•The critical inclination angle of two-phase closed thermosyphon (TPCT) is proposed and obtained.•Optimum operation inclination angle of carbon steel-water TPCT is evaluated and discussed.•The ...temperature, thermal resistance, and equivalent convective heat transfer coefficient of TPCT are analyzed.
Two-phase closed thermosyphon (TPCT) is widely used and usually installed vertically, but the inclination angle has significant effects on TPCT performance. This work presents an experimental study of TPCT with water as working fluid. The critical and optimal inclination angles of TPCT under non-forced convection cooling conditions are investigated from three aspects of start-up, operating, and heat transfer characteristics at different operating temperatures. The results show that TPCT has the critical inclination angle and the optimal inclination angle. A critical inclination angle of 45° is obtained under different operating conditions. The optimal inclination angle of TPCT is 60° at the operating temperature of 80–150 °C, but it is 90° (vertical) at 150–185 °C. Furthermore, the start-up and heat transfer performance of TPCT gradually improves with the augment of heating power. This study provides a reference for future research on heat pipe performance enhancement methods and related applications, and presents experimental basis for performance changes in TPCT applications when accidental dry burning occurs.
To study the influence of hydraulic slotting inclination on the mechanical behaviors of coal seam during mining process, uniaxial compression experiments on coal specimens with a single pre-existing ...flaw inclined at 0°, 15°, 30°, 45°, 60°, 75°, 90° and intact specimens were conducted. Acoustic emission (AE) signals in the loading process were monitored, and fractal analysis method was introduced to investigate the AE characteristics. Additionally, the laboratory experiments were simulated by a finite element code. Both the experimental and numerical results show that the existence of a flaw reduces the mechanical properties of coal. The uniaxial compressive strength and modulus of elasticity increase polynomially and linearly with the increase of inclination angle, respectively. When the coal specimen ruptures finally, the fewer the surface secondary cracks or the more the sudden drops of stress, the smaller the peak value of AE count. According to the stress–strain curve, the loading process is divided into five stages: (I) compaction stage; (II) linear elastic stage; (III) stable crack propagation stage; (IV) accelerating crack propagation stage; (V) post peak and residual stage. AE fractal characteristics in various stages of each specimen were determined by Grassberger and Procaccia algorithm based on phase space reconstruction theory. AE count show fractal characteristics from stage III. The fractal dimension declines rapidly in stage IV, and continues to decline further or rise slightly in stage V, but both are lower than that in stage III. Therefore, the changing rule of AE fractal dimension in different loading stages can be used as a precursor to coal and rock dynamic disasters.
► Pre-existing flaw inclination angle has influences on crack initiation position. ► Pre-existing flaw inclination angle has influences on crack propagation processes. ► Pressure loading rate has ...influences on crack initiation sequence and propagation. ► Maximum pressure has influences on crack initiation and crack type.
With reference to the experimental observation of crack initiation and propagation from pre-existing flaws in rock specimens under compression, the influences of pre-existing flaw inclination angle on the cracking processes were analyzed by means of finite element method (FEM) and non-linear dynamics method. FEM analysis on the stress field distribution induced by the presence of a pre-existing flaw provided better understanding for the influence of flaw inclination angle on the initiation position and initiation angle of the potential cracks. Numerical analysis based on the non-linear dynamics method was performed to simulate the cracking processes. The resultant crack types, crack initiation sequences and the overall crack pattern were different under different loading conditions. Under a relatively low loading rate or a small magnitude of maximum loading pressure, tensile cracks would tend to initiate prior to shear cracks. In contrast, under a relatively high loading rate and a large magnitude of maximum loading pressure, shear cracks would tend to initiate prior to tensile cracks instead.
Recently, imaged-based approaches have developed rapidly for high-throughput plant phenotyping (HTPP). Imaging reduces a 3D plant into 2D images, which makes the retrieval of plant morphological ...traits challenging. We developed a novel LiDAR-based phenotyping instrument to generate 3D point clouds of single plants. The instrument combined a LiDAR scanner with a precision rotation stage on which an individual plant was placed. A LabVIEW program was developed to control the scanning and rotation motion, synchronize the measurements from both devices, and capture a 360° view point cloud. A data processing pipeline was developed for noise removal, voxelization, triangulation, and plant leaf surface reconstruction. Once the leaf digital surfaces were reconstructed, plant morphological traits, including individual and total leaf area, leaf inclination angle, and leaf angular distribution, were derived. The system was tested with maize and sorghum plants. The results showed that leaf area measurements by the instrument were highly correlated with the reference methods (R² > 0.91 for individual leaf area; R² > 0.95 for total leaf area of each plant). Leaf angular distributions of the two species were also derived. This instrument could fill a critical technological gap for indoor HTPP of plant morphological traits in 3D.
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•The start-up characteristics and heat transfer performance of the HTFHP were studied.•Effects of inclination angle and heat power on HTFHP performance are explored.•The feasibility ...of applying the HTFHP to high heat flux environment is verified.•Theoretical analysis of heat transfer characteristics and thermal resistance network.
High-temperature flat heat pipe (HTFHP) is a highly effective heat transfer device in spacecraft thermal control. In this paper, a high-temperature flat heat pipe equalizer (200 × 100 × 30 mm) is designed innovatively, and the metal fiber felt is used as the capillary wick of the HTFHP, and sodium is filled into the compact cavity as the working medium. The effects of heating power and inclination on the temperature uniformity of the HTFHP were experimentally studied. The results show that HTFHP with sodium as working medium has fast start-up characteristics and good thermal uniformity, and can adapt to various variable inclination conditions. The heat transfer coefficient of this HTFHP can reach 498.702 W/m2K when the heat input is 600 W, and the time for the heat pipe to reach a steady-state is 2020 s. In addition, the temperature difference showed a significant decrease from 80 °C to 50 °C when the heat loss from the center to the edge is from 4.2 % to 3.7 %. The inclination has little effect on the temperature distribution of the HTFHP, and the temperature uniformity is better when the inclination angle is 15°. When the heat input is 600 W, the heat loss from the center to the left and right edges is the smallest, which are 5.5 % and 6.2 % respectively. Overall, this HTFHP has good thermal performance and is worthy of further optimization.
•Maximum gas temperature rise beneath the ceiling was studied in a model-scale tunnel.•Longitudinal ventilation showed significant influence on the maximum gas temperature rise.•A piecewise model for ...predicting maximum gas temperature rise was developed.•This new model obeys reasonably well with the experimental results.
This paper studies the maximum gas temperature rises beneath the ceiling in tunnel fires. The fire scenarios with higher longitudinal ventilation velocities are of key concern. This work was done in a 1/10 model-scale tunnel and propane gas burner was used as fire source. The variables include longitudinal ventilation velocity and heat release rate. In this study, the dimensionless longitudinal ventilation velocity varies from 0 to 0.84 and the dimensionless heat release rate is less than 0.15 in all tests, corresponding to a scenario of small fire. It is assumed that the maximum gas temperature rises in the longitudinal ventilated tunnel fires almost equals that in tunnels without longitudinal ventilation by use of the length of inclined path of plume as the effective tunnel height. By analyzing the length of inclined path of smoke plume that correlates the plume inclination angle, a piecewise model for predicting maximum gas temperature rises was developed, using the dimensionless longitudinal ventilation velocity of 0.42 as the dividing point. The comparisons between the calculations from this new model and the experimental results in this study as well as some data collected from other tests show a good agreement.
•The effect of longitudinal wind and inclination angle on cable fire was revealed.•A predicted model for cable flame spread rate was established.•The heat transfer process during the cable flame ...spread was discussed.
Tables in utility tunnels pose a major fire hazard. This work aims to provide a comprehensive understanding of the effects of cable inclination angle and longitudinal wind (U∞) on the flame spread behaviors of cables in a utility tunnel. Flame inclination angle (β) increases with the increase of cable inclination angle and longitudinal wind speed, while the amplification decreases as the longitudinal wind speed increases. Both flame length (xf) and pyrolysis length (xp) increase linearly with sinθ when U∞ is smaller than 0.65 m/s and they also increase with the increase of longitudinal wind speed. The increasing inclination angle and longitudinal wind speed contribute to the increasing flame spread rates. The flame spread rate accelerates significantly when the longitudinal wind speed and inclination angle are 0.65 m/s and 12° respectively. In addition, a model based on heat transfer analysis was established to predict the flame propagation rate under different cable inclination angles, and the experimental results were in good agreement with the predicted results. The results of the study contribute to cable fire risk assessment, which is beneficial for cable fire prevention and control in utility tunnels.
•A new solar still with angle bars on the basin is proposed.•Two flat-plate external reflectors as well as a cooling system are installed.•The inclination angles of the basin and reflectors are ...adjustable.•Applying bottom reflector is more effective than one top reflector in the spring.•Installing reflectors at optimum angles in winter is more effective than spring.
This study was done to improve the productivity of an inclined solar still through some modifications include installing angle bars on the basin to increase the water residence time, fabricating the basin with adjustable inclination angle to achieve the highest amount of solar radiation in each season, installing top and bottom flat-plate external reflectors and a cooling system on the glass cover. The effect of the basin inclination angle, feeding water flow rate, cooling water flow on the glass cover, installing top and bottom reflectors at their optimum inclination angles on the productivity of the still were experimentally investigated under the climatic conditions of Tehran (35°N Latitude and 51°E Longitude) during summer, winter and spring. The results showed that in the case of applying only one modification, passing the cooling water on the glass cover has the most effect on productivity enhancement in spring while applying top reflector at its optimum inclination angle gave the best results in winter. Also, the maximum productivity of 4.2 kg/m2 was obtained for a basin inclined at 25° with top and bottom reflectors inclined at 10° and 45°, respectively. In this case, the feed water and cooling water flow rates were equal to 90 and 720 ml/min, respectively in solar radiation of 800 W/m2, air temperature of 22.5 °C, and wind velocity of 2.4 m/s. Moreover, the efficiency of the still was obtained as 36.7%, which was 14.2% higher than that of the still at an optimum inclination angle of 25° without reflectors and cooling water under the same weather conditions.
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