Proceedings of the Institution of Mechanical Engineers

Many theories predicting the critical (or burnout) heat flux in saturation pool boiling have been proposed during the past decade. Although most are able to correlate existing experimental data, it is evident that the theoretical models upon which they are based are widely different in concept. Moreover, owing to lack of experimental evidence it is not clear which, if any, are based upon the more correct models. Certain of the theories implicitly contain the acceleration due to gravity raised to a different power; by performing a relatively simple experiment it may be possible to accept or reject certain of the theories. An experiment of this type is described in the present paper. On the basis of the results of this experiment it is possible to reject several of the above theories.

The extent to which the acceleration of the boiling system is important as a parameter in determining the critical heat flux was ascertained experimentally. A simple centrifugal apparatus is described which was used for determining the critical heat flux in pool boiling to water at atmospheric pressure and accelerations in the range 1 < (a/g) < 160. A two-variable non-linear correlation involving a logarithmic transformation was made upon the experimental results after allowing for the possible effect of pressure and potential sub-cooling by extrapolation to zero subcooling. The resulting equation is of the form:

Several papers (1)-(5)^† have been written in recent years dealing with various aspects of the performance of turbocharged two-stroke compression ignition engines. None of these, however, provides a general method of performance prediction for a given engine-turbocharger combination over the complete range of load and speed, in terms of given design operating conditions and given compressor and turbine characteristics. Such calculations are complicated further by the inclusion in the system of a mechanically driven scavenge blower, usually in series with the turbocompressor.

The paper provides a complete solution of this complex problem on the basis of certain necessary simplifying assumptions relating primarily to the engine cycle.

Since the gas generator and compound engine have been recognized in recent years as, in certain circumstances, superior alternatives to the turbocharged engine, the method is extended to cover also these two cases. In all three cases the engine is assumed to be of the opposed-piston type, which is now recognized as being particularly suitable for high-pressure supercharging (6).

The paper may be considered supplementary to a recent paper by Chatterton (6), in which the turbocharged, gas generator and compound cycles are compared purely on a basis of design point operating conditions.

In an earlier paper (1)^†, the performance characteristics of combinations of two-stroke compression ignition engines with compressors and turbines were analysed under the headings

(1)

Turbosupercharged engines with mechanically driven scavenge blowers,

The object of the present paper is to extend the method of analysis outlined in the previous paper to cover various compound engine arrangements with differential rather than fixed ratio gear connection between the members of the aggregate. It is shown that such units meet to a very high degree the specific requirements of the traction application, namely

(1)

High unit power achieved by the use of high boost pressures,

Two arrangements, both meeting these requirements to a high degree, are considered. These units constitute a significant advance over existing traction prime movers.

Uni-directional torsion fatigue tests were carried out on heat-treated En 36A (nickel-chromium) alloy steel which had been given various surface treatments. Recarburization raised fatigue strength relative to the scaled and decarburized condition by 160 per cent. Pre-strained, polished or shot-peened surfaces produced increases in strength ranging from 16 to 60 per cent. The effects of hardening and residual stress are discussed.

The problem of Hertzian bodies in rolling contact and supporting radial and shearing forces in the rolling direction is considered.

A modified form of the conventional photoelastic frozen stress technique has been used to study the particular case of flat elliptical contact surfaces. Existing theories are reviewed and new theories are presented which permit the analysis of the frozen stress results. The dependence of the measured stresses on the hysteresis of rolling is studied.

An experimental approach to the problem of rib-reinforced cover plate design is outlined.

Exact tractable methods for calculating the deflections of radially ribbed plates are not available. Outlines of formal mathematical treatment which use several approximations are presented to highlight the theoretical difficulties.

The technique of Fizeau interferometry was employed to study the deflections of a series of laterally loaded ribbed plates of varying proportions. From the results, values of the rigidity of the plates were found together with the best combination of parameters to ensure optimum stiffening with a minimum of localized curvature for plates of fixed total weight.

The nature and character of the localized curvatures developed in an over-stiffened ribbed plate was revealed by photographic records obtained by means of the Salet-Ikeda slope-contouring technique.

It was concluded that, for optimum design on a basis of rigidity of plates of given total weight, 40 per cent of the total weight of a ribbed plate should be in the ribs or webs and 60 per cent in the basic plate or flange. Localized curvature with attendant stress concentrations were found not to be serious under such a degree of stiffening. Frozen stress photoelastic studies have been initiated to elucidate stress distributions in the vicinity of the ribs.

This paper describes the application of turbocharging to the loop scavenge diesel engine.

The first part is concerned with the important effects on the practicability of the cycle of the turbocharger efficiency, scavenge air pressure and temperature, exhaust pressure and temperature, and the pulses in the exhaust, the allowable maximum pressure in the cylinders, the pressure drop across them in relation to the air flow and the air utilization of the engine. It then goes on to a discussion of the way in which these many factors may be arranged to result in a practical engine of high efficiency and utmost reliability. Reasons are given for preferring, in the present state of knowledge, to retain the crankshaft-driven scavenge pump and the merits of series and parallel arrangements are discussed together with the possibilities of cooling during the compression stages.

The application of these considerations to the development of a range of engines is described. Results of tests on the berth and in service are given together with some details of the mechanical design and construction.

The aseismic design specification to which the Tokai plant was designed is summarized and explanations of certain of its requirements are given. A general review of the main features of the plant, with particular reference to aseismic problems, follows. Finally, certain elements of the design are selected for more detailed explanations of how their earthquake resistance was developed and demonstrated.

The paper describes briefly the mechanical aids that have been brought into use in the various fields of postal work; the public office counter, collection and delivery of mail and the sorting operations. The major part of the paper., however, is devoted to details of segregation, facing, sorting and coding of letter mail.

In this lecture instrumentation will be interpreted as the ways and means to transport and modify signals so as to make them suitable for the input channels of human beings and automatic controllers.

A difference may be made between measuring and control systems; the first present the value of the measured quantity in an appropriate way, the second also formulate and execute command signals. Modern control theory and techniques have an increasing influence on the arts of instrumentation.

An important part of all instrumentation systems is the transducers, which convert the value of the signal to be measured to another physical dimension, more suited for transport or evaluation. Typical are the conversions to electric voltages, pneumatic or hydraulic pressures. The main requirements for the design of a transducer are a low energy consumption from the measuring source, fast response and low susceptibility to disturbing signals and noise.

At the input there exist besides the value of the signal to be measured x_m an associate signal y_m , such that x_my_m has the dimension of energy W (watt). The generalized impedance Z is defined as Z = x_m/y_m , so that W = x_m ²/Z. In general W should be small, requiring Z being large, sometimes approaching infinity. On the other hand, examples will be given where Z must have a certain specified value. A low value of W can be obtained either by using a very sensitive primary sensor and applying sufficient signal amplification afterwards or by using feedback techniques. Most of the primary sensors transfer the measured quantity into a displacement or elongation of the measuring element. A fast response requires small moving parts and a high stiffness. This lowers the sensitivity and efficiency of the signal conversion. Feedback techniques make it possible to increase the high-frequency response without undue miniaturization of the mechanical parts.

The shape and the way of loading of the measuring elements have great influence on the efficiency of signal conversion and a figure of merit will be defined and applied to a number of common elements.

An instrumentation system should be insensitive to disturbing signals and noise. This requires no, or a non-changing, interaction between adjacent components. Further the design should be such that such disturbances as temperature and barometric changes, accelerations, vibrations and gravity have no influence on the output. The first step is to make the design as insensitive as possible for these errors and thereafter by means of series—or parallel-compensation techniques—the remaining effects can be reduced to the required values.

An insight into the mechanism of oil whirl is obtained by investigating theoretically and experimentally its two main characteristics, frequency and amplitude. It is shown that the ratio of steady oil-whirl vibrational frequency to shaft speed may be predicted qualitatively by a linear treatment and some conclusions of a nonlinear treatment are also given. It is also concluded that oil-whirl amplitude can be restricted by the oil supply pressure.

Experiments involving the use of a rigid rotor supported on two fully lubricated 360° journal bearings are described and ratios of steady oil-whirl frequency to shaft speed as low as 0.37 reported.

A burst cartridge remaining in a reactor may eventually release such quantities of radioactive fission products into the coolant circuit as to cause a potential health hazard or maintenance difficulty. It is important, therefore, to be able to detect and locate a burst so that the reactor operator can discharge the cartridge concerned. Of all the possible methods, only detection by the released fission products is satisfactory.

Gaseous fission products diffuse through the leak in the can wall against a coolant inflow induced by oxidation of the fuel, and their presence in the coolant has to be detected against an unavoidable background count. The leak size at the threshold of detection can be estimated from the operating conditions, and the manner in which b.c.d. (burst cartridge detection) signals arise from a developing burst merits special study.

To discriminate against the radioactive decay of the coolant gas itself the precipitation system of monitoring is used. From each fuel channel in the reactor a sample of gas is drawn periodically. This is passed through a precipitation chamber where particular fission product nuclides decay to give ionized daughter products which are collected on a charged wire. The wire is moved to a shielded scintillation counter and the fission product nuclides, which undergo a second radioactive transition, are measured to the exclusion of the active nuclides in the coolant which do not. The performance and sensitivity of the system can be calculated and optimized by considering the expression for the count from the wire.

The mechanical design of the equipment varies in detail from station to station. In later designs the mechanical equipment is simpler and easier to maintain, and greater use is being made of automatic processing and presentation of the signal.

The author presents some of the more recent ejector design theories and compares them with experimental data, and he describes the operation of a few different types of ejector used at present in industry. He also gives a short survey of the relevant literature.

The design theory developed in the first part of the paper is based on the momentum exchange between motive and suction fluid and the assumption that entrainment occurs at constant pressure and mixing at constant area. The equations in which the use of experimental coefficients is kept to a minimum give the motive-to-suction mass-flow ratio in terms of the pressure ratio and certain velocity ratios, as well as the required entry and mixing tube lengths and profiles. Optimization of the ejector for fixed pressure levels enabled the best ejector geometry to be determined with regard to nozzle position, mixing tube entry profile, and mixing tube length. The nozzle was in its optimum position when it reached up to the mixing tube. For this condition the optimum mixing tube length was seven tube diameters and the entry profile did not affect the operation. Although the theory is developed in more detail for an ejector using liquids the methods necessary for calculating gas ejectors and multi-phase and multi-component ejectors are outlined.

The operating characteristics given in the second part of the paper emphasize the limitations of the jet pump but it is pointed out that both efficiency and compression ratio can be improved by the use of multistage designs. A particular application for a turbine condenser is discussed.

The time taken to construct large-capacity thermal power stations is becoming increasingly important and demands close attention. During the constructional period large capital sums are invested without return and as the demand for electricity is ever increasing early availability of generating plant is of consequence.

Subject always to satisfactory load-bearing conditions the level of a coastal or esturine power station turbine house is hydraulically related to sea level. An investigation has been made into the economical depth of excavation for the turbine house as plant erection cannot commence until basic building work is complete.

The investigation shows that the optimum level of a turbine house is amenable to calculation and two methods of establishing the level are described. The first method involves equating the financial value of lost generation to the savings in civil engineering consequent upon reduced excavation. The second method balances generation lost at low water with increased generation at high water.

The results demonstrate that acceptance of periodic small reductions in electrical generation reduce excavation depth, construction time, capital cost or operating cost. The study involves variation in sea level with moon phase, cooling-water pump flow, hydraulic gradients, condenser vacuum and turbine power.

Extension in coverage of the conclusions permits power station design engineers to select an optimum turbine house level, subject to consideration of relevant civil engineering factors, in the early design stages.

The scope of the paper is limited to the design and construction of heat exchangers of the type used in gas-cooled nuclear power plant for the purpose of raising steam. Among the earliest examples of such heat exchangers were the steam-raising units at Calder Hall and Chapelcross: the paper discusses their development and behaviour in operation. Subsequent improvements exemplified by the plant at Hinkley Point and Sizewell are described and reference is made to considerations affecting current designs. Although the design and construction of these nuclear heat exchangers represent little extrapolation beyond well-established principles and practice, certain peculiarities do require special attention. Amongst these is their radiation environment and necessity of placing ancillaries requiring routine attendance in appropriately shielded positions. Another requirement is a knowledge of the transient behaviour of the heat exchangers both in normal and in emergency operation. Yet another relates to virtual elimination of the possibility of leakage. The paper concludes with reference to future trends and designs of steam raising plant suitable for advanced conditions.

A method of balancing axially-symmetric flexible shafts has been given previously. The process of balancing requires the distortion to be magnified in successive modes so that each may be considered singly near its corresponding critical speed. It may be impossible to isolate a mode with sufficient purity when the shaft has a gross component defect (of bend or unbalance) in an adjacent mode or when critical speeds happen not to be widely spaced apart. Methods are suggested for overcoming the difficulty and the results of an experimental investigation of these proposals are included. The experiments were carried out both on a laboratory scale and on a large industrial rotor.

Profound hypothermia involves the cooling of a patient from 37°C to 13-15°C, using the patient's own blood as a secondary heat transfer medium.

The problem presented is one of heat transfer in viscous flow, demanding apparatus of absolute reliability and ensuring thermal and hydrodynamic conditions which would in no way damage blood cells. Apparatus must be easily sterilized and all blood contact surfaces readily examined. The paper presents a solution using an annular heat exchanger design capable of cooling a patient weighing 10 stone in a period of 30 minutes, the same heat exchanger being suitable for body weights of between 8 and 186 lb. The heat transfer theory presented compares published work in this field, in particular the Graetz result for viscous flow. In the paper it is suggested that measurement of local heat transfer coefficients under similar conditions of both heat flux and velocity gradients gives a better approximation for design than lengthy arithmetic analysis of theoretical equations.

Blood is a complex non-Newtonian fluid and consideration is given to viscosity variations with both temperature and rate of shear.

Finally, there is a description of automatic controls installed with the heat exchanger unit now operating at the Westminster Hospital.

The operation of the heart and of the human circulation system is described and the flow properties of blood are considered in relation to an artificial pumping and oxygenation system. The requirements of such a system are described and discussed with particular reference to their practical operation, including the requirements for a simple and reliable control system. Some ideas are presented on the future trends of such machines.

The paper presents an example of the practical application of the principles of controlled long distance pumping of a mixture of flue dust and water, at comparatively high concentration and low velocity, based on recent research into the hydraulic transportation of solid materials. Precise hydraulic theory is not discussed as this has been dealt with in detail elsewhere.

General details of the main features of the generating station, its location, the reasons for choosing hydraulic transportation, and the arrangements for ultimate storage of the flue dust are described. Brief details are given of design parameters, plant arrangement, test results, running costs and operating experience.

The principle of assisted circulation and the reasons for its adoption for large high-pressure boilers. The process of development that has taken place in the designs for High Marnham 200 MW, Thorpe Marsh 550 MW, and West Burton 500 MW boiler units. Improvements in compactness achieved without sacrifice in operating efficiency. (Reference is made to the firing system and the heat-recovery plant.) The use of flow models. Operating experience with the High Marnham units. Some subsequent modifications. Possible future developments in the light of foreseeable limitations.

The present paper reviews the principal aspects of some work carried out between 1958 and 1961 to obtain a thermocouple capable of operating in the range of 1200-2000°C in the combustion chamber and reheat tailpipes of advanced turbojet aero-engines with an inherent accuracy of about ± 1 per cent.

The work of previous experimenters is reviewed and a consideration of existing thermocouple combinations indicates that oxidation-resistant refractories might be well suited to the applications envisaged. A number of refractories and high-temperature metals and alloys were selected for evaluation on an oxidation-resistance basis, and their thermoelectric output against EY4 graphite (Morgan Crucible nomenclature) is presented. Thermocouple pairs were selected on the basis of the above tests and complete assemblies were evaluated in the laboratory and on test-bed engines, a total of over 1000 hours being accumulated for the final design. Such factors as repeatability, stability and response time are presented.

It is concluded that in order to obtain adequate response times only refractories having a high thermal conductivity are suitable. Greater immersions are therefore required in order to avoid excessive cooling of the hot junction by conduction. This in turn requires greater strength in the thermocouple in view of increased stresses due to gas loading. As a result a refractory thermocouple will be dimensionally larger than conventional thermocouples, but the thermoelectric output will be one magnitude greater. By stringent control during sintering or hot moulding and subsequent selection, adequate accuracy may be maintained and repeatability achieved. Some limitations exist as regards shape and size in view of the difficulty in obtaining sintered or hot-moulded bodies of high length/diameter ratio. In view of the fact that the thermocouple impedance could be less than 10 Ω in conjunction with thermoelectric outputs of 200 mV or more, the possibilities of power generation are considered.

The paper describes equipment which is used to assist in the maintenance of the permanent way and deals particularly with changing methods and the effects of new designs of track components.

Powered plant is employed on all sections of this work on British Railways. In depots and for day-to-day maintenance on the line small machines such as rail saws, nut runners, mechanical hoes, hedge trimmers and welding machines are used.

The cleaning of ballast is done by special machines and pockets of deep clay are removed by excavators. Track is renewed in pre-assembled lengths by purpose-designed track-laying machines, and rails are welded into continuous lengths. The ballast is consolidated and levelled by powered tampers with levelling equipment and track-recording trolleys are used to pin-point any unevenness which would prevent smooth running.

The limitations imposed on plant design are stressed, since equipment must be within the loading gauge—an onerous condition in Britain—and must cause as little interruption as possible to traffic. Consequently plant must travel rapidly and be quickly set up and disengaged. Plant must have a high speed of operation, and also be extremely reliable.

The plastic flow which occurs when two cylinders are rolled in line contact at loads exceeding the yield point has been examined. It has been found to consist of a circumferential movement of the surface in the rolling direction accompanied in some circumstances by radial corrugation. The resistance to rolling and distribution of pressure in the contact have been measured and the results are compared with the theoretical predictions of Merwin and Johnson in their accompanying paper (1)^†.

When two metal cylinders roll together under a contact pressure sufficient to cause yielding, a surprising mode of plastic deformation occurs. The surface of each cylinder is progressively displaced in the forward direction of rotation relative to the core by plastic shearing in a thin subsurface layer. This phenomenon was first observed by Crook (6) in 1957 and the results of a more complete experimental investigation are reported by Hamilton (9) in an accompanying paper. In this paper an attempt is made to explain the mechanism of ‘forward flow’ by an approximate numerical analysis of the elastic-plastic stress cycles to which the material is subject in repeated rolling contact. On the basis of an idealized material which is elasticperfectly plastic and isotropic, it is shown that a forward displacement of the surface would be expected as a result of the complex cycle of stress and strain encountered in rolling. It is also shown that residual compressive stresses are introduced into the immediately subsurface layers during the first few cycles of the load. If the load does not exceed the elastic limiting load by more than 66 per cent further plastic deformation would then cease. At higher loads a steady pattern of plastic deformation is predicted which in its principal features is consistent with the observed behaviour.

An attempt is made to identify the main points that the teaching of design in a university seems to raise. Despite the existence of a large literature, this still appears to be an essential preliminary to an objective discussion. Following on from this attempted clarification, a tentative suggestion is made as to a particular form that such teaching might profitably be given.

The results of a photographic technique for the determination of the complete temperature distribution in the orthogonal metal cutting process are presented; they are found to disagree with previous theoretical predictions. The temperatures along the tool rake face are of particular interest because they are thought to affect the wear of the cutting tool and friction between the chip and tool; it is found that these temperatures have been considerably over-estimated by previous work. By introducing the width of the secondary deformation zone, i.e. the extent of sub-surface deformation due to friction at the tool-chip interface, as a new variable, it is found that more consistent predictions of rake face temperatures can be made. From this work information has been obtained on the shape of the zones of plastic deformation in metal cutting and on the distribution of heat generation within these zones.

The dual function of a surge tank is to reduce water-hammer waves in power station piping systems and to act as a rate-of-flow equalizer, from which immediate water or storage requirements following turbine load changes can be met.

Design requirements are based on predictions of surging in the tank. Experimental performance figures from model and full-scale tanks are compared with various theoretical methods.

Experimental investigations include comparison between the simple, widened, conical, throttled, differential and twin-type tanks, showing their uses and respective advantages. The effects of modifications of design are also examined.

Finally, experimental results are presented which show the variation of water-hammer pressures with the different types of tank and system arrangement.

In the past decade or two the pace of technical development has accelerated sharply, and for the technological industries research and advanced technology are now essential both to support and stimulate the advance. By brief descriptions of selected projects, it is shown that one industrial research laboratory finds its function in the support of product divisions by: (1) providing a background of expert knowledge to support and stimulate a rapid rate of technical advance, (2) increasing design potential by the application of advanced philosophies of design and analysis, (3) reducing the labour and cost of designing and tendering by the application of advanced technological tools and providing a consulting service.

A brief description is given of the situation leading to the introduction of aero jet engines as power units for emergency generating plant to be put into service in Great Britain by the Central Electricity Generating Board. The characteristics and economics of these power units are discussed, in comparison with those of more orthodox types of prime mover. An examination is then made of statistics relating to the world market for gas turbines and sales to date, with a commentary on future prospects in which the aero turbine is expected to take an important place.

This lecture first presents an outline of research work by which many troublesome problems in the design and construction of large tankers were solved, and secondly introduces the largest tanker ever built in Japan, the Nissho Maru, of 130 000 deadweight tonnage.

With regard to design of such tankers, two points, that is,

(1)

reduction in length of ship (L), and

should be taken into account from the standpoint of weight saving and of easy fabrication.

Researches into structural problems of tank parts and into the dynamic pressure of cargo oil tank, due to ship motions, are described briefly, and show that the maximum impulsive pressure in model tests may be up to 5 times the static fluid pressure and may be observed at the tank top when the natural period of fluid in the tank is resonant with the oscillation period of the ship.

Special care should be taken in the detailed design of longitudinals, struts and so on, otherwise cracks will initiate easily at the point of stress concentration.

As regards hull construction practices in such large tankers, there seem to be no special problems except in the fabrication and welding of very thick plate of up to 50 mm thickness. Very thick plates thus offer several problems to be solved such as groove shapes, application of ‘Unionmelt’, doubling plate, weld cracking, and back-wave welding technique, etc. Brief discussion and some test results on these problems are included and mention is made of the superiority of KZ-type groove for automatic single-pass submerged-arc welding and of ‘Uranami’ welding electrode (which offers a perfect one-side welding without backing plate).

Finally, construction methods for large tankers are briefly introduced to give an idea of the hull construction of such large tankers in the building berth.