Heat, material theory

The phenomena of heat require explanation, however, and he expresses himself in favor of the material theory of heat—as an imponderable fluid pervading all space, which condensing in the pores of a substance accounts for the various phenomena of absorption or evolution of heat. The physicists, in fact, were divided for a long time after Lavoisier upon the nature of heat—whether it were a mode of motion or an imponderable fluid. An English writer, Metcalfe, in a two volume work on caloric, 1837, presents the material theory about as strongly as possible. 

In a long note describing his experiments on the variation of the latent heat of steam with temperature, Watt acknowledged that Mr. Southern is inclined to conclude, from the experiments on the latent heat of steam at high temperature [presented in the Appendix]... that the latent heat is a constant quantity, instead of the sum of the latent and sensible heats being so .55 This seems tantamount to an abandonment of what is known as Watt s Taw - that the sum of the latent and sensible heats is a constant. Watt had used this idea not only in his development of expansive working of steam engines but also, as we will see, it was important to his ideas about the chemical transformation of water into air.56 So, to abandon Watt s Law was to jettison a key part of Watt s chemical material theory of heat. We will see shortly, however, that a place was retained for it in a clever fashion. 

In all this, Forbes does not delve at all deeply into just what the theory was that Watt brought into such productive relation to his engineering practice. Vague talk of the theory of heat, of physical principles and the like is all that his readers were offered, and this vagueness allowed for awkward issues such as Watt s commitment to a material theory of heat, let alone a chemical one, to be elided. Many of the grounds on which Watt s chemistry had been judged by Whewell, Harcourt and Forbes himself as outside the bounds of sound philosophical practice were used to rule his engineering practice as within those bounds. The mechanical Watt was awarded the tide philosopher , which the chemical Watt had been denied. 

After Watt moved to Birmingham in 1774 he remained loyal to the Blackian tradition. Thus, for example, in 1779 he reported to Black that he was standing firm against those who challenged him with a non-material theory of heat ... 

Watt, like Black, was committed to one of three major views of heat extant at the time. The first of the three views was that heat was motion, or the vibration of the parts of ordinary material bodies. This mechanical theory of heat had been favoured by Boyle and had been endorsed by Newton. But the mechanical theory was not fashionable in the mid- to late eighteenth century. We know that a mathematical theory of heat as motion was developed by Henry Cavendish in the 1780s but, typically, not published.42 This type of theory was, of course, to become the correct view of heat by the mid-nineteenth century. The second and third accounts of heat are often collapsed together as material theories since in both heat was a special substance rather than the motion of ordinary matter. The distinction between these two material theories is clearly described by McCormmach ... 

Joseph Black subscribed to a version of the first material theory. He considered heat to be a special form of matter that combined with ordinary matter as a result of chemical forces of attraction. The phenomenon of cold produced by evaporation was explained by Black as follows. The cold experienced when water evaporates is the result of the water absorbing sensible heat as the water becomes vapour. The heat is not lost, rather the heat combines chemically with the vapour and it is this that gives the vapour the property of elasticity. Thus water absorbs the matter of heat, which becomes latent (or fixed as Black termed it initially) because it is now chemically combined with the water. Through this combination, the latent heat confers the property of fluidity or elasticity upon the vapour, that is upon the steam. 

This fundamental property of matter must have its origin in the nature of heat itself. The fluid theory of heat assumed that the caloric fluid tended like a gas to distribute itself uniformly over the whole of the available space, and hence to travel from places of higher to places of lower density. The discovery that heat could be converted into mechanical work, and vice versa, led to the abandonment of the material theory of heat and to the acceptance of the kinetic theory, which looks upon heat as the kinetic energy of the ultimate particles of which... 

The reverse process,. e. the production of heat when work is done, was discovered at the beginning of the nineteenth century. The exponents of the material theory of heat, guided by the assumption of the constancy of the heat substance in nature, explained the evolution of heat on turning metals by a supposed decrease in their specific heat. Count Rumford showed, however, by experiments on the large scale that the rise in temperature caused by the boring of a cannon cannot be accounted for by the decrease in the specific heat of the turnings. In 1798 he was the first to state clearly that the motion of the horses, which were used to drive the drill, was the true cause of the observed rise in temperature. 

In this book, it is intended to provide the reader with useful and comprehensive experimental data and models for the design and application of FRP composites at elevated temperatures and fire conditions. The progressive changes that occur in material states and the corresponding progressive changes in the thermophysical and thermomechanical properties of FRP composites due to thermal exposure will be discussed. It will be demonstrated how thermophysical and thermomechanical properties can be incorporated into heat transfer theory and structural theory. The thermal and mechanical responses of FRP composites and structures subjected to hours of reahstic fire conditions will be described and validated on the full-scale structural level. Concepts and methods to determine the time-to-failure of polymer composites and structures in fire will be presented, as well as the post-fire behavior and fire protection techniques. 

The above understanding forms the basis for the development of thermophysical and thermomechanical property sub-models for composite materials at elevated and high temperatures, and also for the description of the post-fire status of the material. By incorporating these thermophysical property sub-models into heat transfer theory, thermal responses can be calculated using finite difference method. By integrating the thermomechanical property sub-models within structural theory, the mechanical responses can be described using finite element method and the time-to-failure can also be predicted if a failure criterion is defined. 

Wessling et al. reported the first polyurethane foam produced in reduced gravity in which they found major differences in the foam and cell structures formed, compared to those formed on Earth. 4,5) Bergman proposed that the space-based production of foams would prevent imperfections in the finished product caused by cell drainage and sedimentation. ) Curtin et al. sought to produce high quality foams in reduced gravity, free of defects in order to test heat transfer theories and for uses as a standard reference material. (7)... 

The heat transfer theory exposes that when a made wall of a given material it is exposed to a heat source that maintains a constant temperature in the surface of the exposed side and the unexposed side is protected from heat loss (insulated), the unexposed face will reach a given temperature increase inversely as the square of the wall thickness [24]. 

An important approach was introduced by Cleghorn, who in 1779 related the material theory of heat in his book De igne as follows ...since the quantity of fire distributed among bodies increases with the attraction for fire that the bodies exert and decreases with the repulsion between the fire particles themselves, it follows that if in any body the former quantity is diminished or the latter increased, then the fire will flow from that body until equilibrium is again restored. Heat is then said to be generated. On the other hand, if the attraction of any body were to be increased or if the repulsion between the fire particles were diminished, more fire would flow into the body and in this case cold is said to be generated... ... 

With the reference block method the distance law of a model reflector is established experimentally prior to each ultrasonic test. The reference reflectors, mostly bore holes, are drilled into the reference block at different distances, e.g. ASME block. Prior to the test, the reference reflectors are scanned, and their maximised echo amplitudes are marked on the screen of the flaw detector. Finally all amplitude points are connected by a curve. This Distance Amplitude Curve (DAC) serves as the registration level and exactly shows the amplitude-over-distance behaviour" of the reference reflector for the probe in use. Also the individual characteristics of the material are automatically considered. However, this curve may only be applied for defect evaluation, in case the reference block and the test object are made of the same material and have undergone the same heat treatment. As with the DGS-Method, the value of any defect evaluation does not consider the shape and orientation of the defect. The reference block method is safe and easy to apply, and the operator need not to have a deep understanding about the theory of distance laws. 

Stahl subsequently renamed the terra pingnis phlogiston, the motion of fire (or heat), the essential element of all combnstible materials. Thns the phlogiston theory was born to explain all combnstion and was widely accepted for most of the eighteenth centnry by, among others, such luminaries of chemistry as Joseph Priestley. 

In an amorphous material, the aUoy, when heated to a constant isothermal temperature and maintained there, shows a dsc trace as in Figure 10 (74). This trace is not a characteristic of microcrystalline growth, but rather can be well described by an isothermal nucleation and growth process based on the Johnson-Mehl-Avrami (JMA) transformation theory (75). The transformed volume fraction at time /can be written as... 

Tritium has also been observed in meteorites and material recovered from sateUites (see also Extraterrestrial materials). The tritium activity in meteorites can be reasonably well explained by the interaction of cosmic-ray particles and meteoritic material. The tritium contents of recovered sateUite materials have not in general agreed with predictions based on cosmic-ray exposure. Eor observations higher than those predicted (Discoverer XVII and sateUites), a theory of exposure to incident tritium flux in solar flares has been proposed. Eor observations lower than predicted (Sputnik 4), the suggested explanation is a diffusive loss of tritium during heating up on reentry. 

Other theories proposed dissipation of energy through crack interaction localised heating causing the material to be raised to above the glass transition temperature in the layers of resin between the rubber droplets and a proposal that extension causes dilation so that the free volume is increased and the glass transition temperature drops to below the temperature of the polyblend. 

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