bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations into Cyclone Dust Collectors
Authors: ter Linden A. J. 
Published: October 2007

The paper describes experimental investigations made in the mechanical engineering laboratory at Delft, in the field of cyclone separators. These investigations aimed first at determining the most efficient shape of a cyclone, by measuring the effect of a variation of each of its principal dimensions on the efficiency; as a result, a very efficient cyclone shape was developed. The influence of the position of a cyclone on the efficiency was examined, and a new type of cyclone with curved axis, horizontal gas exhaust, and vertical downward dust outlet was constructed. The flow of gas and dust inside a cyclone was examined. The static pressure and the three components of the gas velocity at different points in a cyclone were measured with a globe-Pitot tube. In a cyclone exhausting to atmosphere, a core of low pressure extends over the entire height of the cyclone. Inside this core the flow is very turbulent and unsteady, so that the gas velocities cannot be measured exactly; outside, the pressure is high throughout the remainder of the cyclone. With the exception of the turbulent area in the centre, the total velocity of the gas deviates only slightly from the tangential component V t, which increases as the distance from the centre of the cyclone diminishes. The vertical component V h is directed downwards along the cyclone walls and carries the dust particles to the bunker, and the radial velocity V r is directed towards the centre in the greater part of the cyclone; but in the very turbulent centre, V r is directed outwards and V h upwards. From these measurements a simple cyclone theory was developed, enabling the approximate calculation of the size of the largest dust particles that may escape a cyclone. The effect of a variation in the quantity of gas on the efficiency was determined; this effect was small for a well-constructed cyclone. Efficiencies are given for different sizes of similar shaped cyclones and for various sizes of dust particles. These data enable the selection of a cyclone collector suitable for a particular kind of dust, and the choice of cyclone dimensions for a given efficiency. A method of measuring the dust content of a gas-flow, by means of a small cyclone, is described.
The Seizure of Metals
Authors: Bowden F. P. , Tabor D. 
Published: October 2007

When metal surfaces are placed together, the area over which they touch is usually very small. As a result, the localized pressures at the points of real contact are sufficiently high to produce plastic flow of the metal. Even under static conditions, these high pressures may produce “cold-welding” between the surfaces, and the metallic junctions so formed may be very strong. These junctions are sheared during sliding, and if they are stronger than the parent metals, heavy damage may result which is not limited to the interface at which intimate contact occurs. The growth and extension of this localized damage constitutes seizure. It follows that those factors which facilitate localized welding will, in general, increase the chances of large-scale seizure. Similarly, surface films which are capable of reducing localized adhesion will reduce the chances of seizure.
Hydraulic Seals
Authors: Beacham T. E. , Towler F. H. 
Published: October 2007

Leakage is the most common source of complaint with regard to hydraulic machinery. During recent years considerable advances have been made in the prevention of leakage of liquid past moving surfaces. New materials and constructions have come into common use, and there has been a small but valuable amount of research into the action, wear and friction of packings and seals. The object of these papers is to initiate a comprehensive discussion of existing knowledge on the subject, which will perhaps indicate the fields to which future research and development might best be directed. The authors' experience has been mainly in connexion with hydraulic machinery in which oil is the working medium; in this field particularly, the improvement of sealing methods has been very marked. It is hoped that contributors to the discussion will also deal with water, acids, and other liquids, and with the special problems encountered owing to high temperature, corrosion, dirty liquids, etc. As the subject covers a wide field, it has been limited by excluding hydraulic joints. For the purpose of this paper, a hydraulic seal will be defined as one whose function it is to prevent the leakage of liquid between surfaces having relative movement.
Discharge of Exhaust Gases in Two-Stroke Engines
Authors: Weaving J. H. 
Published: October 2007

The paper points out that the two-stroke engine still has a field of great importance, i.e. the compression-ignition engine, and that, although the two-stroke cycle has been known for so long, the theory of the discharge of exhaust gases from the cylinder is still in doubt, and some of the generally accepted assumptions have been challenged in recent years, in particular by Kadenacy. A description is given of apparatus built at the Engineering Laboratories, University of Cambridge, to simulate the discharge portion of the cycle only. This apparatus utilizes the gases nitrogen and hydrogen under compression, these being respectively denser and less dense than exhaust gases. Experiments were made to ascertain whether the older theories were valid, and to investigate the claims of Kadenacy of supersonic discharge and resultant vacuum pressures in the cylinder. These tests demonstrated that the older theories, based on the assumption of steady flow and Bernoulli's theory, were substantiated, provided that modifications were made to the index of expansion and the coefficient of discharge. Finally, a simplified system is derived for the calculation of the size of exhaust ports or valves, and this system is applied to a practical case.
The Engineering Implications and Economics of Surface Preparation of Mild Steel Prior to Fabrication
Authors: Johnson W. A. 
Published: October 2007

Those steel structures which are subject to repainting during service are considered, particularly those subject to exposed atmospheric conditions. Since any major improvement in paint life is dependent on surface preparation, alternative methods are examined. Mechanical shot blasting is the cheapest method for structural steel, but it is only possible prior to fabrication. The choice of prime coats, which must satisfy several requirements, lies between paint, oil, and metallic coatings. It is believed that suitable paint could be developed. No suitable oil is yet available, and of the metallic coatings sprayed aluminium is the most suitable. Fabrication difficulties, and in particular welding, require further investigation. The cost of painting a structure during a life of fifty years shows that surface preparation prior to fabrication is economical.
An Investigation of the Performance and Design of the Air Ejector Employing Low-Pressure Air as the Driving Fluid
Authors: Kastner L. J. , Spooner J. R. 
Published: October 2007

The air ejector, in its various forms, is a device which has many applications in engineering practice, and several attempts have been made to analyse its mode of action, some of these having been supported by experimental work. Most of the experimental results available are related to ejectors in which relatively high-pressure steam is utilized as the driving fluid, but even in these cases the information provided is restricted to a narrow field. The investigation described relates to an air ejector employing as the driving fluid air at a relatively low pressure, not exceeding 40 lb. per sq. in. (abs.), and covering a wide range of operating conditions by means of interchangeable nozzles. Two distinct experimental arrangements were built—one for the set of conditions in which the ejector draws in a relatively small quantity of suction fluid and pumps it through a relatively high pressure-ratio, and the other covering conditions in which the quantity of suction fluid is much larger, but the pressure ratio is quite small. For a given initial pressure and quantity of driving fluid, the rate of mass flow of suction fluid depends chiefly on the diameter of the combining tube, in which the driving and suction fluids mix; in the experiments, the ratio of com-bining-tube area to driving-nozzle area was varied in twelve steps, covering a range of area ratios from 1·44 to 1,110·0, and compression ratios ranging from about 3 to about 1·001. Efforts were made to find the best proportions of those parts of the ejector which exert a major influence on performance, and certain conclusions are drawn from the results of the experiments. Theoretical aspects of the problem are briefly discussed.
Dust Deposition from Chimney Stacks
Authors: Bosanquet C. H. , Carey W. F. , Halton E. M. 
Published: October 2007

Economic competition compels many firms to operate processes which emit gases carrying a dust burden many thousand times that of atmospheric air. Even after treatment in the most expensive deduster this effluent will still hold some 5 per cent of its original dust, so that it must be discharged up a tall chimney. Wind eddies then dilute the chimney gases until they can be tolerated at ground level; however, during dilution the coarser dust is liable to settle and cause objectional deposits in the vicinity. The problem of designing an installation to avoid nuisance is therefore to remove the coarser grits in a deduster and to arrange the stack to dilute the finer residue so that deposits will not be noticed. The authors have developed a set of reasonably simple formulae and charts for predicting the path of particles emitted from a stack and spread by the wind. Experimental checks have been applied to the predictions, but the subject is complex, and at this stage it is unlikely that it will be possible to predict the rate of deposit within a factor of 2. In order to illustrate the implications of the paper a worked example is given on a powdered-coal boiler installation. This shows that with properly designed cyclones and a moderately high stack there will be no noticeable deposits. The implication is that it should be possible in time to extend the treatment given in the paper to specify a deduster exit which will avoid nuisance with fair certainty and at a relatively moderate cost.
The Use of Mild Steel for Service at Sub-zero Temperatures
Authors: Keating F. H. , Mathias E. V. 
Published: October 2007

The paper describes an investigation undertaken to determine the limiting sub-zero temperature at which mild steel may safely be used, in relation to notch brittleness. After a brief discussion of the literature on the subject, experimental work is described on the effects of variation in notch dimensions on impact value at sub-zero temperatures. Further work determines the effect on impact values of the surface cold-working resulting from grinding and machining, and indicates the beneficial effect of stress-relieving in removing the harmful effects of cold work on the surface. Practical experiments on small welded vessels in mild steel are then described, the vessels being tested to destruction at −80 deg. C. This work indicates that, while such vessels ultimately fail in a brittle manner, actual rupture is preceded by a considerable amount of plastic flow. It is argued, from these results, that the observed plastic flow gives adequate assurance that properly constructed mild-steel welded vessels will be able to absorb local overstressing to an appreciable extent without rupture, and this conclusion is supported by stress-strain diagrams taken at sub-zero temperatures. The results of the investigation are the basis for the conclusion that, provided the recommended precautions as to quality of material and care in fabrication are taken, mild-steel welded equipment may safely be used at sub-zero temperatures down to −50 deg. C.
A Contribution to the Theory of Natural Draught Cooling Towers
Authors: Wood B. , Betts P. 
Published: October 2007

In recent years the mechanical draught cooling tower has had the benefit of theoretical analysis developed in Germany and in the United States, resulting in the evolution of the “total heat method” of heat transfer calculation which together with empirical data provides a sound background for thermal design. The natural draught tower contains the same elements with the difference that its performance is also dependent on the atmospheric dry bulb temperature, which introduces a fourth variable in addition to the wet bulb, the load and the water rate which apply in mechanical draught towers. Because of the greater complication it has hitherto resisted a theoretical approach. The present paper offers an extension of the theory to cope with varying air rate, establishes the relevant equations and shows how these can be solved. After deriving the basic characteristics of a tower and fill from analysis of the test data, it is possible to predict the performance of a similar tower under other conditions. Though the analysis may be rather involved for routine design work it offers a basis for the formation of logical ideas as to how the various factors influence performance and enables the effects to be visualized with the aid of diagrams. An explanation is offered to account for the observed effect of wind in increasing the draught. The issues of water loss by evaporation and carryover, the formation of the visible plume, and the avoidance of nuisance are discussed from physical principles.
Thin Aerofoil Theory and the Application of Analogous Methods to the Design of Kaplan Turbine Blades
Authors: Hutton S. P. 
Published: October 2007

In order to increase the power and working heads of Kaplan turbines it is necessary to avoid any low local pressures round the blades. The problem is similar to that encountered in high-speed aerofoil design, and the possibility of using similar methods to evolve blade sections for Kaplan turbines is explored in the paper. A general survey for those unacquainted with recent developments in aerofoil design is given, which is intended to demonstrate the advantages of the use of profiles with specific velocity distributions and to illustrate the general methods by which they may be derived. A brief summary is made of methods of designing aerofoils in cascade to allow for blade interference and a few examples are quoted from British and American practice.
The Friction of Flexible Packings
Authors: Denny D. F. 
Published: October 2007

At any time there are anomalies and difficulties in the prediction of friction, and these are accentuated if one of the surfaces is deformable, as in flexible piston seals, since the surface strain introduces an additional variable. Such surfaces, although exhibiting the three usual kinds of friction—dry, boundary, and film—show peculiar characteristics at low speeds, when the friction is usually less than that at higher speeds. The static friction itself depends on the time during which the surfaces have been in contact, and preliminary work indicates that there is a law connecting these two quantities, the probable form of which is given in the paper. The experiments suggest that the total friction force need be no greater than 1 per cent of the force on a 3-inch diameter piston at pressures of the order of 2,000 lb. per sq. in. (and may be much less in the case of specially shaped seals) though the accuracy of prediction is unlikely to be better than ± 10 per cent.
The Problem of Burning Residual Oils in Gas Turbines
Authors: Lloyd P. , Probert R. P. 
Published: October 2007

The burning of residual oil fuels in gas turbines raises some special problems: the efficient combustion of the solid particles to which these fuels give rise, the avoidance of ash deposits, and the protection of turbine blades and other components from corrosion effects peculiar to these fuels. This lecture discusses these problems and the methods which are being considered for solving them. It is shown that the burning of these heavy oils is not the greatest of the difficulties, since with suitably designed equipment this process can be quite efficiently performed. What is difficult is the avoidance of ash deposition and of the secondary effects, notably blade corrosion, to which this deposition gives rise. These effects are considered in some detail.
Some Problems in the Manufacture of Experimental Gas Turbines
Authors: Leedham L. H. 
Published: October 2007

The gas turbine has created new workshop problems arising from the use of special materials and from the complexity of some of its component parts. The construction of experimental sets calls for much improvisation to avoid heavy expenditure on special tools and machines, and the paper gives examples of methods which meet this requirement. Blading for axial turbines and compressors when required only in small numbers, as in the manufacture of experimental sets, is probably the major problem and cannot be met without the provision of some special facilities, the basis of which is usually copy machining. One of the most notable developments has been the use of sheet metal in the gas turbine, not only for the combustion system but also for structural parts, many of which are subject to severe conditions imposed by high temperatures, and fatigue stressing. The highest grade workmanship is essential in this connexion, to ensure reasonable life, free from failure. The special demands of gas-turbine design are constantly giving rise to new manufacturing techniques and the paper deals briefly with some of these, such as those associated with welded rotors and precision forged blading.
Investigations Concerning Flow Conditions in a Centrifugal Pump, and the Effect of Blade Loading on Head Slip
Authors: Peck J. F. 
Published: October 2007

The object of the paper is to examine the flow conditions observed in a specially designed 6-inch centrifugal pump; firstly, when the directions and magnitudes of velocities of flow were obtained by means of Pitot tubes, and secondly, when the flow was examined with an electronic stroboscope, through an inspection window of “Armourplate” glass in the casing. To provide uniform entry conditions a single-entry pump was chosen, preceded by a long length of straight suction-piping, but at small discharges a powerful forced vortex was found to exist with a spiral flow extending backwards for some distance from the pump inlet. This phenomenon was investigated by traverses with a direction vane and Pitot tubes, and an explanation of its cause is offered. The direction and magnitude of the absolute velocity at the impeller outlet were measured by cylindrical Pitot-tube traverses across the passage at two positions, and at small discharges a component of flow from the casing towards the suction side was found to occur through a portion of the impeller on the side nearest to the suction pipe. Similar traverses were made at two positions around the volute casing. These indicated a symmetrical, double spiral-flow at the best-efficiency point, and at other discharges this was modified to a single-direction vortex having a core at a much lower pressure than that on the outside of the casing. Pressure tappings on the casing, with an open-sided impeller and diffuser, showed the effect of shock on the inlet tips of the diffuser vanes, and inspection through the window confirmed a flow surging to and fro at small discharges. The effect of impeller blade loading on “head slip” is also investigated—two impellers showed a direct relationship—and values of the resulting “slip constant” are given. A graphical analysis shows the head slip, and head losses in the impeller and casing for the full range of discharge. Finally the performance curves of the pump, operating in reverse as a turbine, are given, from which the “runaway” speed under any head and any resisting torque may be estimated.
Contribution to Improved Accuracy in the Calculation and Measurement of Torsional Vibration Stresses in Marine Propeller Shafting
Authors: Archer S. 
Published: October 2007

Methods of calculating torsional vibration stresses in marine propeller shafting have differed mainly in the apportionment of damping energy between engine and propeller, and for this purpose a propeller damping constant of average value has commonly been assumed. The author has long considered this simplifying approximation unjustified, since no account is taken of variations in geometrical design factors as affecting propeller damping properties. As the propeller is usually by far the major damping influence in the single-node mode, the accuracy of stress prediction must often suffer correspondingly. The paper details a convenient method of deriving damping coefficients for modern three- and four-bladed bronze propellers. Curves are plotted, for a series of pitch ratios, against a non-dimensional power coefficient involving only quantities usually known in the design stage, namely, horse-power, propeller revolutions and diameter. Allowance for disk area ratio is by interpolation between limiting values. Attention is also drawn to possible serious errors in interpreting torsiograph records taken from the crankshaft end of marine heavy-oil engine systems, arising from the phase difference between engine and propeller vibration at resonance—a consequence of heavy propeller damping. Here again improved knowledge of propeller damping characteristics is desirable if maximum accuracy is to be achieved. The paper concludes with a worked example from practice, indicating the order of magnitude of errors involved, with details of a simple vector method of allowing for the phase effect in any given instance.
New Formulae for Water Flow in Pipes
Authors: Blair J. S. 
Published: October 2007

As a result of extensive investigation of water flow formulae and test data on water mains and experimental test pipes, four new formulae for water flow in pipes have been evolved. These apply to pipes in new condition using water at normal temperatures, and cover all classes and sizes of pipes and a very wide range of velocities. The constants in the formulae do not require to be varied to suit the condition or the size of pipe. It is only necessary to choose the appropriate formula to suit the material of which the internal surface of the pipe is made. These four formulae are:— (1) For smooth non-ferrous pipes: V = 47 m***0·71 i0·57. (2) For bare steel, wrought iron, asbestos cement, or bitumen lined pipes: V = 40 m0·69 i0·555. (3) For bitumen coated steel pipes or concrete pipes: V = 36 m0·68 i0·54. (4) For galvanized cast iron, or other coated cast iron pipes: V = 300·67 i0·52. An approximate estimate of the conditions arising when fluids other than water are used can be obtained by plotting these formulae on a Reynolds number diagram, and taking the value of F at the appropriate Reynolds number, but this is not recommended, since these formulae have not been compared with practical test results for fluids other than water. The use of these formulae will give the discharge to be expected from any class and size of pipe to an error of not more than about ±10 per cent. Such accuracy is adequate for all ordinary water flow calculations, and is better, over the whole range of pipe surfaces, sizes, and velocities, than has been previously possible by the use of any other formula.