacing and steam injection parameters. When the steam injection volume is 200 m3/d and the steam injection valve spacing is 20 m, a more stable steam injection effect can be obtained. The findings of this study can help for better understanding of improving the uniformity of steam injection and enhancing the recovery factor.

Combustion efficiency and CO/NO[formula omitted] emissions for a biomass plancha-type stove: Effect of the air excess ratio

For plancha-type stoves, the chemical model of the combustion process and the influence of the air excess ratio (λ) have received little attention. The goal of this work is to use numerical simulations to study the influence of λ on the performance of a plancha-type stove. To simulate species transport, heat transfer, and fluid dynamics, the ANSYS FluentTM software is used. A two-reaction chemical model is employed to calculate volatile combustion efficiency (VCE), emissions of carbon dioxide (CO2), carbon monoxide (CO), and nitrogen oxides (NOX). Additionally, global parameters like thermal efficiency (TE) and heat transfer through the comal (Q) are evaluated. The following comparisons are offered to validate the numerical methodology: (i) to experimental measurements for the TUYA plancha type stove, (ii) to a one-reaction chemical model, and (iii) for various solid biofuels (fuelwood, charcoal, and peat). Results show that λ has a considerable impact on both VCE and CO2 emissions. VCE values were found to be up to 98% for λ=2.5 and λ=3. Lower combustion temperatures and higher values for λ increased NOX and CO emissions. Aside from the two-reaction model, the comparison to experimental performance is better when the air excess ratio and secondary-air were considered. Finally, with λ=3 and a temperature of injection of 1123 K, fuelwood has a higher VCE than charcoal and peat. Emissions and energy performance might vary dramatically for the different solid biofuels.

One-Dimensional Numerical Simulation on Removal of CO2 Hydrate Blockage around Wellbore by N2 Injection

CO2 sequestration in sediments as solid hydrate is considered a potential way to capture and store anthropogenic CO2. When CO2 hydrate is formed in front of CO2 migration, the injection channel will be blocked, and the removal of hydrate blockage becomes the first problem that must be faced. This work proposed an N2 injection method to remove CO2 hydrate blockage. Based on numerical simulation, a study was conducted using TOUGH+MIXHYD v.1.0 to confirm the feasibility of N2 injection and compare it to depressurization. The spatial and temporal distribution characteristics of pressure, temperature, hydrate saturation, and gas saturation were investigated. Under the combined effects of temperature, pressure, and gas composition, secondary CO2-N2 hydrate can form far from the injection point, causing an increase in local temperature and hydrate saturation. The rate of CO2 hydrate dissociation using direct depressurization is significantly slower compared to N2 injection methods. As the pressure of N2 injection increases, the rate of CO2 hydrate dissociation notably accelerates, which does not show a significant increase with increasing injection temperature. This work introduced a novel approach to addressing the issue of CO2 hydrate blockage, which holds prominent significance for the advancement of hydrate-based CO2 geological sequestration.

Optimization of double layered horizontal directional drilled ground heat exchangers by water injection into the borehole

Ground Heat Exchangers (GHEs) drilled using Horizontal Directional Drilling (HDD) technology have been proven to be a cost-efficient way of installing ground source heat pump systems (GSHP). They can also be installed in places where conventional horizontal ground heat exchanger (HGHE) would not be possible e.g., due to lack of land.In this research, a double layered horizontal borehole was installed as a GHE in Saga City, Japan. The two holes had a diameter of 114.3 mm and a length of 59 m and 56 m, respectively, while reaching depths of 5 m and 9.5 m. A polyethylene pipe with an outer diameter of 60 mm was inserted as a borehole heat exchanger (BHE). In March 2022, a two days thermal response test (TRT) showed the influence of rainfall on the system. A numerical model developed in FEFLOW based on the GHE dimension and the region's geology was validated using the measured temperatures of the heat medium at the return point and outlet of the GHE during the TRT. The validated model was then used to carry out sensitivity analysis examining different conditions of water injection into the borehole. The result of the sensitivity analysis showed that water injection into the borehole can improve the performance of the system and reduce the temperature change of the heat medium. Varying the injection rate can improve performance to a certain degree and the injection point has a strong influence on the performance. The injection temperature was also found to play a role in the performance, but even high temperatures in the case of heating showed significant improvement. Lastly, the influence of permeability was investigated and showed that impermeable layers are more favorable for injection compared to permeable layers.