Large Diameter Fan Research Articles

Agricultural Engineering Technologies in the Control of Frost Damage in Permanent Plantations

The occurrence of late spring frosts due to climate change causes great damage to plantation production worldwide. The main objective of the paper is to provide a comprehensive overview of the problem and to outline effective protective measures against late spring frosts. The nature of frost depends on regional, altitudinal, and geographic differences, but they all share a common problem: they remove heat, resulting in the freezing of new plant growth and flowers. Tissue freezing is affected by critical temperatures and the frost type, intensity, and duration. Protection against late spring frosts can be broadly divided into three categories: active, passive, and chemical measures. In the field of agricultural engineering, various techniques have been thoroughly researched, and their effectiveness has been confirmed by research. These include various sprinkler systems, different heating devices, and large-diameter fans. Conclusive findings are being made on the performance of these systems in sub-zero temperatures and their cost-effectiveness. Climate change increases the importance of protecting permanent crops from late spring frosts and requires advances in agricultural technology to meet changing production demands and challenges.

Performance Testing of an Axial Flow Fan Designed for Air-Cooled Heat Exchanger Applications

An axial flow fan developed in the previous study is tested in order to characterize its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary computational fluid dynamics (CFD) results obtained using an actuator disk model (ADM) as well as a periodic three dimensional model indicate that the fan meets the specified performance targets, with an expected total-to-static efficiency of 59.4% and a total-to-static pressure rise of 114.7 Pa at the operating point. Experimental tests are performed on the M-fan in order to determine its performance across a full range of flow rates. A range of fan configurations are tested in order to ascertain the effect of tip clearance, blade angle, and hub configuration on fan performance. Due to the lack of a suitable facility for testing a large diameter fan, a scaled 1.542 m diameter model is tested on the ISO 5801 type A fan test facility at Stellenbosch University. A Reynolds-averaged Navier–Stokes CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. The results of the CFD model will be validated using the experimental data obtained. Both the CFD results and the experimental data obtained are compared to the initial CFD results for the full scale fan, as obtained in the previous study, by means of fan scaling laws. Experimental data indicate that the M-fan does not meet the pressure requirement set out in the initial study at the design blade setting angle of 34 deg. Under these conditions, the M-fan attains a total-to-static pressure rise of 102.5 Pa and a total-to-static efficiency of 56.4%, running with a tip gap of 2 mm. Increasing the blade angle is shown to be a potential remedy, improving the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap, with larger tip gaps substantially reducing fan performance. The losses due to tip gap are also shown to be overestimated by the CFD simulations. Both experimental and numerically obtained results indicate lower fan total-to-static efficiencies than obtained in the initial CFD study. Results indicate that the M-fan is suited to its intended application, however, it should be operated with a smaller tip gap than initially recommended and a larger blade setting angle. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.

A new low-turbulence wind tunnel for animal and small vehicle flight experiments.

Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s−1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s−1. To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.

Performance Comparison of Destratification Fans for Large Spaces

Ceiling fan is proven to have a beneficial effect on increasing air velocity and reducing temperature stratification and thus saving energy for high ceiling applications. Studies show that the velocities produced by large diameter, ceiling mounted fans do not produce a negative or positive effect on human comfort. Recently, smaller, high velocity fans have been introduced to the market as an alternative to these large diameter fans that provides similar energy savings due to reduced destratification, while still not moving the air fast enough to cause human discomfort, though these products have been studied less. This study simulates and compares the performance of both large and small diameter fans using a validated computational fluid dynamics (CFD) model. Two different types of destratification fans are investigated for their performance in destratifying the air temperatures in warehouse style retail stores. A portion of a retail store is used as a base to create the test environment. Simulations show that the small diameter high speed fan (SDHSF) is very good at bringing a well-mixed column of air all the way to the floor, but the spaces without a fan directly overhead are hardly affected. The large diameter low speed fans (LDLSF) are able to mix nearly the entire space, though they created uncomfortable drafts near head height. Between these two fans, the LDLSF is more successful at destratifying the entire space, though the SDHSF is better at only destratifying a specific, smaller area. Varying the speed of the LDLSF also allows for successful destratification, while maintaining acceptable draft velocities.

The Energy-Saving and Noise Reduction of Fan Equipped in Evaporative Condenser in Refrigeration System

To study practical methods about energy-saving and noise reduction of fan,by analysising energy consumption and noise formation mechanism of fan in evaporative condenser. on the basis of the fan structure optimization (large diameter fan equiped width blade, anteversion structure),adopting multi-blowers starting and stopping control independently and Variable frequency fan, Optimum solution of energy-saving and noise reduction of fan was obtained.

Fan Size and Energy Efficiency

The use of ceiling mounted circulating fans to provide air movement for cooling in industrial premises and animal houses is particularly essential in warm, humid climates. Methods to substantially improve the efficiency of this approach are demonstrated in this paper. Fan laws are identified as one source of strategies for increasing energy-efficiency of fans. Industrial ceiling fans are used to demonstrate that using larger, slower, fans will not only improve energy efficiency but also reduce fan noise. By using large diameter fans (7.3m diameter) in place of conventional fans, energy savings of over 40% are demonstrated. Field studies of air flow characteristics from ceiling fans are shown to provide further opportunities to increase air flow efficiency in industrial buildings. Utilising lower friction losses associated with the Coanda effect in air flow adjacent to the floor is shown to increase air flow toward the outer limits of the radial outflow. Lower fan mounting heights are also shown to provide increased air flow toward the outer limits of the radial outflow. For situations where the floor plane has numerous obstructions to air flow, CFD software is suggested as a means to simulate air flow before installation of fans. Where possible, validation of CFD software output against physical measurements is advised.