Injection Time Increases Research Articles

Interpretation and reporting considerations of low-level DNA profiles following MinElute® purification of PowerPlex® 21 amplified products

The generation of high-quality DNA profiles from trace amounts of DNA continues to be an issue in forensic casework. Several methods have been proposed over the years to increase recovery rates for low input DNA, including purification of PCR products, an increase in PCR cycle numbers and increasing injection time or voltage during electrophoresis. In this study, the characteristics of DNA profiles generated using QIAGEN MinElute® purification of Promega PowerPlex® 21 amplified products for low DNA input samples, ranging from 80 pg down to 4 pg, were evaluated. MinElute® purification was found to be a simple, effective and time efficient method, which can greatly improve the resolution of amplified PCR products, recovering 100% of donor concordant alleles from as little 16 pg of input template DNA and generating sufficient allelic information for interpretation from as low as 4 pg inputs. However, as is commonly observed with low template DNA samples, the results exhibited extensive disparity in the effects of stochastic variation in amplification, including increased heterozygote peak height imbalance, stutter ratios and instances of allelic drop-in and drop-out, both within and between replicates. As such, it is important that the extent and variability of these stochastic effects are appropriately incorporated in the development of robust profile interpretation guidelines for DNA profiles generated from purified PCR products.

Effects of injecting L-Arginine on immune responses and intestinal structure of the hybrid grouper (Epinephelus fuscoguttatus ♀× Epinephelus lanceolatus ♂)

To study the effects of L-Arginine (Arg) on immune responses and intestinal structure in a hybrid grouper (Epinephelus fuscoguttatus ♀× Epinephelus lanceolatus ♂), intraperitoneal injection of different Arg doses (0, 50, 100, 200 mg per kg body weight of grouper) was administered once every seven days, repeating the process three times in the present study. A total of 216 groupers (initial weight of 349.42 ± 0.67 g) were randomly divided into four groups with three replicates, and each of the replicates comprised 18 fish. Serum was sampled at the seven, 14, and 21 days post-injection. The results showed that injection of Arg had a significant effect on serum albumin, immunoglobulin M (IgM), total protein (TP) and nitric oxide (NO) content, as well as nitric oxide synthase (NOS) and lysozyme activity (P < 0.05). With an increase of Arg dose, serum NO, TP, and albumin levels initially increased and subsequently decreased, and were significantly higher in fish injected with Arg at doses of 50 and 100 mg/kg in comparison to the control group. On days seven and 14, the highest serum albumin, TP, and IgM levels were observed in the 100 mg/kg group. With an increase in injection time and frequency, the 50 mg/kg group showed the optimal immune status after the third injection. Based on the results of the intestinal digestive enzyme activity and morphology, the injection of Arg at 50 mg/kg was the most beneficial, followed by the 100 mg/kg dose. Injection of 200 mg/kg Arg, especially after three injections, had adverse effects on immune responses and intestinal structure. These findings indicated that the intraperitoneal injection of L-Arg at a certain concentration can enhance the immunity and intestinal morphology of groupers. Notably, the most significant benefits were observed after three consecutive injections of Arg at 50 mg/kg in this experiment.

Fracture propagation laws of staged hydraulic fracture in fractured geothermal reservoir based on phase field model

Hydraulic fracturing is widely used in geothermal resource exploitation, and many natural fractures exist in hot dry rock reservoirs due to in-situ stress and faults. However, the influence of natural fractures on hydraulic fracture propagation is not considered in the current study. In this paper, based on the phase field model, a thermo-hydro-mechanical coupled hydraulic fracture propagation model was established to reveal the influence of injection time, fracturing method, injection flow rate, and natural fracture distribution on the fracture propagation mechanism. The results show that fracture complexity increases with an increase in injection time. The stress disturbance causes the fracture initiation pressure of the second cluster significantly higher than that of the first and third clusters. The zipper-type fracturing method can reduce the degree of stress disturbance and increase fracture complexity by 7.2% compared to simultaneous hydraulic fracturing. Both low and high injection flow rate lead to a decrease in fracture propagation time, which is not conducive to an increase in fracture complexity. An increase in the natural fracture angle leads to hydraulic fracture crossing natural fracture, but has a lesser effect on fracture complexity. In this paper, we analyzed the influence of different factors on initiation pressure and fracture complexity, providing valuable guidance for the exploitation of geothermal resources.

Investigation of the Oil-Soluble Particulate Temporary Plugging Agent-Assisted Water Huff ‘n’ Puff Enhanced Oil Recovery in Tight Oil Reservoirs

Summary Water huff ‘n’ puff is an effective enhanced oil recovery (EOR) technology for tight oil reservoirs. However, the oil production of horizontal wells declines seriously after several huff ‘n’ puff cycles, and a large amount of oil is still trapped in the reservoir due to the heterogeneity of fracturing sections. The temporary plugging agent had been used for plugging high-permeability areas and thus diverting the following fluid into small permeability areas. It would improve the sweep efficiency of flooding fluid, enhancing oil recovery. However, the use of the oil-soluble particulate temporary plugging agent in the water huff ‘n’ puff application is barely reported. Therefore, the feasibility and influencing factors of oil-soluble particulate temporary plugging agent-assisted water huff ‘n’ puff (TAWHP) in enhancing oil recovery was investigated in this study. First, based on the evaluation of the performance of the oil-soluble particulate temporary plugging agent, the oil recovery of fractured core samples with different apertures for water huff ‘n’ puff and TAWHP was compared via the parallel-core experiment to verify the feasibility of TAWHP in enhancing oil recovery. The temporary plugging agent had good oil solubility, a low residual rate in the formation, and little damage to the formation. The oil recovery yielded by TAWHP was 5.17% higher than the traditional water huff ‘n’ puff process. More oil (i.e., about 1.71%) could be expelled from the fractured core samples with a small aperture. It indicated that the EOR performance yielded by water huff ‘n’ puff after several cycles could be enhanced by adding the oil-soluble particulate temporary plugging agent. After that, a mathematical model of TAWHP was established to investigate the effect of TAWHP parameters on EOR performance. The simulation results showed that the cumulative oil production increased with the increase in injection time of the temporary plugging agent solution, but the trend would level-off after 10 minutes. Moreover, as the diversion index increased, the effect of the injection rate on cumulative oil production gradually enhanced while the effect of the soaking time gradually weakened. Furthermore, the difference in cumulative oil production at different diversion indexes gradually increased as the huff ‘n’ puff cycle increased. This work could provide theoretical guidance for water huff ‘n’ puff enhancing oil recovery after several cycles.

Numerical study on the influence of temperature on CO2-ECBM

CO2-ECBM can not only improve the production of CBM, but also contribute to CO2 geological sequestration, which has multiple economic effects. In this paper, COMSOL simulation software was used to conduct numerical simulation studies on the 3# coal seams in Qinshui Basin. A fully coupled model of coal deformation, gas flow and migration, and thermal transfer was established to evaluate the effect of temperature on the production of CBM by CO2 injection. The results indicates that temperature is a key factor affecting CH4 production and CO2 storage. Increasing injection temperature can significantly accelerate the process of gas displacement and the CO2 storage is more sensitive to temperature than the CH4 production. In contrast, both the CH4 production and the CO2 storage decrease with the increase of initial temperature of coal seam and the permeability will decrease faster. With the increase of injection time, the effective influence radius of displacement increases, but the increment of influence radius decreases gradually. The lower the initial temperature of the coal seam, the larger the influence radius, the influence radius increases as a whole with the increase of time. Low Young's modulus or high Poisson's ratio can effectively increase CO2 storage and CH4 production.

Advance Time to Determine Injection and Flushing Times in Drip Fertigation

Drip fertigation has shown unquestionable benefits in recent decades compared to traditional farming fertilization practices. However, a fertilizer dissolved in the irrigation water must be evenly distributed in the fertigated area. Irrigation system and fertigation system characteristics and operational management potentially affect the uniformity of fertilizer and water distribution. Advance time (AT), which is an intrinsic and determinable characteristic of the irrigation system, has not been assessed as a useful technical criterion for managing the uniformity of fertilizer distribution in drip fertigation. The objective of this study was to assess the use of advance time as a technical criterion for determining the duration of injection time and flushing time that provides a satisfactory uniformity of spatial distribution of the fertilizer in drip fertigation. Therefore, the distribution uniformity of potassium chloride (KCl) fertilizer and water was evaluated at six injection times equivalent to 25, 50, 75, 100, 150, 200% AT, and two flushing times equivalent to 100 and 200% AT through Christiansen’s uniformity coefficient (CU) and distribution uniformity (DU). The used drip irrigation system had 10 drip strips with 12.5 m length, a flow rate of 1.40 L h−1 per dripper, and AT of 12.5 min. The injection solution was prepared with 40 g L−1 of KCl. The results indicate that the distribution uniformity of KCl improved significantly with increasing injection time. The injection time of 200% AT promoted the greatest uniformity of distribution of KCl with CU of 0.977 and DU of 0.962. The flushing time of 100% AT was sufficient to rinse the irrigation system and promoted a satisfactory spatial distribution uniformity with a CU of 0.983. In both tests, the uniformity of irrigation water distribution was satisfactory, with CU of 0.988 and DU of 0.982 (average). Advance time is an intrinsic characteristic of the irrigation system that is useful in determining the duration of injection time and flushing time in a more technical way for drip fertigation with satisfactory spatial distribution uniformity of the fertilizer.

Investigation on the Injection Pattern of Intermittent Natural Gas Flooding in Ultra-Low Permeability Reservoirs

Natural gas is a viable oil displacement agent in ultra-low-permeability reservoirs due to its good fluidity. It can also cause gas channeling during continuous injection, which limits its oilfield application. In order to relieve gas channeling during natural gas flooding, the injection mode should be changed. The use of intermittent natural gas injection (IGI) after the continuous natural gas injection in an ultra-low-permeability reservoir is proposed, and optimization of the injection parameters is discussed. The results show that IGI can be divided into three stages, the gas injection stage, the well shutting stage and the oil production stage. With the increase in injection time, the oil recovery enhances obviously as a result of IGI because the gas fingering can be controlled at the well shutting stage, and the gas/liquid ratio grows slowly because the gas breakthrough can be reduced at the oil production stage. The oil recovery improves with the increase in cycle time of IGI, while the increase rate reduces evidently after the cycle time reaches 360 min. The oil recovery increment is low if the cycle index exceeds 3 in the ultra-low-permeability reservoir. Thus, the optimal cycle time for each round and the appropriate cycle index of IGI are 360 min and three rounds.

Experimental study of multi-bubble hydraulic efficiency of spark-generated bubbles

We investigated the hydraulic efficiency of spark-generated bubbles under conditions of different discharge polarities and different electrode numbers. A positive polarity discharge can generate a larger spark-induced bubble than a negative polarity discharge generated using the same electrical and electrode parameters. The hydraulic efficiency of both the positive and negative polarity discharges decreases with the increasing number of electrodes. Increasing the number of electrodes leads to faster energy injection times and higher average powers. We found that the hydraulic efficiency increases when energy injection time increases but that it decreases when the average power increases. When the energy injection time is longer than 100 µs and the average power is less than 100 kW, hydraulic efficiencies of more than 15% and 10% were realized for the positive and negative polarity discharges, respectively. These results indicate that longer energy injection times will be helpful in gaining higher hydraulic efficiency for these bubbles.

Optimal Parameters of Gas Drainage and Carbon Dioxide Inerting Technology and Its Application in a High Gassy and Spontaneous Combustion Mine.

In the process of coupling disaster prevention and control of gas and coal spontaneous combustion in goaf, there is a great contradiction between the gas drainage and carbon dioxide inerting technology. The key performance indexes are put forward to solve the coupling disaster, such as the air quantity of the intake airway (A), the gas drainage rate (B), the carbon dioxide injection rate (C), and the injection depth (D). Using the numerical simulation method and the orthogonal test of four factors and three levels, we establish the coupling disaster model of the no. 7436 working face in the Kongzhuang coal mine. Using a combination of the relative membership degree method and range analysis, the optimal level of each factor is determined, which is AIIBIIICIIDII. Furthermore, the distribution law of the airflow field is obtained under the conditions of different gas drainage rates and carbon dioxide injection rates. The results show that the gas concentration decreases with an increase in gas drainage in the upper corner, but it has little impact on the width of the oxidation zone. The gas concentration can be reduced to 1%, while the gas drainage rate is higher than 35 m3/min. With an increase in gas injection rate, the carbon dioxide emission rate increases in the upper corner, but the width of the oxidation zone decreases. Also, the gas injection rate should be less than 800 m3/h. Moreover, with an increase in injection time in the upper corner during the injection process, the carbon dioxide and gas concentrations increase, and the maximum carbon dioxide concentration is 1.3%, and the maximum gas concentration is 0.42%, which is consistent with the results of numerical simulations.

Competition between cooling contraction and fluid overpressure on aperture evolution in a geothermal system

Comprehensive understanding of aperture evolution of HDR (hot dry rock) fracture is critical for enhancing permeability in a geothermal system. Coupled HM (hydro-mechanical) and THM (thermo-hydro-mechanical) simulations are conducted to elucidate the competition between cooling contraction and fluid overpressure in fracture aperture enhancement during heat extraction. The effects of critical factors, including fracture geometry, reservoir properties, and injection settings on this competitive relationship, are systematically examined. We find that (1) fracture aperture is dominated by the competing effect of cooling contraction and fluid overpressure; the cooling-induced aperture grows as the injection time increases, declining the overpressure-induced aperture; (2) high thermal expansion coefficient and low fracture normal stiffness tremendously enlarge total and cooling-induced apertures and mildly shrink the overpressure-induced aperture; (3) decreasing fracture spacing and increasing fracture length remarkably improves the total aperture; the former increases the cooling-induced aperture while the latter enhances the overpressure-induced aperture; (4) the reduction of injection temperature increases the cooling-induced aperture and lowers the overpressure-induced aperture; the growth of flow rate expands both the cooling-induced and overpressure-induced apertures. We thus unveiled the mystery of the invisible aperture evolution during heat extraction. The findings largely benefit the optimization of mining parameters of a geothermal reservoir.

Performance and emission characteristics of biogas-bio diesel fuelled RCCI engine at various butanol-gasoline injection timings

Energy, a basic need of human life, has been playing significant role behind many technological developments. Most of the world’s commercial energy requirements are fulfilled by using fossil fuels. Combustion of fossil fuels releases toxic gases which in further turns as a source of pollution for the environment, globally. The present research work focused on minimizing the emissions that emerges during combustion in an IC engine through Reactivity Controlled Compression Ignition (RCCI) mode. The performance and emission characteristics of a single-cylinder CI engine are analyzed with 3 different fuels; biodiesel, butanol-gasoline (1:4 ratio), and biogas. The operational loads taken for the present study falls in the range from 5 N-m to 20 N-m at the engine speed of 1800 RPM. The influence of biogas on the emission characteristics is exclusively carried out with two different flow rates; 12lpm and 16lpm. The injection timings for butanol-gasoline blend are varied from 0 to 8ms. Fuel properties such as Viscosity, Vapor pressure, Density, Cloud point, Pour point, and Flashpoint are estimated. Engine parameters such as Brake Thermal Efficiency (BTE), Volumetric Efficiency (VE), HC, CO, NOx and smoke emissions, Peak pressure, Heat Release Rate (HRR), Ignition Delay, are analyzed. It is observed from the experiments that increasing injection time of pilot fuel - increases the HC and CO emissions; reduces the NOx emissions; decreases the smoke level with increase in biogas flow rate; and decreases the BTE, VE, and HRR

Experimental study on effect of effect time of supercritical CO2 fracturing fluid on mechanical properties of sandstone

Supercritical CO2 fracturing is a novel hydro-free fracturing technology, which has the characteristics of minor damage to reservoirs and higher efficiency. During the process of fracturing, the CO2 fracturing fluid will infiltrate into the pore of rock, resulting in the change of rock mechanics properties. The rock samples were drilled from the same layer, then the supercritical CO2 fracturing fluid was used to soak the rock samples to measure the changes of rock mechanical properties under different soaking time. When the pore pressure is 0 MPa, the fracture initiation stress of rock sample is about 40% of its peak strength, and with the increase of pore pressure, the elastic stage decreases and the plastic stage increases, while the pore pressure reaches 31 MPa, the core fracture initiation stress is about 20% of its peak strength. The results show that with the longer CO2 soaking time, the shorter elastic stage with the longer plastic stage and the weaker compressive strength, the smaller elastic modulus, and the higher Poisson's ratio. This indicates that the strength of rock decreases gradually with the increase of injection time in supercritical CO2 fracturing process, which is conducive to the formation of longer fractures.

Coupled seepage-damage effect in fractured rock masses: model development and a case study

The stability of rock engineering is generally dominated by existing seepage , particularly the seepage evolution due to the rock masses damage. However, the current research generally overlooks the seepage-damage coupling when studying the hydraulic-mechanical coupling effect in rock masses. This study aims to propose a dual-medium model, including equivalent continuous and discrete fracture media to study the coupled seepage-damage effect in fractured rock masses . The dual-medium seepage model considers the substantial water storage of the fracture network and the high conductivity of major large-scale fractures. Also, the seepage evolution is constructed to be a function of stress, seepage pressure and length of crack propagation in the rock mass. To illustrate the new model's application, a case of high-pressure water injection in a coal seam has been investigated to reveal the damage evolution in the coal seam. The results indicate that during the initial stage of the water injection, the seepage pressure in the discrete fracture medium increases faster than that in the equivalent continuous medium. Moreover, the seepage pressure difference between the two media gradually decreases with the increase of the seepage time, eventually forming a stable seepage field in the coal seam. Notably, the high-pressure water injection in the coal seam significantly affects the distribution of the coal seam's stress field, resulting in the effective minimum principle stress changing from compression to tension states. Also, during coal seam water injection, the damage zone and major fracture apertures in the coal seam gradually increase with increasing injection time .

Perforation Optimization of Intensive-Stage Fracturing in a Horizontal Well Using a Coupled 3D-DDM Fracture Model

Intensive-stage fracturing in horizontal wells is a potentially new technology for reservoir stimulations of deep shale oil and gas. Due to a strong stress interaction among the dense fractures, the fracture geometry and stress field are very complicated, which are the bottlenecks of this technology. Aiming at simulating the intensive-stage fracturing, a coupled three-dimensional (3D) fracture model of multiple-fracture simultaneous propagation is proposed. The dynamic behavior of the fracture propagation and stress field was analyzed using this model. The perforation parameters were optimized for improving the fracture geometry equilibrium. The results showed that the exterior fractures of the multiple fractures penetrated by the horizontal well become the main fractures, while the interior fractures are drastically restrained. The exterior fracture widths increased with increasing injection time, while the interior fracture widths decreased with increasing injection time. An extruded region was created among the multiple fractures, which restrained the propagation of the interior fractures. Only increasing the perforation cluster number did not improve the fracture geometry equilibrium in the intensive-stage fracturing. To improve the fracture geometry equilibrium, we suggest designing more perforation numbers in each perforation cluster and ensuring that both the perforation number and diameter in the interior perforation cluster are greater than those of the exterior ones.

Numerical Simulation of Channelization Near the Wellbore due to Seepage Erosion in Unconsolidated Sands during Fluid Injection

The channels may be formed in the unconsolidated sands reservoir due to formation failure during high-pressure water injection or frac-packing. Based on the continuum mechanics, a mathematical model has been established to simulate the formation process of big channels in unconsolidated sands reservoir during fluid injection. The model considers the effect of reservoir heterogeneity, solid particles erosion, and deposition. The dynamic formation process of channels around the borehole and its influencing factors are analyzed by this model. The results indicate that the seepage erosion plays a very significant role in the formation of the channels during fluid injection for the unconsolidated sands with extremely low strength. The formation of the channels is closely related to the duration of fluid injection, injection pressure, reservoir heterogeneity, formation plugging, and critical fluid velocity. The long channels are more likely to form as injection time increases. Higher injection pressure will lead to higher flow rate, thus eroding the solid particles and forming big channels. The increase of the rock strength will enhance the value of critical fluid velocity, which makes it difficult for the occurrence of erosional channelization. The near-wellbore damage of the formation will decrease the flow rate, and the preferential flow channels are less likely to be induced under the same injection pressure when compared with undamaged formation. In addition, we also found that the reservoir heterogeneity is essential to the formation of preferential flow channels. The channels are especially prone to be formed in the regions with high porosity and permeability at the initial time. The study can provide a theoretical reference for the optimal design of high-pressure water injection or frac-packing operation in the unconsolidated sands reservoir.

A Semi-Analytical Model Based on the Volumetric Source Method to Predict Acid Injection Profiles of Horizontal Wells in Carbonate Reservoirs

Abstract Acid treatment is an important measure to improve production for horizontal wells of carbonate reservoirs. Acid injection profile of horizontal wells (AIPHWs) is the most critical indicator of the success of the acidification. Currently, most previous works studied AIPHW based on the point source method. However, an inherent singularity exists in the point source solution, and hence, the calculation speed is too slow or the solution does not converge. To solve this problem, a semi-analytical model (coupling the wellbore flow model and reservoir seepage model) by the volumetric source method is presented to determine AIPHW in carbonate reservoirs. In this new coupled model, the permeability heterogeneity, formation contamination, acid-induced wormhole formation, and wellbore pressure drop are all considered. The results of the validations show that the results from the proposed method match well with the model results from the literature. Then, the effects of the acid injection flowrate, acid injection time, and permeability heterogeneity on the AIPHW are studied. According to the sensitivity analysis, we find that the disequilibrium degree of AIPHW becomes stronger as acid injection flowrate increases, acid injection time increases, and permeability heterogeneity coefficient increases. This study provides a guide for the design of horizontal well acidification and the evaluation of acid treatments of horizontal wells in carbonate reservoirs.

A Numerical Model for Investigating the Steam Conformance along the Dual-String Horizontal Wells in SAGD Operations

Non-uniformity of the steam-assisted gravity drainage (SAGD) steam chamber significantly decreases the development of heavy oil reservoirs. In this study, to investigate the steam conformance in SAGD operations, a wellbore model is developed for fluid flow in dual-string horizontal wells. Then, a three-dimensional, three-phase reservoir model is presented. Next, the coupled wellbore and reservoir model is solved with a fully implicit finite difference method. Finally, the effects of the injector wellbore configuration, steam injection ratio and injection time on the steam conformance are investigated. The results indicate that under different injector wellbore configurations, the closer the differences between the pressure drop from the landing position of the short string to the heel of the wellbore and the pressure drop from the landing position of the short string to the toe of the wellbore, the better is the steam conformance. The smaller the difference in the steam injection rate between the long and short injection strings, the higher is the uniformity of the steam chamber. The injector annular pressure profile uniformity is consistent with the steam conformance. Creating a more uniform steam pressure in the annulus of the injector improves the uniformity of the steam chamber. The steam conformance decreases with increasing injection time, so the optimization method of steam chamber uniformity should be adjusted according to different injection times.

Displacement infiltration diffusion model of power-law grout as backfill grouting of a shield tunnel

Shield tunnel is widely adopted in the metro construction, and backfill grouting is the significant part. With power-law fluid grouts as the study object, a cylindrical infiltration diffusion model and spherical infiltration diffusion model are developed by applying the generalized Darcy law and theories of seepage mechanics based on the displacement effect of grout on groundwater. Through examples, the impact of factors including grouting pressure and formation permeability coefficient in the spherical displacement infiltration diffusion model on diffusion radius, flow rate, total pressure of grout in segments, and uniform equivalent pressure in grout diffusion area (grout pressure per unit area in a segment) is analyzed. The result shows that, the diffusion speed, injection flow rate and the pressure received in segments increase with an increase of the grouting pressure. Meanwhile, as the injection time increases, the flow rate of grout under conditions of different grouting pressure all decreases, and a sharp decrease exists. The diffusion speed and grouting pressure are positively correlated to the permeability coefficient, and with the increasement of the injection time, the diffusion displacement of grout in different permeability coefficient varies increasingly, the increase amplitude of the pressure acting on the segment by grout increases gradually.

Experimental investigation of the impact of liquid carbon dioxide injection on temperature in pulverized coal

AbstractUsing liquid carbon dioxide (LCO2) as a medium for underground coal fires prevention and control, while reducing the emissions of CO2, is a promising option for CO2 utilization worldwide. However, the mechanism of LCO2 flow with phase transition on coal temperature is still not clear. In this work, an experimental system was designed and fabricated to investigate the phase transition behavior and temperature variation during injecting LCO2 into pulverized coal and the impact of mass flow rate, nozzle diameter, and injection pressure on cooling effect. The results indicate that when LCO2 was injected into the pulverized coal, the instantaneous phase change into solid and vapor occurred just after leaving the release port. An intensive heat transfer process occurred because of the throttling effect, flashing effect, and sublimation and thereby formed a cooling area (&lt;−56.6°C), which was the main area of cooling effect and phase transition; as injection time increases, the range of this area increases in the form of logarithmic function. In addition, the cooling area exhibited a strong dependence on the injection conditions, and its correlation with mass flow rate, nozzle diameter, and injection pressure are identified as exponential, logarithmic, and linear relationship by dimensionless analysis, respectively. Meanwhile, an empirical formula was developed for calculating the cooling effect under various injection conditions. In summary, the experiments provided fundamental data and regime for predicting the effect of LCO2 injection on the temperature of pulverized coal, which can be used to guide the utilization of LCO2 for coal fires prevention. © 2020 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Temperature characteristics and influence of water-saturated soil resistivity on the HVDC grounding electrode temperature rise

The temperature rise process has always been the main factor for the safe operation of high-voltage direct current (HVDC) grounding electrodes, and the soil resistivity is the key parameter affecting the temperature rise of the grounding electrode. In some region where rainfall is high or groundwater is abundant, the soil moisture content at the electrode site may be very high or saturated. Therefore, studying the temperature characteristics of soils with saturated water content (water-saturated soil) for grounding electrode heating is particularly important. In this study, the resistivity measurement of temperature rise was conducted on different types of water-saturated soil. On the basis of this measurement result, an electro-thermal coupling finite element model of grounding electrode in water-saturated soil was established. Then the reliability of the coupled model is verified through an experiment of the vertical electrode in water-saturated soil. The comparison of experimental and simulation results shows that the maximum temperature error is 3.5%. Finally, the influence of water-saturated soil resistivity on practical engineering application was analyzed. Under the condition of water-saturated soil, the saturation of electrode temperature rise curve gets more pronounced as the current injection time increases. Thus, the temperature rise rate of the actual grounding electrode is lower than the calculation result without considering the water-saturated soil resistivity. Therefore, using the temperature characteristics of water-saturated soil resistivity to simulate the temperature rise of the grounding electrode can provide a theoretical basis for the grounding electrode to work under water-saturated soil conditions.