Heating, by friction

The production of heat by friction, the passage of heat from one body to another at a lower temperature by conduction or radiation, and the diffusion of material substances, are intrinsically irreversible processes. A process (Carnot s cyclic process) will be described in the next chapter by means of which heat generated by friction may be withdrawn and reconverted into work. 

The pressure at every instant during an expansion or contraction of the working substance must be only infinitesimally greater or less respectively, than the external pressure, otherwise turbulent motions occur, the kinetic energy of which is ultimately converted into heat by friction, and this heat production is intrinsically irreversible. 

Examples of such processes are the equalisation of temperature differences by conduction or radiation, the production of heat by friction, the expansion of gases into vacuous spaces, and the mixing of chemically different substances. 

C06-0108. Strike anywhere matches contain P4 S3, a compound that ignites when heated by friction. It reacts vigorously with oxygen, as follows ... 

Some Of its salts are expl Ammonium salt, yei Ifts, mp 105-20° vith violent decompii Potassium salt, yei powd, expl violently on heating, by friction, c- when brought in conta i-with w perfectly stable In dry air and Silver salt, AgC3HgN203, yei powd, expl when heated insol in w or AcOH sol in NH40H or mineral acids(Refs 1 2)... 

The extruder is used since it mixes, melts, and degases the polymer. However, as said in the previous paragraph, from an exergetic point of view, it is not an efficient apparatus, since it dissipates mechanical work into heat by frictional forces. A possible alternative to the extruder could therefore be a separate degasser, a static mixer, or a gear pump to push the polymer melt through the mixer and perforated plate (Figure 11.6). 

The sources of other igniters are hot plates, hot moving parts of some instruments, engines, radiators, overheated wiring, boilers, metals heated by friction, metal being welded, or sometimes a cigarette. 

Of late years a number of very careful measurements of the mechanical equivalent of heat have been undertaken for this purpose. The methods employed in these measurements are the same in principle as those of Joule, and differ only in the greater refinement of the apparatus. The methods which have been employed hitherto are all based on the production of heat by friction or by the electric current. The results are tabulated below. In column 3 is given the number of ergs which is equivalent to a small 15° calorie. 

Polystyrene was simultaneously carbonized which was probably caused by an increased temperature due to heating by friction. 

Vaporized phosphorus is condensed to a white solid (mp = 44.2°C, bp = 280.3°C) under H2O to prevent oxidation. Even when kept under H2O, white phosphorus slowly converts to the more stable red phosphorus allotrope (mp = 597°C sublimes at 431°C). Red phosphorus and tetraphosphorus trisulfide, P4S3, are used in matches. They do not burn spontaneously, yet they ignite easily when heated by friction. Both white and red phosphorus are insoluble in water. 

Work can be completely converted into heat (by friction, for example), but heat can only be partially converted to work. This is accomplished by means of a heat engine. The science of thermodynamics developed out of the need to understand the limitations of steam-driven heat engines at the beginning of the Industrial Age. A fundamental law of Nature, the Second Law of Thermodynamics, states that the complete conversion of heat into work is impossible. Something to think about when you purchase fuel for your car ... 

According to procedure published previously the cylindrical samples were heated by friction during sample rotation [1], Hard alloy blocks being pressed to sample surface were used for friction process. Friction treatment was held either in Ar-gas (FT) or in ammonia medium (FN). The temperature of sample ranged from 773 to 853K was controlled by chromel-alumel thermocouple. Duration of treatment was about to 60 min. After FT and FN processes the sample surface was smooth similar to that of original polished one. 

The tides driven by the orbital resonance have other important geological and geophysical effects as well on Europa. Because the body is regularly worked, the material is heated by friction. This heating seems to be adequate to maintain a liquid water ocean just below the icy surface. The existence of the ocean allows the tidal distortion of the surface... 

The energy quantum (0.0016 eV) of the microwave irradiation is totally inadequate for exciting atom-atom bonds or specific parts of a molecule and hence cannot induce chemical reactions, as opposed to ultraviolet or infrared radiation (Table 25.1). When molecules rotate in a matrix, they generate heat by friction. The amount of heat generated by a given reaction mixture is a complex function of its dielectric property, volume, geometry, concentration, viscosity, and temperature. Thus, two samples irradiated at the same power level for the same period of time will most likely end up with rather different final temperatures. 

Depending on capital investment limitations, extruders may be heated by passing steam through the barrel jacket and/or by direct steam injection. Low-cost autogenous machines, which create heat by friction between the feed material and the surfaces of the barrel, screw and steam locks, and do not require steam-generating equipment, are also used (Wiejratne et al., 2004). This process is referred to as dry extrusion, and the extruder can be powered by a farm tractor and was originally developed to cook whole soybeans on-farm to prepare feeds. 

I the last paragraph we explored the interplay of particle diameter, column, and column diameter with only one constraint imposed on the design 1 the column the pressure capability of the HPLC instrument. As we will see ithis paragraph, there are other constraints on the column design. One is a Dtal one—flow through a packed bed generates heat by friction. 

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