Cooling by radiation

Fig. 4.22 Infrared image of the central part of the reactor consisting of the reaction plate and two insulation modules (the temperature decrease of the pipes is only due to passive cooling by radiation and convection).

Let us remember also that the ionization is usually carried out with a 70 eV electron beam, and that 1 eV corresponds to 96.48 kJ mol 1. The ion excess energy can be several electronvolts. In the condensed phase, the cooling of an excited ion or molecule results from the collisions or from the emission of photons. Under high vacuum, only the latter possibility remains. The time delays necessary for cooling by radiation can be measured... 

Consider a sealed 20-cm-high electronic box whose base dimensions are 40 cm X 40 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components in the box dissipate a total of 100 W of power and the outer surface temperature of the box is not to exceed 55 C, deicrmi ne the temperature at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. Assume the heat transfer from the bottom surface of the box to the stand to be negligible. 

Y. S. Kadaner, Y. P. Rassadkin, and E. L. Spektor, Heat Transfer in Laminar Liquid Flow through a Pipe Cooled by Radiation, Heat Transfer-Sov. Res., (3/5) 182-188,1971. 

Cooling systems in liquid-cooled engines are affected by the mineral content and corrosiveness of water put into the system—be it cooled by radiator, heat exchanger, or standpipe. In all cases, recommended practice is to use treated water so as to minimize long-term effects on the engine. 

There is some cooling by radiation, but this is not very great because the temperature difference between the metal parts and the glass is kept small during cool-down so that the glass is not locally stressed. 

Rod-fed sources are often used with e-beam evaporators where the end of the rod, the side of which is cooled by radiation to a cold surface, acts as the crucible to hold the molten material. Feeding sources are used to keep the liquid level constant in a crucible, so as to retain a constant vapor flux distribution from the source and to allow vaporization of large amounts of material. 

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