Alternative geometry for cylindrical natural draft cooling tower with higher cooling efficiency under crosswind condition

Lately, the drip irrigation systems find more and more application, which led to the production of a new type of drip laterals – with flat to elliptic cross section and comparatively small thickness of the wall – from 0.2 to 0.9 mm, compared to the conventional ones with circular cross section and wall thickness over 1 mm. The main advantage of the first type is that they are comparatively cheap and are offered in the form of small rolls, the length of the hose being from 500 to 3500 m which makes their transportation to warehouses, assembly and disassembly very convenient. With the smaller thickness of the walls, the laterals have almost clenched form and are intended to be used for one irrigation season, while those with higher thickness, with elliptic form, may be used for several seasons. The inside welded emitters are flat and have a very small water-stopping head area compared to the annular water-stopping cross section of the cylindrical drippers in the conventional circular type of laterals. This is connected with the smaller head losses in the movement of water in them, which is an important advantage. The paper presents and analyses the results of the hydraulic test of the two types of drip hoses – with circular and elliptic cross section, in order to find the head losses for different lengths - 40, 60 and 80 m and heads in the beginning of 6, 8, 10, 12, 14 and 16 m, as well as the coefficients of uniformity for both types. The following hoses of both types were tested: JUNIOR, with circular cross section and internal diameter of 13.8 mm, nominal diameter 16 mm, thickness of wall 1.1mm, cylindrical type of drippers with a flow rate of 2.1 l/h and interval between nozzles 0.30 m (Irritec, Italy); DP Line (D5), with elliptic cross section, with the same sizes and intervals but with a wall thickness 0.6 mm and flat type of drippers (Irritec, Italy). The results indicate that irrespectively of the elliptic form of the cross section which is with a very small hydraulic radius, the head losses are almost equal to those with the circular cross section with cylindrical drippers, which is due to the minor head losses because of the flat nozzles in them. The values of the absolute coefficient of uniformity and the calculated one according to the method of Christiansen for all options are presented. The test is performed for zero slope, while modelling is performed for slopes 1% and 2%. The analysis of the data indicates that for zero slope of the terrain the increase of head leads to increase of the coefficients of uniformity for the three tested lengths of laterals; for 1% are observed very small tendencies for reduction of those coefficients, while for 2% the coefficients have higher values compared to the other slopes, again with slightly expressed tendency for change. The higher values in the 2% slope are due to the additional head caused by the geodetic level difference of the terrain.

Tall RC chimneys form an important component of major industries and power plants. Since pollution control standards are getting stringent every passing day, the mandatory height requirements of chimneys are increasing. Such increased heights pose structural challenges for designing against dynamic loads such as wind gust and seismic forces. Arriving at an economic and efficient structural profile is one of the important aspects of the analysis and design of tall chimneys. Most of the chimneys constructed in industry are of circular cross section. With increase in heights, chimneys become more vulnerable to dynamic loads. In order to combat these loads and design an economical and efficient structural solution needs to be evolved. Elliptical cross-section provides one such possible alternate solution. Therefore evaluating the behavior of chimneys of varying heights with elliptical cross-section and comparing the same with that of circular cross-section assume significance. Chimneys with circular and elliptical cross sections of five different heights viz. 275m, 300m, 325m, 350m and 400m with two different profiles in elevation - one tapering from bottom to top and the other tapering from bottom to 2/3 H and straight afterwards - have been analyzed for seismic and vortex shedding effects caused by wind forces; further, analyses have been carried out for three R/t ratios - 15, 20 and 25. In total 120 models have been analyzed 60 for seismic forces and 60 for vortex shedding effects. Analytical results in terms of stresses induced on the structure, earthquake base shear, joint acceleration, joint displacements and vortex shedding base shear are evaluated. Maximum values of seismic forces induced base shear is only 1% of the self weight of the structure for all heights. It is interesting to note that chimneys with elliptical cross section experience less accelerations compared to that with circular cross section. Circular chimneys undergo higher displacement than the elliptical chimneys which is attributed to the higher accelerations they are subjected to by seismic forces. As the height of the chimneys is increased vortex shedding phenomenon induces increased forces compared to that due to earthquakes.

The cross sections of solar coronal loops are suggested to be rarely circular. We examine linear kink oscillations in straight, density-enhanced, magnetic cylinders with elliptical cross sections by solving the three-dimensional magnetohydrodynamic equations from an initial-value-problem perspective. Motivated by relevant eigenmode analyses, we distinguish between two independent polarizations, one along the major axis (the M-modes) and the other along the minor one (the m-modes). We find that, as happens for coronal loops with circular cross sections, the apparent damping of the transverse displacement of the loop axis is accompanied by the accumulation of transverse Alfvénic motions and the consequent development of small scales therein, suggesting the robustness of the concepts of resonant absorption and phase mixing. In addition, two stages can in general be told apart in the temporal evolution of the loop displacement: a Gaussian time dependence precedes an exponential one. For the two examined density ratios between loops and their surroundings, the periods of the M-modes (m-modes) tend to increase (decrease) with the major-to-minor-half-axis ratio, and the damping times in the exponential stage for the M-modes tend to exceed their m-mode counterparts. This is true for the two transverse profiles we examine. However, the relative magnitudes of the damping times in the exponential stage for different polarizations depend on the specification of the transverse profile or the density contrast. The applications of our numerical findings are discussed in the context of coronal seismology.

To calculate the equilibrium and stability of finite aspect ratio tokamaks, even for circular and elliptical plasma cross-sections, intricate numerical methods must usually be employed, which require a fast and large computer. So far, these calculations have been carried out analytically only for infinite aspect ratio. In fact certain analytical equilibrium solutions at finite aspect ratio are known, but these do not include such important cases as elliptical cross-sections. In this paper, finite aspect ratio equilibrium solutions are derived for circular, prolate and oblate elliptical cross-sections and for a flat current profile. In addition, the problem of axisymmetric stability is studied for prolate elliptical cross-sections, the approach being almost entirely analytical.

Experimental research of heat transfer performance on natural draft counter flow wet cooling tower under cross-wind conditions

A zero-order rainbow angle may be defined as the relative minimum angle of deviation of geometrical light rays transmitted without internal reflections through a transparent particle. If the incident rays are parallel and the particle is a sphere, such a minimum does not exist. But if the incident rays are not parallel or if the particle has an elliptical rather than circular cross section, an angle of minimum deviation, hence a zero-order rainbow, can occur. For a spherical water droplet, the zero-order rainbow will occur when a point source is placed less than a droplet radius away from its surface. If a column of water with an elliptical cross section is illuminated by a plane wave, a zero-order rainbow will occur if the length of the major axis of the cross section is more than twice the length of the minor axis.

When a homogeneous prismatic shaft of an arbitrary cross section is subjected to a twisting moment at its end, an axial displacement, referred to as warping displacement, will be induced in it. The only exception known to date is that the shaft is an isotropic one with circular cross sections. In this work we find that elliptical cross sections may also exhibit zero warping. But now the shafts need to be rectilinearly orthotropic in which the ratio of two associated shear rigidities equals to the square of the aspect ratio of the ellipse. Physically, this means that the elastic orthotropy of the shaft can serve to compensate the geometric deviation from a circular cross-section to an elliptical one. The idea can be further generalized to show that the zero warping property also holds for a number of composite cylinders consisting of an elliptical core or cavity coated with many similarly elliptical layers of different materials.

The cyclone dust collector is applied to many kinds of industries and also there are many types of cyclones which are selected for the application and the placement of the establishment. However the cross section of these cyclones is the circular cylindrical section for the optimum condition of the turbulent rotational flow. However from the energy consumption and the collection efficiency points of view, the circular cross section of the cyclone is not always recommended but the elliptic cross section is recommended. Therefore in this paper, the detailed experimental results of the collection efficiency for the circular cross section and for the elliptic cross sections of the eccentricity ɛ=0.5,0.6and 0.7 are reported. The test dust for these experiments is fly-ash of the mean diameter Xpm=18.0 µm and 18.3 µm. The feed particle concentration is Co=1.0–50 g/m3.

By various manufacturing techniques straight pipes with initially circular cross sections can be processed into smooth bends but usually with noncircular cross sections and with variations in thickness. These changes from the ideal are normally referred to as “ovality” and “thinning”; their influence on the subsequent behaviour of curved pipes is not yet fully understood. Here theoretical work on constant thickness circular and elliptical cross sections has been extended to cope with typical variations in thickness. The theory which is based on a classical energy approach is outlined for in-plane bending loading and is easily extended to cover out-of-plane bending. Linear elastic small displacement limitations apply. It is concluded that normally accepted values of thinning have virtually no effect on the flexibility due to bending of smooth pipe bends with or without initial ovality. Similarly, the peak meridional bending stresses were found to be insensitive to thickness variations.

The muffler shell of an automotive exhaust system can cause numerous NVH (Noise, Vibration and Harshness) issues such as radiated noise, buzzing, rattling and implosion. In general, the problems are detected and solved after the mufflers are built and assembled in a vehicle, which are expensive and time consuming to correct at that stage. It would be beneficial to develop an analytical technique to predict the vibration behavior of a muffler shell during the early stages of exhaust system design. In this paper, shell vibration theories are investigated by comparing the solutions with the results from modal tests and finite element analysis. Utilizing these theories, an analytical model to predict the natural frequencies and mode shapes of muffler shells with circular cross section, elliptical cross section and cross section with two constant radii has been developed. A novel approach for accurately predicting the natural frequencies of muffler sections with two constant radii is also presented in this paper. Case studies are presented to demonstrate that the theoretical analysis can be applied effectively to predict and solve NVH issues of muffler shells

Wind tunnel tests at Mach numbers of 0.8 and 1.5 for two groups of bodies are described. The bodies, having equal cross section area and length, were tested up to high angles of attack. The cross sections are a square with rounded corners, and a circle. In addition, a code has been written and developed based on NKP method, including an analytical and a numerical method. Results obtained by this code and wind tunnel have been compared and discussed. The value of lift coefficient for body with square cross section is larger than the body with circle cross section in all subsonic, transonic, and supersonic Mach numbers. For pitching moment coefficient, the results are entirely opposite. Therefore, the fact that bodies with noncircular crosssectional areas have better aerodynamic performance is confirmed again. The good agreement between these two different results validates the correct use of NKP method for the estimation of wing-body flow interaction effects.

In previous studies only circular cross section reactor plasmas were considered. The purpose of this research is to examine the effects of elliptical plasma cross sections. Several technological benefits have been determined. Maximum magnetic field strength requirements are 30 to 65 percent less than for 5000 MW (th) reactors and may be as much as 40 percent less than for circular cross section reactors of comparable size. Very large n tau values are found (10$sup 15$ to 10$sup 17$ sec/cm$sup 3$), which produce large burn-up fractions (15 to 60 percent). There is relatively little problem with impurity build-up. Long confinement times (60 to 500 seconds) are found. Finally, the elliptical cross section reactors exhibit a major toroidal radius reduction of as large as 30 percent over circular reactors operating at comparable power levels. (auth)

The capillarity-induced negative pressure of water flow has been investigated innanochannels of a rectangular cross section by using computational fluid dynamics (CFD)simulation. As a consequent effect of negative pressure, the cavitation probability has beenanalyzed numerically. The numerical relation between the critical radius of cavitation (Rc) and geometrical characteristics of channels shows that cavitationdoes not occur in channels of uniform cross section (UCS), since2Rc is larger than the smallest dimension of the channel. However, it may occur in channels ofnon-uniform cross section (NUCS), except for planar or high aspect ratio channels. Theinequality in height and width is favorable for the absence of cavitation. The findingscan also be applied to channels of elliptical or circular cross section. The resultsshow the influence of geometrical characteristics of channels on the cavitationprobability, which is important to engineer the channel geometrical structure inorder to avoid undesirable filling problem ‘cavitation’ during the flow process.

ABSTRACTProcesses observed in experiments with the initiation and propagation of divergent detonation in a narrow gap between plates was simulated. The detonation wave is formed in a round tube adjoined to one of the plates at a right angle. Complicated cellular structures of the 2D detonation have been obtained. The process of formation of 3D cellular detonation in channels of square, rectangular, circular, and elliptical cross sections was studied. The process of spontaneous formation of spin detonation in channels of circular cross section was considered. Calculations of the transition of spin detonation to the channel of larger or smaller diameter were conducted and conditions of self-sustained spin detonation were formulated. Detonation is initiated in a quiescent combustible mixture by an instantaneous homogeneous electric discharge in a finite-width zone near the flat closed end of the channel. All computations of 3D detonation were performed in a correct formulation for the entire channel of large length (1 m) rather than only in a certain zone moving together with the wave.

Asymmetric magnetic field inside a cylindrical flux rope