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Sampling and recognizing the wind pressure performance curve from the wind performance curve image, and then fitting the wind pressure performance function, is a key technology for solving the mine ventilation network. Currently, manual methods are commonly used to recognize wind pressure performance curves, which have low efficiency and poor accuracy. This study proposes an automatic recognition method for the wind pressure performance curve of ventilator based on image processing technology. The method uses bilateral filtering, image sharpening, and binarization techniques to preprocess the original ventilator wind pressure performance curve image, in order to improve image quality. The method extracts grid lines and coordinate text from the performance curve image of the ventilator based on corrosion algorithm and contour detection algorithm. The method uses logical operation, median filtering, contour detection, and K3M algorithm to extract the wind pressure performance curve. The pixel coordinates of the wind pressure performance curve are recognized using a row by row pixel recognition method. The method uses template matching algorithm to recognize coordinate numbers, and then complete the conversion from pixel coordinates to physical coordinates, achieving wind pressure performance curve recognition. The automatic recognition method for the wind pressure performance curve of the ventilator is integrated into the ventilation network calculation software. The recognition experiment is conducted on the wind pressure performance curve of the ventilator. The results show that the sampling speed of the method for a wind pressure performance curve is 24 Samples/s. The recognized wind pressure performance curve has a high overlap with the original curve. The maximum error between the wind pressure fitting value and the original value is only 0.88%. Compared to manual recognition methods, the method greatly improves the efficiency and accuracy of the ventilation network calculation .

With the rapid development of the national economy, China's transportation industry is experiencing accelerated development, and, at the same time, the number of long tunnels is constantly increasing. In order to examine the influence of jet fan spacing on gas transport law during the construction of long highway tunnels, this study used the Baima Highway Tunnel in Sichuan as an engineering prototype and established a numerical tunnel ventilation model based on Fluent numerical simulation software. The gas transport characteristics of jet fans in tunnels at different spacings (200 m, 400 m, 600 m, and 800 m) were studied. The results showed that with the increase in jet fan spacing (200 m, 400 m, 600 m, and 800 m), the gas concentration at the tunnel face showed a trend of decreasing and then increasing. Moreover, by analyzing the gas distribution cloud map and the wind flow line diagram, it was determined that the ventilation system effect was the best when the jet fan spacing was 600 m, which met the requirements of a gas concentration of less than 0.5% at the tunnel face and a minimum wind speed of 0.25 m/s. At the same time, according to the optimal spacing for the optimization of the site ventilation system, it was observed that after the ventilation was stabilized (after 600 s), the minimum value of the gas concentration in the left and right tunnel holes diminished from 0.38% to 0.31% and from 0.41% to 0.31%, with rates of reduction of 18.42% and 24.39%, respectively. This indicated that after optimizing the ventilation system at the tunnel site, the concentration significantly decreased compared with before the optimization. Moreover, when the jet fan spacing was 600 m compared with 200 m and 400 m, the annual energy savings were 1900.8 MW·h and 950.4 MW·h, respectively. The research results clarified the optimal layout parameters of jet fans in the Baima Highway Tunnel, providing a reference for the rational layout of jet fans in long-distance tunnels. In addition, the results of this study provide an important theoretical basis for the gas prevention and safe construction of long highway tunnels. Furthermore, this study contributes to research in energy conservation, emission reduction, and sustainable development of energy in the ventilation process during tunnel construction. [ABSTRACT FROM AUTHOR]

In order to accurately calculate the convective heat transfer coefficient between the mine roadway air flow and the roadway wall, according to the heat and moisture exchange principle between the roadway air flow and the roadway wall, and considering the actual production conditions of the mine such as the wet roadway wall, the humid air of the roadway air flow and the roughness of the roadway wall, the convective heat transfer coefficient is expressed as the wind temperature, wind speed, moisture rate, roadway size, roadway wall temperature, thermal physical parameters and friction resistance coefficient. Based on the expression of convective heat transfer coefficient, the sensitivity of convective heat transfer coefficient to the three factors of roadway wind speed, roadway radius and roadway friction resistance coefficient is mainly discussed by using sensitivity analysis method. The results show that the sensitivity of the three factors is significantly different, among which the wind speed of the roadway is the most sensitive factor affecting the convective heat transfer coefficient, and the sensitivity of convective heat transfer coefficient to roadway friction resistance coefficient is second, and the sensitivity of convective heat transfer coefficient to the roadway radius is the lowest. When the roadway radius changes within a certain range, the convective heat transfer coefficient is less sensitive to the roadway radius, and its influence on the heat transfer coefficient can be ignored at this time.

Aiming at the problem that the air resistance needs to be adjusted manually and repeatedly when the network solution method is used to simulate a mine ventilation system in operation, and the consistency between the simulation results and the measured results is not high, a double constraint optimization model for correcting air resistance was established. The optimization model takes the measured air volume and primary air resistance as the original data, takes the minimum correction to the primary air resistance as the objective function, takes the loop air pressure balance equation and node flow balance equation as the equality constraints, and takes the upper and lower bounds of roadway air resistance as the inequality constraints. The Lagrange multiplier method is used to solve the optimal solution of air resistance modification under equality constraints, and then the iterative method is used to obtain the final solution under inequality constraints. The corresponding software was developed. The example application shows that the iterative solution process for inequality constraints obtained the convergence result after 12 iterations in the application example. The air resistance corrected by this model can make the air volume and fan air pressure calculated by the network completely consistent with the measured values. It is possible to obtain minimal or even negative unintentional air resistance only by considering the optimization model under equality constraints and the double constraint model considering the wind resistance limit can limit the air resistance to a reasonable range. The developed software applies the ventilation network solution and optimization method to simulate the mine ventilation system at the same time, which reduces the cumbersome operation of manual repeated adjustment of air resistance.

The wind flow in underground coal mine is changing all the time. The coal mine ventilation network solution is a static calculation method, which can not solve the dynamic wind flow in real time, and requires wind speed sensor to obtain the dynamic wind flow data. However, the current wind speed sensor has poor stability and incomplete coverage. In order to solve the above problems, a real-time calculation method of mine ventilation network based on ultrasonic full-section wind measurement is proposed. The time difference between downwind and upwind of ultrasonic propagation between two points is used to measure the wind speed of the whole section of the roadway. The wind speed measurement result is independent of the sound speed and is not affected by the parameters such as the sound speed, temperature and humidity and air pressure. The problem that the air duct of the traditional wind speed sensor is easily blocked by mine dust is avoided. The resolution of the wind measuring device reaches 0.03 m /s. By continuously collecting the real-time working conditions of air volume and air pressure of main fans and the real-time air volume of some shafts and roadways, the ventilation network is calculated. And the fixed air volume method is used to integrate the monitored air volume into the ventilation network, and the real-time air volume of the whole ventilation network can be obtained through calculation. The Lagrangian multiplier method is used to correct and calculate the air volume and wind resistance in real time, so as to solve the problems of unbalanced air volume of nodes caused by redundant air volume monitoring branches and unbalanced air pressure of loop caused by fluctuation of the wind resistance. It is verified by an example that the calculation results of the real-time calculation method are highly consistent with the monitoring values. At the same time, the results strictly follow the constraints of the loop air pressure balance and the node flow balance. The real-time calculation of the ventilation network with 1 319 branches and 945 nodes in Ningtiaota Coal Mine is carried out. The time for one calculation is only 0.9 s, the number of iteration convergence is about 105, and the calculation results are continuously updated with time. The results verify the feasibility of the real-time calculation method.

Aiming at the thermal hazards of mining face in Mengcun Coal Mine, a movable air chilled refrigeration system for coal mining face is studied based on the mine water supply and drainage system to reject heat. According to the present situation of thermal hazards in Mengcun Coal Mine, the chilling requirement of coal mining face is calculated. The applicability of two local refrigeration systems, water cooling and air cooling, in coal mining face is analyzed. The characteristics of water gushing from coal seam roof and low water temperature are analyzed. The technology of moving air-chilled refrigeration system in coal mining face is proposed, where the cooling water of refrigeration unit is taken from mine water supply pipeline and discharged to tunnel water ditch. A ZLF-450 movable air-chilled refrigeration unit was selected to test in the first mining face. The results show that: the return water temperature of the cooling water from the refrigerator is slightly higher than that of the mine water, and the water temperature rising after mixing with the water from the mining face in the ditch is only 0.4 ℃; the refrigeration unit operates normally, energy efficiency ratio reaches 3.05 and average temperature of the working face reduces by 2.8 ℃; the system uses mine water supply and drainage system to reject heat without laying any special pipeline for refrigeration system, which greatly reduces the cost of the refrigeration system.

In order to analyze influence of surface air leakage of shallow-buried coal seam on mine ventilation system and goaf flow field, a coupling model of shallow-buried goaf flow field and roadway ventilation network under surface air leakage was established. According to feature of many branches in goaf network, a LDLT decomposition method was put forward to improve ventilation network calculation performance of Newton method. Taking surface air leakage of 15207 goaf of Hongliulin Coal Mine as an example, affection of large-scale surface air leakage on ventilation system and goaf flow field under different surface air leakage were simulated, and conclusions were gotten such as unnormal distribution of spontaneous combustion 'three zones' in goaf caused by surface air leakage and surface air leakage should not exceed 5 m3/s, which provided technical support for safety mining of working face.

Study design: Retrospective cohort study. Objective: To identify risk factors and predictive models for proximal junctional kyphosis (PJK) in a long-term follow-up of patients with adult degenerative scoliosis (ADS) following posterior corrective surgeries. Materials and Methods: A consecutive 113 ADS patients undergoing posterior corrective surgery between January 2008 and April 2019 with minimum 2-year follow-up were included. All patients underwent preoperative, postoperative, and final follow-up by X-ray imaging. Multivariate logistic analysis was performed on various risk factors and radiological predictor models. Results: PJK was identified radiographically in 46.9% of patients. Potential risk factors for PJK included postoperative thoracic kyphosis (TK) (P <.05), final follow-up Pelvic Tilt (PT) (P <.05), PT changes at final follow-up (P <.05), age over 55 years old at the surgery (P <.05), theoretical thoracic kyphosis–actual thoracic kyphosis mismatch (TK mismatch) (P <.05) and theoretical lumbar lordosis–acutal lumbar lordosis mismatch (LL mismatch) (P <.05). As for the predictive models, PJK was predictive by the following indicators: preoperative global sagittal alignment ≥45° (Model 1), postoperative pelvic incidence–lumbar lordosis mismatch (PI–LL)≤10° and postoperative PI–LL overcorrection (Model 2), and TK+LL≥0° (Model 3) (P <.05). Postoperative TK mismatch (OR = 1.064) was independent as risk factors for PJK, with the cut-off values respectively set at −28.56° to predict occurrence of PJK. Conclusion: The risk of radiographic PJK increases with an age over 55 years old and higher postoperative TK. In addition, postoperative TK mismatch is an independent risk factor for developing PJK. All three predictive models could effectively indicate the occurrence of PJK. [ABSTRACT FROM AUTHOR]

Glycerol, as the major byproduct of biodiesel industry, is a cheap and green chemical feedstock. Following the expanded production of biodiesel, the oversupply of glycerol has led to increasing research of the catalytic conversion of glycerol. The selective hydrogenolysis of glycerol is an economical and sustainable way to produce 1,3‐propanediol, which experiences a global growing demand, and valorize glycerol. However, the secondary hydroxy group of glycerol is sterically hindered by two primary hydroxy groups. As a result, 1,2‐propanediol is the preferential product rather than 1,3‐propanediol during conventional hydrogenolysis of glycerol. Currently, tungsten‐containing bifunctional catalysts with metal and Brønsted acid sites are considered as a highly effective and atom‐economical catalytic system for the selective hydrogenolysis of glycerol to 1,3‐propanediol. Therefore, this Minireview summarized various tungsten‐containing bifunctional catalysts for the hydrogenolysis of glycerol in detail and deeply discussed the relationship between tungsten species, metal active sites, and glycerol for selectively producing 1,3‐propanediol. [ABSTRACT FROM AUTHOR]