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3.2 Room to rattle: modelling thermal expansion

In general, as the temperature of a piece of solid is raised the volume it occupies increases. I say ‘in general’ because as we shall see it is not always the case, and we ought to investigate whether we can exert any control over the phenomenon – which could be useful. Evidently, if a solid expands, the average spacing between its constituent parts must have increased. Since matter is made up of atoms, the issue is really about the volume occupied by the arrangements of atoms that make
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3.1 Modelling properties

This section provides a model for properties interpreted in terms of the average thermal energy of all the constituent atoms of a material. Since absolute temperature T is a measure of average atomic kinetic energy, we shall expect to be looking at properties that change gradually with T, roughly proportionally, over a wide range. In terms of the classification introduced in Author(s): The Open University

2.4 Summary of Section 2

  • Thermometers sense temperature. They are transducers providing observable and quantifiable signals in variables other than temperature. Thermometers are calibrated to give numbers in accord with an internationally agreed scale. Various attributes influence the selection of an instrument for a task.

  • Temperature can determine the rate at which certain physical and chemical changes proceed, and whether some changes can occur at all.

  • <
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1 Temperature – problem or solution?

‘Have you taken the temperature effects into account?’ (Figure 1) is nearly always a valid question in any discussion about a proposed engineering solution. Everything has a temperature, and everything behaves differently at different temperatures. It therefore deserves its own special plac
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Learning outcomes

After studying this unit you should be able to:

  • relate the temperature of a solid to the mean kinetic energy of its atoms;

  • use models for thermally induced effects that involve linear, exponential and step changes;

  • use exponentials, logarithms and graphical methods to interpret data from a thermally activated process in terms of Arrhenius's law;

  • identify the changes of phase taking place in a variety of critical phenomena;


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6.5 RSS

RSS (‘Really Simple Syndication’ or ‘Rich Site Summary’) newsfeeds supply headlines, links, and article summaries from various websites. By using RSS ‘feedreader’ software you can gather together a range of feeds and read them in one place: they come to you, rather than you having to go out and look for breaking news. The range of RSS feeds on offer is growing daily. There is probably a feed to cover all aspects of your life where you might need the latest information, and you may
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6.4 Blogs

The founder of Technorati  claims that the number of ‘blogs’ doubles every five months and that the creation rate is approaching two per second. One estimate I read in July 2010 put the number at 400 million blogs. Because these online diaries offer instant publishing opportunities, you potentially have access to a wealth of knowledge from commentators and experts (if they blog) in a wide ra
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2.2 What is a team?

Activity 1

Write your own definition of a ‘team’ (in 20 words or less).

You probably described a team as a group of some kind. However, a team is more than just a group. As noted above, when you think
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2.1 What is a group?

Our tendency to form groups is a pervasive aspect of organisational life. As well as formal groups, committees and teams, there are informal groups, cliques and cabals.

Formal groups are used to organise and distribute work, pool information, devise plans, coordinate activities, increase commitment, negotiate, resolve conflicts and conduct inquests. Group working allows the pooling of people's individual skills and knowledge, and helps compensate for individual deficiencies. It has been
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Introduction

Are you always the quiet one when it comes to group discussion? This unit will help you improve your working relationships with other people in groups of three or more. This unit also deals with project life cycles, project management and the role of the leader.

This unit is from our archive and it is an adapted extract from Systems thinking: principles and practice (T205) which is no longer in presentation. If you wish to study formally at The Open University, you may wish to ex
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Acknowledgements

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Grateful acknowledgement is made to the following sources for permission to reproduce material in this block:

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6.4.1 Materials selection

Among the common thermoplastics available in the mid-1970s, polypropylene appeared as a front runner on grounds of toughness, density and cost Table 9). However, it is subject to creep (being uncrosslinked) and possesses a low tensile modulus of ca. 1500 MN m−2. Its merit index is 12.7 due to the low density of 0.
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5.3.2 Effects of structure on viscoelasticity

If a single measurement of ER(t) is taken at an arbitrary but fixed interval of time, say 10 seconds, then it will vary with temperature in a way rather similar to the viscoelastic master curve. Such a curve for atactic polystyrene is shown in Figure 48, where the various zones of behaviour are identif
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5.1 The behaviour of polymers

The manufacture of polymer products is controlled by two often conflicting demands: the quality of the finished article in terms of its response to its environment and the ease or difficulty of processing it to shape. Both factors are controlled by what is termed viscoelasticity, namely, the behaviour of the polymer in response to applied stress or strain, and temperature. It is important to appreciate the duality in terms of the elastic and viscous responses of polymer solids and poly
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4.6.1 Prices of polymers

Prices of bulk and speciality polymers (Table 9) broadly reflect the degree of chemical processing and treatment needed to make them. Thus the polyolefins, which are directly polymerized from cracker streams, are generally the cheapest followed by vinyl derivatives of ethylene like PS and PVC. Derived polymers which require mo
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4.5.2 Commercial copolymers

The main reason for copolymerizing different monomers is to adjust the physical properties of a given homopolymer to meet a specific demand. SBR elastomer, for example (Table 1), based on 24 wt% styrene monomer shows better mechanical properties and better resistance to degradation than polybutadiene alone. By increasing the s
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3.3.2 Benzene, toluene and xylene

In addition to benzene itself, the catalytic reformer also produces ethylbenzene, toluene and the isomeric xylenes directly. The demand for ethylbenzene is always great as a source of styrene monomer, but toluene does not find great use apart from a relatively small application in polyurethane. This is why most toluene is de-alkylated to increase overall benzene production. A similar problem exists with the xylenes:

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3.2.2 Ethane cracking

Although ethane can be cracked thermally, the reaction is slow and does not necessarily yield ethylene at high severity. Careful control of reaction conditions, however, allows the reaction to occur

The yield of ethylene is typically nearly 50 wt% with the rest composed o
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3.2 Petrochemical processing

Following distillation of petroleum into the major fractions (gasoline C5 up to 95 °C, naphtha 75–175 °C, kerosine 175–225 °C), the naphtha cut is subjected to cracking to yield smaller, double bonded molecules. The reaction is conducted at high temperatures (400–800 °C), but under low pressure using steam for cracking. This process can yield monomers directly, such as ethylene (C2), propylene (C3) and butadiene (C4), but often further rea
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2.3 Some general categories of model

The preceding text has probably suggested several examples of different types of model to you, and at a very broad level, we can categorise the sorts of model we are likely to use in systems work as

Mental models: We have already seen how the ways in which we think and act are shaped by these. As well as the internal representations discussed in Section 2.1, mental models also include language and linguistic models, in particular the metaphors that we use in thinking and talking
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