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	Time: 40 hours Level: Intermediate

	Introduction Introduction Resource In this unit we examine one factor that very often seems to be found skulking around close to problems and solutions: temperature.

	1 Temperature – problem or solution? 1 Temperature – problem or solution? Resource ‘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...

	2 Getting into hot water 2.1 Boiling water Resource Whether it's to wash clothes, make a cup of tea, or just make it safe to drink, water often has to be heated – sometimes to boiling point. There are many ways to do this, but a very common means is some... 2.2 Thermal effects in outline Resource Temperature is, of course, the measure of ‘thermal’ conditions. Nowadays it is measured by thermometers and expressed as a number on an agreed scale. Some features of thermometers and of their use are... 2.3 How things change with temperature Resource The temperature-dependent effects used in most thermometers have a fairly steady change over a good range of temperature (Figure 3a). By contrast, phase changes, of which melting and boiling are the common... 2.4 Summary of Section 2 Resource 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...

	3 Gradual temperature effects 3.1 Modelling properties Resource 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... 3.2 Room to rattle: modelling thermal expansion Resource 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... 3.3 Thermal stresses Resource When the temperature of an object increases (say, by ΔT) it expands. According to the linear model of thermal expansion the length increase is described by 3.4 Summary of Section 3 Resource The temperature of an object is intimately linked to the average kinetic energy of the atoms from which it is made. As a result, some materials properties such as electrical resistance and mean atom spacings...

	4 Accelerating temperature effects 4.1 Characteristics of processes activated by thermal energy Resource This is a long section and needs to be studied carefully. Keep your eye on the overall goal of seeking useful thermal effects on which to base devices. 4.2 Energy distribution Resource Atoms without much thermal energy will not be doing very much. Consider fifty million million million (50 × 1018) silicon atoms, bonded into a single massive network; I've chosen silicon, but any elemental... 4.3 Thermally activated processes Resource Thermally activated processes are those that get going not because of average effects, but because the fraction of particles in the tail of the distribution increases with temperature. This is a... 4.4 Summary of Section 4 Resource Thermal energy is a random thing, so any group of particles possessing it will have a distribution of kinetic energies.

	5 Sudden temperature effects 5.1 Sudden changes Resource The third category of thermal effects identified in Section 2 are those associated with sudden changes. Here are some technically important examples where things change suddenly at a particular temperature:... 5.2 What's in a phase? Resource In an engineering and scientific context, a phase is an arrangement of atoms that is identifiable through its recurrence – the same pattern is found time and again. For instance, the compound of hydrogen... 5.3 Order and chaos Resource How can we explain a sudden switch of behaviour at a particular temperature? There must be two competing influences (say X and Y) that depend differently on temperature. Figure 23 indicates how a unique... 5.4 Critical modelling Resource Critical phenomena are the simplest to model of the three classes of temperature-dependent changes we have been examining. We don't need a power series such as 1 + αT+ βT2+…, nor exponentials such as exp(−Ea/kT).... 5.5 Summary of Section 5 Resource The phase of a material is characterised by its physical state (e.g. solid, liquid or gas), a distinctive arrangement of the atoms, and its chemical composition.

	6 The water boiler again 6.1 Review Resource Let's see if we have made any progress in studying thermal effects. The following SAQ is based on Exercise 3, although this time I have a higher expectation of how much you should be able to do. 6.2 Refining the specification Resource The ideas for the boiler cut-out switch can now be based on some real knowledge about temperature effects. You are now ready to tackle the next exercise. 6.3 Summary of Section 6 Resource In trying to find solutions to the specific problem of the water-boiler, where the need was for a particular response to a certain temperature change, we have gone into the principles behind the three...

	References and Acknowledgements Acknowledgements Resource

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