Characteristics Of Fan Research Articles

Internal Flow and Heat Transfer Characteristics of Different Diameter Centrifugal Fans with Functions as Heat Exchanger

Internal Flow and Heat Transfer Characteristics of Different Diameter Centrifugal Fans with Functions as Heat Exchanger

Performance and inter-blade flow of axial flow fans with different blade angles of attack

The predictions of fan performance on the pressure and flow rate characteristics of the axial flow fans using the conventional computational flow dynamics (CFD) approaches generally show a large deviation of about 20–30% from the experimental results. This article modifies the conventional CFD approaches by engaging the flow resistance of the fan test bench on the downstream area of the computational domain. The downstream pressure and flow rate are adjusted iteratively during the computational process. The results show that the prediction deviations using this method can be reduced to at most 3%, which is a great improvement compared to the conventional method. The inter-blade flows of three axial flow fans with different blade angles of attack are subsequently studied using this method. The results show that the flow patterns are drastically sensitive to the variation of the blade angle of attack, and the fan performances are closely related to the inter-blade flow behaviors. In the pre-stall regime, inappropriately designed blade angle of attack would cause the inter-blade flows in the region near the blade tip and the flows in the tip clearance region to present larger lateral and smaller axial velocity components with recirculation bubbles near the blade trailing edges. These flow behaviors cause the degradation of the fan performance. In the stall regime, boundary layer separation occurs to the suction surface of fan blades. Large recirculation bubbles appear near the trailing edges of blades and cause blockage effect against the axial flows. For the fans with inappropriately designed blade angle of attack, reverse flows can even be observed in the inter-blade passages with huge recirculation bubbles attaching to the trailing edges of fan blades.

대형 디젤엔진 자동변속기 오일쿨러 냉각팬 성능에 관한 연구

This study has investigated numerically and experimentally the flow characteristic of air-cooling fan for transmission oil cooler in the large-size diesel engine. Impellers of cooler were composed of eight normal-scale and eight small-scale blades in the zig-zag pattern. In order to increase the discharge pressure of cooling fan, turbo type of fan blade is proposed in the impeller for transmission oil cooler. The fluidic performance of cooling fan has been estimated numerically by using the commercial code and experimentally carried out with reference on AMCA Standard 210-99. As a result, it is confirmed that the numerical result for performance curve is in good agreement with experimental data.

Experimental study of frost accumulation on fan-supplied tube-fin evaporators

Compact tube-fin evaporators have been extensively used in refrigeration cassettes for light commercial applications. Such refrigeration systems are space constrained and, therefore, the heat exchangers (condenser and evaporator) must have a large area-to-volume ratio. In addition, such applications require a subfreezing evaporating temperature that induces the growth of a frost layer on the finned surface, which may block the evaporator if a proper defrost strategy is not used. Before completely blocking the evaporator, the frost layer depletes the heat exchanger performance by adding an extra thermal resistance and also by reducing the fan-supplied air flow rate. Understanding the way the frost forms on these compact heat exchangers and also the way the fan is affected by frost clogging is mandatory for the design of robust refrigeration systems and also to devise more efficient defrost strategies. In this study an experimental investigation on the frost accretion of tube-fin evaporators considering the fan characteristics is carried out. To this end, a specially designed, constructed and calibrated closed-loop wind-tunnel facility was used. Experimental tests were carried out with four different (three wavy-fin and one louvered-fin) evaporator coils under different conditions. It was found that the frost formation rate increases with the air flow rate, supercooling degree and the density of fins. A strict relation between accumulated mass of frost, air-side pressure drop and cooling capacity was also observed. It was also noted that the fan characteristics play an important role on the evaporator thermal performance, indicating that under frosting conditions the fan-evaporator pair must be designed as a coupled system. Furthermore, for the same operating conditions, the louvered-fin evaporator showed to be more sensitive to the frost formation effects than the wavy-fin coils.

Modelling and simulation of a jet fan for controlled air flow in large enclosures

Jet fans are applied for control of air flow and support of pollutant dispersal in large enclosures. In The Netherlands, application is well known for car parks as part of the fire safety design. In the design phase often the Computational Fluid Dynamics (CFD)-technique is used to verify the fire safety level afforded by the application of jet fans. However, very little is known on the modelling requirements of jet fans in CFD. This includes paucity on experimental data that can be applied for validation of the jet fan model. In this study results are presented as measurements for a specific type of jet fan in a large enclosure and of validation of modelling characteristics of the jet fan in CFD. Both free and near-wall positioning have been investigated and a modelling proposal is made. For the modelling of the jet fan, point-of-departure is a low complexity, as the model generally will have to be included in large computational domains. Applicability of the developed approach and assessment of efficiency of jet fan positioning in large enclosures is shown through a case study.

Ammonia Emissions from a U.S. Broiler House—Comparison of Concurrent Measurements Using Three Different Technologies

There is a need for robust and accurate techniques for the measurement of ammonia (NH3) and other atmospheric pollutant emissions from poultry production facilities. Reasonable estimates of NH3 emission rate (ER) from poultry facilities are needed to guide discussions about the industry’s impact on local and regional air quality. The design of these facilities features numerous emission points and results in emission characteristics of relatively low concentrations and exhaust flow rates that vary diurnally, seasonally, and with bird age over a considerable range. These factors combine to render conventional emissions monitoring approaches difficult to apply. Access to these facilities is also often restricted for biosecurity reasons. The three objectives of this study were (1) to compare three methods for measuring exhaust NH3 concentrations and thus ERs, (2) to compare ventilation rates using in situ measured fan characteristics versus using manufacturer sourced fan curves, and (3) to examine limitations of the alternative measurement technologies. In this study, two open-path monitoring systems operating outside of the buildings were compared with a portable monitoring system sampling upstream of a primary exhaust fan. The position of the open-path systems relative to the exhaust fans, measurement strategy adopted, and weather conditions significantly influenced the quality of data collected when compared with the internally located, portable monitoring system. Calculation of exhaust airflow from the facility had a large effect on calculated emissions and assuming that the installed fans performed as per published performance characteristics potentially overestimated emissions by 13.6–26.8%. The open-path measurement systems showed promise for being able to obtain ER measurements with minimal access to the house, although the availability of individual fan characteristics markedly improved the calculated ER accuracy. However, substantial operator skill and experience and favorable weather conditions were required to obtain good quality results.

환기용 축류송풍기의 유동해석 및 모터 위치에 따른 성능 특성 연구

Flow analysis and performa nce evaluation have been performed for a ventilation axial-flow fan with different positions of the motor. Two different positions of motor have been tested; one is in front of the impeller and the other is behind the impeller. Flow analyses are performed by solving three-dimensional Reynolds-averaged Navier-Stokes equations through a finite-volume solver. Preliminary numerical calculations are carried out to test the performances of different turbulence models, i.e., SST model, k- model, and k- model with and without using empirical wall function in the flow analysis. The validation of numerical analyses has been performed in comparison with the experimental data. The numerical results for the performance characteristics of the ventilation axial-flow fan with two different positions of the motor have been presented.

Local heat transfer performance and exit flow characteristics of a miniature axial fan

Dimensional restrictions in electronic equipment have resulted in miniaturization of many existing cooling technologies. In addition to this, cooling solutions are required to dissipate increased thermal loads to maintain component reliability. Axial fans are widely used in electronics cooling to meet such thermal demands. However, if the extent of non-uniform heat transfer rates, produced by highly three-dimensional air patterns is unknown in the design stages, premature component failure may result. The current study highlights these non-uniformities in heat transfer coefficient, using infrared thermography of a miniature axial fan impinging air on a flat plate. Fan rotational speed and distance from the flat plate are varied to encompass heat transfer phenomena resultant from complex exit air flow distribution. Local peaks in heat transfer coefficient have been shown to be directly related to the air flow and fan motor support interaction. Optimum locations for discrete heat source positioning have been identified which are a function of fan to plate spacing and independent of fan rotational speed when the Reynolds number effect is not apparent.

원심 다익홴의 유동에 대한 컷 오프 각도의 영향

This study investigated on details of flow characteristics of a multi-blade fan for domestic ventilation. Experiments and analysis were carried out to describe on flow pattern with variations of cut-off angle near the scroll housing throat, which were performed by PIV measurement for the flow field and by total pressure probes. The stagnation point at cut-off region of the fan moves to the exit of the scroll housing as the cut-off angle increases. The movement of stagnation point and the variation of throat area of the scroll housing influence to the distribution of velocity magnitude at the exit of the fan. Furthermore, a large distortion of the velocity distribution at the scroll exit causes to increase mixing loss along the flow path.

Quantitative assessment of landform equifinality and palaeoenvironmental reconstruction using geomorphic models

We present results from a study of post-glacial alluvial fan evolution in New Zealand, in which a series of > 83,000 numerical simulations of fan formation were conducted, within a Monte Carlo framework, in order to evaluate the potential for reconstructing past environmental conditions by matching simulated and observed fan morphologies. Our results indicate that simulations based on a wide range of model boundary conditions and internal process parameterisations are able to reproduce the observed fan characteristics. Such equifinal behaviour is a product of an imposed limit on fan progradation and associated autogenic feedbacks, which drive fan entrenchment even in the absence of external changes in water or sediment supply. We find little evidence that the majority of preserved fan terraces that formed post-entrenchment did so during periods of higher than average discharge or sediment supply to the fan apex, or that evidence for significant changes in sediment supply associated with major climate shifts are likely to be preserved in the current fan morphology. These results illustrate the difficulties that are inherent in the interpretation of alluvial landforms as records of past environmental conditions. They also highlight the need for more rigorous quantification of uncertainties in field and model-based interpretation of landscape responses to environmental change.

주거환기용 시로코홴의 공력 및 소음 특성 연구

This paper presents a procedure for the aerodynamic and aeroacoustic characteristics of a sirocco fan. For the aerodynamic and aeroacoustic analyses of the sirocco fan, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes equations are solved with a shear stress transport turbulence model for turbulence closure. The flow analyses were performed on a hexahedral grid using a finite-volume solver. The validation of the numerical results is performed by comparing with experimental data for the pressure, efficiency and power. The internal flow analyses of the sirocco fan are performed to understand the unstable flow phenomenon on the casing for the wall pressure and internal flow characteristics at each position. It was found that fluctuation of pressure and locally concentrated noise source are observed near the cut-off and expansion regions of the casing.

A technique for presentation and application of the propeller fan multidimensional characteristics in semi-full-scale simulation of a gas turbine engine and its automatic control system

A technique for linear interpolation of the multidimensional characteristics of a coaxial propeller fan with opposite rotation propellers is proposed; the technique makes it possible to simulate the turbofan engine operation in the entire range of flight conditions and reduce expenses for fullscale tests. The mathematical models obtained meet the requirements imposed in the semi-full-scale simulation.

Computational and experimental investigations of performance curve of an axial flow fan using downstream flow resistance method

Abstract A newly developed computational approach different from the conventional methods which are popularly adopted by the fan designers is employed to study the flow field and performance characteristics of an axial flow fan by using the commercial code (STAR-CD) of computational fluid dynamics. The new approach, which is termed the “downstream flow resistance” (DFR) method, engages the flow resistance of the fan test bench in the downstream area of the computational domain. Both the static and moving grids are employed in the computation. The results show at least three emphases. Firstly, the deviations of the calculated fan performance curves from the experimental results can attain levels less than 3% and 1.5% by using the DFR method with static-grid and moving-grid schemes, respectively. These results present dramatic improvement over the maximum deviation of about 26% obtained by using the conventional method with the static-grid scheme. Secondly, usage of the static or moving grids for the purpose of fan performance prediction is no longer an important issue when the DFR method is employed because both the static and moving grids show almost identical results. Thirdly, the stall occurs when the aerodynamic contour of the fan blade is inappropriately designed for the mid and high back-pressure operations. Under this situation, recirculation bubble would appear around the trailing edge of the suction surface of the fan blade, and therefore obstructs the development of the flow. At deep-stall , large recirculation flow structures may even appear around the pressure surface and block the passage between the neighboring fan blades to cause the reduction of flow rate.

Characteristics of a sublacustrine fan in a half-graben rift lake basin and its petroleum prospects: Case study on the second member of the Tenggeer Formation, Saihantala Sag, Erlian Basin

Abstract Analysis has been carried out on the petrology, context and structure of sublacustrine fan sand bodies in the second member of the Tenggeer Formation. The sublacustrine fans are well developed, and are characterized by the Bouma sequence resulting from typical turbidite deposition and the presence of AAA and ABABAB sequences of non-typical turbidite systems. The depositional textures feature grain distributions typical of turbidite deposits and contain abundant turbidite deposit structures. The sublacustrine fans mainly develop in the lower part of the fault slope break formed by syn-sedimentary faulting in the fan delta front of the gentle slope in the sag and in the troughs in front of offshore subsea fan deposits in the down-thrown areas at boundary of the basin, controlled by an abrupt slope change. The formation of the sublacustrine fan is closely related to the long period of syn-sedimentary faulting activities, and the scale is controlled by the fault activity, slope gradient of palaeogeomorphology and the sediment supply. The sublacustrine fan sand bodies are adjacent to source rocks, and easily form lithologic traps and are favorable for petroleum migration and accumulation, which is significant for the petroleum prospecting in this area.

Correlations of control parameters determining pressure distributions in a vertical exhaust shaft

The pressure distribution in a vertical exhaust shaft is important in determining the ventilation performances of local exhaust hoods in high-rise buildings. Uneven pressure distribution can cause insufficient exhaust airflows from hood fans, and can cause excessive exfiltration resulting in unwanted noise through any gap openings. There are various system parameters that affect the pressure distribution in a vertical shaft, such as building height, shaft size, roof fan characteristics, concurrent hood fan usage, and outdoor temperature. The objective of this study is to quantify and investigate the effects of these parameters numerically on the overall ventilation performance of a vertical shaft. In order to achieve this goal, specialized simulation software has been developed, which implements the principles of fluid dynamics in vertical air columns with horizontal branches. Simulation results have been obtained based on a model of a 25-story apartment building, according to the experimental design method. Analysis of the variance has been conducted to investigate any correlations between the parameters. The results show that the deviation of the pressure distribution based on a slight negative value (i.e. −30 Pa or −40 Pa) has a strong correlation with the maximum pressure in the shaft. This indicates the possibility of using the pressure deviation as a single objective parameter, which represents both the insufficiency and unevenness of the pressure distribution throughout the shaft. Roof fan rpm and inlet damper opening can be used as operational parameters, and the pressure and pressure gradient at the top-most level, and outside temperature can be used as sensing parameters for pressure control in a vertical shaft.

Improvement of Stalling Characteristics of an Axial-Flow Fan by Radial-Vaned Air-Separators

An improved construction of air-separator device, which has radial-vanes embedded within its inlet circumferential opening with their leading-edges facing the moving tips of the fan rotor-blades so as to scoop the tip flow, was investigated with respect to the stall-prevention effect on a low-speed, single-stage, lightly loaded, axial-flow fan. Stall-prevention effects by the separator layout, relative location of the separator to the rotor-blades, and widths of the openings of the air-separator inlet and exit were parametrically surveyed. As far as the particular fan is concerned, the device together with the best relative location has proved to be able to eliminate effectively the stall zone having existed in the original solid-wall characteristics, which has confirmed the promising potential of the device. Guidelines were obtained from the data for optimizing relative locations of the device to the rotor-blades, maximizing the stall-prevention effect of the device, and minimizing the axial size of the device for a required stall-prevention effect, at least for the particular fan and possibly for fans of similar light-load fans. The data suggest the changing internal flow conditions affected by the device conditions.

Effects of Compact Radial-Vaned Air Separators on Stalling Characteristics of an Axial-Flow Fan

The stall-prevention effect of air separators incorporating radial vanes in place of the existing axial vanes was investigated on a low-speed, single-stage, lightly loaded axial-flow fan for effective and compact air separators of a simplified structure. From the survey, paying attention to several geometrical dimensions of the device, the following conclusions are obtained: (1) Simplified radial vanes made of flat plates could show strong stall-prevention effect comparable to those of the curved-vane type one. The most favorable ones showed no stall up to the fan shut-off conditions. (2) Radial heights of the recirculation passage within the air separator showed significant influences on the stall improvement. It should be larger than some critical size experimentally given in the study. (3) The axial length of the device should be larger than some critical size given experimentally in the study. Too much reduced axial length could give rise to an abrupt loss in the effect. (4) The optimum axial locations of the rotor-tip blade leading edge within the device inlet opening were found to lie near the center of the width of the inlet opening from both aspects of stall improvement and fan efficiency.

Guard grill impact on aerodynamic integral and acoustic characteristics of an axial fan

This paper presents the impact of a guard grill design on the aerodynamic integral characteristic, the spectrum of sound pressure level and total sound power level. Four characteristic operating points of axial fans with a standard guard grill, with an optimized guard grill and without a guard grill were studied. Measurement results of the local outflow velocity vector of the axial fan without a guard grill at an optimal operating point were used to model the optimized guard grill contour. The guard grill of axial fan has a significant impact on the aerodynamic integral characteristic in the mostly used operating region. The influence of a guard grill is more characteristically reflected in the spectrum of the sound pressure levels via the vortex shedding frequency and consequently in the total sound power level of compared axial fans. Flow properties around grill wires were studied using an in-line cylinder cascade in the free velocity field at appropriate Reynolds numbers. Results are presented as power spectra of velocity fluctuations and spectra of sound pressure level and show good agreement with results of fan measurements

125 後流特性に基づくリングファンの空力騒音の予測(空力騒音(2))

The ring fan is a propeller fan by an axial-flow impeller that has a ring shape shroud on the blade tip side. In this study, the whole flow field of the ring fan is simulated by a CFD code; the aerodynamic noise generated by the fan is predicted based on the wake characteristics. Moreover, the accuracy of the CFD code has been verified by comparing with the aerodynamic characteristics of the propeller fan of a current model. The aerodynamic characteristic of the ring fan by the CFD can represent the tendency of the measurement value qualitatively, however, the flow rate in the CFD becomes 30% lower than the actual measurement value. The main flow domain of the ring fan is formed at the tip side of the blade since the blade tip vortex is not formed at the blade tip side. Therefore, the relative velocity of the ring fan becomes fast by the circumferential velocity. The sound pressure levels of the ring fan in the frequency band less than 200 Hz become larger than the propeller fan. According to the analysis on the wake characteristics, it clarified that (1) Karman vortex at the main flow domain is shedding in the frequency domain lower than 200 Hz, (2) the aerodynamic sound of the ring fan in the vortex shedding frequency becomes large because of an increase in the relative velocity and the velocity fluctuation.

J0504-5-1 プロペラファンの離散周波数騒音と環状後流の破れ([J0504-5])流体関連の騒音と振動(5))

In order to clarify the relation between the discrete frequency noise of the propeller fan and the circular flow formed in the wake, the characteristics of the propeller fans were analyzed by the measurement of the flow and the CFD. The absolute velocity in the main flow domain of the meridional plane in the wake of the propeller fan became 30 m/s while the velocity in the inclined plane was decreased to 25 m/s. The velocity fluctuations on the vertical plane in the wake were weakened at the diagonal line by the velocity deformation formed to the circumferential direction around the impeller. Then the circular wake formed in the propeller fan was broken by the velocity deformation. It is considered that the discrete frequency noise of the propeller fan in the second harmonics became large since the fourteen dynamic rotors and the pseudo four stators made by the broken circular wake resonated.