Penetration of heat

At the outlet of the pump the feedstock flows through a duct with a diameter of, say, 200 mm. Supply of heat through the wall of the duct would require virtually all of the heat transport to occur by conduction. The penetration of heat to the core of the "solid cylinder of feedstock would require many hours. It is therefore not a practical solution. Hence, alternative ways of preheating are called for. 

Chipping, the process of reducing a log to chips of about 2.5 x 2.5 x 0.5 cm thick is a common preliminary to all pulping methods except stone groundwood. Wood chips are more convenient and uniform for solids transport within the mill complex by conveyor belt or pneumatic delivery systems than are whole logs. Also a chip format is more amenable to direct physical conversion to fibers because of the much easier and more uniform penetration of heat and moisture through the thin sections of wood. 

Other measures to improve the penetration of heat to deeper soil levels are the installation of a permanent steam-piping system under the plot (Nederpel, 1979) systems operating under reduced pressure provided by fan action (Runia, 1983) and the use of steam-air mixtures, provided by blowing air into the steam supply (Belker, 1990 Labowsky, 1990). The latter technique permits more control of the temperatures achieved, and is favoured where a soil pasteurisation procedure is desired rather than complete sterilisation. 

Figure 15-10. Penetration of heat from the interfacial rubbing area into the moving body as calculated from the temperature analysis. Data by J. C. Jaeger [2]...

The penetration of heat in the can is dependent almost wholly upon the ease with which convection currents are set up, occurring most rapidly in products which permit the free circulation of water, weak brine, or sirup between the solids, as in peas, and least rapidly in the absence of free liquid, as in dry-packed sweet potatoes. Products... 

Chemistry rests largely upon the theory of atoms and molecules. The idea of an atomic constitution of things was arrived at by the ancients, though the basis of their speculations differed considerably from that of modern chemistry. They thought that there must be a limit to the divisibility of matter, that living creatures must be reproduced from Tiltimate primordial bodies of the appropriate kind, that various natural phenomena such as the penetration of heat and cold depend upon the hidden motions of tiny particles, and so on. It is hardly conceivable that chemistry as we know it could have arisen directly in this way. 

Infrared drying Near-infrared spectroscopy Penetration of heat into the sample Specific absorption of near-infrared radiation (1400-1450,1920-1950 nm) by the water molecules of the food 10-25 min... 

Under the influence of high temperatures on a surface of the object protected from fire an in tumescent surface appears which obstructs penetration of heat and fire spread over the surface of the material. 

One drawback to this system is the large heat losses and the penetration of heat to the mould plates, which is a reason for designing additional cooling channels. There is a need for compensation for the thermal expansion of the distributor and for the introduction of extra design features to make the system leakproof. 

For skin packaging, ionomer films provide outstanding protection, especially for sharp objects. Films can be drawn down tightly around regular shapes without penetration. Characteristics of heat seals can be adjusted so that convenient peelable seals are obtained (31—35). 

Steam (qv) sterilization specifically means sterilization by moist heat. The process cannot be considered adequate without assurance that complete penetration of saturated steam takes place to all parts and surfaces of the load to be sterilized (Fig. 1). Steam sterilization at 100°C and atmospheric pressure is not considered effective. The process is invariably carried out under higher pressure in autoclaves using saturated steam. The temperature can be as low as 115°C, but is usually 121°C or higher. 

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