MARKET DEVELOPMENTS

Lawton Smith (1994, cf. Kinghorn 1988) gave some overall figures (cf. Chapter 20) for the flow measurement industry worldwide, which, with likely growth, suggest that by the year 2000 it could be in excess of US $1 billion.

With this growing market in mind, we look at the new challenges that face the flowmeter engineer, the current and future devices that may provide solutions, the implications of information technology, and new production methods. The chapter concludes with some suggestions for the way ahead, after a brief review of comments that I made on future developments in an earlier book (Baker 1988/9).

EXISTING AND NEW FLOW MEASUREMENT CHALLENGES

Oil Exploration and Processing

The oil industry, dealing as it does with high value products, is likely to continue to ask for more accurate meters capable of operating in adverse conditions, in multiphase flow, and in subsea installations.

Corneliussen (1991) of the Amoco Norway Oil Company described field experience with Hod metering, which was the first small unmanned production platform in the Norwegian sector of the North Sea and started production in September 1990. Gas and liquid were transported in a three-phase pipeline 13 km to another platform from which Hod was operated. He described problems that appeared to have stemmed from trapped air and gas in the pipeline and from a highly acidic well that eventually caused the destruction of some of the meters. This is one example of the increasingly difficult environment in which North Sea instrumentation must work.

INTRODUCTION

This is one of the most important recent meter developments, and its application in the next few years is likely to impinge on many areas of industry. Its importance is recognized by the main national and international advisory bodies (cf. Mandrup-Jensen 1990 who described initial work in Denmark on pattern approval and ISO developments).

BACKGROUND

Plache (1977) makes the interesting point that mass cannot be measured without applying a force on the system and then measuring the resulting acceleration. This is a point that I have long considered a possible requirement, and it is certainly supported in the Coriolis meter.

Possibly the first application of the Coriolis effect for mass flow measurement was proposed by Li and Lee (1953). The meter is shown in Figure 17.1. The T-piece flow tube rotated with the outer casing and was linked to it by a torque tube. As the flow increased, so the T-piece experienced a displacing torque due to the Coriolis acceleration, and this was measured from the displacement of the T-piece relative to the main body.

In the Li and Lee meter, the liquid was forced to move radially, and therefore a force was applied to it through the tube. This force, in turn, was balanced by an equal and opposite one applied by the liquid to the tube. The force caused the tube to twist, and the small rotation was sensed to obtain the mass flow rate.

INTRODUCTION

The possibility of inducing voltages in liquids moving through magnetic fields was known by Faraday in 1832, but the first flowmeter-like device was reported by Williams in 1930. The first real advance in the subject came from the medical field where Kolin (1936, 1941) introduced many ideas that are now standard practice.

The industrial interest in electromagnetic flowmeters (sometimes referred to as EM or magnetic flowmeters) grew in the 1950s with

• the Tobiflux meter (Tobi 1953) in Holland for rayon viscose, sand and water, and acid slurries;

• Foxboro, to whom the patent was assigned in 1952;

• the first commercial instruments in 1954 (Balls and Brown 1959).

• nuclear reactor applications;

• the work that resulted in an essential book by J. A. Shercliff (1962).

In this chapter, we shall concentrate on the application of the flowmeter to fluids that are of low conductivity, such as water-based liquids (Baker 1982). The flowmeter has also been used with liquid metals (Baker 1969, 1970b, 1977), and a few designs have been built for use with nonconducting dielectric liquids (Al-Rabeh et al. 1978). The reader is referred to the original papers because space prevents their inclusion here. Three papers by Wyatt (1961, 1977, 1982), a pioneer in blood flow measurement research, are referenced for those interested.

OPERATING PRINCIPLE

We start with the simple induction, which occurs when a conductor moves through a magnetic field. Figure 12.1 shows a copper wire cutting the flux of a permanent magnet.

INTRODUCTION

The measurement of mass flow, a fundamental requirement for any fluid, has been an elusive goal due to the problems of developing a suitable flowmeter. Despite this, the availability of mass flowmeters has increased greatly over the last 15 years. This is partly due to the increasing value of products (Hall 1990), but it is also due to an increasing realization that volumetric flow measurement is often inappropriate. In addition, the advent of the Coriolis flowmeter has stimulated engineers to find other mass flowmeters. General reviews of mass flowmeters were given by Sproston et al. (1987), Betts (1990), and Medlock and Furness (1990).

Mass flow measurement is commonly categorized as direct (true) or indirect (inferential). However, it may be useful to allow a few more than two categories.

1. a. True (direct) mass flow measurement by a single instrument is rare. It appears that to achieve it we need to use one of the fundamental acceleration laws. We can do this by creating:

• the force (or torque) resulting in a linear (or angular) acceleration (Chapter 16 describes an example) or

• the force that produces Coriolis acceleration (Chapter 17).

1. b. Fluid-dependent thermal mass flow measurement uses the temperature rise resulting from heat addition but is affected by other parameters such as the specific heat of the fluid (Chapter 15).

2. c. Multiple differential pressure flowmeters used in a dedicated system (Section 14.2) depend on the nonlinearity of the flowmeter equation.

INTRODUCTION

This meter uses a fascinating effect that occurs when gas flows at very high velocity through a nozzle. As the gas is sucked through the nozzle, the velocity increases as the cross-section of the nozzle passage decreases toward the throat. At the throat, the maximum achievable velocity is sonic – the speed of sound. Downstream of the throat, the velocity will either fall again returning to subsonic or will rise and become supersonic. In normal operation of the nozzle, the supersonic region is likely to be small and to be followed by a shock wave that stands across the divergent portion of the nozzle and causes the gas to drop, very suddenly, from supersonic to subsonic. The existence of a shock wave does not mean that one will hear a “supersonic bang”! Such bangs are usually caused by moving shock waves carried forward by high speed aircraft.

The fascinating effect of sonic conditions at the throat is that changes in the flow downstream of the throat have no effect on conditions upstream. The sonic or critical condition, as it is called, appears to block any information that is trying to penetrate upstream. A simple picture of this is that the messengers carrying such information travel at the speed of sound and so are unable to make any headway over the fast flowing gas stream.

INTRODUCTION

I do not claim an expertise in manufacture, but I want to make three points briefly in this chapter and then to enlarge on the last of them.

Market information is usually inaccessible, and there may be a case for research centers to work together to provide a better source of data for industry. It is clear that there is not always an entirely satisfactory information flow, even within companies, between the marketing department and the technical and manufacturing operations.

My first point is, therefore, to suggest the need for better market information both within and outside companies.

My second point is to indicate the need for the flow metering industry, on the one hand, and the science base as it relates to instrumentation, on the other hand, to create an effective means for technology transfer, which in the process will raise the profile of the sector and ensure that government is aware of its importance. Past experience of encouraging collaboration suggests that industry and the science base do not always appreciate the value of working together. Collaboration between industry and the science base should be mutually beneficial in providing an antenna for new information on developing technologies.

The third point is that the production of instrumentation is a special case in which the effect of the production process on the final accuracy of the instrument may, in some cases, be predicted and used to specify the production requirements.

INITIAL CONSIDERATIONS

Some years ago at Cranfield, where we had set up a flow rig for testing the effect of upstream pipe fittings on certain flowmeters, a group of senior Frenchmen were being shown around and visited this rig. The leader of the French party recalled a similar occasion in France when visiting such a rig. The story goes something like this.

A bucket at the end of a pipe seemed particularly out of keeping with the remaining high tech rig. When someone questioned the bucket's function, it was explained that the bucket was used to measure the flow rate. Not to give the wrong impression in the future, the bucket was exchanged for a shiny new high tech flowmeter. In due course, another party visited the rig and observed the flowmeter with approval. “And how do you calibrate the flowmeter?” one visitor asked. The engineer responsible for the rig then produced the old bucket!

This book sets out to guide those who need to make decisions about whether to use a shiny flowmeter, an old bucket, nothing at all, or a combination of these! It also provides information for those whose business is the design, manufacture, or marketing of flowmeters. I hope it will, therefore, be of value to a wide variety of people, both in industry and in the science base, who range across the whole spectrum from research and development through manufacturing and marketing.

Why another aircraft design book?

Aircraft design is a complex and fascinating business and many books have been written about it. The very complexity and dynamic nature of the subject means that no one book can do it justice.

This book, therefore, will primarily act as an introduction to the whole field of aircraft design leading towards the subjects summarized in Fig. 1.1. It will not attempt to duplicate material found in existing design books, but will give information about the whole aircraft design environment together with descriptions of aircraft and component design. It also presents otherwise unpublished data and design methods that are suitable for aircraft conceptual, preliminary and detail design activities.

Topics

The following chapters are arranged as a series of questions about aircraft design, the answers to which give largely descriptive overviews of all aspects of aircraft design. This will provide an introduction into the conflicting requirements of aircraft design specialists in a design team, with a view to improving understanding, and the integration of a sound overall design.

The book is divided into chapters which answer a number of significant design questions.

The question ‘why design a new aircraft?’ is answered in Chapter 2 which shows the derivation of aircraft requirements for civil and military aircraft from market surveys, and gives examples of operator-derived specifications.

Introduction

The author and V C Serghides have performed statistical analyses to produce combat aircraft reliability and maintainability prediction methods. These are applicable for use at the conceptual design stage, because they only require the use of readily-available parameters such as wing span, engine thrust, mass, etc. These methods predict whole-aircraft values of confirmed defects per 1000 flying hours and defect maintenance hours per 100 flying hours. Predictions are also made for individual systems and allowances may be made for technology improvements, relative to the empirical data-base used in the method derivation. These may be used as targets for reliability performance of individual systems during the preliminary design stage.

Earlier work by the author produced a similar method for the prediction of commercial aircraft dispatch reliability. The whole-aircraft equations produced are reproduced in Section C2, below.

Commercial aircraft dispatch reliability prediction

The work reported in ref C2 showed that some systems exhibited different traits according to the type of airline operation. For example long-haul aircraft tended to have higher delay rates because they may be away from their home base for more than a week, and defects might accumulate, whereas short-haul aircraft tended to return to their home-bases more often. Other considerations were also affected by the operational type, in such things as Chapter 28 – fuel systems, where long-haul aircraft had more complicated systems which were more delay-prone than those of short-haul aircraft.

General

This Chapter discusses the costs of buying and operating civil and military aircraft. The former costs are termed acquisition costs for both classes of aircraft, whilst the latter are termed operating costs for civil aircraft, and life-cycle costs for military aircraft (LCC). The acquisition costs are included as important elements of both operating and life-cycle costs. The costs associated with aircraft reliability and maintenance are significant contributors to operating and LCCs, and design to reduce these costs is outlined at the end of this chapter.

Acquisition costs (the costs of buying, or acquiring the aircraft)

The reasons for high aircraft acquisition costs

The main reasons are:

1. (i) High performance requirements – Civil and military aircraft operations are competitive, hence each new type is required to show improvements relative to existing aircraft. It is therefore necessary to undertake extensive research programmes and also to incorporate customer/operator refinements, which imply complexity.

2. (ii) Safety considerations – Civil and military aircraft have, rightly, very stringent safety requirements which must be proved before the aircraft enters service. Extensive proving and testing is required and there is a need for added complexity so that failure of individual components or systems can be tolerated. An aircraft has to continue functioning safely even after a failure has occurred. This applies to both hardware and software.

3. […]

The previous chapters have shown the complexity of aircraft, and their constituent parts. Their design is a daunting, but potentially satisfying task. Designers need all the help which they can get to achieve successful results.

The usual starting point is a sound aeronautical education. Design is learnt by a combination of theoretical education and design experience at University and/or in Industry. It must be stressed that design is much more than analysis. It is a creative process involving the synthesis of knowledge from many disciplines, monitored by qualitative and quantitative checks. These should assess the value of the necessary design compromises and lead to optimum designs. Advice from, and work alongside, experienced designers is an invaluable part of the education process. People learn how to design by actually doing it! Less experienced design organizations can be helped by specialist consultants. Such help is, however, not always available, but much design knowledge and experience has been encapsulated in the publications and programs described later in this chapter.

Many individuals and organizations publish reports, papers and memoranda, many of which contain relevant data. Modern libraries use on-line computerized data bases which sort and codify these date sources on the basis of key-words. A description of such reports is beyond the scope of this book. The most exciting new development has been the advent of the internet.

Introduction

The aircraft industry is littered with a plethora of aerospace terms and units, which leads to considerable confusion. The early part of this appendix aims to translate terms used by the English-speaking nations on either side of the Atlantic ocean.

Conversion tables are also provided to allow comparison between commonly-used English or US units and their equivalent International System of units (SI).

Relevant, accurate, empirical aircraft design data are food and drink to an aircraft designer. It is important to learn from the past and use information about it as a guide for the future. Data comes from many sources, some more easy to acquire than others. Chapter 9 lists many data sources, but these still leave significant gaps of information. The author has accumulated much data over the years, and has extracted others from regular sources to present what is hoped will be useful information in a simple form for use in the early design processes. These data, by their nature, become obsolete after a few years, but it will be possible to up-date them as more information becomes available.

This appendix gives information in tabular or pictorial form in such areas as aircraft geometric, mass and performance data. It also gives information on powerplants, aerodynamics, structures, landing gear, interiors and weapons.

Background

There is almost no limit to the variety of the shapes of aircraft that have been conceived. This chapter will give a brief introduction describing wing, fuselage and powerplant arrangements followed by descriptions of the characteristics of civil, military and rotorcraft types.

Aircraft are essentially aerodynamic vehicles and every aircraft designer must develop considerable aerodynamic skills. This book is not aimed at providing those, as there are many excellent texts available, as shown in the bibliography section of this book. Appendix A6 contains some limited information to enable the evaluation of simple aerodynamic predictions for use during the conceptual design process.

The aerodynamic shape of the aircraft will determine aircraft speeds, manoeuvrability, flying qualities, range, field performance, costs, altitudes and many other parameters. There is a close interaction between such disciplines as aerodynamics, structures, propulsion and aircraft systems. For example, a high subsonic aircraft usually requires a very thin or swept wing, or a combination of these, to achieve low aerodynamic drag. Thin or swept wings adversely affect weight and may require more thrust from the propulsion system. A good compromise is therefore required. An optimum shape must be determined to maximize a chosen performance parameter. This may be minimum life cycle cost, initial cost, weight, fuel burn, etc. depending upon the type of aircraft required. In all cases, however, a good aerodynamic shape is vital, as in the areas now described.