Fan Array Research Articles

Dynamic modeling, validation and analysis of direct air-cooling condenser with integration to the coal-fired power plant for flexible operation

Coal-fired power plants with direct air-cooling condensers (DACC-CFPPs) have been widely used in areas rich in coal but short of water since they can significantly reduce water consumption. Despite its water-saving advantages, direct air-cooling condensers have inherent defects such as environmental and load sensitivity, higher costs and poor cooling performance, which deteriorate the economics and flexibility of the integrated system. For safe, efficient and flexible operation, this paper presents the development of a direct air-cooling condenser dynamic model integrated with a 600 MWe coal-fired power plant to study the interactions between heat and power within the entire DACC-CFPP under various load and ambient conditions. The condenser is modeled in a one-dimensional multi-section manner to reflect the impacts of crosswind and ambient temperature disturbances. A detailed turbine-feedwater heater system model is also developed to link the direct air-cooling condenser and power plant together. Steady-state and dynamic validations under various operating conditions are conducted, which demonstrate the high fidelity of the developed model. Simulation studies are then carried out to investigate the dynamic interactions between boiler-turbine, condenser and environmental conditions. We find that manipulating the fan array speed controls the condenser pressure effectively in terms of environmental disturbance rejection and load ramping. Motivated by this finding, a novel variable condenser pressure operating mode is proposed to coordinate the direct air-cooling condenser and coal-fired power plant operation, which can significantly improve the load tracking performance of the integrated plant.

Numerical simulations of flow induced noise from a dual rotor cooling fan used in electronic cooling systems

Hard Disk Drive (HDD) system enclosures in a data center require effective cooling systems to avoid HDD overheating. These systems often rely on air cooling because of their cost effciency and maintainability. Air cooling systems typically consist of an array of axial fans which push or pull the air through the system. These fans emit high level tonal noise particularly at high tip speed ratios. High-capacity HDDs, on the other hand, are sensitive to high acoustic noise, which consequently increases the risk of read/write error and deteriorates drive performance. Therefore, cooling fan noise adversely affects the function of the HDD enclosure systems which emphasizes the need to understand the noise sources and develop methods to mitigate HDD noise exposure.

Aerodynamic modeling for streamlined box girders using nonlinear differential equations and validation in actively generated turbulence

In classical buffeting analysis theory, aerodynamic forces are usually expressed by a linear quasi-steady formula, and they are improved by aerodynamic admittances suitable for streamlined bridge girders. Recent studies have shown that admittances change obviously with incoming flow characteristics and aerodynamic nonlinearity, such as the frequency multiplication phenomenon, and motion-induced amplitude-related aerodynamic effects cannot be ignored in some cases. To address these problems, a nonlinear condensed subsystem equation (NCSE) suitable for wind-induced aerodynamic force modeling is established in the time domain. It characterizes aerodynamic nonlinearity with series of nonlinear differential equations and data-driven parameters. The proposed framework can be used for complex aerodynamic re-illustration related to the strong nonlinearity of streamlined box girders. To validate the precision and feasibility of the framework, sectional model experiments performed on a streamlined box girder were carried out in an active turbulence generated wind tunnel in which an adjustable array of multiple fans was assisted by actively controlled vibrating wings for a 2D turbulence condition. The case study shows that the NCSE model can be used to predict nonlinear aerodynamic forces in the time and frequency domains, even under complex stochastic flow conditions. The proposed method provides an alternative way to predict possible aerodynamics based on the condition of incoming flow with sufficient accuracy, and it can illustrate multifrequency components of aerodynamic forces.

Energy-Saving Strategies of Axial Flow Fans for Direct Dry Cooling System

The operating conditions of axial flow fans are closely related to the thermo-flow characteristics of the mechanical draft direct dry cooling system. Moreover, the uneven distribution of cooling air driven by axial flow fans may lead to the deterioration of the heat transfer capacity of air-cooled condensers (ACCs). Therefore, developing energy-saving operating methods for axial flow fans is very meaningful. In this work, two kinds of adjustment strategies to make the flow field more uniform are proposed for a 2 × 300 MW direct dry cooling power-generating unit. The performance of ACCs in the prevailing wind direction is predicted with the help of the macro heat exchanger model. It is found that the inlet air temperatures of fans are significantly reduced by proposed strategies, especially at high wind speeds. Moreover, the minimum cooling air can meet the cooling demand of ACCs for the strategy which made the air flow rates of all fans consistent. Compared with the case without adjustment of fans, the total power consumption of the fan array was cut down effectively, up to 13.94% at the wind speed of 12 m/s. In conclusion, the energy efficiency of ACCs can be improved by the uniform flow field.

Noise Source Identification for a ±800kV Converter Station Based on Beam-forming Acoustic Imaging Technology

In this paper, a beam-forming acoustic imaging technology is applied to identify the spatial position and frequency characteristics of the main noise source on the key position of a ±800kV DC converter station. The test results show that the main noise sources of the AC filter field are the reactor group and the capacitor group, the noise of the reactor group has obvious peak value at 600Hz, and the noise of the capacitor group has obvious peak value at 100Hz. The main noise of DC filter field is from the reactor. The main noise source in the converter transformer area is the cooling fan array arranged outside the transformer. The maximum noise of the water cooling system is generated by the spray water on the bottom water pan of the cooling tower.

Experimental Testing on an Air-Cooled Condenser Motor, Gearbox and Fan

The majority of South Africa’s electricity is generated from coal-fired power stations. After expansion through the turbine stage the heated steam is condensed by air-cooled condensors (ACCs). In water scarce areas air-cooled condensers are used to reject heat by means of convection through an array of fans that force air over the heated steam tubes positioned in a A-frame structure above the fan. The ACC system consists of an induction motor, two-stage gear reducer and an axial fan. For this research, the rotational velocity of the gearbox’s output shaft is measured as well as the bending and torsional strain experienced during different stages of operation. A proximity sensor and various sets of strain gauges are used to record the measurements respectively. Testing was conducted at three different sites that utilize different control methods for the induction motors. The purpose of testing at different sites was to evaluate the effectiveness of each start-up control system and its application inside an ACC. The results obtained in each of the three cases are quite clear that any motor controller is beneficial to the overall system simply due to the reduced inrush current and torque peaks.

Heat transfer enhancement research of dynamical vortex generator in a solar air heater by using the piezoelectric fan array

Most of the vortex generators are static and used in fin-and-tube heat exchangers, whereas this paper presents experimental and numerical research on the effects of piezoelectric fan array in single pass solar air heater having one side heated and the other three sides insulated. The average Nusselt number of the rectangular channel is compared in detail with different Reynolds number of the air. Two different flow direction configurations including counter flow and downstream flow has been tested. The results show that the piezoelectric fan as a vortex generator can increase the local and average Nusselt number effectively. The average Nusselt number is increased by 40~100%, whereas the pressure drop is increased by no more than 30%. The counter flow has higher local and average Nusselt number compared to the downstream flow, while higher pressure drop in the counter flow setup can be found compared to the downstream flow setup. According to the numerical simulation results, this is because the most longitude vortices are concentrated in the middle of the absorber plate and attached or reflowed to the plate in the counter flow setup. However, most of the vortices are concentrated in the back end of the plate or out of the plate in downstream flow. All of these, result from the different velocity gradient distribution at the near-wall of the heated surface. The existences of the PE fan bracket decreases the pressure drop in the downstream flow setup.

Latticed mode: A new control strategy for wind field simulation in a multiple-fan wind tunnel.

On the basis of the actively controlled multiple-fan wind tunnel we designed, this paper proposes a latticed mode-based control strategy for the fan array. The so-called latticed mode is the overall topology of the working fans. In order to investigate the simulation ability of the latticed mode, several latticed modes are designed to analyze the temporal and spatial properties of generated wind fields. Airflow data under different latticed modes are measured using nine two-dimensional anemometers, and then, statistical indicators of wind speed and wind direction, as well as the spatial uniformity and complexity of generated wind fields, are calculated to analyze the characteristics of wind records. The results indicate that the distribution of active fans in the latticed mode has significant influence on the statistical properties and spatial evolutions of wind speed and direction. Besides, the latticed modes can regulate the spatial uniformity and complexity of the wind fields. The latticed modes with a high clustering degree of active fans can generate wind fields with low spatial uniformity and high complexity. In addition to the fan voltage and the rotation angle of swivel plates, the proposed latticed mode provides more possibilities for wind field simulation.

Experimental study on thermal performance improvement of solar air heater using piezoelectric fan

This paper presents experiment research about piezoelectric fan array in solar air heater (SAH) at the frequencies 45-60Hz by using lamp array as solar radiation simulator. The effectively heat transfer coefficient (HTC) of the traditional method such as strip rib on the solar collector and enhancement by piezoelectric fan are compared in detail with different mass flow rate of the air. A prototype solar collector with dimension of 300(L)×150(W)mm is fixed in a wind tunnel in the experiment. Three configurations of piezoelectric fan array have been tested, the results show that the piezoelectric fan can increase the HTC effectively, the HTC is increased 3-3.5 times compared with smooth plate and the additional power consumption of the piezoelectric fan as low as 0.6W for 2×2 piezoelectric fan array, whereas for the pressure drop of the SAH increased no more than 5%. The resonance frequencies of the two types of piezoelectric fans in experiment are 55Hz and 53Hz respectively, the maximum amplitude and the HTC achieved at the resonance frequency. It’s an effective way for SAH application compares to other methods of heat transfer enhancement in SAH and rarely be reported in the area of SAH.

Investigation on thermal-hydraulic performance of the absorber plate using a piezoelectric fan in the solar air heater

This paper presents experimental and numerical research about piezoelectric fan array in solar air heater (SAH) at the frequencies 45-60 Hz by using lamp array as solar radiation simulator. The effective heat transfer coefficient (HTC) of the traditional method such as strip rib on the solar collector and the HTC enhanced by the piezoelectric fan are compared in detail with the different flow rate of the air. A prototype solar collector with a dimension of 300 mm (L)×150 mm (W) is fixed in a wind tunnel in the experiment. Three configurations of piezoelectric fan array which include through-pass and double pass mode have been tested. The results show that the piezoelectric fan can increase HTC or Nusselt number effectively. The Nusselet number is increased by 50∼100%, whereas the pressure drop is increased by no more than 5%. The additional power consumption of the piezoelectric fan is only as low as 0.96 W for 2×2 piezoelectric fan array. The maximum amplitude and the HTC or Nusselt number will be achieved at the resonance frequency, and the vertical setup is the most effective for heat transfer enhancement.

Optimisation of low energy cooling through phase variation between adjacent piezoelectric fan blades

Piezoelectric fans are highly efficient and low energy air-movers. The technology may be applied to reduce the power requirements of thermal management systems in a range of power electronics. The understanding of piezoelectric fan arrays, in which multiple blades are beneficially coupled, is of paramount importance for the research field. In the present research, a numerical model consisting of two piezoelectric fan blades is developed and validated against previous experimental work. The model is used to investigate the effect of phase variation, ϕ, between two adjacent piezoelectric fan blades in face-to-face orientation, operating within a channel. When ϕ≠0°, 180°, an asymmetrical flow domain is observed. Considering an incremental increase of phase variation from ϕ=0°, the skewness of the downstream velocity profile is increased heavily when ϕ⩽60°, whilst the magnitude of the average downstream velocity is only enhanced when ϕ⩾75°. The generated skew is attributed to the dominance of one vortex over another between the adjacent blade faces during their opening period. At peak skewness (ϕ=75°), the vortex behind the phase leading blade is 101% larger than its counterpart. Evenly matched vortices between the two blades are optimal for generating peak mass transfer. This is observed when the blades are in counter-phase, ϕ=180°. Conclusions in the present study build upon and are in good agreement with those previously published.

Geometric optimisation of piezoelectric fan arrays for low energy cooling

A numerical model of a typical piezoelectric fan blade is derived and validated against experimental data. Numerical error is found to be 5.4% and 9.8% using two data comparison methods. The model is used to explore the variation of pitch as a function of amplitude, A, for a confined two-blade piezoelectric fan array in face-to-face orientation, with the blades oscillating both in-phase and counter-phase. It has been reported that in-phase oscillation is optimal for generating maximum downstream velocity and flow rate in unconfined conditions, due at least in part to the beneficial coupling between the adjacent blades that leads to an increased oscillation amplitude. The present model demonstrates that confinement has a significant detrimental effect on in-phase oscillation. Even at low pitch, counter-phase oscillation produces enhanced downstream air velocities and flow rates. Downstream air velocity from counter-phase oscillation can be maximally enhanced, relative to that generated from a single blade, by 17.7% at P=8A. Flow rate enhancement at the same pitch is found to be 18.6%. By comparison, in-phase oscillation at the same pitch outputs 23.9% and 24.8% reductions in peak downstream air velocity and flow rate, relative to that generated from a single blade. This optimal pitch, equivalent to those reported in the literature, suggests that counter-phase oscillation is less affected by confinement. The optimal pitch for generating bulk airflow from counter-phase oscillation is large, P>16A, due to the small but significant downstream velocity across the span between adjacent blades. However, by considering design in a confined space, counter-phase pitch should be minimised to maximise the bulk airflow generated from a certain cross-sectional area within a channel flow application. Quantitative values are found to deviate to a small degree as other geometric and operational parameters are varied, but the established relationships are maintained.

Numerical analysis from the rotational speed regulation within the fan array on the performance of an air-cooled steam condenser

As the driven devices, forced draught fans are always applied to extract the ambient air for cooling the turbine exhaust steam in an air-cooled steam condenser (ACSC). Accordingly, the influences from the fan array (FA) on the performance of the ACSC is significant for the corresponding design and optimization. In this paper, a numerical model for a large scale power plant, with a designed output power of 2 × 600 MW, is built to study the relations between the rotational speed distribution within the FA and the power plant performance at the local prevailing wind angle. The simulation results indicate that after the rotational speed increase for the fans, the improvement of the power plant performance will be obtained. In comparison with the original design situation, it is acquired that the peak elevation amplitude of final net power approaches 41.33 MW, when the wind speed arrives at 10 ms−1 for the FA case. Accordingly, based on the aforementioned comparisons, it can be summarized that a maximum benefit of the net power will be found at all the designated wind speeds, when the rotational speed for the entire FA is regulated.

On the dynamic modeling and control of the cold-end system in a direct air-cooling generating unit

Direct air-cooling is considered as a promising technique in power generation because of its distinct water-saving advantages, where ambient air is utilized instead of water, to cool down the exhaust steam in the direct air-cooling condenser. However, the relatively poor heat transfer characteristics and thermodynamic properties of air also brings higher backpressure in the direct air-cooling generating unit compared with conventional water-cooling generating unit, as well as the sensitivity of condenser performance to meteorological and ambient conditions. Therefore, the unit backpressure control for the direct air-cooling generating unit has been a challenging task in the recent years. To this end, a control-oriented mechanism dynamic cold-end system model is built for the direct air-cooling generating unit in this paper. The modified moving boundary method is utilized to capture the dynamic process of exhaust steam condensation in the condenser, wherein a time-variant mean void fraction is adopted to enhance model accuracy and robustness. Validation results with operating data have shown the established model can capture the dynamics of direct air-cooling cold-end system with satisfied accuracy. Based on the established model, a model predictive controller with feedforward compensation is proposed to keep unit backpressure steady at the desired set-point while suppressing the time-varying stochastic ambient temperature disturbances by regulating the rotation speed of fan array appropriately. The simulation results have verified the merits and effectiveness of the proposed strategy in achieving both satisfactory backpressure regulation and disturbance rejection performance.

Simulations on arrangements of induced jet-fans as auxiliary ventilation for a mechanical ventilated space with openings

Underground garages, indoor stadiums, or more commonly used seagoing ships, can be used as large multi-purpose spaces, which are suitable for the carriage of a wide range of cargoes, as well as evacuation of people at overseas. The indoor environment in a multi-purpose cabin usually varies, in terms of pollutant emissions, hazardous levels and the corresponding ventilation requirements. A possible solution, in addition to a single regular HVAC system, is to use multiple induced jet fans. However, to pre-determine a universal design of fans, e.g., numbers, locations, directions, angles and flowrates, etc., may not be practical. In this preliminary work, methods to design the auxiliary ventilation system were discussed. The heat sources are located in the four corners on the floor. CFD method is used to further study the effects of six regular and four irregular arrangements of a 2×2 array of fans on local heat dilution with or without natural ventilation (e.g., additional openings in the space). Heat exhaust efficiency is used to evaluate the effects of different arrangements of fans on local heat dilution. The results show that adjustable ventilation using induced fans would be useful to provide various airflow distribution for a large space and the dilution of the heat can be improved and the areas of high temperature inside the space can be reduced. Furthermore, the heat exhaust efficiency would be higher and the induced fans have a more significant effect, especially when additional natural ventilation is available.

Aero-Propulsive and Propulsor Cross-Coupling Effects on a Distributed Propulsion System

This study aims to characterize the complex propulsive-airframe and cross-propulsor interactions that occur on an overwing distributed propulsion system with boundary-layer ingestion. Wind tunnel experiments were performed on a NACA airfoil model with an array of five ducted fans integrated across the upper-surface trailing edge. Net forces lift, drag, and pitching moment characteristics, as well as pressure distributions and particle image velocimetry (PIV) velocity fields, were experimentally characterized as a function of fan throttle setting. Additionally, various mixed-throttle cases were investigated with certain fans inoperative windmilling. The experimental results revealed nonlinearities in the changes of the streamwise and stream-normal forces lift, drag, and pitching moment polars as a function of and throttle setting. These nonlinear variations in the airfoil model forces and moments were attributed to variation in the magnitude and direction of the fan thrust vector, which is tied to changes in the airfoil pressure distribution and an induced circulation effect. The ingested boundary-layer height was seen to decrease linearly with a uniform increase in throttle setting. The fan-out cases showed that a windmilling inoperative fan on the edge of the array was more detrimental to performance than a windmilling inoperative fan located within the fan array, and a highly three-dimensional flow was observed from the PIV velocity fields and surface pressure distributions.

Modelling and Optimization of the Direct Air Cooling Power Generation Unit

Abstract Fossil fuel power plants dominate the energy structure in China. However, the water scarcity, in Southeast/Southwest China, results in the development of the dry cooling power plants. Direct air cooling condenser (DACC) is appealing for its water saving ability. In DACC, the exhaust steam is cooled and condensed to water by the air flow, which is provided by the fan array at the cost of electricity. There exists a varying optimal exhaust steam pressure under different air temperatures and loads. The static model of the turbine-DACC system is built to quantify the influences of the air temperatures and loads. An on-line optimization is used here to set the reference value of the exhaust steam pressure for the turbine-DACC system for economic operation. The objective is to maximize the net power production while satisfying the constraints on the safety pressure and the available air flowrate. The optimization is conducted in a model 660MW power plant selected on a random summer/winter day. The hourly optimal exhaust steam pressure and the operation instructions are calculated as the reference values for the control layer. The optimization results show that the optimal exhaust steam pressure may be too close to the safety limits in winter, suggesting the safety also to be considered in the optimization. In summer, the DACC system cannot satisfy the condensation load sometimes. Thus, a complementary cooling method, for example, the wet cooling, is needed to reduce the burden on the DACC system.

Effectiveness of Rack-Level Fans—Part I: Energy Savings Through Consolidation

In general, smaller fans operate at lower efficiencies than larger fans of proportional linear dimensions. In this work, the applicability of replacing smaller, 60 mm baseline fans from within the chassis of web servers with an array of larger, geometrically proportional 80 mm and 120 mm fans consolidated to the back of a rack is experimentally tested. Initial characterization of the selected fans showed that the larger fans operate at double peak total efficiency of the smaller fans. A stack of four servers were used in a laboratory setting to represent a rack of servers. When all four servers were stressed at uniform computational loadings, the 80 mm fans resulted in 50.1–52.6% reduction in total rack fan power compared to the baseline fans. The 120 mm fans showed similar reduction in rack fan power of 47.6–54.0% over the baseline. Since actual data centers rarely operate at uniform computational loading across servers in a rack, a worst case scenario test was conceived in which the array of larger fans were controlled by a single server operating at peak computational workload while the other three in the rack remained idle. Despite significant overcooling in the three idle servers, the 80 mm and 120 mm fan configurations still showed 35% and 34% reduction in total rack fan power compared to the baseline fans. The findings strongly suggest that a rack-level fan scheme in which servers share airflow from an array of consolidated larger fans is superior to traditional chassis fans.

Sensitivity analysis from the blade angle regulation of the forced draught fans in an air-cooled steam condenser

For enough cooling air flowing through the finned tube heat exchangers, the performance of the forced draught fans are always pivotal for the final characteristics of the air-cooled steam condenser (ACSC) as well as the power station. Hence, it is necessary to optimize the fan operation for a superior performance. In this paper, a previous numerical model is designated to execute the impact analysis from the blade angle regulation for forced draught fans with different positions on the performance of the air-cooled system at the prevailing wind angle of β=22.5°. The simulation results indicate the fan volumetric effectiveness, heat transfer rate and the related equilibrium back pressure are influenced significantly once the fan blade angle is regulated. Compared with the design case, it is found that a maximum elevation of net power, 17.76MW, is obtained for the fan array case when the wind speed is vm=2m·s−1. Furthermore, it is found that the windward and peripheral case almost have a same effect to raise the net power of the power plant.

The development of hybrid longitudinal windcatcher for basement ventilation in warm humid climate

ABSTRACTThis paper reports the development of a longitudinal hybrid windcatcher (LHWC) to provide thermal comfort and healthy ventilation for basement in warm humid climate. Two full-scaled computer models and a one-tenth physical model were constructed. The computer simulation found that outdoor wind speed of 1–5 m/s generated air velocities of 0.19–1.01 m/s at the occupants’ zone when the inlet's height was 1 m above the surrounding roofs. Raising the inlet 3 m higher did not produce significant difference air velocity at the occupants’ zone. The physical model experiment outdoor found that 3 m/s wind induced 0.3 m/s air velocity inside it. Meanwhile, with the absence of outdoor wind, the four small exhaust fans could induce 0.05 m/s air velocity inside it. From the computer simulation and physical model, it can be concluded that outdoor wind air could induce physiological cooling and ventilation at the basement. The array of exhaust fans could only induce very low air velocity but it was considered able to ventilate the used air for the basement.