Helium, heat capacity ratio

Effect of Addition of Inert Diluents. The addition of inert gases to an explosive mixture will have two major effects. It will increase the heat capacity of the mixture, and depending upon the nature of the added gas, it will change the mixture thermal conductivity. Equation 26 shows that an increase in the heat capacity of the mixture will tend to increase the induction period. The addition of a high thermal conductivity gas such as helium will increase the limiting pressure. Rearranging Equation 18 shows that for a given vessel diameter, reactant concentration, and furnace temperature, the ratio... 

For certain monatomic gases, such as helium, neon, argon, and mercury and sodium vapors, the ratio of the heat capacities at moderate temperatures has been found to be very close to 1.67, as required by equation (15.6). The values of the individual heat capacities at constant pressure and constant volume are 5.0 and 3.0 cal. deg. mole , respectively, in agreement with equations (15.5) and (15.4). It appears, therefore, that for a number of monatomic gases the energy of the molecules, at least that part which varies with temperature and so affects the heat capacity, is entirely, or almost entirely, translational in character (see, however, 16f). 

It was pointed out in the section on gas coolants that the heat removal capacity of helium or CO2 could be made equivalent to that of sodium by choosing appropriate coolant pressure and flow rate conditions for the gas coolant. The studies on the GCFBR have shown that the heat transfer with oxide fuel elements is not limited by the coolant when the coolant pressure is 1000 psia. Under these conditions, it is found that a net plant efficiency of 40 % can be obtained in a large GCFBR having a fuel rating of 900 kW/kg of fissile fuel, a power density of 240 kW/liter, an overall conversion ratio 1.55, and a doubling time of 8 years (see Table I). 

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