Airflow Velocity Designing for Air Classifier of Manufactured Sand Based on CPFD Method

Airflow classification is the key technology for the dry separation of manufactured sand. To solve the problem of low separation accuracy and poor gradation grade, the classification process of manufactured sand under different inlet and outlet airflow velocities changes in the multi-air inlet classifier is simulated by using Barracuda based on Computational Particle Fluid Dynamics (CPFD) method. The influence of various airflow velocity in air inlets and outlet on the sand classification is analyzed. The optimal combination of airflow velocity that meets the design goals is obtained. The results show that the airflow velocity and location of the air inlet and outlet have a significant impact on medium-grained (0.15~1.18 mm) and fine-grained (0.075~0.3 mm) sand. Adjusting the airflow velocity at air inlet 2 and air outlet can most effectively change the overall sand separation effect, while 41 m/s (inlet 2) and 6 m/s (outlet) would be the best velocity combination.

Improving Energy Efficiency by Utilizing Wetted Cellulose Pads in Passive Cooling Systems

The effectiveness of using wetted cellulose pads on improving the performance of two conventional passive cooling systems has been evaluated. First, an experimental design was developed to determine the impact of using a wetted cellulose pad on the temperature and velocity of the airflow. A cellulose pad (7090 model) with a cross-sectional area of 0.5 × 0.5 m2 and three different thicknesses of 10, 15, and 30 cm were selected and tested. The results indicated that using wetted cellulose pads with thicknesses ranging from 10–30 cm decreased the outlet airflow temperature from 11.3 to 13.7 °C on average. For free airflow at velocity 3.5 m/s, the outlet airflow velocity from the wetted cellulose pad decreased to 0.9, 0.7 and 0.6 m/s, respectively, for cellulose pads with thicknesses of 10, 15, and 30 cm. By applying experimental results on a psychrometric chart, the humidity ratio of outlet airflow was obtained between 40–70%. The study established airflow velocity as the critical parameter in passive cooling systems. With the novel concept of combining wetted cellulose pads for passive cooling systems (i.e., wind catchers and induced ventilation), there is good potential to reduce the energy requirements for thermal comfort in buildings in regions with a hot and arid climate.

Investigation of a Portable Wind Tunnel for Energy Harvesting

Current wind tunnels possess a large space volume and high manufacturing cost, which are not suitable for investigating micro energy harvesters. This paper aims to design and fabricate a small, portable and low-speed wind tunnel for energy harvesting. A wind tunnel structure was first designed, a finite element analyses is then utilized to obtain the airflow velocity and turbulence intensity at the testing section, and the influence of the structural parameters of the wind tunnel on the flow field performance is finally investigated to achieve better performance. An experimental prototype of the wind tunnel was fabricated to verify the simulation results. Results demonstrated that the distribution uniformity and average turbulence intensity at the test section decrease first and then increase with the increase of both the diffuser and contraction lengths. The rectifying and damping effect of the honeycomb increase with increasing porosity and thickness. When the diffuser and contraction lengths are 850 mm and 480 mm, respectively, a better distribution uniformity and a lower turbulence intensity can be achieved. Experimental results were in good agreement with the simulation values. The maximum airflow velocity can reach up to 24.74 m/s, and the minimum error was only 1.23%. The designed wind tunnel achieved low-speed, small, portable and stable functions. This work provides an important guidance for further investigating the piezoelectric energy harvesting.

Wind Conditions at Pedestrian Level in Different Types of Residential Urban Development for a High Degree of Land Use Efficiency

This paper addresses wind conditions in urban building development at the pedestrian level. The article aimed to identify aerodynamic phenomena around three types of multi-family housing developments with different forms and the same urban parameters of building development density (high density was taken into account). The aim of the research was mainly to achieve qualitative results that would lead to understanding fundamental processes and phenomena. Wind tunnel experimental studies were conducted on physical models at a scale of 1: 400 using visualization and erosion methods. These experiments yielded data regarding the arrangement of airflow directions and changes in airflow velocity, expressed as the amplification coefficient (α), the occurrence of which was caused by the presence of buildings. An analysis was conducted concerning wind conditions that constitute pedestrian comfort and influence the possibility for ventilation of spaces between buildings for the three selected models. The research results were compared, and an attempt was made to assess the most beneficial and the least favorable building development types in this respect.

Experimental investigation of the effects of intermediate gravity waves on the water evaporation rate

This experiment was done to predict the evaporation rate from the wavy water surface under the different convection regimes ( free, forced, and mixed) at turbulent airflow conditions over a wide range of the ratio(Gr/Re2 ). Evaporation rate from wavy water surface is strongly affected by combinations between wave steepness and main airflow velocity above the wavy water surface. Experimental results show that no pattern can be followed for which combinations of evaporation rate will increase. Thus, only two facts can be noticed: the evaporation rate is larger than that measured under the same airflow velocity conditions with no waves existing on evaporated water surface because the airflow is smooth and attached along the still water surface and when increasing the wave steepness(H/L,H/T), Airflow will separate at the lee side of wave crest near to the bottom of the wave trough. Thus, vortex will generate in the airflow separation region. These vortexes are unstable and cause an increase in turbulence, reducing the water surface's resistance to vertical transport water vapor and increasing the evaporation rate. Also, experimental results show that the evaporation rates are somewhat less than that measured under the same airflow velocity with smaller wave steepness due to air trapped region observed at the leeside of the wave crest near the bottom of the wave trough. Evaporation rate is increasing with increase airflow velocity under the same convection regime.

Analysis of Ventilation Efficiency in the Earth Covered Magazine for Ammunition Storage Using Numerical Simulation

Internal environment parameters such as temperature, relative humidity and airflow velocity in ammunition storage facilities have a significant impact on the condition and overall life of ammunition, especially on the process of ammunition degradation in situations when their values deviate from required standards for safe storage. High temperatures inside the magazine, as well as in the ammunition packaging, can have a very negative effect on the structure of ammunition and explosives, and high values of relative humidity can result in corrosion and rapid decomposition of chemical compounds. Therefore, a properly designed ventilation system should ensure that the values of internal temperature and relative humidity are within the permitted limits, which is a very important aspect of the storage process itself, so that ammunition and explosives can be completely safe and ready for transport, use and handling. Experimental studies conducted in several magazines of ammunition and explosives in Bosnia and Herzegovina (BiH), had aim to monitor changes of environmental parameters such as temperature, relative humidity and airflow velocity. During these experimental measurements, high values of relative humidity were in these magazines observed, as well as uneven airflow in some ventilation ducks. The main cause of such measured values can be related to the inadequate performance of the natural ventilation system of the analysed magazines. Using numerical simulations (finite volume method) in the ANSYS – Fluent program, the analysis of the existing ventilation system of earth covered magazine in BiH from the aspect of airflow velocity was performed, as well as analysis of modifications that can improve airflow within the analysed magazine. The results of numerical simulation for the existing state of analysed magazine corresponded to the results of airflow measurements at certain places in the magazine. It was confirmed that the existing ventilation system does not provide proper ventilation, which further causes higher relative humidity values. The results of numerical simulation for the proposed modifications of the ventilation system have shown significantly better air circulation in the magazine, i.e. that a more efficient natural ventilation was achieved.

Determining Position of the Evaporator in a Smart Classroom Concept Using CFD Method

Various, different evaporator placements in a room have produced different airflow patterns, temperature distribution, and airflow velocities. In this study, the average room temperature and airflow velocity measured at 27 points of the CFD simulation for 4 positions of the planned evaporator placements were compared to determine the most ideal position based on the comfortable temperature and the maximum airflow velocity pursuant to the SNI 03-6572-2001 recommendation. On Position 1, two evaporators were given to the west wall. Position 2, two evaporators were placed on the south wall. On Position 3, two evaporators were given to the north wall. Moreover, on Position 4, two evaporators were placed opposite to each other where an evaporator was placed on the south wall, and the other evaporator was placed on the north wall. An ANSYS Fluent software was employed to make the CFD simulation. Based on the results of the study, it was found out that Position 2 was the most ideal evaporator placement position since it met the comfortable temperature limit and has the highest number of airflow velocity points meeting the recommended maximum airflow velocity pursuant to the SNI 03-6572-2001 recommendation.

Computational Analysis of Lung and Isolated Airway Bifurcations under Mechanical Ventilation and Normal Breathing

Mechanical ventilation is required for many patients who cannot breathe normally as a result of lung disease and other factors that result in reduced lung function. In this study, we investigated the effects of mechanical ventilation and normal breathing on whole lung geometry as well as isolated bifurcations through computational fluid dynamic (CFD) simulations. Results of flow characteristics (airflow velocity, wall pressure, and wall shear stress) obtained from the CFD simulations are presented. Similar flow patterns and pressure drops were obtained between the whole lung geometry and isolated bifurcations under both normal breathing and mechanical ventilation, respectively. Results obtained from simulations suggest that analyzing specific local bifurcations may be a more feasible alternative as it may reduce the computational time and numerical errors resulting from computations as compared to simulating a complex whole lung geometry. The approach presented in this study also demonstrated that analyses of isolated bifurcations gave similar flow characteristics to that of whole lung geometry. Therefore, this approach may be useful for quickly obtaining results that will assist in making clinical predictions and other applications.