Tower Diameter Research Articles

Study of aerodynamical interference for a wind turbine

A two-dimensional interference model of upwind wind turbine, based on NREL Phase VI, was simulated by an available Navier–Stokes solver under parallel process. The simulation domain was divided into a stationary tower domain and a sliding blade domain with varying geometric factors, including blade chord to tower diameter ratio and tower-blade gap to tower diameter ratio, to figure out the unsteady problem. The turbulence model was treated with SST k – ω turbulence model and the boundary layers around the solid walls were refined by the y + value. The simulated results of velocity field were compared with the potential cylinder flow, and some phenomena were exhibited, including the movement of stagnation point of tower, the skewed wake of tower and the excess of velocity in the field. The lift force coefficient of blade was different from the ideal angle of attack for the blade passing in front of the potential cylinder flow.

A Simplified Pump Tower Approach for Realistic CFD Simulation of Sloshing in LNG Tanks

The complexity of the sloshing analysis for liquefied natural gas carriers can be reduced by neglecting the pump tower. The validity of this assumption is examined by studying the effect of the pump tower, located near the aft bulkhead of a typical LNG tank on the sloshing flow evolution. Results are compared for surge-induced sloshing in a rectangular tank with pump tower to that without such an obstruction. A commercial flow solver is used to solve the unsteady Reynolds Averaged Navier Stokes equations for an inhomogeneous multiphase flow. Initial validation of the sloshing flow uses the experimental data of Hinatsu. It was found that a simplified pump tower consisting of a single vertical tube was suitable to capture the effect of the pump tower without the necessity of discretising the fine geometric detail of the pump tower structure. A suitable size for the simplified tower diameter was found using the total fluid force on a real pump tower in a steady flow for a similar range of Reynolds Number. This reduces the required mesh size by an order of magnitude. Although it is found that the effect of the pump tower on the overall force levels is small reductions of local impact pressures of up to 50% are observed and the sloshing flow develops a phase lag compared to the unobstructed tank.

Energy and exergy analysis for cocurrent gas spray cooling systems based on the results of mathematical modeling and simulation

Abstract The present study provides a descriptive mathematical model for energy and exergy analysis for a cocurrent gas spray cooling system. Conservation laws of mass, energy and momentum are used to predict the variation of temperature and enthalpy of gas and liquid streams along the tower length. The same procedure is also used to calculate the energy and exergy efficiencies. The validity of the model for predicting variations in gas and liquid characteristics along the tower length was examined against some operating data measured in a commercial cement plant. The results show that in spite of high energy efficiency, the gas spray cooling systems have relatively low exergy efficiency. This was due to thermodynamic irreversibilities and entropy production during heat and mass transfer processes. Also the effect of some operating parameters, including tower diameter, tower length, liquid drop size distribution and water flow rate was investigated, on the amount of exergy destruction. This study also concluded that the exergy of water is not completely absorbed by gas and a remarkable portion of exergy is destroyed. Results of such investigations may provide us with the true energy potential carried by fluids.

Toxic Acid Gas Absorber Design Considerations for Air Pollution Control in Process Industries

This paper analyses the design parameters for an absorber used for removal of toxic acid gas (in particular sulfur dioxide) from a process gas stream for environmental health protection purposes. Starting from the equilibrium data, Henry’s law constant was determined from the slope of the y-x diagram. Based on mass balances across the absorber, the minimum liquid-to-gas ratio was determined from which the minimum liquid flow rate and the actual operating conditions were established. Using a generalized flooding and pressure drop correlation, and the mass flow rates of liquid and gas, the mass flow rate of the gas per unit cross sectional area of the tower was determined. The operating point (ranging from 50 to 75% of flooding velocity) was used to determine the required cross-sectional area and diameter of the absorption tower. The operating liquid flow rate was observed to depend strongly on the inlet gas flow rate, solute concentration in the inlet liquid, and solute removal efficiency. The solute removal efficiency was varied from 80 to 99% at a fixed inlet toxic gas concentration of 3%. The tower diameter was observed to depend strongly on: the inlet total gas flow rate, percent of the flooding velocity selected, packing factor, size of packing, and on the type of material used (at fixed size of packing). The tower height, which was observed to depend strongly on toxic gas concentration in the inlet gas, and on the required toxic pollutant removal efficiency, was, however, independent of gas and liquid flow rates. Key words: Gas absorption; packed tower; solubility data; design criteria; removal efficiency; minimum liquid flow rate; operating line equation, packed tower size.

The effect of a meteorological tower on its top-mounted anemometer

The wind-speed at a site can be measured by installing anemometers on top of meteorological ( met) towers. In addition to other sources of error, accelerated airflow, or speed-up, around the top of met towers can cause incorrect anemometer measurements. We consider a particular example where an anemometer was located only 2 tower diameters above the met tower. Using a standard computational fluid-dynamics package, we found the maximum error for this configuration to be 2% of the wind-speed. We conclude that a top-mounted anemometer should be located at the windward side of its met tower, raised 5 diameters above the top. This will reduce speed-up error to less than 1%.

A new liquid distribution factor and local mass transfer coefficient in a random packed bed

Liquid distribution and local mass transfer in a packed bed of 25.4 mm metallic Pall rings were investigated. The liquid collecting method and electrochemical technique were used to measure local liquid flow rates and local mass transfer coefficients, respectively. Measurements were carried out at various radial and axial positions in the bed at varied liquid flow rates with three different liquid distributor designs: single point (SLD), cross (CLD), and ladder type (LLD) distributors. A new liquid-distribution factor for the liquid flow pattern in a packed bed was proposed and used for evaluation of liquid distribution in the bed. Liquid distribution and the local mass transfer coefficient for SLD were more sensitive to the bed height than those for CLD and LLD, as expected. Liquid redistribution was observed at x / D (the ratio of the packing height to the tower diameter) level of 4.9. The effect of the inlet liquid flow rate on local mass transfer was found to be significant for all liquid distributors. Local mass transfer coefficient increased with the inlet liquid flow rate. A correlation of the overall mass transfer with the particle Reynolds number was also developed taking into account the volume segments of different radial and axial regions in the bed. The mass transfer coefficient, in terms of the Sherwood number, was found to be proportional to the Reynolds number to a power of 0.26 for CLD and 0.44 for SLD.

着底式大型洋上風車に供するトラスタワーの構造特性と風荷重と後流域の乱れに関する風洞実験

The offshore wind turbines (OWTs) are getting larger in scale in order to efficiently generate the electricity. Therefore the natural period of OWT becomes longer due to heavier weight of a nacelle and higher supporting towers for OWTs, resulting in possible fatigue damage. As we estimate that the diameter of the conventional tower to be more than seven meters, the tower having large rigidity such as a truss may be alternatively required. Therefore we made a comparison of required weights and rigidities through structural analyses of the cylindrical and truss towers for 5000kW OWTs. We also conducted a 1/100 scale model test on the both towers to obtain the wind loads acting on a rotor and the tower and to examine the differences in their downstream flow. The paper describes the ascendancy of the truss over the cylindrical tower.

Experimental investigations of water intake/outlet towers (shafts)

1. In a pump regime the discharge openingsoperate full section at a height h≤(0.2–0.3)dc; separation of the flow from the sill of the openings occurs at larger values of h. For tower diameter Dtw=2dc the height of the throughgoing flow increases slightly at the exit with increase of the the height of the discharge openings to h<0.6dc and for Dtw≥3dc it decreases. When h≥0.6dc the height of the throughgoing flow is constant and at the exits is about (0.55–0.6)h for Dtw=4dc, (0.27–0.35)h for Dtw=3dc, and (0.18–0.22)h for Dtw=4dc. During operation of the discharge openings full section (\(\bar h\) ≤ 0.3), an increase of the tower diameter is accompanied by an increase of nonuniformity of the distribution of velocities over the height of the openings; the opposite picture is observed with the occurrence of separation of the flow from the sill, i.e., for\(\bar h\) > 0.3. 2. In the pump operating regime for a height of the openings h≥(0.5–0.6)dc, the intakes/outlets with an outside diameter of the discharge openings Dtw=2dc have smaller values of the resistance coefficients (by 0.02–0.06) than for Dtw≥3dc, and for h<(0.5–0.6)dc intakes/outlets with a tower diameter Dtw≥4dc are preferable with respect to head losses. 3. In a turbine regime without trash racks, smaller head losses are observed in intakes/outlets with Dtw≥3dc; a decrease of the tower diameter to Dtw=2dc leads to a considerable increase of the head loss coefficient: by 0.05–0.18 in the range of heights of the openings h=(0.6–0.3)dc; the presence of trash racks of the same height leads to an increase of the resistance coefficient of the intake/outlet with Dtw=2dc. 4. With consideration that with a change in the outside diameter of the discharge opening, the increase of the head loss coefficient with increase of their height in the pump regime changes in magnitude and signt and also that investments in construction depend on the outside diameter of the discharge openings (tower), the final choice of the size of the intake/outlet can be made only on the basis of a technicoeconomic comparison of variants with the use of the results of the studies presented in this article.

Ammonia absorption into water in a packed tower II: Measurement of mass transfer coefficients

A simple method is outlined for the experimental determination of mass transfer coefficients in gas absorption. The modification of existing theory shows that the mass transfer coefficient should be constant within a tower but hydrodynamic conditions limit this to a region of the tower below five to ten tower diameters where the water radial distribution is constant. The theory is extended to meet all possible operational variables but in most cases the result demands computer techniques to achieve solutions. Details are given of experimental procedures which are necessary to enable meaningful data to be obtained. One important point in experiment design is to keep the gas rate constant and to vary the liquid rate. In this way, plots of ln y versus the tower height Z give a straight line whose slope is approximately proportional to K G a. Using the technique, laboratory data have been obtained which parallel the operation of a number of industrial installations.

Numerical study of the performance of tornado-type wind energy systems

The tornado-type wind energy system was proposed to utilize the pressure drop created by an intens vortex in a tower. The tower serves as a low pressure exhaust for the turbine. The author carried out a numerical solution of the tower flow, using the two-equation (kappa-epsilon) turbulence model, for the small size system tested by Yen, with a 0.127-m- (5-in.-) diam tower standing in a uniform wind flow. A comparison of the results with the measured pressure values verified the model. In the present work the same numerical model is used for a system with a tower that is completely embedded in an atmospheric boundary layer. The results show, for a tower in a boundary layer of the one-seventh power-law profile, about a 28% reduction of the values of power coefficient from those for a tower in a uniform stream. Calculations for the performance of a system with different tower heights and the same tower and turbine diameters show a sharp decrease of power for H/D less than or equal to 0.5. Analysis of the tangential velocity shows that the vortex should be maintained up to heights /ZETA//D less than or equal to 0.9 to avoid the decrease in powermore » extraction. Numerical predictions are made for systems with tower diameters between 0.5 and 8 m (1.64 and 26.24 ft) using the same system geometry and approach flow conditions. The results show that the scale effect is negligible for systems of 4-m tower diameter or larger.« less

Distillation Performance of Beehive Packings

Using beehive packings which were regular and had nowall effect, a relationship between HOG and the reflux ratio γ (1 to ∞) was observed. Experimental conditions were as follows; tower diameter : 78 mm, packed height : 500 mm, sample : methanol-water system, determination of vapor concentration : differential condensation temperature method. HOG varies largely depending on r when r is less than 10 and mass velocity of vapor G is less than 60% of flooding velocity. This relation can be expressed by the following equations : packing A (ε = 0.92) HOG = 0.99 γ-0.82packing B (ε = 0.90) HOG =0.01 G 0.45 γ-0.47When γ is greater than 10, HOG approaches the values at total reflux.

THE DRY SPINNING OF POLYACRYLONITRILE SOLUTION

The dry spinning condition to obtain continuous filaments of polyacrylonitrile from dimethylformaide solution was investigated as to residual solvent, yellowness (YI) and longitudinal dispersion of denier of undrawn filaments.In this study, length and diameter of the spinning tower were fixed. Results obtained are;1) The higher the temperature of hot air and spinning tower, the smaller the residual solvent content; and the increase of hot air intake results in the decrease of the residual solvent content of the undrawn filaments.2) The spinning solution with larger yellowness (YI) results in the undrawn filaments with larger Yl obtained under the same spinning condition.3) The larger the volume of hot air, the higher the concentration of the spinning solution and the smaller the spinning draft, the smaller is the longitudinal dispersion of denier.Optimum range for temperature and concentration of the spinning solution, and temperature of hot air also results in the smaller dispersion of denier.4) The dispersion of denier is not so much influenced by the viscosity of the spinning solution.5) The larger initial drying rate of dimethylformamide from the extruded filaments, which is thought to be proportional to the constant drying rate, makes the longitudinal dispersion of denier smaller.

Aeration in tower‐type fermentors: Effect of tower diameter and number of aeration disks

AbstractThe rate of oxygen absorption by aqueous sodium sulphite solutions in tower‐type fermentors up to 6 in. in diameter was related both to tower diameter and to the number of sintered Pyrex disks used for dispersing air entering the towers. Maximal rates of absorption were obtained in towers 2.5 in. in diameter. Under comparable conditions, rates of oxygen transfer in towers containing one aeration disk were approximately 30% higher than those in similar towers containing two or more disks. In towers greater than 6 in. in diameter, the absorption rate was independent of vessel diameter and number of aeration disks when more than one disk was used. Bubble coalescence was the main cause of the difference in the rate of oxygen absorption.

Holdup and Mixing Coefficients of Liquid Flowing through Irrigated Packed Beds

In our previous paper, the holdup and the mixing characteristics of liquid flowing through the irrigated packed towers (I.D., 4-7cm) had been determined. An attempt was made, in this paper, to extend the range of experimental variables, in order to larify the influences of packing size and type as well as the ratio of packing diameter to tower, either on the holdup or on the mixing characteristics of the liquid in packed beds.For this purpose, the transient response curves were measured, by using larger packed beds, whose properties are listed in Table 1. From these response curves, the holdup and the mixing coefficients of liquid were determined by the graphical integration of the curves, based on Eq.(5) and by the method described in our previous paper, respectively.The experimental results of this study and of the other sutdies previously reported and summarized in Figs. 2, 3 and 4, show that the packing type and the ratio of the packing diameter to the tower diameter have little influence either on the holdup or on the mixing coefficients of the liquid in packed beds. Therefore, the generalized correlations have been obtained as follows:Eqs.(8) and (9) for the operating holdup of the liquid in irrigated packed beds.Eqs.(11) for the mixing coefficients of the liquid in irrigated packed beds.Eq.(10) for the mixing coefficients of the liquid in liquid-packed beds.

Effects of tower and guys on performance of side-mounted vertical antennas

The omni-directional pattern of a vertical antenna when side-mounted on a mast or tower, is distorted as a function of tower diameter and separation in wavelength. The pattern is further effected by obstruction of metallic tower guys. Laboratory and field measurements of these effects are analyzed. Possibility of taking advantage of these effects for special coverage is suggested. Tower effect on antenna impedance is briefly discussed.

大型油拡散ボンプの理論

The dependence of pumping speed on the nozzle was considered theoretically to obtain as completely as possible a description of the high speed oil diffusion pumps, By moans of this theory it is shown that for greated speed. There is an optimum combination for the nozzle angle and the diameter of the central tower.

Retification in a Wetted-wall Tower

A series of rectificat on tests on the methanol-water, ethanol-water, benzene-toluene, and carbontetrachloride-toluene mixtures were performed in a wetted-wall tower.The wetted-wall tower used was a glass tube, 22mm in inside diameter and 1010mm in length. Vapor from the electrically heated kettle rose up through the tower, and mass transfer took place between vapor and reflux, which flowed in layer form down the inner wall of the tower. Part of the vapor from the tower was condensed in the partial condenser directly coupled to the tower, and admitted to the tower as reflux at its boiling point. The remainder of the vapor was condensed in the total condenser and fed back to the kettle. The equipment was operated as a closed system. The tower and the lower part of the partial condenser were enclosed in heater jackets to minimize heat losses.Vapor flow was varied considerably by adjustment of the power input to the kettle, and reflux rates were controlled by cooling water supply to the partial condenser. Rates of vapor flow were determined by direct measurement of reflux liquid from the tower and distillate for a 30-second period. The compositions of liquid and vapor were varied over wide range. Analyses were made on the distillate and the reflux at the top and bottom. Vapor compositions were obtained by calculation.The experimental results in turbulent flow showed that the overall coefficient of mass transfer Ky [kg-mol/m2. hr. Δy], based on the vapor compesition differences as driving forces, was affected mainly by the velocity of vapor, and was independent of the rate and compesition of reflux or the slope of equilibrium curve. For a given system, Ky was proportional to the 0.8 power of the mass velocity G or Reynolds number Re of vapor; and at the same value of G, Ky was proportional approximately to the 3/4 power of the molal vapor diffusivity Dm of the mixture.The data could be correlated by the following equation:where d=inside diameter of tower;X=effective total vapor film thickness;ky=vapor film coefficient of mass transfer;Dm=in the brackets in kg-mol/m. hr.For vapor mixtures, whose viscosity was in the vicinity of 0.01 centipoiscs, the following approximate equation could also be used:where, ky in kg-mol/m2. hr. Δy, G in kg/m2. hr, Dm in kg-mol/m. hr, and d in m.The experimental data were w thin ±15% of these equations.