======================ELECT_PHYSICS================================ TOTAL THERMAL EiuissivITY OF ELECTRON-TUBE MATEiiIALS. Temperature Thermal Material K Emissivity Aluminum 450 0.1 Anode graphite 1000 0.9 Copper 300 0.07 Molybdenum 1300 0.13 Molybdenum 1300 0.5 quartz-blasted Nickel 600 0.09 Tantalum 1400 0.18 Tungsten 2600 0.30 TYPES OF COOLING. Average Cooling Specific Dissi Surface Temperature Cooling Surfa Type (0C watts/cm2 Cooling-Medium Supply Radiation 400-1000 4Ñ10 Water 30-150 30Ñ110 0.25Ñ0.5 gallon,minute/kilowatt Forced air 150-200 0.5Ñ1 50Ñ150 feet3/minute1 kilowatt Evaporative 100-120 80Ñ1 Water- air-, or convection-cooled con- denser. A water-cooled condenser would require 0.07Ñ0.1 gallon/minute/kilowatt Conduction 100-250 5-30 Heat sink operating at 50-1000C can be removed in this manner is given by P=et*sigma(T^4 Ñ T0^4) P= radiated power in watts/centimeter~, et= total thermal emissivity of the surface, sigma= Stefan-Boltzmann constant= 5.07e-12 wattcentimeters Ñ2 X degrees KelvinÑ4, T= temperature of radiating surface in degrees Kelvin, T0= temperature of surroundings in degrees Kelvin. Total thermal emissivity varies with the degree of roughness of the surface of the material and the temperature. Values for typical surfaces are in Table 7. Water Cooling circulated through a suitably designed structure. The amount of heat which can be removed by this process is given by P = 264*Q_w(T2-T1) P= power in watts, Qw= flow in gallons pemÕ minute, T2, T1 outlet and inlet water temperatures Kelvin,. This same relationship is given in the nomogram of Fig. 0 with the temperature rise in degrees Fahrenheit or Celsius and the power in kilowatts. Forced Air Cooling With forced air cooling a stream of air forced past a suitable radiator. beat which can be removed by this process is given by P= 169*Q_A[( T_2/T_1) Ñ 1] QA= air flow in Ieet3/mmntrte, other quantities as above. Evaporative Cooling consists of a tube with a specially designed anode immersed in a boiler containing distilled water. When power is dissipated on the anode, the water boils and the steam is conducted upward through an insulating pipe to a condenser. condensate is then gravity fed back to the boiler, thus eliminating the pump required in a circulating water system even with a pump only about 0.05 of the amount of water required for a water-cooled system because exploitation of the latent heat of steam. heat-exchanger is less than one-third mean temperature differential between the cooled liquid and the secondary coolant. Typical temperature differentials for the two systems are 750C and 300C, respectively. anode dissipation should not exceed 135 watts/cm2 external anode surface this point, often referred to as the 'Leidenfrost' or 'calefaction' point, surface completely covered with sheath of vapor thermal conductivity drops to 30 watts/cm2, with resultant overheating of the anode. Special designs of the external anode surface (such as the 'pineapple') allow up to 500 watts/cm2 centimeter internal anodesurface