Proceedings of the Institution of Mechanical Engineers

Consideration of the conditions existing within the turbulent zone formed by a free disperse jet mixing with fluid at rest surrounding it, leads to the conception of an equation for the mean velocity of the jet in an axial direction. Combining the latter equation with that for the upward drift velocity of the gases in a furnace, an expression is obtained for the trajectory of an overfire, or secondary air jet, projected into the furnace. By a similar process the method is extended to the case of a flame jet, taking into account its acceleration due to buoyancy.

The mechanism of combustion is next considered, commencing with an examination of the factors controlling the position of the ignition point in a flame jet, and the derivation of an expression for its location in a powdered-fuel flame. This is followed by the development of a formula for the burning rate of powdered fuel suspended in air, which when combined with that for the mean velocity in a flame jet, enables a relationship to be established between the flame length and the particle size, for the ideal case of a uniform powder. Subsequently, the grading or non-uniform nature of actual powders is taken into account. A method is also described for plotting a flame characteristic, showing the effect of fineness of grinding, turbulence, and burner design on the losses due to unburnt combustible.

The advent of the self-contained hydraulic press, with its many advantages, has necessitated the development of a compact high-speed pump. For most pressing operations a variable-delivery pump is of little advantage, and such pumps, having rotary valves, are only capable of comparatively low pressures. On the other hand a working pressure of 5,000 lb. per sq. in., with its attendant advantage of compactness, is readily obtainable with pumps having positively seating mushroom type valves. Such a pump is described, which the authors have perfected, and which has a volumetric efficiency of over 97 per cent at 1,500 r.p.m. High volumetric efficiency is essential to obviate noise and vibration at such speeds and to reduce pulsations in the flow to a practically imperceptible amount.

To obtain high volumetric efficiency at high speeds the shape and construction of the suction valves are of paramount importance. Some comparative experimental figures are given for the discharge of valves of various shapes.

Oil is used as the hydraulic medium as it prevents corrosion and ensures that all working parts are copiously lubricated. The pump is immersed in the hydraulic medium and all rotating parts are mounted on ball or roller bearings. The conditions of loading, the effect of deflexion on the journal bearings, and the special design of shaft are fully described. The paper concludes with various illustrations of self-contained hydraulic presses to which this type of pump has been applied.

An analysis is made of the various items of locomotive operating costs and the degree to which each is influenced by the type of tractive unit selected, namely, steam or Diesel. The effect of the possibility of a higher “availability” or “serviceability” factor with Diesel locomotives is not likely to be as high as may be supposed. Specification and design details of the various components of a Diesel tractive unit are discussed and in the particular case of a locomotive designed to haul a load of 600 trailing tons at a maximum speed of 60 m.p.h., the main design data and performance curves are worked out with and without supercharging.

The author's general conclusion is that Diesel operating costs compared with steam become more and more favourable as the power output required from the tractive unit decreases, when the advantage of a self-propelled vehicle, such as a railcar, over a train hauled by a locomotive becomes more pronounced.

The work described in the paper was carried out to determine simultaneously the friction and heat transmission coefficients of metal pipes of various cross-sections. A technique has been worked out and apparatus constructed for the simultaneous determination of the friction and heat transmission coefficients of the central portion of a pipe through which a fluid is flowing. With this apparatus, and with water as the working fluid, tests have been carried out upon a series of drawn copper pipes whose cross-sections varied from circular through square, to rectangular with sides in the ratio of 8/1; in addition two drawn brass pipes, one of which had had its internal surface artificially roughened, have been tested. The extreme values of velocity and Reynolds number are in the ratio of about 300/1; the maximum values being about 340 cm. per sec. (11 ft. per sec.) and 30,000 respectively. The friction coefficient of the rough pipe under isothermal conditions has been determined for values of the Reynolds number up to 50,000, using air as the working fluid.

The observations made have been reduced by the method of dimensional analysis and the following conclusions drawn:—

(1) That the results of the heat transmission tests on the various pipes can be correlated on the basis of the hydraulic diameter.

(2) That an increase in friction coefficient is not necessarily accompanied by an increase in heat transmission coefficient.

(3) That the friction coefficient under heat transmission conditions is the same as that under isothermal conditions if the viscosity in the former case is that pertaining to the wall temperature of the pipe.

In a previous paper, on “Heat Transfer between Metal Pipes and a Stream of Air”, presented to the Institution in 1933, an account was given of measurements on the transfer of heat between plain pipes and a stream of air. The present paper is an extension of this investigation to gilled pipes. Observations have been made on the heat loss from four gilled pipes of diameters between 1 and 2½ inches, with gills varying in diameter from 2 to 4⅓ inches. Each pipe was studied as a single unit in the wind tunnel, whilst one size of pipe was also examined when built into a battery of similar pipes placed with their axes across the direction of the air flow.

The result found for plain pipes, namely, that H/ κ θ is a function of Vd/v only (where H is the heat loss per unit length from a pipe of diameter d at a temperature excess θ over air of thermal conductivity κ and kinematic viscosity v, moving at velocity V), requires modification in the case of gilled pipes. In the former case, H is the heat loss per unit length, and is thus equivalent to the product of the circumference and the heat loss per unit area. The latter interpretation, when dealing with the results for the gilled pipes, does not give systematic results, if the heat loss per unit area is calculated on the total exposed area of the pipe. Moreover, in defining the surface emitting heat, the quantity d, the pipe diameter, is only unambiguous for plain pipes. In the case of gilled pipes, it is found that the most consistent treatment of the results is obtained if d is taken to be the “effective diameter” of the pipe, i.e. the total exposed area per unit length divided by π

If the interpretations just explained are given to the quantities H and d, then it is found that to a first approximation, the relationship between H/ κ θ and Vd/v is the same for a gilled and a plain pipe. The observations have also been analysed from the point of view of the temperature of the edge of the gill, relative to that of the air and that of the pipe.

The paper reviews various theories used in estimating impact effects on a freely supported beam, and points out the error which may be introduced if the assumption is made that elastic forms are similar under dynamic and static loading.

An apparatus is described, in which the beam is a railway rail of 8 feet span, subjected to central impacts, strain measurements being made along the flange by means of small scratch-extensometers. An analysis of records from these instruments gives an indication of the instantaneous bending moment distribution occurring at time intervals of 1/1,000 second during impact, and the bending stresses are shown to be approximately 20 per cent greater than those calculated by assuming “statical equivalence”.

The variation of load between weight and beam during impact is recorded by the vertical strain of the rail web under the load, and a complete series of records for various weights and velocities is given. These records demonstrate the occurrence of “sub-impacts”, the weight in certain cases striking the rail five times under what the human eye observes as a single impact. Diagrams of results obtained by calculation from an equation derived by Timoshenko show agreement in form with the load variations recorded by the scratch extensometers. Results obtained by measurement from the area of the ellipse of contact are also given, and loads—obtained by four independent methods—are drawn to a base of impact velocity for various weights. The experimental results are shown in all cases to be at least 2½ times those predicted by the assumption of “statical equivalence”, and (allowing for calibration difficulties) are in fair agreement with those obtained from the Timoshenko equation. Mention is made of the practical significance of the results.

The installation of an overhead electric crane is often left in the hands of specialist manufacturers. Plant engineers, however, need to ascertain service and performance requirements when considering an installation, and they often rebuild or modify existing cranes in order to reduce production and maintenance costs by improving the reliability of the crane service.

The paper considers some of the factors affecting the installation of suitable cranes for particular duties, and deals briefly with some of the important features of design. A few service troubles are dealt with and some instances are quoted from the experience of a steelworks maintenance department with reference to the subject of improvements and maintenance costs.

The paper deals with current conceptions of cold working and its varied effects on the metal undergoing deformation. The mechanism and behaviour of single metal crystals and polycrystalline aggregates, whilst undergoing cold working deformation, are outlined. Two aspects are treated, namely, block slip and “twinning”.

The X-ray examination of a polycrystalline metal under deforming stresses is mentioned, together with the formation of flow lines, better known as Lüder's lines. The effect of cold work on the mechanical, physical, electrical, and chemical properties of materials is then considered in some detail, together with the practical aspects of the changes wrought.

The paper concludes with a brief summary of the subject, and the more important theories are reviewed in order to see how far they explain all the phenomena observed.

The medieval guilds were the forerunners of engineering societies and were followed by scientific bodies. The activities and objects of the Institution of Civil Engineers and the Institution of Mechanical Engineers are described, with notes on other national and local associations in Great Britain.