Shaft Height Research Articles

Constant static pressure strategy for residential kitchen exhaust system: Deducing control parameters from required exhaust rate and non-distributed data transmission

Roof fans have gradually replaced the non-powered hood as supplementary power to increase exhaust rate in high-rise residential kitchen shafts. However, an effective control strategy for roof fans is lacking. This paper studies the constant static pressure strategy and deduces its control parameters based on required exhaust rate and non-distributed data transmission. First, the static pressure set value (SV) is investigated under the worst exhaust condition, considering variations in shaft heights and measuring positions (MP). Then, an on/off mechanism is set up based on the measured static pressure and the fan frequency when the exhaust rate is adequate. Results show that under the recommended shaft sizes and design concurrent usage rates, the SVs for users' exhaust rate reaching 500 m³/h are −60, −60, and 0 Pa for 10/18/26-floor shafts when the MP is at a shaft's outlet, and roof fans are turned on when the static pressure reaches 100, 90, and 90 Pa and turned off when the fan frequency is below 32, 30, and 22 Hz. The MP at the shafts' outlet can keep the shaft at a slightly negative pressure. Control parameters for specific applications can be obtained through the proposed calculation process. An 18-floor shaft study found that the constant static pressure strategy can achieve 50 % energy savings compared to the constant frequency operation of the roof fan. These findings contribute to reliable control without users' distributed data transmission and to lower energy consumption of the residential kitchen exhaust system.

Experimental study on the performance of synergistic ventilation system combining shaft with mechanical ventilation in extra-long road tunnels

Ventilation shafts are widely equipped in extra-long road tunnels. Due to the plug-holing phenomenon, it may be impossible to improve smoke extraction performance solely by increasing extraction velocity in a traditional ventilation shaft. Taking reference from practices in mine ventilation shafts, a novel mechanical board-coupled ventilation shaft (MBCS) was introduced. A total of 120 experiments in a 1:20 reduced-scale tunnel model were conducted to validate the effectiveness of the novel shaft. The effects of shaft height, board location, and extraction velocity were investigated, and the interaction dynamic mechanism of synergistic smoke extraction between fan-driven and shaft-driven was revealed. The results indicate that the novel MBCS can achieve better smoke extraction performance as the extraction velocity increases. Besides, compared to the traditional MBCS in our previous study, the smoke extraction efficiency of the novel MBCS improves by 19.8 %, the heat extraction performance improves by 75.7 %. Moreover, based on theoretical and dimensional analysis, a model to analyze the dynamic mechanism of synergistic smoke extraction was established, which may provide positive insights for smoke control and extraction design both in extra-long road tunnels and mine ventilation shafts.

Effect of unpowered ventilation caps and shaft parameters on fire smoke spread in the natural ventilation tunnel with shafts

Shaft-type natural ventilation offer a sustainable and cost-effective alternative to mechanical systems for the mitigation of smoke hazards. This study investigated the behavior of smoke with the application of unpowered ventilation caps in 1/15 scale shallow-buried urban road tunnels with shafts, and analyzed parameters such as the shaft axis wheelbase, shaft width, shaft width-to-height ratio, and heat release rate (HRR). The results show that the dimensionless HRR as an independent relationship with the dimensionless ceiling temperature rise in both the presence and absence of the unpowered ventilation cap. According to the experimental results, dimensionless length of smoke backlayering increases significantly with the increase of the HRR. In addition, the smoke backlayering length is positively correlated with the shaft width, and the backlayering length decreases and then increases with increases of the axis wheelbase. Moreover, the chimney effect is facilitated with the shaft height increase, which enhances exhaust effect, and the backlayering length decreases with the increase in the shaft height when the aspect ratio is greater than 0.5. Once the critical shaft width-to-height ratio is reached, the change in the shaft height no longer has an effect on the backlayering length. Finally, a dimensionless backlayering length calculation model based on the shaft parameters with different shaft exhaust effects is developed by combining the discriminant factors. The findings have crucial implications for fire prevention and safety management, and provide a valuable reference for future studies and engineering applications.

Effects of innovative reinforced concrete slit shaft configuration on seismic performance of elevated water tanks.

Elevated water tanks are considered crucial infrastructure due to their significant role in supporting essential services. A strong ground motion may result in a failure or significant damage to a reinforced concrete shaft of an elevated water tank because hysteric energy dissipation is limited to the formation of plastic hinges at the base of the shaft, while the nonlinear properties of the rest of the shaft remain underutilised. The innovative system of assembling RC shafts for elevated water tanks using a slit wall technique was developed to enhance energy dissipation along with the shaft height by introducing slit zones. The comparative nonlinear dynamic analysis between three-dimensional models of elevated water tanks with different shaft diameters and heights was conducted using SAP2000 software. The results of elevated water tanks with slit and solid reinforced concrete shafts were compared. The research findings showed that during a seismic event, the slit zones increased the ductility of the shaft, reduced stress concentration in the lower part of the shaft, and provided uniform stress distribution throughout the shaft's height. The effect of the innovative system is especially noticeable in the elevated water tanks with tall and slender shafts.

Smoke exhaust characteristics under stack effect of natural ventilation by shaft in high-altitude tunnel

The number of high-altitude tunnels is increasing year by year and natural ventilation of shafts is widely used as a critical component of the ventilation system. For the design of ventilation systems, it is particularly crucial to consider the smoke exhaust performance of shafts in low-pressure environment. Therefore, this study simulates tunnel fires with natural ventilation by shaft in high-altitude areas, aiming to analyze the impact of atmospheric pressure on smoke exhaust performance and smoke exhaust capacity by natural ventilated shafts at 50 to 100 kPa atmospheric pressure. It appears from the results that the increasing of ambient pressure can enhance the ability of air entrainment and natural smoke exhaust, and thus plug-holing is more likely. In which condition, fresh air can be expelled straight from the shaft, reducing smoke exhaust efficiency. As ambient pressure increases, the critical shaft height for plug-holing decreases. By analyzing the smoke exhausting process by shaft and smoke flow, smoke exhaust capacity can be evaluated by obtaining the mass flow rate of exhausted smoke and fresh air from the shaft under various atmospheric pressures and fire source power and. It could be said that increasing ambient pressure and shaft height can improve the smoke expulsion performance before plug-holing. However, once plug-holing happens, the increase of shaft height can no longer expel more smoke but much more air is exhausted by shaft. It is hoped that this work will serve as a guideline for ventilation systems design in high-altitude tunnels.

Stability analysis of two-dimensional flat solar trackers using aerodynamic derivatives at different heights above ground

In this paper the aerodynamic stability of a flat-plate solar tracker under two-dimensional conditions is studied for different conditions of incident wind speed, U∞, nominal angle of attack, αn∈−40∘,40∘, and shaft height - chord ratio H/B=0.3,0.4,0.5,0.6,1and2. The stability is studied through the analysis of the aerodynamic derivatives A2∗ and A3∗ whose behaviours as a function of U∞ are presented for the H/B range studied. Two methods of obtaining the derivatives (one in the time domain and the other one in the frequency domain) are presented. A method for calculating the effective damping coefficient of the solar tracker, ξeff, as a function of the incident wind speed, U∞, is presented. This method can be used for any solar tracker structural characteristics (Jmech, Cmech and Kmech). With this method, the critical speed, Ucrit, can be determined by imposing the condition ξeff=0. The method was validated experimentally using the results of two different experimental set-ups.

Assessment of cellulose nanofibers from bolaina blanca wood obtained at three shaft heights

This study evaluated cellulose nanofibers from bolaina blanca wood (Guazuma crinita) obtained at different heights of the longitudinal axis of the shaft of trees from a three-and-a-half-year-old plantation. The wood was subjected to pulping, bleaching and subsequent mechanical milling using a Changsha Samy XYQM-2L planetary ball mill to obtain cellulose nanofibers. The product was characterised using analytical techniques: scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy. Additionally, the degree of polymerisation was determined. The effect of longitudinal position on cellulose nanofibers characteristics was evaluated by comparing means using ANOVA and Kruskal–Wallis statistical tests. The yield of cellulose nanofibers production from the high, middle and basal sections was 32,1 %, 33,6 % and 31 %, respectively. The obtained cellulose nanofibers exhibited a significantly larger diameter for the high zone (84 nm) compared with the middle (75 nm) and basal (69 nm) zones; the length remained above the micrometre range. With respect to degree of polymerisation, a decrease was evidenced with respect to the increase in shaft height; the basal zone exhibited a degree of polymerisation of 300, a significantly higher value than the middle and high zones, which exhibited degree of polymerisation of 249 and 211, respectively. The product showed typical cellulose type I polymorphism and crystallinity indexes of 76 %, 93 % and 96 % for the high, middle and basal sections, respectively. Regarding the thermostability of cellulose nanofibers, the maximum degradation rate of cellulose nanofibers occurred between 335 °C and 341 °C, with cellulose nanofibers from the basal area being the most stable. The adsorption of the methylene blue dye on cellulose nanofibers was evaluated; an efficiency > 60 % was found.

Experimental investigation on the hazard of geyser created by an entrapped air release in baffle-drop shafts

The geyser phenomenon seriously threatens the safe operation of deep tunnel drainage systems and drop shaft structural safety. To simulate the geyser process in a baffle-drop shaft, a 1:50 scale model test system was used to research the response relationship between the geyser mechanism and test parameters such as water depth, inlet pressure, and inlet volume. The results show that the pressure in a baffle-drop shaft fluctuates sharply during the geyser process. This is caused by the release of a high-pressure air mass, and high-speed movement of the air–water mixture causes a local pressure imbalance in the drop shaft. A prediction formula for the maximum geyser height of a baffle-drop shaft was established by a multiple linear regression model. Geyser occurrence conditions for the baffle-drop shaft were proposed combined with the response relationship between different influence variables and geyser intensity. Except for the inlet pressure, submerged state of the baffles, and measured location, the hydrodynamic load on the bottom of the baffles is also related to the randomness of the air–water mixture jetted on the baffle bottom. The maximum hydrodynamic load on the baffle bottom during the geyser is 10 times the hydrodynamic load on the baffle surface under normal discharge conditions. This research provides a theoretical reference for the structural design and safe operation of baffle-drop shafts.

Simulation Research on Effects of Ambient Pressure on Plug-Holing Phenomenon in Tunnel Fires with a Shaft

This paper studied the effects of ambient pressure on the plug-holing phenomenon in tunnel fires with a shaft by a Fire Dynamics Simulator. The influence of ambient pressures on the smoke movement, temperature distribution, critical Richard number (Ric) and critical shaft height for plug-holing were analyzed in detail. A new prediction formula of smoke flow velocity considering different pressures was modified. A prediction formula of smoke temperature distribution beneath the ceiling under different pressures was developed. As a result, a prediction model of Richard numbers to determine whether the plug-holing occurs was proposed by combining smoke flow velocity and smoke temperature distribution. The critical Richard numbers (Ric) and critical shaft height (hc) increases as the pressure decreases. Outcomes in this study can provide references for the design of a natural ventilation system in tunnel fires at a higher altitude.

Experimental Study on the Smoke Temperature Decrease near Natural Vents Induced by Air Entrainment in a Tunnel Fire

Previous studies have shown that there is a large difference in the temperature of smoke in the upstream and downstream of a vertical shaft, but no quantitative study on the subject has been conducted. In this paper, a model experimental test was conducted to study the effect of a natural vertical shaft on the distribution of smoke temperature in tunnel fires. A laser sheet was used as an assisting tool to show the smoke flow field. A series of tests were conducted with shaft heights varying from 0.2 m to 1.2 m and a heat release rate (HRR) of 9 kW, 17 kW, 29 kW, and 65 kW. The entrainment phenomenon around the vertical shaft was analyzed, and the results showed that the amount of fresh air entrainment is the main reason for the temperature decrease in upstream and downstream smoke temperatures. Based on the experimental results, an empirical model for predicting the amount of fresh air entrainment and a prediction model of the downstream smoke temperature were proposed, and the predicted values are in good agreement with the experimental values.

Study on the Air Inlet Velocity and Temperature Distribution in an Inclined Tunnel with Single Shaft under Natural Ventilation

The emergence of inclined tunnels under natural ventilation has brought many new fire safety issues. The smoke movement in the tunnel is affected by the chimney effect induced by the shaft and the downstream tunnel. The characteristics of temperature distribution in inclined tunnels are different from horizontal tunnels, which is worthy of further study. A series of conditions were carried out in an inclined model tunnel with a single shaft to investigate the temperature distribution characteristics. In this study, the longitudinal air inlet velocity is used to replace the longitudinal ventilation wind velocity. Results showed that the variation of fire source location Lf,, shaft height Ls, and the tunnel slope φ have obvious effect on the air inlet velocity. Based on the previous theories and the non-dimension analysis, the formulas of the dimensionless longitudinal inlet air velocity and the distribution of the maximum smoke temperature under the ceiling are proposed, which show good consistency with the simulation results. The reduced-scale experiments were conducted to validate the results of numerical simulation. The error range between the theoretical results and the simulation results is less than 20%.

Determination of pressure difference coefficient of shuttle elevator doors in super high-rise buildings under stack effect

The stack-induced airflow of super high-rise buildings in winter results in obvious indoor environmental problems at the shuttle elevator shaft. Strong pressure difference can cause malfunction of elevators. The estimation of pressure differences at the shuttle elevator doors under different building layout and climate conditions is still a challenge to obtain in engineering application. Considering the difficulties of measuring and simulating the air leakage characteristics of various components, a dimensionless metric, the Pressure Difference Coefficient of Elevator Doors, Cele, is defined according to the theory of pressure distribution in buildings. First, the accuracy of the index calculation results was verified in an elevator test tower. The hand-calculated method to predict the pressure differences at the shuttle elevator doors is convenient and reliable when compared with measurement and simulation. Then, two influence factors on Cele, floor plan and flow exponents are discussed. The determination method of recommended Cele is proposed by analyzing with different building partition layers. The recommended values are given under different shaft heights and temperature difference. Moreover, the novel method and metric were applied in an actual building to determine the number and air tightness of partition layers under the target conditions. This paper provides an evaluation reference for the convenient and effective design of elevator type selection and building layout of super high-rise buildings under stack effect.

Снижение потерь угля при работе карьерных мехлопат

A significant part of operations that are engaged in surface mining of coal are currently using hydraulic excavators, i.e. backhoes and less often face shovels, which reduces losses and improves productivity. However, a certain number of strip mines, especially those where mining activities are coming to a close, are still using mining rope shovels mostly domestically produced and of outdated models. Based on the method developed by the authors earlier and partially described in this article, the calculation of the layer height is made which will prevent additional losses of coal from the insufficient cutting depth. Formulas for calculating the layer height are proposed for five models of domestically produced rope shovels. The differences in geometric parameters of relative location of the elements that are used in the method described do not make it possible to establish a unified dependence of the worked-out layer height on the influencing factors. However, this method can be used to define the layer height for any model of the rope shovels, but this will require to know its operating parameters, i.e. the height of the shipper shaft, the distance from the excavator rotation axis to the tail piece of the boom, the minimum digging radius, etc.

Seismic Performance and Optimization Design of a Post-Installed Elevator Shear Wall Structure

Post-installed elevator projects have grown significantly in recent years in response to the problem of insufficient vertical traffic capacity in existing buildings, but research on the seismic performance of post-installed elevator structures has been relatively limited. This study takes a 26-story-frame shear wall structure as an example. The seismic response characteristics of this structure before and after the installation of elevators were analyzed. In order to optimize the design scheme of the post-installed elevator structure, this study further analyzed how factors such as the standard height of the elevator shaft frame, the elevator location, and the way the post-installed elevator is connected to the structure affect the seismic response of the elevator structure. The results show that the post-installed elevators have a small impact on the seismic performance of the existing building and can slightly reduce the seismic response of the structure. In addition, the stiffness of the elevator shaft will be reduced, and its seismic response will be slightly increased as the standard shaft height is increased, but the construction cost can be reduced. The installation location has a greater impact on the seismic response of the post-installed elevator. The seismic response of the post-installed elevator is minimal when it is arranged near the elevator shaft of the existing building.

Numerical simulation of heat transfer and hydraulic losses of air-cooled exhaust-shaft apparatuses

The article presents the numerical simulation results on heat transfer and hydraulic losses of air-cooled exhaust-shaft apparatuses. Studies were made on air-cooled apparatuses in which four-row bundles of staggered finned tubes were placed. Numerical simulation used a gas dynamic solver Ansys Fluent. Menter’s shear stress transport κ-ω model was invited to close the Reynolds equations. The obtained numerical results allowed us to visualize air flow in the bundle and the exhaust shaft, as well as to establish an inhomogeneous distribution of velocities and temperatures. We found that the temperature distribution in the flow passing through the exhaust shaft depends on the height of the exhaust shaft. We also established that at small shaft heights in the wake behind a bundle because of the wake oscillatory motion, the dynamic and temperature inhomogeneous distributions take place, resulting in the cold air suction through the shaft from the environment. With an increase in the shaft height, the inhomogeneous temperature distribution moves upstream the air flow in the shaft and the inhomogeneous temperature distribution attenuates. We can say that maximum heat transfer at the same hydraulic losses is achieved when mounting a shaft with a height of H > 1.16 m. The results obtained can be used for the modernization of existing air-cooled apparatus, as well as for the design of new devices with an exhaust shaft.

Numerical simulation of the chimney effect on smoke spread behavior in subway station fires

To reveal the chimney effect on smoke spread behavior, three-dimensional numerical simulations of subway station fires in a 1/8 scale model were presented by using large eddy simulation. The impacts of the cross-sectional area of the shaft, fire location and shaft height on the smoke spread behavior were analyzed. The results show that the chimney effect significantly influences smoke movement. For the cases with heights of 1 m for the left and right shafts and the fire location at the hall center, when the ratio of small cross-sectional area to large area equals 0.4 or more, the smoke exhausts from the shaft with a small area; otherwise, the smoke exhausts from the shaft with a large area. With equal cross-sectional areas and heights of 1 m or more for the two shafts, the smoke exhausts from the shaft closer to the fire location. The left and right shafts are both passages for flowing upward smoke and flowing downward air when the heights of the two shafts are less than 1 m. In the stable flow stage, the chimney effect increases with decreasing cross-sectional area and increasing shaft height and is not affected by the change in fire location.

Study on the smoke back-layering length in a tilted tunnel with vertical shaft under natural ventilation

By varying tunnel slope, shaft height and fire source location, a series of numerical simulations were conducted to investigate the smoke back-layering length in a tilted tunnel with a vertical shaft. The simulation results were verified by corresponding reduced-scale experiments. Five possible smoke exhaust modes in tilted tunnels with single shaft were concluded through the flow field analysis. The dimensionless relationships between tunnel slope, shaft height, fire source distance and back-layering length were analyzed. When the fire source is located upstream of the shaft, smoke back-layering occurs when the tunnel slope is less than 1.5%. When the fire source is located downstream of the shaft, smoke back-layering disappears until the tunnel slope is bigger than 2.5%. The dimensionless analysis shows that the back-layering length is related to the fire source location and the tunnel slope, but has no significant dependency on the shaft height. Using the Froude number, the location of hot smoke is identified, when Frc < 1, part of the high-temperature smoke below the shaft cannot enter the shaft but spread to the tunnel exit. Dimensionless correlations between smoke back-laying length and Richardson number (Ri) were proposed. Moreover, the critical conditions that changes the smoke exhaust mode of the tunnel were determined only by the tunnel slope and the shaft height.

Development of a mathematical model to monitoring the velocity of subsidence of charge material column in the blast furnace based on the parameters of gas pressure in the furnace tract

A problem of estimating the velocity of subsidence of a column of charge materials using non-contact methods was considered. This is important because the level of furnace charge materials and the velocity of their subsidence are main indicators of melting intensity determining the furnace productivity. The design of a blast furnace and its blast path were described and existing methods and means of controlling the velocity of charge materials in the blast furnace were analyzed. A mathematical model was presented for estimating the velocity of subsidence of charge materials in a blast furnace based on the magnitude and fluctuations of gas pressure along the furnace shaft height. The model is based on the fact that the furnace gases rise up in the furnace shaft through elementary channels in the column of charge materials consisting of a combination of capacitances and resistances. Volume of capacities and values of resistance of elementary channels are constantly changing. This changes hydraulic resistance to gas movement in the blast furnace. The system of differential equations describes the dependence of the amplitude of pressure fluctuations on the amplitude of change in coefficients of resistance and frequency of pressure fluctuations on the frequency of change in coefficients of resistance. The experimental data on velocity of the column of charge materials and fluctuations in the pressure differential in the furnace were processed and their significant relationship was shown to confirm the previous theoretical study results. To assess the model adequacy, the simulation method was used. The results of the simulation model work were confirmed by experimental data. The developed mathematical model can be introduced into production. This will make it more economical and safer through better and more predictable control and improved flexibility in operation under different production conditions.

Assessment of the effect of shapes of a shaft intake structure using the PIV method

The construction of shaft intake structures in Slovakia has increased. The shaft intake structures overcome significant vertical height over short horizontal distance. In their front horizontal section, the water flows with free surface, then in the vertical section the flow changes its direction and character to a pressurized flow. The flow of water in these shaft intake structures is therefore very complicated. A hydraulically suitable design of the intake structure is associated with achieving the required parameters of the small hydropower plant (SHPP), but due to the reduction of project costs, the shapes of shaft intake structures of SHPP are often not correctly hydraulically designed. One of the important aspects is the distribution of flow velocity of these intake structures. Uneven distribution of flow velocity causes negative effects on turbine performance. Therefore, the investigation of the effects of shaft intake structure design on flow velocity distribution has been realized. The velocity field at a shaft intake of a small hydropower plant was investigated on a physical model in a hydraulic laboratory using the PIV (Particle Image Velocimetry) method. The PIV measurements were realized for different shaft heights and proved negative effects of the design on the flow homogeneity in the turbine intake.

The influence of shaft stiffness on joint kinematics and kinetics during hiking

Hiking boots provide an interface for walking in challenging environments, typically equipped with a shaft to provide ankle joint stability in rough terrains. Currently it is unclear if the ankle joint is stabilized to an extent that protects against ankle injuries, and if so, to what degree this added ankle stability sacrifices ankle mobility and hence decreases efficient gait propulsion. The aim of the present study was to compare the effect of shaft construction and stiffness on lower extremity kinematics and kinetics during level and step-down walking to simulate hiking conditions. Thirteen healthy males walked in one low-cut and three shafted commercially available hiking shoes with varying shaft stiffness. Lower extremity kinematics and ground reaction forces were recorded simultaneously. During level walking, ankle plantar-dorsiflexion range of motion was significantly reduced for the stiffest shaft hiking shoe compared to the low-cut shoe. A reduction in the muscle contribution to ankle joint work was found for all shafted shoes compared to the low-cut shoe. The reduced ankle joint work for the shafted shoes conversely increased eccentric knee joint work. Kinematic and kinetic differences between shoes diminished during box step-down walking. The present study shows that shaft height and stiffness can influence ankle joint range of motion, and ankle and knee joint work, with the high-shaft shoes redistributing load from the ankle to the knee joint. This may have implications for gait efficiency and increase the risk of knee joint loading or injuries.